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 Post subject: SLD Steel
PostPosted: Fri Feb 20, 2015 4:58 pm 
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I asked my friend Dr. O about SLD steel and he was very generous with giving me a detailed answer about it and how it's used, heat treated, etc. Take a look.

Dear Mark,

Thank you for your e-mail of February 18, 2015 in regard to the hardness of SLD
and sorry for the delay in replying.

Please let me answer as follows.

Speaking of SLD, we normally understand it as one of the steels in the industrial field,
where the hardness range HRC64-65 shows HSS. HSS fits cutting tools etc, but does
not fit dies etc where toughness is required.

SLD is not developed as HSS but as a die-steel. Any steels of this category are
originally designed to work most effectively with enough toughness by reducing the
hardness to be a little softer than HSS around HRC60.
Of course, each elements are different, but I am now focusing on the hardness only.

I attach herewith a copy showing the hardness curve of SLD when hardened and
tempered.

The hardness at 0 degree Celcius means the hardness after quenching. It depends
on the temperature. About HRC62 in case of 975dgrC, and HRC65 in case of 1,025
& 1,050dgrC. Supposing the quenching at 1,025 or 1,050dgrC and tempering around
100dgrC, HRC64-65 might be possible in theory. But in practice, in case of clad steels,
the hardness tends to be a little lower by say 1-2points. On the contrary, forging tends
to make it higher by say 1-2points.

As to the tempering, it is normally made in 150-200dgr C to improve toughness.
I never say that there is no effect on it in case of 100dgr C tempering, but cannot
say to be enough.

As a whole, considering the steel according to the theory, what I think when hearing
the hardness of SLD around HRC 64-65, it is not the hardness range of die-steels,
disregards the original performance the steel itself originally has, and risky to be used,
because the knife seems to be too brittle, to be easily chipped off and not to have
enough wearing.

I hope that this answers to your question.


With kind regards.

Dr. O.



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 Post subject: Re: SLD Steel
PostPosted: Fri Feb 20, 2015 5:06 pm 
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 Post subject: Re: SLD Steel
PostPosted: Fri Feb 20, 2015 6:11 pm 

Joined: Tue Oct 28, 2014 12:29 am
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Good discussion of the steels characteristics and heat treatment response but, did you ever find out if the Konosuke GS knives are SLD steel?

I just ordered one of the 150mm GS Pettys so, I guess I'll find out how the edge holds up over time.

Jack


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 Post subject: Re: SLD Steel
PostPosted: Fri Feb 20, 2015 6:46 pm 
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I bought my mom an SLD knife last x-mas(Tadafusa), and it has held up very well. Only problem was that she has a habit of dragging the knife sideways(edge down) across the cutting board to move product out of the way. This sideways dragging on the edge caused some slight chipping, so I pointed out that it might be better to flip the knife upside down onto the spine to move product. Imo, this would be a problem for any knife tho, that is very thin at the edge and composed of HH steel.

Other than that, the knife gets sharp, holds a good edge and is stain resistant(more or less). Good steel.



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 Post subject: Re: SLD Steel
PostPosted: Fri Feb 20, 2015 7:18 pm 

Joined: Thu May 24, 2012 6:20 am
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I have the Addict SLD from Kono. In my limited ability to discern differences between steels, I find it compares well with other semi-stainlesses like the HD steel.


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 Post subject: Re: SLD Steel
PostPosted: Fri Feb 20, 2015 7:50 pm 

Joined: Thu Mar 21, 2013 7:06 pm
Posts: 306
Cedar,

Do you find it harder to sharpen? The semi stainless in my tkc and carbonext are very nice to grind and deburr, but I've sharpened some D2 outdoor type knives (Queen/KOA) and they've been considerably harder to work with. Still absolutely doable and took great edges, just more work to get there. As far as I know SLD is the same as D2.

If you do find it similar in sharpening, maybe it's the difference in edge thickness that accounts for the ease, or maybe a difference in heat treat?


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 Post subject: Re: SLD Steel
PostPosted: Fri Feb 20, 2015 8:06 pm 

Joined: Thu May 24, 2012 6:20 am
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"maybe it's the difference in edge thickness that accounts for the ease"

I'm guessing this is a big part of it. The Addict is basically HD thin.


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 Post subject: Re: SLD Steel
PostPosted: Fri Feb 20, 2015 9:06 pm 
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Thanks for posting that Mark.

This is a good but lengthy write-up on D2 as a knife steel: http://www.knivesillustrated.com/does-d ... ood-knife/

I'm still skeptical about buying another knife in SLD/D2. I view it a bit like VG10 in this sense: there are certain bad tendencies the steel is known for unless heat treated just right by a skilled smith. Run of the mill VG10 knives are thought to chip easily while some knives, like Ryusen, are considered to be done very well by those that have used them. Many D2 knives, including the couple that I've used, are thought to have very large grain structure and carbide size, limiting their ability to refine in sharpening. Some claim you can tell if D2 has a large grain structure and carbide size by the type of polish finish it takes- smooth and it's fine, orange peel and its course.

From what I've read in several articles and various knifemakers forums, D2/SLD is a tricky steel to work with. Forging is said to be next to impossible because it must be kept close to 2000°F while hammering and begins to air harden below 1925°F- that's not a very wide range. Variation in any step of the heat treat can dramatically affect the grain structure and carbide size. If the maker is very skilled and has tightly controlled forge temps, the carbides can be kept small and allow for good refinement in sharpening. Unskilled smiths or innacurate equipment can cause grain growth and carbide size to top 25-30 microns and be brittle at higher hardness. Some have employed cryo-quenching to improve toughness at a hardness where it might have been too brittle before.

If Kono has been making the Richmand SLD line for some time and you haven't noticed some of these negative tendencies, then perhaps they are doing a very good job with it. 61-62 seems to be the ideal range for D2- any lower and it loses its abrasion resistant advantage to edge retention, any higher an it can be too brittle. A 63-64HRC blade seems possible if cryo-quenching really does add 25% of toughness like some have claimed- although how they are measuring that objectively I don't know.



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 Post subject: Re: SLD Steel
PostPosted: Fri Feb 20, 2015 9:20 pm 
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Luca and cedar, it's my theory that the grain structure and carbide size, as a result of the heat treating, would greatly impact sharpening. Finer carbide size, to me, would make it easier to sharpen as the carbides are easier to displace than larger carbides in courser steel. The large carbides resist sharpening more than steel, causing the blade to skate over the sharpening medium.

This was one of the original marketing points of PM steels- that the smaller, more distributed carbides made it easier to grind and finish at the same alloy content.



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 Post subject: Re: SLD Steel
PostPosted: Sat Feb 21, 2015 1:06 am 

Joined: Thu May 24, 2012 6:20 am
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Smokie, you points about the limitations of SLD seem legit. I am not an exceptional sharpener, but I like that Addict plenty well. It may be that kono has nailed that heat treat.

...it may also be that I am full of crap :roll:


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