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4130 and heat treatment

zr1nsx

Aluminum
Joined
Dec 31, 2007
Location
indianapolis
I have some questions about heat treatment of 4130 and brittleness. I have a component (shaft with keyway and thread) that I make which we heat treat to Rockwell 45C and do some finish machining after heat treatment. After approximately 1000 pieces I have had a few pieces break and am curious about hardness versus brittleness. I want a tough surface for wear, but I don't want it to crack or become brittle. Perhaps there is a better material for the application. 45 isn't very hard, but does provide some resistance to scratching and galling. Anyone have any experience with the working threshold of 4130?
 
Not enough information
1. what was your heat treat process? Pre-heat, soak, quench, temper?
2. Do you have any sharp inside corners on your part?
3. Size of the part with min and max cross-sectional areas?
4. 45 Rc is on the high end for 4130 hardness. Most of the time, it's drawn to around 28-32 Rc.

I don't know about the part design, you capabilities, or cost constraints, so suggesting another material is a mute point. I could name half a dozen that might work or not.
JR
 
Why 4130? It's not really known for being "shaft" material. How about 4340?

I agree with JR on the hardness... that's way to hard for 4130... but it sounds right for 4340.... at least for racecar half-shafts....
 
300M? Not sure how the pricing goes up there for it though, it could be a factor in the decision.

Are the shafts breaking at the same point? If so perhaps look beyond steel grade.
 
This is easy. At 45Rc you are asking 4130 for everything it's got. It has the lowest carbon content of any directly hardenable alloy steel which is why it's used for welded structures. Like JRIowa said, 28-32 Rc is more appropriate for it. It's greatly overrated for machined parts.

The relationship of hardness to tensile strength is a direct translation in steel. It can't get stronger without being correspondingly harder. The trick is to go with enough carbon to comfortably achieve the hardness level you want. For 45Rc you had better use at least 4140. That will probably solve your problems. If you need higher hardness/strength go to 4150. If you need extra toughness, shock resistance, etc. at high hardness the progression is thru richer alloys like 4340 and 6150.
 
Thanks Oldwrench. That's what I was looking for. I'm not sure why 4130 was chosen to begin with. It is a motor sport application so I imagine that's what drove the material selection.
 
Having come from aftermarket automotive, there were a few applications using 4130/4150, but most of the high volume stuff used either 8620 or some form of low carbon steel forging. Both need to be case hardened.
JR
 
Most heat treaters will want to have a talk with you if you're asking for a temper between 500 and 900F with 41XX. At 45RC for 4130 it's about a 650F draw... The reason they wanna talk is there is a large dip in the impact properties through this temper range.

In your case you can expect about a 30% drop in toughness compared to a 400F draw and 49-50RC hardness, and only 25% of the toughness of 4130 drawn at 1000F with 32RC hardness. 4340 has less of a toughness dip at 45RC, but it's still not wonderful.

Most people that really want impact properties in a shaft with high hardness go to case hardening something where a high temp draw still goes over 50RC at the surface and the core is pretty much max toughness for the given material.

Another way to skin this cat is to go with induction hardening, which can give you the 4130 with much higher surface hardness if you want it.

Good luck
Matt
 
I I want a tough surface for wear, but I don't want it to crack or become brittle.

Nitriding/hot salt or another surface hardening process is a better idea in this case (Pun intended ;) ).
Nitriding - Wikipedia, the free encyclopedia
Use Salt Bath Nitriding For Uniform & Consistent Layers / North East Coating Technologies

If you are worried about toughness get a Charpy or izod test performed
Charpy impact test - Wikipedia, the free encyclopedia
Izod impact strength test - Wikipedia, the free encyclopedia
 
Hi folks,
The full background of what I'm up to right now would take an hour to explain, so I won't.

I may get more specific in the details of my adventures, and more into input if I run into problems, but right now I just want to keep it simple : numbers for tempering 4130 below 400 F ?

Thanks, I'm glad I stumbled onto this forum.

"Bart"
 
Last edited:
Okay, another question : what's a minimum soak time before quenching, for thin plates 1/16" thick, average?
I got some fully hard samples with a torch, no soak but my kiln samples , no soak, quech in fast quench oil from 1575F , didn't get all that hard.
I want to minimize leaching of carbon, and scale, so the faster I can get them in and out, the better, and I am not going to foil wrap the pieces.

Thanks !

edit : never mind, I'll find out IRL tonight :D
 
Bart, a typical rule of thumb is one hour soak per inch of thickness. So 1/16" thin plates should not require much soak time. In fact, I'd probably be worried more about confirming they actually reached the target temperature before quenching, than about time spent soaking.
 
Thanks, s, I'll keep that in mind with my tests. I was pretty surprised that my kiln samples didn't harden fully, like my torch samples did, and since both were no-soak tests, the critical temperature does stick out as the difference. But I'm real happy with how the pieces behaved in fast quench oil vs. water (minimal distortion and warping, which would be a big concern).
 
To minimize heat treat distortion, it is common practice to sandwich thin plates between thicker plates of low carbon steel. Wires,screws, or clamps (tack welds?) hold the temporary assembly together.

Read the relevant chapters in a short book

[h=1]Heat Treatment, Selection, and Application of Tool Steels 2E [COLOR=#565959 !important]2nd Edition[/h]
[/COLOR]
by William E. Bryson [COLOR=#565959 !important](Author)

It has all the needed basics for understanding and applying the process for those who use tool steels but aren’t formally trained. It is a classic.

Denis

[/COLOR]
 
Hi folks,
but right now I just want to keep it simple : numbers for tempering 4130 below 400 F ?
"Bart"

A real heat treat outfit won’t temper 4130 below 400°F without a long talk & NO guarantees. At about 350F impact properties just drop off the table, the hardness of ALL the XX30 steels max out just under 50Rc.

There are legendary tales from toolmakers dropping XX30-50 direct hardening steels in the quench & leaving to return later & find a bunch a small pieces in the tank… Attached are properties of 4130 and Izod chart 4140 showing properties going down to room temp draws.

Good luck,
Matt
 

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Wondering what is the goal here ? 4130 is actually harder to come by than 4142 (which is what I always ended up with when I ordered 4140).

If it's just a hard surface and smeone is in love with 4130, I'd occasionally make gears of 4130 because you can get away from distortion that way ... rough, q&t to the mid-30's, finish, cut teeth, then nitride. Nitriding gives a very hard case, while mid-thirties core is hard enough to avoid spalling from thixotropic steel ... easy to machine at 30's and nitriding doesn't cause distortion. 4130 nitrides better than 4140 so there's an actual reason to use it.

But what is the goal with these plates ? There's probably a better way to do it than this ...
 
To minimize heat treat distortion, it is common practice to sandwich thin plates between thicker plates of low carbon steel. Wires,screws, or clamps (tack welds?) hold the temporary assembly together.

Read the relevant chapters in a short book

[h=1]Heat Treatment, Selection, and Application of Tool Steels 2E [COLOR=#565959 !important]2nd Edition[/h]
[/COLOR]
by William E. Bryson [COLOR=#565959 !important](Author)

It has all the needed basics for understanding and applying the process for those who use tool steels but aren’t formally trained. It is a classic.

Denis

[/COLOR]

Gads, that's way too much trouble for my needs. I mixed fast quench oil half nad half with regular and that may be a good compromise for fast cookling and low distortion, but i'll keep experimenting. Vertical quenching of my small die plates does minimize warping , and almost eliminates it with 0-1 (which I've been using all the time for 35 years. Thanks for the link, I am not trained in anything except the self-trained process I'm doing (pancake blanking dies).
 








 
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