Manufacturer's heat treat of a known steel

cchu518

cchu518

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Mar 6, 2013
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We live in a modern times where manufacturing goes through set process flow, design of process and evaluation and still more reevaluation to fix errors.

This fact alone generally leads me to never believe that the issue with a blade chipping or failing is because of manufacturers heat treat.

This is especially true if the material that the major manufacturers (pick a name) is using is in that manufacturer's normal lineup of steels.

In any case does anyone have any first hand account/photos etc... Of how mass produced knives get heat treated by the steel makers and then what happens at the knife manufacturers?
 
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No first have experience here, just know what I've learned from here.

Steel isn't heat treated by the steel manufacturer, but by the knife manufacturer. Knives are ground while annealed (soft), then usually heat treated in large batches. These large batches are where the variation comes from. The statistical process control/six sigma processes that are in place are there to ensure that no more than "x" percent (usually far less than .3%) have flaws. The variance comes from where the blades are in the ht oven (and other stuff like that).

At least that's how I understand it.
 
I've heard the theory about the placement in the oven. Somewhat makes sense. But then, if this were known to produce rejects...why not just minimize warranty claims by...not placing blades in those few (I guess) square inches?
 
The problem as I understand it, is that it is just not that simple. It's not a "this place in the oven produces rejects", it could be more of a "this area of the oven has a 3% chance of producing a defect, vs .005%" or something like that. That makes the decision harder. Now the manufacturer has to decide between operating at higher efficiency (meaning, not all of the area in the oven is being used because of our guess), or lower amounts of defects.

A company "may" decide that is a better financial choice to use that "spot", and sell them all, accepting that one in 20 "may" have to be replaced.

And again, I don't have inside knowledge. I just know that any number of factors could impact the ht of a blade, and its not as cut and dry as it may seem, especially in bulk. In fact, you've probably noticed that production knives have a range of hardness, rather than an exact measure. This is because they usually don't check every blade in the batch, they just spot check a few to confirm that the results were "according to plan". Custom knives are usually checked individually, so they're much more accurate.

Anyway, just some more thoughts. I'm no ever expert. Perhaps a manufacturer rep can speak to this more specifically, as all I've got to go off of is what I learned about statistical process control in college.
 
I'd love to here some thoughts from the manufacturers regarding failure due to the fault of heat treatment.
 
One difficulty is that the steelmakers suggestions are for typical applications of their product. Most steels have more common uses than knives so their recipe is not often the best for knives !! That's where you as a knife maker should experiment to get the best for a1/8" cross section rather than a 1" for example.
 
쌍칼잡이;15656189 said:
Here is a video about TOPS. Although the content is generally about how their knives are made, it does mention about thwir heat treatment (differential heat treatment)
https://youtu.be/JR7KLWx6aYg
Click to expand...

Very cool video, thanks. I always thought that tops had Rowen do their HT. Guess not. Also, I had no idea that their knives were Diff heat treated.

But back to mfg HT. I doubt that the super high production manufacturers have a very involved heat treat and I would not be surprised if their HT ovens hold a crap load of knives. Finding the sweet spot in the oven is where the best knives will come from. Just look at the pocket knife video above and how the blades are piled together. Do you think there will be a high number of blades that do not receive proper HT?

But I don't think a blade chipping is the sign of a poor HT. There are way to many factors for that.
 
Here's a shop tour video from Peter's Heat Treat where a lot of manufacturers send their stuff for HT.

[video=youtube;OvC4M_JrJlw]https://www.youtube.com/watch?v=OvC4M_JrJlw[/video]
 
philllll said:
Here's a shop tour video from Peter's Heat Treat where a lot of manufacturers send their stuff for HT.

[video=youtube;OvC4M_JrJlw]https://www.youtube.com/watch?v=OvC4M_JrJlw[/video]
Click to expand...

Never knew about these guys, and yet I go to school a few blocks away.
 
ocnLogan said:
The problem as I understand it, is that it is just not that simple. It's not a "this place in the oven produces rejects", it could be more of a "this area of the oven has a 3% chance of producing a defect, vs .005%" or something like that. That makes the decision harder. Now the manufacturer has to decide between operating at higher efficiency (meaning, not all of the area in the oven is being used because of our guess), or lower amounts of defects.

A company "may" decide that is a better financial choice to use that "spot", and sell them all, accepting that one in 20 "may" have to be replaced.

And again, I don't have inside knowledge. I just know that any number of factors could impact the ht of a blade, and its not as cut and dry as it may seem, especially in bulk. In fact, you've probably noticed that production knives have a range of hardness, rather than an exact measure. This is because they usually don't check every blade in the batch, they just spot check a few to confirm that the results were "according to plan". Custom knives are usually checked individually, so they're much more accurate.

Anyway, just some more thoughts. I'm no ever expert. Perhaps a manufacturer rep can speak to this more specifically, as all I've got to go off of is what I learned about statistical process control in college.
Click to expand...

Interesting, and appreciated.
 
Moonw said:
I've heard the theory about the placement in the oven. Somewhat makes sense. But then, if this were known to produce rejects...why not just minimize warranty claims by...not placing blades in those few (I guess) square inches?
Click to expand...

Because they do not have thermocouples in many places within the oven to know exactly the best place to locate the blades or what adding a ton of blades spaced half an inch apart does to the HT of many blades. They guess and you gamble.
 
There are so many factors, heat up time, cool down times, batch sizes, air pressure, all that sort of thing will be making very slight changes to the process. The trouble would be, which of those things is the variable that matters. Maybe the one factor that really matters (I dunno, daily strength of the earth's magnetosphere) might be the hardest to control for, or even detect. Cakes fail for any number of reasons, heat treat isn't simpler than a cake. If most of the time you are within your window, then most of the time it works out as well as it should. But maybe something causes a gravitation bubble to stick to the blade during quenching, and that causes a surface stress. Without a lot of x-ray how would you know? even then, how would you know that was the cause, and not a slight contamination of the material that lead to a defective section.

the simple truth is that there is a large amount of metallurgy that is really close to alchemy. We might know what works, but not always why. I know there was some big excitement back when the ISS was being planned as there was talk of a foundry, so that the effects of micro-gravity could be studied in micro-crystaline structures in steel, and other materials (titanium alloys and ceramics) We know a lot, but that also means the holes in the knowledge are just that much more interesting.
 
My bigger question though are knife failures caused by a heat treat. EG "I can't get this knife sharp after the third sharpening...it must have a bad heat treat, even though everyone else seems to not have a problem with it and it's a powdered steel." Do you think it's the heat treat in this case or the lack of diamond sharpening tools.
 
cchu518 said:
My bigger question though are knife failures caused by a heat treat. EG "I can't get this knife sharp after the third sharpening...it must have a bad heat treat, even though everyone else seems to not have a problem with it and it's a powdered steel." Do you think it's the heat treat in this case or the lack of diamond sharpening tools.
Click to expand...

Again, way to many factors to just blame it on HT. If it holds an edge well, and performance is good, and you just can't get it sharp, it could be many things including sharpening technique, stones used, etc. In other words there will be more than one factor to show you that HT is bad.
 
Cobalt , a commercial HT company does not guess ! They have it all figured out.How far from the oven walls you can go etc.

cchu518 , Knife makers , both knife companies and small makers often want to make it fast and grind dry or grind too fast and that means over heating the edge. Remove that damage by grinding wet and not try to take off too fast .
 
Cobalt , a commercial HT company does not guess ! They have it all figured out.How far from the oven walls you can go etc.

cchu518 , Knife makers , both knife companies and small makers often want to make it fast and grind dry or grind too fast and that means over heating the edge. Remove that damage by grinding wet and not try to take off too fast .
 
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