Carburizing treatment is one of the earliest and widely used surface chemical heat treatment processes. It infiltrates carbon into the surface of the steel to increase the carbon content on the surface of the forging. Through quenching, the surface layer can obtain high hardness, while the core part can obtain higher hardness. Low ones have better tissue toughness.

　　For the inspection of carburizing quality of large heavy-duty forgings, according to the above standards, the carburizing quality of large heavy-duty forgings is mainly inspected and controlled through the following five aspects.

　　Surface hardness. After final heat treatment, the surface hardness of the forging should reach 58-62HRC. The specific value range is subject to the design drawing.

　　Heart hardness. Heart hardness should be in the range of 30-46HRC.

　　Effective hardening layer depth. It is roughly controlled by 0.2m, and the specific value range is subject to the design drawings. During the inspection, the hardness and depth change curve of the sample after final heat treatment should be measured and drawn according to the standard. The distance from the surface of the sample to 550HV in the curve is the effective hardened layer depth of the carburized quenching strengthened forging. For forgings with a surface hardness requirement of 52-56HRC, the limit value of the effective hardened layer depth is 500HV.