Granular bainite
Granular bainite consists of large, irregular ferrite grains with embedded martensite or austenite islands. It is a bainitic microstructure with increased hardness and toughness.
Physical-Chemical Mechanism of Action
Granular bainite forms by slow cooling of high-temperature austenite. During cooling, ferrite crystallizes in large grains, while martensite or retained austenite remains as islands within these grains.
Metallurgical Relevance & Risks in Welding
Granular bainite is a robust microstructure with high stress levels and good toughness. It reduces susceptibility to cracking and improves performance under mechanical load. However, too rapid cooling can lead to the development of martensite, which increases hardness but also reduces ductility.
Workshop Practice & Action Guidelines
To create granular bainite, the weld should be cooled slowly. A typical cooling time of 10 to 30 seconds is often suitable. At high carbon contents (above 0.5%), even longer cooling may be required to minimize the risk of excessive martensite proportion.