Martensitic Hardening
Martensitic hardening is a structure transformation by rapid cooling, where carbon is trapped in the tetragonal lattice, greatly increasing hardness. This process boosts toughness but can lead to crack-prone structures.
Physical-Chemical Mechanism of Action
Martensitic hardening occurs when a metal is rapidly cooled from the austenite region. This prevents the complete transformation of the lattice into the cubic copper lattice and forces carbon into the tetragonal lattice. Rapid cooling also prevents the formation of decomposition products such as Fe₃C, leading to extreme hardness.
Metallurgical Relevance & Welding Risks
Martensitic hardening increases the strength and toughness of steel, but it can also lead to crack-prone structures like martensite. This can cause hot cracks and weld metal tears in the weld seam. Hardness testing is therefore crucial for quality control.
Workshop Practice & Action Guidelines
To achieve martensitic hardening, the metal must be cooled rapidly. This can be done by a short time span (t8/5 s < 5) or by using cooling water. During hardness testing, a Brinell hardness of at least HB300 should be ensured. Make sure the metal is not cooled too quickly to avoid crack-prone structures.