Heat Treating Cast Steel - Quench Medium?

[Robert Rozaieski]

I need a little help from the toolmaking experts here. I've got an old strike block plane with a non-original iron that has some issues. The iron needs heat treating as the edge folds over (doesn't chip but actually rolls, I can feel the burr after planing something as soft as poplar). I figure before I give up on it, I may as well try to heat treat it as I can't make it any worse than it already is. I've done some home heat treating before so I am somewhat comfortable with the process, however, I've never redone the heat treating on an iron this old. All of my heat treating to date has been on new O1.

What would be the best quench medium for this old cast steel, oil or water/brine? The iron is an Ibbotson Bros Warranted Cast Steel. It is not a laminated iron but is solid tool steel. I'm assuming that it was likely originally done in a brine quench? Any one have an idea?

[joe oski]

Didn't know you could heat treat that brittle stuff!
I don't have a MACHINISTS MANUAL 54 handy or I'd look it up for you.
Instead I'll watch the thread and wait. (its at work and I haven't been there in 6 months- THANKS NAFTA)

[Bob Barkto]

I'd try oil first.
Much less likely to warp or distort.
If it doesn't get close to file hard in oil try water.

"Cast steel" can be anything, really. But most of the old ww'ing stuff is just plain high carbon steel. Similar enough to 10xx stuff we buy today.

You might want to soften it first. Get it critical for 10 - 30 minutes or so and then let it cool very slowly. Putting the red steel in a can of ashes works good. Otherwise very still air until room temp.


I need a little help from the toolmaking experts here. I've got an old strike block plane with a non-original iron that has some issues. The iron needs heat treating as the edge folds over (doesn't chip but actually rolls, I can feel the burr after planing something as soft as poplar). I figure before I give up on it, I may as well try to heat treat it as I can't make it any worse than it already is. I've done some home heat treating before so I am somewhat comfortable with the process, however, I've never redone the heat treating on an iron this old. All of my heat treating to date has been on new O1.

What would be the best quench medium for this old cast steel, oil or water/brine? The iron is an Ibbotson Bros Warranted Cast Steel. It is not a laminated iron but is solid tool steel. I'm assuming that it was likely originally done in a brine quench? Any one have an idea?

[Ron Hock]

Re-hardening a blade is always a risky business. As you have some experience with heat treating I'll not go into detail. For those who want the procedure, read this (http://www.hocktools.com/diyht.htm).

That the blade is so soft may indicate that it simply won't harden for some reason that we'll never know. But if you're still willing to try, I'd start by quenching in oil. It's likely to be a water-hardening alloy but it's always safer to quench water-hardening steels in oil than the other way round. If its hardness is improved by heating to non-magnetic (1450 - 1500F) and quenching in oil, that's a good sign. Temper to about 325F and if it's useably hard at that point, great, use it. If not, you can try again with a water quench. My experience with water quenching is limited and generally disastrous -- a friend's chisel shattered into little pieces -- so I won't opine about water or brine, chilled or warmed; I'll let others help out here. Water quenching can also cause warpage or distortion that may render the blade hard, but unusable.

Try to minimize exposure to air while the steel is red hot. That's when the carbon is migrating about and will combine with oxygen in the air and fly away creating a soft skin of de-carburized steel that must then be ground off. If you're using a torch, get it up to temperature and quench. Don't dawdle or you'll risk too much carbon loss. If you have an oven, throw in a charcoal briquette to scavenge some of the oxygen but, again, don't dawdle. The rules say to hold the piece at temperature for 20 minutes per inch of cross section. So with a thin blade, once the magnet isn't attracted, you're there. Close enough. Quench it.

Good luck.

[george wilson]

The blade will warp across its width because of the bevel making the surface area of the 2 sides different. It would be best if you ground the cutting edge completely square,or you may ruin the blade by warping it.

Oil is the safest first option,and if it doesn't get so hard you can't file it,you can try brine next. Make brine by dissolving ice cream salt in water till a potato will float in it.

If you heat the blade to orange,it will harden fully,but the magnet test is a good way to judge also. DO NOT leave the magnet attached to the steel as you heat it!!! I read a post by a guy who did that. The magnet loses its magnetism if it is heated. Try the steel against the magnet very quickly till it doesn't attract any more,then quench.

Brine is best for water hardening steel as it prevents a gas envelope from surrounding the blade,and promotes more even hardening. Water will still work if you don't want to make brine. Sand the blade bright on 1 side,and heat it carefully to a medium brown color.

Ron Hock's info is also perfectly good. I offer mine in case the oil doesn't get the blade hard. DO GRIND THE BEVEL AWAY IN ANY CASE. You only need to heat the first 1 1/2" of the cutting end of the plane. I wouldn't suggest trying to heat any more than that.

[Robert Rozaieski]

Thanks Bob, Ron & George! I figure the iron is useless as it is anyway since the edge just rolls over, so I can't really make it any worse than it already is. If it's still useless after trying to treat it, I haven't lost anything. I'll try the oil first. That's what I have experience with anyway so it's good to know that it might work. I have no experience with brine. Thanks again!

[harry strasil]

Cast steel is blister steel that was remelted and then cast into ingots that were rolled or hammered out to size, Cast Steel was developed to intigrate the surface carbon into the base. The magnet test is to not overheat the metal which forms a larger grain structure, Non Magnetic is 1460 degrees.

[Mike Henderson]

Cast steel is blister steel that was melted...
That was generally only true in the early days of crucible steel (cast steel). The crucible steel people soon learned that if they put cast iron (high carbon) with wrought iron (low carbon) they could make cast steel cheaper than they could if they used blister steel. Sweden initially prohibited the export of the low phosphorus cast iron so the English makers of crucible steel had no choice but to use blister steel made from Swedish low phosphorus wrought iron. But once Sweden allowed the export of cast iron, the English steel makers generally switched over.

This is not to say that blister steel was not used to make crucible steel all the way to the end of crucible steel, but the majority of cast steel was made from a mixture of Swedish cast iron and wrought iron made from Swedish cast iron.

You can see the difference in cost by looking at the process. Ore was smelted in a blast furnace to make cast iron. That cast iron was further processed to make wrought iron. To make blister steel, the wrought iron was hammered or rolled into long thin bars, maybe 3/8" to 1/2" thick. These bars were packed into a chest with carbon (powdered charcoal) and heated for a relatively long time, perhaps 10 days. To make cast steel, the ends which were cut off of the blister steel, along with any bars that had too high a carbon content, were sold to the cast steel makers to be melted in their pots.

Making cast steel from a mixture of wrought iron and cast iron eliminated completely the cost of the cementation step (rolling the wrought iron and the making of blister steel), and eliminated the cost of making the wrought iron for the cast iron portion of the charge.

Mike

[BTW, the blisters in blister steel were due to a chemical reaction between the carbon diffusing into the iron and the slag entrained in the iron - the reaction produced carbon monoxide. This was proven when one of the scientist investigating the question had wrought iron melted in a crucible, which caused the slag to leave the iron and float to the top. That iron was then rolled and then put into a cementation furnace to produce "blister steel". Upon removing the processed iron, there were no blisters found. That piece of steel was donated to a museum in Sheffield (If I remember correctly) and is still available for examination.]

[Bob Barkto]

There were/are many processes that can be, and are, called cast steel.
But the methods mentioned by Harry and Mike are most historically accurate, as the methods are quite different from Bessemer and a few other processes. Sometimes the distinctions get a little blurry. Often times those differences have a dramatic effect on consistency and quality.

Many steel and tool makers put the monicker of "cast steel" on their tools even if produced by some other method.

Depending on when your blade was made the purity and carbon content can be anybody's guess as Ibbotson were around during many of the most dramatic tranistional periods in steel making history. They were making tools when Swedish wrought iron was being cooked with charcoal and on through the early Bessemer era.

All that said, the steel itself will likely be just a plain carbon steel from about .60 - .90% C.

[Ron Petley]

It might be worth soaking the blade in vinegar and this will tell you if it is a laminated blade. I have a old blade and I was amazed how thin the quality steel was, just a thin sliver. So maybe this part has been removed through flattening the blade or a back bevel.
The heat to non magnetic is the way to heat it. If your fire is really hot heat the blade form the back and let the heat creep towards the cutting edge, the thin edge will over heat easily. Heat your quench oil to about 135f. Quench the blade and remove it before it is totally cool you want about 350f, just hot to a quick touch with your fingers.If the blade is smoking the oil sr insert it into the oil. Examine it at this temp and of warped you can hammer it lightly to straighten it, but go quick before it cools to much. If it is straight you can re insert it into the oil. The brief ineruption of the quench will not harm the quality, some feel this adds to its quality.
I would go oil first, if you want to try brine add enough salt to float a egg with the brine at room temp. Warm the brine as well.
Cheers Ron.

[lowell holmes]

The collective knowledge base of this forum is absolutely amazing and the willingness to share it is appreciated.

[Jim Paulson]

Lowell said it well. I thoroughly enjoyed what was discussed here and I appreciate that Bob Rozaieski got it going. Thanks.

Hopefully, some of this conversation will also help some of us who want to eventually make or refurbish plane irons for wooden moulding planes. After watching Tod Herrli's DVD, Hollows and Rounds, it gives you the bug to heat treat and temper irons yourself.

Jim

http://www.chairsbypaulson.com