A2 iron micro chipping

[Mike Cherry]

Yeah that 25 degree shot definitely is not how A2 should look at 25 degrees in a low angle plane. As Barney says, grind back down to that at some point. If that's happening after a stroke or two your blade is either too brittle or its too soft and the edge is rolling.

Yea it seems to be holding up fine at this new angle. Eventually I will grind it back to 25 and see what happens.

[Mike Cherry]

What is the diameter of the wheel that you are using to grind that HOLLOW GROUND 25º angle on your A2 iron? If the wheel is fairly small,the angle it is grinding at the cutting edge could be considerably less than 25º.

Mr. George, the diameter is 8". I see what you mean, a 6" wheel would produce a more acute hollow grind yes?

[Kees Heiden]

Yes, but when you hone, resting the hollow on the stone, you reintroduce a true 25 degrees again.

[Adam Cruea]

Most of my A2 does this. You just have to grind off the very end sometimes to get to good steel.

[Stewie Simpson]

http://www.hudsontoolsteel.com/technical-data/steelA2

[Derek Cohen]

http://www.hudsontoolsteel.com/technical-data/steelA2

What's your interpretation of all that data, Stewie?

Kindly explain what you see there.

What I understand from this data is that A2 has about 50% greater wear resistance than O1, and is by far the better steel to manufacture blades from. Interestingly, at 60 HRC, A2 will chip quicker than O1. However, I read that the way one gets to 60 makes a difference to toughness.

Regards from Perth

Derek

[Stewie Simpson]

Hi Derek . Comparisons between steel quality is beyond my expertise. I will leave that to you.

regards Stewie;

[Derek Cohen]

Stewie

It was an interesting link. You often post interesting links. However I think I am not alone in suggesting that you say why you find these links useful when you do post them.

Regards from Perth

Derek

[ian maybury]

Just reading from Stewie's tables, but the information is interesting.

They seem to suggest that the primary strengths of A2 versus O1 are wear resistance and dimensional stability in heat treatment (both really useful properties in a plane iron where less sharpening and a nice flat back are so important) - but that it's actually a bit less tough. Toughness in engineering terms usually being a measure of how much energy/how heavy a blow is required to cause a material is to fracture on impact.

If asked i'd have suspected that as an alloy steel (containing chrome, molybdenum and vanadium) it'd be tougher than a straight carbon steel like O1, and that toughness and wear resistance came as a package deal. Apparently not - or at least not always.

In practice the combination of manganese (especially the manganese), carbon and these alloying elements probably results primarily in improved hardenability. (including easier through hardening) I don't know much more, but it wouldn't be unreasonable to surmise (depending on what actually goes on during heat treatment and grinding) that the particular hardening characteristics of A2 (it tends as a result of the managanese to require a significantly slower cooling rate and less carbon to harden than would a straight carbon steel delivering similar properties) might somehow result in some extra hardness at a thinned edge that can cause localised chipping?

This same easy hardening combined with the alloying elements (especially the chromium and molybdenum) though may also with the carbon deliver the high the wear resistance - treated correctly they form finely dispersed carbides which tend to be pretty hard.

It's a picture that perhaps makes practical sense in that while i'm no expert i've been surpised at how well e.g. the A2 in Lee Valley plane irons sharpens. I've seen no very obvious signs of the sort of overly persistent wire edge commonly seen with chrome vanadium steels for example. This may well be a side benefit of this slight brittleness/lack of toughness….

[Stewie Simpson]

Hi Ian. Appreciate your input on A2 steel.

For those unfamiliar; the following is a list of the alloys; and their purpose; within tool steels. http://www.simplytoolsteel.com/alloying-elements.html

Stewie;

[Brian Holcombe]

A2 looks great when presented in that fashion, but I am more interested in what can hold a keen edge for a long time as opposed to what can simply hold an edge for a long time. I believe A2 is a very good steel for tool and die, tool and die are generally very high angle, once that angle begins to narrow I believe there are more suitable steels. I have my A2 blades at 35 degrees (bevel down) because I can maintain the edge very well at this angle without annoying micro chipping cropping up constantly.

If you look at other forms of blades needed for purposes which require an even more keen edge you only very rarely see A2, it is more more common to see plain carbon steel. A2 is common in survivalist knives, why? Because it can hold a dull edge forever, but look at straight razors and you probably will not find it.

My experience with A2 in plane blades and chisels has not been a love affair, I find that it rolls the edge more more quickly than fine plain carbon steels. I also find that it will form micro chips at almost any angle eventually and that will show in the results of what your working long before the edge is sufficiently dull. Furthermore on a finish plane I can only maintain a high sheen for a very short period of time with an A2 blade, it tends dull down to a matte finish pretty rapidly and stays there for hours of use.

I was a hobbyist knife maker as a teenager, I really loved getting caught up in these comparison sheets of steels and wound up using a lot of D2 and ATS-34 because O1 and W2 were really boring on paper. I also spent an incredible amount of time polishing the blade after heat treat....

[ian maybury]

For sure Brian - what i wrote is only a very highly arms length take on A2 steel drawn from Stewie's piece and my recollections from college years ago. There's the potential for all sorts of much more detailed issues to arise in manufacturing and use. It wasn't intended to suggest that it's necessarily superior.

This territory must have been covered before by people with a lot more expertise and experience. The fundamental question here about A2 is perhaps whether or not edge chipping is an inherent issue at the level of hardness of the iron/as required to hold an edge. If it is then there's not much option but to use a steeper bevel. If the problem is local (only close to the edge) then or down to a bum iron then grind back further or maybe changing it for another might be worth while.

It could be that it's ability to harden at a slower rate of cooling than a carbon steel more easily gives rise to issues with localised variations in hardening. If for example an iron cools in the air it's possible that a thinned edge (if it's already had the bevel cut) might cool enough faster to create some local variation in properties. Which might mean it's difefrent or harder to handle in manufacturing.

PS Taking a look just now brought up this page on the relative properties of tool steels by this knife guy: http://www.cliffstamp.com/knives/rev...materials.html (O1 and A2 are addressed well down the page)

I don't know how credible the information is, but the closing summary comment on A2 is interesting - as is the more detailed stuff on both steels. He seems to have concluded that A2 and O1 are generally very similar, and that very minor variations in heat treatment can result in greater variations in properties than are necessarily inherent between the steels themselves.

Grain size may be a related factor too, although he doesn't really address it. Carbon steels are well known for their fine grain structure when handled right, i don't know if A2 is different. (if coarser it might restrict it's ability to take a fine edge) He says that A2 is best quenched down to well below room temperature, and that failure to do so can leave it with retained austenite (the basic softer form of iron) leading to brittleness of the edge.

He quotes Derek's findings (dovetail chopping tests with chisels in awkward wood) that a good Japanese white (carbon) steel (Koyamaichi) or PM-V11 (Veritas) are both well ahead of either the A2 or O1 like chisels he tested.

It all brings to mind the stuff about just how effective the very subtle working of carbon steels (white steel) by Japanese smiths can be in terms of determining it's properties. Which suggests also that there could easily be differences in the performance of O1 and A2 by different plane and tool makers, and maybe even between batches. Perhaps also as a result of how they are handled during manufacturing of the blade.....

[Brian Holcombe]

Certainly possible that different manufacturers will have slightly different results. It's very apparent in Japanese blades that smith-to-smith can have a huge effect on results.

I find it surprising that we do not hear more about the heat treating process from manufacturers, who presumably, would stand to gain an edge by providing insight into the procedure. Even in my short experience making knives (2-3 years worth) a quality heat treater was very highly considered. I sent my blades to a man out in Montana who had the best equipment and ability available to hobbyists.

[Larry Frank]

Some of the commentary about tools steels is a bit off. The tools steels such as A2 are fairly complex. It is really more like two different materials mixed together. You have the carbide which are very hard and in the heat treatment want to keep them fine and well dispersed. The remainder of the steel after heat treating is tempered martensite. In the case of A2, the heat treatment is critical in avoiding retained austenite and properly tempering.

To heat treat properly and consistently, you would need a well controlled heat treat facility and follow tight processing.


My guess is that there is a wide range in how well A2 is heat treated and results in major differences in how they perform. Without looking at the microstructure and properties it is difficult to diagnose problems.

I think that Derek's approach to testing the different grades of tool steel makes the most common sense for most wood workers and his results are great guidelines. Trying to understand the metallurgy of these grades takes a lot of background and study.

(My comments are my own opinion and based on my long experience as a Metallurgical Engineer. )