A-2 Plane irons

[Lee Schierer]

I'm thinking of making some plane irons using A-2 tool steel. Does anyone know what hardness plane irons are made to?

[Dave Anderson NH]

Hi Lee- For the short answer to your question, it varies by manufacturer. Most however run between 60-62 Rockwell C scale (Rc). I would like to warn you though that A-2 is something that you can't harden yourself like the Water and Oil hardening steels unless you have special equipment or get really lucky. do you have access to heat treating at work, or will you be using an outside vendor?

[Rob Millard]

I use to work part time at a machine shop, and I had a few A-2 blades made before they were commercially available. The heat treating company had a range of Rockwell hardness, and I picked the 62-64 range, and have been very happy with the results.

Rob Millard

[Ray Thompson]

Hi Lee,

I think A2 would make a great steel for plane blades. You will have to send them out for heat treatment, but I know you have access to heat treaters. Ask them about cryogenic treatments also, I don't remember off hand if A2 falls into that category or not but your heat treater will know.

Ray

[Alan Turner]

I seem to recall rumors, and that is all they were, that the cryo heat treating of A-2 required LN to go through a number of test batches, esp. on the chisels. If that is true, then perhpas you could find a heat treater who had done this before.

[Rob Millard]

I seem to recall rumors, and that is all they were, that the cryo heat treating of A-2 required LN to go through a number of test batches, esp. on the chisels. If that is true, then perhpas you could find a heat treater who had done this before.

Alan,

When I had my blades made, they were not cryo treated, and I found them to be superior right out of the box to the LN blades I have, that were treated. I attributed this to a poor grinding technique at LN, that lead to drawing some of the temper from the edge, but now you have me wondering if it was due to the cryo treatment. This makes even more sense because not all the LN tools I have had this problem, the No. 9 miter plane was the worst offender. After I ground the iron back about 1/32" the problem disappeared, and they hold an edge very well and are equal to my shop made blades, but not any better, which leads me to believe the cryo step is unnecessary.

Rob Millard

[Alan Turner]

Rob
Interesting observation. I have 2 older LN's, a 60 1/2 LA block, and a No. 2 smoother, and neither has the A-2, although for the LA Block, I bought a 2d iron in A-2 as this guy gets used so often. The older irons are not that good at holding an edge, and need to go to the stone with some frequency, although I don't use either very often. (I ususally just put to older iron in the LA Block when I go to Groff to check wood grain, color, end griain, etc., but that is about the only use it really sees.) I don't work on job sites.

All on my A-2 irons, including the No. 9, are fine, but I wonder if you perhaps got an earlier production run of the A-2. My No. 9 is about 2 - 3years old, from what I recall.
For a 604C Bedrock, I installed the Hock A-2, w/ new capiron, and it has been quite good at edge retention.

Since I now have to outfit a second shop, I will now pull the trigger on a LN 4.5, corrugated, Rosewood, which I have lusted after for a very long time. I know it is your go-to smoother. Mine will not sit on the mantle either.

[James Mittlefehldt]

To further muddy the issue I recall reading a bit by Leonard Lee which said that after doing tests on A-2 steel with and without the cryogenic treatment he could not find enough improvement to justfy the process. If Rob Lee happens to see this he might be willing to comment.

[Gene Collison]

Before retirement I was a technical sales representative for the largest supplier in the world for cryogenic liquids. I had numerous commercial heat treaters for customers, I know their processes well. My company was a world leader in developing uses for Liquid Nitrogen and did extended research looking for new ways to sell the product. Cryo quenching of steel was not an application that was even considered. I had one customer that did sell a service for cold stabilization of aluminum. I'm talking about large aerospace providers such as Western Gear etc. If it was a viable application for Liquid Nitrogen my company would have chased it and promoted it around the world. But you can't support an application for your product without the liabilities that go with it. It needs to work.

Gene

[Jim Reed]

I worked in IT at a research cryo lab for ten years. I suspect cryo treatment of steel is more marketing than science. There are many variables in A2 steel composition that complicate testing and can keep the results from being applicable to all batches.

[Dennis McDonaugh]

Alan,

When I had my blades made, they were not cryo treated, and I found them to be superior right out of the box to the LN blades I have, that were treated. I attributed this to a poor grinding technique at LN, that lead to drawing some of the temper from the edge, but now you have me wondering if it was due to the cryo treatment. This makes even more sense because not all the LN tools I have had this problem, the No. 9 miter plane was the worst offender. After I ground the iron back about 1/32" the problem disappeared, and they hold an edge very well and are equal to my shop made blades, but not any better, which leads me to believe the cryo step is unnecessary.

Rob Millard

Rob, I read an article in popular science and what you describe is one of the pecuilarities of cryo treatment. You have to grind off the exposed surface to reach the hardened steel. They don't know why, but it was one of the things mentioned specifically in the article.

[Ben Knebel]

Hi Folks;
A couple of comments from a manufacturer who uses cryo'd A2 irons in thier planes.
Firstly I believe that hardening above Rc 59 for A2 is contrindicated. The steel becomes too hard and can chip out making regrinding a very difficult task.
On the advice of our mettalurgist we harden only to Rc 58-59 ---gives us excellent edge retention and the potential for chip out is greatly reduced.
Further we cryo our irons and although we have not done exhaustive testing I can say there is a definite difference between irons that have been cryo'd and those that have not.
We manufactured Stanley replacement irons out of A2 and as a cost saving measure decided not to cryo them.
I tested these and was unhappy with the results in terms of durability of the edge and retention of sharpness. To be sure that I wasn't just smoking dope we had another batch go through the same process except these were cryo'd. The edge retention and durability was significantly improved when compared to the non cryo'd irons.
As I say--these tests weren't exhaustive but good enough for me to determine that we should continue to cryo the irons.

BTW--The cryo process does change the steel at the molecular level as it reduces the austenite(sp?) content of the steel from around 10-12 % to something less than 3%. It is the Austenite that burns when you are grinding an iron and it is this burning that draws the temper.
With such a low austenite(sp?) content you are less likely to draw the temper from an A2 cryo'd iron. Indeed our metallurgist told us you would really have to work at it to draw the temper from a cryo'd A2 iron.
Apparently the steel changes over time any way so I think perhaps the cryo process is speeding up a natural process and taking the steel to where it needs to be sooner than if simply hardened.
Best regards
Ben

[Gene Collison]

Ben,

A2 tool steel or any air hardening tool steel for that matter is typically treated in a vacuum oven; this has been the preferred method for about the last 15-20 years. The advantage that the vacuum oven has is that it is an oxygen free atmosphere that prevents carbon burnout. The batch of material to be treated is placed in the oven and heated to the sensitizing temperature of the steel, typically over 1600F. After soaking the batch at this temperature for a period of time, the furnace is backfilled with gaseous nitrogen; this is known as the quench cycle. The whole idea here is to never permit the steel to come in contact with oxygen during the heat treat cycle, this prevents carbon burnout and loss of hardness. The steel comes out of the furnace at maximum attainable hardness as determined by the carbon content of the steel. When the steel is placed in the oven, you do not get to choose the hardness level, it is determined by the carbon in the steel. The steel is then placed in a tempering oven for a predetermined time and temperature to bring it to the hardness level that the customer prefers. Tempering increases the toughness and reduces embrittlement.
I would have to see proof by analysis to substantiate your metalurlogists claim to changes in austenite by a soak in Liquid Nitrogen. There are numerous companies making a lot of noise about cryo soaking but no one is producing any analysis like photomicrographs or analytical analysis before and after. Just seat of the pants testing.
I called one of my old heat treating accounts this morning, Supreme Steel treating in El Monte, California. These guys are one of the major heat treaters in the Los Angeles area, they have never heard of cryo soaking for A2 further saying it would offer no advantage on A2. These guys do it all, aerospace, everything. I have numerous irons of both A2 and HCS, I can honestly say, I can’t tell the difference between a LN iron or a LV. I understand that Ron Hock has similar feelings although this is hearsay on my part. So, until I can see some legitimate testing and results, I don’t buy into it.

Gene

[Gene Collison]

Ben,

I was thinking more about the difference that you observed while comparing cryo'ed to non-cryo'ed plane irons. If you don't buy steel with a guaranteed analysis, the carbon content can vary somewhat. A few points of carbon increase in the analysis can change the characteristics of hardened steel substantially. Much more so than a bath in LN2. Also the tempering determines the final hardness. There are some carbides that wear better than others also but in A2 it is iron carbides that are responsible for the hardening.
HNT Gordon sells HCS irons and M2 irons (M2 is high speed steel). Terry Gordon will tell you that for North American hardwoods the HCS will work as well as M2. For scraping applications the M2 is better. I can tell you from using both that even M2 and HCS perform much the same.

Gene

[Rob Lee]

To further muddy the issue I recall reading a bit by Leonard Lee which said that after doing tests on A-2 steel with and without the cryogenic treatment he could not find enough improvement to justfy the process. If Rob Lee happens to see this he might be willing to comment.

Hi James -

In the process of making over 100,000 cuts, using multiple blades, from multiple manufacturers and using an electron microscope to examine wear, we have found cryo treatment of A2 steel to be neither a benefit nor a detriment.

We did find some other interesting conclusions though...

But as for cryo treating A2, We're not spending your money on it!

Cheers -

Rob