SU1006508A1 - Method for heat treating cast iron - Google Patents

Description

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The invention relates to heat treatment of cast iron. It can be used in any industry, using wear resistant cast irons. The known method of heat treatment of wear-resistant cast irons, aimed at eliminating the deficiencies of the state and growth (plasticity before machining the workpieces, including slow heating for up to 600 + 10 ° C, holding at this temperature for 4 hours, heating to .9 O0 + 10 ° С for 2 h and holding for 2 h. Next, slow cooling is performed at a speed of 25-30 C / up to 400 + 20 0 and final air cooling. Total treatment time is 30-32 h 1 The disadvantage of this method. The heat treatment process is longer. The closest to the invention to the technical essence is the method of heat treatment of cast iron, including multiple heating at a speed of 30-100 C / min to 980-1050 C, followed by air cooling to 600-650 ° C and final air cooling to room temperature after 5-8 processing cycles. The total processing time is 3-5 hours 2. However, the known method provides for the decomposition of primary cementite and the graphitization process in white low-alloy wear-resistant cast irons and is not suitable for processing high-alloyed o. resistant cast iron. . . . . The purpose of the invention is to increase the processability of resandem by reducing hardness and reducing; heat treatment time. The goal is achieved by the fact that according to the method of heat treatment of cast iron, predominantly high-alloy wear-resistant, including thermal cycling relative to Ac1, and the final air cooling, the cast iron after thermal cycling is subjected to isothermal aging for 1.5 to 2.5 hours at a temperature below Ah 2 O-80 ° C. During thermocycling, heating and cooling are carried out at speeds of 150-250 and 1800 g-3600 s / min, respectively, the temperature of heating and cooling during thermal cycling is 1100-1150 and 400-500 C, respectively Naturally, and at 400–500 ° C, the shutter speed is reduced by decreasing from cycle to cycle. Heating to accelerates diffusion processes for the dissolution of carbides in austenite. When heated above 1150 ° C at acceptable speeds, there is a danger of melting down thin edges and edges of the product. The heating rate of 150–25 ° C / min is the maximum for a received product under actual production conditions. This heating rate contributes to the suppression of polygonization and the development of austenite recrystallization processes. A. The difference between thermal conductivity and linear phase expansion coefficients under conditions of rapid heating determines a sharp increase in the dislocation density in the alloy, which in subsequent cycles can reach a level of cm. Slow heating with increasing total treatment time helps to obtain a coarser structure. The cooling temperature in each processing cycle (400-500 s) is determined by the feasibility of obtaining a bainitic structure with a high degree of dispersion of carbides and their uniform distribution in the matrix volume. Cooling to 400-500C is accelerated in order to suppress the process of carbon separation from austenite on the surface of the honeycomb ledeburite and to maintain the supersaturated solid solution of austenite to the required decomposition temperatures. At the same time, thermal and phase voltages increase the dislocation density of fine-grained austenite, which reduces its resistance to decay and transformation time. A further increase in the cooling rate leads to the formation of quenching stresses at a high level. The feasibility of reducing the exposure time in the process of thermal cycling at 400-500 ° C from cycle to cycle is determined by the fact that the eutectoid and secondary cementite, when the austenite is subcooled below 160-780 ° C, is unincubated. Besides. The incubation period of y- + oC + to transformation at 400-500 ° C is minimal) from cycle to cycle the size of grain, austenite decreases, the degree of spheroidization of carbides in austenite increases with their uniform distribution in the matrix volume. At the same time, the initial stages of each subsequent warming up lead to an intensive completion (about., + To an increase in the degree of spheroidization of carbides; their resistance to dissolution increases during subsequent short-term heatings, as the surface energy decreases and the level of carbon interatomic bonds increases. 400-500 0 unnecessarily increases the processing time. The choice of the isothermal temperature is 20–80 s below Ah after thermal cycling or is determined by the conditions of decomposition of the supersaturated fine grain of that ay stenite at a sufficiently small incubation period with the formation of an abnormal structure. At higher temperatures (above 7QO ° C), carbon is preferentially allocated to the ledeburitic skeleton, and overcooling of austenite below 700 ° C leads to the formation of lamellar pearlite. The blanks are heated in the molten salt to 1100-I50 ° C, followed by cooling on the steel or copper plate with compressed air blowing to 400-500 C, short-time exposure is carried out at this temperature in the molten salt and Torr dissolved cycle naked roar and cooling with reduction of time posledovatelnELM isothermal vvderzhki at 400-500 ° C of 8 to About 4-6 minutes after the workpiece machining cycles from the last heating temperature, transferred to a salt melt at a temperature below at Ah. 20-8Q ° C and produce an isothermal heat for 1.5-2.5 hours with final cooling in calm air. As a result of the proposed treatment, the skeleton of ledeburite is partially destroyed, the grain size is reduced, the spheroidization and coagulation of carbides is caused by the repeated imposition of thermal and phase hardening on the carbides and their spheroidization. The isothermal expansion after thermocycling provides the final stabilization of the structure, reduces the dislocation density in the matrix volume, and contributes to the development of the coagulation process of carbides. The thus obtained fine grain structure with spheroidal carbides uniformly distributed throughout the matrix provides. Reducing hardness and good workability by cutting blanks from. wear-resistant high-alloyed, cast iron. In addition, the resulting structure is highly technological for the subsequent strengthening heat treatment of finished products and will provide an increase in their performance properties. Example. Billets of highly carbonated wear-resistant cast iron ICHH12M (ZOOH12M) with a cross section of 8–15 mm are heat treated in three modes; . G. Slow heating in an electric chamber furnace up to, lightening F h, heating up, holding 2, h, slow cooling with a furnace before and unloading from the furnace to the air. Total time 33 h. II. - Heating at a speed of 80-90 C / min in a salt bath with a temperature of (1000 - 1030) + 5 ° С, cooling with a speed of 80-160 s / min with calm air up to 620 +, reheating in a salt bath and so further (8 cycles in total). The latter heating is completed by cooling to room temperature in air. The total time is 4.5 h. Sh. Heating at a speed of 180–200 ° C / min to IZO + in a salt bath with a temperature of 1260–1270 s, accelerated cooling on a copper plate with blowing air squeezed to 500,450 s, transfer of blanks to an alkaline bath with a temperature of 460 +, holding at this temperature for 8 minutes and reheating to, FROM + 10 ° C. On each subsequent cycle, the exposure time at 460 + 5 ° C is reduced (6, 4, 2.0 min). From the temperature of the last heating of the billet, they are transferred to a salt bath with a temperature of 700 + with an isothermal heat of 1-2.5 hours. The final cooling is carried out in air. Total time 2.5h. The processing results are shown in the table. Thermal treatment according to the proposed sp6s: shoe provides almost the same hardness and processing. cutting ability with slow kiln annealing. Thermal treatment by the proposed method provides the required structure 15 times faster than. with slow furnace annealing and 1.5-2 times faster than by a known method.

Heat Treatment Modes

1 (slow furnace annealing)

tl (known method)

W (the proposed method)

HRC

Cutting speed I with hourly cutter durability in m / min (t 2 mm S 0.29 mm / rev

30-33

36.5 62-64 6.2

34,8

35-37

Claims (4)

1. METHOD OF THERMAL TREATMENT '^ OGUN, mainly high-alloyed? Wear-resistant, including thermal cycling relative to Ac * and final cooling in air, characterized in that, in order to increase the processability of cutting, cast iron after heat. They are subjected to isothermal aging for 1.5-2.5 hours at a temperature below Ah. at 20-80 ° C. 2. The method according to π. 1, from l and h a rain and th with the fact that, with the Purpose of Socra-. the time of heat treatment during thermal cycling, heating and cooling are carried out at speeds of 150-250 ° C / min and 1800-3600 ° C / min, respectively, 3. The method according to PP. 1 and 2, wherein the heating and cooling are carried out to 1100-1150 ° C and up to 400-500 ° C, respectively. 4. The method according to PP. 1-3 ,. The reason is that in the process of thermal cycling at 400-500 ° C, an exposure is carried out, decreasing ότ of the cycle to the cycle.