Metallurgical approach to estimating fracture toughness of BCC iron alloys at low temperatures

Abstract

Fracture toughness tests were performed at temperatures ranging from 4.2 K to the temperature of the brittle-ductile transition for 34 kinds of polycrystalline iron alloys. Test results indicate that: (1) the critical strain energy release rate G(sub ic) of crack extension may be expressed as G(sub ic) = G(sub 0) exp (T/T(sub 0)) and 1/T(sub 0) = (1/T(sub 0.1))(d/d(sub 0.1))(exp -1/7), where T is the testing temperature and d is the grain size in mm; and (2) under quenched conditions G(sub 0) and T(sub 0) depend upon ((C) + 4(N)) at. percent and (-(C) -4(N) -0.2(Si) -1.2(P) -1.2(S) +0.2(Mn) +0.2(N)) at. percent, respectively.

34種類の多結晶鉄合金について、4.5Kから脆性-延性遷移温度までの温度範囲で、脆性破壊試験を行った。試験の結果、(1)亀裂伝搬の臨界歪エネルギー解放速度Gicは、Gic=G0{T/To}および1/To=(1/T(0.1))(d/d(0.1)){-1/7}と表せることが分かった。ただし、Tは試験温度、dはmm表示の結晶粒径である。(2)急冷条件下では、G0とT0は、それぞれ([C]+4[N])at%および(-[C]-4[N]-0.2[Si]-1.2[S]+0.2[Mn]+0.2[Ni])at%に依存した。