METHOD OF HARDENING HIGHER THAN 68,0 HRC IN PRODUCTS MADE OF TOOL STEEL Russian patent published in 2009 - IPC C21D9/22 C21D6/04 C21D1/78 

FIELD: metallurgy.

SUBSTANCE: invention is related to metallurgy and machine building industry and can be used for production of cutting tools, dies, working rolls for sheet mills of steel type "90X". It is implemented preliminary preparation of steel product structure, tempering, multiple cold treatment and low tempering, at that preliminary preparation of structure consists in tempering since the temperature 890°C A_cm+(10÷20°C) and following medium-temperature tempering till the temperature 400-480°C during 1-6 hours. Tempering is implemented by means of cooling in oil and through water into oil since the temperature A_cm+(10÷20°C) with following cold treatment at -70°C and low tempering at temperatures 100-120°C. Heating for tempering is implemented accelerated in salt-bath furnaces or by means of electroheat, and cooling at tempering is implemented in oil reservoir with oil temperature not higher than 20°C till the temperature 25-35°C and products are directly fed to cold treatment. Period for the products discharge moment from oil reservoir and its placement to the cold store shouldn't exceed 15 minutes. Cold treatment at -70°C in aggregate with low tempering is replicated from two till six times.

EFFECT: hardening.

4 cl, 5 tbl