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  #1  
Old 03-02-2007, 07:58 PM
Tim Crocker Tim Crocker is offline
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Grain flow and strength

I have a friend who owns a tool forging company. I just saw an interesting issue that made me appreciate hand forging blades. It's not new information but when viewed in a different light it may convince some that forging is the way to go.

He makes a complex shaped piece of metal for a military contractor. It is made by hot forging it. The contractor told him that they were considering having someone else make the piece with a cnc machine out of the same alloy.

This didn't bother him much because the piece isn't too profitable to begin with. The only problem is that the piece will not pass the strength test by a stock removal manufacturing method. The piece must have "grain flow" in order to be strong enough to pass. The grain flow is achieved by hot forging. I'm told that the grain is visible through a magna-flux test and it flows around the corners and turns of the piece. (I haven't seen the piece magna-fluxed).

Another good reason to forge to shape.
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  #2  
Old 03-02-2007, 10:04 PM
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NuViking NuViking is offline
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What I am finding concerning in this statement is that the army brass hasnt done the reserch to find what is a superior product for our young men who are risking their lives not only for us but for the brass that give them orders.
I had made a knife for a soldier here in Canada and after I hardened it [a forged file] and tempered it I found a week spot in the blade. The rest of the blade held an edge well but in the center was a spot that I could feel as I was sharpening it was soft. So I started cutting some boot leather soles and found this same spot dulled fast. I annealed this knife and put it in the todo list because I didnt know what my mistake was and I was not going to send what I beleive an inferior blade to somebody who may need it in a life situation.
One of the next blades I made forged and hardend well and I tryed a new to me meathod of tempering and after cutting paper and soing a little wood carving I was satisfied that this knife will hold an edge very well. I hope the young fellow that recieves my knife never needs to depend on it for life but if he does I know in my heart and the best of my abilities that I did everything to make sure that it will not fail him.
What else does does this military contractor willing to do to give the young fellows a cheaper product. Perhaps bullets with less powder?


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  #3  
Old 03-03-2007, 11:36 AM
toddhill toddhill is offline
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That's very interesting Tim. Thanks for sharing. Todd
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  #4  
Old 03-03-2007, 12:16 PM
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Raymond Richard Raymond Richard is offline
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I truly believe the more steel is manipulated by forging the better the piece of steel is. You alway here the argument that the heat treat is the deciding factor and if done correctly there will be no difference between a forged and a stock removal blade. I've really been down with the forging bug the last couple weeks and must have forged at least 20 blades. About half the blades are from saw steel. I've been starting with pieces that are 1 3/4" X 5/32" X 7". I start out by hammering the width back into it self and working the sides at the sametime. I've been stopping when I reach 1 1/4" in width and the thickness is just under 1/4" and the length of the bar is 9". I did the same thing with a old piece of leaf spring Thursday. Started with a 4 1/2" X 1/4" X 2 1/2" piece. Forged it down to 1 1/4" X 1/4" X 8". My calculations tell me it should have ended up at 9" so where did that 1" go? Next time I'll cut two pieces exactly the same and weigh them before and after forging. I did weigh the blade I forged and I cut a 4 1/2" piece of leaf spring afterwards and there was maybe a 1/2 oz difference. I feel that the missing inch just got compacted into a tighter mass. I'll be doing some testing with this. BTW I do notice a lot of difference in the steel when it is forged like that. It feels much harder and stiffer while forging.


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  #5  
Old 03-03-2007, 01:45 PM
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Ray Rogers Ray Rogers is offline
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Ray,

Steel is a pretty dense material to begin with, you won't be able to compress it, i.e., increase its density with a hand held hammer or even a 100 ton press to any noticeable degree. To do so would require a change in the atomic structure of the material or a change in the laws of physics. If you test carefuly, I think you will find that your missing inch of steel simply burned away and formed scale. Your forged blade, even with all the scale included, will weigh less than the bar you started with because some of it vaporized. If the density had increased a cubic inch of the forged steel would be heavier than a cubic inch of the unforged steel and you would need a labratory to measure the difference.

This is not to say that forging does not impart some desireable properties to the blade but I am saying that any serious increase in density won't be one of those properties....


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  #6  
Old 03-04-2007, 09:44 AM
Ed Fowler Ed Fowler is offline
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One inch is a lot of change. Try checking your math, you will probably find it there. I do note when you harden a forged blade as opposed to at stock removal blade the scale will stick on the stock removal blade much more tenashiously (sp) than on the forged blade. This is because of the finer grain structure.

For a long time I found that an 8 inch blade would drop down during multiple quench. Sometimes as much as 1/4 inch. I talked to Rex a lot about it. The same malady is heard about when they talk about Japanese blades raising up in heat treat. this would have to be a result of shrink or grow somewhere in the blade. We changed a lot of variables over time and one day I checked another long blade and it did not change provile during heat treat. What happened and why it does not happen now remains a mystery. I am glad it no longer happens, but still wonder why.


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  #7  
Old 03-04-2007, 12:15 PM
Tai Google Tai Google is offline
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Quote:
Originally Posted by Raymond Richard
I truly believe the more steel is manipulated by forging the better the piece of steel is. You alway here the argument that the heat treat is the deciding factor and if done correctly there will be no difference between a forged and a stock removal blade. I've really been down with the forging bug the last couple weeks and must have forged at least 20 blades. About half the blades are from saw steel. I've been starting with pieces that are 1 3/4" X 5/32" X 7". I start out by hammering the width back into it self and working the sides at the sametime. I've been stopping when I reach 1 1/4" in width and the thickness is just under 1/4" and the length of the bar is 9". I did the same thing with a old piece of leaf spring Thursday. Started with a 4 1/2" X 1/4" X 2 1/2" piece. Forged it down to 1 1/4" X 1/4" X 8". My calculations tell me it should have ended up at 9" so where did that 1" go? Next time I'll cut two pieces exactly the same and weigh them before and after forging. I did weigh the blade I forged and I cut a 4 1/2" piece of leaf spring afterwards and there was maybe a 1/2 oz difference. I feel that the missing inch just got compacted into a tighter mass. I'll be doing some testing with this. BTW I do notice a lot of difference in the steel when it is forged like that. It feels much harder and stiffer while forging.
Scale could account for shrinkage or loss or mass.


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  #8  
Old 03-04-2007, 12:24 PM
Tai Google Tai Google is offline
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Quote:
Originally Posted by Ed Fowler
One inch is a lot of change. Try checking your math, you will probably find it there. I do note when you harden a forged blade as opposed to at stock removal blade the scale will stick on the stock removal blade much more tenashiously (sp) than on the forged blade. This is because of the finer grain structure.

For a long time I found that an 8 inch blade would drop down during multiple quench. Sometimes as much as 1/4 inch. I talked to Rex a lot about it. The same malady is heard about when they talk about Japanese blades raising up in heat treat. this would have to be a result of shrink or grow somewhere in the blade. We changed a lot of variables over time and one day I checked another long blade and it did not change provile during heat treat. What happened and why it does not happen now remains a mystery. I am glad it no longer happens, but still wonder why.
The steel expands and contracts during heating and cooling.

Changes in grain size should not effect the amount of mass, should it?

I've heard that with Japanese blades beyond a certain length that are quenched with clay along the back, will warp upwards if quenched in water, and downwards when quenched in oil. I have had blades warp upwards in an oil quench, but with no clay along the back. These phenomenon are mysterious and I've never heard a good explanation for it. My feeling is that it has to do with blade geometry, and cooling rates.


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  #9  
Old 03-04-2007, 12:30 PM
Tai Google Tai Google is offline
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Grain flow and grain size reduction are the main two arguments for forging over stock reduction. However, the mechanism for grain refinement from forging is not totally understood and maybe completely thermal, not mechanical. In essence, faster cooling rates promote grain refinement. If you think about it, the thinner edge, in the wedged shaped cross section geometry of a blade, will account for a faster cooling rate of the edge or thinner area. If you couple this with the chilling effect of steel anvils, dies and hammers,... a thermal reaction to forging makes a lot of sense.


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Last edited by Tai Google; 03-04-2007 at 12:33 PM.
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  #10  
Old 03-04-2007, 01:49 PM
Tai Google Tai Google is offline
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The steel is like a super sensitive "recording" medium. Everything we do to it has an effect on it.

How important is it to understand the mechanisms behind the effects, and why,... as long as you understand how the steel reacts?

Forging does stuff to the steel!

The obvious thing is that,... forging and casting are both more efficient and less wasteful ways of forming a blade, as opposed to strict stock reduction. Between those two extremes,... which would you want?


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Last edited by Tai Google; 03-04-2007 at 02:31 PM.
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  #11  
Old 03-04-2007, 03:17 PM
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Ray Rogers Ray Rogers is offline
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Devil's advocate here. Tai, please define 'efficient' as you used it in the previous post.

It seems intuitively obvious that forging and casting are more conservative of the steel itself but what of the other materials involved? It takes a considerable amount of fuel to forge and, I believe, even more to cast a blade. Then there is the environmental impact of all those gasses and fumes and the disposal of any scale that might form. Are we really confident that those processes are more efficient over all that simple stock removal ?

Not that stock removal is without it's pollutants. The metal dust could be recycled but usually isn't. The belts may sit in a landfill for centuries and refuse to break down. In terms of sheer energy required to produce the blade though, it seems to me that stock removal is far and away more energy efficient than forging since the energy required is literally pennies.

But, that is just my lay opinion and I do plan to do as much forging as possible this summer.....


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Old 03-04-2007, 03:57 PM
Hammond Hammond is offline
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There is a big difference between graphite, coal, diamond nanotubes and fullerines.

We know there are definite differences between the different crystal structures of steel.

I now feel the need to do more research on the crystal structues of steel. While it would make a difference it would probably not make an inch. It would be proportional to the length of the blade and this combined with all the other factors such as shrinkage, expansion and losses to scale and other factors would all contribute.
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  #13  
Old 03-05-2007, 07:44 AM
Tai Google Tai Google is offline
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Quote:
Originally Posted by Ray Rogers
Devil's advocate here. Tai, please define 'efficient' as you used it in the previous post.

It seems intuitively obvious that forging and casting are more conservative of the steel itself but what of the other materials involved? It takes a considerable amount of fuel to forge and, I believe, even more to cast a blade. Then there is the environmental impact of all those gasses and fumes and the disposal of any scale that might form. Are we really confident that those processes are more efficient over all that simple stock removal ?

Not that stock removal is without it's pollutants. The metal dust could be recycled but usually isn't. The belts may sit in a landfill for centuries and refuse to break down. In terms of sheer energy required to produce the blade though, it seems to me that stock removal is far and away more energy efficient than forging since the energy required is literally pennies.

But, that is just my lay opinion and I do plan to do as much forging as possible this summer.....
By more efficient I mean less wasteful,... unless of course you're vaporizing the steel!
It has the "potential" to be more efficient.


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  #14  
Old 03-05-2007, 11:36 AM
Tai Google Tai Google is offline
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At what point does the steel "vaporize" at?


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Old 03-05-2007, 12:14 PM
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Ray Rogers Ray Rogers is offline
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Good question. About 5400 F will get the steel to its boiling point. Probably out of reach for most of our forges.

I was thinking of the erosive effect that comes with high volumes of fast moving hot gasses when I said 'vaporized'. In that sense, my use of the term 'vaporized' is very similar to your use of 'efficient' ....


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