Vacuum Heat Treating

A vacuum furnace is a sealed chamber connected to vacuum pumps that evacuate the air to extremely low pressures. Once we’ve pumped down to these ultra-low pressures, we introduce a small amount of inert gas (argon or nitrogen) and heat the parts using internal heating elements. Because there’s essentially no oxygen present, parts don’t oxidize during heating, which is why they come out bright and clean.

Advantages include excellent control over part appearance (parts often come out bright and shiny because there’s no oxidation), precise control over heating and cooling rates at every step of the process (tight process control), minimized distortion, and you can process contamination-sensitive materials like titanium and nickel alloys that would react badly to standard furnace atmospheres.

However, vacuum heat treating is more expensive than conventional oil quenching methods, so cost is the primary consideration for most customers. Additionally, because vacuum quenching can’t cool parts as rapidly as oil quenching, you’re limited in which materials can achieve full hardness through vacuum processes. Some alloys simply need the faster quench rates that oil provides to reach specification hardness levels.

Vacuum heat treating is heat treatment processing performed in a sealed, low-pressure protective atmosphere. Instead of heating parts in air or a standard furnace atmosphere, we evacuate virtually all atmosphere from the chamber and introduce controlled amounts of inert gases like argon or nitrogen. This prevents oxidation and contamination, giving you precise control over both the process and the final appearance of your parts.

Tool steels (A2, D2, S7, H13) are very commonly vacuum heat treated, as are martensitic stainless steels like 410, 420, and 440C. Austenitic stainless steels (304, 316) are often vacuum annealed to achieve bright, clean surfaces. High-temperature alloys including titanium alloys (Ti-6Al-4V) and nickel-based superalloys (Inconel 718, Inconel 625) are almost always vacuum processed because they’re so sensitive to atmospheric contamination at elevated temperatures.

We can perform vacuum hardening (heating and quenching to harden tool steels and stainless steels), vacuum annealing (slow cooling to soften materials), vacuum tempering (reheating after hardening to reduce brittleness), solution treating (for precipitation-hardenable alloys), aging (to increase strength after solution treating), and vacuum brazing (joining components with filler metals in a contamination-free environment).

Vacuum hardening itself leaves parts bright and shiny. However, the subsequent tempering process, if done in air, can still discolor parts. If bright, shiny appearance is critical for your application, you’ll want to specify both vacuum hardening and vacuum tempering so that all heat-exposed steps occur in the protective vacuum environment.

Vacuum furnaces are horizontal cylinders, which means the geometry can be a bit tricky. We list working dimensions for the base tray on our equipment pages, but because of the cylindrical shape, there’s actually some flexibility for larger parts. If you elevate a part above the base tray toward the center of the cylinder, you can often accommodate slightly larger dimensions. If your parts are close to our published limits, reach out to discuss whether we can make it work—we evaluate these situations on a case-by-case basis to avoid turning away parts that we can actually accommodate.