The Effect of Austenitizing Temperature on Hardenability, Precipitation and Mechanical Properties of Boron Bearing Cr–Mo Alloy Steel

The effects of B content and austenitizing temperature on hardenability and toughness of Cr–Mo alloy steel have been studied. The results show that the hardenability is deteriorated with increasing B content and austenitizing temperature. With increasing temperature, more and more B containing particles were dissolved in austenite and increase the amount of B atoms segregating at grain boundaries. Moreover, the coarsening grains reduce area of grain boundaries and also increase the amount of B atoms at unit grain boundary, excessive B atoms segregating at grain boundaries promotes precipitation of M₂B, which accelerates ferrite nucleation and reduces hardenability. The main elements in M₂B phase are Fe, Cr, Mo and B. The B atoms segregating at grain boundaries during austenitizing promote precipitation of M₂B during tempering which deteriorate toughness significantly.