1045 carbon steel (0.45%carbon). Most common steel used for gears, pins, bushes, washers and wear plates. Typical hardness 45-55HRc
4140/709M alloy steel (0.40%carbon). Higher core strength than 1045. Used for the same items but more highly stressed applications. Typical hardness 50-60HRc
4340 alloy steel (0.40%carbon). Nickel content provides a good combination of hardness and toughness. 4340 is used in highly stressed applications. More difficult to heat treat than 1045 or4140 since it is prone to quench cracking. Typical hardness 50-60HRc
EN25 alloy steel (0.30%carbon). High strength alloy steel with high hardenability, toughness and fatigue resistance. Used for gears, shafts and axles of large section. Typical hardness 45-55HRc
EN26 alloy steel (0.40%carbon). EN26 is similar to EN25 but higher levels of hardness and wear resistance. Typical hardness 55-60HRc
XK1340 carbon steel (0.40%carbon). Used for similar applications as 1045. Manganese content provides improved toughness over equivalent plain carbon steel. Typical hardness 45-55HRc
K245 tool steel (0.65% carbon). Shock resisting tool steel with extreme toughness, edge retention and wear resistance. Typical hardness 55-65HRc
Martensitic stainless steel (400 series) and many other carbon steels, alloy steels, tool steels and cast irons may be successfully flame or induction hardened.
Remember to centre pins both ends and leave machining of any details in the heat affected zone until after hardening. These simple actions will save you time and money.
Nitriding Steels are steels that contain the strong nitride-forming elements aluminium, chromium and molybdenum. Nitriding consists of heating the part in an atmosphere containing ammonia at about 500 degrees Celsius. The parts are not quenched which minimises distortion. A thin, very hard case results from the formation of nitrides. 4140 is commonly available steel suitable for nitriding. It is ideal for small intricate parts that require hardening.
Cast Irons Malleable iron, gray iron and ductile iron (also called SG or nodular iron) may be successfully flame hardened to hardness levels of 45-60 Rockwell C depending on the composition and microstructure of the iron.