Twinned martensite structure
Twinned martensite is a special form of martensite with high carbon content, where hardness is increased by internal twinning. This makes the steel very brittle and prone to cracking.
Physicochemical mechanism of action
In martensite, a heavily distorted crystal lattice forms, which leads to twin structures at high carbon content. This twin formation increases hardness through improved atomic ordering and deformability.
Metallurgical relevance & welding risks
The twin martensite structure is very brittle and can form from too-fast cooling or too-high carbon content. This increases susceptibility to cracking and hot cracking, which can make the material unusable.
Workshop practice & instructions
To avoid twin martensite, ensure controlled cooling after welding. Use appropriate shielding gas mixtures and keep the carbon content in the material below 0.7 %. For highly brittle steel, post-weld heat treatment such as tempering or austenite transformation is advisable.