Influence of heat input and post-weld heat treatment on boiler steel P91 (9Cr–1Mo–V–Nb) weld joints Part 2 – Mechanical properties

Abstract

Three thick pipes of modified 9Cr–1Mo steel were welded using three different levels of heat inputs: low heat input 1·1 kJ mm⁻¹, medium heat input 2·3 kJ mm⁻¹ and high heat input 3·16 kJ mm⁻¹. Two types of heat treatments were employed, namely subcritical post-weld heat treatment and normalising/tempering treatment. The influence of heat input and post-weld heat treatment on the microstructure of boiler steel P91weld joints has been investigated in the previous paper. In the present work hardness, tensile, impact toughness and stress rupture properties were evaluated. Our results show a great influence of heat input and heat treatment on mechanical properties. The best combination of properties was obtained in low to medium range of heat input, between 1 and 2·8 kJ mm⁻¹ for both treatments and a 90% increase in time to rupture was observed for normalising/tempering treatment compared to subcritical post-weld treatment.

Keywords:

• Mechanical properties
• δ-ferrite
• Modified 9Cr–1Mo steel
• Welding
• Heat treatments
• Heat input
• Stress rupture