Effects of partitioning parameters in quenching and partitioning on microstructure and mechanical properties of an ultra-high low-alloy steel

In this research the effects of partitioning temperature and time in quenching and partitioning (Q& P) heat treatment was studied by applying the two-step quenching and partitioning on a novel low-alloy medium carbon steel. Partitioning was carried out at 250 degrees C and 300 degrees C for various times to obtain different amount of retained austenite and carbide precipitation. Microstructural studies revealed that after 3000 s at 250 degrees C same as 500 s at 300 degrees C, the matrix transformed from martensite to tempered martensite and lower bainite. The increase in partitioning time, due to carbide precipitation led to yield strength improvement, while it caused the reduction in elongation. The tensile test results showed that all quenching and partitioning specimens had tensile strengths higher than 1500 MPa and yield strengths over 1000 MPa.