HEAT TREATMENT OF EXTREMELY LOW CARBON TOUGH STEEL

摘要

PURPOSE:To provide a steel material excellent in the impact value preventing distortion accompanied by the heat treatment by cooling an extremely low carbon alloy steel controlled to become a bentonite structure at a state of hardening at a specified rate from the AC3 transformation point. CONSTITUTION:An extremely low carbon alloy steel containing C of less than 0.10%, Mn of 1.8 to 4.5% or the like whose components are controlled to become a bainite structure or a bainite structure containing martensite in a state of hardening is cooled at a rate of more than 200 deg.C/min. from a temperature range above the AC3 transformation point. Otherwise, after heated above the transformation point, it is cooled in the air at a rate of 200 deg.C/min. after an air cooling within the temperature range above the bainite formation level. With such a method, a low carbon tough steel excellent in mechanical characteristics can be produced without annealing following the hardening.