Formation mechanism of granular bainite in a 30CrNi3MoV steel

摘要

The transformation behavior from austenite to granular bainite in an super high-strength 30CrNi3V1oV steel was explored by means of dilatometric measurements and microstructural observations. Two kinds of granular bainite, named as Bgl and Bg2 were formed in the investigated 30CrNi3MoV steel subjected to cooling slowly from the high-temperature austenite field (1-5 °C/min). All secondary particles existing in the Bgl tend to be irregular, which is resulted from the formation and growth of ferrite in an equiaxed way from carbon-poor austenite areas. Granules in the Bg2 are parallel to each other at some preferred orientations, and the massive matrix form by merging of the ferritic laths. All secondary particles in the Bgl and in Bg2 are decomposed from carbon-rich regions of the austenite. As compared to the Bg1. the temperature window for the separation of the Bg2 is relatively lower than that of the Bg1.