Whether weathering steel requires post-weld heat treatment (PWHT) to maintain weather resistance and mechanical properties depends on factors like steel grade, plate thickness, joint stress, and service environment, rather than being universally mandatory.
For low-strength weathering steels (e.g., Q235NH) with thin plates (≤16mm) in simple, low-stress structures or mild environments, PWHT is often unnecessary. Proper preheating and low-hydrogen welding can preserve base metal properties, as residual stresses are minimal and the weld zone's alloying elements (Cu, Cr, Ni) can still form a protective rust layer over time.
However, for high-strength grades (e.g., Q355NH, Q460NH), thick plates (>20mm), or components in harsh environments (coastal, industrial) or under heavy loads, PWHT is beneficial. It relieves residual stresses (reducing cracking risk), softens brittle heat-affected zones (HAZ), and helps the weld zone's microstructure align with the base metal-supporting uniform rust layer formation (critical for weather resistance) and maintaining consistent mechanical properties like toughness and strength.
Common PWHT methods like stress-relief annealing (500–560°C) balance these needs without compromising the steel's inherent weathering capabilities.
