Why Choose 17-7 Stainless Steel for Your Tubing Application?
17-7 stainless steel, otherwise known as 17-7 PH, UNS 177700, or AISI 631, is a precipitation-hardened alloy that exhibits good formability, minimal distortion upon heat treatment, and corrosion resistance comparable to 304SS tubing. 17-7 has a chemical composition consisting of 17% chromium and 7% nickel, with added aluminum that contributes to the alloys' cold worked and precipitation hardened qualities. When cold worked, 17-7 tubing has excellent machinability, even improved from 304SS. Typically Vita Needle offers 17-7 in either Condition C, the post-cold working, drawn temper that typically produces 150 -170 KPSI or greater tensile strengths depending on OD and wall thickness, or CH900, hardened via a single low 900° temperature heat treatment in a vacuum furnace that yields the highest tensile strength for this alloy. While 17-7 material is subject to minimal distortion during heat treatment due to the low temperature required compared to heat treatment processes used on other alloys, any heat treatment may cause slight dimensional changes or affect straightness in longer lengths and is still best performed once other fabrication and processes have been completed.
17-7 tube has been found to be well suited for minimally invasive and endoscopic surgical tools. While heat treatment anneals or softens 304SS, short low-temperature heating hardens 17-7, so selecting a cutting method for 17-7 requires consideration about the process and if it generates heat, as this will harden the material. Due to the tensile strength, corrosion resistance, and formability, 17-7 is used by our customers in fields ranging from aerospace and the gas & oil industry to medical applications such as orthopedic and endoscopic surgical tools.
Mechanical testing depicted below calculates Ultimate Tensile Strength (UTS), Yield, and Elongation through destructive testing of tubing. While 17-7 as drawn tube typically has a similar tensile as hard temper 300 series stainless, the UTS of 17-7 can be increased via CH900 precipitation hardening.