This article presents the different hardness test methods used to measure the effectiveness of surface carbon control in carburized parts of steel. Common test methods include Rockwell hardness measurements, superficial Rockwell 15N testing, and microhardness testing. The article provides information on the microscopic method used to detect smaller variations in carbon content, and reviews consecutive cuts analysis and spectrographic analysis that are used to accurately evaluate the carbon concentration profile of carburized parts. It describes procedures of and precautions to be undertaken during shim stock analysis, which is used to measure the atmosphere carbon potential. The article includes a discussion on the electromagnetic nondestructive tests that are used to evaluate the case depth of case-hardened parts.
This article describes the thermodynamics and kinetics of gas carburizing reactions, and details the mass transfer mechanism during gas carburizing. It discusses the various considerations involved in carburizing process planning, and reviews successful operation of the gas carburizing process based on the control of three principal variables: temperature, atmosphere composition or carbon potential, and time. The article also describes the selection criteria for alloy, carbon sources, atmosphere types, and carbon monoxide level for endothermic carburizing atmospheres. It provides information on carburizing modeling, case depth prediction, case depth measurement, and case depth evaluation as well as on carburizing equipment, and also covers the factors affecting distortion after carburizing.