Material hardness
Material hardness is the resistance of a material to the penetration of a solid body. It indicates how hard a material is and influences its mechanical properties.
Physical-Chemical Mechanism
The hardness of a material is determined by the structure of its atoms. Solids with tightly packed atoms are harder than those with atoms spaced further apart. Hardness can be influenced by mechanical stress, chemical reactions, or thermal changes.
Metallurgical Relevance & Welding Risks
Excessive hardness can make the material prone to cracking and fracturing. In a weld, uneven hardness distribution can lead to stress concentrations that cause hot cracks or fracture points. On the other hand, too low hardness can make the material too soft and susceptible to deformation.
Shop Practice & Actions
To achieve optimal hardness, welding parameters such as temperature, time, and voltage must be precisely controlled. For steels, hardness is determined by the microstructure. Rapid cooling can lead to hard martensite, while slow cooling results in soft austenite. Hardness can be measured using methods like the Brinell hardness test or the Rockwell hardness test.