摘要:
某钢铁联合企业采用Ti微合金化开发超低碳SM490A钢过程中,出现了因Mn含量不同带来的强度波动超标问题,为此分析了Mn对超低碳Ti微合金钢组织与力学性能的影响。数据表明,在0.07%C+0.06%Ti成分保持基本一致的情况下,Mn含量由0.4%提高到0.8%,钢的力学性能明显提高,屈服强度提高约161 MPa,抗拉强度提高约142 MPa,断后延伸率略有降低。Mn含量提高后,钢的基体组织未发生明显改变(均为铁素体+珠光体),但铁素体晶粒度由9.5级提高到11~11.5级,依据Hall-Petch公式计算对应的强度增量约为44 MPa和61 MPa,再结合Mn对转变点降低引起位错密度提高、[Si]和[Mn]置换固溶强化带来的共计约35 MPa的强度增量,可推测因Wagner相互作用Mn元素引起TiC第二相强化增量的改变约为65~82 MPa,由电镜照片可见Mn含量提高后TiC的体积分数提高约3倍,粒子尺寸约10 nm,利用第二相强化公式进行估算可知,与上述结果吻合良好。由分析结果可以推断,实际生产过程中,可以通过调整Mn含量实现对微合金钢的强度调控,无疑对微合金钢的发展具有较好的推动作用。
Abstract:
In the process of developing ULC SM490 A by Ti microalloying,excessive strength fluctuation was caused by different Mn content. Therefore,the influence of Mn on the microstructure and mechanical properties of ULC Ti microalloy steel has been studied. It is found out that when the Mn content was increased from 0.4% to 0.8% for base chemistry of 0.07%C+0.06%Ti compositions,the mechanical properties of the steel were significantly improved,the yield strength was increased by around 161 MPa,the tensile strength was increased by around 141 MPa,and the elongation after fracture decreased slightly.As the Mn content is increased,the microstructure of the steel has not changed,composed of ferrite and pearlite,but the ferrite grain size number is increased from 9.5 to 11～11.5,and the corresponding strength increment is about 44 MPa and 61 MPa calculated by the Hall-Petch formula.The total strength increment of about 35 MPa by those of Mn decreasing transition point and cause an increase in the dislocation density,plus [Si] and [Mn] substitute solution strengthening.Then it can be assumed that the strength increment due to TiC second phase strengthening by Wagner interaction of Mn element was about 65 to 82 MPa.TEM observation showed that when Mn mass fraction was increased,the TiC volume fraction was significantly improved about 3 times and particle size was about 10 nm,which was coincided with the second phase strengthening calculation.Therefore,it can be inferred that in the actual production process,the strength control of microalloyed steel can be achieved by adjusting Mn content,which undoubtedly has a positive effect on the development of microalloy steel.
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