Rail steel

FIELD: ferrous metallurgy; production of rail steel.

SUBSTANCE: the invention is pertaining to the field of ferrous metallurgy, in particular, to production of steel for manufacture of railway rails. The offered rail steel contains its components in the following ratio (in mass %): Carbon - 0.83-0.5; manganese - 0.6-1.1; silicon - 0.3-0.7; vanadium - 0.08-0.15; aluminum - no more than 0.005; nitrogen - 0.012-0.02; calcium -0.0005-0.005; chromium - 0.05-0.5; one of the devices sampled from a group including zirconium and REM, namely, zirconium -0.0005-0.005; REM - 0.0005-0.005; molybdenum - 0.11-0.3; nickel - 0.05-0.3, iron and impurities - the rest. The technical result of the invention is an increased complex of mechanical properties, firmness of steel and its resistance to brittle fracture, which improves operational stability of the rails. Out of the steel of a stated composition it is possible to manufacture the rails hardened both in oil and in a compressed air with a troostite structure.

EFFECT: the invention ensures an increased complex of the rail steel mechanical properties, firmness of the steel, its resistance to brittle fracture and production of rails with a troostite structure.

2 tbl

 

The invention relates to ferrous metallurgy, in particular to the production of steel for rails increased wear - and cold-resistance and contact resistance.

Known steel having the following chemical composition (wt.%):

1. 0,65-0,8; 0,18-0,40 Si; 0,6-1,2 Mn; 0.001 to 0.01 Zr; from 0.005 to 0.04 Al; 0,004-0,011 N; one element from the group consisting of CA and Mg 0,0005-0,015; 0,004-0,040 Nb; 0,05-0, 3 si; Fe-leave [1].

2. 0,69-0,82; 0,45-0,65 Si; 0,6-0,9 Mn; 0,004-0,011 N; of 0,005 0,009 Ti; of 0,005 0,009 Al; 0,02-0,10 V; 0,0005-0,004 Sa; 0,0005-0,005 Mg; 0,15-0,4 Cr; Fe-OST. [2].

Significant disadvantages of steel No. 1 and No. 2 are low impact strength and gladstonos, reduced reliability and operational stability.

In the steel 1 is defined by the absence of vanadium and low nitrogen content. It has a relatively large grain of austenite (scores 7-8). The high content of aluminum in it leads to contamination of its gross strochechnyh inclusions of alumina, significantly reducing the contact fatigue strength of rails.

These limitations have 2 associated with the presence of titanium, low content of vanadium and nitrogen. Formed in the liquid steel at cooling carbonitrides of titanium dramatically reduce the impact strength and resistance to brittle fracture of rails.

A relatively low content of vanadium and nitrogen does not provide the education required number of nitrides of aluminum and vanadium carbonitride is, needed to crush the austenitic grain and simultaneous increase of the strength properties and cold resistance steel. Austenite grains in the steel is relatively large and is 7-8 points.

The closest analogue of the invention is a rail steel, which is revealed in the author's certificate of the USSR No. 1633008 A1 from 07.03.1991 year, With 22 38/28 [3]. This steel contains components in the following ratio, wt.%:

Carbon0,65-0,89
Manganese0,6-1,2
Silicon0,18-0,65
Vanadiumof 0.01-0.1
Titanium0,001-0,03
Aluminum0,005-0,02
Nitrogen0,004-0,03
Calcium0,0004-0,005
Chrome0,05-0,4
Molybdenum0,003-a 0.1
iron and inevitable impuritiesrest

Significant disadvantages of steel are low impact strength, increased susceptibility to brittle fracture and low operational stability, due to the presence of titanium in steel, low vanadium content, high concentration of aluminum. Forming carbonitrides of titanium dramatically reduce shock is Ascot and resistance to brittle fracture.

Low concentration of vanadium does not provide the education required amount of carbonitrides of vanadium, for grinding grain and improve the strength properties and cold resistance of steel.

Applying large amounts of aluminum for deoxidation of steel together with calcium leads to the pollution of its clusters of aluminates of calcium, rich in alumina, which reduces the contact fatigue strength.

The presence of steel sulfur and phosphorus in large quantities leads to increased respectively red and jednoralski steel.

Desired technical result of the invention is to improve the strength properties and cold resistance of steel that provides increased operational stability of rails.

To achieve this, the proposed steel containing carbon, manganese, silicon, vanadium, aluminum, nitrogen, calcium, chromium, molybdenum, and iron, also contains Nickel and one of the elements selected from the group comprising zirconium and rare-earth metals, in the following ratio of components (wt.%):

Carbon0,83-0,95
Manganese0,6-1,1
Silicon0,3-0,7
Vanadium0,08-0,15
Aluminumnot more than 0.005
Nitrogen0,012-0,02
Calcium0,0005-0,005
Chrome0,05-0,5
Molybdenum0,11-0,3
Nickel0,05-0,3

one of the elements selected from the group comprising zirconium and rare-earth metals:

Zirconia0,0005-0,005
REM0,0005-0,005
iron and impuritiesthe rest,

the number of impurities is limited in the following ratio (wt.%):

sulfurless than 0.015
phosphorusno more than 0,020
coppernot more than 0.20

The claimed chemical compound selected based on the following conditions. Selected carbon content increases the yield strength, a temporary rupture strength, hardness and wear resistance of steel. The transition to zaevtektoidnyh steels reduces the grain growth of austenite compared with momtective steel.

When the carbon content is less than or 0.83%, the hardness on the surface of thermally hardened rails is relatively low and does not exceed 363 HB, at a depth of 10 mm from the surface - HB 352.

Rails made of steel, with the containing a series of more of 0.95%, have low toughness at minus 60° (0,15 MJ/m2). The introduction of Mn, V, Mo, Cr is also associated with the need to improve the toughness and durability zaevtektoidnoj steel with an operating contact wheel-rail and, together with the silicon to the desired hardness on the surface and the cross section of the rail head.

The increased content of silicon is connected with the necessity of increasing raskalennoi steel while reducing the aluminum content in it that enhance the purity of the steel plastic inclusions of silicates, which reduce toughness. With the increased content of silicon when heated to temperatures less than 1000°it turns out the small grains.

The selected ratio of Mn, Si, Cr, Mo in steel containing 0,83-0,95%, reduces the temperature of austenite transformation and more dispersed patterns of troostite compared with sorbitol hardening.

The decrease in the content of manganese in comparison with the prototype due to the introduction of steel of sufficient amounts of chromium and molybdenum to increase hardenability and its resistance to wear. While the claimed concentration of Ni and Cr, Mo exclude formation in the microstructure of the upper bainite, which is not allowed in the working part of the rail head. However, when the content of 0.83-0.95 percent and With high concentrations of manganese (>1.1 percent) and the lack of chromium in steel and molyb the s in the structure of heat-treated rails are plots of the upper bainite. Manganese contributes to a significant refinement of the austenite grain especially in chromomagnetic steel, reduces the tendency to deformation, increases hardenability, reduces the critical cooling rate.

In the end, the claimed contents of Mn, Si, Cr, Mo, Ni provide the desired reduction in temperature of austenite transformation and the formation of patterns of troostite, which has a higher hardness and wear resistance than sorbitol hardening.

The positive impact of small additives of chromium that it, forming carbides, increases resistance to wear. In the presence of chromium increases the ability of Mn, Mo, V to restrain grain growth of austenite.

In turn, the molybdenum in the steel increases the efficiency of the effect of chromium on its hardenability. Molybdenum slows down the allocation of ferrite and perlite, increases the solubility of nitrogen in iron and resistance vacation, grinds grain of austenite increases strength, hardness, toughness and wear resistance of 1.5-2 times. The chopping action of molybdenum increases in the presence of manganese and chromium. Introduction molybdenum enhances the action of aluminium, reducing the contents of which will not lead to a decrease in resistance to brittle fracture. Alloying with molybdenum reduces the tendency of steel to temper embrittlement and the threshold jednoralski and efficient when n is izvodstve high-carbon steels.

The introduction of Nickel in the present limits of provides along with aluminum and vanadium receive guaranteed impact toughness of the steel at positive and negative temperatures. Its content up to 0.05% does not have a positive effect on impact strength, and at a concentration of more than 0.3% of this characteristic does not exceed the determined values. In addition, when the Nickel content of more than 0.3%, as and when the same concentration of molybdenum may receive invalid in the rails of the structure of the upper bainite having a lower hardness and wear resistance, increased tendency to form contact fatigue defects (fishermen). The increase in the content of Nickel and molybdenum greatly increases the cost of the steel.

Reducing the aluminum content to 0.005% and the modification of the steel is reduced by the amount of calcium ensures the production of high-purity metal inclusions aluminates, leads to the formation of globular inclusions and to decrease their size and number. However, the introduction of calcium 0.005% or polluting its globulare large size and increases the cost of steel. Calcium at a concentration of less than 0,0005% practically does not influence the modification of inclusions.

The use of zirconium in the claimed steel composition is due to the fact that he grinds structure, modifies and vos who shall set the oxide inclusion and helps to reduce contamination of the steel strochechnyh inclusions fragile silicates. In the inventive steel it is injected in small quantities for binding oxygen, grinding austenitic grain and increase toughness. Recyclemania ability zirconium great and even exceeds the corresponding properties of aluminum.

Zirconium in a small amount is entered in the inventive steel because it contains a small concentration of aluminum (up to 0.005%) and may be contaminated plastic silicates, which reduce the toughness of steel. The inventive zirconium content is sufficient and reduces the oxygen content and eliminates the formation of plastic silicates. When the zirconium content in the steel is less than 0,0005% of its effectiveness is greatly reduced. The increase of its content to 0.01% leads to an increase in contamination of the steel oxide inclusions and reduce technological plasticity and the deterioration of the surface of the rails. However, the use of vanadium together with small additions of zirconium eliminates the use of aluminum or reduce its consumption for deoxidation of steel and the metal-free strochechnyh inclusions of aluminates and globular inclusions of large size.

The use of vanadium in steel due to the fact that he, as CR, Mn, Mo increases the solubility of nitrogen in the metal, connecting it in strong chemical compounds (nitrides carbonitrides of vanadium), which are crushed grains of austenite and reduce its tendency to rise when heated.

Introduction V, N in the present limits of the steel leads to grinding grains of austenite to points 9-12 and reduce the tendency of its growth during heating due to the formation of dispersed particles of carbonitrides of vanadium, in the increase of strength and frictional properties and resistance to brittle fracture (brittle fracture). However, without the use of nitrogen vanadium at high concentrations (>0.1 percent) reduces the impact strength increases jednoralski steel. Vanadium increases the limit of endurance, improves weldability.

In the steel containing not less than 0,012% N, the optimal concentration of vanadium is 0.08 to 0.15%. The lower limit of the content of vanadium in the steel chosen because he starts to grind grain at a concentration of more than 0.07%. The upper limit of the content of vanadium is selected based on the fact that with increasing concentrations higher than 0.15% of the relative proportion of nitrogen in the carbonitride of vanadium falls, carbonitride is formed, similar to the carbide of vanadium, which reduces the impact strength.

The nitrogen concentration of less than 0,012% in steel containing less than 0.08% vanadium, does not provide the required level of mechanical properties, impact toughness at -60°and grinding the grains of austenite. With the increasing content of vanadium and nitrogen has become the prior to the proposed limits increases the amount of carbonitrides in it, providing increased strength properties and cold resistance. However, with increasing nitrogen than 0,0 2% of possible cases spotted segregation and nitrogen boil" (bubbles in steel).

Introduction vanadium together with the nitrogen can also reduce the consumption of aluminium in the deoxidation of steel to reduce contamination of its inclusions of corundum, which reduces the contact fatigue strength of rails.

Microalloying of steel rare-earth metals selected based on the following considerations.

Surpassing the calcium affinity for sulfur and oxygen, REM ensure the purification of the metal from impurities (phosphorus, sulfur)emissions of non-metallic inclusions, their globularization. More effective recyclemania and desulfuriza ability REM compared with calcium is related to the fact that they are in the process of deoxidation are present in the form of residual contents in the metal and react with the dissolved oxygen in the entire interval of crystallization. Linking the oxygen and sulfur in refractory compounds, crystallizing in the first place and employees additional crystallization centers, REM crush the structure of the cast steel, facilitate purification of the grain boundaries of cast metal.

The use of REM is most effective for steel, cast by a continuous casting machine. They increase the rate of solidification of continuously cast billets by 15-20%, which leads to the reduction R is stoane between dendritic axes of the first order and increase the zone size equiaxial crystals.

While also improving the cleanliness of the steel of detrimental impurities, the changing nature and globularization non-metallic inclusions, grinding cast steel structure, REM improve hot ductility of the metal, as a result decreasing the incidence of NLS surface defects (cracks, flaws) and increasing yield.

Improving the quality of metal REM provide grinding grain austenite, improve plastic properties, especially impact strength at low temperatures. So microalloying REM it is advisable to spend on rail steel, cast on caster for billets having a lower section and subject to less deformation than the bars.

Microalloying of steel REM will increase gladstonos rails due to more deep deoxidation, increase the purity of the metal oxide and sulfide inclusions, globulariaceae sulphides and exclusions of education plastic silicates, reducing resistance to brittle fracture.

For this purpose the most effective small additives of rare-earth metals, excluding education as plastic silicates and fragile sulfosalicylic containing oxides of rare-earth metals.

REM effectively inhibit the grain growth of austenite. At high temperatures the effect exceeds the effect of vanadium and niobium, which is especially important when load is ve continuously cast billet steel rail (up to 1200-1250° C).

Small additives of rare-earth metals are introduced in the inventive steel to further reduce the oxidation of steel containing a small amount of aluminum (≤0,005%), exclusion of education plastic silicates, increase toughness and brittle fracture resistance. In addition, the surface activity of REM slows down the rate of grain growth in the case, unless their number is not sufficient for the segregation and discontinuities in steel. The number of REM, which is in a solid solution, contributes to the inhibition of grain growth. Contained in the solid solution amount of REM is enough for grinding grain and improve the cold resistance of rail steel.

The increase in the content of REM to 0.005% improves the impact strength at low temperatures.

The REE content in the steel more than 0,007% leads to the formation of inhomogeneities in it. In addition, when the concentration of REE the effectiveness of their grinding grains is weakened, causing an increase in the rate of grain growth. Microalloying of steel REM increases the total work of fracture, at minus 60°promotes the work of crack initiation.

Limiting the content of copper, sulfur and phosphorus selected with the aim of improving the quality of the surface and improve the ductility and toughness of steel. In addition, the end of the acidity of sulfur determines krasnodoncoal, phosphorus - jednoralski steel.

The inventive chemical composition of rail steel provides obtaining high-strength, abrasion - and cold-resistant troostite rails high contact fatigue endurance when cooled compressed air.

The steel of the proposed structure (table 1) was melted in a 100-ton electric arc furnace EAF-100 I and bottled in CCM. The obtained preform was heated and rolled over conventional technologies on rails type P65, which was subjected to oil quenching from a temperature of 800°and leave at 460°C. are Shown in table 2 data show that the mechanical properties, hardness volume quenched rails of the inventive steel is significantly higher than the rails of steel AT [4]. The inventive chemical composition of rail steel provides a high level of plastic properties and high resistance to brittle fracture (KCU-60°C≥0,2 MJ/m2). The increase in hardness, strength, plastic and viscous properties of the rails increases their wear and gladstonos, contact fatigue strength and reliability.

Sources list

1. As the USSR №1435650 Ál With 22 38/16, 1987

2. As the USSR №1239164 Ál With 22 38/16, 1984

3. As the USSR №1633008 A1 Ál With 22 38/28, 1991

4. THE 0921-125-2001 railway Rails of increased wear resistance and contact vinol the news.

Steel containing carbon, manganese, silicon, vanadium, aluminum, nitrogen, calcium, chromium, molybdenum, and iron, characterized in that it further contains Nickel and one of the elements selected from the group comprising zirconium and rare-earth metals, in the following ratio, wt.%:

Carbon0,83-0,95
Manganese0,6-1,1
Mimni0,3-0,7
Vanadium0,08-0,15
AluminumNot more than 0.005
Nitrogen0,012-0,02
Calcium0,0005-0,005
Chrome0,05-0,5
Molybdenum0,11-0,3
Nickel0,05-0,3

one of the elements selected from the group comprising zirconium and rare-earth metals:

Zirconia0,0005-0,005
REM0,0005-0,005
Iron and impurities- Rest

the number of impurities is limited in the following ratio, wt.%:

Sulfur
PhosphorusNo more than 0,020
CopperNot more than 0.20.



 

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