Coarse-Grained Martensite
Coarse-grained martensite is a highly dislocation-rich, hard needle structure that forms during rapid cooling from coarse-grained austenite. It exhibits high hardness and low toughness.
Physical-chemical mechanism
During rapid cooling of austenite, martensite forms through rapid dislocation movements of the atoms. This leads to a highly dislocation-rich needle structure with great hardness.
Metallurgical relevance & welding risks
Coarse-grained martensite is very hard and brittle, which can lead to cracks and hot cracks. The toughness is low, which impairs the mechanical properties. This can particularly lead to failure under stiff loads.
Workshop practice & instructions
To avoid martensite, cooling should be controlled and slow. For heavily loaded parts, high toughness is essential. Use steel grades with low carbon content and increased nickel content for such applications to control cooling.