A. Ganguly, B. L. Choudki, J. Mathur, V. Lade, Mukand Ltd, Mumbai, Maharastra, India, Thane, India
Martensitic stainless steel AISI-420 grade of diameter 55mm was taken for experiment to study the mechanical and microstructure properties of the steel in hardened and tempered condition. Before hardening hot rolled samples are analysed for magna-flux to detect the surface cracks. In this experiment hardening temperature was fixed at 1000 0C and tempering temperature was fixes at 700 0C. Quenching media was oil metaquench-40 and metaquench-44. Quenching oil temperature was maintained in the range of 50 0C to 60 0C. Tempering media was air-cooling. Hardening soaking time is 4 hrs and 2 hrs. Hardened and tempered hardness of each sample was measures and compared the results. Microstructures of hardened, tempered and hot rolled samples are compared. Hot rolled samples are observed that fine-grained martensitic structure with carbide precipitates. In hardening grain coarsening and precipitates are in solution were observed in microstructure. Due to this the hardness is similar to hot rolled sample. In two hours soaking, hardened samples having similar hardness compared to 4 hours soaking. It means that hardening is sufficient for 2 hrs soaking the samples at 1000 0C for achieving the desired mechanical properties. Grain coarsening was observed in the microstructure after hardening and most of the precipitates are in the solution. Precipitates are the nuclei sites for initiating the corrosion. Therefore hardened and tempered martensitic stainless steels are having better corrosion resistance than hot rolled/ annealed martensitic stainless steel. Hardness was achieved in the range of 225 BHN to 260 BHN after tempering. Metaquench-40 hardened samples are having lesser hardness than metaquench-44. As per literature hardened and tempered AISI-420 grade having better corrosion resistance and wear resistance than hot rolled/annealed AISI-420 grade.
Summary: Martensitic stainless steel AISI-420 grade of diameter 55mm was taken for experiment to study the mechanical and microstructure properties of the steel in hardened and tempered condition. Before hardening hot rolled samples are analysed for magna-flux to detect the surface cracks. In this experiment hardening temperature was fixed at 1000 0C and tempering temperature was fixes at 700 0C. Quenching media was oil metaquench-40 and metaquench-44. Quenching oil temperature was maintained in the range of 50 0C to 60 0C. Tempering media was air-cooling. Hardening soaking time is 4 hrs and 2 hrs. Hardened and tempered hardness of each sample was measures and compared the results. Microstructures of hardened, tempered and hot rolled samples are compared. Hot rolled samples are observed that fine-grained martensitic structure with carbide precipitates. In hardening grain coarsening and precipitates are in solution were observed in microstructure. Due to this the hardness is similar to hot rolled sample. In two hours soaking, hardened samples having similar hardness compared to 4 hours soaking. It means that hardening is sufficient for 2 hrs soaking the samples at 1000 0C for achieving the desired mechanical properties. Grain coarsening was observed in the microstructure after hardening and most of the precipitates are in the solution. Precipitates are the nuclei sites for initiating the corrosion. Therefore hardened and tempered martensitic stainless steels are having better corrosion resistance than hot rolled/ annealed martensitic stainless steel. Hardness was achieved in the range of 225 BHN to 260 BHN after tempering. Metaquench-40 hardened samples are having lesser hardness than metaquench-44. As per literature hardened and tempered AISI-420 grade having better corrosion resistance and wear resistance than hot rolled/annealed AISI-420 grade.
