Martensite

What is Martensite in Metallurgy?

Martensite is a hard, crystal structure in stainless steel formed through rapid cooling, resulting in a body-centred tetragonal (BCT) phase. In metallurgical terms, it’s recognised for exceptional hardness and strength, often found in stainless steels requiring high wear resistance. 

How Martensite is Formed in Stainless Steel

1. Austeniutizing
   Stainless steel is heated to around 900-1100°C, converting its internal structure to austenite- a face-centred cubic (FCC) phase that can dissolve more carbon.
2. Quenching
   The hot stainless steel is quickly cooled using oil, air, or water. This sudden drop in temperature prevents the formation of softer structures, such as ferrite or pearlite.
3. BCT structure formation
   As carbon atoms remain trapped during rapid cooling, the austenitic transforms into a strained body-centred tetragonal (BCT) lattice – martensitic. This phase is hard but brittle.
4. Cold Working
   Mechanical deformation at room temperature, such as rolling or pressing, can increase the martensite content, thereby further enhancing strength and hardness.
5. Tempering
   To reduce brittleness and relieve internal stresses, the stainless steel is reheated to a moderate temperature. This improves toughness while retaining most of the hardness.

What is Martensitic Stainless Steel?

Martensitic stainless steel contains 10.5–18% chromium and 0.1–1.2% carbon, offering high strength, wear resistance, and magnetic properties. These grades are hardenable through heat treatment or work hardening, making them ideal for applications such as knife blades, surgical instruments, fasteners, shafts, and turbine blades. Though less corrosion-resistant than austenitic types, they perform well in mild environments and benefit from post-weld stress relief if welded.