Thinking of Tempering Stainless Steel in a Conventional Oven?
Here’s What You Need to Know About Trying This Heat Treatment at Home
Tempering stainless steel seems like one of those steps you can DIY, right? The critical temperatures of tempering processes are lower than with other heat-treating processes. So many knifemakers and other metalworkers wonder if they can temper stainless steel in their kitchen oven at home.
If so, what’s the process? Is it worth the effort? Let’s explore the issue of using your home oven as a tempering oven.
Why Temper Stainless Steel at Home?
The high-heat hardening process weakens steel. After hardening, all steel gets brittle—stainless steel even more so. (Here’s more about stainless steel heat treating.)
The tempering process improves the toughness. Because it happens at a lower temperature than hardening and other heat treatments, it’s possible (in some cases) to temper stainless steel at home in your conventional oven.
If you can do it yourself, you can save money and get it done more quickly than you would by outsourcing this step.
What Heat Treating Can’t You Do in Your Kitchen Oven?
The answer is pretty much anything else. Tempering is the only heat treating you can do in a conventional oven.
The reason is that your oven can’t reach the critical temperatures (well over 1,000 °F) needed for hardening, annealing, or normalizing.
Even the high-temperature cleaning cycle on many kitchen ovens doesn’t get that hot. Besides, ovens with this feature typically lock closed during cleaning. Meanwhile, the temperature fluctuates wildly.
That’s not good for heat-treating processes, which you must monitor and control carefully.
Steps to Tempering
OK, so you want to do just the tempering in your oven. Here’s an overview of what you need to do.
Please note that these steps are only a broad guideline. Optimal parameters vary by stainless steel type and your application / desired mechanical properties / desired corrosion resistance.
1. Clean your steel.
Contaminants (dirt, oil, grease, even fingerprints) can affect your results. Clean your stainless steel with an alcohol-based cleaner.
Make sure your oven is as clean as possible, too!
2. Preheat.
Be patient. It takes a while for the typical oven to reach a good tempering temperature.
And what is that temperature? It varies with the type of stainless steel you have. You can achieve some level of tempering for many types of steel starting at 400 °F. (That’s good news for you because most conventional ovens don’t get hotter than 500 °F.)
On the plus side, tempering most stainless steels at ~400 °F will maintain a hardness level close to what the steel was after hardening.
For example, you can harden 440C stainless to Rockwell C 58 - 60. Tempering at this temp will drop the hardness, but only slightly, to 55 - 56.
The drawback is that you won’t improve the toughness as much at the low end of the tempering range.
3. Hold at temperature.
Returning to the 440C stainless example, put your workpiece in the oven and let it equalize at 400+ °F.
Hold at that exact temperature for at least two hours, plus 1 hour per inch of thickness over 2 inches.
4. Air cool.
Remove the workpiece from the oven.
Many experts recommend repeating the temper at least once. This approach can produce a finer grain structure, optimizing toughness.
Explore tempering and other heat-treating processes for specific stainless steels in further detail:
Key Considerations
Here are some things to remember about using a conventional oven to temper stainless steel.
- Home oven temps vary. Built-in thermometers and temperature controls are often imprecise. So, it isn’t easy to control the process tightly.
- Lower temps in the tempering range yield less toughness. Will the results be satisfactory for your application?
- Experts advise tempering promptly after hardening. Otherwise, the stresses can build up and be difficult to rectify.
- You can do all the heat treating yourself with a dedicated heat treat oven. Hot Shot knife making ovens, for example, can handle normalizing, hardening/quenching, and tempering.
Temper Your Expectations
Enjoy homespun experiments? Go ahead and try tempering stainless steel in a conventional oven. Getting optimal results might be challenging.
Given that tempering should be done in short order after the quench, many artisans may be better off with a more immediate and precise approach.
If you prefer DIY heat treat but want to do even more and get it right, Consider Hot Shot ovens. With Cool-Touch technology, precision control, and a range of sizes in stock, we’ve got an excellent solution for all your home heat treating needs.