Case Hardening — Definition of Carburising Carburising is the process of inducing carbon into which category of carbon steels in order to produce a hard, wear-resistant surface (case)?

Introduction / Context:Carburising is a classic case-hardening process used to achieve a hard, wear-resistant surface while maintaining a tough, ductile core. It is widely applied to gears, shafts, and pins that require surface durability with core toughness to resist shock and bending.

Given Data / Assumptions:

• Base material is plain carbon steel before treatment.
• Objective is to increase surface carbon content for subsequent quench hardening.
• Core should remain relatively low in carbon to retain toughness.

Concept / Approach:Carburising introduces carbon into the surface of low-carbon steels (typically around 0.1–0.25% C) by exposing them to a carbon-rich environment at austenitising temperatures. After diffusion increases surface carbon to about 0.8–1.0% or as specified, the part is quenched so that the high-carbon surface transforms to hard martensite, while the low-carbon core transforms to a tougher, lower-hardness structure. This gradient yields the desired combination of wear resistance and impact toughness.

Step-by-Step Solution:Select a low-carbon steel substrate (e.g., 0.15% C).Heat in a carbonaceous atmosphere (solid, liquid, or gas carburising) at austenitising temperatures.Allow carbon to diffuse inward for the required case depth.Quench to form martensite in the carbon-enriched case; temper as needed.

Verification / Alternative check:Design handbooks specify low-carbon case-hardening grades (e.g., 16MnCr5, 20MnCr5, 8620) explicitly for carburising.

Why Other Options Are Wrong:Medium/high/ultra-high carbon steels already have sufficient carbon for through-hardening; carburising them is unnecessary and can cause excessive brittleness.Cast iron is not the standard substrate for carburising in case-hardening practice.

Common Pitfalls:Confusing carburising with carbonitriding or nitriding; carburising specifically increases carbon content, not nitrogen alone.

Final Answer:low