Titanium alloy blank forging method and blank of titanium alloy for forging

FIELD: metallurgy, namely processes for forging titanium alloys and blank of such alloy suitable for forging.

SUBSTANCE: method comprises steps of preparing blank and forging it. Forging is realized at providing mechanical hardening factor equal to 1.2 or less and at difference of hardness values between central (along width) zone and near-surface zone equal to 60 or less by Vickers. Factor of mechanical hardening is determined as HV(def)/HV(ini), where HV(ini) - hardness of titanium alloy blank before forging; HV(def) -hardness of titanium alloy blank after forging at forging reduction 20%. Forging may be realized at deformation rate from 2 x 10 -4 s -1 to 1s-1 while keeping relations (T β - 400)°C ≤ Tm ≤ 900°C and 400°C ≤ Td ≤ 700°C, where Tβ (°C) -temperature of β-phase transition of titanium alloy, T m(°C) - temperature of worked blank; Td(°C) - temperature of die set. Blank has factor of mechanical hardening 1.2 or less and difference of hardness values between central (along width) zone and near-surface zone equal to 60 or less by Vickers.

EFFECT: possibility for forging titanium alloy blanks at minimum difference of material properties along depth, simplified finishing of blank surface after forging, reduced cracking of blank material, good workability of blank with favorable ductility and fatigue properties.

8 cl, 5 tbl, 6 dwg, 4 ex

 

The technical FIELD TO WHICH the INVENTION RELATES.

This invention relates to a method of forging billet of titanium alloy and billet of titanium alloy for forging.

The level of technology

Thanks to the excellent properties of titanium and titanium alloys are widely used in chemical plants, power generators, medical instruments and aircraft components. In particular, titanium alloy type α +β has light weight and high strength, making titanium alloy of this type is widely used in various fields of technology. For example, turbine blade with increase in the size demands simultaneously low weight to increase their efficiency. In this case it is successfully used titanium alloy. This type titanium alloy is also used in aircraft structures, such as the chassis where you want weight reduction, given the object's use. In addition, titanium alloy type α +β used in moving machine parts, such as automobile parts, including the connecting rod and the valve, and in commercial products, such as the putter for Golf.

In General, however, titanium alloys have high sensitivity to cracking compared with steel, widely used in industry at present. The hot deformation resistance is fanovich alloys are also relatively high in the range of low temperatures, so you want to work with titanium alloys in high temperature range. These characteristics are described in the publication “TITAN NO KAKO GIZYUTSU”published by the Japan titanium society. In the workflow within the range of high temperatures, particularly when crafting there are several technical problems, such as oxidation of the surface and increase grains in the range of higher temperatures, and the formation of cracks due to brittle α shell when the temperature drops. In contrast, in the workflow within the range of low temperatures as one of the technical problems is the high resistance to hot deformation. In addition, the temperature drops by contact with the tool, there is such a technical problem, as the subsequent deterioration of workability. There is also the problem of the formation of inhomogeneous microstructure with adiabatic heating at high strain rate.

As mentioned above, the processing interval titanium alloy is very narrow. In addition, in the case of conventional forging process, the resulting microstructure is different in the zone near the surface, where the temperature drop is caused by contact with the stamp, and the average thickness of the portion where the temperature is reduced slowly or temperature on asaeda due to adiabatic heating. In addition, in particular near the surface layer of the work in the range of low temperatures sometimes leads to the formation of elongated microstructure, and work within the range of low temperatures leads to an increase in hardness. As a result, may experience some problems related to the deterioration of material properties.

However, from the point of view of manufacturing process of repeated heating and re-forging are inevitable due to the narrow interval of titanium. In addition, the deterioration of material properties such as ductility and fatigue properties, is also a problem, further complicating the process of forging. There are also other problems that lead to the inevitable need finishing oxidized surface after forging. In particular, in the case of complex forms of wrought products, taking into account the microstructure when re-heating, the number of repeated cycles of heating and forging should be limited. And with only forging is not always possible to achieve the desired final form. In this case, the tolerance on the final machining increases the workload and reduces the output relative to the source material. In addition, the oxidized scale and deteriorated condition of the surface layer, such as α shell, have a significant impact on the properties of the material so that it becomes necessary to remove a damaged layer in the practical use of forging. In addition, in case of impossibility to provide the required final form you need to perform intensive grinding. Thus, a narrow processing interval and the need for grinding after forging increases the cost. In accordance with this manufacturer of titanium products is associated with a large value of work performed in addition to the high cost of the material.

These problems can be solved by improving methods of forging, known from the prior art, i.e. associated with high costs of labor and time. One particular method according to the invention consists in the isothermal forging and hot forging closed die. Some variants of methods have been described in recent publications ASM Handbook on the properties of titanium alloys”, “Technology of titanium and Titanium and titanium alloys”. In addition, there is a method of forging billets of titanium alloys, as well as billet, produced by forging of titanium alloys described in the book Alexandrov VK and other Semi-finished products from titanium alloys. M.: metallurgy, 1979, s-294. These methods use forging by heating not only the material, but also of the stamp. The processed material and the stamp is heated to the same temperature required for the forging material. Or the processed material and W is the amp is heated to a temperature very close to the temperature of the material processing.

When using these methods, the rate of deformation is strictly limited to the value of about 10-4-10-5with-1. For example, isothermal forging alloy Ti-6Al-4V perform by selecting the temperature of the processed material in the range of from about 900° With up to 950° C. the temperature of the stamp also support in the range of from about 900° With up to 950° C. When the forging is performed with a hot stamp, the temperature of the stamp support within the range of from about 650° 800° C. This range is very close to the temperature of the processed material. These methods help to prevent the temperature drop of the processed material. The methods provide favorable fluidity of the material to obtain the exact shape through forging. In addition, the decreased number of repeated heating. Save the original weight of the processed material. In addition, it is possible to obtain a uniform microstructure throughout the thickness.

Because these methods depend largely on processing at low strain rate, the forging load to some extent reduced. In addition, forging in such environments, when prevented oxidation of titanium, for example when using an inert gas or vacuum, ensures the prevention of oxidized who I am.

However, in these methods, the material is kept at a high temperature for a long time, since the heating of the material and the stamp has limitations, so there is a problem of increase of the grains. In addition, the stamp is heated to a high temperature, which is equal to the temperature of the processed material. In other cases, the stamp is heated to a temperature which is very close to the temperature of the processed material. So you need to use these types of stamps. For example, use a very expensive alloy based on Nickel, which has a resistance within the range of high temperatures, and which has excellent heat resistance and oxidation resistance, as described in the publication ASM Handbook on the properties of titanium alloys”. In addition, problems may occur in the manufacture of the stamp, because the machine using the electric discharge are very expensive. So, just to ensure a good flow of metal through the use of the method of isothermal forging and heat stamp. However, the top layer of material that comes into contact with the stamp, experiencing friction with the sides of the stamp. And therefore there is a difference in the microstructure between the interior and part of the near surface zone for some ti is s titanium alloys.

The invention

This invention offers a method that allows to solve the problems associated with the peculiarities of the material and the stages of the manufacturing process. More specifically, the objective of the invention is to provide a method of forging billet of titanium alloy, and the creation of a billet of titanium alloy for forging, which has a smaller difference of material properties in the direction of depth, requires less final surface treatment after forging, has a low sensitivity to cracking, excellent machinability and good ductility and fatigue properties.

The problem is solved in that in the method of forging billet of titanium alloy, comprising preparing a billet of titanium alloy and forging, according to the invention for harvesting with uniform properties in the Central thickness and close to the surface area of the forging billet lead to providing ratio mechanical hardening, equal to 1.2 or less, and the difference in hardness between the Central thickness and near-surface zone 60 or less on a scale of Vickers, the coefficient of mechanical hardening is defined as

Hv(def)/Hv(ini),

where Hv(ini) - the hardness of the billet of titanium alloy for forging,

Hv(def) - the hardness of the billet of titanium alloy p and ukovka 20%.

In another preferred embodiment of the invention the problem is solved in that in the method of forging billet of titanium alloy, comprising preparing a billet of titanium alloy and forging, according to the invention for harvesting with uniform properties in the Central thickness and close to the surface area of the forging is carried out at a strain rate of 2× 10-4with-1to the 1-1while maintaining the ratio (Tβ -400)°≤ Tm900° 400°≤ Td700° C

where Tβ (° (C) temperature β -a phase transition in titanium alloy

Tm(° (C) is the temperature of the workpiece,

Td(° (C) is the temperature of the stamp.

It is reasonable forging is carried out at the condition of a temperature difference of stamp Tdand temperature of workpiece Tm, (Tm-Td)≤ 250° C.

It is desirable, furthermore, to use a billet of titanium alloy containing, wt.% Al 4-5, V and 2.5-3.5, Fe, 1.5 to 2.5, Mo 1.5 to 2.5, Ti - rest.

In the preferred embodiment, receive a billet of titanium alloy with α +β -microstructure, tensile primary α phase 5 or less, the average grain size of primary α phases 10 μm or less and a volume fraction per the primary α -phase from 20 to 80%, while the coefficient of relative elongation is defined as the ratio of the length of the primary grain α -phase in the longitudinal direction of its width.

The problem is solved also by the fact that the billet of titanium alloy for forging according to the invention has a coefficient of mechanical hardening of 1.2 or less and the difference in hardness between the Central thickness and near-surface zone 60 or less on a scale of Vickers, the coefficient of mechanical hardening is defined as

Hv(def)/Hv(ini),

where Hv(ini) - the hardness of the billet of titanium alloy for forging,

Hv(def) - the hardness of the billet of titanium alloy when ukovka 20% within the temperature range (Tβ -400)°≤ Tm900° and

Tβ (° (C) temperature β -a phase transition in titanium alloy

Tm(° (C) is the temperature of the workpiece of titanium alloy.

In a preferred embodiment, the billet of titanium alloy for forging made of titanium alloy, wt.%: Al 4-5, V and 2.5-3.5, Fe, 1.5 to 2.5, Mo 1.5 to 2.5, Ti - rest.

It is reasonable to titanium alloy had α +β -microstructure, tensile primary α phase 5 or less, the average grain size of primary α phases 10 μm or less, and volume fraction of primary α -phase from 20 to 80%, while the ratio against the sustained fashion elongation is defined as the ratio of the length of the primary grain α -phase in the longitudinal direction of its width.

Brief description of drawings

In the drawings shows:

figure 1 is a graph showing the relationship between the temperature of the heating and oxidation of the surface of titanium alloys;

figure 2 is a graph showing the relationship between the average grain size of primary α -phase and elongation;

figure 3 is a graph showing the relationship between the average grain size of primary α -phase and fatigue strength;

4 is a diagram of forging according to example 1;

5 is a diagram forging according to example 2;

6 is a diagram forging according to example 3.

Description of the preferred embodiments

Below is a detailed description of the invention on the example of the preferred embodiments.

This invention is characterized by a specific technical characteristic, consisting in the fact that during forging of titanium alloy is effectively used the mechanism of cross-border slip grains with the diffusion distribution during deformation at a given temperature. Some types of titanium alloys have this mechanism.

Know that you can provide significant deformation due to border-slip grains with the diffusion distribution at a given temperature and a given strain rate for some types of titanium alloys. In this case, no p is oshodi work hardening and it is possible to obtain a homogeneous microstructure in exposed forging of titanium alloys.

By the usual method of forging can easily go beyond the right conditions due to the temperature drop of the processed material and friction in contact with the stamp, even when the initial conditions correspond to an edge of the sliding of grains with the diffusion distribution. To solve this problem, this invention provides the desired temperature of the processed material and the temperature of the stamp in the optimal range. This invention also provides that the titanium alloy is subjected to forging for optimum composition and optimum microstructure. Therefore, the method of forging according to the invention provides excellent machinability, excellent material properties and excellent surface properties.

The mechanism of boundary slip grains with the diffusion distribution in the forging process can be checked by comparison with the hardness of the material before and after forging. In the ideal case, when the mechanism boundary sliding grain with the diffusion distribution is valid during forging, then there is no accumulation (accumulation) dislocation (transformation). As a result, the hardness does not increase due to the energy of forging. However, in a real way, the increase in hardness is inevitable during the actual forging due to the uneven temperature of the treated m the material. Considering the above facts, it is believed that the mechanism of boundary slip grains with the diffusion distribution is effective at forging, when the ratio Hv(def)/Hv(ini) is 1.2 or less than 1.2 according to this invention. Thus Hv(ini) denotes the hardness of the titanium alloy in the form of a forging billet before forging, and Hv(def) denotes the strength of the forged titanium alloy when ukovka 20% within the temperature range from (Tβ -400)° or more to less than 900° where Tβ (° (C) is the temperature β -phase transition of the titanium alloy. Yovka valid when the forging is from 20% to 80%, although it depends on the final form. Therefore, it is assumed that Hv(def) is the hardness of the material being forged with youkai 20%.

When the material is deformed under the action of the mechanism boundary sliding grain with the diffusion distribution, mechanical hardening is small. Therefore, the difference of hardness between the Central thickness of a part of the processed material and close to the surface area of material to be processed is small. Therefore, it is possible to obtain uniformly forged material. Specifically, no differences in the material properties in all parts, irrespective of the different arrangement of parts. If the value specified above, the Electromechanical coefficient is th hardening does not exceed 1,2, this type titanium alloy has material properties that correspond to the difference in hardness Hv 60 or less between the surface layer and the inner part. This hardness prevents the formation of different material properties in each part, such as plasticity or fatigue strength (it should be noted that as in the preceding text and in subsequent, similar to the surface area means the area within the range of approximately 5 mm or less from the surface of the material after forging, although this distance depends on the size of the exposed forging products.

Below is a description of the conditions of forging to obtain the coefficient of mechanical hardening of 1.2 or less.

According to this invention performs the forging of titanium alloy, which has a temperature of β -a phase transition Tβ (° (C)at strain rate of 2× 10-4with-1to the 1-1while maintaining the ratio (Tβ -400)°≤ Tm900° 400°≤ Td700° C. When Tm(° (C) is the temperature of the source material for forging, and Td(° (C) is the temperature of the stamp.

First, according to this invention perform forging within a specified range of temperatures and under given conditions relative to the strain rate for which especiany deformation. The deformation is caused due to the mechanism of boundary slip grains with the diffusion distribution. More generally relatively titanium alloys temperature range, which causes deformation due to boundary sliding grain with the diffusion distribution is below β -a phase transition.

If the forging temperature below Tβ -400)° s, the ratio of mechanical work hardening becomes much more than 1.2. When Titan comes to forging, there is a probability of formation of a large number of cracks, even in the case where the titanium has excellent machinability. Hence, there is one difficulty, namely the difficulty of influencing the creation of primary products and secondary products. In addition, during the processing of titanium increases the deformation resistance. From a performance perspective, forging machine, preferably not meet the specified type of difficulties.

On the other hand, in the high temperature range, there is a strong oxidation. Therefore, from the point of view of spending too much time on the final machining of the surface of the forged titanium alloy after forging, and from the point of view of high performance after forging, it is essential that the implementation of forging titanium alloy when the tempo is the atur below 900° For restrictions oxide layer with a thickness of 100 μm or less. Figure 1 shows the relationship between the temperature of heating and the thickness of the oxidation layer to a titanium alloy. In the case of titanium alloys, as shown in figure 1, it was found that the oxidation on the surface of the titanium alloy increases rapidly when the temperature of the heating exceeds 900° C. Within a temperature range below 900° oxidation of titanium alloy is suppressed. And the thickness of the oxidized layer is satisfactory, i.e. sufficiently below 100 microns, due to this suppression. In the case of selection of the temperature range for forging 870° With or below the thickness of the layer of oxidation is suppressed and is about 50 μm or less. Thus, the invention provides the possibility of strong suppression layer oxidation of titanium alloy.

In addition, the choice of temperature stamp Td(° (C) equal to 400° With or above allows to suppress the temperature fall of the processed material in contact with the stamp. In addition, temperature control stamp ensures the prevention of the lowering of the workability of wrought material. Simultaneously with the achievement of the above results the following favorable results. It is possible to ensure good ductility and prevent the formation of cracks. Good ductility and otsutstvie cracks always preferred. This is especially true for parts having a small thickness. The higher the temperature of the stamp, the more suppressed the temperature of the processed material. However, in case of excess temperature stamp temperature β -a phase transition occurs the problem of increasing the temperature of the treated material is subjected to forging, to a temperature of β -phase transition and above. In addition, even when the temperature of β -a phase transition or below, and further at a temperature above 700° needs an expensive material such as an alloy based on Ni, which has heat resistance and oxidation resistance. Thus, the solution to this problem is not preferred from the viewpoint of cost ratios and parameters of forging. Additionally, for the manufacture of products made of the above material requires expensive method of manufacture, such as the use of machines with electric discharge. Higher temperature re-heating leads to oxidation of the stamp, so in addition to the oxidation of the processed material, oxidation of the instrument. This causes short lifetime of the die and tool.

Another technical point of view, i.e. from the point of view of life mentioned above, it is preferable not to exceed a temperature of 700°C.

To call the deformation caused by the mechanism of boundary slip grains with the diffusion distribution during forging, and the purpose of the retention factor of the mechanical hardening equal to 1, 2 or less, the following rate of strain, which is in the range from 2× 10-4with-1or more to the 1-1. Compared with the rate of deformation in the conventional forging process uses a slightly slower rate of strain. And compared to the strain-rate in isothermal forging process uses a higher strain rates. That is, between 2× 10-4with-1or more and 1 s-1. This rate of strain leads to the exclusion too long processing time during isothermal forging and provides effective forging. In addition to this mechanism is used, the edge sliding of grains with the diffusion distribution. The result is favorable machinability and uniform microstructure after forging. The above factors lead to improved material properties, such as ductility and fatigue properties.

In addition, the retention factor of the mechanical hardening is 1.2 or less, and for holding the difference between the hardness of the Central thickness of the part being processed mater is Ala and hardness near the area of the surface of the processed material, equal Hv 60 or less, preferably forging under conditions in which the above conditions is added keeping the ratio [(Tm-Td)≤ 250°] between the temperature Td(° (C) stamp and temperature Tm(° (C) processed material subjected to forging. Performing forging [(Tm-Td)≤ 250°] leads to the improvement of the differences in microstructure between the zone near the surface, where the cooling rate is high, and the Central thickness of a part where the cooling rate is low. Thus, it is possible to obtain forged products with uniform material properties. If the difference between the temperature Tdstamp and temperature Tmthe processed material exceeds 250° it is unfavorable, since it is likely the creation of non-uniform material properties in the forged product caused by the temperature difference during the forging between close to the surface area and the Central thickness part. In the case of particularly large size subjected to forging materials require more time for crafting material. Also increases the load for forging. From this point of view you want to control the temperature so that the temperature Tmthe processed material and the temperature Tdstamp were close to each other, so that cuts estolate value [(T m-Td)≤ 250°].

According to this invention used for forging, the billet of titanium alloy preferably consists essentially of from 4 to 5% Al, 2.5 to 3.5% of V, 1.5 to 2.5% Fe, 1.5 to 2.5% Mo in mass percent and the balance essentially of Ti. The term “balance essentially of Ti” refers in this case to the material, which inevitably contains impurities and other elements present as trace contaminants, and which may exist within the range defined in this invention, if these inevitable impurities, and other trace amounts do not exclude the function and effect of this invention.

Compared with the conventional titanium alloys, the invention provides the possibility of deformation of titanium alloy, caused by the mechanism of boundary slip grains with the diffusion distribution in the range of low temperatures from 700° C to 870° C. Therefore, this invention provides a forging titanium alloy without the colon caused by oxidation scale, without deterioration of the surface layer without deterioration of education α -shell. The reason for this is described above, with the obligatory task of the composition of the titanium alloy.

Aluminum is an essential element for titanium alloy type α +β to stabilize α -phase, and aluminum leads to increased strength. If the content is of luminia less than 4%, the aluminum may not result in a sufficient increase in strength of the material.

If the aluminum content exceeds 5%, then deteriorate ductility and toughness. In both cases, this is undesirable from the standpoint of strength, ductility and toughness.

V, Mo and Fe are the elements for stabilization β -phase and lead to an increase in strength. Contents V if a is less than 2.5%, can significantly affect the increase in strength. In this case, β -phase becomes unstable. Conversely, if the V content exceeds 3.5%, the lowering β -the phase transition leads to the problem of narrowing the interval and, in addition, increases the cost due to the addition of large quantities of expensive alloying element.

Mo causes a refinement of the microstructure and the suppression of grain growth. Fe has a large diffusion coefficient in titanium. The action, called Mo and Fe, increases the ductility. Conversely, the hot deformation resistance increases during forging. The above results lead to additional positive effects such as improved ductility and fatigue properties after forging.

If the content of Mo is less than 1.5%, there can be obtained sufficient strength increases. May not be sufficiently stable β -phase. If the content of M is superior to 2.5%, the decrease β -the phase transition leads to a narrowing of the range of the processing interval. In addition, the effect of Mo and Fe saturated adding Mo and Fe within the range of 2.5% or more, and by adding large amounts of expensive alloying element increases the cost. Additionally β -the phase transition becomes too stable. In this case, it is harmful to harden using a processing solution and aging. If the Fe content is less than 1.5%, the effect of Fe on the hardening is insufficient, while an additional β -phase is unstable. Moreover, regardless of the good properties of Fe, i.e. on the ability of Fe to the rapid diffusion in titanium and improve machinability, the advantage of the characteristics that has iron, has no effective impact on the preferred results. Conversely, if the Fe content exceeds 2.5%, the lowering β -the phase transition leads to a narrowing of the processing interval. In addition, segregation affects the material properties. In addition, when determining the composition of the alloy, as mentioned above, the mutual ratio of the number α phase I β -phase approaching each other within a temperature range from 700° C to 870° C. Becomes easier to activate the mechanism boundary sliding grain with the diffusion distribution is.

According to this invention titanium alloy used as forging billet, preferably has a microstructure of type α +β , elongation primary α -the phase of which is 5 or less, which has an average grain size of primary α phases 10 μm or less, and volume fraction of primary α -phase is in the range from 20% or more to 80% or less, while the elongation is defined as the following:

a) the longitudinal length of the grain to

b) the width of the grain, which is perpendicular to its longitudinal direction.

That is, a)/b).

More preferably, the titanium alloy has an average grain size of primary α phase 6 μm or less.

Figure 2 shows a graph of the relationship between the average grain size of primary α -phase and elongation. As can be seen in figure 2, if the average grain size of primary α phase exceeds 10 μm, the elongation in a tensile test at a high temperature rapidly decreases, which affects the sensitivity to cracking and precision forging.

In addition, the grain size of primary α -phase affects the properties of the material forged products, such as ductility and fatigue properties. Figure 3 shows the relationship between the average grain size of primary α -phase and fatigue properties. As for Asano figure 3, if the average grain size of primary α phase exceeds 10 μm, the sensitivity to cracking during forging increases and decreases the possibility of precision forging, in addition to the deterioration of such material properties as plasticity and fatigue properties.

Form of primary α -phase influences the sensitivity to cracking and precision forging. When the coefficient of relative elongation is defined as the ratio of the longitudinal length, grain width, perpendicular to its longitudinal direction, as mentioned above, and in case of exceeding the ratio of primary α -phase values 5, primary α phase cannot become equiaxial grains. Consequently, reduces the possibility of precision forging.

In addition, fine equiaxial microstructure improves the sensitivity to cracking during hot forging, inhibits the formation of cracks at high strain rate and improves precision forging. Titanium alloy type α +β consists mainly of primary α -phase and transformed β -phase. However, when the volume fraction transformed β -phase is in the range from 20% or more to 80% or less, i.e. when the volume fraction of primary α -phase becomes less than 20% or more than 80%, the sensitivity of the images is of cracking during forging is also increased. Along with the problem of cracking deteriorate also the possibility of precise forging, ductility and fatigue properties of the material.

According to this invention even after forging forged product may have a microstructure which is similar to the microstructure of the forging billet. This is due to the use of edge-slip grains with the diffusion distribution. Due to such preferred characteristics of the invention is extremely effective for increasing the workability and properties of the material, even in case of re-forging, and even in the case of using such a forging process to handle complex wrought forms.

Embodiments of the

To explain the above effective functions below is a description of the impact conditions of forging a titanium alloy, the chemical composition of the forging billet. In addition, a description of examples of the influence of microstructure on ductility and properties of the material after forging.

Example 1

Cylindrical samples for testing the compression size of 15 mm and a diameter of 22.5 mm were cut from material “A01”, as shown in table 1. The sample was forged when ukovka 20% using a stamp made of SUS 310, when the forging temperature, the temperature of the stamp and strain rate. Table 2 shows the conditions of forging, adjusted ient mechanical hardening [Hv(def)/Hv(ini)] and the difference in hardness between the area near the surface and the Central thickness of a part.

The temperature of the processed material Tmin the formula (Tm-Td) corresponds to the range of temperatures at the beginning and end of the forging.

Samples No. 1 and 3 forged in the forging temperature conditions, the temperature of the stamp and strain rate, the magnitude of which satisfy the conditions of this invention. The result is the value of the coefficient of mechanical hardening 1, 2 or less, and the difference in Vickers hardness between the area near the surface and the Central thickness of part 60 or less. Therefore, the process of hot forging under the conditions of this invention leads to deformation caused by boundary sliding grain with the diffusion distribution. And hot forging according to this invention leads to excellent results obtain uniform and homogeneous forged products, which means that there is no difference in all parts of the wrought material.

Conversely, titanium alloys, which are forged under conditions not relevant to this invention, showed the ratio of mechanical hardening more than 1.2, and a hardness difference between the zone close to the surface, and a Central thickness of part 60 and over.

Table 1
SymbolAlloy (amounts in wt.%)Microst is ucture forging billet
β -phase transition (°)The average grain size (µm)The volume fraction of primary α -phase (%)The coefficient of elongation
A01Ti-4,5 Al-3.2 V-2,2 Fe-l,8 Mo9002,6274,4
A02Ti-4,5 Al-3.2 V-2,2 Fe-l,8 Mo9003,7301,8
A03Ti-4,5 Al-3.2 V-2,2 Fe-1,8 Mo9003,0481,1
ATi-4,5 Al-3.2 V-2,2 Fe-l,8 Mo9005,0451,3
WTi-6,l Al-3,9V10008,385the 4.7
WTi-6,l Al-3,9V10005,9801,9
WTi-6,l Al-3,9V10006,4836,9
WTi-6,l Al-3,9V100012,9821,7
WTi-6,l Al-3,9V100010,3791,1
WTi-6,l Al-3,9V1000-0-
C01 Ti-10.2 V-2,2 Fe-2,9 Al8005,1101,1
D01Ti-6,1 Al-1,9 Sn-1,8 Zr-1,9 Mo-2,0 Cr9603,0501,1

Because W in the table above has β -microstructure, the average grain size of primary α -phase and the coefficient of relative elongation was not measured.

Table 2
SymbolThe processed materialThe temperature of the processed material (°)The temperature of the stamp (°)Rate of strain (-1)Tm-Td(°)Hv(def)/Hv (ini)The difference of hardness Hv
The pace. re-heatingThe initial temperatureThe final temperature
1A01830800750620-6000,051≤ 1801,0530
2A01830800750700-6700,004≤ 1001,028
3A01830800750600-5800,085≤ 2001,0721
4A01950920850600-5800,085≤ 3201,2268
5A01830800750620-6001,1≤ 1801,2985
6A01830800750300-2900,037≤ 5001,33101
7A01850830800550-5300,037≤ 2801,2474

Example 2

Using cylindrical specimens for compression, having a diameter of 15 mm and a height of 22.5 mm, which had the chemical composition and microstructure indicated in table 1, served hot forging, as shown in figure 4. Hot forging was performed under the same conditions as in table 3 using stamp SUS 310 and without lubrication. Machinability was evaluated, the conditions of oxidation of the surface microstructure after forging in near-surface zone of the serving part IV Central thickness portion, made in the form of a disk at the bottom. The results are shown in table 3. In table 3 the icon in the column “Crack” refers to the absence of cracks, and the X in this column indicates the occurrence of cracks. Number 1, 13 and 24 in table 3 have β -microstructure, so that the average grain size of primary α -phase and the coefficient of relative elongation was not measured.

The microstructure of the forging billet and the microstructure of the forged products was estimated at an average grain size of primary α -phase volume fraction of primary α -phase and the coefficient of relative elongation. Ductility was measured by the ability to accurately forging in the actual result of forging and sensitivity to cracking, primarily through inspection of the surface condition of the forged products. The ability to accurately forging was estimated by comparing the height of the protrusion, i.e. the degree of filling of the metal round holes in the stamp (see figure 4). That is, as shown in figure 4, the height, including the height of the protrusion is in the form of a spike, defined as N. And the thickness of the disk portion was defined as So Finally, precision forging defined as the ratio of N/T. To obtain favorable ductility value N/T must be greater than 1.5 or more, preferably 2.0 or more. In addition, results concerning with apani finishing surface treatment after forging material was measured layer thickness (layer oxidation), which was caused by oxidation of the surface layer wrought iron products.

Relative to the numbers 1 and 13, the forging temperature which was above β -a phase transition, observed the formation of cracks. And the value of N/T, which assessed the possibility precision forging was small and amounted to about 1.2. From the point of view of assessing the precise forging she was small. As for No. 1, 13-18 and 20-22, the forging temperature was above 900° With the size of the layer of oxidation exceeded 100 µm. As for # 8 and 19, the temperature of the forging which was low, it was observed cracks. In addition, the value of H/T was low and amounted to about 1.2, indicating a low possibility of precision forging.

With regard to No. 6, 8, 18 and 19, the temperature of the stamp which came out of the temperature range according to this invention, the value of N/T was small and amounted to about 1.5 or less. In a small number of cases, cracks did not occur, however, in most cases, the precision forging was insufficient.

As for No. 5 and 17, in which the rate of deformation was outside the range according to this invention, the value of N/T, which determines the possibility of precision forging was less than 1.5. In a small number of cases, cracks were not observed. However, in most cases, the quality was low from the point of view of exact Chowk is.

As mentioned above, in case of conditions outside the range according to this invention were observed cracks and deteriorated the possibility of precision forging. In this case, you can assume that there was no deformation due to boundary sliding grain with the diffusion distribution.

Secondly, we studied the effect of chemical composition of forging billet, the average size of grains, the volume fraction ratio and the relative elongation of primary α -phase forging billet on the ductility.

From the point of view of conformity to the range of the composition according to this invention, the No. 01-a were satisfactory, and their microstructure was within the range according to this invention. Cracks were not detected in No. 2-4, 7, and 9-12. In the forging process, it is absolutely necessary to withstand the conditions according to this invention to obtain good results. Additionally, in No. 2-4, 7, and 9-12 appears excellent ductility, which can be explained by an extremely large value of N/T, equal to more than 2. In addition, regardless of the observed part, such as a Central thickness of the part or close to the surface area after forging, the result can be seen the same microstructure. In this case, the same microstructure means that forging the billet has an average grain size of primary α -f is s 10 microns or less, volume fraction from 20% to 80% and the relative elongation factor 5 or less. In addition, it means that is not shown significant differences in the microstructure between the Central thick part and close to the surface area. Therefore, even in close to the surface area you can get a fine microstructure, so that does not form a rough surface.

In the case of forging blanks with numbers V-V, C01 and D01, whose chemical composition was outside the range according to this invention were obtained the results displayed. That is, in rooms 16, 20-22 and 26, except for the forging temperature of the workpiece, the material was processed during curing conditions forging according to this invention. In this case, the obtained value of N/T from 1.6 to 1.9, which is greater than 1.5, shows the ability to perform precision forging. However, compared to values N/T greater than or equal to 2.0, which were obtained using the forging of the workpiece according to this invention, the value of N/T is not satisfactory and shows that the chemical composition and the microstructure of the forging billet also affect ductility. Among these rooms, rooms 20 and 26, in which the materials are used In 02 and D01, respectively, and the microstructure which corresponds to the range according to this invention, exhibit high value N/a is, equal 1,80 and 1,91 respectively. However, the microstructure after forging is outside the range according to this invention. The result is a rough surface. Not only numbers, but also for numbers 23 and 25 microstructure after forging is outside the range according to this invention. In this case manifests the same problem, i.e. the formation of rough surfaces.

With regard to the number 23, the chemical composition and microstructure are outside the range according to this invention. In addition, the forging temperature was lower than in the case of rooms 16 and 20-22. Although these values were within the range according to this invention, the value of H/T was 1.5 or less. In addition, the number 24, which was used alloy V with β -microstructure was observed cracks and was a low value of N/So

Since the temperature β -a phase transition material from V to V was high and amounted to 1000° With these materials it was possible to strike only in the high temperature range, as the resistance of the hot deformation was small in the high temperature range. However, forging at such high temperatures increases the thickness of the formed layer of oxidation. In accordance with examples of this invention for materials V-V used what was ovalis temperature re-heating 950° With the initial temperature for forging 900° C. compared with materials A01-a, which have a temperature of β -a phase transition 900° materials V-V and V require higher forging temperature. Thus, the thickness of the oxidation layer is 150 μm.

As for the material W, which requires the temperature re-heating 880° to suppress oxidation, and the initial temperature for forging a $ 850° C, the lowest temperature was lowered ductility, causing the value of N/T, is equal to 1.5 or less, while the thickness of the layer of oxidation decreased. In addition, these examples, which are compounds that do not match the range according to this invention, lead to differences in microstructure between close to the surface area and the Central thickness of the part after forging. And formed a rough surface due to coarse grains and elongated structure of the grains.

Example 3

Forging the workpiece, are shown in table 1, the size of which is 30 mm in width, 60 mm in height and 70 mm in length, were subjected to hot forging, shown in figure 5, under the conditions in accordance with table 4. Received the forged product had a size of about 30 mm in width, 20 mm in height and 210 mm in length. From each of forged products were cut and prepared samples. The mechanical properties of these samples were evaluated with t is his view of the hardness Vickers hardness and fatigue properties of flat test plate. The results are shown in table 4. 1, which satisfies the conditions of a temperature of the material to be forged, the temperature of the stamp and strain rate according to this invention, results in a difference (Δ Hv)60 or less on a scale Vickers hardness between the two parts. That is one part means close to the surface zone, where the temperature drop due to contact with the stamp is significant. The other part is a Central thickness of the portion where the cooling rate is relatively slow. In this case, the difference (Δ Hv)is 60 or less, is in accordance with the recommended conditions according to this invention. From the point of view of tensile properties and fatigue properties the difference between these parts is smaller. Thus, the result shows that the excellent and a possible method of manufacturing forged products, which has a uniform and homogeneous material properties. On the other hand, the number 2, which forged under conditions outside the range according to this invention resulted in the largest (Δ Hv)is 60 or more. In case 2, you receive the difference in hardness between close to the surface area and the Central thickness of a part.

There are also other differences in the properties of the mater is Alov, such as static strength, ductility, fatigue strength between these parts. From the point of view of uniformity and homogeneity of material properties, the result is not preferred. As mentioned above, the forging according to the invention is absolutely necessary from the point of view of high-tech forged products, which has a uniform and homogeneous wrought material.

Example 4

Using forging billet A01 in table 1 with a diameter of 150 mm and a length of 750 mm, served hot forging to obtain the form shown in Fig.6. Hot forging was performed under conditions of temperature forging billet 800° With initial forging temperature 780° With, the final forging temperature 670° C, the temperature of the stamp within the range from 650° 620° during forging and strain rate of 2.3× 10-3. In this case, the estimated ductility in respect of forged products of large size. Samples were cut and prepared in wrought forms at each position shown on Fig.6.

Evaluated the tensile strength properties of the material. In addition, it was evaluated as material properties fatigue strength during use of the sample, which was tested on bending with torsion. The results are presented in table 5.

It was found that through the use of forging billet, which has a chemical composition and microstructure, which meet the conditions of the present invention, it is possible to obtain a forged item large size of the titanium alloys. And even when such forging is carried out with titanium alloys, which are difficult to process, you can achieve the same results. It was found that according to this invention the material properties corresponding to the received forged product are extremely favorable.

The effectiveness of this invention

As mentioned above, the invention provides the possibility of forged products of high strength titanium alloy. Features forged high-strength titanium alloy have a small scatter of material properties in the thickness direction. This invention provides the ability to remove the layer of oxidation, and the invention provides the possibility of finishing the surface of the forged product after forging, during processing to obtain the final shape and size. In addition, the invention provides the possibility of obtaining a lower sensitivity to cracking, providing excellent machinability forged titanium alloy, good quality regarding plasticity and the mouth of lustnau strength. Finally, this invention provides a titanium alloy, suitable for precision forging strength is very high. Thus, this invention provides a high efficiency industrial applications.

1. The method of forging billet of titanium alloy, comprising preparing a billet of titanium alloy and forging, characterized in that for receiving the workpiece with uniform properties in the Central thickness and close to the surface area of the forging billet lead to providing ratio mechanical hardening, equal to 1.2 or less, and the difference in hardness between the Central thickness and near-surface zone 60 or less on a scale of Vickers, the coefficient of mechanical hardening is defined as Hv(def)/Hv(ini), where Hv(ini) - the hardness of the billet of titanium alloy for forging, Hv(def) - the hardness of the billet of titanium alloy when ukovka 20%.

2. The method of forging billet of titanium alloy, comprising preparing a billet of titanium alloy and forging, characterized in that for receiving the workpiece with uniform properties in the Central thickness and close to the surface area of the forging is carried out at a strain rate of 2× 10-4to the 1-1while maintaining the ratio (Tβ -400)°≤ Tm900° 400°≤ Td700° where Tβ (° (C) temperature β -a phase transition in titanium alloy

Tm(° (C) is the temperature of the workpiece,

Td(° (C) is the temperature of the stamp.

3. The method according to claim 2, characterized in that the forging is conducted under the condition of a temperature difference of stamp Tdand temperature of workpiece Tm, (Tm-Td)≤ 250° C.

4. The method according to claim 2, characterized in that make billet of titanium alloy containing, in wt.%: Al 4-5, V and 2.5-3.5, Fe, 1.5 to 2.5, Mo 1.5 to 2.5, Ti - rest.

5. The method according to claim 2, wherein receiving the billet of titanium alloy with α +β -microstructure, tensile primary α phase 5 or less, the average grain size of primary α phases 10 μm or less, and volume fraction of primary α -phase from 20 to 80%, while the ratio of elongation is defined as the ratio of the length of the primary grain α -phase in the longitudinal direction of its width.

6. Billet of titanium alloy for forging, characterized in that it is made of a titanium alloy having a coefficient of mechanical hardening of 1.2 or less and the difference in hardness between the Central thickness and near-surface zone 60 or less on a scale of Vickers, the coefficient of mechanical hardening is defined as Hv(def)/Hv(ini), where Hv(ini) hardness billet of titanium alloy for forging, Hv(def) - the hardness of the billet of titanium alloy when ukovka 20% within the temperature range (Tβ -400)°≤ Tm900° and Tβ (° (C) temperature β -a phase transition in titanium alloy, Tm(° (C) is the temperature of the workpiece of titanium alloy.

7. Billet of titanium alloy for forging according to claim 6, characterized in that it is made of a titanium alloy containing, in wt.%: Al 4-5, V and 2.5-3.5, Fe, 1.5 to 2.5, Mo 1.5 to 2.5, Ti - rest.

8. Billet of titanium alloy for forging according to claim 6, wherein the titanium alloy has a α +β -microstructure, tensile primary α phase 5 or less, the average grain size of primary α phases 10 μm or less, and volume fraction of primary α -phase from 20 to 80%, while the ratio of elongation is defined as the ratio of the length of the primary grain α -phase in the longitudinal direction of its width.



 

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