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