17-7 Alloy Stainless Steel

General Properties

Stainless Grade 17-7 PH ® is a precipitation hardening stainless steel that provides high strength and hardness, excellent fatigue properties, good corrosion resistance, good formability, and minimum distortion upon heat treatment. The alloy provides valuable property combinations particularly well suited for aerospace applications. This special alloy also provides benefits for other applications requiring high strength and good corrosion resistance, as well as excellent properties for flat springs at temperatures up to 600°F (316°C).

Applications

• applications requiring good strength, corrosion resistance and mechanical properties up to 800 F in service.
•  used for very detailed, intricate parts due to its low distortion in heat treatment.
• commonly found in a variety of springs and washers.

Corrosion Resistance

Corrosion resistance of Type 17-7PH stainless steel in all heat treated conditions, like other types of stainless steels – will develop superficial rust in some environments. For example, in a marine atmosphere, stainless steels show evidence of rusting after relatively short exposure periods. However, after exposure of one or two years, the amount of rust present is little more than that present at six months. As with all martensitic steels, 17-7PH stainless steel may be subject to cracking when exposed under stress in environments containing hydrogen sulfide. Such applications are not recommended.

Formability

In Condition A, the alloy can be formed comparably to Type 301. It work hardens rapidly and may require intermediate annealing in deep drawing or in forming intricate parts. Springback is similar to that of Type 301. This alloy is extremely hard and strong in Condition C. Therefore, fabrication techniques for such material must be used.

Weldability

The precipitation hardening class of stainless steel is generally considered to be weldable by the common fusion and resistance techniques. Special consideration is required to achieve optimum mechanical properties by considering the best heat-treated conditions in which to weld and which heat treatments should follow welding. This particular alloy is generally considered to have poorer weldability compared to the most common alloy of this stainless class, 17-4 PH stainless steel. A major difference is the high Al content of this alloy, which degrades penetration and enhances weld slag formation during arc welding. Also, the austenite conditioning and precipitation hardening heat treatments are both required after welding to achieve high strength levels. When a weld filler is needed, 17-7 PH is most often specified.

Chemical Properties

Mechanical Properties

Physical Properties