RU2068449C1 - Method for thermal treatment of steel cast cores of frogs - Google Patents

Abstract

FIELD: ferrous metallurgy, mainly, manufacture of hardened steel cast cores of frogs made of steel 100 KhSF with thermal treatment. SUBSTANCE: cores made of steel 100 KhSF are subjected to granular annealing, for which purpose, it is heated up to temperature of 810-830 C with heating rate of 50- 75 C/h. After one-hour holding, cores are cooled at the rate of 15-20 C/h down to temperature of 650 C with subsequent cooling in the air. After annealing, the cores are heated for hardening to temperature of 810-830 C and held for 1 h. Then, cores in suspended position are cooled down to 600-650 C with the help of sprayer or in the device with organized water flow. Further cooling down to 280-300 C is carried out in oil. Then, cores are subjected to tempering in the suspended position at 300-280 C for 3 h with subsequent cooling with furnace down to 20 C. EFFECT: increased service life of parts. 4 cl, 1 tbl

Description

 The invention relates to the field of ferrous metallurgy, mainly to the production of hardenable steel cast cores of crosspieces of railroad switches, made of steel 100SHF during their heat treatment.

 The goal is to increase the service life of parts.

 To perform the proposed method, the heat treatment of cast steel cores made of steel 100HSF was carried out. For this, three heats of 8 cores of the following chemical composition were cast (see table).

Example 1. Using the well-known existing heat treatment of cores according to GOST 7370-86, one core was taken from each heat, which was heated in a gas furnace to 1100 1150 ^o C and after two hours exposure at this temperature were quenched in a water well. As a result, the cores had significant warpage and quenching martensite structure.

Example 2. To obtain comparative data, another core was also produced using the well-known heat treatment from each heat with heating to 700,750 ^° C and two-hour exposure. In this case, the cores were practically not tempered and had an unsatisfactory structure.

Example 3. Annealing on granular perlite. The core of the cross was heated to 810 ^° C in a shaft electric furnace in suspension with a heating rate of 50 ^° C / h for 1 hour at 810 ^° C, then it was cooled at a speed of 15 ^° C / h together with the furnace to 650 ^° C and then cooled in air outside the oven up to 20 ^o C. Warpage of the core was not observed. The structure of the core metal after annealing is granular perlite.

Quenching. Heated to 810 ^o C in a shaft electric furnace in suspension at a speed of 50 ^o C / h, followed by exposure at 810 ^o C for 1 h to equalize the temperature throughout the core, removed the core from the furnace and cooled in a suspended state in a device with an organized flow water from 810 to 600 ^o C. After this, the core was removed from the cooling device and cooled in an oil bath from 600 to 280 ^o C, after which the core was placed in a heating shaft furnace in a suspended state, heated to 280 ^o C, and kept in it at this temperature for 3 hours. Then the core is cooled together with the furnace without limitation to a cooling rate of 20 ^o C and removed from the furnace.

 The structure of the core metal over the cross section, the depth of the hardened layer (8 12 mm), its hardness (400 450 HB) corresponded to the required values, the core was not warped.

Example 4. Annealing. The core of the cross was heated to 830 ^o C in a shaft electric furnace in suspension with a heating rate of 75 ^o C / h and 1-hour exposure at 830 ^o C, then it was cooled at a speed of 20 ^o C / h with the furnace to 650 ^o C and then cooling in air in a suspended state outside the oven to 20 ^o C. Core warpage was not observed. The structure of the core metal after annealing is granular perlite. The heating time due to the higher heating rate was reduced by about 30% compared with the time in example 1.

Quenching. The core was heated to 830 ^o C in a shaft electric furnace in suspension at a speed of 75 ^o C / h, followed by exposure at 830 ^o C for 1 h to equalize the temperature throughout the core, the core was removed from the furnace and cooled in a suspended state in a device with an organized the flow of water from 830 to 650 ^o C. the Heating time due to the higher speed was reduced by about 30% compared with the time in example 1.

After that, the core was removed from the cooling device and cooled in an oil bath from 650 to 300 ^o C, after which the core was placed in a heating furnace in a suspended state from 300 ^o C in the furnace and kept in it at this temperature for 3 hours. Then the core was cooled together furnace without limitation up to 20 ^o With and removed from the furnace.

 The structure of the core metal over the cross section, the depth of the hardened layer (8 12 mm), its hardness (400 450 HB) corresponded to the required values. No warping of the core was observed.

Example 5. The technological operations are the same as in example 1, but the heating rate was 40 ^o C / h The results are positive, but the process time and power consumption have increased.

Example 6. The technological operations are the same as in example 1, but the heating rate was 100 ^o C / h Warpage of the core was observed, and cracks appeared in some of the most massive parts of it, and further heat treatment had to be abandoned. The results are negative.

Example 7. The technological operations are the same as in example 1, but the heating rate was 80 ^o C / h A slight warpage of the core was observed, which is a disadvantage associated with an increase in the heating rate. The result is unsatisfactory.

Using the proposed method of heat treatment of steel cast cores made of steel 100HSF provides the following advantages compared to existing methods:
a) increasing the service life of the cores by obtaining differentiated hardness along the cross section of the core, gradually decreasing to its core, which is especially important for the operating conditions of the cores of crosspieces of railroad switches;
b) significantly improves the quality and service life of the cores, more than 2 times, increases their fatigue strength and wear resistance compared to the prototype according to the results of laboratory, bench and preliminary pilot tests;
c) the absence of crushing of the cores in the zone of rolling wheels on them during operation in any climatic conditions of operation, ensuring the safety of train traffic.

Claims (4)

1. The method of heat treatment of parts, mainly steel cast cores of crosspieces of railroad switches, including annealing, hardening and tempering, characterized in that, in order to increase the service life of the parts, heating under annealing is carried out at a speed of 50 75 ^o C / h with exposure to for 1 h and subsequent cooling with a furnace at a speed of 15 20 ^o C / h to a temperature of 650 ^o C, and then cooling in air, holding at the quenching temperature for 1 h, cooling is carried out first in water to a temperature of 650 ^o C ^{- 2 0} , and then in oil. 2. The method according to claim 1, characterized in that during the heat treatment of 100XCF steel, annealing and quenching is carried out by heating to 810 830 ^o C, and tempering is carried out at 280 300 ^o C for 3 hours 3. The method according to claim 1, characterized in that when quenching the core from a temperature of 650 ^o C ^{- 2 0 is} cooled in oil to a temperature of tempering.  4. The method according to claim 1, characterized in that, in order to avoid warpage, the core is heat treated in a suspended state.

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