40CrNiMo钢淬火组织调控及其对力学性能的影响

Control of quenched microstructure of 40CrNiMo steel and the correlation with mechanical properties

为了优化热处理工艺、调控淬火组织的配比,开发出强塑性更佳的超高强钢,通过金相显微镜、扫描电子显微镜和电子背散射衍射表征手段,结合显微硬度测试及拉伸实验,研究了淬火温度对40CrNiMo钢组织与性能的影响。研究发现:淬火温度低于Ac_1时,实验钢组织由粒状珠光体及片状珠光体组成;两相区淬火时,随着温度的升高,渗碳体逐渐溶解,淬火马氏体逐渐增多,不规则的未溶解铁素体比例不断降低;790℃淬火时,实验钢组织为完全马氏体,呈板条状;进一步提高淬火温度,原奥氏体晶粒尺寸增大,马氏体板条粗化。随着淬火温度的升高,实验钢组织中马氏体占比越来越大,导致其硬度和强度均大幅提高。相比于完全马氏体组织,保留一定比例的铁素体能进一步提高材料的强度,同时兼具良好的加工硬化性能和塑性。通过合理的组织调控,实验钢获得了铁素体(28%)+马氏体双相组织,利用不同组织的相互协调性实现了淬火钢的高强韧性,进一步改善了传统结构材料的力学性能。

In order to optimize the heat treatment process,control the ratio of quenching microstructure and develop ultra-high strength steel with better strength and plasticity,the effect of quenching temperature on the microstructure and properties of 40CrNiMo steel was studied by means of optical microscope,scanning electron microscope and electron backscatter diffraction combined with microhardness test and tensile test.It is found that when the quenching temperature is lower than Ac1,the microstructure is composed of granular pearlite and lamellar pearlite.During quenching in the two-phase region,as the temperature increases,the cementite gradually dissolves,the quenched martensite gradually increases,and the proportion of irregular undissolved ferrite continues to decrease.When quenched at 790℃,the microstructure is complete martensite in lath shape.With further increase of the quenching temperature,the original grain size increases,martensite lath coarsening.With the increase of quenching temperature,the proportion of martensite in the microstructure increases,resulting in a significant increase in the hardness and strength of the experimental steel.Compared with the complete martensite structure,retaining a certain proportion of ferrite can further improve the strength of the material,while having good work hardening properties and plasticity.The ferrite(28%)+martensite dual-phase structure of 40CrNiMo steel is formed by reasonable regulation of microstructure.The high strength and toughness of quenched steel are realized by the mechanical incompatibility of different microstructures,which provides a theoretical support for further exploring the mechanical properties of traditional structural materials.