固态脱碳过程中锰钢微观组织演变及力学性能

Microstructure evolution and mechanical properties of manganese steel during solid state decarburization

兼具高强度和高塑性的钢铁材料具有广阔的应用前景。为了提高钢铁材料强塑性,提出了一种利用固态脱碳制备具有梯度结构的钢铁材料的工艺策略,并以厚度为1 mm、碳质量分数为2.7%的中锰钢板为研究对象,在H_(2)O-H_(2)气氛下开展固态脱碳试验研究,利用碳硫仪测定脱碳后中锰钢平均碳含量,利用光学显微镜观察脱碳后中锰钢显微组织和表面氧化情况,对脱碳后中锰钢进行一次热轧-回火处理,利用万能拉伸试验机测量中锰钢力学性能。结果表明,随着脱碳温度升高,脱碳量逐渐增加;随着脱碳时间延长,中锰钢表面氧化层厚度逐渐增加。升高温度会增加固溶碳迁移速度,并非温度越高氧化层厚度生长越快,脱碳过程氧化层的调控应根据目标碳含量合理调节脱碳温度、气氛条件和脱碳时间。在1383 K温度下50 min可将中锰钢碳质量分数由2.7%脱至0.5%以下,氧化层厚度可控制在15μm以下;采用固态脱碳处理后的中锰钢形成了从表面到内部逐渐变化的梯度结构,随脱碳时间延长梯度层逐渐向中心迁移,梯度层的演变是由固态脱碳过程中锰钢内固溶碳向表面迁移导致的,利用固态脱碳制备钢铁材料,有利于产生额外的应变硬化,获得高延展性;固态脱碳后的中锰钢进行简单的热轧-回火处理后,应变硬化能力显著增强,获得了良好的强度与塑性匹配,强塑积最高可达45.1 GPa·%。固态脱碳法不破坏材料的整体性,形成了具有较强应变硬化效果的梯度结构,而这种效果不存在于相同处理条件下的均质材料中。

High-strength and high-plasticity metal materials have broad application prospects.In order to obtain high-strength and high-plasticity metal materials at the same time,a process strategy of solid state decarburization to produce steel materials with gradient structure is proposed and 2.7%C-medium ferromanganese alloy plate with thickness of 1 mm was selected as the research object.Solid state decarbonization was carried out in H_(2)O-H_(2) atmosphere,the average carbon content of medium manganese steel after decarburization was determined by carbon-sulfur meter,the microstructure and surface oxidation of decarburized medium manganese steel were observed by optical microscope.The simple hot rolling-tempering treatment of decarburized medium manganese steel was carried out,then the mechanical properties of medium manganese steel were measured by universal tensile testing machine.The results show that the amount of decarbonization increases gradually with the increase of decarbonization temperature and the thickness of oxide layer on the surface of medium manganese steel increases gradually with the extension of decarbonization time.The increase of temperature will increase the migration rate of solid solution carbon,so the growth of oxide layer thickness does not increase with the increase of temperature.Therefore,the control of oxidation layer in the process of decarbonization should reasonably adjust the decarbonization temperature,atmosphere conditions and decarbonization time according to the target carbon content.The carbon mass percent of medium manganese steel can be removed from 2.7% to less than 0.5% and the thickness of oxide layer can be controlled below 15μm at 1383 K temperature for 50 min.After solid state decarbonization,the structure of the medium manganese steel change gradually from the surface to the interior.The gradient layer gradually migrates to the center with the extension of decarbonization time.The evolution of gradient layer is caused by the migration of solid carbon to the surface of manganese steel during solid decarburization.This mechanism of using solid state decarbonization to create gradual changes in the internal structure of the steel material from surface to interior is conducive to additional strain hardening and high ductility.The strain-hardening ability of solid decarburized medium manganese steel was enhanced significantly after simple hot-rolling and tempering treatment,and the strength and plasticity matching were obtained,with the highest product of strength and ductility of 45.1 GPa·%.Solid state decarbonization method does not destroy the integrity of the material and creates a gradient structure with strong strain hardening effect,which does not exist in homogeneous materials under the same treatment conditions.