Heat Treating 6150 Spring Steel

A Word on 6150 Spring Steel

6150 is reputed to be even tougher than 5160. Typically 6150 has about 10 points less carbon plus it has the addition of a bit of Vanadium, otherwise it is the same as 5160. Our 6150 was formulated to have a slightly higher carbon content. It was specifically designed to be forged and quenched.

Under the hammer it’s a little stiffer than 5160 and it can suffer from micro cracking if worked too cold. However, it doesn’t really hurt this stuff to run it up to a welding heat and work it while it is more ductile.

Hardening is where people sometimes run into trouble, it doesn’t harden unless you soak it awhile at austenitizing temperature (from 1500°F to 1600°). Most alloys you can get to temperature, quench, and everything is good. With this stuff you need to get to temperature, maintain temperature for 10 minutes or so before quenching. The Vanadium does slow down the transformation to austenite, so if you don’t let it soak (maintain temp) it may harden incompletely.

Vanadium retards grain growth even after long exposures at high temperatures. It also helps to control grain structures during heat treating.

Heat Treat

Soak around 1550° for about 10 minutes
Quench with oil, either Parks 50, Parks AAA, Canola or similar heated to 150°


After quench run two one hour tempering cycles to achieve a specific HRC range.
1. 375° – 57-58hrc
2. 400°- 54-55hrc
3. 500°- 50-52hrc

Make sure to visit the steel shop page for a full list of available sizes.

Typical Chemistry

Hardening: (Atmosphere or Vacuum Furnace).
Preheat: 1200-1250F (650-675C), equalize.
High Heat: 1550-1650F (845-900C), soak 10 to 30 minutes. For vacuum hardening, use the high side of the high heat range and soak times.
Quench: Oil quench to hand warm, 150F (65C). Temper immediately. Note vacuum furnaces must have oil quench capability.
Temper: Tempering at 400-1200 (205-650C) for 1 hour per inch (25mm) of thickness at temperature is recommended. (2 hrs min.). Air cool to room temperature.​

Click to View AISI 6150 Chemical Composition Data Sheet