DeLong Diagram for Ferrite Determination
The DeLong diagram is an extension of the Schaeffler diagram that takes nitrogen content into account to determine the delta ferrite content in austenitic welding materials. It helps optimize hardness and mechanical properties.
Physicochemical Mechanism of Action
The DeLong diagram is based on phase diagrams of austenitic steels and considers the effects of carbon, nickel, and nitrogen on the ferrite structure. It shows how delta ferrite content changes when these additions vary.
Metallurgical Relevance & Welding Risks
Delta ferrite content affects the hardness and mechanical properties of the steel. Too much ferrite leads to excessive hardness, making the material prone to cracking. Too little ferrite can make the material too soft and lack toughness. The DeLong diagram helps control these properties and avoid such risks.
Workshop Practice & Instructions
To use the DeLong diagram, you need to know the carbon and nitrogen contents of the steel. Cooling temperature and time are decisive for ferrite formation. With correct application, the diagram can help achieve optimal delta ferrite content, improving weld material hardness and toughness.