Method of making fasteners from high-strength titanium alloys

FIELD: process engineering.

SUBSTANCE: invention relates to metallurgy and may be used at making rods with heads from titanium alloys. Billets are subjected to thermal treatment to perform hot heading. After heading thread is cut and head fillet is hardened. Thread is cut in two steps. First, preliminary incomplete knurling is performed after tempering of billets with deformation. Said deformation is defined by percentage between formed tooth thread depth to required depth to make 85-98%. Then workpiece is age-hardened to perform final thread cutting.

EFFECT: high strength bolts from titanium alloys with flaw-free thread, lower production costs.

3 cl, 1 tbl, 6 ex

 

The technical field

The invention relates to the field of metallurgy, in particular, to methods for producing rod parts with heads made of titanium alloys, and can be used in aerospace engineering, chemical engineering, shipbuilding, automotive industry.

The level of technology

A known method of manufacturing a rod parts with the heads of the two-phase (α+β) titanium alloys comprising annealing the workpiece, the coating on the surface of the solid oxalate coating, landing head, multiple reduction of the rod, aging, machining, rolling radius under the head and shaft and the rolling thread (EN 94004583 A1, 20.10.95; 2156828 C22F 1/18, 27.09.2000).

The known method provides for the preliminary heat treatment rods by quenching in vacuum oven at 800-850°C with subsequent cooling with the oven up to temperature 580-600°C, and then in the water and aging at 300-400°C for 6-8 h, machining, comprising the operation of forming by cold plastic deformation, running their outer surface and the rolling of the thread.

The main disadvantage of this method is the inability to receive fasteners with a diameter of 8-10 mm above and not sufficiently high strength and toughness of the products, due to the presence of the of digging and layers in the surface layer after rolling thread which are stress concentrators.

A known method of manufacturing bolts of the two-phase (α+β) titanium alloys, for example, W 16, by means of hot landing ("the Manufacturer of hexagon head bolts made of titanium alloy W 16 in conditions of mass production, V.A. Chernyshov, N.G. Evlanov, DSC. Osipov, E, Gavrilin, A.V. Mitin. Annex No. 2 to the magazine "Aviation industry", 1975, and "Standardization of fasteners made of titanium alloys", №2, 2001) includes the segment blanks, hot landing, heat treatment, machining, hardening of the bucket and the knurling thread. This method allows you to produce bolts 4-36 mm

A significant impact on the core strength of fasteners has a thread, which in this respect, the most dangerous place in determining the strength of the bolt with static stretching. The normal flow of the process of formation thread by the method of plastic deformation (rolling) is provided on the titanium alloys of the type W 16 with tensile strength αB≤1150 MPa, elongation δ≥12% and the relative contraction ψ≥40%.

The disadvantage of this method is the limitation of the strength properties of the material of the bolts due to the inability of the education quality thread (without gaps and sunsets) by the method of plastic deformation.

Somnos the ü inventions

The present invention is the development of technological process of manufacturing high-strength bolts made of titanium alloys with flawless carving and strength above 1150-1200 MPa at reducing the cost of its implementation by eliminating heating operation under the knurling thread.

This object is achieved in that in the method of manufacturing of fasteners made of high-strength titanium alloys containing a rod with a head and a threaded end, including the production of semi-products, heat treatment, hot landing heads, machining, thread rolling and hardening the bucket head, knurled thread carried out in two stages: first make a preliminary incomplete knurling thread on the blanks after hardening, deformation, defined as the percentage ratio of the height of the formed tooth thread to the desired height of the tooth of the thread equal 85-98%, then after hardening aging produce a full knurling thread to get the thread with the required geometrical parameters.

In addition, preliminary incomplete knurling thread on the blanks perform at temperatures below its recrystallization temperature, deformation 90-95% and subsequent final full knurling perform holodnuju at normal temperature.

It is possible for high-alloyed titanium SP is avow preliminary incomplete knurling thread on the workpiece to perform holodnuju after quenching with deformation of 85-95%, and subsequent final full knurling to perform holodnuju at normal temperature.

This embodiment of the method allows to obtain high-quality fasteners made of titanium alloys at minimal cost.

The implementation of the invention

In accordance with the invention, a method of manufacturing of fasteners made of high-strength titanium alloys containing a rod with a head and a threaded end in accordance with the invention is implemented as follows.

The method includes the production of semi-products, heat treatment, hot landing heads, machining, thread rolling and hardening the bucket head. The thread rolling is carried out in two stages: first make a preliminary incomplete knurling thread on the blanks after hardening, deformation, defined as the percentage ratio of the height of the formed tooth thread to the desired height of the tooth of the thread equal 85-98%, then after hardening aging produce a full knurling thread to get the thread with the required geometrical parameters

In addition, preliminary incomplete knurling thread on the blanks of high-alloyed titanium alloys (e.g., W-22) perform at temperatures below its recrystallization temperature, deformation 90-95% and subsequent final full knurling in the discharging holodnuju at normal temperature.

Possible preliminary incomplete knurling thread on the workpiece (for example, from an alloy of W-16) to perform holodnuju after quenching with deformation 85-95%), and the subsequent final full knurling to perform holodnuju at normal temperature.

Examples of specific implementation method

1. Part annealed and hardened bolts with a diameter of 12 mm alloy W 16 after the operation of cutting and hot landing heads on the crank press at a temperature of 750°C was subjected to the machining of the rod under the knurling thread. Then the workpiece was held operations running special rollers chamfers at the transition from the stem to the head for strain hardening. After this operation, the workpiece was placed in the roller rolling machine. The billets were rolled thread at normal temperature with a deformation of the alloy capable of forming a thread with dimensions specified by the standard. Mode roll: roll 3, the pressure in the hydraulic system of the machine 5 MPa. After rolling the threads controlled by gauges, investigated the thread surface at magnification ×30 and explored sections of the longitudinal slits at magnification ×200. Cracks, delaminations and chips of metal were found. After rolling 5 samples, the bolts were tested for ultimate strength (see table 1, item 1).

2. The samples of the second batch subjected to all videopix is authorized in claim 1 operations to strain hardening of the chamfers at the transition from the stem to the head and roll the threads were then noncorrosive hardening aging at a temperature of 560°C in flowing argon in the container, placed in an air furnace. The dwell time at the temperature of 560°C - 6 hours. The implementation of this operation is possible in a vacuum furnace. The knurling thread after aging at normal temperature and run-in chamfers in the transition region from the rod to the head was performed according to the mode of formation of the first batch of samples. In the same way exercise control and evaluation study thread. It was found cracks in the hollows of the thread and its local destruction in the area of the peaks of the thread (see table 1, item 2).

3. Third party samples, the previous operations are similar to operations of the first batch before the operation running fillets, pressing the thread in the quenched state of the alloy under the condition of deformation of the alloy, providing not fully formed thread profile. The value of this conditional deformation, defined as the percentage ratio of the height of the formed tooth thread to the height of the tooth, the required standard, was equal to 95-98%. This strain was obtained by reduction of the stroke of the rolling of the rolling roller machine for knurling. After pre-rolling the billet was held operation of aging on aging second batch of samples. Then the workpiece was donativo with conditional deformation 5-2% in order to obtain a thread with the required standard geometrical parameters and produced a run-in chamfers in places the transition from rod to the bolt head of each sample. In conclusion, the samples underwent follow-up research and evaluation strength in accordance with the above procedures. In the absence of any damage in the thread (see table 1, p.3). the strength of the samples did not differ significantly from the strength of the samples of the 1st party.

4. The next batch of samples was fabricated similarly to the samples of the 3rd party when the value of conditional warp thread 90-95% with tokatkoy samples in aged condition 10-5%. In the absence of any damage in the thread strength of the samples increases significantly (see table 1, item 4), which indicates the formation of a hardened surface layer in the thread.

5. The next batch of samples was fabricated similarly to the samples of the 3rd party, but with the value of the conditional deformation when the knurling and decade thread accordingly 85-90% 15-10%. The result is a quality thread with the same strength as that of the samples of the 4-th party.

6. Sixth batch of samples was fabricated similarly to the samples of the 3rd party, but with the value of the conditional deformation when the knurling and decade thread accordingly 80-85% 20-15%. The results of the carried out researches have allowed to detect the beginning of the formation of cracks in the thread.

As the experiments showed, not all titanium alloys suitable for knurling thread even in the quenched condition, ensuring maximum plastices the properties. For example, the workpieces from signalisierung alloy VT (system Ti-Al-Mo-V-Fe-Cr) due to its high strength and low ductility due to the high content of β-stabilizing elements cannot obtain defect-free thread even in the quenched condition alloy characterized by high ductility (elongation alloy δ=9%).

To obtain a good thread on the blanks of alloy type VT 12 mm in diameter were placed in the inductor with an inner diameter of 18 mm, coupled with a semiconductor generator HDTV power 25And kW and installed in the immediate vicinity of the rolling machine, which made the knurling thread. When the current in the inductor 43OA the workpiece was heated to 400°C for 4 seconds. Then the workpiece was placed in the roller rolling machine, which made the knurling thread according to the above mode with conditional deformation of 90-95%. After roll threaded procurement aged very early because in an atmosphere of flowing argon at 500°C for 8 hours. After hardening of running fillets in places of transition from the stem to the head of procurement has donativo at normal temperature with the conventional deformation 10-5% to the required standard thread sizes with the formation of a hardened surface layer, i.e. the hardening treatment was performed without pre-heating under the knurling. In the result, the received samples with a high quality thread without discontinuities of the metal due to the slight deformation of the metal during dokecki, but sufficient to harden the threads. The ultimate tensile strength of the samples was in the range of 1250-1300 MPa.

Table 1
№ p/pThe state of the alloy, with preliminary knurledConditional deformation in the pre-knurled, %The condition of the alloy when decadeConditional deformation at decade, %Quality threadUltimate tensile strength, MPa
1Tempered100-Defects850-950
2Hardened by aging100-Cracks, spalls, delamination of metal
3Tempered95-98Hardened by aging5-2 Defects950-1 100
4Tempered90-95Hardened by aging10-5Defects1200-1250
5Tempered85-90Hardened by aging15-10Defects1190-1240
6Tempered80-85Hardened by aging20-15Cracks, partial delamination of metal

Technical and economic effect

The proposed technology allows you to:

1. To obtain high-quality fasteners with strength 1150-1200 MPa, including a large amount of high-strength billet of titanium alloys without heating for knurling thread.

2. Direct replacement for aircraft steel bolts for high-strength titanium can reduce their weight by 35-40%.

3. The application of cold rolling threads eliminates structural and GE the metric changes threaded part fasteners, and two knurled - numerous defects that occur when a single-pass formation of the thread.

1. The method of manufacturing of fasteners made of high-strength titanium alloys containing a rod with a head and a threaded end, including the production of semi-products, heat treatment, hot landing heads, machining, knurling thread and strengthening the bucket head, characterized in that the knurling thread carried out in two stages, firstly make a preliminary incomplete knurling thread on the blanks after hardening, deformation, defined as the percentage ratio of the height of the formed tooth thread to the desired height of the tooth of the thread equal 85-98%, and then, after hardening of the aging of the workpiece, producing a full knurling thread to get the thread with the required geometrical parameters.

2. The method according to claim 1, characterized in that the preliminary incomplete knurling thread on the blanks perform at temperatures below its recrystallization temperature, deformation 90-95%, and subsequent final full knurling perform holodnuju at normal temperature.

3. The method according to claim 1, characterized in that the preliminary incomplete knurling thread on the blanks perform holodnuju after quenching with deformation of 85-95%, and the subsequent final full knurling perform whole is dnow at normal temperature.



 

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