Influence of Segregation on Microstructure and Hot Workability of Grade 250 Maraging Steel

The optimal process parameters of grade 250 maraging steel for hot forging were investigated with a process map and microstructure analysis. To generate the process map, hot compression tests were performed at 800-1200 degrees C and strain rates of 0.01-5 s(-1). The flow stress-strain curves were calibrated by Bayesian artificial neural network (ANN) modeling to compensate the heat generated by dynamic deformation. The Ni and Mo segregation during the solidification of the ingot caused alternating layers of Ni- and Mo-rich and -lean bands, which affected the recrystallization behavior during hot compression. According to the calculated process map, 1100-1200 degrees C x 0.01-0.7 s(-1) and 1000-1200 degrees C x 0.01-0.2 s(-1) are favorable process conditions that ensure wide process windows in terms of strain rate and temperature, respectively. The common features of the microstructure deformed under both conditions were relatively coarse martensite blocks and low values in the electron backscattered diffraction (EBSD) kernel average misorientation (KAM) results (i.e., low residual stresses), which were attributed to a low fraction of fine martensite block region. Graphic

Automated summary

The study investigated the optimal process parameters of grade 250 maraging steel for hot forging using a process map and microstructure analysis. Flow stress-strain curves were calibrated by Bayesian artificial neural network modeling to compensate the heat generated by dynamic deformation. The Ni and Mo segregation during solidification impacted the recrystallization behavior during hot compression, revealing favorable process conditions for wide process windows.