Processing maps for the analysis of hot workability of microalloyed steels 38MnSiVS5 and 0.39C1.47Mn

Microalloyed steels are gaining increasing importance as substitutions for carbon steels because they possess higher mechanical properties, such as strength and toughness after hot forging, without a need for post-deformation heat treatment. To increase machinability, sulfur is added to microalloyed steels to facilitate chip removal, increase productivity, and enhance the life of cutting tools. Otherwise, the sulfide particles that benefit machinability may cause a significant loss in hot workability. Therefore, it is important to understand the effect of initial grain size, phase constituents, and inclusion content on flow stresses during hot working in order to establish ideal processing conditions, which prevent the formation of defects and simultaneously improve mechanical properties. The aim of the current study is to construct processing maps to evaluate the hot workability of microalloyed steels DIN 38MnSiVS5 and 0.39C1.47Mn in order to define the constitutive behavior of both steels under hot working and identify the safe regions for metalworking. The processing maps for both steels showed a region of instability at temperatures between 1100 and 1150 °C and the highest strain rates (namely, 10.0 and 30.0 s−1) that should be avoided. Cracks were found in the sample of 0.39C1.47Mn steel and voids were found in the central region in the DIN 38MnSiVS5 steel. These defects might be caused by MnS inclusions and are probably the cause of instability. Therefore, it can be concluded that a higher sulfur content has a negative effect on workability, and might be the cause of instability under some processing conditions.