Eutectoid steel

There appears to still be some discussion of where the eutectoid composition lies. I've seen it as low as 0.77% C and Kevins graph is the highest I've seen. Anyone know if its been nailed down? My books are from the late 90's. Until seeing Kevin's chart, I thought 1075/1080 was the closest to the eutectoid composition.
 
Hey, that diagram is in my materials science book! :D

The teacher told us all to look at it, make sense of it over the week-end, and come back in ready to discuss it. I must talk too much like I know what I'm doing, because several kids in class wanted me to break it down for them.

So I did. "It's just like magic, but slightly different." ;) :D

Thanks again for the info guys... makes me keep realizing just how little of this I actually UNDERSTAND. It's easy to throw around big words, it's a different story to understand all that theory AND be able to apply it. I appreciate you guys working to help us bridge that gap!!! :thumbup:
 
me2, they'll never nail it down! Just consider 1080 +-5 . I think Kevin has a book where they give different compositions in the same book ! Don't worry about it because that's the equilibrium diagram of just iron and carbon.Steels you use will differ.
 
bambright said:
Kevin,

At which temperature or which line that the nucleation starts on the heating cycle.
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If I had to assign one point on the diagram to the point of the initiation of new crystalline formation it would be Ac1, but that would be a rather inaccurate oversimplification. In the formation of new austenite grains there are several steps- recovery, recrystallization, and grain growth. Recovery starts well below Ac1 and is the process behind proper stress relieving heat treatments which are entirely subcritical in temperature. Recrystallization cannot be assigned a fixed temperature since it is accomplished over a range and is affected by many factors (residual strain energy, rate of heating etc…), but the conditions that promote it are definitely under way at Ac1. “nucleation” the process that will determine the point of the new embryonic grains actually has its origins in the recovery phase when very tiny sub-grains can begin to from in areas of high energy of the current grain boundaries.
 
mete said:
me2, they'll never nail it down! Just consider 1080 +-5 . I think Kevin has a book where they give different compositions in the same book ! Don't worry about it because that's the equilibrium diagram of just iron and carbon.Steels you use will differ.
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I have couple of books that on one page shows he eutectoid at .77% and on the very next page assigns it at .8%:confused:. the highest I have seen it assigned is .85%:eek:. But then it all depends on even the slightest of alloying, even in the trace ammounts, the diagram is based in pure iron and carbon at equilibrium conditions, Murphy irrefutably established that perfect conditions in the real world are incredibly unlikely. A case could be made to explain the alloying effects in the way the earlier books tend to place the eutectoid at the lower end than newer texts, perhaps reflecting and increase in trace elements and alloying in all steels.
 
Pure carbon/iron equilibrium is 0.80% C at eutectoid? Other elements and amounts of elements cause eutectoid to be higher or lower than 0.80% carbon? Like... if iron is in a mix with other elements, the carbon amount has to change to be eutectoid?

This is "the real" question... If a specific batch-chemistry of steel has a number of elements besides carbon/iron and it is eutectoid at 0.77% C, is the same percentage mix of other-than-iron elements with a carbon amount of 0.83%-0.85% hypereutectoid in the sense of excess carbon that can go to grain boundries?

Mike
 
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Mike Krall said:
Pure carbon/iron equilibrium is 0.80% C at eutectoid? Other elements and amounts of elements cause eutectoid to be higher or lower than 0.80% carbon? Like... if iron is in a mix with other elements, the carbon amount has to change to be eutectoid?

This is "the real question"... If a specific batch-chemistry of steel has a number of elements besides carbon/iron and it is eutectoid at 0.77% C, is the same percentage mix of other-than-iron elements with a carbon amount of 0.83%-0.85% hypereutectoid in the sense of excess carbon that can go to grain boundries?

Mike
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Well, it's been a while now but I'd still like an answer to "The real question"...

Mike
 
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This chart along with your explanation really helps alot. Im starting to get some of the reasons behind different HT for different alloys. This really made sense. Thanks a bunch!
 
You want the real, real, real answer ? If the eutectoid is .77 C then any more carbon can then be a problem.Depending on what you do with it it will appear in the final knife as carbide spheres or in the grain boundary. Much of the point of this thread is to be aware of the carbides in hypereutectoid steels and learn how to make them do what you want them to.
Understand grain boundaries .There is physically more room in them and they have higher energy levels. That means things tend to collect in them ,good and bad, and things happen there , transformations etc. Carbides and phosphorous can collect there resulting in brittleness.Vanadium collects there to retard grain boundary movement thus grain growth.
 
mete said:
You want the real, real, real answer ? If the eutectoid is .77 C then any more carbon can then be a problem.Depending on what you do with it it will appear in the final knife as carbide spheres or in the grain boundary.
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Thank you, "mete"... real would have done me but three times real is better, right?

How do you like that I did that almost without "talking numbers"? =]

Mike
 
Just thought with all the latest discussion of the simple steels these needed a bump.

Mike, I would venture a guess that most steel made now is fully killed, not just tool steels. All the material certs I've collected for structural steel over the last few years have shown it is fully killed.
 
me2 said:
Just thought with all the latest discussion of the simple steels these needed a bump.

Mike, I would venture a guess that most steel made now is fully killed, not just tool steels. All the material certs I've collected for structural steel over the last few years have shown it is fully killed.
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Me2,

I was figuring most steel is fully killed but didn't know for sure... I've already got a world's worth of teeth marks on my butt from "figuring"...

I'd like to see this thread bumped again and again, to tell the truth, along with this thread http://www.bladeforums.com/forums/showthread.php?t=615086

Both of them are tremendous and could easily get bigger and better over time. They'll likely just disappear into the vastness of this place, though.

Mike
 
dixiechopshop said:
Im new to the world of starting from scratch.Ive made knives before but never from a total blank steel.I would like some advice on which steel to start with.Im wanting to make some Tactical/survival knives,full tang with a para cord wrap handle. Id like something not to expensive(ya know for practice sake) and realitive available.Also somthing not to tough to work with.Any Ideas? thanks,Jeff.
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I would trade any of the stickies with my name on them for one good one by anybody on the topic of this question. In the line up of most asked question that could wear out the most determined veteran forumite this is very near the top. But as is so often the case, it is not the person asking the question that makes the topic difficult, it is all the confusing answers that keep resurfacing as if the question was never asked or discussed before. One thing that would help with this topic is to remember the question itself. We are not being asked what our favorite steel is, we are not being asked what the new steel in vogue this month is, and we are not being asked what’s the best super-duper indestructible forever cutting steel is. The question is- what is a good steel for beginners to get started with; an easy steel for anybody to learn on without huge investment in tools or materials. If we are going to get down on free scrap steel we should probably have an alternative answer, and on that point I am tickled to death and almost giddy to be able to help out a new guy who is on a budget but still wants to know about a real steel and not how to make a knife out of mystery scrap they found. Jeff, I applaud your approach and would honor any request for information you may have based upon that position which allows us a good starting point from which to help you. :thumbup:

The easiest steel to get optimum results with little effort or equipment first and foremost must itself be simple! If you plan on doing shade tree mechanics work, a Ford or Chevy from the 60’s or the 70’s is going to be much more rewarding than a 2009 Ferrari or Formula 1 car, which you will probably just foul up without the proper experience and tools.

In steel there are two things at odds in easy heat treatment- how it has to be heated, and how it has to be cooled. Since it appears that most bladesmiths have enormous difficulty wrapping their minds around effective quenching concepts, too many in the business have focused far too heavily on steels that will “appear” to easily harden in any quenchant (I won’t even get into how this can immediately be solved by quenchant choices ).

Alloying is what makes the steel respond to a wider range of cooling in hardening. Two elements are most used for increasing hardenability- chromium and manganese. Of the two, chromium is the more powerful but it also forms carbides and makes the heating more critical. Manganese greatly increases hardenability but does not give the same issues in heating. So in the big picture the element that will allow you to harden in more quenchants and still allow a carefree heating is manganese. I could go into carbide formers and edge retention but, once again, we are talking about a beginners steel choice, so let’s go for skating that file and cutting a few things and worry about the ultimate super knife that can cut through granite and still shave for a few months later in our career.

The next thing we have to worry about is carbon content, too little and the beginner will have a bit of sorting to do to figure out why that file doesn’t skate. Too much and there can be some serious annealing issues and embrittlement problems as well as steel that is much less tolerant of overheating which is a common problem for beginners. Less carbon will increase soak temp requirements to put excess iron into play, more carbon will increase soak time to break the carbide groupings up and put them into play- particularly, once again, if there are any carbide forming alloy elements- like chromium. What we want is a Goldilocks zone for carbon, not too much, not too little, but just right. That Goldilocks zone for iron/carbon systems is around .80%, and is called the eutectoid. It takes the least heat and time to go happily into solution without any leftover material to cause you problems.

So let me see, alloys that are really simple and have around .80% carbon and manganese to help in hardening… perhaps 1070, 1075, 1080, 1084. Hmmm, yes they seem to fit the bill!

5160 is hypoeutectoid and relies on chromium just to be able to reach 62 HRC. It is hard to make a bad knife out of it but it is also hard to make a really great knife out of it without very special attentions, indeed it excels in mediocrity in the hands of a beginner.

And then we have the old favorite on the list of beginners steels, O-1. Why is it believed to be so good for beginners? Because you can quench it in anything cooler than an oven or forge and expect to see some gains in hardness, but the soak time and precise temperature requirements in dealing with all the alloying present make it so the beginner is only getting a fraction of the steels potential at over 3 times the price!

With all of its proeutectoid carbon wandering around with no guidance to keep it out of mischief, and its significantly lower Mn content 1095 is not too much better than O-1 for a beginner. It will challenge your quench speed abilities as well as your heating skills.

Lowest price- 1070, 1075, 1080, 1084
Easiest accuracy and time requirements in heating- 1070, 1075, 1080, 1084
Hardenability in any decent quenchant matched to is cooling needs- 1070, 1075, 1080, 1084
Easy to temper for excellent edge holding or high toughness- 1070, 1075, 1080, 1084
Easy to anneal by simple heating and cooling or full lamellar via insulative methods- 1070, 1075, 1080, 1084
Easy to grind, file, drill or forge-1070, 1075, 1080, 1084
Readily available most anywhere- 1070, 1075, 1080, 1084

So what may be some of the best steels for a beginner to start with, hmm let’s see… perhaps 1070, 1075, 1080, 1084.


P.S. Going back to the concept of addressing the question of "best for beginner" versus "our pick for the best steel ever", I would like to go on the record as saying that I rarely work with 1070, 1075, 1080 or 1084. Not because they are bad steels, they are really good steels, but I have spent more than a few years of my life studying steels and developing experience and equipment that can unlock the potential of other steels that a beginner would probably waste their money on. Thus the steels I suggest for this topic are rarely the same that I choose to use or would suggest for anybody with years of experience and a well equipped shop.


rayban said:
Can 1084 be air quenched, unlike 1095 which has to be oil quenched?
I've been wondering why folks recommend 1084 over 1095 for most carbon steels. Do they grind different too??

Hope ya don't mind me joining in Dixie, but I'm after the same answers you are, I believe.
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All of the 10XX steels are shallow hardening, none will do anything but get soft by air cooling, as all they will do is form pearlite. All are technically "water hardening" steels in thicker sections due to their lower hardenability. So I would prefer not to call 1084 a deeper hardening steel since it is one of the shallowest hardening, just 1095 is even more shallow hardening due to less Mn. It is kind of like saying a tortoise is a fast animal simply because it beat a snail in a foot race.

1095 has both the whammies- trickier in the heating as well as in the cooling. 1084 is ready to quench as soon as you get it evenly to the popular non-magnetic standard. 1084 will just want to make 100% fine pearlite on every heating a cooling cycle so it is easy to keep it very homogeneous and even on the inside from forging to final quenching. 1095 on the other hand has carbides to deal with, albeit simple ones but carbide all the same. It can set itself up in the forging, normalizing and annealing stages with some very obnoxious issues that could still be there during and after quenching. It takes a little bit more of a knowledge and skill set to effectively deal with these quirks. Because of this we have gotten some of the unorthodox heat treatments that bladesmiths come up with, or the steel gets an undeserved bad rap because its particular needs were not met.
 
Kevin R. Cashen said:
So what may be some of the best steels for a beginner to start with, hmm let’s see… perhaps 1070, 1075, 1080, 1084.
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On one hand, I lucked into this, I think it's fantastic, I've had extremely good results with 1084 (except the few times I managed to crack it messing with brine). I've done a little with 1060, 1070, 1075, but mostly Al's 1084. It really is a good starter material and you can easily learn heat treat variations for other steels by way of their differences from 1084. (hold times, temperatures, etc.)

On the other, 15N20 wouldn't have ever been on the list- and I love that steel. I'd put it on any list of great beginners' steels if it was more widely available, especially in 1/8 inch thicknesses. The availability makes it not work out for the list, though (unless you are crazy enough to use 3/32 blades to baton through logs and then sell knives based on that usability.)
 
koyote said:
On one hand, I lucked into this, I think it's fantastic, I've had extremely good results with 1084 (except the few times I managed to crack it messing with brine). I've done a little with 1060, 1070, 1075, but mostly Al's 1084. It really is a good starter material and you can easily learn heat treat variations for other steels by way of their differences from 1084. (hold times, temperatures, etc.)

On the other, 15N20 wouldn't have ever been on the list- and I love that steel. I'd put it on any list of great beginners' steels if it was more widely available, especially in 1/8 inch thicknesses. The availability makes it not work out for the list, though (unless you are crazy enough to use 3/32 blades to baton through logs and then sell knives based on that usability.)
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You are correct and if it were not for the size and availability issues I would put 15n20 on the list as well since one can consider it 1075 with some nickel added. It is worth noting however that 1084 should be a better edge holder than 15n20. In my steel selection categories 15n20 falls under tough chopping and cleaving type blades and not under fine slicing and edge holding, but it is a serious problem to make a beefy bowie out of shim stock:confused:.
 
I just wanted to say a quick thank you to everyone (particularly Kevin) who spends so much time helping us newbies out by contributing to threads like this. I started gathering materials and tools 4 months ago to build my first knife. Trying to dig through all of the information, or should I say MISinformation has been one of the most challenging aspects to this endeavor. When answering questions such as the "Which steel is best for beginners?", its so nice to get an answer that is backed up by sound reasoning and science, and not just "1084!" or "O1!", or "Get some spring steel!". Thanks again, for your time and efforts. I hope you all don't go crazy answering the same questions over and over and over.
 
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