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The temperature field distribution and thermal history of Fe-9Cr2WVTa reduced activation steel prepared by laser melting deposition (LMD) have been calculated with Gaussian and Ring laser beams, and the nucleation and growth behaviors of M23C6precipitates in the 1st, 7th and 19th layers have been calculated using the modified classical nucleation theory and Svoboda Fischer Fratzl Kozeschnik model. The energy distribution shows W-shape with Ring laser beam while it shows V-shape with Gaussian laser beam, which results in the more uniform M23C6size in the same layer with Ring laser beam. Precipitates in the bottom (i.e., the 1st layer) have the minimum size and the size increases with the layer number with Gaussian and Ring laser beams. The temperature history, the instantaneous nucleation rate and the size evolution of M23C6have been systematically discussed. The results indicate that the nucleation, growth and re-dissolution of precipitates in reduced activation steel depend on the amount of energy absorbed in the thermal cycle during LMD. The continuous accumulation of energy during the thermal cycle leads to larger M23C6at the top area. The unsteady state precipitation dynamics of M23C6carbides during thermal cycling are consistent with the simulation results.

A new linear yield criterion, referred to as average apothem (AA) yield criterion is developed in this paper based on the Tresca and Twin Shear Stress (TSS) yield criteria. This criterion is a piecewise linear function and its locus on the π-plane in Haigh Westergaard stress space is an equilateral and non-equiangular dodecagon. Comparison with the Tresca and Mises yield criteria shows that the locus of the proposed yield criterion lies between those of the Tresca and Mises loci and is much closer to that of Mises yield criterion. Further, its specific plastic work rate is developed. As an application of the proposed criterion, the AA yield criterion is applied to the analysis of a generalized worked example of strip forging and an analytical solution of the stress effective factor is obtained. Comparison with the results by Tresca, Mises and TSS yield criteria shows that the proposed criterion provides an intermediate solution between the results of Tresca and Mises criteria.