PROCESS FOR CRYOGENIC THERMAL TREATMENT FOR HIGH-CARBON STEEL PARTS

摘要

The invention relates to a process for complex thermal treatment, the cryogenic treatment included, to be applied to metal parts made of high carbon steel, reducing the duration of the thermal treatment by more than 50% as compared with the standard thermal treatment duration, i.e. from 72 h to 16 h, increasing the repeatability of results by up to 25% and leading to an enhancement in the mechanical quality of pieces, in particular the wear resistance thereof. According to the invention, the process consists in increasing the maximal heating temperature for tempering by 20...30 K above the maximal recommended standard temperature, the constant critical temperature for cooling the piece being replaced by a modest oscillation of the cooling temperature in a 20 K-range during the cooling to intensely negative temperatures of up to 77 K, the piece being subjected to a number of 2...5 heating/cooling cycles between the minimal temperature and the critical cooling temperature, the said critical cooling temperature, calculated according to the formula T= M- 20 K, where Mis the temperature of finishing the martensitic transformation, dividing the temperature range of 273...77 K into technological thermal intervals characterized by different cooling/heating rates.