耐候结构用Q460NHE热轧带钢的开发与性能研究

Development and properties study of Q460NHE weathering structural hot rolled strip

随着用户对耐候钢需求量的不断攀升,对其性能提出了更高的要求。采用低C、低Si、低Ni设计,通过提高Mn、Nb、Ti等强韧化元素的含量,并控制Si、Cr、Ni、Cu等耐蚀合金元素含量和Cu、Ni含量的比例,同时合理设计轧制工艺,成功开发了Q460NHE耐候结构钢,并对该试验钢的力学性能、组织、原生氧化膜特点及耐腐蚀性能等进行了研究。结果表明:试验钢的显微组织主要由铁素体+贝氏体+珠光体(少量)组成,析出相主要为TiC及Nb-Ti碳氮化物,其中铁素体晶粒形状为等轴状,该组织结构特征保证了试验钢力学性能和低温冲击性能的优越性,其屈服强度达到490 MPa以上,抗拉强度达到610 MPa以上,-40℃冲击韧性可达到80 J以上;试验钢原生氧化膜厚度小于10μm,其致密性及平整性较好,与基体结合紧密,存在Cr、Si、Ni、Cu等耐蚀元素不同程度的富集,其中Cr、Si元素富集最为明显,该氧化膜的特点有利于抑制腐蚀介质的扩散;试验钢的耐腐蚀性指数I为6.76,相对Q345B钢的腐蚀速率仅为58%,腐蚀后锈层表面形貌相对平整致密,部分锈层呈絮状,有利于阻止腐蚀介质的渗透,其锈层中稳定相α-FeOOH含量较多且α/γ-FeOOH(质量分数)>2,锈层已达到稳定状态。所开发Q460NHE耐候结构钢的力学性能、低温冲击性能和耐腐蚀性能均满足标准要求。

With the increasing demand of users for weathering steel,higher requirements are put forward for its properties.Low C,low Si,low Ni design was used,by increasing the content of strengthening and toughening elements such as Mn,Nb,Ti,and controlling the content of corrosion resistant alloy elements such as Si,Cr,Ni,Cu and the proportion of Cu and Ni content,while reasonably designing the rolling process,Q460NHE weather-resistant structural steel was successfully developed.The mechanical properties,microstructure,characteristics of primary oxide film and corrosion resistance of the tested steel were also studied.The results show that the microstructure of tested steel is mainly composed of ferrite,bainite,and a small amount of pearlite.The precipitated phases are mainly TiC and Nb-Ti carbonitrides,in which the ferrite grain shape is equiaxed.The characteristic of the microstructure ensures the superior mechanical and low-temperature impact properties of the tested steel.Its yield strength can reach more than 490 MPa,the tensile strength can reach more than 610 MPa,and the impact toughness can reach more than 80 J at-40℃.The thickness of the primary oxide film of the tested steel is less than 10μm,its density and flat property are good,and it is closely bound to the matrix.There are different degrees of enrichment of Cr,Si,Ni,Cu and other corrosion resistant elements,among which Cr and Si are the most obvious enrichment.The characteristics of the oxide film are conducive to inhibiting the diffusion of corrosive media.The corrosion resistance index I of the tested steel is 6.76,and the corrosion rate is only 58%compared with Q345B steel.After corrosion,the surface morphology of the rust layer is relatively flat and dense,and part of the rust layer appears flocculent,which is conducive to preventing the penetration of corrosive media.The stable phaseα-FeOOH content in the rust layer is relatively high andα/γ-FeOOH(mass fraction)is greater than 2,indicating that the rust layer has reached a stable state.The mechanical properties,low-temperature impact properties,and corrosion resistance of the developed Q460NHE weatheringstructural steel meet the standard requirements.