Structure Formation in the Heat Treatment of Alloy Steel Bar

摘要

The structure formation in 42Cr4Mo2 electrosteel on continuous cooling is studied. The results are presented in the form of a thermokinetic diagram. It follows from the diagram that bainite structure is predominantly formed in thermochemical treatment with cooling of the rolled steel at a mean-mass rate of 0.4- 1.0°C/s, while ferrite-pearlite structure is mainly formed at rates less than 0.4°C/s. The influence of the treatment temperature and time on the structure and properties of the chromomolybdenum steel is investigated. If the cooling rate after hot deformation is increased by a factor of 1.6, the proportion of bainite in the metal is greater. In subsequent annealing with isothermal holding at 650-680°C, the bainite accelerates the spheroidization of the carbides. Consequently, the holding time may be reduced from 6.5 to 4 h, with consequent energy savings but without loss of metal quality.