Effect Of Hot Rolling And Annealing Process On Microstructure And Properties Of AISI430 Ferritic Stainless Steel

AISI430 ferritic stainless steel was widely used in the field of household appliances such as water heater liners,washing machine drums,kitchen appliances due to its low cost,high thermal conductivity,small linear expansion coefficient and good resistance to chloride stress corrosion.M₂₃C₆ will appear in the low temperature range and the martensite phase transformation will appear in the high temperature range during the process of hot rolling and annealing for AISI430 ferritic stainless steel because of its high carbon content?0.35wt.%?,which lead to pitting and plasticity decreasing.Nowadays,long-time-batch annealing between 825?and 850?was mainly used for the production of AISI430 ferritic stainless which has low production efficiency and high cost.In the paper,AISI430 steel samples were hot-rolled at 830°C which is a ferrite single-phase temperature region and annealed between 838°C and 1270°C which is a two-phase??+??temperature region to study the microstructural evolutions,mechanical properties and corrosion resistances of AISI430 test steel via SEM,EBSD,tensile tests and immersion tests.It provides theoretical and experimental basis for rolling production process of the ferritic stainless steel.Firstly,the AISI430 test steel was hot-rolled to study the microstructure evolution,texture evolution,precipitation behaviour and mechanical properties under different rolling reduction.The results show that the microstructure of AISI430 test steel consist of single ferrite and?Fe,Cr?₂₃C₆ along the ferrite grain boundaries and intragranular subgrain boundaries after hot rolling with air cooling at 830°C.The texture of AISI430 test steel mainly composed of?and?fibre texture.The intragranular structure increases gradually with the increase of hot rolling reduction leading to the precipitation of?Fe,Cr?₂₃C₆ increasing gradually.So the?-fibre texture increases while the?-fibre texture decreases as the hot rolling reduction increases,which is beneficial to the forming properties of AISI430 test steel.Besides,as the rolling reduction increases,the strength and hardness of the test steel increase,and the plasticity decreases.When the reduction up to 30%,the tensile strength up to 706.2MPa and the Vickers hardness up to266.9HV but the elongation was 15.3%.The experimental results demonstrate that hot rolled at 830°C with 30%rolled reduction is an appropriate method for AISI430 ferritic stainless steel with good mechanical properties and formability properties.Secondly,the AISI430 test steel was annealed at 840°C¹150°C together with water or air cooling to study their microstructural evolutions,mechanical properties and corrosion resistances the effects of annealing on the microstructure,texture evolution,mechanical and corrosion resistance.The results show that after annealing at less than 880°C,the microstructure of the AISI430 test steel consists of ferrite grains along the rolling direction and?Fe,Cr?₂₃C₆ along the ferrite grain boundaries.After annealing at 950°C¹150°C,martensite transformation occurs during cooling process,and martensite structure is formed at ferrite grain boundaries.As the annealing temperature increases,the ferrite grains coarsen,the martensite content increases and then decreases,and the martensite volume fraction reaches a maximum of 50.3%at 1000°C.In comparison with the steels annealed at the temperature lower than 880°C,the AISI430 test steel annealed at high temperature?>950°C?shows higher strength and lower plasticity.Specifically,the mechanical properties of AISI430 steel annealed at 950°C with tensile strength of 634MPa,yield strength of 300MPa and Vickers hardness of297HV are far more outstanding than that annealed 880°C,which shows that tensile strength,yield strength and Vickers hardness are 360MPa,188MPa,192HV,respectively.While,the AISI430 steel annealed at 950°C?16.8%?shows lower elongation rate than that at 880°C?25.2%?.With the increase of annealing temperature between 950°C and 1150°C of AISI430 steel,there is a decrease in the strength,plasticity and corrosion resistance.The AISI430 steel in water quenching after annealing has better strength,hardness and corrosion resistance than that in air cooling.It can be concluded that annealing at intermediate temperatures?900°C⁹50°C?and cooling in air is an appropriate method to enhance the mechanical properties,corrosion resistance and formability properties for the AISI 430 ferritic stainless steel.With cooling in the air after keeping 30min at the temperature of 950°C,the precipitated phase,?Fe,Cr?₂₃C₆,along the ferrite grain boundaries in the AISI430 steel decrease significantly,thus improving the anti-corrosion properties.The corrosion-resistant weight loss rate is 11.2g/m²·h.Grain recrystallization of the deformed ferrite improve the elongating performance?16.8%?.The transformation from?to?texture is beneficial to the formability performance.The martensite phase transformation along the grain boundary of the ferrite enhance the tensile strength?635MPa?,yield strength?300MPa?and Vickers hardness?297.4HV?.