Peritectic melting reaction
Peritectic melting reaction: On heating, a solid phase decomposes into several new solid phases and a liquid melt. This leads to coarsening of the microstructure and can reduce toughness.
Physicochemical Mechanism of Action
In the peritectic melting reaction, a solid phase breaks down on heating into several new solid phases and a liquid melt. This process is a reverse thermal process to the eutectic melting reaction, where a liquid melt condenses into a single solid phase on cooling.
Metallurgical Relevance & Welding Risks
The peritectic melting reaction can lead to coarsening of the structure, which reduces the toughness and the modulus of elasticity of the material. This raises the susceptibility to cracks and lowers the mechanical properties of the weld. It can also lead to uneven stresses, which can cause hot cracks or drawing fractures in the material.
Workshop Practice & Instructions
To avoid the peritectic melting reaction or minimize its effects, it is important to choose the correct welding process and material. This includes holding the right temperature curve during welding. For stiff steels with a high carbon content (e.g. HSS), it is especially important to control the maximum melting temperature and the cooling time. Cooling too fast can cause the peritectic melting reaction to happen and the structure to coarsen. It is therefore recommended to cool slowly after welding to stabilize the structure and keep the mechanical properties of the material.