Excavator rock breaker steel

[steveh]

Does anyone have an idea what the steel might be for an excavator rock breaker chisel?At work we got ours back from the machine shop and they had put a chisel point on it where as we wanted a dull point.It is 3in round and approx. 2ft. long.I brought it home and hammered it out on my Anyang 88lber,then finished it off with the grinder.Not knowing the type of steel I just let it cool without hardening and tempering.After a month of daily use it is hardly showing any wear,so this got me thinking it might be air hardening.Any thoughts would be appreciated,thanks Steve.

[bigfootnampa]

I assume that you meant a "Bull" point. I don't know what type steel is in those but for most tools of that type the steel is quite tough even in it's unhardened state. I am pretty sure that is what you are experiencing for even air hardening steel (quite unlikely IMO) would not be likely to harden in such a thick heavy mass. You may have achieved some work hardening though as an 88 pound Anyang can really put the hammer down. In any case good results are far better than good intentions. Tools destined for such heavy impact applications shouldn't be hardened much anyway (though they SHOULD be made of VERY tough steel) because they might crystallize and break under the constant hammering stress that they are meant for.

[Nakedanvil - Grant Sarver]

I've manufactured 100's of thousands of bit for hydraulic demolition hammers, from 1-3/4" up to 8" diameter and re-sharpened many thousands more. Most are made from A.I.S.I. 4340, although some (smaller ones) are 1045 (case hardened) and many very large ones are a European alloy EN30B, sorta like 4340 with a lot more nickel. Mast are heat treated to 50-52Rc. Unless annealed, 4340 comes out pretty hard no mater what you do. You're going to get a bit more than an "air quench" when you only heat the end of a piece. The body of the steel "sucks" a lot of the heat out just by conduction giving a faster quench.

bigfootnampa: The is no phenomenon in metallurgy known as "crystallizing" in relation to failure. At room temperature all steel has a crystalline structure and any failure will expose a crystal surface, but you're right they do accumulate a lot of stresses. Also, no work-hardening occurs at forging temperatures, and lets hope he wasn't hammering it cold!

[steveh]

Thanks for the info,much appreciated.Was it supposed to be hot to hammer it out???LOL

[bigfootnampa]

Thanks for setting me straight on the crystallization Grant. I guess having witnessed broken ends of similar type tools led me to such erroneous description.

The work hardening thing I have discussed before and IT HAPPENS. Perhaps it is not theoretically possible BUT I experience it at my forge. It is difficult for me to accept what you say when I experience metal becoming stiffer and more rigid (appearing stronger) after forging than it was before. Perhaps the problem is my terminology or something? I mean as a jewelry smith I often worked with metals which were routinely work hardened as this was often the only reasonably practical method. I am perhaps confused as a result of my unusual path of development as a smith but I would like to better understand and perhaps you can help me?

Some of my reading has led me to think that work hardening is one of the most reliable ways to harden various metals and alloys... I think of it as a near universally successful method. Is it possible that I am "anvil quenching" my steels instead of "work hardening" them? It would almost seem to amount to the same thing in a practical sense, although it could be that more than one type of alteration is occurring and perhaps there is not an existing term that is technically correct and properly descriptive? OR maybe I just don't know what it is?

[Nakedanvil - Grant Sarver]

Bigfootnampa: Well, I'm never one to hold theory above experience. The science behind what you have experienced is probably partial hardening from the forging heat. Certainly "as forged" parts are stronger/harder than the annealed bar we usually receive. We don't usually think of it, but any time we heat a piece and cool it (thermal cycle) we are "heat treating" it.

What you have read about work hardening usually is refering to "cold working". Now, exactly what goes on above "cold" but below re-crystallization temperature, I must plead ignorance. Maybe one of our matallurgists can enlighten us. Often in forging the finishing is being done below the lower critical temperature. What effect that has, I don't know.

[ThomasPowers]

Heavy forging when hot does help refine the grain structure of steel that can help with it's toughness afterwards.

[bigfootnampa]

Thanks Grant and Thomas. I am beginning to see that this is a complex thing perhaps not easily described or understood. So my use of "as forged" materials may be difficult to describe but if they work well I'll figure out how to live with the vagaries of the technical details.

They have seemed to work well for some things too... I make a small scythe/billhook that I like to leave that way. The cutting blade has been heavily forged and I don't like them to be too hard to file sharpen. They seem about right as I take them off the anvil and cut weeds like a whole herd of string trimmers. Even my wife says she wouldn't use a string trimmer now "for all the tea in China". Usually this strategem is most useful when I am working with moderate carbon content steels.

[Nakedanvil - Grant Sarver]

It's nice to be able to explain thing we do, but if what we're doing works, there can be no arguing with it. On your scythe, with something that thin you are almost certainly getting a degree of hardness just from how fast it air cools, and it satisfies your needs. All the theories and science in the world can't change that. That's the way blacksmiths have been doing things for thousands of years.

[Axefanatic]

Late Post

Some work hardening is likely to occur with use also, as the tip will be under a fair bit of

pressure. Maybe not so much with a chisel point, but a bull nose bit would have high

stresses at the contact point, radiating out around the point.

My 2 cents !

[ThomasPowers]

The problem with experience vs theory is that folks often ascribe what happens when they do something to a completely erroneous explanation. So what they experience is real; what they say caused it can be very off indeed! (exp "crystalization" causing parts failures; especially common as parts with larger crystals are more likely to fail than finer ones...and so folks invert the cause and the effect)

[Mainely,Bob]

How does this explain the common practice of "packing the edge" done at a dull red heat?
I`ve also dealt with stonecarvers who swear that the tools forged to sharp and packed far outlast those just ground to refresh the edge.They refer to these tools as "firesharps".

[ThomasPowers]

Firstly heating to forging temps will "cure" any work hardening issues that haven't propagated to cracks yet and then re-hardening makes for a good edge---for shallow hardening steels just grinding can move you past the hard layer fairly fast.

Secondly the idea that packing increases the density is pure BS; if it did we smiths will be dieing of radiation poisoning---you don't compress atoms.

In early steels with little or no alloying, heating to higher temps for forging can cause crystal growth that forging at lower temps before heat treat can refine. With modern steels you can thermally refine the grain structure *much* better than the old "packing" method.

Lastly there is always the observation effect where observations that match our pre-held beliefs are remarked upon and observations that contradict them are often discarded.