Process Study On AISI420Martensitic Stainless Steel Modified By Plasma-based Low-energy Nitrogen Ion Implantation

Plasma-based low-energy ion implantation (PBLEII) technology as a modified technology characterized with low temperature and low pressure has a major mass transfer mechanism of low energy ion implantation combined with simultaneous thermal diffusion. It can achieve the control of ion energy, ion implantation dose and ion implantation dose rate independently, and has high nitriding efficiency, high process stability and reliability. PBLEII technology can efficiently improve extensive industrial plasma thermal diffusion technology at present, has a wide development in the industrial field.AISI420martensitic stainless steel was modified by plasma-based low-energy nitrogen ion implantation at a range processing temperature of350-550℃and a current density of0.63mA/cm2for a treatment time of4h. The modified layer had a range thickness of80-110μm, a high supersaturated nitrogen concentration up to30%(atomic fraction) and surface microhardness of HVo.25N12-16GPa. The modified layer was mainly consisted of a-Fe(N) phase, with much γ’-Fe4N phase and a few CrN phase at350℃. Up to450℃, the modified layer was mainly consisted of a-Fe(N) and CrN phases, along with a few y’-Fe4N phase. Increasing temperature to550℃, the modified layer was mainly consisted of y’-Fe4N, with much CrN phase and a few a-Fe(N) phase. From XRD result of the modified layer in various depths, the modified layer was consisted of a-Fe(N) and CrN phases at the depth of30μm,70μm and100μm from the surface at350℃; the modified layer was consisted of a-Fe(N) and CrN phases at the depth of30μm and70μm while it was consisted of a α-Fe(N) monophase at the depth of100μm at450℃and550℃.AISI420martensitic stainless steel was modified by plasma-based low-energy nitrogen ion implantation at a processing temperature of450℃and a current density of0.44mA/cm2and0.63mA/cm2for a treatment time of4h. With a current density of0.44mA/cm, an εN monophase modified layer with a thickness of12μm formed on the AISI420martensitic stainless steel. It has a high supersaturated nitrogen concentration up to35%-40%(atomic fraction) and surface microhardness of HV0.25N15.7GPa. The modified sample has a low surface roughness of0.090μm. With a current density of0.63mA/cm2, the modified layer consisted of γ’-Fe4N, α-Fe(N) and CrN phases had a thickness of90μm, a high supersaturated nitrogen concentration up to30%(atomic fraction) and surface microhardness of HV0.25N14GPa. The surface roughness of the modified sample reached to0.221μm.