Refining Technics for Improving Ductility and Embrittling Factors of Corrosion-Resistant Fe-Al Alloy

为了弄清高铝钢的脆化因素，确定其改进工艺，进行了试验研究。结果表明：1)超低碳钢的硬度和抗拉强度随Al含量的增加而增加，而延伸率随Al含量的增加而降低。10质量%Al钢的延伸率在2~15%之间变化。2)随着10质量%Al钢中C含量的增加，硬度增加。但抗拉强度和延伸率下降，合金钢在拉伸试件制作过程中发生断裂。EPMA分析表明，晶内及晶界有大量针状析出物，为Fe3AlC相。随着含碳量的增加，高铝钢的脆化似乎归因于上述复合碳化物沿晶界析出。3)为了将碳固定为稳定的碳化物，在含碳质量分数为10%的高铝钢中加入了钛和锆元素。随着钛含量的增加，Fe3AlC转变为TiC，塑性得到一定程度的改善。4)Ca、Ce和工业精炼剂对塑性没有影响。5)根据实验结果和文献综述，高铝钢的脆化不能从根本上防止，因为高铝钢在潮湿环境中容易发生环境脆化。6)最后，研究了添加Si对5质量%Al钢力学性能的影响。Al-1质量%Si钢具有较好的延性，且具有较高的耐氯化物性能。

In the present study, experiments were conducted in order to make clear the embrittling factors of high Al steel and to establish their improvement technics. The results are summarised as follows :1) In the case of ultra-low carbon steel, the hardness and tensile strength increased with the increase of Al content, whereas the elongation decreased. The elongation of 10mass% Al steel varied from about 2 to 15%.2) With the increase of C content in 10mass% Al steel, the hardness increased. However, the tensile strength and elongation decreased, and the alloy steel containing 0.09mass%C ruptured during the manufacture of specimen for tensile test. Many needle-like precipitates were observed within the inside of crystal grains and along their boundary and identified as Fe3AlC phase by EPMA analysis. The embrittlement of high Al steel with increasing C content seemed to be attributed to the fact that the above complex carbide precipitated along the boundary of crystal grain.3) In order to fix carbon as stable carbide, Ti and Zr were added to the 10mass% Al steel containing carbon. The increase of Ti content converted Fe3AlC to TiC and resulted in some improvement of ductility. While Zr addition refined the grain size, it assisted the embrittlement because of the formation of network composed of Fe2Zr.4) Ca, Ce and commercial refining agent had no effect on the ductility.5) Based on the experimental results and literature survey, it was concluded that the embrittlement of high Al steel cannot be prevented essentially, because high Al steels are susceptible to environmental embrittlement in a moisture atmosphere.6) Finally, the effect of Si addition on mechanical properties of 5mass% Al steel was investigated. The 5mass%Al-1mass%Si steel had acceptable ductility and seemed to have a high order of resistance to chloride.