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

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Discussion Overview

The discussion revolves around the heat treatment of steel, specifically focusing on the effects of heating a bearing outer race to approximately 200°C on its hardness. Participants explore the implications of temperature changes on material properties, particularly in a practical context rather than a theoretical one.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Ian questions whether heating steel to 200°C will permanently reduce its hardness or if it will return to its original hardness upon cooling.
  • Some participants suggest that heating to 200°C should not significantly affect the hardness of bearing races, referencing that 150°C is a common tempering temperature.
  • There is mention of annealing temperatures ranging from 260°C to 760°C, indicating that the effects of heat treatment can vary based on the specific alloy and treatment process.
  • One participant notes that tempering primarily reduces brittleness in hardened materials rather than affecting hardness significantly at lower temperatures.

Areas of Agreement / Disagreement

Participants express differing views on the effects of heating steel to 200°C, with some asserting minimal impact on hardness while others raise questions about the permanence of hardness changes. The discussion remains unresolved regarding the specific outcomes of the heating process.

Contextual Notes

There are limitations in the discussion regarding the specific alloy composition of the steel in question and the precise definitions of terms like "hardness" and "tempering." The effects of heat treatment may depend on these factors, which are not fully explored in the posts.

mrfoxy
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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
 
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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.
 
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...
 
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
 

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