Questions for Cutlery Gurus

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-Kiku-

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Do you consider yourself fairly knowledgeable in cutlery, particularly metallurgical aspects of Japanese cutlery? If so, I have some questions for you:

1. Why are all kitchen knives made of SRS13 or SRS15 alloys clad in much softer SUS405 stainless steel? For a couple of weeks, I've been hunting around for a nakiri made of either SRS13 or SRS15. Every such nakiri was found to be clad in much softer stainless steel. Isn't SRS15 hard and tough enough to stand on its own? It is considered to be a fully stainless steel. Why would it need to be protected by another stainless steel? If the cutting core was made of something more corrosion-prone such as YXR7, then I can understand the reason behind the cladding. SRS15 is also considered to be a tough material, much tougher than ZDP189 so it's not like there's a much risk of chipping. So again, why the clad?

2. What exactly is the difference, if any, between SUS405 vs ANSI405? Are they both same stainless steel but made by the same/different manufacturers under different standards?

3. Has anyone here been crazy enough to own or have had experience with kitchen knives made of ZDP189? While I was searching for SRS15 nakiri, I did happen to come across several sites selling cutlery made of ZDP189. ZDP189 is a fine steel, but it's only a semi-stainless steel at best. And using it for food prep seems ... questionable, especially given the relative instability of ZDP189 edge at acute angles. ZDP189 also stains very easily from handling anything even remotely acidic. Vulnerability to acid is ZDP189's Achilles' heel. Knowing this, why would anyone be crazy enough to sell cutlery made of ZDP189??

Editor's Note: If you're crazy enough to make one, there'll always be someone who's crazy enough to buy it.
 
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-Kiku- said:
Do you consider yourself fairly knowledgeable in cutlery, particularly metallurgical aspects of Japanese cutlery? If so, I have some questions for you:

1. Why are all kitchen knives made of SRS13 or SRS15 alloys clad in much softer SUS405 stainless steel? For a couple of weeks, I've been hunting around for a nakiri made of either SRS13 or SRS15. Every such nakiri was found to be clad in much softer stainless steel. Isn't SRS15 hard and tough enough to stand on its own? It is considered to be a fully stainless steel. Why would it need to be protected by another stainless steel? If the cutting core was made of something more corrosion-prone such as YXR7, then I can understand the reason behind the cladding. SRS15 is also considered to be a tough material, much tougher than ZDP189 so it's not like there's a much risk of chipping. So again, why the clad?

2. What exactly is the difference, if any, between SUS405 vs ANSI405? Are they both same stainless steel but made by the same/different manufacturers under different standards?

3. Has anyone here been crazy enough to own or have had experience with kitchen knives made of ZDP189? While I was searching for SRS15 nakiri, I did happen to come across several sites selling cutlery made of ZDP189. ZDP189 is a fine steel, but it's only a semi-stainless steel at best. And using it for food prep seems ... questionable, especially given the relative instability of ZDP189 edge at acute angles. ZDP189 also stains very easily from handling anything even remotely acidic. Vulnerability to acid is ZDP189's Achilles' heel. Knowing this, why would anyone be crazy enough to sell cutlery made of ZDP189??

Editor's Note: If you're crazy enough to make one, there'll always be someone who's crazy enough to buy it.
Click to expand...

After weeks of independent search, I finally have the answers to my original questions:

1. Japanese kitchen knives are made of very thin cutting core (typically less than 1 mm thickness) clad in softer stainless steel. There are two reasons this.
  • For ease of putting initial bevel when the knives are made. Cutting cores are typically made of harder metals, thus they cause more wear and tear on the tools used to grind them. To minimize wear and tear, cutting cores are made very thin (typically less than a 1 mm), and clad in softer stainless steels such as SUS405 or SUS410 for added strength (so the knife doesn't snap in two) and protection (against corrosion).
  • For ease of sharpening. Most people use their kitchen knives much more often than their sporting knives. For this reason, kitchen knives will typically require sharpening more frequently. Thinner core means easier sharpening and their sharpening stones will be subjected to less wear and tear.
2. SUS (Steel Use Stainless) is the JIS (Japanese Industrial Standard) designation for stainless steels. ANSI stands for American National Standards Institute. Both SUS405 and ANSI405 refer to the same grade of stainless steel. ANSI405 also goes by AISI405. AISI = American Iron and Steel Institute. For knife collectors, all we need to know is that SUS405 = ANSI405 = AISI405. SUS405 and SUS410 are common clad materials in Japanese cutlery applications.

3. Cutlery manufacturers make knives out of ZDP-189 precisely due to its amazing edge-retention. Vulnerability to acidic food is somewhat exaggerated and often a non-issue as long as the knife is cleaned immediately after use. If one needs to cut acidic food continuously for long periods of time, however, then that person should consider something other than ZDP-189.

As for the 'chippiness' of ZDP-189, I spoke directly with the several manufacturers of ZDP-189 Japanese kitchen knives who all assured me that their knives will not chip as long as their knives are used in a proper manner for which they are intended. That means don't use a brand-new ZDP-189 nakiri to cleave that huge pineapple or coconut and expect things to turn out fine. Nor should J-knives be placed in a dishwasher or left in the sink unwashed for an extended amount of time, etc. Many of the complaints stemming from users about J-knives are often unfounded and damages were usually result of improper handling and misuse.
 
I recommend you not worry too much about steel types other than stainless or reactive. It is vastly more important getting a knife from a reputable maker. Even after you get a knife from a reputable maker, you will likely not be able to tell the difference in steel types without extensive use and sharpening of several different examples.
 
I had an interesting experience with a William Henry pocket knife that has a ZDP-189 San Mai blade with a 410 cladding. When exposed high heat and humidity, the 189 exhibited less rust than did the 410, and the corrosion was quite superficial.
 
tiguy7 said:
I had an interesting experience with a William Henry pocket knife that has a ZDP-189 San Mai blade with a 410 cladding. When exposed high heat and humidity, the 189 exhibited less rust than did the 410, and the corrosion was quite superficial.
Click to expand...

ZDP-189 has 20% Chromium, 410 has 12%Chromium.
 
tiguy7 said:
I had an interesting experience with a William Henry pocket knife that has a ZDP-189 San Mai blade with a 410 cladding. When exposed high heat and humidity, the 189 exhibited less rust than did the 410, and the corrosion was quite superficial.
Click to expand...

Slim278 said:
ZDP-189 has 20% Chromium, 410 has 12%Chromium.
Click to expand...

ZDP-189 may have the higher Cr but unlike the SUS410, most of that Cr is locked up in carbides, rendering the ZDP-189 semi-stainless at best. SUS410 is considered a fully stainless steel with good corrosion resistance properties (as long as it was properly heat-treated.)

Corrosion resistance is also a function of surface finish. All else being equal, satin-finished surface will render the material more corrosion-prone than those of highly polished surface.
 
-Kiku- said:
ZDP-189 may have the higher Cr but unlike the SUS410, most of that Cr is locked up in carbides, rendering the ZDP-189 semi-stainless at best. SUS410 is considered a fully stainless steel with good corrosion resistance properties (as long as it was properly heat-treated.)

Corrosion resistance is also a function of surface finish. All else being equal, satin-finished surface will render the material more corrosion-prone than those of highly polished surface.
Click to expand...

You are correct in this as the chromium oxide layer is what gives the corrosion resistance.
 
-Kiku- said:
ZDP-189 may have the higher Cr but unlike the SUS410, most of that Cr is locked up in carbides, rendering the ZDP-189 semi-stainless at best. SUS410 is considered a fully stainless steel with good corrosion resistance properties (as long as it was properly heat-treated.)

Corrosion resistance is also a function of surface finish. All else being equal, satin-finished surface will render the material more corrosion-prone than those of highly polished surface.
Click to expand...

This was my understanding of the difference between 410 and 189. The former is killer stainless, the latter is semi-stainless. Yet my experience was the opposite of what was expected. The surface finishes of each area of the blade were identical.
 
T tiguy7 , that's very unusual. But without a full knowledge of the conditions leading to that outcome, we can't draw any objective conclusion from a single incident. If there were many other owners of the exact model of your William Henry pocket knife, who also experienced similar incidents with theirs under similar environmental conditions, usage and care, etc., then you could be onto something. Otherwise, a single incident by itself doesn't mean much. Maybe yours came from a bad batch? :confused:
 
image.jpeg image.jpeg I don't think it was a bad batch because I have samples from many batches. My placket carry is an accelerated corrosion test venue in the summertime. When I go on long bicycle camping trips in the summer, the elevated temperatures and humidity go after the corrodibles. After 1000 or so sweaty miles, the shortcomings of various materials are revealed. I have used different knives on different trips, and the results were often surprising.image.jpeg
 
tiguy7 said:
When I go on long bicycle camping trips in the summer, the elevated temperatures and humidity go after the corrodibles. After 1000 or so sweaty miles, the shortcomings of various materials are revealed.
Click to expand...

Aha! There's your culprit. Instead of your entire blade drenched thoroughly and homogeneously in sweat, there was only a localized contact. And localized contact = localized corrosion.

SUS410 is a full-fledged stainless steel with quite good corrosion resistance. But not against salt!
 
The 410 exhibits more localized corrosion than the 189 in my experience.
 
T tiguy7 , Wow! Are all those yours? If so, you have a lot of pocket knives!

tiguy7 said:
The 410 exhibits more localized corrosion than the 189 in my experience.
Click to expand...
Then there's something unique about your sweat, if it's your sweat. Exactly where you do keep your knife when you take it with you on your bicycling trips?
 
image.jpeg Even if my sweat was Aqua Regia (dissolves Gold), it shouldn't affect the 410 more than the 189, but it does. That is the mystery. My opinion of 189 corrosion resistance has improved.
The placket carry allows me to access the knife with either hand even when seated. The knife weighs only 55gm, so the shirt doesn't sag.
My knives are not pocket knives, they are placket knives.
 
Mystery indeed. FYI, Iodine solution - the dark brown liquid that they used to rub on wounds - will also dissolve gold. Sometimes I would use iodine soln to etch gold thin films in a nanofab, or various acids depending on what I am etching on patterned wafers. But I am not aware of anything that will attack SUS410 while leaving ZDP-189 alone. You'll have to consult a chemist or a metallurgist for that.
 
Japanese knife making and the steels used confuse and intrigue me. Folding knifes and the steels used in them were fairly easy to grasp not so much with Japanese knives. So I put my trust in my local knife guys. Luckily I live minutes away from Carbon Knife Co. I can spend the entire day there. Last time it only took me 3 hours to pick out a knife from the hundred or so on the wall. I narrowed it down to 3, one of them was a Yoshikane Gyuto. The shop keep told me he himself owned 4 of their knifes. I was sold. The core steel is SDK which is a tool steel presumably similar to d2 here. Don’t quote me on that. In conclusion it’s the best knife I’ve owned and I plan to have it for life. Here’s a link

https://carbonknifeco.com/collectio...ikane-nashiji-skd-gyuto-210mm-chestnut-handle
 
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