Alloy banding / Carbide segregation

It's interesting in any way. You don't notice a lack of performance in the blade, just like I didn't in my Hitachi Blue blade from the other thread. It was suggested that my blade was a heat treatment "problem" but the performance suggests otherwise. I suspect we sometimes luck out with cool effects that don't have performance negatives. I think my blade was some segregation, as the previous HB blade I did did not harden properly so I cycled this one like it was 52100. I found it was wearing belts out very quickly, so I gave it a 4h subcritical anneal. Being 1.1 to 1.2% carbon, I think carbides started segregating with the cycling.

In any event, the customer loves it. It's his favorite knife in the kitchen, and he has quite a few of mine. He knows that I will replace the knife if it shows any negative effects, but so far, he's thrilled. He's been using it for at least four months now, maybe 6. I'd have to look back at the records.
 
Abstract
The life of through-hardened 52100 anti-friction bearing components is improved if the excess carbides, undissolved during austenitization, are small and uniformly dispersed. One kind of carbide-refining heat treatment consists of 1) dissolving all carbides, 2) isothermally transforming the austenite to pearlite or bainite, and 3) austenitizing, quenching and tempering in the usual manner. Each step in this sequence of treatments was investigated, and the behavior of pearlitic and bainitic microstructures during subsequent austenitization was contrasted with the behavior of ferrite/spheroidized-carbide microstructures. It was shown that: 1) The usual hardening treatments given spheroidize-annealed bearing components result in an inhomogeneous microstructure, possibly due to the faster dissolution of carbides near austenite grain boundaries. 2) Austenitization of pearlite or bainite produces very uniform dispersions of ultra-fine carbides on the order of 0.1 µm diameter or less. 3) Specimens with ultra-fine carbides tend to have more retained austenite. 4) The rate of coarsening of ultra-fine carbides at austenitizing temperatures of 840°C and below, is slow enough so that conventional furnace heat treatments are satisfactory for producing this microstructure.
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http://link.springer.com/article/10.1007/BF02643140

I suspect the bolded part is what happened to my steel.
 
I'm no pro on this topic either, but I've seen similar effects on a lot of my knives. There is a distinct 'pattern' like very fine random damascus. It usually can only be seen when etched and is mainly above the hardening line on clay quenched and differentially heat treated blades.

I get this a lot on my 1075 blades. It seems like it can't be alloy banding because 1075 doesn't have too much in the way of extra alloying. I can get it on 1095 too. It seems like the stuff alot of folks call wootz. It also looks exactly like what a book I have on ancient weapons refers to as 'watered' steel. Evidently, many of the blades showing this 'watered' pattern were superior blades (for the time period that is) because it meant they were high carbon steel. Maybe this is the carbon segregation?

In any case, it looks pretty cool and I haven't noticed any detrimental effects on performance and I test my blades pretty hard.
 
I bought a Verhoeven article on the banding from JMEPEG through Springer. In hypereutectoid steels (52100 in this case) there are a few methods and processes that result in the banding. Spheroidizing, and quenching from bainite will create the banding. The banding requires carbide formers, Cr and Si were both mentioned. Quenching from pearlite will not create the banding. The quench at the final step of thermal cycling may be the process that caused my banding, but that's a guess as I just cooled to black and quenched. A low austentizing temp will not disolve the carbides, but a high temp will. I'll have to re read this a few times to really grasp it. The divorced eutectoid transformation was discussed, but I have some reading to do to get a better grasp on this. The process of banding in hypereutectoid steels is different from hypoeutectoid steels.
 
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Blue#2(for most low alloy carbon steel as well) ht aust grain diameter is below 20um. At this micro level, it either all fuzz/grey or not visible at all.

Pattern shows in your chef knife... Maybe, high mart% mixed with % of fern/finger cementites <= it might even enhance edge slicing (back/forth) performance, while giving up a tad on push cutting. Regardless, your customer is happy with it, that's a good bottom line. Sorry, my post on W2 thread was purely interested in guessing the pattern, ignoring performance altogether.

Willie71 said:
http://link.springer.com/article/10.1007/BF02643140

I suspect the bolded part is what happened to my steel.
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edit to add: what a coincident, this morning someone asked me about DET & UHC. Basically, I wrote: gap/space between spheroidized carbides are in 1-4um ...
 
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J. Doyle said:
I'm no pro on this topic either, but I've seen similar effects on a lot of my knives. There is a distinct 'pattern' like very fine random damascus. It usually can only be seen when etched and is mainly above the hardening line on clay quenched and differentially heat treated blades.

I get this a lot on my 1075 blades. It seems like it can't be alloy banding because 1075 doesn't have too much in the way of extra alloying. I can get it on 1095 too. It seems like the stuff alot of folks call wootz. It also looks exactly like what a book I have on ancient weapons refers to as 'watered' steel. Evidently, many of the blades showing this 'watered' pattern were superior blades (for the time period that is) because it meant they were high carbon steel. Maybe this is the carbon segregation?

In any case, it looks pretty cool and I haven't noticed any detrimental effects on performance and I test my blades pretty hard.
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I see some damascus like pattern in almost every blade we etch here, usually subtle. But nothing close to the damascus like pattern in the W2 blades I've posted. I'll see if I can find a photo of one of the others.
 
There are many different types of processing of steel one may produce banding more than others. As steel solidifies you will get dendrites . You want them broken into little pieces !! But the bigger the original
cross section the bigger the dendrites. The light colored pieces you see in a wootz blade are the broken dendrites ! The best solution is the use of one of the "powder Metal" methods like CPM.

Willie , did Verhoven go into the details of the processing , such as time ? Some steels have a very long time to get to bainite [thinking here of industrial things.] As I'm retired I don't get all the research unfortunately !
I was involved with Timken's continuous casting process which goes back a few years but it's microstructure was better than pouring large ingots.

J.D. , that 1075 ,any idea where that was from ? Some places can mess up any steel !
 
This has been an informative thread for sure.

The 1075 I got was from Aldo, everytime. I've ordered at least 3 different times at least a year apart and all of the 1075 does it. Again, performance seems quite fine but since every piece I've gotten will produce the banding, maybe there's still something left on the table? I don't know. Like Don said, it's VERY subtle and usually can't be seen even the first couple etchings. It's repeated etching and polishing that brings it out.
 
mete said:
There are many different types of processing of steel one may produce banding more than others. As steel solidifies you will get dendrites . You want them broken into little pieces !! But the bigger the original
cross section the bigger the dendrites. The light colored pieces you see in a wootz blade are the broken dendrites ! The best solution is the use of one of the "powder Metal" methods like CPM.

Willie , did Verhoven go into the details of the processing , such as time ? Some steels have a very long time to get to bainite [thinking here of industrial things.] As I'm retired I don't get all the research unfortunately !
I was involved with Timken's continuous casting process which goes back a few years but it's microstructure was better than pouring large ingots.

J.D. , that 1075 ,any idea where that was from ? Some places can mess up any steel !
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I'll look through the article for details tomorrow. Times, cooling rates from different temps and structures were discussed. In one section, cooling rates was not causal, but I need to read more to see if that was just for that condition. It was a lot to take in. He was clear that the processes were different from hypo and hyper. Whether HB2 is similar enough to 52100 is another question. He talked about needing the carbide formers for this to happen. Fe + C + X(carbide former) so I think it's likely.
 
For those who didn't see the blade in the other thread, here it is:

26944044063_3014f51e26_b.jpg
[/url]image by Wjkrywko, on Flickr[/IMG]

If you zoom in, you can see the pattern quite clearly above the Hamon, it's more broken up below it, but the pattern is there at the tip. It's a swirly sort of random pattern.
 
This blade is from the 'clean' W2 and shows a very fine wootz like pattern. I can't find a photo of one with the fine random like pattern, it's hard to pick it up in a photo.

 
Don, the banding in your old stock was mentioned in the article. That steel likely came from the top center, the last point to freeze at the mill. He said this type of banding will not be broken up at forging temps or through normalization. The other type of banding like my HB2 blade and the last pic you posted are caused by our cycling of the steel. We can erase these through high enough heat. Your old steel is caused by primary carbides, where our subtle banding is caused by secondary carbides.
 
Willie71 said:
Don, the banding in your old stock was mentioned in the article. That steel likely came from the top center, the last point to freeze at the mill. He said this type of banding will not be broken up at forging temps or through normalization. The other type of banding like my HB2 blade and the last pic you posted are caused by our cycling of the steel. We can erase these through high enough heat. Your old steel is caused by primary carbides, where our subtle banding is caused by secondary carbides.
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Now starting to sink in. Make sense, Warren.
 
When you start out with a 20"x20" ingot it takes a long time to cool and in that time "massive carbides " form which are a real pain to deal with if you're using large cross sections . Only a good bit of forging to smaller sizes will break it up. I worked with those tool steel sections with frustrations !! That's why when I learned about the CPM steels I was very interested . I saw them at a gun show where knife makers were using it when it first came out ! ~ 1970 ----I told you Don, I've been there , done that ! LOL
 
mete said:
When you start out with a 20"x20" ingot it takes a long time to cool and in that time "massive carbides " form which are a real pain to deal with if you're using large cross sections . Only a good bit of forging to smaller sizes will break it up. I worked with those tool steel sections with frustrations !! That's why when I learned about the CPM steels I was very interested . I saw them at a gun show where knife makers were using it when it first came out ! ~ 1970 ----I told you Don, I've been there , done that ! LOL
Click to expand...

I know Mete and have great respect for you and your knowledge.
 
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