Martensite and Austenite

The main components of fasteners are carbon and steel. Today, let's take a look at the two microstructures of stainless steel fasteners, namely martensite and austenite.

Martensite has hardness, and austenite has no hardness because it is in a hot state. The main differences fall into three categories: different shapes, different densities, and different characteristics, as follows:

1. Different forms

Martensite is a body-centered square structure, and the three-dimensional structure usually has a sheet or lath shape, and sheet martensite usually appears as needles in metallographic observation (two-dimensional);

Austenite has a face-centered cubic structure, and interstitial atoms such as carbon and nitrogen are located in the center of the octahedral gap of the austenite unit cell, and the center and edge midpoint of the face-centered cubic unit cell.

2. Different densities

The transformation of austenite to martensite requires very little energy because the transformation is of the non-diffusion displacement type, only rapid and minor rearrangements of atoms. Due to the volume expansion after transformation, it can be seen that the density of martensite is lower than that of austenite.

3. Different characteristics

Martensite has high strength and high hardness, but poor toughness, which is characterized by being hard and brittle;

Austenite has good plasticity, low strength, certain toughness, no ferromagnetism, poor thermal conductivity, and large linear expansion coefficient.