To study the effects of various types of precipitates and precipitate evolution behavior on austenite (size and phase fraction) in reduced activation ferritic/martensitic (RAFM) steel, RAFM steel was heated to various austenitizing temperatures. The microstructures of specimens were observed using optical microscopy (OM) and transmission electron microscopy (TEM). The results indicate that the M23C6 and MX precipitates gradually coarsen and dissolve into the matrix as the austenitizing temperatures increase. The M23C6 precipitates dissolve completely at 1100 °C, while the MX precipitates dissolve completely at 1200 °C. The evolution of two types of precipitate has a significant effect on the size of austenite. Based on the Zener pinning model, the effect of precipitate evolution on austenite grain size is quantified. It was found that the coarsening and dissolution of M23C6 and MX precipitates leads to a decrease in pinning pressure on grain boundaries, facilitating the rapid growth of austenite grains. The austenite phase fraction is also affected by the coarsening and dissolution of precipitates.
In order to study the effect of Ri/T on welding residual stress in forging presses for Auto parts material, a welding experiment program was developed. The residual stress of thick pipe 10mm joint was measured by the blind hole drilling method. The simulation results within and near the weld joint, the transverse residual stresses are tensile on the inside surface which already close to yield strength with creasing the Ri/T ratio, and compressive on the outer surface; The prediction results from FEM are in a good agreement with the experimental measurement which are important to apply data for manufacturing plant.
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