Abstract
The effects of hot stamping (HS) and tempering on the hydrogen embrittlement (HE) behavior of a low-carbon boron-alloyed steel were studied by using slow strain rate tensile (SSRT) tests on notched sheet specimens. It was found that an additional significant hydrogen desorption peak at round 65–80 °C appeared after hydrogen-charging, the corresponding hydrogen concentration (CHr) of the HS specimen was higher than that of the directed quenched (DQ) specimen, and subsequent low-temperature tempering gave rise to a decrease of CHr. The DQ specimen exhibited a comparatively high HE susceptibility, while tempering treatment at 100 °C could notably alleviate it by a relative decrease of ~24% at no expanse of strength and ductility. The HS specimen demonstrated much lower HE susceptibility compared with the DQ specimen, and tempering at 200 °C could further alleviate its HE susceptibility. SEM analysis of fractured SSRT surfaces revealed that the DQ specimen showed a mixed transgranular-intergranular fracture, while the HS and low-temperature tempered specimens exhibited a predominant quasi-cleavage transgranular fracture. Based on the obtained results, we propose that a modified HS process coupled with low-temperature tempering treatment is a promising and feasible approach to ensure a low HE susceptibility for high-strength automobile parts made of this type of steel.
Highlights
One of the most important challenges for the automobile industry is to further enhance passenger safety coupled with a simultaneous reduction of vehicle weight regarding energy consumption and exhaust emissions [1]
In the present investigation, the influences of hot stamping (HS) and low-temperature tempering on the hydrogen embrittlement (HE) behavior of a low-carbon boron-alloyed steel were studied by using slow strain rate tensile (SSRT) tests, in an attempt to ensure the safety performance of automobile parts made of this type of steel grade under hydrogen-related service environments
The kernel average misorientation (KAM) value, which is regarded to be proportional to the micro-strain induced by crystal defects such as dislocations [29], was measured using the SEM electron backscatter diffraction (EBSD)
Summary
One of the most important challenges for the automobile industry is to further enhance passenger safety coupled with a simultaneous reduction of vehicle weight regarding energy consumption and exhaust emissions [1]. Materials 2018, 11, 2507 a press where they are simultaneously formed and quenched at a controlled cooling rate between continuously internally cooled dies to ensure the austenitic microstructure transforms into a martensitic one Such HS automobile components are mostly structural elements like A/B-pillar (Pillars are the vertical or near vertical supports of a car’s window area—designated respectively as the A, B, Cor (in larger cars) D-pillar, moving from the front to rear), bumper, tunnel and rocker and roof rail [6]. In the present investigation, the influences of HS and low-temperature tempering on the HE behavior of a low-carbon boron-alloyed steel were studied by using slow strain rate tensile (SSRT) tests, in an attempt to ensure the safety performance of automobile parts made of this type of steel grade under hydrogen-related service environments
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