Warm V-Bendabilites and Hydrogen Embrittlement Properties of Ultrahigh-Strength Quenching and Partitioning-TRIP Steel Sheets

The warm V-bendabilities and hydrogen embrittlement properties of ultrahigh-strength Quenching and Partitioning (QP)-Transformation-Induced Plasticity (TRIP) steel sheets were investigated to apply the QP-TRIP steel sheets for automotive structural parts manufactured by cold or warm press forming. V-bending tests were carried out at a crosshead speed of 1 mm/min at V-bending temperatures of 25, 100 and 150°C using a hydraulic servo testing machine with a 88-deg. V-punch (punch tip radius R = 2 mm, R/t0 = 1.7) and a V-dice (dice groove size l = 12 mm, dice shoulder diameter 0.8 mm) using V-bend specimens with dimensions of 5-mm width, 50-mm length and 1.2-mm thickness without and with hydrogen charging. Hydrogen charging was conducted by means of cathodic charging using a 3 wt% NaCl + 3 g/L NH4SCN solution at a current density of 10 A/m2 for 48 h before V-bending. The main results were obtained as follows.