Need advice on 1084 Rockwell.

Apr 11, 2014
Just got back for getting a blade tested at the local heat treater and they tested my latest Aldo's 1084 blade at 57. I took it just past NM and quenched in canola and the did a 1 hour tempering at 410-415. Should I try to reheat treat to get a bit higher then retemper? I usually do 2-2 hour tempers at 410. But I only tried to do a shock temper this time just to see what my Rockwell was at.

I'd actually like to do another temper but I'm afraid of loosing another point or two and then being to soft. What would you guys recommend I do at this point?

A couple of things from my experience...

If you're at 57 after a 415 temper, you're not getting full hardness. Could be the austentizing temp, the soak time (shouldn't need much), or the oil. Canola can work, but is better pre-heated than room temp.

If you've tempered at 415, another temper at 410 shouldn't result in any lost hardness.

From 1500 with a 5 minute soak, into 10 second quench oil, I have to temper at 450 to get RC 60, as a point of reference.
I heated the oil to warm bath water temp before quenching. I put a magnet to it and it was not sticking. Should I reheat and then after non magnetic Should I stick back in for 10-15 seconds just to sure it's above NM temp?
Yes put it back in the forge to bring it back up to heat. For most noneuctoid steels you don't have to soak the steel but you do have to get it about 100 degrees above non magnetic to make sure everything goes into solution. And definitely make sure your oil is up to temp.
Yes...I would suggest re-hardening it as Jason recommended. If you are at 57 with a 410 or 415 sounds indeed like you did not reach full hardness in the quench. If using a magnet to determine temperature....remember the magnet stops sticking at 1414F. But you still must go to 1500F or the usual recommendation is "a shade more past non magnetic". If you reach 1500F and allow just a minute or two for the whole blade to equalize, quench in 130F canola oil. Should get 65 or so out of the quench. Tempering at 400f or so should give about 61. (looks like Rusty and I were typing the same thing at the same time. BTW...there is no "noneuctoid". 1084 is eutectic. 1095 is hypereutectic 1050 is hypoeutectic. Non-eutectoid would actually mean any steel that is NOT at the eutectoid point...which 1084 is.)
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So would I be safe to redo the HT process leaving it in heat for 10-15 seconds past non magnetic and then quench again in warm oil? The first one I did was much harder. I may have done mag test and quenche without additional heating. Maybe I was on the low end of critical and testing and quick quench may have allowed the steel to cool below critical a bit? I don't remember putting it back in for a bit to maintain temp before quench.
Hypo, that's the word(prefix) i was looking for, thank you sir.:D

Back in for sixty seconds would be better.

As a side not make sure that your oil is not getting to hot as well. if the oil is to hot it will affect the viscosity of the oil and actually cause a slower transformation in the steel. That may also account for a lower RC out of the quench.
Ok thanks guys I'm headed to the store in the morning for a thermometer for the oil. I will be re heat treating tomorrow.

Look at the blade when it stops sticking to the magnet. You want it a full shade brighter red...or about 75-100F hotter for 1084.
Went back and did a second heat treat and actually test the temp on the oil instead if just sticking my finger in it and saying "yeah it's warm". Went and bought a thermometer. Then went an reheated the blade to NM and left it in moving it around for about 30-40 seconds longer and quenched. This time when I did the file test it skated BIG TIME!!! File actually left no visible make what so ever. Almost like it was glass. That's what concerned me the first time was the file slightly removed material from the edge and that's what lead me to take it and have it Rockwell tested. Way harder now. I may do a single temper and have it retested before the final temper cycle. Thanks guys!!!

Question on 1084. The most reliable way I've been able to get 1084 hard with my primitive means has been to get it what is probably a shade hotter than needed before quench. Will seconds too hot greatly affect grain size? I haven't had any chipping problems except in situations like edge dropped on concrete, but I also don't test to failure.
1084 doesn't need to be "a shade hotter than needed before quench". 1084 needs to be "a shade hotter than the temp where the magnet releases". Magnet releases at 1414F, you need to be at 1500F. If you mean a few more seconds in the heat once the blade is already AT 1500F...that will not hurt at all. As a matter of fact, once you have reached 1500F, it is a good idea to "soak" for a minute with 1084....just to equalize the temp of the entire blade. From what I gather....grain growth will not occur until 1520F....and is MANY TIMES more temperature dependent than time. I recall reading where 52100 was left at 1500F for 5 hours, and no noticeable grain enlargement occurred. Remember, you don't have to go light speed from the forge to the quench. Just smoothly and quickly. Make a few practice runs. But it's not like you have 1 second to get to the quench. The 1 second means the quench medium has about 1 second to bring the blade down below the pearlite nose.
Also it could be the testing technique. Is the point where the steel is tested flat and parallel? Also has all decarb been cleaned off the area to be tested? These two things can cause lower readings when the steel is actually harder.
Grain growth is both time and temperature dependent. Below 1600F and for less than ten minutes, it isn't a significant issue.
No not the testing technique. It was done by our local industrial heat treating company who heat treats for hundreds of local and regional manufacturing, die, mold, and machine shops. It was not tested on the bevels but behind the ricasso. Good point though for future reference.

Also right from the first temper I was concerned due to failure of the file test. All is good now though.