Role of Silicon in Quenching and Partitioning Treatment of Low-carbon Martensitic Stainless Steel

Abstract

Quenching and partitioning (Q&P) treatment was applied to 12%Cr low-carbon martensitic stainless steels containing different amount of silicon, and then the effect of silicon content on the formation of retained austenite was discussed in terms of the behaviors of phase transformation and carbide precipitation during the partitioning treatment. It was suggested that the nearly ideal constrained carbon equilibrium (CCE) condition was realized in the specimens used in this study because a large amount of chromium suppressed bainitic transformation during the partitioning treatment, although cementite was partly observed at the retained austenite/martensite interface. The cementite precipitation was greatly retarded with increasing silicon content, resulting in an increase in the amount of retained austenite and an enhancement of the thermal stability of austenite. Tensile testing for the Q&P-treated specimens revealed that the increment of silicon content leads to a marked improvement of strength-ductility balance of the 12%Cr steels through the increase of retained austenite.

Critical Assessment 7: Quenching and partitioning

“…Residual ductility of press hardened parts (in service) is limited, and Q&P processing has been investigated in a hot stamping context to enhance tensile ductility of formed parts with encouraging results. 56,91 Application of Q&P to other sheet steel product areas such as hot rolled carbon 92 and stainless steel [41][42][43]93 also remain fruitful focus areas. Coil cooling may be employed in the hot strip mill to obtain carbon partitioning, 92 following controlled run-out table cooling and coiling.…”

Improving impact toughness of high-C–Cr bearing steel by Si–Mo alloying and low-temperature austempering

“…3a), the volume fraction of retained austenite was determined to be about 11.6%, 14.7% and 17.0% in 0.8Si, 1.2Si and 1.5Si steels respectively by using direct comparison method. This suggests the retained austenite fraction in austempered Si-Mo-alloyed bearing steels increases with Si content and it is in according to Sourmail and Smanio [26] and Tobata et al [27]. It is well known, Si can retard the carbide precipitation in the process of austempering and hereby increase C content in untransformed austenite by partitioning, which enhances the untransformed austenite stability and makes them retain to room temperature.…”

Effect of intercritical temperature on quenching and partitioning steels originated from martensitic pre-microstructure

“…Although autobody application represented the first implementation of Q&P on an industrial scale, this heat treatment is also applicable to a range of other potential applications. 6 In general, a Q&P process includes quenching from full austenization or intercritical region and partitioning at the quenching temperature between the martensite start temperature (M s ) and the martensite finish temperature (M f ) or above M s temperature. [3][4][5][6][7] Generally, a ferrite plus pearlite initial microstructure is used prior to the Q&P process.…”

“…6 In general, a Q&P process includes quenching from full austenization or intercritical region and partitioning at the quenching temperature between the martensite start temperature (M s ) and the martensite finish temperature (M f ) or above M s temperature. [3][4][5][6][7] Generally, a ferrite plus pearlite initial microstructure is used prior to the Q&P process. However, mechanical properties after the Q&P process significantly depend on the original microstructure prior to the Q&P process regardless of the heat treatment conditions.…”