SU901302A1 - Method of thermal treatment of cast austenite steels - Google Patents

Description

(54) METHOD OF THERMAL TREATMENT OF LNTY AUSTENTIC STEELS

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The invention relates to metallurgy and can be used in the heat treatment of cast parts made of carbon austenitic steels.

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The known method of heat treatment of steel is mainly of structural grades, including quenching, thermal cycling and cooling in water or oil, according to which quenching is carried out before thermal cycling, the thermal cycling is carried out with holding at heating until complete dissolution of carbides and drying in the interval Aj. 600 ° C until the completion of the decay of auste.chita

However, this heat treatment mode is used mainly for multiphase steels (pearlitic or martensitic-pearlitic class) and it does not give a positive effect for austenitic steels working in

contact fatigue loading conditions combined with impact.

There is also known a method of hardening metastable austenitic steels by phase hardening, including direct and reverse martensitic transformation and aging, according to which reverse transformation and aging are carried out under isothermal conditions of C21.

The disadvantage of this method is the presence in the structure of martensite and carbides, as well as the complexity of the process.

The closest to the proposed is a method of heat treatment of carbon austenitic steels, including double annealing and quenching for Cz austenitic-carbide structure

The disadvantage of this method is the presence of carbides in the structure.

20 re austenitic, resulting in a decrease in the contact and fatigue endurance of parts when operating under conditions of impact loading: wk. 390 The purpose of the invention is to increase the wear resistance and durability of cast cores and solid-cast crosses made of G13L steel, which work under conditions of contact fatigue loading in combination with impact. This goal is achieved by the fact that in the method involving double annealing and quenching, the second annealing is carried out stepwise, for which the product is heated to a temperature of 170,200 ° C below AC, maintained at this temperature for 2 hours and then heated to 50- 110 ° C above Ag with a vacuum at this temperature for 0, 1.0 h, after which the product is cooled with the furnace to 500-540 ° C, kept at this temperature for 2 h and after aging, it is heated under quenching and quenching on austenitic structure. The main task to be solved with step-by-step annealing is to eliminate the adverse effects of the factors responsible for both the reduction and instability of the physicomechanical properties of the steel and the service characteristics of the parts due to the grinding of the grain, a more complete solution of the primary carbides, none of the grain boundaries: reduction of pores and foundry submicrocracks, transfer to austenite solid solution at boundary atoms, crushing of phosphide eutectics, etc. In order to achieve maximum phase slope, especially at the grain boundaries, in 110ZL steel, during heating for quenching, it tends to heat the steel to 540 ° C (optimal range is 550-540 ° C) with an isothermal dehumidification at this temperature for 2 hours. The parameters of the crystal lattice in 110G13L steel are in the range of 500-540 ° С. This is due to the release of carbon from the solid solution, austenite, which is in the form of carbides (Fei Mn) j C along the grain boundaries, and the lean solid solution of the sustenite at the temperature of maximum precipitation of carbides begins to decompose with the formation of the CX phase. Under the influence of phase hardening, arising from differences in specific volumes of lamer carbides of the CX-th phase and austenite, fragmentation of the brittle components along the grain boundaries (oxides, phosphide eutectic, primary submicrocracks, microcracks, etc.) is achieved. The use of a longer holding time and temperature is impractical, since it leads to the appearance of too large and large amounts of carbides, which then slowly dissolve. Subsequent heating to 800 ° C is necessary for more uniform carburizing of austenite with carbon over the grain volume (central areas) due to partial dissolution of carbides, improvement of the state of grain boundaries; acceleration of diffusion processes in solid solution due to conversion of impurity elements into solid solution, destruction and partial dissolution of oxides, phosphide eutectic, etc. . The holding time at 800 ° C is limited by the minimum time required for fixing a given temperature by thermal engineering devices, but not more than an hour. In contrast, an undesirable decrease in defects of the crystal structure in the central zone of the grains is observed and grain growth begins. Subsequent cooling to 500 ° C and an isothermal surcharge for 2 h is associated with the need to obtain a larger number of recrystallization nuclei, a larger value of the internal (ignition) austenite energy due to phase hardening during the separation of carbides and CX phase, more crushing of oxides, phosphide eutectic and t .P. Therefore, during this period, the separation of carbides and the CX phase is sought, both along the grain boundaries and in their central zone. Subsequent heating from 550 ° C to 1,100 ° C H1 is required to completely dissolve the oC carbides - to transform the dissolution of phosphide eutectics, oxides of the conversion of impurity elements into a solid recrystallization solution and to obtain a pure austenitic structure. In contrast to the known recrystallization regimes, obtaining pure austenitic structure with fine grain boundaries is more intensive and fuller due to phase hardening and plastic deformation as a result of (transformations. The positive effect of heat treatment according to the proposed mode is confirmed when considering hardness data, details after heat treatment and comparative analysis of the microstructure of steel before and after heat treatment. The steel hardness is noticeably increased due to phase hardening, in the microstructure, the grinding of the primary grain and the cleaning of grain boundaries are observed, which ultimately leads to an increase in the wear resistance and durability of the cast parts. The proposed method is carried out as follows. Cast cores and solid crosses made of G13L steel were knocked out from the casting mold to 500540 ° C, maintained at this temperature for 2 hours and cooled in air to room temperature 10-30 ° C.}. The parts are then subjected to stepwise annealing in the following mode. The parts are heated to 500-540 and held at this temperature for 2 hours, from this temperature they are heated to 780-850 ° C and held at this temperature for 0.5-1.0 h, after which the parts are cooled together with a furnace up to 500-540 ° C and kept at a temperature of 2 hours. After the step annealing, heating for quenching is from 500-540 ° C and quenched to an austenitic structure. Parts from G13L steel are heat-treated from one melt smelted in the main electric furnace and having the following chemical composition, wt.%: Carbon 1.34 Manganese 12.93. Silicon 0.72 Phosphorus 0.044 Sulfur 0.012. The point Ac, determined during heating at a rate of 70 ° C / h, is 710 ° C. Table 1 shows the heat treatment options for cast parts according to the proposed method in comparison with the known (control) heat treatment mode (option b), as well as data for comparative modes. . Table 2 shows the service characteristics of cast parts. Figure 1 shows the graphs of the hardness value versus the number of working glasses on the EMC-60 machine for parts that have been heat-treated in the known mode; in fig. 2 - the same for parts that have undergone heat treatment according to the proposed mode and comparative modes (curves 1U and U according to, mode J, as well as 4 and 5; curves U and UE according to mode 4; curve USH through mode ZX. As a result heat treatment according to the proposed mode increases the steel's ability to work hard. The proposed heat treatment mode reduces the elimination of manganese, carbon and other elements and thereby increases the steel's ability to work hard, which leads to an increase in the durability of parts from it. (1) Figure 1 shows that the wear resistance and durability of cast parts as a result of the proposed heat treatment is higher compared to the parts that have undergone heat treatment according to a known regime. Analysis of the data in Table 2 shows that the number of working cycles before the appearance of the first contact fatigue cracks for parts subjected to heat treatment according to the proposed mode {mode 1), defined as the average for three samples, is O, 9710, while the same characteristic for the known mode (mode 6, defined as average for the three samples, it is 0.5910. The service life of products increases by 67%. Wear and tear attributed to 10 cycles is respectively for the proposed mode of 4.1 mm and 4.5 mm for the known mode (the average value for 3 samples, i.e. the increase in durability, is em 10%). Repeated (two or three times) repetition of the step annealing in the temperature range of 500-850 ° C allows to increase the durability of the products in addition. The durability of parts that have undergone heat treatment in mode 4 will increase on average to 1.05MO, i.e. It has an increase in durability by another 0% and an increase in wear resistance by 5-20%.

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The method of heat treatment of cast austenitic steels, predominantly high-manganese, including double annealing and hardening, characterized in that, in order to increase the durability and wear resistance of cast parts, the second annealing is carried out stepwise with depletion in the first 55 stage at a temperature of 170-200C below AL in for 2 h and the second at a temperature of 50-110 ° C above the AU

they are cooled together with the furnace to the temperature of the first one. The annealing steps, they withstand heat from the temperature and they are heated under the temperature.

. Sources of information taken into account in the examination

1. USSR author's certificate No. 583185, cl. C 21 D 1/78, 1976.

2. Authors certificate of the USSR R 454265, cl. From 21 D I / 7 & 1972.

3. USSR author's certificate No. 444819, cl. From 21 D 1/78, 1973.

Claims (3)

The method of heat treatment of cast austenitic steels, mainly high manganese, including double annealing and hardening, characterized in that, in order to increase the durability and wear resistance of cast parts, the second annealing is carried out in steps with exposure to the first stage at a temperature of 17O-2OO ° C lower AC for 2 hours and the second at a temperature of 50-110 ° C above Ata for 0.5-1 hours, after which the parts are cooled together with the furnace to the temperature of the first Annealing step, kept from the temperature, they are heated under s yalku. . Sources of information taken into account during the examination 1. USSR Copyright Certificate No. 583185, cl. C 21 1/78, 1976. 2. / USSR copyright certificate P 454265, class S 21 0 1/78, 1972 .. 3. Copyright certificate of the USSR No. 444819, cl. C 21 D 1/78, 1973. 32ΰ ./* Λ. > 5 # * · „ gg- ”7 f - // O * 2nd * fy'10? 8th ^5th number of cycloff 'ri? -1 VNIIIPI Order I2303 / 24 Circulation 586 Subscription Branch of PPP Patent, Uzhhorod, st. Project, 4