影响40Mn钢链片淬回火硬度的原因分析

The Factors Influencing Quenching and Tempering Hardness of 40Mn Steel Chain Plate

采用金相显微镜、洛氏和显微硬度计对40Mn钢链片淬火硬度不足的原因进行分析,并探讨影响淬回火试样显微组织和硬度的因素。结果表明,40Mn钢链片淬回火后表面脱碳300μm左右时,表面洛氏硬度只有HRC16.8;脱碳66~84μm时,表面洛氏硬度约为HRC30,表面洛氏硬度随脱碳层的增加而急剧降低。较高的淬火加热温度能促进马氏体转变,回火组织更粗大,从而提高淬火硬度。40Mn钢热轧状态容易形成带状组织,带状组织在热处理时增加奥氏体化难度,从而影响淬硬性。理论计算40Mn钢的Ac3点为795℃,6mm厚度的试样淬火所需最小保温时间约为7min。

Causes of deficient quenching hardness of 40Mn steel chain plate are analyzed by means of metallographic microscope,Rockwell hardness meter and microhardness meter,the factors influencing microstructure and hardness of tempering specimen are discussed.The results show that the surface Rockwell hardness is only HRC 16.8 when the surface of 40Mn steel chain plate after quenching and tempering is decarburized by approximate 300μm,the surface Rockwell hardness is approximate HRC 30 when the surface of 40Mn steel chain plate after quenching and tempering is decarburized by 66-84μm,the surface Rockwell hardness decreases sharply as decarburized layer thickness increases.Higher quenching heat-up temperature makes martensite transformation,tempering microstructure coarsened,quenching hardness improved.Band structure easily forms in 40Mn steel at hot rolled status,which makes austenization even harder during heat treatment and affects the hardenability.The Ac 3 of 40Mn steel is 795℃according to theoretical calculation.Minimum holding time of 40Mn sample with 6 mm thickness during quenching is about 7 min.