RU2322516C2 - Method for periodic heat treatment of cast iron - Google Patents

Abstract

FIELD: metallurgy, possibly improvement of properties of gray iron castings.

SUBSTANCE: method providing decreased volume content of graphite, disintegration of graphite inclusions and their uniform distribution along cross section of castings comprises steps of heating and cooling in each cycle while heating in each cycle is realized till 700 - 750°C and then casting is cooled in water. Number of cycles is equal to 2 - 4.

EFFECT: possibility for providing decreased volume content of disintegrated and uniformly distributed graphite in cross sections of castings.

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Description

The invention relates to metallurgy of cast iron and can be used to improve the properties of gray iron castings.

It is known to use thermal cycling for cast iron processing [1] in order to reduce the size of graphite inclusions in the structure of castings, to increase the uniformity of the chemical composition of the metal and the plastic properties of cast irons.

Closest to the claimed is a method of thermocyclic treatment of cast iron, including multiple heating to temperatures of 50-200 ° C above A _C3 and cooling in air to temperatures of 50-200 ° C below Ar ₃ [2]. However, the level of decrease in the volume fraction of graphite is insufficient, which negatively affects the mechanical properties of gray iron castings.

The objective of the proposed method of heat treatment is to reduce the volume fraction of graphite, grinding its inclusions and their more uniform distribution over the cross section of the casting. Thus, the problem of improving the mechanical properties of cast iron can be solved, which ultimately can lead to a decrease in the metal consumption of parts with the same values of structural strength.

The essence of the proposed method lies in the fact that thermal cycling is carried out by heating and cooling in each cycle, heating of cast iron in each cycle is carried out to 700-750 ° C, followed by cooling in water, while the number of cycles is 2-4.

The use of thermocyclic treatment of gray cast iron allows one to obtain a decrease in the volume fraction of graphite in the structure and grinding of graphite plates (thickness and length) due to the intensification of diffusion processes during thermal cycling. The optimal number of cycles is 2-4. An increase in the number of cycles of more than 4 is impractical, since there is no significant decrease in the volume fraction of graphite and a decrease in CRC.

Example: Used cast iron grade SCH-20, smelted in a foundry of OJSC "ZSMK". Melting was carried out in an induction furnace IChT-10M No. 5, melting number - 2-8377. Chemical composition of cast iron: C - 3.65%; Si - 1.77%; Mn - 0.56%; S - 0.021%; P - 0.16%; Cr - 0.32%; Ni - 0.17%; Ti - 0.04%; V - 0.05% (GOST 1412-85). The castings were heated at 730 ° C with holding for 15 min, and cooled in water. The number of treatment cycles was 6. For comparison, thermocyclic treatment of cast iron was carried out according to the method adopted for the prototype. The heating temperatures were 900 ° C, cooling in air was carried out to temperatures of 600 ° C, and then in water. The number of cycles was 6. After every two cycles, a metallographic analysis was performed. The processing efficiency was evaluated by the results of quantitative metallography on an EPIQUANT optical analyzer and CLC determination on an optical dilatometer of the Schevenar system. The results are summarized in table.

As can be seen from the results in the table, the effectiveness of the proposed method of thermocyclic treatment of cast iron when using the number of cycles from 2 to 4 is higher compared to the known method.

The proposed method of thermocyclic processing can be used in metallurgical and engineering plants to improve the properties of gray iron castings.

Table Cast iron processing method Number of cycles Microstructure characteristic Volume fraction of graphite,% The average thickness of the graphite plates, microns The average length of the graphite plates, microns Famous: Cycle: 900 ° C, 15 min, cooling one 14.2 9.5 108 up to 600 ° C and further in the water 2 13.5 9.2 103 2 13.0 8.8 95 2 12.3 8.5 93 Proposed: Cycle: heating to 730 ° С, 15 min, without water cooling processing 19.3 5,6 31 2 7.8 2.2 fifteen four 7.2 1,6 13

Information sources

1. Fedyukin V.K., Smagorinsky M.E. Thermocyclic processing of metals and machine parts. - Leningrad, mechanical engineering, 1989, p.128-138.

2. A.S. No. 412262, cl. 21 D 5/00 "Method for thermocyclic treatment of cast iron." / Lebedev T.A., Marinets T.K., Fedyukin V.K. LPI them. Kalinin. Publ. BI No. 3, 1974.

3. RF patent №2130084, cl. С21D 5/02 “Method for thermocyclic processing of cast iron” / Afanasyev V.K., Chibryakov M.V., Prudnikov A.N., Sarlin M.K. Siberian State Industrial University. Publ. 05/10/99, bull. No. 13.

Claims (1)

The method of heat treatment of gray cast iron, including thermal cycling by heating and cooling in each cycle, characterized in that the heating of cast iron in each cycle is carried out to 700-750 ° C followed by cooling in water, the number of cycles being 2-4.