Question about multiple heat treatment of )1 tool steel

dcsipo · May 14, 2021

Question about multiple heat treatment of O1 tool steel

Hi,

I made some parts out of 1/8" and 3/8" thick O1 and the thinner parts did not get fully hard after following the instructions from Hudson steel. High Speed Steel | Tool Steel | O1 | O1 Technical Data

I assume the thinner parts had just enough time to cool a bit before quenching. The 3/8" thick parts got fully hard, 60+RC, while the 1/8" stuff is more like 55RC. My question is, do I really have to anneal O1 before trying to harden again, or just put it through a second heat treat. It is that slow cooling part that really sucks

. Maybe raise the temp to 1525F so it is more likely 1500F when quenched. I will try to move faster from kiln to oil. I thought I was fast enough, but steel does not lie.

dee
;-D

implmex · May 14, 2021

Hi Dee:
I bet you can just re-harden it without issue, and ignore the annealing step.
With regard to heating it, can you clamp it to a heavier plate and cook both together so the heavy plate acts as a heat reservoir?

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Kingbob · May 14, 2021

No comment on the reheat but I have had trouble in the past with the tongs I use to take things out of the oven cooling small parts before they make it to the quench. I use a little boat made of stainless foil and just grab that instead of the part and just dump them in the tank from there. I don't know if that was helpful.

dcsipo · May 14, 2021

Kingbob said:
No comment on the reheat but I have had trouble in the past with the tongs I use to take things out of the oven cooling small parts before they make it to the quench. I use a little boat made of stainless foil and just grab that instead of the part and just dump them in the tank from there. I don't know if that was helpful.

These parts aren't that small one is about 2.5"x3.5"x.125" the other is .75"x5"x.125" so I wasn't expecting them to cool too fast. I had about 2 feet between the kiln and the oil, I had the oil heated to about 180. The parts did not seem to change color while in transfer from the kiln to oil. But I like the plate or the carrier ideas. I will try it with some of the smaller ones.

tnmgcarbide · May 14, 2021

do you have an argon atmosphere , use stainless foil ,or just go bareback in the oven?

are you sure you don't just have a layer of decarb on the surface ? i have seen that on o-1 before, where the outside didn't get as hard as the core.

dcsipo · May 14, 2021

tnmgcarbide said:
do you have an argon atmosphere , use stainless foil ,or just go bareback in the oven?

are you sure you don't just have a layer of decarb on the surface ? i have seen that on o-1 before, where the outside didn't get as hard as the core.

bareback...I'll check the surface that I ground

Dave G. · May 14, 2021

Martensite is more brittle and more likely to crack during heating. Use a slow ramp when reheating for the reheat treating. Agree that a second anneal is not required if you're careful bringing the part to temperature.

dcsipo · May 14, 2021

Dave G. said:
Martensite is more brittle and more likely to crack during heating. Use a slow ramp when reheating for the reheat treating. Agree that a second anneal is not required if you're careful bringing the part to temperature.

Would you recommend a slower ramp? The normal is 400f/h would 300f/h be better? I have a ramp control on the kiln I can program pretty much anything I want. Would you put a longer soak at 1200f? and then bring it to 1500F or maybe a bit higher?

dcsipo · May 14, 2021

tnmgcarbide said:
do you have an argon atmosphere , use stainless foil ,or just go bareback in the oven?

are you sure you don't just have a layer of decarb on the surface ? i have seen that on o-1 before, where the outside didn't get as hard as the core.

uhm....what puzzles me is that the thicker parts all got pretty much as hard as I expected. I admit I am a novice at this, trying to learn as much as I can. Kinda feel sorry for me not going with A2 for these parts

.

plastikdreams · May 14, 2021

dcsipo said:
uhm....what puzzles me is that the thicker parts all got pretty much as hard as I expected. I admit I am a novice at this, trying to learn as much as I can. Kinda feel sorry for me not going with A2 for these parts .

We have a bunch of o1 at the shop. I harden it from time to time, I've had pieces 6 x .750 hit 60 on one end and 53 on the other. I'd much rather use an air hardening steel or, if I can, 17-4...I love that shit lol.

Dave G. · May 14, 2021

dcsipo said:
Would you recommend a slower ramp? The normal is 400f/h would 300f/h be better? I have a ramp control on the kiln I can program pretty much anything I want. Would you put a longer soak at 1200f? and then bring it to 1500F or maybe a bit higher?

Actually 400F/hr isn't bad. I'd hold just a little hotter at 1250F. Hold should be 15 to 30 minutes. Then 1500F is the top of the recommended temp for O1. Move the oil closer to the furnace. Have you checked the hardness on a ground section yet? A little decarb would also explain why the thinner parts are soft.

dcsipo · May 14, 2021

Dave G. said:
Actually 400F/hr isn't bad. I'd hold just a little hotter at 1250F. Hold should be 15 to 30 minutes. Then 1500F is the top of the recommended temp for O1. Move the oil closer to the furnace. Have you checked the hardness on a ground section yet? A little decarb would also explain why the thinner parts are soft.

Thanks, Dave, will do a bit more grinding and re-check...

dcsipo · May 14, 2021

plastikdreams said:
We have a bunch of o1 at the shop. I harden it from time to time, I've had pieces 6 x .750 hit 60 on one end and 53 on the other. I'd much rather use an air hardening steel or, if I can, 17-4...I love that shit lol.

That is fascinating, why do you think it is uneven in hardness? one would think as long it is chilled at the same rate it would be the same harness.

gbent · May 15, 2021

If decarb is the problem, it could be the thinner pieces got hot sooner. Decarb is a time and temperature process, so the longer it is above 1250F the more decarb will occur.

Mcgyver · May 15, 2021

You may be able to skip the annealing step depending on the shape, but I don't think its a given...depending on the part and stresses in it. There can be residual stresses there that are not removed by your taking it up to the critical temp a second time.

I've experienced this first hand. I was trying to heat treat a file (basically W1) into a tool - essentially what you are doing, re-heating a piece. After a few attempts the tool kept breaking along along the diagonal lines where the teeth would have been (no teeth left, ground off before heat treating). I then annealed the files before heat treating and no breakage. Anneal by taking up to critical heat and then box of ashes trick...produces a very slow cooling

Those grooves from the files original manufacture probably are an extreme case of stress, however the fact is the prior stresses in the work survived through the second heat treating and led to a faulty part.

dcsipo · May 15, 2021

gbent said:
If decarb is the problem, it could be the thinner pieces got hot sooner. Decarb is a time and temperature process, so the longer it is above 1250F the more decarb will occur.

that makes sense, so even if I tried to re-harden, it would likely fail because the steel lost carbon.

Bummer one more vote for A2.

gbent · May 15, 2021

dcsipo said:
that makes sense, so even if I tried to re-harden, it would likely fail because the steel lost carbon. Bummer one more vote for A2.

Unless you use some form of atmospheric protection, all carbon steels will experience decarb at elevated temperatures. You need something to limit the oxygen exposure of the hot steel. Stainless steel bags with a small piece of kraft paper to burn all the oxygen are the simplest.

lr harner · May 16, 2021

O1 is dead simple to HT. when i do it for knives i go 1550f 10 min soak bare steel or maybe if im worried light clay coating i dont get alot of decarb cause i pre heat the oven let it soak a bit then put the knives in. 10-15 min later pull and quench in room temp parks 50. yes i know thats a fast oil but i dont have AAA in the shop for medium speed steels.
clay extra fine furnace clay dust mixed with vinegar (helps with cracking/ shrinking) old pottery trick

dian · May 16, 2021

in theory you should get better properties if heat treating from martensitic condition. it might even work.

(annealed gets you wort properties, thats why you usually start with normalized.)

dcsipo · May 16, 2021

Quick update, I lapped off about 5 tho and it is harder underneath, The core appears to be fully hard 5 thou below the skin is not quite 60 but much harder than 55. I only have the colored files to test hardness. The 60 HRC file just grabs the surface and the 55 HRC skates over the surface no matter hard I try to press it in.

I think it is good enough to hold an edge

dee
;-D

Question about multiple heat treatment of )1 tool steel

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