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┃ Material
17-7PH, Type 631, UNS S17700, 17Cr-7Ni
┃ Overview
17-7PH is a chromium-nickel-aluminum semi-austenitic stainless steel which is austenitic in the annealed condition, but martensitic in the hardened condition. 17-7PH provides high strength and hardness, excellent fatigue properties, good corrosion resistance and minimum distortion upon heat treatment. It is easily formed in the annealed condition, then hardened to high strength levels by simple heat treatments.
┃ Characteristics
17-7PH may be formed in a soft austenitic condition and hardened to a high strength level by low temperature heat treatments. The low temperature allows minimum distortion compared to conventional quench and temper hardening processes. In addition to material produced by the standard refining procedures, material which has been vacuum arc or electroslag remelted is available for further increase in resistance to fatigue, for those applications subject to cyclic stresses.
┃ Application
17-7PH has been found application in aerospace, surgical parts and many spring type applications requiring high strength.
┃ Chemical composition (wt% as per AMS 5568)
|
C |
Si |
Mn |
P |
S |
|
≤0.09 |
≤1.0 |
≤1.0 |
≤0.040 |
≤0.030 |
|
Cr |
Ni |
Al |
|
|
|
16.0~18.0 |
6.50~7.75 |
0.75~1.50 |
|
|
┃ Corrosion resistance
Tests have shown that the corrosion resistance of 17-7PH is comparable to that of Type 304 stainless steel in most media. In general, the corrosion resistance of 17-7PH is superior to that of the hardenable 400 series stainless steels. Its intergranular corrosion may be a problem if the material is heated between 800°F (427°C) and 1650°F (899°C) or cooled slowly through that range.
┃ Mechanical property (AMS 5568)
Solution heat treated condition
Tensile Strength: 150 KSI min (1034 MPa min)
Yield Strength(0.2% Offset): 55 KSI min(379 MPa min)
Elongation: 20% min
Hardness: HRB92 max.
After austenite conditioning and precipitation heat treated
Ultimate Tensile Strength: 180 KSI min (1241 MPa min)
Yield Strength: 150 KSl min (1034 MPa min)
Elongation: 6%min
Hardness: HRC38 max.
┃ Heat treatment
17-7PH, in all forms, the material is furnished in the annealed condition.
Solution Heat Treatment
Tubing shall be solution heat treated by heating to1950±25°F (1066℃±14℃), holding at heat for a time commensurate with wall thickness and heating equipment and procedure used, and cooling in air or quenching in water.
After austenite conditioning and precipitation heat treating, tubing shall have the properties shown in above after being austenite conditioned by heating to 1400±25°F (760±14°C), holding at heat for 90±5 minutes, cooling to 55±5°F (13±3℃) within one hour, holding at that temperature for not less than 30 minutes, and precipitation heat treated by heating to 1050±10°F (566±6℃), holding at heat for 90±5minutes, and cooling to room temperature.
┃ Available Process
(1) Hot formed, annealed, descaled
(2) Cold worked and bright annealed
┃ Common Tests
Chemical composition
Tension
Hardness
NDT
Surface condition
Shape and dimension
Positive Material Identification
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