Металознавство та обробка металів (Mar 2020)
Heat treatment of castings using foundry heat
Abstract
On the example of R6M5L steel, the possibilities of hardening heat treatment (hardening, normalization) and annealing of an instrument made by the technology of chill casting using casting heat are considered. For this purpose, tool-cutting steel P6M5L was poured from a temperature of 1570 ºС into copper water-cooled and cast iron molds, which provided the possibility of receiving castings with a diameter of 40 mm and a height of 180 mm. Based on the fact that these heat treatment modes are associated with many hours of stepwise heating to high temperatures, it is proposed to extract the casting at a certain temperature from the mold and cool it according to standard hardening, normalization, or annealing modes. The desired temperature of steel castings was determined by experimentally constructed cooling curves at a certain point in time. The desired temperature of steel castings was determined by experimentally constructed cooling curves at a certain point in time. It was found that the hardness of castings that crystallized in a water-cooled copper chill mold at a cooling rate of 350 °C/sec and at 45 °C/sec in a cast iron chill mold, after quenching from 1240 °C, was 63 HRC and 62 HRC, respectively. A decrease in casting extraction temperature in the range 1240 – 900 °С is accompanied by a decrease in steel hardness to 55 HRC during quenching and to 50 HRC during normalization. During annealing, the ingots were removed from the chill mold at 880 – 900 °С and processed according to the continuous cooling modes providing hardness of castings 27 HRC and 25 HRC crystallized in a water-cooled copper and cast iron chill molds; under isothermal annealing, the hardness was 22 HRC and 21 HRC, respectively; under cyclic annealing, 23 HRC and 21 HRC, respectively. The research results can reduce the duration and reduce the cost of heat treatment operations of cast products from high speed steel.
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