Abstract
In the present study, the feasibility of laser surface melting (LSM) of AISI 430 ferritic stainless steel to minimize hydrogen embrittlement (HE) was investigated. LSM of AISI 430 steel was successfully achieved by a 2.3-kW high power diode laser (HPDL) with scanning speeds of 60 mm/s and 80 mm/s (the samples are designated as V60 and V80, respectively) at a power of 2 kW. To investigate the HE effect on the AISI 430 steel without and with LSM, hydrogen was introduced into specimens by cathodic charging in 0.1 M NaOH solution under galvanostatic conditions at a current density of 30 mA/cm2 and 25 °C. Detail microstructural analysis was performed and the correlation of microstructure with HE was evaluated. By electron backscatter diffraction (EBSD) analysis, the austenite contents for the laser-surface melted specimens V60 and V80 are found to be 0.6 and 1.9 wt%, respectively. The amount of retained austenite in LSM specimens was reduced with lower laser scanning speed. The surface microhardness of the laser-surface melted AISI 430 steel (~280 HV0.2) is found to be increased by 56% as compared with that of the substrate (~180 HV0.2) because of the presence of martensite. The degree of embrittlement caused by hydrogen for the charged and non-charged AISI 430 steel was obtained using slow-strain-rate tensile (SSRT) test in air at a strain rate of 3 × 10−5 s−1. After hydrogen pre-charging, the ductility of as-received AISI 430 steel was reduced from 0.44 to 0.25 while the laser-surface melted AISI 430 steel showed similar tensile properties as the as-received one. After LSM, the value of HE susceptibility Iδ decreases from 43.2% to 38.9% and 38.2% for V60 and V80, respectively, due to the presence of martensite.
Highlights
Hydrogen is the most available renewable energy for its abundance
The degree of embrittlement caused by hydrogen for the laser-surface melted specimens without and with hydrogen pre-charging were assessed using slow-strain-rate tensile (SSRT) tests in air at a strain rate of 3 × 10−5 s−1 at 25 ◦ C according to ASTM standard G129-00 [14]
The cross-sections and microstructures of the laser-surface melted AISI 430 steel fabricated at different processing speeds (60 mm/s and 80 mm/s) under different magnifications are shown in
Summary
Hydrogen is the most available renewable energy for its abundance. In addition, only water vapor is produced from hydrogen reaction. Ferritic and austenitic stainless steels and nickel-based alloys exhibit a minimum ductility at a specific temperature not far from room temperature. LSM is a rapid solidification process which can achieve the formation of metastable phases, homogenization and refinement of microstructure, and dissolution/redistribution of precipitates or inclusions, while the bulk properties can be preserved It brings great economic and social benefits, including lower energy consumption, reduction of pollution, saving precious materials, and high-value is added to the engineering components. It has been proven to be a promising method for improving corrosion, wear, and fatigue resistances of a wide range of engineering alloys [11] Conde and his co-workers [12] reported that the laser processing parameters were critical to corrosion behavior of laser-surface melted AISI 430 FSS. After LSM, detailed microstructural analysis was performed and the correlation with HE was evaluated
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