Enhancement in hardness and corrosion resistance of AISI 420 martensitic stainless steel via friction stir processing

• Published in: Surface & coatings technology 2019-01, Vol.357, p.339-347
• Main Authors: Pan, L., Kwok, C.T., Lo, K.H.
• Format: Article
• Language: English
• Subjects: Corrosion; Friction stir processing; Hardness; Martensitic stainless steel
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2018.10.023

Surface modification of martensitic stainless steel AISI 420 was achieved using friction stir processing (FSP) with a W–Re pinless tool. The microstructure, hardness and corrosion resistance of the FSPed 420 fabricated at various traverse speeds (150 to 250 mm/min) of the tool were investigated and compared with annealed and conventionally hardened 420. The depth and width of the FSPed zone decrease as the traverse speed increases due to decrease in heat input. The volume fraction of retained austenite at the center and advancing side of the FSPed zone increases with the traverse speed attributed to the high cooling rate. The hardness (up to 697 HV1) and corrosion resistance in 3.5 wt% NaCl solution at 25 °C of the FSPed specimens are higher than that of the conventionally hardened one. •Depth and width of FSPed zones decrease as traverse speed increases.•Volume fraction of retained austenite at center and advancing side of FSPed zone increases with increase in traverse speed.•Hardness of FSPed 420 was in range of 654–698 HV1 and higher than that of conventional hardened 420 (631 HV1).•Pitting corrosion resistance of FSPed specimens was improved as evidenced by the noble shift in corrosion and pitting potentials.•Corrosion attack in retreating side (anodic) is more serious than in center/advancing side (cathodic) due to presence of carbides in the former.