This article is all about heat treating silver steel. There are many different types of steel, silver steel a really useful material for the hobbyist if you learn about heat treating it.
Heat uniformly to 770-780°C until heated through. Quench in water. Sizes up to 8mm or 5/16” dia may be oil hardened from 800-810°C.
In this particular instance I’m hardening a piece of silver steel that is to be used as a rivet punch. Hence it has a concave dome machined into one end.
I’m hardening just the end that fits over the rivet.
The colour of the steel can be used as a rough guide to it’s temperature and the table below gives that relationship.
Colour Temperatures
The colour of a piece of steel may be used as a guide to it’s temperature. These are particularly useful when hardening or tempering steel.
| Colour | °C |
| Pale yellow | 221 |
| Straw | 230 |
| Golden yellow | 243 |
| Brown | 254 |
| Brown to purple | 266 |
| Purple | 277 |
| Bright blue | 288 |
| Blue | 293 |
| Dark blue | 316 |
| Just visible red | 500 to 600 |
| Dull cherry red | 700 to 750 |
| Cherry red | 750 to 825 |
| Bright cherry red | 825 to 875 |
| Brightest red | 900 to 950 |
| Orange | 950 to 1000 |
| Light orange | 1000 to 1050 |
| Lemon | 1100 to 1200 |
| White | 1200 to 1300 |
Quenching
The difference in quenching media determines how fast the steel is cooled, with water cooling the fastest and air cooling the slowest.
Tempering
From the first quench from “cherry red” the steel is very hard. It is so hard that it can not be used as a tool without breaking. It is too brittle.
When you temper, you are taking a piece of steel that is as hard as glass from the first quench, and making it just a little softer. This redeuces the brittleness and makes it tougher.
After quenching, heat the part back to around 100°C to 150°C. I’ve done this again in a blow torch, but it is better if this temperature and time is better controlled. As the temperature is within the range of a conventional household oven it is possible to anneal it at 150°C for 30 minutes.
The higher the temperature the lower the final hardness, but also the less brittle it will be.
Further Notes:
Silver steel bar is supplied annealed.
When hardening consideration should be given to heat treatment temperatures, including rate of heating, cooling and soak times. Note that soak times will vary due to a number of factors such as the shape and size of each silver steel component.
Other considerations during the heat treatment process include the type of furnace, quenching medium and the work piece transfer facilities.
References
- What is Quenching? – Sheffield Gauge Plate blog post on quenching and a comparison of the different quenchants: air, water, oil, vegetable oil
- Oil hardening steel – Sheffield Gauge Plate blog post on the subject of oil hardening steel. Overview, benefits and selecting the correct oil.
Having hardened the silver steel, if you temper at 150C do you then quench in water ?
I don’t think it matters either way. Personally I just let it cool gradually after being in the oven at 150°C
What Rockwell ‘C’ is normally achieved when quenched in water?
If you temper at 100°C for an hour then Rockwell C hardness is around 66, tempering at ~150°C reduces the hardness to around 63.