显微组织对460MPa级抗震耐火建筑钢性能影响的研究

Study on the Influence of Microstructure on the Properties of 460 MPa Seismic-Resistant and Fire-Resistant Construction Steel

为研究不同组织对于建筑用抗震耐火钢的性能影响,设计一种节钼(Mo)型含量的试验钢,其组织由铁素体+贝氏体组成。研究发现,采用不同的轧制工艺,可获得具有不同贝氏体体积分数的建筑钢。由于奥氏体变形促进了铁素体相变,二阶段轧制相较于一阶段轧制会获得更多体积分数的铁素体组织,经过铁素体相变后,保留的未转变奥氏体体积分数会减少,因而会获得更多体积分数的贝氏体组织。通过对显微组织、室温及高温力学性能进行分析研究,发现包括一阶段轧制和二阶段轧制的两种轧制工艺都能获得建筑钢原型,其室温性能优异,符合460 MPa级钢的强度标准,屈强比小于0.80,表明钢种具有优异的抗震性能。高温力学性能测试及分析结果表明,具有较多贝氏体体积分数的试验钢具有更优异的耐火性能,一阶段轧制钢的高温屈服强度约为402.5 MPa,二阶段轧制钢的高温屈服强度约为294.1 MPa,前者比后者高约108.4 MPa。在600℃高温下,生成大量的大尺寸合金渗碳体。同时通过高温应力-应变曲线可以测量出,一阶段轧制试验钢的高温弹性模量约为104.6 GPa,明显高于二阶段轧制试验钢的87.5 GPa。通过对600℃3 h后试验钢的几何必须位错密度进行统计,可以看出,贝氏体体积分数更高的一阶段轧制试验钢的位错密度明显高于二阶段轧制试验钢的。通过强度贡献计算可以看出,一阶段轧制试验钢在600℃时的位错强化贡献值约为141.7 MPa,而二阶段轧制试验钢只有约91.7 MPa,表明贝氏体具有更高的高温稳定性。更高贝氏体体积分数的钢具有更加优异的耐火性能,其在耐火试验中位错密度和高温弹性模量仍保持较高,位错强化带来的强度贡献是其耐火性能差异的最重要原因。

We have designed a new kind of Mo-saving low carbon seismic-resistant and fire-resistant constructional steel which consists of bainite and ferrite.The study found that constructional steels with different volume fractions of bainite were obtained by different rolling processes.Due to the deformation of austenite promoted the transformation of ferrite,more volume fraction of ferrite could be obtained by two-stage rolling than by one-stage rolling.After ferrite transformation,the volume fraction of retained austenite decreased and more volume fraction of bainite was obtained.The microstructure,properties at room temperature and properties at elevated temperature were analyzed.They all met the design standard of 460 MPa grade steel.The yield ratio of two experimental steels was lower than 0.80 and this indicated that they had superior seismic-resistance.It could be found that constructional steels with excellent properties at room temperature could be obtained by either one-stage rolling or two-stage rolling.The yield strength at 600℃of the one-stage rolling experimental steel was about 402.5 MPa,and that of the two-stage rolling experimental steel was about 294.1 MPa.The former was~108.4 MPa higher than the latter.During the tempering process at 600℃,a large amount of large-size alloy cementite was formed.Meanwhile,the Young’s modulus of the one-stage rolling experimental steel was about 104.6 GPa,which was significantly higher than 87.5 GPa of the second-stage rolling experimental steel.By statistically calculating the geometrically necessary dislocation density of the experimental steels after holding at 600℃for 3 h,it could be seen that the experimental steel by one-stage rolling with a higher volume fraction of bainite has a significantly higher dislocation density at 600℃than the experimental steel by two-stage rolling.By calculating the contribution of strengthening,it could be seen that the contribution of dislocation strengthening at 600℃of the one-stage rolling experimental steel was about 141.7 MPa,while the second-stage rolling experimental steel was only about 91.7 MPa,which indicated that bainite has better thermal stability.The higher the volume fraction of bainite,the higher the dislocation density and Young’s modulus at 600℃.The contribution of dislocation strengthening was proved to be the most important reason for the difference of fire-resistance.