Need some help re-hardening/tempering vintage steel

[Steve Voigt]

Hi all,
I recently started building a skew mitre plane around a vintage W. Butcher single iron, probably late 19th c.
Unfortunately, the iron was too soft--the edge folded over and left nasty scratches on end grain.
A couple days ago, I re-hardened the iron in a charcoal forge and quenched it in brine. I tempered it immediately in an electric oven at 350°. I have a second thermometer in the oven, so I'm reasonably sure that the temp is pretty accurate.
When I went to sharpen the iron, the edge actually chipped/flaked away once I got to the wire edge--it's like a barbed wire edge! The burr also has no integrity--it falls apart when I roll it over with my finger.
I re-tempered at 375°, which gave me a nice light straw color, but to no avail. Still the same problem.
I wanted to ask for some advice before I try again at 400°. It seems very odd that 375° wouldn't do the trick.
Anybody else ever had this problem?

[Mel Fulks]

Is it possible it was a bitted iron and the steel is gone?

[Steve Voigt]

Is it possible it was a bitted iron and the steel is gone?
No, there is quite a thick lamination. I don't think the iron was ever used.

[David Weaver]

Too much or too little carbon right at the edge for it to crumble like that after any reasonable temper temperature. I'd grind off about a 16th of iron edge, give it a brisk lap on the back and then see how it works out.

A lot of japanese irons that are charcoal forged are a bit funny at first, very similar steel, too.

Hopefully it wasn't an iron that someone else ruined first. IME, butchers have been on the soft side of irons that I've gotten (in terms of vintage), but they are very favorable when edge holding and sharpening ease are considered together, and the steel should be a very dry steel off the stones - one that doesn't attempt to have a ragged or persistent wire edge.

[george wilson]

So,the iron is still too hard? Have you tried to file it with a fine cut filer in decent shape? If it is too hard,it can be tempered much higher. In fact,I have said before that the best old laminated irons I used for the whole time I was in costume,could barely be filed. The cut of the file is important: A fine cut file will file harder steel than a more coarsely cut one. The file must not have polished teeth. That means it is dull.

Try David's suggestion first,then you can proceed to re temper the blade. I often heard old timers say that their chisels worked better when ground way back from use. They got softer back from the cutting edge,and also got tougher. The hardeners heated the chisels back from the cutting edge,and let the temper creep towards the cutting edge. Same with plane irons.

The irons I found to stand up the best were a bit on the hard side of a spring temper. You could heat the iron until it is purple(comes before blue),then try it. A light straw color is too hard. If you want to carefully sneak up on the right temper,try heating to a dark brown color first. The blade will not be harmed by successively hotter tempering colors. If you go TOO SOFT,you can't go back. But,you can work up to softer tempers.

I do not understand why a Butcher iron would be soft in the first place. Hopefully it was not made of defective steel to begin with. I have seen and repaired antique tools that were not properly heat treated from the maker. Quality control in those days was a bit on the trickier side. It depended upon the skill of the workman,and if he was SOBER(a big problem back then). The iron could have been over heated late in a long day,whatever. It could have been through a fire long ago.

I had an antique chisel brought to me that was a good brand,but the cutting edge peeled back like a fish hook,pulling the lamination a little loose. I had to grind it back past the fractured part,and re harden and temper it. Then,it was o.k.. Had that sort of thing happen several times over the years as tool maker and catch all problem solver(I never thought tool maker was an adequate term for the problems people brought me,often not about tools!)

Anyhow,purple is before spring blue and should do the job. Carbon content in those days was a bit of a guess. Your plane iron could have too little carbon,or too much also. If it still remains too hard,heat it to a full dark blue. Then,if still too hard,heat to a LIGHT blue. Any higher than that,and it will turn gray,and should be fully softened (annealed).

A problem you face is that the blade will be very apt to curve across its width. When it is beveled,each side has a different amount of surface area. That causes unequal cooling rates,and curves the iron. Either grind the bevel entirely off,or take your chances is what it amounts to. If it does warp,you need to heat the blade past blue,until the surface of the steel part turns gray. Then,bury the cutting end in pre heated hot sand. Blacksmiths just used hot ashes. A can full of hot sand will do just fine. Then,carefully hammer the blade flat,grind the bevel off,and re harden. Make sure the blade is indeed fully softened,or the lamination can crack,and forever leave a scratchy line on your planing work.

I want you to Google "normalizing". The steel really needs to be normalized before you re harden it. You might get by with it for a second try,but I had an excellent hardness tester at work,and after 3 or 4 rehardenings(I was doing a demonstration for someone),the hardness started doing unpredictable things. I tested the piece of W1 after each hardening,and started getting weird results. Normalizing is the professionally recommended procedure.

P.S.: I have often found that antique tools that were never used,were never used because they were defective. Bear that in mind. In our collections,we had many unused tools. That's how they survived without being worn out and used up.

[Mel Fulks]

Another wild guess! Some of those respected brands were counterfeited. I saw one Butcher chisel a friend bought on ebay
that had a Butcher stamp different from any others I've seen and I wondered if it was real. He had just gotten it and I never heard anything about quality.

[Steve Voigt]

I'd grind off about a 16th of iron edge, give it a brisk lap on the back and then see how it works out.

…

IME, butchers have been on the soft side of irons that I've gotten (in terms of vintage), but they are very favorable when edge holding and sharpening ease are considered together, and the steel should be a very dry steel off the stones - one that doesn't attempt to have a ragged or persistent wire edge.

Dave, thanks for the suggestion, I will give it a try.
So, do you associate a "persistent wire edge" with excessive softness?

[george wilson]

Try filing the blade to see if it is too soft.

[Steve Voigt]

George, thanks for the suggestions and the very detailed information. All of it will be helpful and was very interesting to read.
Follow-up question: I am never exactly sure where/how to do the "file test" for hardness. On the edge (I assume not), the side, or flat across the back? I tried flat across the back (but not right at the edge) with a new-ish file. It scratches a little but just barely. So I'm thinking it is plenty hard.
Thanks again George.
- Steve

[David Weaver]

Dave, thanks for the suggestion, I will give it a try.
So, do you associate a "persistent wire edge" with excessive softness?

In water hardening steel, yes. Something like a butcher iron will let go of the wire edge with very little work. If you take something that's known to not be full hardness like a vintage cap iron (not stanley, but like one that came with a butcher iron) and raise a fat wire edge on an oilstone with it and then strop it, you'll notice that it's reluctant to let go of the end of the cap iron. It's obnoxious (thankfully that only needs to be done once with each double iron set).

When you get to really hard water hardening steels like full hardness japanese chisels, they do not seem to want to hold on to anything at all once you get to polishing stones. I'm convinced that it's not the absolute sharpness of them that makes people feel that they're so sharp, but instead a combination of their hardness limiting the depth of abrasive cut combined with their lack of desire to hold a wire edge. An old softer buck "cast steel" chisel will get just as sharp on natural stones if it's given the appropriate amount of work to get rid of the wire edge.

The good vintage irons are like what george describes - just barely filed by a quality file. they sharpen like nothing does today, they let go of their wire edge very easily and they do wear a little faster than something like a hock iron, but they return the favor by sharpening and grinding super easy. I like hocks irons, but I've come to like the "dryness" of vintage irons better. I've got one by a company called dwight and french that yields so fast to a broken in washita that it seems like it shouldn't even be able to hold an edge, but it does so quite well, and has the same dryness. As opposed to something like HSS that holds it's wire edge even on very fine grit aluminum oxide stones.

[Warren Mickley]

David, I like your term dryness. I have been using the word gummy for chrome steels like O1, A2 etc. and crisp for steels that grab the stone nicely.

Steve, I think the evidence is that your iron needs more tempering. It was soft enough that it would bend when you first got it, and now it is not bending, but rather chipping. You want something in the middle. If you use an oil stone regularly you may be able to judge the hardness of the iron when you sharpen. An iron that is not tempered enough will sort of skid across the stone and not want to be abraded. I don't know how much experience one needs to get a feel for this, but try thinking in these terms.

Moxon says to temper edge tools to a "dark goldish" color. However Ken Schwartz, blacksmith at Williamsburg, told me that the right temperature can vary quite a bit for different steels and you have to experiment and get a feel for a specific steel or batch of steel.

[Ron Hock]

It may be that the steel was overheated during heat treatment. If steel is allowed to exceed its critical temperature before quenching it will grow large grains and, while testing as fully hardened, will have little strength. When I was doing my own hardening for my knives (way back when) I'd always include a sacrificial test piece or two to break after hardening. Examining the inside of the steel at the break will reveal either a very fine matte gray, like gray primer paint, indicating proper hardening. If the break is sparkly, those are the too-large grains that grew when/if the steel was overheated. They're hard but the grains don't stick together with much strength. Hence the edge failure. I'm sorry I don't know of any but the destructive test. But if you try the other tricks suggested here and fail to get what you need, it may have been overheated.

[Steve Voigt]

David, I like your term dryness. I have been using the word gummy for chrome steels like O1, A2 etc. and crisp for steels that grab the stone nicely.

Steve, I think the evidence is that your iron needs more tempering. It was soft enough that it would bend when you first got it, and now it is not bending, but rather chipping. You want something in the middle. If you use an oil stone regularly you may be able to judge the hardness of the iron when you sharpen. An iron that is not tempered enough will sort of skid across the stone and not want to be abraded. I don't know how much experience one needs to get a feel for this, but try thinking in these terms.

Moxon says to temper edge tools to a "dark goldish" color. However Ken Schwartz, blacksmith at Williamsburg, told me that the right temperature can vary quite a bit for different steels and you have to experiment and get a feel for a specific steel or batch of steel.

Warren, thanks for info about moxon etc. I am hoping you are right about tempering. Taking the iron back about .100" didn't help, but tempering it 25° higher just now was a distinct improvement. I'll try another 25° and see if that does it.
Thanks for the advice about "feel." I do use oilstones, but I don't think my tactile sense is quite there, yet. I'll work on it.
I think part of the problem, though it's a good problem to have, is that the vast majority of my irons have been just fine. If I had more faulty irons, and knew exactly what their faults were, it might be easier to develop a feel for this. Oh well.

[Steve Voigt]

It may be that the steel was overheated during heat treatment. If steel is allowed to exceed its critical temperature before quenching it will grow large grains and, while testing as fully hardened, will have little strength. When I was doing my own hardening for my knives (way back when) I'd always include a sacrificial test piece or two to break after hardening. Examining the inside of the steel at the break will reveal either a very fine matte gray, like gray primer paint, indicating proper hardening. If the break is sparkly, those are the too-large grains that grew when/if the steel was overheated. They're hard but the grains don't stick together with much strength. Hence the edge failure. I'm sorry I don't know of any but the destructive test. But if you try the other tricks suggested here and fail to get what you need, it may have been overheated.

Ron, thanks very much for answering. I think there is a distinct possibility of this. It was the first time using my forge, and I was having a tough time judging color accurately. I may have erred on the side of too high.
If I did get it too hot, will annealing and re-hardening solve the problem, or is the grain growth a one-way street?

[george wilson]

When steel is hardened by eye,by someone who is not real experienced at it,the hardening temperature can be quite different each time. That means you must go ahead and try increasing the temper a little at a time until you get what you want.

In hardening steels,there is a 25º "window" which gives the optimum performance to the steel. That is tricky to achieve by eye. I now use an accurate pyrometer controlled electric furnace,though I only use it for special important jobs,like making punch and die sets where the punch and die must last as long as possible between sharpenings,of which there can only be so many before they get worn out.

[David Weaver]

You can fully anneal it to get it relaxed again, but the schedule for it would probably have it at a temperature that it could decarburize. You'd need steel foil to do it, and all of the W1 schedules (and probably O1, too) want the steel soaked at 1400 or so degrees for a half hour, and then very slowly reduced.

Temper temperature is going to depend on how much carbon is in the steel. I incorrectly guessed that the temper temperature would be as low as O1 - if it's 1%, it can get to 500 degrees and still be almost 60 hardness.

Proceeding at small intervals for an hour per is a better idea, though, in case it has more carbon than that.

[Ron Hock]

Ron, thanks very much for answering. I think there is a distinct possibility of this. It was the first time using my forge, and I was having a tough time judging color accurately. I may have erred on the side of too high.
If I did get it too hot, will annealing and re-hardening solve the problem, or is the grain growth a one-way street?

You can try to anneal: heat to "just starting to glow" then pack it in ashes or sand and let it cool Very Slowly. Then reheat to 1450F (non-magnetic), quench and temper to 325F. I'd say it can't hurt to try but without atmosphere control, it actually can. As the steel starts to glow, it will start losing carbon to the surrounding air -- oxygen's tempting nature being too much for weak-willed carbon to resist -- forming a de-carburized skin on the steel. The core may harden but the soft skin will have to be ground off before you'll be able to use the blade. I'd say give it a try. It's not working now so you have little to lose and a lot to gain in the education category. If it was easy, everyone would do it. Good luck!

[Steve Voigt]

I'd say give it a try. It's not working now so you have little to lose and a lot to gain in the education category. If it was easy, everyone would do it. Good luck!

Thanks for the advice, Ron. I've tried everything, and nothing's working, so it might be time to accept defeat and move on.
I forgot to mention, I hardened an old dead-soft mortise chisel in the fire at the same time, and that turned out pretty well. So either I got the plane iron too hot, or maybe it was defective from the start.
Regardless, I learned a lot from the experience and from this thread, so I'm not disappointed. A few modifications and I'll bet the next time goes better. Thanks for the help everyone!

[Warren Mickley]

Steve, here is what you need to do to reduce crystal size, if that becomes a problem and the steel is too soft again. First heat the steel above the critical temperature. At the critical temperature the steel completely changes crystal structure from body centered cubic to face centered cubic. All memory of previous crystal size is wiped away by this structure change. If you then cool it very slowly it forms large orderly crystals as it changes back to body centered cubic structure; this is annealing. If you cool it very quickly (quench it) small crystals form in a jumble because they don't have a chance to form an orderly structure. This is hardening. Subsequent heating of the steel to temperatures below the critical temperature will ease stresses and soften the steel; this is tempering.

You can go through this cycle several times, but heating the steel to high heat burns off small amounts of carbon eventually degrading the steel. I have occasionally treated the same tool three or four times before being satisfied. That can happen when one is not treating regularly or with a known steel. There is no need for you to anneal unless you want to reshape the tool with hacksaw or file or something.

[george wilson]

Heating to just above glowing is not hot enough to cause decarbing. In fact,the only steel I wrap in stainless steel is A2 air hardening. I have had no problem with W1 or 01 decarbing enough to be noticable.

[Steve Voigt]

… I have occasionally treated the same tool three or four times before being satisfied. That can happen when one is not treating regularly or with a known steel.

Warren, that's good to know, and it fits with what Ron said, that if it were easy everyone would do it. My first dovetails weren't too good, so I wouldn't expect this to be any different.
Actually, this is not my first time--when I was a machinist, I did heat treating from time to time. But as I discovered, using a DIY forge is a whole different ballgame from using a commercial heat-treating oven.
Anyway, thanks for the tips, I will keep at it…

[george wilson]

Steve,I assure you that if you do not anneal after the first couple of tries at hardening,the steel will start doing unpredictable things. I experimented with this myself,using a high class Versitron hardness tester to test the hardness each time. You might get the steel hard after each quenching,but exactly how hard is very iffy. Then,the tempering becomes very iffy too. Certainly the steel does not have its best performance after being tortured thus.
If I recall,the first hardening yielded 67 Rc. The tempering yielded an expected 58 RC. The 3rd yielded a hardness of 60 RC. The 4th yielded 50 RC. This was not due to decarbing: I test filed the surface of the sample after each quench.The sample was the same hardness all the way through. Of course,after the hardening,the tempering was entirely dependent upon the initial hardness achieved. I have tested hundreds of blades of various types,and of different types of metals in my very long career.

Repeatedly re hardening without annealing is risky business.

The Versitron is one of the finest hardness testers available.

The steel I tried my little experiment with was W1,which is the type of steel in your antique plane iron.

[Steve Voigt]

George, I appreciate your advice. I think I'm done with this blade, but I'm planning to anneal some old, shot files soon.
I'm wondering if you saw the question I asked you in post #9? Here it is again:

Follow-up question: I am never exactly sure where/how to do the "file test" for hardness. On the edge (I assume not), the side, or flat across the back? I tried flat across the back (but not right at the edge) with a new-ish file. It scratches a little but just barely. So I'm thinking it is plenty hard.

I *think* I answered my own question--filing flat across the back on several different irons gave me interesting feedback about their relative hardness--but I'd still appreciate your thoughts.

[george wilson]

Instead of scratching up a larger surface,I'd just file as if you were trying to sharpen the cutting edge. Or,you could file the side of the blade,and still save making scratches on larger surfaces.