Mechanical and metallurgical properties of autogenous laser welded P92 material

• Detailed metallurgical analysis were carried to interpret the results obtained w.r.t the phases in the microstructure.
• Room and elevated temperature tensile properties were evaluated and the results are interpreted and discussed.
• Indentation creep test properties of welds were evaluated and compared to the base material.
• Room temperature charpy impact properties were evaluated and the mode of fracture were evaluated.
• Detailed microhardness survey were carried out and the properties were compared.

Laser welding with focused heat source and very low heat input is gaining prominence for welding heat sensitive materials. In the present work, autogenous laser welding process has been attempted for welding of 6 mm thick Cr-Mo-W-V-Nb steel, the P92 material. Laser welds were characterized for mechanical properties at both room temperature and high temperature and metallurgical properties after post weld heat treatment at 760 °C for 3 h. Macrostrucures of laser welds have shown good fusion with full penetration and did not exhibit any hidden weld defect. Also, no coarse grained heat affected zone (CGHAZ) could be observed. Microhardness measurements at room temperature have shown that weld zone had hardness in the range of 310–358 HV0.2, HAZ in the range of 260–300 HV0.2 against the base material hardness of 228–248 HV0.2. There is no significant softening observed in fine grained heat affected zone (FGHAZ)/base material (BM) interface. Tensile testing of laser welds at both room temperature and at 650 °C has consistently exhibited 100% joint efficiency and the failure was always located at the base material, well away from the weld and HAZ. All welds had 180° bend ductility in both face and root. Indentation creep testing has shown that weld made with comparatively higher heat input had better creep properties and weld with low heat input had inferior creep properties compared to the base material. Microstructures in fusion zone (FZ), heat affect zone (HAZ) and BM had tempered martensitic structure with no deleterious phases like δ-ferrite in the fusion zone (FZ).