METHOD OF STRUCTURAL STEEL THERMAL TREATMENT Russian patent published in 2009 - IPC C21D1/20 

FIELD: metallurgy.

SUBSTANCE: invention concerns thermal treatment and provided for products tempering made of structural steel with carbon content not more than 0.35 wt %, for instance, plates of multiple-strand drive roller chains of extended precision. Products are subject to isothermal graded hardening, including heating of products till the hardening temperature, cooling in bath with molten alkali till the isothermal cure temperature, corresponding to top or bottom part of bainitic area in the range of meso-ferrite microstructure formation with speed, not less than critical. At the end of isothermal isolation products are pulled out of bath with liquid hot medium, located on permanently moving conveyor and cooled on air. In the end of the first stage product microstructure contains of austenite and meso-ferrite. In the process of cooling on air in steel it is formed microstructure of granular bainite. Minimal time of isothermal isolation corresponds to time of beginning of austenite time-temperature-transformation, and maximal time of isothermal isolation is not more than 40% of total time, required for austenite time-temperature-transformation.

EFFECT: reduction of products buckling at saving of mechanical properties complex.

1 dwg, 1 tbl, 1 ex