材料期刊网

奥氏体化温度对硼钢淬透性的影响,从实验结果得到,在各种热处理条件下均随温度的提高逐渐降低。氧化及氮化的因素对硼钢淬透性的下降是有一定的影响,但硼原子本身在奥氏体中的分布情况对淬透性的影响是更重要的一个因素。 在渗硼试样中观察硼化合物的形成,指出,从高奥氏体化温度直接淬火后,硼的沉淀物是在奥氏体晶界上及晶粒内均匀分布的,但在等温处理、正火处理或慢冷试样中,硼化合物大部份沉淀在奥氏体晶界上。因此,硼钢在高温奥氏体化后失去良好淬透性的原因,可能是由于硼原子从奥氏体晶界上的回扩散作用,使晶界上得不到足够的硼原子降低晶界能,引起硼的效能暂时的消失。

The influence of austenitising temperature upon hardenability was determinedfor two boron-treated steels; and it was shown that under different conditions ofheat treatment, the hardenability of boron steel decreases with increasing tempera-ture. The presence of oxygen and nitrogen has an appreciable effect in decreasingthe hardenability of boron steels, but the distribution of free boron atoms in aus-tenite has a more profound effect on hardenability. Investigations on the formation of boron constituent in boronised specimensshowed that by direct quenching from high austenitising temperatures, the boronprecipitate was distributed uniformly both at the austenite grain boundaries andwithin the grains. While in the isothermally treated, normalised, or slowly cooledspecimens, the boron constituent mainly ptecipitated at the austenite grain boundaries.Thus it was proposed that the loss of hardenablility of boron steels at high auste-nitising temperatures was probably due to the desorption of boron atoms from thevicinity of the austenite grain boundaries; consequently there will not be enoughboron atoms to lower the grain boundary energy and the boron hardenabilityeffect was temperarily lost.