17-7PH Cooling Rates 2

[Bruce62]

I am having trouble getting to the TH1050 condition.

I am following a Boeing spec and the end results call for 40<HRC<43.

Austenizing at 1400F for 90 minutes and cooling at 15 psig, placing in water at 55F for 30 minutes, yields a HRC=~29. But when we go to ageing at 1050F for 90 minutes, we cool at a slower rate (3 psi). Our results exceed (HRC=~44.5) the Boeing limits as listed above. We can reheat the material again and get to the desired results, however, I would like to get there the first time.

Does the cooling rate affect the results? A faster cooling rate seems to increase hardness.

Bruce

 

[EdStainless]

The cooling rate has no effect unless you cool too slowly and that will result in low strength.
Speaking of which, have you actually measured the strength on these?
What atmosphere are you using?
Given the imprecision of HRC working to 40-43 as a range sounds like you will always be re-treating.
Which do they want, TH1050 or the hardness?
Or you could bump the age temp up 15F and see if that gets you there. It will still be in the tolerance range but should lower the strength slightly.

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P.E. Metallurgy, Plymouth Tube

 

[Bruce62]

I sent samples to the lab to be tested last week, should get results early this week.
We use vacuum furnace with argon cooling.
The requirement states to use the Boeing spec and the spec says TH1050. The required strength states 180-200 KSI.
I have thought about raising the temperature like you stated, but no where in the spec does it say I can do that without running at 1050F first. It says to re-age at a higher temp (10F per 1 point hardness) if the strength is greater than required. I wonder if the end justifies the means?

Bruce

 

[EdStainless]

The 180ksi min is standard, we often see results as high as 225ksi on thin small diameter tube.
In most applications if you have enough elongation (or impact toughness) people will use the higher strength.

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P.E. Metallurgy, Plymouth Tube

 

[israelkk]

Hardness for PH steel can vary up to 10Rc. The spec always specify only Yield and Tensile strength. You can not specify H1050 and ask for hardness too. When you specify H1050 you agree for any hardness you get as long as the yield and ultimate strength are within the spec.

 

[EdStainless]

That was my point Israelkk, I was being polite.
Either tell me how to do it, or tell me what you want, you can't dictate both.

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P.E. Metallurgy, Plymouth Tube