Most bearings for piston-driven aircraft engines and early jet engines were made of through-hardening AISI 52100 steel or carburizing grades of alloy steels. However, as power requirements rose, operating temperatures increased, and alloys with more heat resistance became necessary. Minor improvements in the performance of AISI 52100 were achieved by extra alloying additions, but these incremental changes were not enough to keep pace with the higher operating temperatures. In the 1950's in Europe, T-1 and M-2 high-speed steel (HSS) were used for some jet engine applications. T1, also known as 18-4-1, contains tungsten, chromium, and vanadium as the primary alloy elements. M-2, known as 6-6-2, contains chromium, tungsten, vanadium, and molybdenum (see table).
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