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Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making.

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  #1  
Old 04-03-2008, 09:06 PM
AlanR AlanR is offline
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1095 HT troubles

Hello all,
To start off I'm a newbie who has made around 5-6 knives. I've done all my own heat treating (at work in an oven) and have tried a few different materials. The easiest I've done is 440C. I'm now on my second knife with 1095 and am having trouble. On the first one it took me two attempts but after I realized I didn't get the first quench fast enough, the second one came out fine - I used non-heated olive oil. On this knife, however, I'm not having any luck and would like some advice. I just finished attempt #3 or 4, I've tried searching to see if there is a limit on to how many times you can HT but can't find an answer though it would seem there should be a limit.

So far: 1500-1510, hold for 20-25mins and quench as fast as I can grab it with tongs and dunk it. I started out at 1450-1460 but when it didn't take I had read some have had luck at a higher temp. I know I should probably be heating the oil to around 160 but I'm stubborn - it worked the first time with non-heated and by golly it should again!

I would appreciate any and all comments on a possible solution. Should I anneal and start over? I should probably normalize at the least since it has been through a few cycles.

Thanks,
Alan
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  #2  
Old 04-03-2008, 09:43 PM
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Ed Caffrey Ed Caffrey is offline
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My first question is.... What are you using for a heat source? I ask because unless your using a heat treat oven, I can't image a forge that is capable of holding that kind of tolerance for 20-25 mins. It might sound dumb, but there is a difference between using a heat treat oven and other types of heat.

Next, if your only going to the temps you listed, then your not reaching the critical temp for 1095. Generally the critical temp for 1095 is 1650F.

Finally, I would discourage you from "soaking" any of the simple carbon steels. The reason for soak times with some steels (like the 440C you mentioned) is because of the richer alloy content, which requires soak times to ensure the steel is in "solution" (all elements evenly distributed throughout the steel) before quenching. If you feel you must soak, don't exceed a minute or two! Otherwise all you accomplish is grain growth, and if you soak 1095 at 1650F for 20 mins, the final product is going to be nearly useless as a blade, due to the grain growth.

There is ONE other possibility with 1095.....they have messed with the tolerances of 1095 so much over the past few years, and some pieces, even from within the same lots, have less than 1 second on the Time/Temp curve....meaning that you have less than one second to harden the blade, which in most cases is physically impossible. For that very reason I no longer use 1095 for blades. Others might disagree with me, but I consider 1095 to be unreliable as a blade steel.


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  #3  
Old 04-04-2008, 01:16 AM
son_of_bluegras son_of_bluegras is offline
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Frome the metallurgy I've read the critical temp for 1095 is listed as 1475F. I have never seen a requirement for a soak time for any of the plain carbon steels and have never soaked the 1095 I've used. From the quench you have about 1 second or maybe something under a second to get the steel from critical to less than 850F. I''ve never got there using room temp oil, I preheat my oil to aroun 120 to 140F.
As to the reliability of 1095 I can't say, I only do this as a hobby and haven't made that many knives.

ron


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  #4  
Old 04-04-2008, 07:26 AM
AlanR AlanR is offline
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Thanks for the replies. From the listings I've seen many of the critical temps vary around 1450-1500, some even say 1550. I've also seen a couple places echo your 1650 temperature and given your experience I'll give that a shot. I'm using a heat treat oven at work that has just had a new thermocouple installed, the oven is used everyday successfully so I doubt that is problem but it's a good point to bring up. I believe all the sources I saw mentioned a soak time, I'll try without this next time.

I made my previous knife from the same bar as this one, so I hope that the steel doesn't vary that much. I'd gladly move on to another type of steel but I'd like to figure this out before I do in case I need to use it in the future.

I tried more up/down agitation with the last two tries because I thought that might be the problem. Well, I'll give it one more shot with heated oil, higher temp and no soak then I may try a torch right above some oil for an immediate quench if that doesn't work. I'd rather not throw away this knife, I kinda like it. I'm quenching this one faster than I did the last one so it's just all confusing.

Thanks again for the experienced answers.

-Alan

Last edited by AlanR; 04-04-2008 at 07:31 AM.
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  #5  
Old 04-04-2008, 08:33 AM
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Ed Caffrey Ed Caffrey is offline
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I mentioned the heat treat oven because another individual recently had difficulties trying to use one to achieve hardening temp. What was happening was that the temps were stratifying, and the thermocouple was located near the top of the oven's chamber. The blade was being placed in a rack on the floor of the oven..... when checked with an optical pyrometer, the floor was approx. 500F cooler than the top of the oven (where the thermocouple was located) which meant that the oven was kicking off while the blade was still 500F below the setpoint on the oven......thats why I said that the "type" of heating appliance you use CAN make a difference.

I looked at a number of sources for the heat treatment data I previously wrote..... its seems to be about a 50/50 split on the hardening temp.......some say 1450-1475F, and some say 1650F. I did a little looking into it, and the only difference I can find is that information recommending 1450-1475F was written a number of years ago, while the information recommending 1650F is more recent data.....which is another indication to me that things have changed with this particular steel.

Something else that caught my eye was your mention of "all the sources recommended...."
Something you have to be aware of is that if your referencing heat treating manuals and published data (that is not specifically directed towards knives)......all of that information is based on a 1" cross section for the given material. Those references might be a good STARTING POINT, as they will get you in the ballpark, but from my experience they are certainly not absolutes. Your likely working with a 1/4" or less cross section of the material, and your methodology should be adjusted, taking that into consideration.

I might be spinning my wheels here, but something else that can change a perspective is to understand and realize that very few steels have ever been specifically designed with knife blades in mind. This means that nearly all the steels we use for knife blades have been adapted from a steel that was created for another specific purpose. Therefore we have to take a number of things into consideration when attempting to create a knife blade from those steels........particularly the combination of geometry, combined with heat treatment....meaning that, in order to achieve a usable blade, we have to adjust the heat treatment, or at least portions of it, to achieve our desired end properties.

Hope that made some sense....sometimes my fingers have a difficult time typing exactly what my brain is trying to relay.


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  #6  
Old 04-04-2008, 09:08 AM
Kevin R. Cashen Kevin R. Cashen is offline
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You know, I just have too much on my plate right now to deal with the aggravation of sorting information...

Snip!

Original post deleted.

Alan good Luck you will need it.

Last edited by Kevin R. Cashen; 04-04-2008 at 10:43 AM.
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  #7  
Old 04-04-2008, 11:11 AM
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Probably a stupid question, but have you checked the blade is non magnetic, then taken the temperature marginally higher before quenching. If so the next step would be to try hardening in warm water
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  #8  
Old 04-04-2008, 11:23 AM
Larrin Larrin is offline
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I would use 1450-1475F, not 1650F.
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  #9  
Old 04-04-2008, 11:36 AM
AcridSaint AcridSaint is offline
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1095 has very little significant alloying elements in it and thus it has very little solute drag. My understanding is that this solute drag is the reason for soaking, so I would not worry about soaking for 20 minutes.

Because of the lack of alloying elements, 1095 also has two major drawbacks for you - grain growth and quench speed. If you run your temps up to 1650, you're definitely going to experience grain growth. The oil you're using may also be too slow or your time to the quench may be too slow. 1095 is a true water quench steel, so if you don't have a fast heat treating oil or polymer quench, I'd go with brine or water.

I don't think 1095 has significantly changed (although I think it now has broader tolerances), it's always been a very plain carbon steel and always been susceptible to grain growth at temps above critical. The main reason I prefer 1084/1080 and the like is because at least these have a bit more Mn. in them and they have just a tad bit of cushion in grain growth and quench speed.

I would swap out the quenchant and try to cut back on the time between removing and quenching before I got the steel any hotter. I would also allow the oven to normalize below critical for 20-30 min and then slow ramp up to crit.

I'm no expert, so take my advice with a grain of salt. If someone disagrees with me, please tell me where I'm wrong, it'll help Alan and it'll also help me.


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  #10  
Old 04-04-2008, 04:49 PM
AlanR AlanR is offline
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Thanks all,
These are all great comments which help me understand heat treating slightly more or at least enough to stir the curiosity - grain growth etc. I would like to figure out 1095 before moving on so it's great to have the support here to accomplish this. I may swing by work for an hour tonight and try a "recipe" of most of the suggestions made here. I'll be sure to post my results and my aggravations

-Alan
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  #11  
Old 04-05-2008, 08:04 AM
Kevin R. Cashen Kevin R. Cashen is offline
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Quote:
Originally Posted by AcridSaint
... If someone disagrees with me, please tell me where I'm wrong, it'll help Alan and it'll also help me.
Cap, I concur with your post with one slight exception, but your open mindedness convinced me to listen to my conscience as I was bothered all night about how I was simply allowing Alan to sort out the information all on his own. Your solute drag (I sense that Verhoeven may have recently been read) will be approximated by the leftover iron carbides not dissolved when you stay below 1500F with 1095, which is very important.

Aggravation or not, here is my original post and if it is contrary to what others believe they will have to examine their sources and reasons for conclusions just as I have:

1650F will cause very serious problems with any steel not containing heavy alloying, particularly higher carbon ones. The temp is around 1475F for 1095, literature that says otherwise needs a serious review as to the procedure and the desired results they are shooting for (perhaps they refer to 1095 modified which may not fully harden no matter what you do). At any rate since the carbon is in a more readily dissolvable position in .95% concentration, the temp is 1475F and there are good reasons for that temp with 1095 that I could elaborate on if folks desire.

All steel will benefit from a soak, some will require less time due to simplicity, but I have found anything less than 5 minutes after reaching temperature to be the minimum for proper solution. This is 5 minutes after the steel has assumed the surrounding temperature, so we could be talking more that 10 to 15 minutes total. 1 or 2 minutes will get a steel file hard but not properly austenitized. Soaking cannot cause grain growth as long as you are in control of temperature, and since we are discussing exact temps I will assume you have the ability to hold precise temps Allan. Overheating will cause problems almost instantly, I would consider 1650F approaching overheating. With controlled soaking at proper temperatures the only concern would be scaling or decarb (which one can grind away).

I have been doing some closer studying of this topic as of late and have some more of those tedious micrographs I am so fond of that shows exactly why soaking can be important for even simple steels, and why 1095 should be kept below 1500F., I can post them if folks are interested, otherwise I will not bore people.

Alan I work with 1095 quite a bit and have had great success with 1475F to 1500F and quenching into Parks #50, any heat treating oil that approaches 6-7 seconds should do the trick. 1095 requires one of the fastest quenches of any simple carbon steel so I would look to your quenchant. As a rule I do not get heavily into discussions about the effectiveness of alternative quenches, but I can say that quench speed (or thermal extraction due to conduction at least) is only one small part of the whole picture on quench speeds. Vapor jackets play as large if not larger role in beating the curve, this is why water should be the fastest and most even but often results in warping and cracking. The comment is often made about how nice the whole shop smells when using olive oil, this should put up a red flag about vapor forming. I would strongly suggest looking into quenchants designed to overcome all the limiting factors clashing with your 1095, or switch to 1080 or 1084.
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Old 04-05-2008, 11:24 AM
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Kevin,
First off let me be the first and little doubt not the last to say thank you for reposting.


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Old 04-05-2008, 11:41 AM
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Quote:
Originally Posted by Kevin R. Cashen
1650F will cause very serious problems with any steel not containing heavy alloying, particularly higher carbon ones. The temp is around 1475F for 1095, literature that says otherwise needs a serious review as to the procedure and the desired results they are shooting for (perhaps they refer to 1095 modified which may not fully harden no matter what you do). At any rate since the carbon is in a more readily dissolvable position in .95% concentration, the temp is 1475F and there are good reasons for that temp with 1095 that I could elaborate on if folks desire.


Yes please


All steel will benefit from a soak, some will require less time due to simplicity, but I have found anything less than 5 minutes after reaching temperature to be the minimum for proper solution. This is 5 minutes after the steel has assumed the surrounding temperature, so we could be talking more that 10 to 15 minutes total. 1 or 2 minutes will get a steel file hard but not properly austenitized. Soaking cannot cause grain growth as long as you are in control of temperature, and since we are discussing exact temps I will assume you have the ability to hold precise temps Allan. Overheating will cause problems almost instantly, I would consider 1650F approaching overheating. With controlled soaking at proper temperatures the only concern would be scaling or decarb (which one can grind away).

To be clear your saying ALL STEEL can and will benefit to some degree from a properly controlled soak not just a hypereutectoid steel?

I have been doing some closer studying of this topic as of late and have some more of those tedious micrographs I am so fond of that shows exactly why soaking can be important for even simple steels, and why 1095 should be kept below 1500F., I can post them if folks are interested, otherwise I will not bore people.

Again a resounding Yes please! I beleive these are the photots I have seen before, Fitz and I were talking about them last night, where your ears burning?HEHE

Alan I work with 1095 quite a bit and have had great success with 1475F to 1500F and quenching into Parks #50, any heat treating oil that approaches 6-7 seconds should do the trick. 1095 requires one of the fastest quenches of any simple carbon steel so I would look to your quenchant. As a rule I do not get heavily into discussions about the effectiveness of alternative quenches, but I can say that quench speed (or thermal extraction due to conduction at least) is only one small part of the whole picture on quench speeds. Vapor jackets play as large if not larger role in beating the curve, this is why water should be the fastest and most even but often results in warping and cracking. The comment is often made about how nice the whole shop smells when using olive oil, this should put up a red flag about vapor forming. I would strongly suggest looking into quenchants designed to overcome all the limiting factors clashing with your 1095, or switch to 1080 or 1084.

The difference between my mineral oil quench of the past and real quench oil ,in my case parks #50 is a very noticable differance, something a person doesnt need a microscope to see/feel a differance, big thank you for the informartion over the years Kevin, We are listening!
Thank you


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Old 04-05-2008, 12:51 PM
AcridSaint AcridSaint is offline
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Hey Romey, haven't talked with you in a while, hope you're well.

Kevin, thanks for the post, I'm with Romey on this one, I'd like you to go into further detail. O-1 and 1095 are some touchy subjects for me, as my close friends can tell you.

I keep a copy of the Veerhoven text handy (since it's one of the few "complete and accurate" resources I have available) and I'm not ashamed to admit that I consult it when chatting on the forums as well as for my own heat treating info. Yesterday I didn't have it open at work, but you can be pretty sure that many of my views are formed at least in part from that text.


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Old 04-05-2008, 02:05 PM
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Ed Caffrey Ed Caffrey is offline
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I think you folks should listen to Kevin on the 1095.....I don't use it, and I don't like it, and I'm sure he has more knowledge about it than I do. The instances I wrote previously are some of the experiences I've had with 1095, and although they might differ greatly from what Kevin believes, I found them to be true for me, in my shop, under my conditions. Thats one of the truths I've discovered in the past 25 years of bladesmithing, there are variables to deal with, and not all us approach them in the same manner......its not about right or wrong...only different.


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