Thread: O1 heat treating problem

I'm with Charlie about tempering. Only one cycle is necessary and O-1 tops out for hardness at about 400F. I'd recommend finding and studying TTT diagrams like this one: (down this page a bit...) Carpenter O1

One of the variables mentioned by Bruno earlier was the time taken between the heat and the quench. His cooling fin example is accurate. This diagram shows that you have about 2 seconds to miss the nose of the curve to get into the martensite range of transformation. Do not dawdle from the fire to the quench...

As to colors for judging hardness, I like that color. I prefer a slightly less deep bronze color. Over time, with the help of a Rockwell hardness tester, my eye has learned to see colors with a fairly low error rate when estimating hardness. You are likely in the range that is good given the vagaries of color in photography/lighting. Once the bevel/honing settle down that should be a several generation shaver.

My advice is to put this razor in rotation and make another. The next one will dial in even closer. Perfection is a fickle mistress. It can suck the life from you and all your work will never be good enough. Anything more on this razor will likely screw it up and break your heart.

Mastery is NOT learning how to correct, or cover up, mistakes. Mastery is learning to avoid making them in the first place.

Thank you so much!

Originally Posted by Mike Blue

I'm with Charlie about tempering. Only one cycle is necessary and O-1 tops out for hardness at about 400F. I'd recommend finding and studying TTT diagrams like this one: (down this page a bit...) Carpenter O1

Many of the makers wrote about the two cycle of tempering. Why, if one cycle is necessary?

Carpenter O1

Why are there two numbers in Effect of Tempering Temperature on Hardness of O1 / Rockwell C hardnes column? For example 60/63 or 60/62.

Hardening

"Without preheating, place the tool right in the hot furnace and let it heat naturally until its color uniformly matches the color of the thermocouple in the furnace. Soak an additional 5 minutes per inch of thickness, then quench in oil. The temperature of the tool should be brought right down to the temperature of the oil in the quench."
Based on this I must leave the razor in the furnace up to 10 minutes or maybe 5 minutes as mentioned Bruno, isn't it?

Quenching time
What is the recommended duration in case of a blade? I usually do between 10-40 sec.

Originally Posted by Mike Blue

One of the variables mentioned by Bruno earlier was the time taken between the heat and the quench. His cooling fin example is accurate. This diagram shows that you have about 2 seconds to miss the nose of the curve to get into the martensite range of transformation. Do not dawdle from the fire to the quench...

I used to be within one second.

I would like Rockwell hardness tester in the future but it is too expensive for me.

Are you using some kid of anti-scale compound and if not, do you have access to some?

After the polish I use Renaissance Wax.

Originally Posted by gregg71

Quenching time
What is the recommended duration in case of a blade? I usually do between 10-40 sec

.

It should be long enough to bring the steel close to the temperature of the oil. If you stop the quench too early you run the risk of the internal heat bringing the steel back up to above 200 C and spoiling the temper.

Since we are talking heat treating O1, here is what I wonder about.

How much soak time (in a stable temperature) at critical temperature is needed for the alloying elements to fully diffuse?

Do the alloys need to be fully diffused to take full advantage of the properties of O1?

I always err on the side of too long a soak time with O1, hoping to get all I can out of the steel.

Charlie

Originally Posted by spazola

... How much soak time (in a stable temperature) at critical temperature is needed for the alloying elements to fully diffuse?

Do the alloys need to be fully diffused to take full advantage of the properties of O1? ...

Okay. Keep O-1 simple.

It's a simple steel despite the small amounts of alloying elements. The specifications by Carpenter, and other companies, is five minutes per inch of thickness. A razor is not an inch thick. Maybe an inch wide, but like any blade it's a tapered triangular section that does not fit well into the steel company's rituals for testing Blocks of steel. I use five minutes to give the carbon time to go into solution since it's the chemical that forms the carbides. All the other stuff in there does not move around so easy. If all the carbon does not go into solution it can affect the result. Usually a non optimal hardness, or grain reduction. It depends on what you intend to achieve.

A long soak, if the temperature of the fire is too hot, could coarsen the grain. A long soak at a stable accurate temperature below the coarsening temperature theoretically could be held for a long time. But you could lose carbon and other degradation via scale depending on exposure to the right atmosphere. Or if the atmosphere is reducing, eg carbon rich, you could add carbon to the steel. About 1mm depth at 4 hours at 925C is a round set of numbers for the time at temperature to achieve this. A scale preventer could be helpful in such cases.

Gregg: the two hardness numbers are probably a range for the values obtained during testing of many samples (low/high) for that temperature.

As to the number of tempering cycles, simple steels do not require complicated rituals. Two cycles at one hour each still equals two hours. A tempering cycle is meant to reduce the hardness or increase toughness/less brittleness of a crystalline structure that developed from a violent quench. Did you know that martensite forms at the speed of sound? In a thin section blade like a razor imagine 700 mph over 0.8mm distance. I can't think of a more shocking event to such a thin section of material. Allowing the blade to equalize to the temperature of the quenchant, say over 10-40 seconds is about too fast to count. The violence is over before you can even think to stop it. As was said, pulling the steel out too soon, could have enough residual heat to affect hardness at the edge but there isn't much mass behind the edge in a razor. It's not a large worry in my mind. A big knife, or a chisel or other tool...could be enough though.

My understanding of the two temper cycles is that on cooling from the first cycle, retained austenite is converted to fresh martensite and the second cycle tempers this fresh martensite.

Multiple tempering cycles were fashionable long before retained austenite became a discussion topic in heat treatment. There are some legendary tales that tempering pauses must be at least 24 hours between cycles.

RA is less of a problem in eutectoid steels and there is more RA with higher carbon content and other alloys at higher temperatures or poor adherence to the controlled heat treatment of a steel requirements of a particular steel. If the material is prepared for HT and heat treated as recommended, RA can be minimized. Things like cryogenic treatment have their place in reducing RA (and require multiple tempering cycles) when conditions are right. You might not get rid of all of the RA despite doing everything exactly right. Sometimes RA is a desirable structure as it's tougher than martensite.

Mike,

thank you for thet details. I will ask for more things soon.

Bad news: retempered, regrinded, repolished, rehoned and reshaved but it does not work. The edge is too sensitive, wear out during the shaving.