Weld Metal Hardness
Weld metal hardness is the resistance of the cooled weld metal to indentation by a test body. It reflects the microstructural composition and the mechanical strength of the joint.
Physical-Chemical Mechanism of Action
The hardness of the weld metal is determined by its microstructure, especially the grain structure and the formation of phases such as martensite or austenite. At high hardness, the crystal structure and grain size are fine, which increases resistance to indentation.
Metallurgical Relevance & Risks in Welding
Too high weld metal hardness can lead to crack-sensitive microstructures, especially when the grain is fine. This can cause hot cracks and cracking in the weld. On the other hand, too low hardness can lead to poor stress transfer and formability.
Workshop Practice & Action Guidelines
To control weld metal hardness, the following measures should be taken:
• Melting process: Correct throttling and temperature control are crucial.
• Cooling system: Controlled cooling is necessary to achieve the desired microstructure. For stiff steels (like HSS), slow cooling should be preferred.
• Testing methods: Use methods like Brinell hardness testing or Rockwell hardness testing to determine the actual hardness and ensure it is within the specified range.