Effect of cooling rate on the microstructures of three low carbon alloys with different manganese and molybdenum contents

Low-alloy 16 to 20MND5 steels are used for the production of nuclear reactor components. During manufacturing, austenitization is followed by a quench; different types microstructures formed during this step. Characterizing impact Mo and Mn cooling rate on these can help understand how mechanical properties will evolve tempering ageing. The molybdenum manganese, as well rate, were studied three model alloys: FeCMo, FeCMn FeCMoMn. This was done using continuous transformation (CCT) diagrams electron backscattering diffraction (EBSD) characterizations. FeCMoMn found be good steels, based its CCT diagram hardness. presence or manganese did not modify misorientation angle/axis pairs martensite. In bainitic however, seemed favor block boundaries with about 59° [433]. On prior austenitic grain (PAG) level, rather continuous, from martensite slowly cooled bainite, same regardless composition, sub-block boundaries. microstructure became coarser decreasing fewer crystallographic orientations per PAG.