SU1382861A1 - Method of thermal treatment of large forgings - Google Patents

Abstract

The invention relates to the field of metallurgy, namely to heat treatment, and can be used mainly in the preliminary heat treatment of large forgings made of flock-sensitive steels of martensitic class. The aim of the invention is to reduce the process time and improve machinability. The method includes the accumulation of forgings after forging at 500 s, cooling to 200 s, overhanging, repeated heating and cooling with isothermal pumps 740 and 640 s. Between the two isothermal vortexes, the forgings are deeply cooled to 150–180 ° C, the final cooling is carried out from, first at a rate of 20 C / h to aging at 5–7 h, and then in air. 2 tab.

Description

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The invention relates to metallurgy, namely to heat treatment, and can be used, mainly, at preliminary heat treatment of large forgings from floc-sensitive steels of martensitic class,

I The aim of the invention is to shorten the process time and improve machinability.

The method is carried out as follows.

After forging, forgings from steel 38KhNMFL (0 660 mm, mm) are held at 600-650 ° C, then cooled to 200-250 ° C and held until the temperature levels off. From this temperature, they carry out 3-crater heating to 7AO-770 C and cooling to 640-660 ° C, produce isothermal, hold at 640-660 C and cool to 150-180 ° C, incubate, heat to 660- 680 C with isothermal The cooling rod is cooled at a speed of 15-25 C / h to 400 ° C, held for 5-7 hours and finally cooled in air. Repeated heating and cooling from the temperature Ac, + (20-50) С 740-770 ° С provide accelerated diffusion of hydrogen from the forging. However, the stability of austenite in the x-martensitic class (for example, 38XNZYFA) is very high and even after repeated thermal cycling and prolonged delivery at 640-660 s in the forgings, up to 6-10% of non-decomposed (residual) austenite remains. The decomposition of this austenite occurs in the proposed method with deep supercooling of forgings up to 150-180 ° C (the temperature of the end of the martensitic transformation in steel of the type HICHMFL). Upon subsequent heating at 640–660 ° C and holding, release of products of austenite-q conversion leads to perlite formation, which leads to a decrease in hardness and an improvement in the workability of cutting forgings, an increase in tool life (ro.zone).

The research results are summarized in table. one; The rationale for the limits of the final cooling mode is: but in the table. 2 (according to method 1 - in a closed furnace up to, VOXA 5-10 ° C / h; according to method 2 - in an oven up to 400 ° C with an open gate and feed B03ijyxa through burners, 15-25 s / h, holding at 400 ° C 5-7 hours, then in the air;

according to method 3 - in the air on the extended hearth, up to 350 ° C, 35-50 0/4, then in an open furnace up to 150 ° C, VOXA 5-10 ° C / h).

Accelerated final cooling of forgings (speed of 15–20 ° C / h from 650 to 400 ° C and a drain of 5–7 h reduce the duration of the cooling cycle by a factor of 2. At the same time, the final cooling mode provides almost insignificant residual stresses in the forgings. So The residual tensile stresses after such a method of final cooling in the center of the forging 0 660 mm are 3-4 kgf / mm, which is slightly higher than the residual stresses in the forgings after complete furnace cooling (1-3 kgf / mm) and fully ensures their quality Twain protivoflokennuyu processing.

As follows from the table. 2, the proposed method 2 of the final cooling provides almost the same level of residual stresses as methods 1 and 3, however, its duration is 2-4 times less.

Forging quality research: metal macrostructure monitoring, ultrasonic testing, performed 7-10 days after heat treatment and after 3 months, did not detect floken. Stripping and drilling of the billet show good machinability (roughing productivity is 2. forgings 660 mm X 1220 mm per shift).

If the duration of heat treatment by a known method is 450-500 hours (15-25 days), then according to the proposed method it is 290 hours (12 days).

Claims (1)

Invention Formula The method of heat treatment of large forgings mainly from flock-sensitive steels of martensitic class, including exposure after forging at 550-650 C, cooling to a predetermined temperature, hardening, repeated heating to Ac, + (20-50) ° C and cooling to 640-660 ° C with a top down and controlled cooling, characterized in that, in order to shorten the process time and improve machinability by cutting, cooling from 550-650 ° C to 313828614 are allowed to 200-250 ° C, controlled at a cooling rate of 15–20 ° C / h, maintained at 150–180 ° C, then at an ambient temperature for 5–7 h and the substance is heated further to 640 ° C. 660 С and cooled to 400 С with cooled in air. speed - 15-20 ° C / h, at this temperature during cooled in air. Table 1 Q Evaluation Criteria Supercooling Temperature, G 140 I 150-180 G 200-250 The amount of residual austenite,% No 1-4 6-10 Processability cutting Good Good Bad dissatisfaction. Presence of defects (floken) Yes No No Table 2 Evaluation Criteria Cooling Method for forgings 1 0 660 mm 1 2 3 I Duration of cooling, h70-30 15-16 35-50 The value of residual tensile stresses in the center, CGS / MM2 1.5-2.0 3-4 4-5 i   - Compiled by A.Oryoshkina Editor N.Gunko Tehred M.Hodanich Corrector I.Erdeyi Order 1264/23 Circulation 545 Subscription VNIIPI USSR State Committee for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5 Production and printing company, Uzhgorod, Projecto st., 4