Kitchen Oven for tempering? Various questions.

[Ferguson]

I have been searching the forums, and picking up bits and pieces of information, but I have not been able to gather all the information that I would like.

I believe that I could use a kitchen oven for tempering. Not sure about temperature or time. I have a couple of ways to check the oven temperature. However, a kitchen oven is not a precision instrument, and the fact that it is a gas oven means that the temperature control is less accurate, as I understand it. What I have read suggests that temperatures in the 300-500F range would work, but how long?

My assumption is that for chisels and drifts, I should quench the tip, but not the rest of the tool. Does that rule apply for raising hammers as well?

I have been using water for quenching, not oil, so I assume that I will not have nasty odors in the kitchen. Still may be something that I should do when my wife is out.

I learned to temper by color, but I am wondering if oven tempering would not be more accurate.

I am asking about 4130 and 1045 alloys.

On a related question, what should I do with my H13 or 4130 drifts and hot chisels? They certainly get pretty hot, so I assume that I have long since lost whatever heat treating might have been done. The H13 holds up pretty well hot, the 4130 drifts not so well. Are they even worth heat treating? If so, how?

Thanks,
Richard

[MattBower]

Oven tempering will be more accurate if you have good temperature control in your oven. Tempering by letting the colors run, e.g., from a hotter, unhardened part of the work, is imprecise and doesn't really give the work enough time at temperature for a proper tempering. Two cycles of an hour or so is a pretty decent rule of thumb for tempering. Of course with some tools the tempering temperature really isn't that critical.

H13 is a very good hot work alloy. Others here can tell you more about it, but if it was properly hardened in the first place, the hardness can be in the mid-30s RC even after heating to up around 1200 F. If you take minimal precautions to keep it from overheating, it can last a long time.

4130 and 1045 are not not hot work alloys. Unless you cool them very frequently during use, they're not likely to
stay hard for long. A lot of folks would say not to bother hardening them if you're going to use them in hot work. Just leave them normalized and cool frequently during use.

[Fosterob]

Unless you are wanting to do large pieces I would guess your chisels and drifts would fit in a toaster oven. You could always add a more precise control with a thermocouple and controller if you needed. No need to risk the wrath of wife that way, and more energy efficient on such a small oven, also easy to have in the shop and cheap at the thrift store.
Rob

[Drq]

I would take a look at the new digital thermometers they have for roasting meat. They're getting pretty accurate these days and then you wouldn't have to rely so much on the oven temp gauge, just play with your temperature knob on your oven till you get the right temp on the digital thermometer. If your doing smaller chisels in a gas oven I might think of building a heavy wall steel box to put them in just to slow down any big temperature swings if they exist.

[pkrankow]

The beauty of oven tempering is that at appropriate temperatures you can leave the part in nearly indefinitely without compromising the heat treat.

Phil

[thingmaker3]

My assumption is that for chisels and drifts, I should quench the tip, but not the rest of the tool. Does that rule apply for raising hammers as well?

One should never strike a hard tool with another hard tool. Chips can fly off and imbed themselves in flesh. This is why the struck end of chisels & punches are left softer. Since you won't be striking any part of your hammer with another hard tool, your hammer need not be differentially hardened.

[Ken Nelson]

while an oven can work well for many simpler steels, H13 should not be tempered in an oven.Crucible steel recommends that the steel is tempered at 1000-1200 deg F. Fully hardened h13 drops only slightly in the range from 400-800 deg, and then gains a point or two of hardness again at 900 deg F. the higher temperatures are recommended to get the H13 out of the brittle tempering range.