高硬度Ni-Cr-Al合金のミクロ組織と硬さに及ぼす熱処理条件の影響

抄録

It is known that Ni-40Cr-4Al (mass%) alloy and Ni-38Cr-3.8Al alloy possess high hardness in aging condition by precipitating α-chromium and γ’ (Ni₃Al). So far the alloys have so poor hot workability that the alloys have been investigated in the condition of as-cast coarse grain structure. Recently we succeeded in hot working of the alloys by optimizing chemical compositions and heating temperature and could obtain the finer grain alloys.
In this study the influence of solution treatment and aging on the microstructure and hardness of two kinds of hot rolled Ni-Cr-Al alloys with fine grain structure was investigated, which were Ni-38Cr-3.8Al and Ni-38Cr-4.2Al.
Both alloys maintained fine grain of austenite phase in solution treatment condition with some of spheroidzing α-chromium and the hardness was under 200HV. However, by dissolving almost all of α-chromium phase, the austenite grain drastically coarsened. In case that the cooling rate after soluntion treatment was slow, the hardness was getting high by precipitating α-chromium and γ’ phase in the grain boundary. In the aging condition, fine grain structure has faster precipitating rate than coarse grain structure because of increasing precipitation site in grain boundary. The peak aging hardness of Ni-38Cr-4.2Al alloy was higher than that of Ni-38Cr-3.8Al alloy. That was due to increasing the amount of α-chromium and γ’ phase.