Do I need to re-heattreat ?

K

Keith Willis

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Oct 24, 2007
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I had 3 knives that I heattreated on Thurs.,I then put them in the toaster oven,as I always do,I did the first cycle at 400~ for 2 hours.I then put them in for the second cycle,but forgot and they stayed in the oven for about 15 hours.I know that was stupid,but I would like to know,do I need to heattreat them again,or did I compleatly mess them up.

Thanks for the help,
God bless,Keith

Sorry I posted this before this before I read Burton's post.
 
My guess is they're probably toast.. Get it, toast? Toaster oven? ...sorry...

They'll certainly be softer than your target, but by how much I don't know.
 
Will do Will,thanks for the advice

Will or someone,could you explain the proper way that is done?Do you sharpen them and roll the adge square with the brass rod? If that makes any sense.

Keith
 
Keith,
Sharpen the edge, put a piece of 1/8 - 1/4" brass or copper in your vise parallel to the floor, I use about a 35-45 Degree angle from horizontal and put enough pressure to see the cutting edge deform. Run the entire edge down the rod, if it chips= too hard, if it stays deformed=too soft and returns=just right. This is a good test to see if you're in the ballpark. Only sustained testing and experience will let you know if it's really right.
 
Is there a machine shop in your area? Take them and have them Rockwell tested. It probably won't cost much. I have left blades in overnight and it did'nt hurt a thing. As long as the oven did'nt overheat you should be fine.And by the way, a rockwell test is the only way you can know for sure what the hardness is.
 
From what I understand, it doesn't matter how long the blade stays in the heat, as long as the temperature does not go above your target. there is no difference between 2 hrs and 20 hrs at the same temperature. Now if during that time, the temp went higher then it might be too soft. Does this make sense?
 
jawilder said:
From what I understand, it doesn't matter how long the blade stays in the heat, as long as the temperature does not go above your target. there is no difference between 2 hrs and 20 hrs at the same temperature. Now if during that time, the temp went higher then it might be too soft. Does this make sense?
Click to expand...

Not quite right, It sure is much more related to the temp but it is also related to the time, but the time doesn't affect the same as temp but surely time affects anyways. If you put 20 hours tempering it will be definitely lower RC than 2 hours temper, but how much lower is I don't know, and I guess it will depend on steel type...
Emre
 
jawilder said:
From what I understand, it doesn't matter how long the blade stays in the heat, as long as the temperature does not go above your target. there is no difference between 2 hrs and 20 hrs at the same temperature. Now if during that time, the temp went higher then it might be too soft. Does this make sense?
Click to expand...


It is time and temperature dependant. If you were to graph the time at temp and resulting hardness you would find it to be a curve. The vast majority occurs early on, but it does keep going. I'm sure it approaches some asymptote. Two hours is a good temper time. 15 hours will yield a different (and lower) hardness for a given temperature, though how much different I don't know.
 
I did the overnight thing once. The entire knife came out the darkest, prettiest blue you could imagine. I thought it was ruined, but sharpened it up just to see. Well, it passes the brass rod test, and looks great with light colored scales. :D
 
Keith,
I would not worry about the blades. They should be fine. The simple thing to do is to put a quick edge on and test it. The brass rod edge test will tell you if the edge is too soft, but I really doubt it.

BTW, when posting a question like this, it really helps t give all the parameters. Steel type, how it was heat treated, etc.

The main variable in this question is how well the toaster oven regulates temperature. If it has worked well for the job in the past, it should be OK.

I use the rule of thumb that ten hours tempering is about the same as ten degrees increase in temperature. So, using that ratio, you did about the same as tempering for two hours at 415F. Not enough to make a noticeable difference.

Stacy
 
Sorry for not giving all information,that may have helped with answering

The steel I use is SKS5,which has always worked out ok,heating with a tourch to non- magnetic and cooling in peanut oil.Then tempering in a toaster oven 2x at 400* for 2 hours each.
I have not had time to check them,but I will be doing so tomorrow.

Thanks for the help,God bless,Keith
 
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