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 is 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 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, and then quench. The Vanadium seems to slow down the transformation to austenite and if you don’t let it soak (maintain temp) it may harden incompletely.
Make sure to visit the steel shop page for a full list of available sizes.
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.