Bake Hardening Behavior of 1.4003 Ferritic Stainless Steel

Low carbon steels are known to be sensitive to static strain aging behavior, i.e., they show bake hardening when they are subjected to press forming and subsequent paint baking during manufacturing of components. However, the bake hardening behavior of ferritic stainless steels has not reached that much attention, even though they are also used in some automotive components. In this research, the bake hardening behavior of EN 1.4003 ferritic stainless steel was studied. Bake hardening tests, consisting of pre-straining to 0%, 2%, 6%, and 10%, following heat-treatments of 170 °C/20 min and 230 °C/20 min, and tensile testing, were conducted. The purpose of the heat treatments was to simulate the paint baking process after press forming. In addition, to evaluate the aging behavior during storage, a heat treatment of 100 °C/30 min was carried out and followed by tensile testing, respectively. The results show that the bake-hardening heat treatments without pre-strain lead to only a minor strength increase. A combination of pre-strain and baking lead to higher increase in yield strength up to around 150 MPa for 170 °C/20 min and up to around 120 MPa for 230 °C/20 min. When baked at 170 °C, the bake hardening index (BH0–BH10) was found to increase from 15 MPa to 26 MPa with the increase of pre-strain. Higher baking temperature, 230 °C, resulted only in slightly higher BH indexes. Aging treatment of 100 °C /30 min did not show any practical influence on mechanical properties.