ABSTRACT

This study investigates the in-situ evolution of the morphology of heated microstructures and sulfides, and to detect the machinability of Bi-bearing high S, low C free-cutting steels. The results show that Bi particles soften, melt, and vaporize during heating process. Its temperature varies slower than that of steel, and causes extensive local expansion of austenite grains. Heat absorbed by small sulfides leads to their volume expansion and formation of larger sulfides by fusion, whereas heat absorbed by large sulfides causes enlargement in dependent spherical or ellipsoidal shapes. During the heating process, at temperatures between 1500°C and 1550°C, the nominal coarsening speed of the tail wave is higher than that of the triple junction, but their movement speeds are similar. The addition of Bi particles to steel enhances its machinability. The cutting heat melts Bi particles to form liquid Bi films, resulting in rapid chip breaking during cutting.

摘要

本研究对原位热显微组织和硫化物形态的演变，并检测含铋高 S、低 C 易切削钢的切削加工性。结果表明，Bi颗粒在加热过程中软化、熔化和汽化。它的温度变化比钢慢，并导致奥氏体晶粒的广泛局部膨胀。小硫化物吸收的热量会导致它们的体积膨胀并通过熔化形成较大的硫化物，而大硫化物吸收的热量会导致相关球形或椭圆形的扩大。在加热过程中，在1500℃～1550℃的温度下，尾波标称粗化速度高于三结，但它们的运动速度相近。向钢中添加 Bi 颗粒可增强其机械加工性。