固态脱碳法制备高强塑性成分梯度中锰钢

Preparation of medium manganese steel high strength plastic with composition gradient by solid state decarbonization

如何打破金属材料强度与塑性的权衡关系一直是材料科学中长期存在的难题。大自然中许多生物体内部都形成了从表面到内部逐渐变化的梯度结构,这使它们更加的坚韧。据此提出了一种利用固态脱碳制备成分梯度钢铁材料的工艺策略,为了证实这一工艺构想的可行性,以厚度为1 mm、成分为2.7%C-12%Mn-Fe(质量分数)合金为研究对象开展固态脱碳研究,试验所制备成分梯度中锰钢获得了良好的强度和延展性。试验结果表明,在H_(2)O-H_(2)气氛下50 min可将中锰钢碳质量分数由2.7%脱至0.23%;利用辉光放电光谱仪和光学显微镜检测,脱碳和热轧后的中锰钢板在厚度方向上均形成了明显的成分梯度,并在中锰钢板截面上获得了一种整体性的梯度结构;利用维氏显微硬度仪检测得到中锰钢板厚度方向上呈现了硬度的梯度分布,在固态脱碳作用下中锰钢表面和中心形成了成分和组织的过渡层,使表面到中心硬度由668HV逐渐过渡至747HV,这种中心与表面的硬度梯度也为产生连续的应变硬化奠定了基础;均质钢提高强度而进行变形时,其延展性通常会急剧下降,制备的成分梯度中锰钢板抗拉强度分别达到了1513.5 MPa和1399.1 MPa,断后伸长率分别达到了29.8%和26.3%。利用固态脱碳方法制备的中锰钢获得了良好的综合力学性能,期望研究成果能够为制造高强、高塑性材料提供一条新的途径。所提出的利用固态脱碳制备成分梯度钢铁材料的工艺策略是一个笼统的概念,其他金属材料如双相钢(DP)、淬火配分钢(QP)、高强度低合金钢(HSLA)和热成形钢(PHS)也可以适用,这也是下一步的重点研究方向。

The strength-ductility trade-off has been a long-standing dilemma in materials science.Many organisms have evolved over millions of years through natural selection and optimization.In many biological systems,structures such as bones and plant stems change gradually from the surface to the interior.This gradient structure can make biological systems strong and tough to survive severe natural forces.A process strategy of solid state decarbonization for preparing composition gradient steel was proposed,breaking the trade-off relationship between strength and ductility.In order to verify the feasibility of this technological concept,solid state decarburization research was carried out with alloy thickness of 1 mm and composition of 2.7%C-12%Mn-Fe(mass percent)as the research object.Excellent strength and ductility of manganese steels prepared in this experiment have been obtained.The experimental results show that the solid state decarbonization method has achieved surprising success in the preparation of medium manganese steels.The carbon mass percent of medium manganese steel can be removed from 2.7%to 0.23%in H_(2)O-H_(2)atmosphere for 50 min.The component gradient was measured by glow discharge spectrometer and optical microscope.The decarbonized and hot rolled medium manganese steel plates have obvious composition gradient and holistic gradient structure in the thickness direction.This holistic gradient structure is a key factor to guarantee the deformability of the medium manganese steel.The cross section hardness distribution of medium manganese steel was measured by Vickers hardness tester.Solid state decarbonization inevitably creates a thick transition layer in the interior and directly resulting in a gradually increased hardness from the surface of the centre layer(668HV)to the interior(747HV).This unique hardness gradient is inherent to the compositional gradient material and lays the foundation for continuous strain hardening.When the homogeneous steel is deformed to increase strength,its ductility usually drops dramatically.In contrast,the strength of compositional gradient steel increased from 1339.1 MPa to 1513.5 MPa and the ductility increased from 26.3%to 29.8%.This indicates that the strategy of solid state decarbonization to prepare compositional gradient steels has obtained good comprehensive mechanical properties.More importantly,the proposed strategy is a general conception,and other metal material such as DP,QP,HSLA and PHS,can also be selected.This is also the future focus.