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Modeling and simulation of powder bed fusion (PBF) remain a great challenge due to the sophisticated and interactive nature of underlying physics. A unified scenario considering interactions among the heat transfer, melt flow dynamics and microstructure evolution (noted as “heat–melt–microstructure-coupled processes”) is therefore essential for a thermodynamically consistent description and thus reliable microstructure prediction. In contrast to the state of the art, where either individual aspects are considered or the thermal history is taken as input from separate numerical scheme, we propose in this work a unified non-isothermal phase-field model for the heat–melt–microstructure-coupled processes during PBF. Simulations on a stainless steel 316L powder bed demonstrate that the model can reproduce well-observed features, but also help to discover new in-process phenomena and reveal the mechanism of the defect formation. Based on massive simulation results, we also present the densification map with respect to beam power and scan speed, and have classified the regions of the parameter combination by the distinct resultant morphology.