Mechanical Properties of Arc Welding Heat-Affected Zone of High Nitrogen Steel

The engineering application of high nitrogen steel (HNS) needs to obtain welded joint with good comprehensive properties. In order to acknowledge the influence of welding thermal cycle on the heat-affected zone (HAZ) of high nitrogen steel (HNS), the microstructure and mechanical properties of HAZ were investigated by using thermo-simulation technique. Experiment results indicate that the microstructure in the HAZ of HNS is composed of austenite and δ-ferrite. Carbide precipitation (Cr23C6) occurs in the HAZ where the peak temperature of welding thermal cycle is about 800°C, and nitride (Cr2N) is not examined. The parameters of welding thermal cycle can affect the amount of δ-ferrite in the HAZ. Under the experimental conditions, the amount of the δ-ferrite in the coarse-grained heat-affected zone (CGHAZ) increases when the cooling rate increases, and it changes slightly while the peak temperature is lower than 1150°C. The hardness of the CGHAZ increases when the cooling rate increases, and that of the HAZ decreases while the peak temperature decreases. The results show that the hardness of the HAZ is higher than that of the base metal, indicating no softening of the HAZ under appropriate welding conditions. The impact toughness of CGHAZ is improved with the increase of cooling rate, whereas two brittle zones exist in the HAZ.