17-7PH, UNS S17700, W.Nr. 1.4568
17-7PH precipitation-hardening stainless steel is a semi-austenitic being austenitic in the annealed condition and martensitic in the hardened condition. It provides high strength and hardness, excellent fatigue properties, good corrosion resistance, good formability, and minimum distortion upon heat treatment, widely used for applications requiring good corrosion resistance combined with high strength. 17-7PH stainless steel is easily formed in the annealed condition, then hardened to high strength levels by simple heat treatments. Also, the material provides exceptional mechanical properties at temperatures up to 900ºF (482ºC) in heat treated condition.
| Material | Cr | Mn | P | S | Si | Cr | Ni | Al |
|---|---|---|---|---|---|---|---|---|
| 17-7PH | 16.0-18.0 | 1.00 max | 0.04 max | 0.03 max | 1.00 max | 16.0-18.0 | 6.50-7.75 | 0.75-1.50 |
| Material | Tensile strength | Yield strength 0,2 | Elongation | Hardness HB30 |
|---|---|---|---|---|
| 17-7PH | 896 N/mm² | 276 N/mm² | 35% | 85HB |
In conditions TH 1050 and RH 950, the corrosion resistance of 17-7PH is superior to that of the standard hardenable chromium types of stainless steels such as types 410, 420, and 431, but not quite as good as the chromium-nickel type 304. But in most environments, the corrosion resistance of 17-7PH approaches that of type 304 in conditions CH 900.
For the heat treatment of 17-7PH condition A products, the following three essential steps are required to develop the high strengths of conditions TH 1050 and RH 950. First, austenite conditioning. Second, cooling to effect transformation of austenite to martensite. Third, precipitation hardening.
Heating of 17-7PH is commonly performed for heat treatment purposes. The process involves heating the material to specific temperatures and holding it for a certain duration in controlled atmospheres, and air cooling or quenching, to prevent oxidation and achieve desired mechanical propertie, improve strength and hardness. Post-treatment processes may be necessary to meet the final product specifications.
Pickling is a common process used to remove surface impurities and oxide layers from 17-7PH. It involves immersing the material in a pickling solution, typically an acid-based solution, to dissolve contaminants and restore the material's corrosion resistance.
17-7PH stainless steel can be formed using both hot and cold forming processes, depending on the desired shape, complexity, and mechanical properties required for the application.
Hot Forming: 17-7PH exhibits good hot workability, allowing it to be easily formed by employed the common hot forming methods such as hot rolling, hot forging, and hot extrusion. The specific temperature range for hot forming can vary depending on the desired deformation and the requirements of the application. Hot forming is typically used for larger and more complex components that require extensive shaping.
Cold Forming: 17-7PH retains its good ductility and formability even at lower temperatures, allowing it to be easily formed by employed the common cold forming methods such as cold rolling, cold drawing, bending, and deep drawing. Cold forming is often preferred for smaller, simpler components or those that require high dimensional accuracy and surface finish. Also, It improves the strength and hardness of this material due to work hardening during the process.
Machining characteristics of 17-7 PH precipitation-hardening stainless steel are same as type 302 stainless steel. It requires appropriate tools, cutting parameters, and techniques to achieve desired results. After machining, the 17-7PH stainless steel can undergo a heat treatment process, such as aging or precipitation hardening, to restore or enhance its mechanical properties.
17-7PH precipitation-hardening stainless steel is weldable by the common fusion and resistance techniques to achieve optimum mechanical properties. When a weld filler is needed, W 17-7PH is most often specified, the austenite conditioning and precipitation hardening heat treatments are both required after welding to achieve high strength levels. Compared to 17-4PH, 17-7PH stainless steel have poorer weldability, which degrades penetration and enhances weld slag formation during arc welding, due to the high contents of Al.
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