17-7 Stainless Steel Tube
Delivering corrosion resistance similar to 304 SS, 17-7 stainless tube delivers considerably greater tensile strength and hardness qualities than other 300 series stainless tubes of equal dimensions. It can readily be cold worked to achieve high strengths, known as “Condition C”, and can be further heat treated to achieve even higher tensile strengths by heat treating the tube at 900 degrees Fahrenheit, known as “CH-900”. 17-7’s unique attributes---maintaining austenitic qualities of good corrosion resistance and delivering martensitic qualities of higher strength levels---make it attractive for products requiring these blended characteristics. These qualities are especially important for high strength, thin wall tubing applications which are increasingly in demand as manufacturers seek to optimize and miniaturize many products.
Aluminum is added to 17-7 with nominal chromium values of 17% and nickel 7% by weight to the alloy, and the aluminum is a key ingredient in giving 17-7 the precipitation hardening qualities that permit greater tube strength than can be achieved by cold work alone. Under different naming conventions, it is called S17700 or AISI 631. An alloy with similar characteristics to 17-7, known as 17-4, is available in seamless tube form. However, market availability for 17-4 in strip form for welded and drawn, thin wall applications, is highly limited. Therefore, customers often rely on 17-7 tubing due to greater availability and lower cost.
Easily fabricated by a variety of cutting and forming methods, the timing of the final heat treat to achieve maximum strength is important when bending, flaring, or forming since these operations are considerably more challenging once the tube is hardened. Otherwise, milling/turning and grinding are routinely used to transform 17-7, as are electrical discharge machining, electrochemical grinding and cutting. Laser machining, welding and mechanical assembly methods are compatible with 17-7 tube.
Industries & Applications:
Applications for 17-7 usually have a need for high strength and good corrosion resistance and include but are not limited to:
- Musculoskeletal / orthopedic instruments
- Surgical instruments including needles or cutting instruments
- Light tubes for endoscopy applications
- Robotic surgical devices including mechanical power transmission
- Lab/ testing products, including biopsy needles
- Industrial products demanding high strength to weight ratios