چكيده به لاتين
Martensitic stainless steels, developed based on Fe-Cr-C tertiary systems, have superior hardness and strength comparing to austenitic categories. Such classes of heat resistant ferrous alloys have obtained extensive applications in gas turbines due to their hot corrosion resistance and high strength. Although martensitic stainless steels have inferior corrosion resistance with respect to ferritic and austenitic ones, strength is the most significant parameter among all design factors in high temperature turbine components. In this study, the effect of carbon and nickel content on microstructure and deformation behavior of 410 steel was investigated using differential thermal analysis, X-ray diffraction, and hot compression experimental test together with the development of constitutive equations, processing maps and microstructural evolutions.
Two steel grades of 414 and 420B containing a higher amount of nickel and carbon, respectively comparing to 410 steel were chosen and their hot deformation characteristics were studied at temperature range of 950-1150°C and strain rate ranging from 0.001 to 1s-1. It was deduced from the results that dynamic recrystallization is the dominant restoration mechanism at lower strain rate (0.001s-1) but fully recrystallized microstructure was not detected while at high strain rate (1s-1), restoration and thermal softening reduce significantly. In the latter situation, dynamic recovery phenomenon is the key governing involved mechanism. However, in middle ranges of strain rates i.e. 0.01 and 0.1s-1, the maximum recovery rate was achieved that was stemmed by the appropriate occurrence of dynamic recrystallization (time and temperature). The transition temperatures of austenite to brittle ferrite delta were recorded to be 1046°C and 1092°C for 420B and 414 steels, respectively and hence, thermomechanical treatment in higher temperatures is prohibited. The hot deformation conditions of 420B and 414 stainless steels in strain rate range of 0.001-1s-1 are the temperature range of 950-1046°C and 950-1092°C, respectively. According to DTA results, austenite stability domain was extended due to carbon and nickel addition and for improving the corrosion resistance of these alloys, Chromium can be added to the composition.
