Al合金化对无Co马氏体时效钢微观结构与力学性能的影响

Effect of Al alloying on microstructures and mechanical properties of Co-free maraging steel

马氏体时效钢中的高密度纳米析出相形成及形貌控制,对提高材料的力学性能至关重要.本文通过成分设计与热处理工艺优化,制备了双相无Co马氏体时效钢.研究结果表明,1.5 wt%Al合金化马氏体时效钢中同时析出了纳米尺度的半共格η-Ni_(3)Ti和完全共格的B2-NiAl有序相.该合金钢具有良好的力学性能,抗拉强度为2065 MPa,延伸率为9.2%.Al含量添加能改变合金中析出相的形貌,由典型的针状η-Ni_(3)Ti结构转变为球状B2-NiAl结构.此外,Al添加还有利于Ni_(3)Ti和NiAl相互竞争生长,加速析出过程,并促进纳米析出相尺寸细化.马氏体时效钢中存在纳米尺度奥氏体,其分布在马氏体板条边界,且随着Al含量的增加,纳米尺度奥氏体和马氏体板条尺寸也随之减小.双相结构、高密度第二相析出及细晶强化是马氏体时效钢获得良好力学性能的重要原因.

To improve the mechanical properties of maraging steel,it is important to control the precipitation and morphology of high-density nano-scale precipitates.In this work,Co-free maraging steel with a dual-phase structure was prepared by composition design and an optimized heat treatment process.The results showed that semi-coherentη-Ni_(3)Ti and coherent B2-Ni Al ordered phases were precipitated in maraging steel with a content of 1.5 wt%Al.The steel had good mechanical properties with a high ultimate tensile strength of 2065 MPa and an elongation of 9.5%.With an increase in the Al content,the morphology of the precipitated phase changed from a needle-like structure(η-Ni_3Ti)to a spherical structure(B2-Ni Al).The addition of Al was also beneficial for the competitive growth of Ni_3Ti and Ni Al,and it accelerated the precipitation process and promoted the size refinement of the nano-sized precipitates.Nano-scale austenite existed in the maraging steel and was distributed at the boundary of lath-like martensite.However,with an increase in the Al content,the sizes of both the nano-scale austenite and the lath martensitic decreased.The good mechanical properties of maraging steel were mainly attributed to the dual-phase structure,high-density precipitation,and fine grain strengthening.