Nickel Equivalent for Austenite Stability
Nickel equivalent is the sum of austenite-stabilizing elements to determine the tendency for austenitic microstructural constituents under welding conditions. It helps in selecting appropriate welding methods and parameters.
Physicochemical Mechanism of Action
The nickel equivalent is a mathematical sum that measures austenite-stabilizing elements like nickel, cobalt, molybdenum, chromium etc. in a material. This sum indicates how strongly the material tends to form austenitic structure under welding conditions.
Metallurgical Relevance & Welding Risks
A high nickel equivalent can cause the material to become austenitic under welding conditions. This can hurt toughness and hardenability, especially at high temperatures and long cooling times. Too low a nickel equivalent, on the other hand, can make the material ferritic or martensitic, which leads to higher hardness and possible cracks.
Workshop Practice & Instructions
For metals with a high nickel equivalent (e.g. > 10), it is important to cool the weld slowly to keep an austenitic structure. This can be done through slow cooling or the use of shielding gases. For metals with a low nickel equivalent (e.g. < 10), it is important to cool the weld quickly to avoid a ferritic or martensitic structure. This can be done through fast cooling or the use of cooling devices.