1095 Issue

[ron horton]

Hello Fellow Smiths - I'm using 1095 for the first time and following clean up after the HT, I have areas of what appear to be almost "blisters" on the blades. These areas appear to be super hard, making it difficult to remove the grinder marks. I used a heat treat oven and quenched in canola oil. The oil may have been closer to 150 degrees instead of the recommended 130. Is this decarb? It seems pretty deep, but does reduce with continued grinding, though I'm getting pretty close to final thickness for these blades. 

 

Thanks for the help!

 

Ron

[Jerrod Miller]

Decarb is soft.  It is from carbon being removed, so it doesn't harden (at least not as well).  What temp and for how long did you soak in your heat treat oven?  

[ron horton]

Hi Jerrod - greetings from Spokane. These blades were stock removal. I normalized 3 times at 1500, 1450, 1400 degrees and quenched at 1475. I held the blades 10 -15 minutes at quench temp. Tempered 3 times for an hour each at 350 degrees. 

[Alan Longmire]

If you hadn't specified the method of heating, I'd have guessed grain growth from overheating or too much time at temperature.  It still may be the latter. Large grain is deeper hardening than small grain.  How long did you hold at heat for each normalization cycle?

[ron horton]

Hi Alan - 10 minute +/- hold at temp during normalizing, air cooled and back into the over for the next normalization cycle. I think I got the sequence pretty good, but I know the oil was too hot, 150 degrees or more, when I quenched. 

[Alan Longmire]

I think too much time at heat. 1095 just doesn't need a soak when it's knife-sized. It has no ingredients to prevent grain growth, and no complex carbides to redistribute.  

 

I know it the oven it needs time to come up to heat, of course.  Maybe try 5 minutes next time?

 

But do whatever Jerrod says, he's the metallurgist. 

[ron horton]

Ok. I was trying to make sure it was to temp. Would breaking one of the blades reveal anything useful? 

[Joël Mercier]

You did not mention if you use anti-scale coating. It would be a good idea.

[Jerrod Miller]

1 hour ago, Alan Longmire said:

But do whatever Jerrod says, he's the metallurgist. 

The day I have to correct Alan on something will be a day we should all fear.  I agree that it sounds like it could just be too long at temp.  

 

32 minutes ago, ron horton said:

Would breaking one of the blades reveal anything useful? 

There are always things to be learned from breaking blades.  Even if it is just that you did indeed nail the process.  In this case you would be looking for nasty grain growth.  

 

2 hours ago, ron horton said:

I know the oil was too hot, 150 degrees or more, when I quenched

The biggest thing to worry about here is whether or not you are going to harden at all, or at least through harden for a given thickness.  With a secondary concern of warping.  It should not give you a "splotchy" hardening.  

[ron horton]

I'll break a blade and see what the grain looks like. 

 

Joel - I did not use any type of anti-scale. I'll try some next time.

 

Thank you all for your help and suggestions. 

 

 

[Joël Mercier]

The atmosphere of a HT furnace will eat your steel if not protected because there's nothing to burn the oxygen like a propane forge does. Google ATP-641, it's relatively cheap considering the amount of blade your can coat with a single pint and it's very potent at preventing scale and decard. 

 

I am not saying it's currently your issue, it's just an observation I did while reading your post.

[ron horton]

I just happen to have a pint on the shelf I bought based on one of your previous posts. Need to put to use. 

[ron horton]

Snapped a blade and the grain is quite large. I'll reduce the hold time and see what I end up with. 

 

Thanks. 

[Alan Longmire]

That's actually not terrible, but yeah, try five minutes instead of ten.  And get the oven up to heat before you add the blades.  I know, grain growth isn't supposed to occur under critical, but those elements cycle until they hit the desired heat and can go hotter than we want.  Kind of like how if you put a cake in the oven cold and then heat to temperature you get a burned bottom.  Not as dramatic, and it's negligible on high-alloy and stainless, but on something as simple and sensitive as 1095 or low-Mn 1075 it makes a difference.

[Joël Mercier]

The grain looks quite smooth except in the middle of the blade, as if it did not fully harden there. Perhaps an etch could give us clues.

[ron horton]

Hello - got around to etching the blade pieces yesterday. I'm not sure what this may reveal, but perhaps someone with more knowledge can make a diagnosis?

 

Thanks.  

[Alan Longmire]

The cross section needs to be polished if you want to see anything with an etch there, but there's no need to do that here.  The surface tells the story.  Where it's black it hardened, where it's not, it didn't harden.  Looks like decarb on top of grain growth from here.  Pretty much what we were thinking.

[ron horton]

Interesting! So maybe not a time issue at temp, but the quench oil being too hot? 

[Alan Longmire]

No, I don't think the oil had much to do with it.  The tip hardened, as did the tang end, which is a bit odd.  Usually the tip will harden but the teng end won't, since it's thicker.  The middle not hardening puzzles me.  How are you supporting the blade in the furnace? Is the middle shielded from heat somehow?

[ron horton]

In this particular batch, I had 4 blades side by side, edge down, tang up, separated and held in place with ceramic dowels. 

 

 

[Alan Longmire]

I continue to be puzzled... . Was this blade from the middle of the pack?