Strength, Hardness & Wear Resistance 2

[PeterCharles]

Generally with carbon steels you can say :-
the stronger the steel, the harder it is,
the harder the steel, the more wear resistant it is.
Does this apply with Precipitation Hardening stainless steels?

My reason for asking is that (if I remember correctly) with carbon steels the heat treatment changes the structure of the grains so that the grains themselves are harder and so harder = stronger = more wear resistant. But with PH stainless steels the heat treatment results in precipitates that make it harder for the grains to deform under load thus overall the material is stronger. However nothing happens to the grains themselves so are they likely to be no more wear resistant than if the heat treatment had never taken place?

Has anyone any knowledge to share on this subject.

 

[unclesyd]

You have asked for information on a very complex subject that would be best presented in the form of a matrix.

A general statement is that the PH steels as a family do increase in wear resistance as the hardness increases as measured on the Taber Met-Abrader. The decrease is not that significant.
17/4 @ 28 Rc 70 mg/1000 cycles
@ 35 Rc 80 "
@ 43 Rc 50 "
17/4 in Condition A, Rc 34 wear rate is 155 mg/1000 cycles.

13/8 @ 33 Rc 60 mg/1000 cycles
@ 47 Rc 50 "

These data is from self-mated couples.
Both of these PH steels, as most PH steels, show an improvement in wear resistance as the speed increases. Most of these steel show increase in wear up to 100 RPM then drop in wear rate.
Also an increase in temperature will also lower the wear rate to some degree.
There wear rate of any of these steels is determined by the particular piece of metal, it's thermal history, surface condition, blue is better, and the enviroment at that particular place in time.

If you have any particular couple in mind please post the materials and conditions.

 

[TVP]

PeterCharles,

As Unclesyd demonstrated there is some improvement in wear resistance with precipitation hardening. Martensitic microstructures consisting of uniformly distributed carbides that are submicron in size offer the best wear resistance. PH stainless steels do not always have a martensitic microstructure, and even when they do, it is typically a low-carbon martensite, and therefore the amount of carbides is not nearly as high as in medium to high carbon martensites.