Heat treating a part for a second time

[mschro]

I have a 4140 plate 1"x6"x13" that is 40 RC. I would like to use the plate for a different application that requires a hardness of 52-55 RC.

Following the heat treat (to 52-55 RC), I will Blanchard grind the part to 3/4" thick.

Do I need to anneal the part before prior to the 52-55 RC heat treat. If I do not anneal the part, do I significantly increase the risk of cracking (or excess warping)?


Thanks

 

[metengr]

No, you should not have to anneal this material prior to re-heat treatment (quench and temper). I would suggest a slower ramp up rate to reach the austenitizing temperature versus placing the plate directly in a furnace at 1600 deg F.

However, one question that I have is your hardness range - are you attempting to thru harden this plate at 52-55 HRC? If so, 4140 will not work for your desired plate thickness.

 

[stanweld]

Additional to metengr, you may wish to perform primary grinding in its current state, followed by heat treating (austenitizing, quenching and tempering) followed by final grinding to remove .005" to .010" per side.

 

[EngJW]

Would it work to grind this plate to size, or a few tenths under to allow for growth, and then nitride it?

 

[Carburize]

Good suggestion jlw I was just about to post a similar yhought.

 

[gearman1234]

I have tried similar to this before but for a gear ring.
We had a gear ring (int. teeth) about 9" OD, 7.5 in ID, and 1.5 in thick. The blank hardness 32 HRC. Final thru hardnes -48-52 HRC. This gear cracked at a few locations.
SO we decided to go in for nitriding and it worked.

Another important thing to remember is the warpage it creates when a 13" length plate is Heat treated 13".

To avoid these problems it is best to nitride. But again do you need this hardness only for wear resistance or the load? If it is load that is driving this H/T then it is best to anneal it prior to hardening. Then grind it to proper size.

 

[metman]

gearman1234:

Interested to know the reasoning for anneal prior to hardening.