Bainitic stage
Bainitic stage is an intermediate structure consisting of ferrite and cementite, formed by combined carbon transport. It lies above the martensite start temperature.
Physical-chemical mechanism
The bainitic stage forms through simultaneous diffusion of carbon and silicon into the ferrite structure. This leads to the formation of cementite, which mixes with ferrite to produce a homogeneous structure.
Metallurgical relevance & welding risks
The bainitic stage can form if cooling after welding is inadequate. It leads to increased hardness and toughness, impairing the steel's formability. This can cause stress and potential cracking in the component.
Workshop practice & instructions
To avoid the bainitic stage, it is important to ensure controlled cooling after welding. This can be achieved using cooling water or special coolants. The cooling rate should be set to keep the structure in the bainitic stage and prevent it from transforming to martensite or excessively coarsened grain.