中文摘要：

研究了激光立体成形技术制备的300M超高强度钢试样热处理前后的组织演化。结果表明，300M钢的沉积态组织呈现细密的初生奥氏体柱状枝晶形态，并导致整体相形态呈现一定的取向性，相组成由底部的马氏体为主经中部的马氏体＋下贝氏体转变为顶部的马氏体＋上贝氏体。经过热处理后，初生的柱状枝晶生长形态消失，组织明显均匀细化，呈现显著细化的板条状马氏体形态。另外，本文还分析了激光立体成形300M钢可能出现的宏观缺陷，并指出了其成因。

英文摘要：

In this paper, the microstructure evolution of 300M ultra high strength steel fabricated by laser solid forming were studied before and after heat treatment. The results show that the mierostructures of as-deposited 300M steel has a fine primary austenite columnar dendrites morphology, and the overall phase showed some form of orientation. At the bottom the phase morphology was mainly martensite, at the middle, changed to martensite ＋lower hainite, and on the top was martensite ＋upper bainite. After heat treatment, the primary columnar dendrite disappeared, the microstructures were uniform and refined clearly, showing a significant refinement lath martensite forms. In addition, this article also analyzes the macro defect may occurred in laser solid forming 300M steel and explain the reasons.