The divorced eutectoid transformation in steel
The divorced eutectoid transformation in steel
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DOI：
10.1007/s11661-998-0245-4
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发表时间：
1998-04-01
影响因子：
2.8
通讯作者：
Gibson, ED
中科院分区：
文献类型：
--
作者：
Verhoeven, JD;Gibson, ED
实验表明，在略低于A(1)的温度下，钢中的共析转变可以以两种不同的方式发生。在正常状态下，转变产物为片状珠光体。第二种模式是当奥氏体内含有间距在几微米或更小的渗碳体颗粒或晶核时出现的。在这种情况下，转变产物由铁素体基质中的球状渗碳体颗粒组成。第二种模式在这里被称为离婚共析转变(DET)，这是Sherby和他的同事最近的研究成果。一项文献调查表明，片状珠光体上非均匀奥氏体相DET的快速动力学是在1940年前建立的，但很少受到关注。不均匀性一般为细小的渗碳体颗粒。实验表明，DET不是像离异共晶生长那样，在共析(渗碳体)的另一相(渗碳体)周围形成一相(铁素体)的外壳。相反，相当平坦的奥氏体铁素体前沿只是简单地进入奥氏体，对渗碳体颗粒产生的形状没有明显影响。建立了片状珠光体生长速度随过冷度A(1)变化的一级动力学模型，并与片状珠光体的生长速度与过冷度进行了比较。SIMPLE模型表明，在低过冷度下，分布在奥氏体核中的渗碳体晶核的离异速度应快于片层模式。这一结果与实验数据相吻合。
Experiments are presented which show that the eutectoid transformation in steel can occur by two different modes for temperatures just slightly below A(1). In the normal mode, the transformation product is lamellar pearlite. The second mode occurs if the austenite contains cementite particles or nuclei with a spacing on the order of a few microns or less. In this case, the transformation product consists of spheroidal cementite particles in a ferrite matrix. This second mode is here called the divorced eutectoid transformation (DET), after recent work by Sherby and co-workers. A literature survey shows that the faster kinetics of the DET over lamellar pearlite in the presence of inhomogeneous austenite was established before 1940, but has received little attention. The inhomogeneities are generally small cementite particles. Experiments show that the DET does not occur by a shell of one phase (ferrite) forming around the other phase of the eutectoid (cementite), as is the case in divorced eutectic growth. Rather, a fairly planar austenite/ferrite front simply advances into the austenite, with no apparent effect on its shape being produced by the cementite particles. A first-order kinetic model is presented for the growth velocity as a function of undercooling below A(1) and is compared to the velocity vs undercooling for lamellar pearlite. The simple model indicates that the velocity of the divorced mode should be faster than the lamellar mode at low undercooling for cementite nuclei distributed in the austenite with spacings less than a few microns. This result is consistent with the experimental data.