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17-7 stainless steel (also called 17-7 PH, UNS S17700, or AISI 631), has a chemical composition of 17% chromium and 7% nickel—thus 17-7. However, there is also a small addition of aluminum that gives this material interesting properties in both cold-worked and precipitation-hardened condition.

Compared with 304 stainless steel, 17-7 has similar corrosion resistance, but in a similar cold-worked condition it has increased strength and better machinability. When heat-treated, 17-7 exhibits increased hardness and tensile strength, which is not achieved by cold-working alone.

Stainless steel has great wearability, good formability, good corrosion resistance, and has minimal distortion upon heat treatment. It is the material of choice for medical, aerospace, and commercial applications.

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  • In cold-worked condition, 17-7 has excellent machinability. A tensile strength above 160ksi provides good strength and dimensional stability when machining. Care must be exercised not to generate high heat when cutting to avoid hardening the material. This is mostly taken care of by machining with a cutting fluid flood of the area.
  • In annealed condition (Condition A), 17-7 has better machinability than annealed 304.

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17-7 has excellent weldability using tungsten inert gas welding (TIG). TIG is also called gas tungsten arc welding (GTAW).

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In annealed condition (Condition A), in cold-worked, or heat-treated condition (RH950 or TH1050), 17-7 is slightly ferromagnetic.

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  • In Condition A (annealed), 145ksi MAX tensile can be heat-treated to RH950 or TH1050.
    • Lengths up to 12 ft can be supplied.
  • As-Drawn, 160ksi MIN—NOT Condition C, but as hard as we can get it. Our As-Drawn (160ksi MIN) can be heat-treated with the CH900 process and results in tensile strengths of about 200ksi.
    • Accu-Tube cannot supply our tubing in the actual Condition C (200ksi MIN tensile), according to the 17-7 Material Data Sheet (MDS), because of the inability for thin-walled tubing to straighten when in the very hard Condition C (200ksi MIN tensile) without damaging the integrity of the material. Since the tubing has a lower tensile strength than the required 200ksi using the CH900 heat-treat process, it will also not be quite as hard as the 17-7 MDS states (240ksi). However, depending on the diameter and wall thickness of the tubing, the strength of our tubing will generally achieve a tensile strength of 180ksi MIN. This 180ksi MIN equates to approximately 40Rc MIN hardness.
    • Lengths up to 12 ft can be supplied.

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RH950 and TH1050 can be achieved on any material we supply. If the RH950 or TH1050 properties are desired, we recommend the following:

  1. Receive As-Drawn 160ksi MIN tubing in 12-ft lengths from ACCU-TUBE.
  2. Machine your part as desired.
  3. Clean your part.
  4. Send your part to your vacuum heat-treat vendor to provide the heat-treat desired. The vacuum-treat vendor needs to understand this because the parts will require a solution heat- treat (Condition A) before heat-treating to the RH950 or TH1050.
  5. Parts in heat-treated condition cannot be bent or formed, but they can still be machined.
  6. If bright parts are desired after heat-treat, mechanical or electropolishing can be performed.

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