SU1735389A1 - Method for heat treatment of high-chromium cast iron - Google Patents

Abstract

Use: metallurgists, mechanical engineering, production of cast parts from wear-resistant cast iron with a content of 17-23% chrome. SUMMARY OF THE INVENTION: The cast billet is annealed at 1150-1200 ° C. After cooling, the casting is twice heated to 830-850 ° C and cooled together with the furnace to 720-730 ° C and to 620-600 ° C at a speed not exceeding 20 ° C / h. Final cooling is carried out in air. 2 tab.

Description

The invention relates to the metallurgy and engineering industries, namely the production of castings from wear-resistant high-chrome iron.

Cast parts of high-chromium cast iron are widely used in the manufacture of wear parts of mining equipment. Their use in mechanical engineering is limited by poor machinability of pigs of this class. In order to improve machinability, cast billets are subjected to heat treatment, including annealing at 1150-1200 ° C and tempering at 680-700 ° C, followed by cooling at a rate of 20-30 ° C / h to 600 ° C and then in air. Such heat treatment reduces the hardness of the workpieces from 57-60 HPC to 30-32 HPC and significantly improves the machinability of the cutting. However, it remains unsatisfactory, which makes it difficult to use serial automatic machines for machining machine-building blanks.

The purpose of the invention is to further improve machinability by reducing the hardness achieved by improving the heat treatment mode.

The essence of the invention is that high-chromium cast iron containing 17-23% chromium is annealed at 1.150-1200 ° C and cooled in air, then heated and cooled again twice, and heated to 830-850 ° C, cooled to 720- 730 ° C is carried out with a furnace, and up to 600-620 ° C - with a speed not higher than 20 ° C / h.

Cast billets of high-chromium cast iron, containing 17-23 wt.% Of chromium, are loaded into the furnace, heated to 1150-1200 ° C, held for several hours (the exposure time increases with increasing mass of the workpiece) and removed into the air, then re-loaded into the furnace and thermocycling is carried out, during which the castings in the furnace are heated to 830-850 ° C and cooled together with the furnace to 720-730 ° C and then to a temperature of 620-600 ° C at a rate not exceeding 20 ° C / h . Thermal cycling was carried out twice. As a result of the first cycle, the hardness decreases to 29-31 LDCs, and after the second it is 27-28 HPC. VHC with such hardness can be processed with high cutting speeds,

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The results of experiments to determine the thermal cycling temperature limit are shown in Table 1. During the experiments on the dilatometer, the temperature range a – y of the transformation was determined on cooling and heating for three grades of cast iron with different chromium contents. During thermal cycling, the a-y transformation upon heating and the transformation upon cooling should proceed completely, resulting in the creation of a prerequisite for the formation of granular perlite, which ensures good machinability. The rate of heating-cooling of samples in the range of 600-800 ° C was 20 ° C / h.

As follows from the results of table 1, heating to 850 ° C ensures the completion of a. transformations for all grades of cast iron.

During the cooling process, the conversion starts at 720-730 ° C and ends at 600-620 ° C for various cast iron grades. It is in this range that it is necessary to ensure such a cooling rate that ensures guaranteed granular perlite in the structure. This is achieved by adjusting the cooling rate in the specified temperature range. Effect of cooling rate in the eutecto range

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uniform transformation and thermal cycling for different annealing temperatures for specimen hardness and their machinability by cutting ICh270x18 are given in Table. 2

As follows from the data presented in Table 2, annealing at 1150-1200 ° C and thermal cycling of the samples, provided they are cooled in the range of 730-600 ° C at a rate not exceeding 20 ° C / h, ensures minimum hardness of the iron and its good machinability.

A specially staged series of experiments in which thermal cycling was carried out 4 times showed that the 3 and 4 cycles did not have a noticeable effect on the hardness of the samples, and therefore it is possible to recommend double thermal cycling for practical use.

Claims (1)

Invention Formula The method of heat treatment of high-chromium iron, mainly containing 17-23% chromium, including annealing at 1150-1200 ° C, subsequent heating and cooling, characterized in that, in order to improve machinability, heating and cooling are carried out twice, 830-850 ° C, cooling to 720-730 ° C is carried out with the furnace, and up to 620-600 ° C - at a rate not exceeding 20 ° C / h. Table 1 Table 2 Continuation of table 2