Effect of Weld Consumable Conditioning on the Diffusible Hydrogen and Subsequent Residual Stress and Flexural Strength o
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ignated as P91 is preferred for high-temperature applications in modern supercritical power plants due to its excellent microstructure stability and mechanical properties with good workability and weldability. The P91 steel is also well known for its superior physical and thermal properties.[1,2] It also shows good microstructure stability during high-temperature exposure.[3–5] The
CHANDAN PANDEY, PRADEEP KUMAR, and N. SAINI are with the Department of Mechanical and Industrial Engineering, Indian Institute of Technology Roorkee, Uttrakhand 247667, India. Contact e-mail: [email protected] M.M. MAHAPATRA is with the School of Mechanical Sciences, Indian Institute of Technology, Bhubaneswar, Odisha 751013, India. Manuscript submitted November 24, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
weldability of such steel depends upon a suitable heat treatment and welding procedure. In the as-received condition, P91 steel processes the tempered martensitic structure with M23C6-type carbide precipitates mainly rich in Fe, Cr, and Mo. The heterogeneous microstructure during the welding cycle results in poor creep rupture life of the welded joint as compared to the virgin metal.[6] The weldability of the P91 steel depends on the microstructure of the weld fusion zone, trapped diffusible hydrogen, and residual deformation. However, the residual deformation and the microstructure can be optimized up to a level by using the proper weld heat treatments. The microstructure of the weld fusion zone deals with the untempered martensite and sometimes residue of austenite and d ferrite patches. The softening of the weld fusion zone is performed by heat treatment, as reported in earlier research.[7] However, the control of diffusible hydrogen in deposited metal-assisted cold cracking or hydrogen-induced cracking (HIC) is difficult. The combination of susceptible microstructure, diffusible hydrogen, and residual stress might lead to the catastrophic failure of the weld joint and term as HIC.
The welding-induced distortion and residual deformation depend on many parameters including welding process and parameters, groove geometry, phase transformation, and properties of the material. The induced tensile residual stresses in the welded component result in HIC, buckling deformation, brittle fracture, stress corrosion cracking, and reduction in other mechanical properties.[8–10] The researchers performed much work on the effect of the welding process parameter and heat treatment on residual deformation in the weld joint of P91 steel. The effect of the solid-phase transformation plays an important role in determining the magnitude of the residual stress, and softening of the structure also affects the magnitude of the residual stress. The effect of postweld heat treatment (PWHT) on residual deformation of P91 welded pipe was studied by Pandey et al.[11] They also studied the effect of the groove geometry on residual stresses and shrinkage stresses. A drastic reduction in the magnitude of the residual stress was reported as a result of the
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