Continuous cooling sensitization and its evaluation in austenitic stainless steel EN 1.4310

Abstract Sensitization in stainless steels is caused by chromium delpleted zones near grain boundaries which can lead to intergranular corrosion and intergranular stress corrosion cracking in service. A lot of work has been done in the past to understand sensitization behaviour under isothermal conditions. However, this study aims at studying the sensitization behaviour in continuous cooling, which is of more practical importance in steel production and in heat treatments such as welding. Conditions for sensitization were determined using experiments (Double-loop Electrochemical Potentiokinetic Reactivation tests (DL-EPR) and compared with DICTRA simulations. Using these conditions a continuous cooling sensitization (CCS) diagram is determined for EN 1.4310 (301) austentic stainless steel. DICTRA is a CALPHAD based simulation software used for diffusion related studies in multicomponent alloys. Solvus temperature for M₂₃C₆ is determined 959°C

Quantification of the severity of ridging in ferritic stainless steel sheets using a profilometric technique

Abstract A new method to quantify the ridging phenomenon in ferritic stainless steels has been developed based on the evaluation of surface profiles after the tensile elongation of 100 mm wide sheet specimens. The ridging components of the surface profiles are extracted by a tailored spline filtering procedure. A ridging index is proposed to quantify the severity of the surface defect based on surface profile height and spacing parameters. The procedure is independent of the type of profilometer used as long as unfiltered raw profiles can be recorded. The reproducibility of the measurement method and its correlation with the visual assessment of strained specimens is discussed

Quantitative prediction of sensitization in austenitic stainless steel accounting for multicomponent thermodynamic and mass balance effects

Abstract Double Loop Electrochemical Potentiokinetic Reactivation testing has been employed to experimentally determine the degree of sensitization (DOS) of an austenitic stainless steel subjected to isothermal heat treatment for various times in the temperature range 700–820°C. For the different heat treatment conditions, the chromium concentration profiles across grain boundaries were calculated using the diffusion module in Thermo-Calc® based on the assumptions that sensitization is caused by grain boundary M23C6 precipitates and that local multicomponent equilibrium and flux balance exist at the carbide - matrix interface. Comparison of the experimental DOS values and the details of the chromium concentration profiles was used to establish a quantitative depletion factor that predicts sensitization at short annealing times

The importance of steel chemistry and thermal history on the sensitization behavior in austenitic stainless steels:experimental and modeling assessment

Abstract The sensitization of austenitic stainless steels is dependent on various factors such as chemical composition, heat treatment temperature and time. To study these effects, the degree of sensitization in five austenitic stainless steel compositions that were subjected to isothermal heat treatments in the temperature range 550–820 °C has been determined using double loop electrochemical potentiokinetic reactivation testing. The nucleation and growth of grain boundary M23C6 carbides, that are responsible for sensitization, has been modelled with the help of the precipitation and diffusion modules in Thermo-Calc, assuming local multicomponent equilibrium, flux balance at the carbide-matrix interface, to quantitatively predict the Cr depletion. Based on the Cr depletion characteristics, a depletion parameter has been established that can predict sensitization in austenitic stainless steels and predict the effects of individual alloying elements