Effects of the Cooling Rate After Annealing Treatment on the Microstructure and the Mechanical Properties of Super-Duple × Stainless Steel

摘要

The aim of this study was to analyze the effect of the cooling rate after heat treatment on the microstructure and mechanical properties of 2507 duple × stainless steels. Heat treatment was carried out at 1050°C for 1 hr, followed by controlled cooling. The cooling rates were 175.6 × 10~(-3)°C/s, 47.8 × l0~(-3)°C/s, 33.3 × 10~(-3)°C/s, 16.7 × 10~(-3)°C/s, 11.7 × 10~(-3)°C/s, 5.8 × 10~(-3)°C/s and 2.8 × 10~(-3)°C/s, which resulted in variations of the jnicrostructure, such as the fractional change of the ferrite phase and sigma phase formation. Fatigue, hardness, impact and tensile tests were performed on the specimens with different cooling rates. The precipitation of the o phase caused a hardness increase and a sharp decrease of toughness and tensile elongation. The fatigue limit of the sample with a cooling rate of 5.8 × 10 C/s was 26 MPa higher than that of the sample with a cooling rate of 175.6 × 10~(-3)°C/s. Our observations of the fracture surface confirmed that the higher fatigue resistance of the specimen with a cooling rate of 5.8 × 10~(-3)°C/s was caused by the delay of the fatigue crack growth, in addition to higher yield strength.