Noobie questions on HT 1095

Tune_up

Active Member
Relatively new to knife making and generally send my blades out for HT but thought I would try to heat treat some 1095. Heated my blank (flat ground) to non-magnetic in my 2-brick forge heated w MAP torch, held for a couple of minutes and quenched in 120 degree canola oil, came out straight, tempered in oven at 400 degrees for one hour twice, file skated so I assumed everything was fine. After heat treating started finishing blade, but when I got to 800 grit started to notice fine irregular scratches/cracks/trails and realized something might be wrong. As I have progressed to finer grits and the sanding scratches have become less I can see more of the lines/stress fractures(?). They are most prominent near the spine, none can be seen in the lower halve of the blade. They are very fine and not noticeable unless you look very close (or are a maker).
Any idea what I did wrong? My guess is that I overheated the steel but I really have no idea. After bringing the blade to dull red I turned the torch to the lowest setting to keep it from getting hotter. I rotated the blade frequently but generally kept the edge out of the hottest part of the forge.
Should I have normalized prior to grinding?

I tried to take a picture but they are hard to see and impossible to photograph, at least for me.
 
Yes, you should have normalized prior to grinding but I don't think that it has anything with what you are seeing. Without being able to see what you're talking about it's hard to say.

Doug
 
After about 30 tries, I got a good picture to show what I am talking about. Maybe this will help. Although this pic makes it look pretty noticeable you have to get the light reflecting just right to see them, they didn't show up until about 800 grit and you can't feel them. This is currently at about 1500 grit but all the 1000 scratches are not gone. mfs blank.jpg
 
I am following this with great interest. I can't imagine that canola quench was too fast. We're likely to get some 'big word' answers here, but is this result possibly from overheating?. I'm just asking based on process of elimination. Your soak doesn't sound too long - underheat not likely to cause cracking - quench medium not likely too fast - no evidence of a gremlin with an engraving pencil and a warped sense of humor.... :les:
 
I've seen 1095 blades crack from canola... not often but, it happens.

... Are you sure it's 1095?
 
Overheating was my best guess, but my best guess is worth next to nothing.
I know it was labeled 1095 and purchased from Jantz Supply; I have no reason to doubt it.
Is there a better quench for 1095 or O1 for the ocassional /novice heat treater?

I wasn' going to finish the knife but the handle parts are fitted and complete so I think I will finish it and just keep it, no prying, but it should skin a deer. Don't want to give it away or sell it since I assume it will break easily on one of these lines/faults/cracks. Would it be possible to heat the spine enough to at least partially correct this? Keep the edge in water and heat the spine with a torch?
 
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I think that a better idea would to break the blade and check the grain size. That could really settle whether or not the steel was overheated. I wouldn't want to carry a knife that I'd have to worry about failing when I needed it. There comes a time when you have to just consign the blade to the junk box and start over.

As far as the quenchant goes, it depends a bit on the actual manganese level. The less manganese, the shallower hardening and the sooner the austinite will convert to other products and the more aggressive the quenchant has to be.

Doug
 
Ha, I'm still new enough at this that intentionally breaking one of my knives would be like beating my dog. Still I would do it if I thought it would help, however since I have never looked at a broken knife I don't think it would help me a bit. Maybe some day sone I will HT several pieces of steel overheating one and underheating one on purpose so I can see the difference.
You did convince me not to finish it though, for now I'm just going to leave in on a shelf and make and identical blank for the guard/handle.
Thanks for the help.
 
Personally, I would break it and take a picture. Whether or not you've seen a broken blade before, it's fairly straight forward: If the break is clean, straight and fairly smooth, chances are the heat treat wasn't the problem. If it's rough and jagged, bingo.

Here's one pic I found showing some different grain structure based on heat treat / normalizing:

grain%20size%202.jpg


You may not see either of those exactly, but it should be closer to one or the other based on the success or failure of heat treat.
 
Ok, both of those above pictures show some degree of grain growth probably due to overheating, though the lower one isn't all that bad; it just could be better. What you want to see is something about as course as 1000-1500 grit emory paper. The upper one in that picture really appears to have been overheated without it being corrected by heat treating. Another thing that you can do for a reference is to break an old warn out file, if you have one, or feel like wasting a new file. Make sure it's a good brand name file to make sure that the manufacturer did a good grain control on the steel.

If you are going to make knifes you are going to have to make some to test to destruction to make sure that your process is right. Just no way around it if you want to know that your product is good.

Doug
 
By the way, I suppose I should give credit and an explanation for the picture... I just googled 1095 grain and came upon Rick Furrer's website.

http://www.doorcountyforgeworks.com/Damascus_steel.html is the source of the pic.

The top is an "as forged" grain, and the bottom is after a normalization process.

It's definitely just a small example of variation you might see between grain and heat treat cycles, but hopefully it gives the OP a little more direction as far as what to look for.
 
Well I broke it, looked a lot like the upper picture, maybe even more coarse. Now did I over heat, was it the quench or does the coarse grain only imply that the heat treatment was poorly executed?
 
Yes, you heated it too hot and for too long. Rather easy to do with something with as high as carbon as 1095. It's a little much to get my head around (especially with a pounding headache) but strongly hypereuticoid steel seems to be more susceptible to grain growth so you really need to be careful about getting the steel just a little above non-magnetic for the soak. It's a bit easier if you can spot the decalesence as the steel heats but the best way is to use a controlled source of heat.

This is a problem that smiths have to deal with (I take it that you do stock removal) because we pretty much overheat our steel while forging and have to correct for it by multiple normalizations. That is something that you can try if for no other reason than to relieve any stress that occurred during grinding. Here's an idea that's a lot cheaper than a regulated kiln for heat treating. First of all, get your forge hot then turn the gas back a bit to allow the steel to heat more slowly. Then get some temperature sensitive markers, Tempilstick is one brand. (Actually you would probably want to do this before you turn on you forge-getting things out of order:5:) You might be able to find them at a welding supply store or you can get them at an online dealer. Have one in 1450° and another at 1500°. Mark both on the blade and heat the blade until the 1450° mark melts but try to keep the 1500° from melting. You will have to be going in and out of the fire to keep within the range. Hold that for about 5 minutes then quench. Just remember when normalizing, however, all you need do is to bring the steel up to heat and then allow it to cool to a dark heat. With normalizations you are only concerned with changing the phase of the iron crystals in the steel, not putting the carbon into solution in the austinite. I think the Tempilsicks ran me about $12-$13 each but I haven't tried the above technique yet.

Large grain contributes to brittleness. That could be the reason that your blade cracked. Or, it could be forge gremlins-nasty beggers:3:.

Doug
 
Thank you for the help. Just out of curiosity, if I had normalized the blank and re- HT would that have fixed the problem or would these cracks persisted? I assume normalization/re-HT would have fixed the granularity?
 
I've seen some 1095 come with a very course grain from the manufacturer. If that was the case then normalizing would have helped, and it may not have been from you over heating it... not sure about those cracks.
 
If I understand your last question, I think you are asking if normalization could have 'healed' the cracks post HT. I don't believe it would.
 
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