Tempered Steel

[FNB8812]

I have a piece of alloy-steel round bar(4140) the dimension are 1/2 diameter and 4 long and the steel has been heat treated and tempered to 40-45 Rc I am heating up the end of the steel bar to about 1500 degrees for 10 seconds. My question is when I do this am I effecting the heat treatment or changing the properties of the steel in any way and is there a recommendations for cooling?

 

[metengr]

My question is when I do this am I effecting the heat treatment or changing the properties of the steel in any way and is there a recommendations for cooling?

The short time duration of 10 seconds is probably of benefit in reducing exposure to additional tempering or softening. My advice is to duplicate this effect on a coupon and have a lab run hardness traverses to verify the affect on bulk properties of the heat treated bar starting from the heated end and progressing away. Otherwise, we can only guess.

 

[TomDOT]

Question is a duplicate:

http://www.eng-tips.com/viewthread.cfm?qid=328491

 

[arunmrao]

How precise and reproducible are your control on temperature and time . As metengr advised,it will only lead to further softening.

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[stanweld]

Are you heating with the induction method or some other method? If so, which?. Do as metengr recommends (make a mock up and test)and you will know; assuming that you are able to control the processing parameters. Mechanical properties will be affected.

 

[redpicker]

When you say

I am heating up the end of the steel bar to about 1500 degrees for 10 seconds.

do you mean
1) you are exposing the end of the bar to a temperature of about 1500F for about 10 seconds?
2) you are heating the bar, with method unknown, so that the temperature of the bar goes from room temperature to 1500F in a ten second period?
3) you are heating the bar, with method unknown and heating rate unknown, until it reaches 1500, where it will be held for 10 seconds then allowed to cool?

If you mean #1, you are probably OK, since in 10 seconds, the actual temperature of the bar is unlikely to exceed 800 F or so, my expected minimum tempering temperature for this material to reach 40-45 HRC. If allowed to air cool from this temperature you should be OK.

If you mean #2, you will need to find out how long the material is at 1500F. I would expect just about any amount of time at 1500F would change the properties of the material. If the material is in the Q&T condition prior to heating (almost certain if it is 40-45 HRC), you can expect transformation to begin rather quickly. With an annealed structure, it would take much longer.

If you mean #3, the question would be how are cooling the bar after heating is complete? The important issue is not just the maximum temperature and time, but the overall thermal history.

Once the temperature of the steel exceeds the original tempering temperature (I've assumed 800F), it will begin to soften. When you are just barely above it, the softening rate is very slow, increasing with increasing temperature.

Once the temperature exceeds the lower critical temperature (1350F or so), an internal structure change (phase change) can occur in the steel. Again, when you are just barely above this temperature, this change proceeds slowly. With this phase change will come significant changes in properties.

At 1500F, you are high enough above both temperatures that change is going to happen and happen rather quickly. If you heating and cooling methods are controlled so that you can be confident that the method that metengr represents the exact same cycle (or at least worst case) you are trying to model, it is a good way to approach it. If you will be repeating the heat exposure to the same part, however, it isn't a good model since the coupon will only have one heat cycle and your process will have multiple cycles.

In short, it's a guess at this point. My guess would be, yes, you would be affecting the properties of the material on the end that was exposed to the heating.

rp