Effect of laser surface hardening on the hydrogen embrittlement of AISI 420: Martensitic stainless steel

The susceptibility of stress corrosion cracking (SCC) of AISI 420 which was surface transformed hardened by a pulsed Nd:YAG laser, was investigated in 5% sodium chloride + 0.5% acetic acid solution by the U-Bend method, in the range of pH value from 3.5 to 6, in the absence and presence of 1 ppm thiosulphate ion, at 25 and 60 °C. The results showed that the laser-treated areas are more susceptible to SCC than the base metal. Hydrogen embrittlement (HE) is the main cause of crack propagating, mostly effective on the grain boundaries and the interface between carbide particles and second phases; tempered martensite or ferrite.

Research highlights
► Laser surface treatment is a practical method to enhance the cavitation resistance of AISI 420: Martensitic stainless steel using in gas turbine blades.
► The stress corrosion cracking susceptibility of laser–treated areas of AISI 420 was examined.
► The rate of crack propagation increases as the temperature increases, while rising in the amount of thiosulphate ion leads to reduction in the time of crack propagation and in pH value for crack initiation simultaneously.
► The most effective mechanism of stress corrosion cracking of AISI 420 is hydrogen embrittlement.
► The carbide-ferrite interfaces are the most yielding area for crack propagation and the energy of crack propagation in the carbide particles boundaries is less than grains.