Residual stress distribution of electron beam welding of 12Cr12Mo martensitic stainless steel considering solid-state phase transformation: Multiscale characterization and FEM simulation

The objective of this study is to elucidate the evolution mechanism of the microstructure and stress during the electron beam welding process of thick-plate martensitic stainless steel. By systematically investigating the evolution mechanism of the residual stress during the electron beam welding process of 12Cr12Mo martensitic stainless steel, the relationship between the residual stress and the microstructure performance is revealed. Critical phase transformation temperatures (Ac₁=802 °C，Ac₃=848 °C，Ms=315 °C) were determined through thermal expansion experiments. Combined with CCT curves under different cooling rates, EBSD analysis, and hardness testing, the results revealed that a uniform lath martensitic structure forms within the cooling rate range of 5–100 °C/s, with hardness stabilized at 510 ±10 HV 0.3 and retained austenite content below 0.2 %, demonstrating excellent hardenability and microstructural stability. A thermo-mechanical-metallurgical coupled finite element model was developed based on the MSC.Marc platform. Simulation results indicated that the weld center zone develops compressive stresses of up to 270 MPa due to volumetric expansion from phase transformation, effectively counteracting thermal tensile stresses. Transverse residual stresses exhibited a alternating tensile-compressive distribution, with peak tensile stress reaching 312 MPa. Experimental and simulation results showed consistent trends, validating the reliability of the model. This study clarifies the regulation mechanism of phase transformation on residual stress and provides a theoretical basis for optimizing the welding process of electron beam welded joints of martensitic steel.