Heat Treatment and Hardness

The hardness of metal materials has a certain empirical relationship with their static strength and fatigue strength, and is related to the processing performance of metals such as cold formability, machinability and weldability. The hardness test does not damage the workpiece and is simple and easy to perform, so hardness is widely used as the most important quality inspection indicator for heat-treated workpieces, and many workpieces also use it as the only technical requirement.

Unqualified hardness is one of the most common heat treatment defects. It is mainly manifested in insufficient hardness, soft spots, insufficient hardening layer of high-frequency quenching and carburized workpieces, etc.

The low hardness of quenched workpieces is generally caused by insufficient quenching heating, insufficient quenching cooling speed, surface decarburization, insufficient hardenability of steel, excessive residual austenite after quenching, or insufficient tempering.

The phenomenon of low hardness in a local area of ​​a quenched workpiece is called a soft spot. The microstructure of the soft spot area is mostly a mixed structure of martensite and troostite distributed along the original austenite grain boundary. Soft spots or uneven hardness are usually caused by uneven quenching heating or uneven fire cooling.

Uneven furnace temperature during heating, improper heating temperature or holding time are the main causes of uneven heating. Uneven cooling is mainly caused by bubbles attached to the surface of the workpiece during quenching cooling, contamination of the quenching medium (such as oil droplets suspended in water) or insufficient stirring of the quenching medium.

In addition, the steel structure is too coarse, with serious structural segregation, large carbides or large free ferrite. Due to the uneven structure, the hardness of the quenched workpiece will be uneven or soft spots will be formed.

Full Mechanical Manual Rockwell Hardness Tester iqualitrol HR-150A with Dial Gauge

Technical Specification: