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intercritical step in heat treatment of 4330 mod

intercritical step in heat treatment of 4330 mod

intercritical step in heat treatment of 4330 mod

(OP)
Does anyone have experience in the heat treatment of 4330 mod?  Right now we're developing a heat treat procedure for a new casting and this is the first we've worked with this material.  We're trying to get test bars to pass yield strength (min 130) and Charpy V-notch (min 20 ft-lbs at -40 F) tests before we heat treat the castings themselves.  

Currently the closest we've come is by using a 4-step heat treat.

1.  2 hours at 1750 F, air cool.
2.  2 hours at 1650 F, water quench.
3.  2 hours at 1050 F, water quench.
4.  2 hours at 1050 F, water quench.

We've played around with the double temper and the tempering temperature some.  We're considering adding an intercrical step in between 2 and 3, roughly 1400 F for 2 hours and water quench.  Is there any reason to think this would do more harm than good?

RE: intercritical step in heat treatment of 4330 mod

What is the exact chemical composition, including nitrogen, aluminum, etc.?  If the grain size is too large, you will never achieve the impact properties.

RE: intercritical step in heat treatment of 4330 mod

(OP)
C 0.29
Mn 0.79
Si 0.42
P 0.010
S 0.009
Cr 0.82
Ni 2.4
Mo .43
Cu 0.006
Al .05
V .01
Ti .06
N .013

RE: intercritical step in heat treatment of 4330 mod

I am not an expert on steel castings, but I think the nitrogen content is too high.  Wrought alloys that are used for low temperature applications would restrict the nitrogen content to less than 0.007% by mass.  Have you measured the grain size?

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