Microstructure and properties of S355J2W weathering steel under different annealing processes

In recent years, S355J2W weathering steel has been widely used in high-speed rail bogies. Stress relief annealing is usually required after bogie welding, but there are few literatures on its heat treatment process. The annealing temperature control range is very important to the strength and toughness of the bogie frame. Therefore, through the study of the microstructure and properties under different heat treatment processes, the most suitable annealing temperature range for S355J2W weathering steel is determined, so as to guide the relevant welding process.

S355J2W weathering steel with a thickness of 12mm was used, annealed at different temperatures (590, 550 ℃) for 3h, and marked as samples P1 and P2, respectively, and then the microstructure and mechanical properties were analyzed.

Micro-group analysis of S355J2W weathering steel
The basic morphology of the original structure of S355J2W weathering steel is a layered structure with obvious rolling characteristics. The grains are obviously elongated along the rolling direction, and the cross-section shows a layered structure with ferrite and pearlite.

The room temperature structure of the P1 S355J2W weathering steel sample is fine pearlite particles, and the main phase composition is F (ferrite) and granular P (pearlite). However, the room temperature structure of P2 sample still obviously retains some pearlite, and the main phase composition is the mixed structure of F and P.

The impact toughness values of P1 and P2 S355J2W weathering steel samples at room temperature and 0 ℃ are close, but at -20, -40 ℃, the impact toughness of P1 sample is significantly greater than that of P2 sample, it can be seen that the toughness of P1 is better than that of P2.

The microstructure and properties of S355J2W weathering steel are better when the annealing temperature is controlled at 590℃, and after holding for 3h with the furnace cooling process.