Carburized steel-update on a mature composite

Hardenability of Steel

“…In some cases, the amount of bainite formed did not affect the hardness, although it did affect fatigue (110). Thus, a better measure of hardenability in the case was proposed by Eldis and Smith, which involves the Distance to the First appearance of Bainite (DFB) based on the Jominy hardenability test (110,112). The determination of DFB is now included in SAE J1975 (111).…”

“…The hardenability of the case controls the hardness and microstructure as well as the formation and magnitude of compressive surface stresses. To adequately resist fatigue failure, a martensite level of 90%, with the remainder being retained austenite, is generally thought to be necessary (112,113).…”

“…It is possible to use the Jominy end-quench test to characterize the hardenability of the carburized case as a function of distance from the quenched end of the Jominy bar. Although this procedure works well with relatively low case hardenability, it is more difficult to apply for higher hardenability case structures since it is often difficult to be assured of complete martensite formation (112).…”

“…Also, as the tensile strength increases, impact strength decreases (117). Furthermore, it is important to note that core hardenability does not predict case hardenability (112).…”

Fatigue Properties of Plasma Carburized Low Carbon Cr-Mo Steel.

“…The oxidation layers were reported to reduce compressive residual stress. [16][17][18] Internal oxidation layer was softer than martensite matrix so it relaxed compressive residual stress on surface and it occurred all grain boundaries in the gas carburized steel as shown in Fig. 4.…”