Heat treatment of steel and the effect on it's hardness

[mrfoxy]

Newbie to the forum, so forgive me if I post this in the wrong place!

If I heat steel (a bearing outer race to be exact) from room temperature to approx 200C, the hardness of the steel will reduce. If the temperature is then allowed to reduce back to room temperature, what will happen to the hardness? Will it rise to what it was previously, or will it stay at its lower value? Thanks

Ian

 

[Mapes]

Hi mrfoxy, welcome to PF. For homework-style questions, we ask that you show how you've tried to answer them first. Then you'll likely get useful comments.

 

[mrfoxy]

Nothing to do with homework, but every question on this forum could indeed be classed as homework?! It's actually a problem we're having at work that's costing us thousands and I had a theory about classic physical material properties. wish it was homework, thanks I'll look elsewhere...

 

[schip666!]

Going up to 200C shouldn't have much effect on bearing race hardness. 150C is a base value for tempering after hardening, but according to the annealing (re-softening) wiki page:

The temperature range for process annealing ranges from 260 °C(500 °F) to 760 °C(1400 °F), depending on the alloy in question.

Once annealed the metal will remain softer, but tempering just reduces stresses in hardened materials such that they are less brittle.

Heat treating is a big, and fascinating if you are a metal-geek, subject. This wiki article and subsequent links are a good place to start:
http://en.wikipedia.org/wiki/Heat_treating

 

[sardar]

,

Welcome to the forum!

I can tell you that the hardness of steel is greatly affected by its heat treatment. When steel is heated, its internal structure changes, which in turn affects its physical properties such as hardness. When heated to 200C, the steel undergoes a process called tempering, which results in a decrease in hardness. This is because the heat allows the steel to release internal stresses and become more ductile.

As for your question about the hardness returning to its previous value after cooling back to room temperature, it depends on the specific steel and the temperature it was heated to. If the steel was heated to its critical temperature (the temperature at which its internal structure changes), then cooled slowly, the hardness may return to its original value. However, if the steel was heated beyond its critical temperature, the change in internal structure may be irreversible and the hardness will remain at its lower value.

I hope this helps answer your question. Keep exploring and learning about the fascinating world of steel and its properties!