General Characteristics AISI ALLOY STEEL 4615

This is a nickel-molybdenum alloy steel that is normally used in a carburized condition

Chemical analysis

C% Mn% Si%   P% S% Ni% Mo%
0.13/0.18 0.45/0.65 0.20/0.35 0.035 max 0.040 max 1.65/2.00 0.20/0.30

This alloy is used for parts where strength and toughness are required, such as forged gears and shafts.

The alloy is forged at a maximum temperature of 2275ºF (1245ºC) and should not be forged below 1650ºF (925ºC).
Heat Treatment

This grade does not normally require annealing, and machining may be carried out after either normalizing or following an isothermal anneal – 1290ºF (700ºC) for 8 hours – after forging.

This grade is normalized at a nominal temperature of 1700ºF (925ºC) followed by air cooling.

A maximum hardness of Rc 35-40 may be obtained from this grade by direct hardening. Surface hardening is normally by carburizing or carbonitriding, when surface hardnesses of Rc 60-65 are easily obtainable.

Tempering will be carried out after surface hardening at temperatures based on acquired experience.

Process routing
This grade might typically be processed as follows:
Forge – Normalize – Anneal (optional) – Rough and Semi-finish machine – Case harden – Temper – Finish machine (case-hardened parts only.)

As noted above, this alloy is readily machinable providing appropriate heat treatments are carried out.

This grade may be welded in the normalized or annealed condition, but should not be welded in the surface-hardened state.