回火温度对低碳Fe-Mn-Si-Al高强钢组织和力学性能影响

Effect of Tempering Temperature on the Microstructure and Mechanical Properties of Low-carbon Fe-Mn-Si-Al High-strength Steel

目的对低碳Fe-Mn-Si-Al高强钢进行不同回火温度研究,以探究适宜的回火温度,避免产生第一类、第二类回火脆性的问题,从而获得性能优良的低碳高强钢。方法首先设计一种合适的热处理工艺对试样进行淬火处理,随后采用光学显微镜、扫描电镜以及拉伸试验及硬度测试等方法,系统研究低碳Fe-Mn-Si-Al高强钢在200~600℃下的组织转变和力学性能。结果与初始试样相比,试验钢在200~400℃范围内回火时,微观组织类型没有明显变化,随着回火温度上升,铁素体晶界逐渐清晰,并在400℃时在铁素体晶界上析出θ-碳化物(Fe_(3)C);当回火温度在500~600℃时,铁素体发生再结晶现象,晶粒过度长大,导致晶界轮廓模糊。随着回火温度的增加,其试样的抗拉强度逐渐下降,初始试样的抗拉强度为1206.0 MPa,回火600℃时,试样抗拉强度为878.8 MPa。材料的强塑积在回火300、400和600℃时较高,分别为32.8、32.5和33.5 GPa%,而200℃和500℃时较低,分别仅为27.3 GPa%和26.9 GPa%,且200℃是试验钢的第一类回火脆性温度,500℃是试验钢的第二类回火脆性温度。试样的硬度在500℃达到最高,为271.3HV。试样的回火拉伸断口断裂方式为韧性断裂,且都存有明显的韧窝状花样。结论系统分析了不同回火温度对低碳Fe-Mn-Si-Al高强钢组织演变规律和力学性能的影响,得出适宜的回火工艺和不同回火温度下的力学性能。对于此类钢,应避免在200℃和500℃的工作环境下使用。

The work aims to study the low-carbon Fe-Mn-Si-Al high-strength steel at different tempering temperatures,in order to investigate the suitable tempering temperature and avoid the problems of type I and type II tempering embrittlement,thus obtaining low-carbon high-strength steels with excellent properties.Firstly,a suitable heat treatment process was designed to quench specimens,and then optical microscopy,scanning electron microscopy,and tensile test and hardness test were used to systematically study the microstructure transformation and mechanical properties of low-carbon Fe-Mn-Si-Al high-strength steel at 200-600℃.Compared with the initial specimen,there was no obvious change in the microstructure type when the test steel was tempered in the range of 200-400℃.As the tempering temperature increased,the ferrite grain boundaries were gradually clear andθ-carbides(Fe_(3)C)precipitated on the ferrite grain boundaries at 400℃.When the tempering temperature was 500-600℃,the ferrite underwent recrystallization,and the grains were overgrown,which resulted in the grain boundaries con-tours being Fuzzy.With the increase of tempering temperature,the tensile strength of the specimen gradually decreased,the ini-tial tensile strength of the specimen was 1206.0 MPa,and the tensile strength of the specimen was 878.8 MPa when tempering temperature was 600℃.The strong plastic product of the material was higher when tempering temperature was 300,400,and 600℃,reaching 32.8 GPa%,32.5 GPa%,and 33.5 GPa%,respectively,and the strong plastic product was lower at 200℃and 500℃,only 27.3 GPa%and 26.9 GPa%.200℃was the first type of tempering embrittlement temperature of the test steel and 500℃was the second type of tempering embrittlement temperature of the test steel.The hardness of the specimens reached a maximum of 271.3HV at 500℃.The tempered tensile fracture mode of the specimens was ductile fracture,and all of them had obvious tough nest-like patterns.The effects of different tempering temperature on microstructure evolution and mechanical properties of low-carbon Fe-Mn-Si-Al high-strength steels are analyzed systematically,contributing to the appropriate tempering process and mechanical properties at different tempering temperatures.In addition,such steels should be avoided in the working environment at 200℃and 500℃.