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用改进的径迹显微照相技术研究了50B钢800—1150℃顶端淬火试样中硼的分布状态及其变化规律与硼钢淬透性的关系。试验表明,硼钢淬透性的变化与冷却时硼向奥氏体晶界偏聚的发展速度密切相关。晶界硼偏聚来自二侧贫硼区,利用成分剖面图技术可定量测定这种偏聚的发展速度。 晶界硼偏聚发展过快与过慢均对发挥硼效应不利。试验表明,只有当晶界硼偏聚的发展速度与基体成分相变孕育期能较好配合时,硼的效应最大。利用这种观点可正确说明硼钢淬透性的变化特征及认识与分析影响硼钢淬透性的各种因素。
The improved track microscopy technique was used to study the distribution of boron in the top quenched sample of 800-1150 ℃ for 50B steel and its relationship with the hardenability of boron steel. The experiment shows that the change of hardenability of boron steel is closely related to the development speed of segregation of boron to austenite grain boundaries during cooling. Boron segregation at the grain boundary is from the boron-depleted zone on both sides, and the rate of development of this segregation can be quantitatively determined using the compositional profile technique. Boron segregation at the grain boundary is too unfavorable for the boron effect to be developed too fast and too slowly. Experiments show that the effect of boron is greatest only when the rate of segregation of boron in the grain boundaries is better matched with the phase change of the matrix composition during the incubation period. The use of this point of view can correctly explain the changing characteristics of boron steel hardenability and understanding and analysis of various factors affecting the hardenability of boron steel.