Decarburization refers to the loss of carbon from the surface layer of an alloy,typically steel,when it is heated to high temperatures(generally above 700℃)in an atmosphere containing oxygen or hydrogen.This phenomenon is categorized based on its extent and cause.
1.Extent-Based Decarburization
In metallurgical testing,decarburization is classified by the degree of carbon loss in the surface layer:
Complete Decarburization(Type 1):This occurs when the carbon is completely removed,resulting in a measurable layer of pure ferrite(carbon-free iron)at the surface.
Partial Decarburization(Type 2&3):This describes the transition layer where the carbon content gradually increases from the surface to the core’s original concentration.The loss is greater than 50%(Type 2)or less than 50%(Type 3)without a completely carbon-free layer.
2.Intent-Based Decarburization
From a process standpoint,decarburization is classified by whether it is an intended or unintended outcome:
Incidental/Undesirable Decarburization:This is the most common and problematic type,occurring unintentionally during high-temperature manufacturing processes like forging,hot rolling,or heat treatment.It severely reduces the surface hardness,wear resistance,and fatigue strength of critical components like fasteners and gears.
Intentional Decarburization:This is a controlled process used to achieve specific material properties.A prime example is the production of electrical steel(silicon steel),where low carbon content is required to minimize magnetic core losses,thus enhancing electrical efficiency.
Preventing incidental decarburization usually involves using controlled atmospheres(inert gases or vacuum)during heating.
