September 2011 / Volume 63 / Issue 9|
A bright idea
By Alan Richter, Editor
In the world of precision metal parts, aesthetics can be everything. For example, metalworking professionals expect precipitation hardenable stainless steel to look bright silver. “When they hear ‘stainless steel’ and then see something other than silver, the immediate question in their minds is ‘is this really stainless steel?’ ” said Don Jordan, vice president of R&D and corporate metallurgist for Solar Atmospheres, which specializes in vacuum heat treating.
The process to anneal and bright age-harden PH stainless steels in a vacuum furnace typically requires the heat treater to cool the metal below the ambient temperature after annealing by placing it in a refrigerator before the age-hardening step, Jordan explained. That requires exposing stainless to air, which causes it to discolor—oxidize—to a golden blue hue during age hardening. “You’re breaking the vacuum,” he said, adding that the discoloration doesn’t negatively impact material properties but people interpret that it does.
Courtesy of Solar Atmospheres
To prevent oxidization, Solar Atmospheres developed a two-step process using advanced gas-cooling technology to anneal and bright age-harden PH stainless in a vacuum furnace without breaking vacuum. The metal is heated to 1,900° F, cooled to 80° F for 17-4 and 15-5 stainless and below 60° F for the 17-7 and 15-7 Mo alloys, and then age-hardened at 900° F or higher depending on the desired end condition, which establishes the mechanical properties. Jordan noted that the typical hardness for 17-4 is 44 to 47 HRC for the H900 condition.
Before Solar Atmospheres developed this process, if the hardened stainless parts could not look blue, an end user would have to remove the oxide layer chemically or mechanically, such as with light glass beading or tumbling.
For more information about Solar Atmospheres, Souderton, Pa., call (215) 721-1502 or visit www. solaratm.com. CTE
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