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

本文通过试验，明确了高铝钢的脆性影响因素，并建立了相应的改进工艺。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，而伸长率则随Al含量的增加而降低。10mass% Al钢的伸长率约为2% ~ 15%。2)在10mass% Al钢中，随着C含量的增加，硬度增大。但拉伸强度和伸长率下降，含0.09质量%C的合金钢在拉伸试验试样制作过程中发生断裂。晶粒内部及晶界有大量针状析出物，经EPMA分析为Fe3AlC相。随着C含量的增加，高铝钢的脆化可能是由于上述复合碳化物沿晶界析出所致。3)在含碳的10mass% Al钢中加入Ti和Zr，以固定碳为稳定碳化物。随着Ti含量的增加，Fe3AlC转化为TiC，塑性得到一定程度的改善。Zr的加入细化了晶粒尺寸，但由于形成了由Fe2Zr组成的网状结构，有利于合金的脆化。4) Ca、Ce和商业精炼剂对延展性没有影响。5)根据实验结果和文献综述，高铝钢在潮湿气氛中易受环境脆化的影响，从本质上无法防止高铝钢的脆化。6)最后，研究了Si添加量对5mass% Al钢力学性能的影响。5mass%Al-1mass%Si钢具有可接受的延展性，并且似乎具有较高的抗氯化物性能。

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.