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 Post subject: Edge Chipping/Rolling
PostPosted: Thu May 09, 2013 7:17 pm 
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I would like to be more clear on edges rolling or chipping on certain steels to better help in general for touch ups. I know the general rule is the edge tends to roll on knives with softer stainless, European knives, and be more chippy with J-knives.

My questions are how about the edges on harder stainless, 60+, do they still roll or do they tend to be more chippy or does it depend on the particular stainless?

Carbon steels, do they all tend to be more chippy or does the hardness and type com into play to rather they chip or roll?

Or am I totally off base and they just dull more so than chip or roll if used properly.



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 Post subject: Re: Edge Chipping/Rolling
PostPosted: Thu May 09, 2013 8:27 pm 
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These are, IMHO, too general to answer accurately.

Even the same stainless, let's us AEB-L, could roll or chip depending on it's heat treat, the cutting surface, your method, how thinly it's ground, how it's sharpened, etc. Too many variables to make blanket statements.



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 Post subject: Re: Edge Chipping/Rolling
PostPosted: Thu May 09, 2013 9:18 pm 
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That's part of what I'm looking for Adam. Can I assume with your example of AEB-l that with a lower HCR it will tend to roll but with a higher HCR it would be more chip prone. I would think the other variables you listed would just cause steels to chip or roll but not determine which they would do. It seems like the biggest factor would be the hardness but I have no idea how the metallurgy affects chipping/rolling.



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 Post subject: Re: Edge Chipping/Rolling
PostPosted: Thu May 09, 2013 9:45 pm 
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As a general rule, the harder the edge, the more likely it is to chip rather than roll. So, AEB-L at 58 would be a lot more likely to roll and at 61 it would be more apt to chip....yes. But, like I said earlier....that depends on a lot of other attributes as well.

But, even a steel hardened to 65 HRC if thin enough would roll and not chip. Reasonably, I don't think you could make a proper kitchen knife that would do that at that hardness. It's to make a point, not show an example.

I also don't think you could draw a conclusion based on what kind of steel it is. We have 3 major categories of steel available to knife makers today....powdered steels, stainless steels, and carbon steels....well, 4 I guess if you take damascus as a category. Soft carbon will roll the same as soft stainless. The problem in this query with powdered steels is that I don't really know of any one making soft powdered steel kitchen knives. I reckon soft powdered steels would roll as well, but I've never encountered one to verify that. Maybe I should try some day. :)

Hardness might hold the biggest share of the pie....but certainly not all of it....perhaps not even half.

If you put a gun to my head and asked at what point knives begin to chip and not roll, I'd say 60 as a general rule. I don't think stainless/carbon/powder/damascus would matter either. I think thickness of edge, how it was HT'd, convex or straight "V" edge, etc. matter though.



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 Post subject: Re: Edge Chipping/Rolling
PostPosted: Thu May 09, 2013 10:12 pm 

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On the topic of chipping, how many times can you chip and fix a gyuto before you figure you've taken off too much metal and have to move on?


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 Post subject: Re: Edge Chipping/Rolling
PostPosted: Thu May 09, 2013 11:12 pm 

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When it no longer serves a purpose. Keep repairing the chips, sharpening the edge, and thinning behind it till its just a worthless peice of metal. ive seen people use a "what use to be 240 gyuto" as a petty. of course there was no knuckle clearance left to chop with, but they still found the value in it to keep in their kit.



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 Post subject: Re: Edge Chipping/Rolling
PostPosted: Fri May 10, 2013 1:10 am 
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Thank you very much Adam, there is probably a lot more information in that answer than you think and it did help me to understand this subject better. Small pieces here, small pieces there and maybe someday I might half ass know something! Thanks again!



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 Post subject: Re: Edge Chipping/Rolling
PostPosted: Fri May 10, 2013 2:11 am 
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There are two major materials properties which relate to an alloy's tendency to chip or impact burr (which is a bending burr formed in a particular way). They are strength and toughness. Strength is the measure of how well a material resists permanent deformation; and toughness is the measure of how much deformation a material can take without breaking or tearing.

To some extent alloys are both tough and strong. The question is how strong, how tough, and how well the properties balance. The ideal alloy will be very strong, very tough, with the properties about equally balanced.

Hardness, to some extent, is a function of strength. Guys who know this stuff real well often say "hardness" when they mean "strength;" while guys who don't know it well at all say "hardness" because they don't know the difference.

Alloys which are very strong but not very tough will tend to chip rather than burr; while alloys which are very tough but not very strong will tend to burr rather than chip.

Hardness as an artifact of manufacturing mostly depends on heat treatment. A manufacturer wants to use the ideal type and amount of heat treatment to give the alloy its best hardness. This can be something of a moving target. Not long ago, knives made from 13C26/AEB-L were hardened to around 57-58RCH. Now though, 13C26/AEB-L which has been hardened to around 60-61RCH seems to present a better balance of strength and toughness and resists both impact burring and chipping.

Some steels, are susceptible to both burring and chipping. It's not uncommon with VG-10, for instance.

There are three major different kinds of hardness which relate to kitchen knives. Those are impact hardness, scratch hardness and indentation hardness. It's pretty obvious why the first two are important. Indentation hardness is only relevant because it stands as a reasonable metaphor for the first two kinds of hardness, and because it's usually the only kind of hardness measured and/or reported. Rockwell "C" hardness is one scale of indentation hardness.

The most important thing about C hardness is that it's reported and the male brain loves to think its making meaningful distinctions. But when one hardness figure is pretty close to another, the difference means far less than most people thing. Rockwell hardness is very difficult to measure accurately; manufacturer's numbers are often wildly optimistic; and not only does it not measure toughness at all, it doesn't directly those aspects of strength which are actually important.

How well balanced an alloy is for strength and toughness depends on its formula and how it's manufactured. More often than not, the most important element of strength is the amount of carbon. Carbon steels are often toughened with chrome. Stainless and semi-stainless steels are often toughened with molybdenum. A few carbon steels, including the excellent Aogami Super are toughened with both.

There are some rules about using formula composition and reported hardness figures to help guess what the materials properties will be, but the best strategy is to ask. Very hard steels can be very tough.

And then there's geometry...

Don't assume. Ask.

BDL


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 Post subject: Re: Edge Chipping/Rolling
PostPosted: Fri May 10, 2013 3:46 am 
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BDL your like an encyclopedia of information. Thanks for taking the time.



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 Post subject: Re: Edge Chipping/Rolling
PostPosted: Fri May 10, 2013 1:42 pm 
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As an engineer, I absolutely love the science behind heat treating steel. Getting to visit with guys like Devin Thomas about it is fascinating and you soon realize you don't know nearly as much as you thought. :)

This is probably getting way off topic, but I'm bored this a.m.

There are some steels that are extremely tough, but horribly inadequate in the strength department.

Here's a really interesting chart:

Image

Toughness in steel is it's ability to resist chipping or breaking....simple definition.

Wear resistance in steel is pretty self explanatory....how well it resists wear. This is the attribute that knife makers hate. High wear resistant steels are a biotch to grind.

The chart doesn't show strength. Strength is a steels ability to resist deformation....simple definition.

Strength and toughness are usually polar opposites.....raise the strength, lower the toughness. Makes sense, right? Raise the hardness of the steel, the more likely it is to chip (lower toughness).

As BDL stated, finding a great balance is the goal.

However, and this is especially true in kitchen knives, we have other factors to consider. We want a steel that is both tough, wear resistant, and strong...but also able to take a very keen edge.



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