O1 tempering issues...

S

Sir_Oblivious

Joined
Feb 4, 2017
Messages
4
Hello everyone.
I'm brand new here and a rookie knife maker with a question.
today I heat treated my first ever knife. It's made of O1 tool steel and the oil quench went great and the blade seemed hard after I tested the edge with a file. Happy with the result I took the main gunk off and put it in the oven at 400 degrees Fahrenheit for an hour. after about 50 minutes i noticed the blade had turned a sort of light blue. Not only that, but on the blade there are straw coloured lines where it lay on the rack. This scares me because not only does this mean my knife is probably too soft for a survival knife, but the lines lead me to believe that those straw lines means it is unevenly tempered.
IS any of this really critical? Do I need to reheat treat and if so how do I do that?
Any advice appreciated.
 
Don't let the colors worry you. They don't really tell you much. I do recommend that you get an oven thermometer because ovens are usually off.
 
If the file skated after the quench than the steel hardened. If you tempered around 400 than you didn't pull too much hardness out. Temper twice for 1 hour.
If you're really worried about it you could put an edge on it and see how it holds up.
 
Rack blocks/reduces oxygen availability in and near contact surface to blade, hence straw color. Blue could mean temperature might flux upward toward upper 400's F range. I temper my O1 around 64-66rc, so won't guess your blade hardness in 400+F range. A cheap file usually is around 60rc (I tested a few CHN cheap files), so often I use the file corner to cut directly into the edge. In your case, if it won't skate after 0.01" depth, good chance your blade is softer than 60rc. Sometime decarb is thick but shouldn't be more than 0.02" deep (unless royal messed up).
 
The colors on the blade in temper after quench are caused by the oils and other stuff on the blade surface. These may be a myriad of colors from straw to purple. They are not at related to the blade being overheated.



They are not the same as the "temper colors" you see charts of. Those are used in "drawing a temper" on tools with a flame. The steel needs to be freshly ground clean and have no oils or other chemicals on it for the proper colors to show right.

O-1 gets quite hard with a normal HT. Austenitize at 1450F and quench in most any oil and it is Rc65 as-quenched. It has a very slow drop in hardness with temper heat. At a temper of 400F, it is in the low Rc60's ( Rc 62/63) Even at a temper of 600F, the blade would still be between Rc 5758. You have to heat it to 700F to get below Rc55, and 800F to drop down to the lower Rc50's.
 
Just to cover/followup to my previous post.

I just tempered 3 O1 blades from 66+rc to 65rc with 2x 1hr at 400F in my Evenheat oven. There is a light straw color for all 3 blades fresh ground surfaces prior 400F temper. I lowered these blades hardness because I want 15dps edge to macro ripple or roll when light chop a 16d nail on anvil. *note: one of O1 blade actually brine quenched, other 2 were P50 quenched.

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Like the others were saying, the tempering colors depend not only on temperature, but time spent at that temp, air environment, surface contamination, etc. The colors are the result of oxidation, so the longer they're cooking, the darker colors will appear, even at the same temp. You're seeing the lighter colors where it was up against the rack because there probably wasn't as much air movement getting to it, so it didn't oxidize as much. You can fire blue mild steel fittings in yer kitchen oven and control the color this same way, just by leaving them in longer at the same temp.
 
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