Many different industries and manufacturers can benefit from salt heat treatments, including blade manufacturers, aerospace, armament and defense, and tool and die. Salt heat treatment is one of the best ways to reduce or to eliminate distortion in a quench and tempered part. Salt heat treatment equipment offers a fast and efficient process; there are a lot of benefits that get passed down to our partners who use salt heat treatment.
Molten salt is a great heat conductor. When the heat treater heats metals in a molten salt bath, the heating process is about four to six times faster than compared to heating in the open air or a controlled atmosphere furnace. As a result, your metal parts can be heated more consistently and with less time to distort in the high heat. The uniformity of salt bath heating and quenching results in more predictable post-hardening size changes than other heating and quench cooling procedures.
According to D. Scott MacKenzie, Ph.D., FASM, a research scientist of metallurgy at Houghton International, “Since metals have high thermal conductivity, the core of the part lags the surface by only a small amount. A 25 mm diameter of steel would require only four minutes to reach the austenitizing temperature [in a high temperature] salt bath, while it would take 20 to 30 minutes in a standard atmosphere radiation furnace.”
This is because molten salt baths transfer 90% of their heat directly to the part using conduction, radiation and convection phases of heat treat transfer, as opposed to atmosphere furnaces, which are only about 60% efficient using gas convection and radiation* for heat transfer (*above 1,200 F).
Molten salt quenching baths are eco-friendly compared to oil quenching; they have low toxicity and reduce overall part manufacturing costs that are passed on to customers by reducing post-heat treatment correction costs, such as blast cleaning, final grinding or part straightening.
Different molten salt blends allow us to reach the specific operating temperatures required to harden a variety of alloy systems at a given hardening temperature. Nitrate salts are primarily used for quenching for their low melting point and high uniformity of temperature throughout the molten bath. Often combining two different salts can help reduce the melting point further, which expands the bath’s operational flexibility to get the optimal mechanical properties for the end users in a quench and tempered part.
The temperature within a salt bath is consistent, with less than ± 5°F variation. All of these factors make size changes to the parts during heat treating more consistently predictable.
Akron Steel Treating Company is one of just a few commercial heat treating companies that offers a wide variety of Martempering and Austempering salt bath heat treatments. When parts are processed through AST’s salt lines, they are carefully racked in fixtures or individually wired and hung in the hot salts to ensure minimal distortion from processing. Since the parts are fully submerged into the molten hot salt baths, there is minimal distortion to parts with complex shapes. The processing salts also prevent the oxidation and scaling of the part surfaces so minimal part clean-up is needed on the part after heat treating and the hardened part maintains its alloy’s full hardened properties on its surface.
Would you like to learn more about our salt heat treatment processes? Contact us at Akron Steel Treating to learn how this process could benefit your products.« Back to General