Characterization of Room and Elevated Temperature Mechanical Properties of P22/P91 Weld Metals Using Small Punch Tensile and Uniaxial Tensile Tests

P22 and P91 heat-resistant steel weld metals (P22WM, P91WM) were tested by uniaxial tensile (UT) and small punch tensile (SPT) tests at room and service temperatures. Their high-temperature mechanical properties, fracture features and UT-SPT mechanical property correlation were systematically studied. P91WM exhibits approximately 43% higher yield strength at room temperature (RT) compared with P22WM. Nevertheless, P22WM retains around 24% more strength relative to its RT value under service temperature, showing better high-temperature stability. Multiple linear UT-SPT correlation models are established, where the Mao model achieves the highest prediction accuracy for yield strength, and the Altstadt model (ALT) exhibits superior ultimate tensile strength (UTS) prediction performance over the classical model (CLA). SPT is proven to efficiently characterize the mechanical properties of heat-resistant steel weld metals, supporting the in-service evaluation of high-temperature welded joints.