Mg和Zr对FH40级船板钢连续冷却转变曲线的影响

以FH40高强度级别船板钢为研究对象,利用真空感应炉冶炼了不同Mg、Zr成分的实验钢,采用Gleeble-3800热模拟试验机测定了实验钢连续冷却转变曲线(CCT)。采用金相显微镜系统研究了实验钢连续冷却条件下的组织演变规律,并探讨了Mg、Zr单独和复合添加对实验钢CCT曲线中铁素体和贝氏体相区的作用规律。结果表明,Mg、Zr及Mg-Zr添加均能影响过冷奥氏体和珠光体开始转变温度;Mg和Mg-Zr添加抑制了铁素体转变,促进了贝氏体转变,在5~30℃/s冷却速度范围内均获得以贝氏体为主的组织;Zr添加扩大了铁素体区,减小了贝氏体区,冷却速度提高至20℃/s以上可得到以贝氏体为主的组织。研究结果对进一步明确Mg、Zr对低碳微合金钢组织特征的作用规律,指导Mg、Zr及Mg-Zr处理在工业上的应用具有重要意义。

Effect of Mg and Zr addition on the continuous cooling transformation of the FH40 ship-building steel

The FH40 ship plates containing different Mg,Zr contents are refined with vacuum induction furnace,and the relationship between magnesium and zirconium addition and the decomposition of austenite during continuous cooling rate from 0.1 ℃/s to 30 ℃/s is systematically investigated by a Gleeble‐3800 thermal simulator.Continuous cooled microstructure is observed by means of optical microscope.Dilatometric experiments and metallographic observations show that,Mg,Zr and Mg‐Zr addition can affect the starting temperatures of the γ‐α phase transformation and the pearlite transformation.Mg and Mg‐Zr addition suppresses the proeutectoid ferrite transformation and promotes the bainite transformation.The matrix can be dominated as bainite at cooling rate from 5 ℃/s to 30 ℃/s for the Mg‐containing steels.It is obviously shown that the addition of zirconium has a significant effect in promoting the nucleation of ferrites.However,the bainite transformation is not well developed,but an evident suppression of the transformation is emerged for the single Zr addition steel.The above studies can provide theoretical foundations for the application of magnesium and zirconium in steel.