The refinement technology for bainite and its application

The relaxation–precipitation-controlled phase transformation technique to refine the bainite has been simulated on a Gleeble-1500 thermo-simulator. This technique has also been applied in large-scale production. Optical and scanning and transmission electron microscopy as well as particle-tracking autoradiography techniques were employed to study the precipitation, and the dislocation configuration during the relaxation. The microstructure and the boron distribution were also investigated. The results show that during the relaxation subgrains can form inside the austenite grains and boron can segregate at the boundaries of subgrains. The subgrains pinned up by strain-induced precipitates, and acicular ferrite firstly formed inside the austenite grains can effectively refine the subsequently formed lathes and packet of bainite. This ultra fine microstructure has also been obtained in the large-scale production.