Experimental investigation of the formability of ultrahigh-strength sheet material using local heat treatment

Abstract

In this study, the effects of local heat treatment temperature on the V-bending formability of Martensitic 1200 steel, was investigated experimentally. In the first stage of the study, local heating temperatures were determined according to the stress-strain curves obtained as a result of the hot tensile test. Other experimental parameters included temperature (room temperature - RT/25, 300, 400 and 500°C), die-punch angle (30, 60, 90 and 120°) and punch holding time (0 and 10 s). The heating procedure in the bending operation was carried out locally only in the bending zone with the temperature controlled heating rod. The hardness values were found as 5.19% HV at the forming temperatures of RT–300°C, 2.31% HV at 300–400°C and 1.85% HV at 400–500°C. Due to the coarseness of the carbides in the microstructure, softening of the sheet material was observed up to 400°C. The slight increase in the flexure observed in the sheet materials bent at 500°C was caused by secondary precipitation hardening.