Alloy content and austentizing temperature

J

Jason Fry

Joined
Jun 5, 2008
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There's a certain steel I've used a bunch of. Good success austentizing at both 1475 and 1500, with no apparent change in performance. Specs (from the internet) for this steel are:
C: 0.80-0.93
Mn: 0.60-0.90
P: 0.03
S: 0.05

With the latest batch of this steel, I have had trouble getting it hard in the 3/16 thickness. Failed to fully harden at both 1475 and 1500, to RC 55-56 max. Checked oven temp with salt melt, and I'm right on. Even tried a different oven.

The distributor ran the specs and said that the steel was labeled correctly. He suggested that I run the temp a little higher.

Ran the blade at 1525 last night and got RC 64 out of the quench.

What alloy element causes this variation? Maybe lower manganese? Maybe carbon toward the higher end of the spec range, spheroidized?

Help me understand what's going on here. What would make a steel need a higher temp to austentize correctly, and still be within the spec range?
 
I tried an increased soak about 20-25 min at 1500. Only soaked maybe 5-10 minutes at 1525.

Could a bit of Cr or V be involved?
 
My GUESS would be that it is so spheroidized that it needs the higher temps for the carbon to come into solution similar to Aldo's 52100. It needs to be brought up to 1650 to get any kind of hardness out of it.
 
Couldn't have said it better than Jason. Suspect spherodizing. Try the normalizing route. 1650F air cool. 1550F air cool. 1450F air cool. Then try a 10 minute soak at 1474F. The formula you gave is 1084 AISI.
 
Is it all the same batch? If you have the higher end of the carbon range, you will be getting retained austentite at the higher temps.

I think Jawilder and Stewart are probably right. I would normalize, and do a coupon at 10f increments up and down from your previous best temp.

What is the quench medium?
 
I'll try a few coupons next time I fire up the oven. Quench oil is Duratherm G, a 10 second oil.

It was not all the same batch... that's the issue. This new batch is a bit different. Previous batch didn't require normalizing for good performance.
 
Jason Fry said:
I'll try a few coupons next time I fire up the oven. Quench oil is Duratherm G, a 10 second oil.

It was not all the same batch... that's the issue. This new batch is a bit different. Previous batch didn't require normalizing for good performance.
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Your quench should be fine with that much manganese.

Time to do some experimenting. I like the oven for normalizing as its a set and forget affair for carbon steels. 52100 is a bit more time consuming to air cool to magnetic between each step.
 
Jason Fry said:
I tried an increased soak about 20-25 min at 1500. Only soaked maybe 5-10 minutes at 1525.

Could a bit of Cr or V be involved?
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Sorry for hitting you with something so obvious. It was just the first thing that came to mind.

I'm not entirely sure honestly.

It is a tiny bit strange, but fwiw I suspect that the root cause is as said below, batch issue. I used to work in manufacturing and having to tweak process temps up and down was pretty normal, as long as it wasn't way outside reason. I even notice differences batch to batch on the high tech stainlesses. This sounds like it's close enough that as mentioned above, it could be state and not composition.
 
Part three of the saga....

After last night, I had the goofy blade at 64, plus three others at 64 also. I ran a 400 degree temper last night, and then set for a 425 temper this evening. I forgot that my big oven overshoots on the low end of the temp range... moral of the story, all three blades were over-tempered, like 55 RC.

So, for proof of concept and replicability, I ran the four blades again from 1525. The suspect blade only hardened to 54 RC in the middle, but was 63 on the edges. Not good enough! (and quite aggravating).

Plan b (or F, G something in this case) was to try the normalizing sequence you guys described. Basically treat it like it was super-spheroidized. 1650 and air cool. 1575 and air cool. 1525 and quench. The tip of the blade dipped down a bit, and the gray martensite color was MUCH more uniform than in all the previous efforts. RC 64. I also did a test coupon with the same normalize sequence. Tested 63, and broke with a super fine grain like a file. Got the blade in the oven for a 400 temper to settle it down, then I"ll walk it in 25 at a time in my small oven tomorrow night.
 
Would it make sense to say, as a general rule, "Run the thermal cycles unless you're absolutely sure that for some reason your steel doesn't need it"?
 
elementfe said:
Would it make sense to say, as a general rule, "Run the thermal cycles unless you're absolutely sure that for some reason your steel doesn't need it"?
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That's what I do now, excepting Aldo's 15n20. It doesn't need it. The hitachi steels don't either but most of us aren't using much of them.
 
When it comes down to it I would say your distributor owes you a refund and some new steel. Seems like they have taken a lot of your time from their mistake.
 
sykes3170 said:
When it comes down to it I would say your distributor owes you a refund and some new steel. Seems like they have taken a lot of your time from their mistake.
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I don't think so... from annealed stock, heavy spheroidized steel is something we should expect and one of the first things to think of when ht starts acting funny ;)
 
Stefano and others - "heavy spheroidized ?" Fine spheroidized is best Course spheroidized is next Don't know what you mean by heavy spheroidized . Typically steel should be hardened from 50-75 F above critical . Check your furnace temp .A eutectoid should be as simple as they come . They go right from ferrite + carbide without a fuss..
 
sykes3170 said:
When it comes down to it I would say your distributor owes you a refund and some new steel. Seems like they have taken a lot of your time from their mistake.
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I don't think so. Spheroidized is industry standard. The fact that previous batches were easier to HT, not requiring normalizing for good performance, is just what it is. Nobody's "fault". I've talked to the distributor several times and they've been cooperative with helping me figure this out. I have intentionally withheld certain information in this thread until things are resolved, at which point I'd like to "publish" that "this distributor's" most recent lot of "this steel" requires "this heat treat" that was not required previously.
 
mete said:
.A eutectoid should be as simple as they come . They go right from ferrite + carbide without a fuss..
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That's why this whole thing is a mystery to me. I have used maybe 200 ft of the previous batch. Grind, 1500 with maybe 5 min soak, then quench, no problems. This batch won't harden right without a higher temp, and seems to work better having been normalized 1650/1575 prior to quenching from 1525. This is certainly "a fuss."

As far as furnace temp, I put some rock salt in. Didnt' melt at 1450, melted at 1475. Running pretty close to dead on.
 
Jason Fry said:
That's why this whole thing is a mystery to me. I have used maybe 200 ft of the previous batch. Grind, 1500 with maybe 5 min soak, then quench, no problems. This batch won't harden right without a higher temp, and seems to work better having been normalized 1650/1575 prior to quenching from 1525. This is certainly "a fuss."

As far as furnace temp, I put some rock salt in. Didnt' melt at 1450, melted at 1475. Running pretty close to dead on.
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0.93C is no longer euctoid. Since the range of %C is so wide, different batches will require different heat treats.
 
Mete...."heavily spheroidized" is just another term, if not proper, for "coarse spheroidized"......as in Aldo's 52100. From what I understand, the steel spends hours upon hours at a subcritical temp. If you try to harden a "heavily" or "coarse" spheroidized steel with the usual austenitizing temps and soak times.....you won't reach max RC. Hence the normalizing routine. If the steel is fine spheroidized, then the usual austenitizing temps with a short soak is all that is needed. And if I understand it correctly, if it is not spheroidized, but lamellar pearlite....no soak is needed (if the right aust temp is chosen for the given steel).
 
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samuraistuart said:
Mete...."heavily spheroidized" is just another term, if not proper, for "coarse spheroidized"......as in Aldo's 52100. From what I understand, the steel spends hours upon hours at a subcritical temp. If you try to harden a "heavily" or "coarse" spheroidized steel with the usual austenitizing temps and soak times.....you won't reach max RC. Hence the normalizing routine. If the steel is fine spheroidized, then the usual austenitizing temps with a short soak is all that is needed. And if I understand it correctly, if it is not spheroidized, but lamellar pearlite....no soak is needed (if the right aust temp is chosen for the given steel). "Heavily spheroidized" is a term Kevin Cashen uses to describe Aldo's 52100.
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Eh eh, Robert knows exactly what heavily spheroidized means ;) Very big balls of carbon!!! LOL
Also coarse pearlite, by the way may require some time to dissolve and spread the carbon evenly into the austenite.

Jason, did you try to austenitize the steel at 1475 °F after the normalization? or just went with 1525? If you did it i may have missed it, otherwise i suggest to try to stay at 1475 after a 1650 normalization (and refining cycles, of course)
 
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