Steel purification not composition is really matter?

[nozh2002]

It is interesting but with all this attention to composition nobody mention about how one or other steel is purified. I know that BG42 is purified by VAR - vacuum arc remelting, as well as 110x18MShd is purified by combination of VAR and ESR - electro slug remelting.

May be good properties of both this steel is due to this purification applied?

May be nonmetallic inclusion content - Nitrides and Oxides, is what really important?

Again 110x18MShd in same 440C but it feel much better (C=1.1-1.2 Mo<3 Mn=0.1-0.5 Ni=0.5 Cr=16.5-18 Ti=0.2 Cu<0.3).

Nobody really mentions how many non metallic inclusion points one or other steel has, but it may be very important, more important then composition itself.

Thanks, Vassili.

 

[HoB]

Well, sulphur and phosphore are known impurties, even though they are added on occation on purpose.

I was wondering the same. Historically, purity was all-important and gave the "swedish steel" its reputation (see Leonard Lee's book for explanation) and not all too long ago 154CM had fallen behind ATS-34 despite essentially the same composition because it wasn't manufactured to the same standards, thankfully that has been corrected for some years now.

The problem though, is that there isn't really a lot of accessible data on this so I fear most of it will remain speculation.

Beyond composition and purity I see another factor which is microstructure. It seem quite clear by now that two steels with essentially the same composition don't necessarily have the same microstructure. Since steel is an alloy you would expect steels with similar chemical composition to have a fairly similar microstructure as well, but this is clearly not the case. And until you know where and how your carbon, chromium etc. is distributed it is obviously very difficult to draw conclusions from the chemical composition.

 

[mete]

They are all important .Inclusions are either sulphides or oxides. The 154CM problem was one of inclusions and the custom makers complained that when mirror polishing you could see the inclusions ! Inclusions also tend to make steel more brittle especially tranverse impact strength. Vacuum refining removes much of that problem and powder steel like the CPM types have even less of a problem.The CPM types also have a carbide structure that is finer and more evenly distributed which is very important for toughness , ease of sharpening and wear resistance. While high quality alloy and stainless steels have less of a problem with inclusions and other impurities ,the steel industry is constantly developing new steels and refining old ones such as the addition of small amounts of rare earth metals .After all that you have to heat treat it properly !!!

 

[Cliff Stamp]

It seem quite clear by now that two steels with essentially the same composition don't necessarily have the same microstructure.

The microstructure is defined by the composition which is based on the thermodynamics of the phases. The precentages of alloy dissolved and carbide retained with a given soak temperature can be calculated (Verhoeven shows examples) very accurately as the metallury is well known. Landes has commented on this in detail on SwordForums on issues such as martensite needle size, retained austenite, carbide size, etc. on the basis of composition.

Now of course you are not dealing with an exact specification (is any theory) and experiment is always needed to check the principles. But experiment is also used to formulate and refine the theory and predict behavior which is the fundamental benefit of doing experimental work and extrapolating the theory. So if someone promotes something similar to D2 for fine edges then it isn't unreasonable to note this has a pretty severe problem because current materials science says that the carbide structure has to be very coarse.

The main variablity in composition is the method of manufacture, specifically ingot vs P/M because P/m will greatly reduce the level of segregation and carbide size. It will also give a much more consistent response to hardening because of the homogenous.

There is much promotion on how clean or consistent one steel is over another but rarely is this actually shown with proof and often is just used to argue a superior upgrade so this really can't be given a lot of weight.

Method such as Vassili noted have a significant effect for example on fatigue strength which would be important in very thin edges on knives, but are not as critical to wear resistance, hardness, etc. .

-Cliff

 

[Satrang]

Structure is dependent on a number of variable's, composition is just one. A significant factor is the amount of reduction from ingot to final product. 1 inch thick D2 has significantly coarser structure than material rolled to 0.125 thick. Carbides will break up and will orient to the rolling directions. Cross rolled sheet will have more uniform carbide distribution than unidirectionally rolled sheet. Thermal treatments such as annealling will also have an effect. Annealling at the mill and heat treatment after can coarsen the grains and precipitate carbides. As far as composition goes there is segregation caused by solidification of the ingots. The top is different from the bottom and the center is different than the outside. The point I'm trying to make here is that many variables are involved in making steel. Many of the variables are controlled by nature some are controlled by processing. Each manufacturer tries to make the process as consistent as possible but it is unique to each their own. Simply, for tool steels, cleaner is better, finer structure is better, and the more homogenous the structure the better. Better being defined as maximizing the material properties of the alloy.

 

[JayAndersson]

It is interesting but with all this attention to composition nobody mention about how one or other steel is purified. I know that BG42 is purified by VAR - vacuum arc remelting, as well as 110x18MShd is purified by combination of VAR and ESR - electro slug remelting.

May be good properties of both this steel is due to this purification applied?

May be nonmetallic inclusion content - Nitrides and Oxides, is what really important?

Again 110x18MShd in same 440C but it feel much better (C=1.1-1.2 Mo<3 Mn=0.1-0.5 Ni=0.5 Cr=16.5-18 Ti=0.2 Cu<0.3).

Nobody really mentions how many non metallic inclusion points one or other steel has, but it may be very important, more important then composition itself.

Thanks, Vassili.

VAR Vacuum Arc Remelting, hmm. Isn't melting by an electric arc furnace the first step. Going from recycled steel/ore to a steel billet? In my opinion doing vacuum arc REmelting would be uneccessary, I'm out on a limb here maybe but I believe thats not the way it's being done.

Some then use ESR. Is purification the purpose for this? I thought it was just to make the steel workable in hot condition like forging or hot-rolling. I might be way off though.

Satrang said:
"Carbides will break up and will orient to the rolling directions. Cross rolled sheet will have more uniform carbide distribution than unidirectionally rolled sheet."

I am pretty sure this is incorrect. All variations in the material in regards to the rolling directions will for sure be relaxed during the hardening of the material when there is a phase transition. The stress levels cross and along the strip can only be made during cold rolling. And there are several heating steps after that, including the high hardening temperature. The steel homogenizes and stresses are eliminated at high temperatures.

Are you suggesting that you can see a clear carbide orientation on your knife blade if put under the microscope? I doubt that is possible.

The purity of the steel is very important in my opinion. Far more than judging knife steels after carbon content which in my humble opinion is crazy.High level of purity, a balanced composition to avoid mega-carbides and a suitable heat treatment together gives the steel a uniform fine-grain structure that allows sharp edges and good edge retention.

//Jay

 

[Satrang]

Jay, absolutely you can see the primary carbide distribution and orientation in the steel. That is of course, those tool steels that have carbide content such as most stainless and tool steels. The term commonly used is carbide banding. The carbides will follow the grain direction. Thermal treatments can have some effect on the grain size but the orientation of the primary carbides will not re-allign during annealing etc. You get some to spherodize but they will not homogenize.

 

[JayAndersson]

Jay, absolutely you can see the primary carbide distribution and orientation in the steel. That is of course, those tool steels that have carbide content such as most stainless and tool steels. The term commonly used is carbide banding. The carbides will follow the grain direction. Thermal treatments can have some effect on the grain size but the orientation of the primary carbides will not re-allign during annealing etc. You get some to spherodize but they will not homogenize.

So is this valid only for primary carbides or both primary and secondary carbides? I define primary as being the big ones that comes from the melting state and due to saturation do not dissolve. If you mean only these I can see how these mega-carbides will align with the cold-rolling direction. But for a fine-grain structure I have been told that the structure is more or less completely uniform after the hardening.

//Jay

 

[Larrin]

So is this valid only for primary carbides or both primary and secondary carbides? I define primary as being the big ones that comes from the melting state and due to saturation do not dissolve. If you mean only these I can see how these mega-carbides will align with the cold-rolling direction. But for a fine-grain structure I have been told that the structure is more or less completely uniform after the hardening.

//Jay

Even in CPM steels the carbides follow the direction of the rolling. In carbon steels the carbides dissolve at the forging temperatures so it isn't as much of an issue. Primary carbides are those formed in casting. Sandvik and Uddeholm say that through the balanced composition and proper forging techniques that all of the primary carbides are broken up in steels like 12C27 and AEB-L, though not for 19C27 (too much carbide volume). Still, the more the steel is forged the more the carbides are broken up. The best way to get the smallest possible carbide size is to buy steel as close to final thickness as possible. Buying steel thick and grinding it down isn't always a good idea. Even for forgers I would recommend buying thin steel, as the factory's rolling is pretty much optimized for reducing carbide size. Ed Fowler is a proponent for reducing grain size through forging, but IMO, most of his grain size reduction comes from normalizing and triple quenching. But carbide size isn't as much an issue with simple forging steels.

 

[the possum]

Are you suggesting that you can see a clear carbide orientation on your knife blade if put under the microscope? I doubt that is possible.

Jay, absolutely you can see the primary carbide distribution and orientation in the steel. That is of course, those tool steels that have carbide content such as most stainless and tool steels.

When I made a big knife from ATS-34, I was grinding with a small belt sander. The scratches left by the sander went from spine to edge. Yet, even when you held the blade out at full arm's length, you could clearly see lines in the steel itself running lengthwise with the blade (from hilt to point).

 

[nozh2002]

VAR Vacuum Arc Remelting, hmm. Isn't melting by an electric arc furnace the first step. Going from recycled steel/ore to a steel billet? In my opinion doing vacuum arc REmelting would be uneccessary, I'm out on a limb here maybe but I believe thats not the way it's being done.

This is from RosArms website - I ask Vladimir to ask their metallurgist in Russia about ESR, because I heart it in Russian Blade Forum as well as article about Yasuki Steel Special mettion that they first in the West who start using ESR after USSR.

As you may see thay directly states that it is about nonmetalic inclusions - not S or P but Nitrides and Oxides actually. So what is this impurity points?
---------------------------------------------------------
...The research of 1966 ascertained that 110x18M steel grade is the one to meet all requirements. To decrease the content of nonmetallic inclusions, vacuum-arc remelting (VAR) was suggested.

Point analysis of maximal nonmetallic inclusion content

Nitrides Oxides
Conventional remelting 4 points 4 points
Electroslag remelting (ESR) 2 points 2 points
Vacuum-arc remelting (VAR) 1 point 0.5 - 1.0 points

Metals undergoing double remelting (ESR + VAR) have half as many nonmetallic inclusions as compared with ESR plus a reduced gas component. The metal density is greather than when applying ESR alone. Thanks to that we have better plastic properties, improved polishabiliti, and good strength characteristics. Milled carbides help to grind the blade's edge and keep it constantly sharp.

All the above factors prolong the bearing service life.

Electroslag remelting process (ESR) is an arcless process of remelting a metal electrode in a flux bath. Electrofluxed metal is noted for its premium quality, lower impurity and gas content, improved micro- and macrostructure, lower anisotrophy (directional property), twice as high mechanical properties, two up to five times more reduced nonmetallic inclusion content (such as oxides, sulphides, globules), higher wear-resistance and contact resistance, plus minor improvment of other characteristics. Electrofluxed metal is used in the production of steels and alloys for defense industry and aircraft industry. Warranty assurance is twenty years.
-------------------------------------------------
And it was 1966!

Thanks, Vassili.

 

[mete]

Yes those were the days when I started my career .There were various methods being developed to improve steel quality for high performance applications such as aircraft and bearing steels.

 

[JayAndersson]

This is from RosArms website - I ask Vladimir to ask their metallurgist in Russia about ESR, because I heart it in Russian Blade Forum as well as article about Yasuki Steel Special mettion that they first in the West who start using ESR after USSR.

As you may see thay directly states that it is about nonmetalic inclusions - not S or P but Nitrides and Oxides actually. So what is this impurity points?
---------------------------------------------------------
...The research of 1966 ascertained that 110x18M steel grade is the one to meet all requirements. To decrease the content of nonmetallic inclusions, vacuum-arc remelting (VAR) was suggested.

Point analysis of maximal nonmetallic inclusion content

Nitrides Oxides
Conventional remelting 4 points 4 points
Electroslag remelting (ESR) 2 points 2 points
Vacuum-arc remelting (VAR) 1 point 0.5 - 1.0 points

Metals undergoing double remelting (ESR + VAR) have half as many nonmetallic inclusions as compared with ESR plus a reduced gas component. The metal density is greather than when applying ESR alone. Thanks to that we have better plastic properties, improved polishabiliti, and good strength characteristics. Milled carbides help to grind the blade's edge and keep it constantly sharp.

All the above factors prolong the bearing service life.

Electroslag remelting process (ESR) is an arcless process of remelting a metal electrode in a flux bath. Electrofluxed metal is noted for its premium quality, lower impurity and gas content, improved micro- and macrostructure, lower anisotrophy (directional property), twice as high mechanical properties, two up to five times more reduced nonmetallic inclusion content (such as oxides, sulphides, globules), higher wear-resistance and contact resistance, plus minor improvment of other characteristics. Electrofluxed metal is used in the production of steels and alloys for defense industry and aircraft industry. Warranty assurance is twenty years.
-------------------------------------------------
And it was 1966!

Thanks, Vassili.

So what you state above is that it reduces inclusions and impurities. So for a good mill with a clean operation and good process control this would be unneccessary then? Steel is purer now than forty years ago, at least swedish steels.

That suggests that ESR is just a fix for poor process control then? And for sure, a marketing thing "spend one dollar extra and sell it two dollars more expensive", sort of.

Take a pure non-ESR processed steel like a Sandvik knife steel 13C26 and compare it to some ESR processed steel out on the market. How do they compare when it comes to non-magnetic inclusions? Do you know? And please compare 2006, not 1966 .

//Jay

 

[Satrang]

Jay, you bring up an excellent point. You can produce steel with a single melt that has very good cleanliness even to the point that it rivals ESR or VAR processed material. What the ESR and VAR process do is drop the cleanliness level down to average levels below what a single melt can do. Essentially taking the whole curve down. For single melt material it is the old garbage in garbage out principal combined with the melt practice.

 

[nozh2002]

Take a pure non-ESR processed steel like a Sandvik knife steel 13C26 and compare it to some ESR processed steel out on the market. How do they compare when it comes to non-magnetic inclusions? Do you know? And please compare 2006, not 1966 .

//Jay

So you saying that Russian has bad steel mills and so this is why they have to purify their steel and Sandvic has a such a good mills and do not need this at all?

Whell, until you provide proof with this impurity points for Oxides and Nitrids it is just unfair to say this. And I want to emphasize the fact that VAR is used for BG-42. Do you also imply that BG42 is impure initially because poor quality of mills and this is why ARC is used, while Sandvic BG42 has no need to do this? Also Yasuka Special Steel using this method on top grade steels and is it because poor quality of their mills?

First you came up with idea that it is not about purification, now you are saying that it is about purification but they need it because initial quality was poor. What is this?

I like Sandvic steel 12C27, but I just has no Sandvic steel so far to compare with BG42 as well as 110x18MShD - and this steels performs very well for me. And with similar composition it is this purification process what differ them from others.

Thanks, Vassili.

P.S. It seems like ESR is what really bother you. But I like to hear how purity of steel - with or without ESR. That article mentioned impurity points - what is it and what points steels on the market have. May be you provide this information about your steel?

 

[mete]

Jay, that's untrue. The requirements for bearing and aircraft steels are higher and there are specific tests for inclusions. There was a demand for higher and higher quality steels driven by ever increasing to get longer life and higher stress levels from steels .These vacuum techniques were developed to achieve that , NOT to make up for poor or substandard steel making.. ..You could not get any better steel making than at Timken [developer of BG-42] but they worked to constantly do it better !!!

 

[JayAndersson]

So you saying that Russian has bad steel mills and so this is why they have to purify their steel and Sandvic has a such a good mills and do not need this at all?

Whell, until you provide proof with this impurity points for Oxides and Nitrids it is just unfair to say this. And I want to emphasize the fact that VAR is used for BG-42. Do you also imply that BG42 is impure initially because poor quality of mills and this is why ARC is used, while Sandvic BG42 has no need to do this? Also Yasuka Special Steel using this method on top grade steels and is it because poor quality of their mills?

First you came up with idea that it is not about purification, now you are saying that it is about purification but they need it because initial quality was poor. What is this?

I like Sandvic steel 12C27, but I just has no Sandvic steel so far to compare with BG42 as well as 110x18MShD - and this steels performs very well for me. And with similar composition it is this purification process what differ them from others.

Thanks, Vassili.

P.S. It seems like ESR is what really bother you. But I like to hear how purity of steel - with or without ESR. That article mentioned impurity points - what is it and what points steels on the market have. May be you provide this information about your steel?

No. I'm not saying russian mills are bad. Or japanese or any others. I have no market reports on impurity levels, thats why I'm asking......

I have not once, in one single post said anything bad about Russian steels or mills. I know Sandviks mill since it's only a couple of miles away from where I live. So I can talk about that one. If you read my posts again you can see that I make NO OTHER references.

I know that ESR, for instance, purifies the steel, but there are several other ways to do this as well. I said that I BELIEVED it was primarily used to increase the hot working properties. I never stated it as a fact as I am not sure. I do know however, having friends working for Sandvik (one of the biggest 5 companies in Sweden), that they dont do ESR at all. Still they have pure steels. So is that impossible then?

I then asked the question if anyone here knew if an ESR processed steel is purer than a pure non-ESR processed steel is? A fair question. This question still lacks an answer. It would be interesting to see, because it could give us all a clue. We can take your BG42 steel as comparison from Russia Vassili. I dont know if Sandvik makes a variant of BG42. They very rarely copiy existing grades, but they might have something similar.

I have no grudge about re-melting steels. I'm not sure it's neccessary most of the time, though. I'll try to explain.

The requirements for non-metallic inclusions for a razorblade steel, a tube to a pacemaker and a surgical scalpel is very high. Still it can be done without ESR. Would ESR make it even better? I'm not so sure. Would it be worth the extra cost? Maybe, hardly. Could it be used for marketing? Damn right.

Vassili, have you tried BG42 without VAC-ESR? Was it full of inclusions? Was it unusable? Or was it as clean as Sandvik 13C26 even before the re-melting, and it that case....why the VAC-ESR?

Mete wrote:
"Jay, that's untrue. The requirements for bearing and aircraft steels are higher and there are specific tests for inclusions. There was a demand for higher and higher quality steels driven by ever increasing to get longer life and higher stress levels from steels .These vacuum techniques were developed to achieve that , NOT to make up for poor or substandard steel making.. ..You could not get any better steel making than at Timken [developer of BG-42] but they worked to constantly do it better !!!"

Compare the amount of steel being made globally with ESR processing and tonnage going in to the aircraft and bearing sectors and you will see a big gap. And when it comes to the aircraft industri in general it takes decades to introduce new standards, so even if other methods would replace re-melting it would take the aircraft industri a while to catch up. Which I believe is a good thing, but still it's a factor in this line of reasoning.

I'm sure Timken is doing a great job with the bearings and the aircrafts, but why do they need to re-melt their steel for knife applications? If indeed they are as good as you suggest?

//Jay

 

[M Wadel]

how does powder and sprayformed steel compare? it has to be even more clean than vim, var, esr etc or?

 

[Satrang]

When you look at cleanliness of steels you need to look at the processes separately. The PM process for example is designed to reduce the structures of the steel to much smaller sizes. This includes both carbides and inclusions. The inclusion size of PM materials will always be smaller than ESR or VAR but there could be quite a volume depending on whether the PM was melted initially in open air or under a vacuum. So essentially, there is dirty PM and clean PM. Comparing it to ESR and VAR is somewhat apples to oranges. As far as cleanliness goes, single air melt material will have the largest inclusions and based on process will have high or low volumes. ESR / VAR will have much less inclusions on average than air melt and slightly smaller sized inclusions. PM will have very small inclusions in high volume or low volume depending on the process.

 

[JayAndersson]

When you look at cleanliness of steels you need to look at the processes separately. The PM process for example is designed to reduce the structures of the steel to much smaller sizes. This includes both carbides and inclusions. The inclusion size of PM materials will always be smaller than ESR or VAR but there could be quite a volume depending on whether the PM was melted initially in open air or under a vacuum. So essentially, there is dirty PM and clean PM. Comparing it to ESR and VAR is somewhat apples to oranges. As far as cleanliness goes, single air melt material will have the largest inclusions and based on process will have high or low volumes. ESR / VAR will have much less inclusions on average than air melt and slightly smaller sized inclusions. PM will have very small inclusions in high volume or low volume depending on the process.

I know that the major advantage of PM is that you can (if done properly) ignore the whole mega-carbide problem. You never have to think about the CR-C (and Mo,V,N) balance. This is a huge advantage for PM.

I have no experience whatsoever with powder steels, but I used to work in a plant making tungsten carbide and the process is fairly similar. Powder as starting material, pressing and sintering (Vacuum of HIP). The carbide industri is not a very clean industri. It's not terrible but there were issues, for instance making a non-magnetic tungsten carbide is almost impossible even though it is completely non-magnetic in theory. Inclusions and metallic impurities actually keeps tungsten carbide out of some businesses like medical and food processing. These are easier for steels to enter, even though they are airmelted.

Is it not hard to keep the powder steel clean from inclusions? Who has some of the purest powder steels out there, Crucible, Hitachi, Uddeholm? Or this BG42 some talk about? Do you know Satrang?

//Jay