17-7 Stainless Steel Technical Data Sheet
Technical Information for 17-7
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Alloy
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UNS Number
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SAE Number
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GENERAL PROPERTIES
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The 17-7 alloy is a chromium-nickel-aluminum precipitation hardening stainless steel used for applications requiring high strength and a moderate level of corrosion resistance.
The 17-7 alloy has been available for many years and has found application in aerospace and many spring type applications requiring high strength. The 17-7 alloy may be formed in a soft austenitic condition and hardened to a high strength level by low temperature heat treatments. The low temperature heat treatment required for developing high strength 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. |
RESISTANCE TO CORROSION
| Tests have show that the corrosion resistance of the 17-7 alloy is comparable to that of Type 304 stainless steel in most media. In general, the corrosion resistance of 17-7 is superior to that of the hardenable 400 series stainless steels. |
PHYSICAL PROPERTIES
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Melting Point
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Density
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Specific Gravity
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Modulus of Elasticity
in Tension |
.282 lb/in³ 7.81 g/cm³ |
7.81 |
RH 950 & TH 1050 29 X 106 psi 200 Gpa |
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Alloy
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Temper
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Tensile Strength
Minimum (psi) |
Yield Strength
Minimum 0.2% offset (psi) |
% Elongation
in 2" Minimum |
Notes
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Alloy
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C
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Mn
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P
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S
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Si
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Cr
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Ni
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Mo
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Cu
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N
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Other
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The 17-7 alloy is weldable by conventional inert gas methods. The precipitation hardening reaction in the alloy is dependent on the presence of aluminum, a reactive element. For this reason, inert gas methods are used to protect against the loss of aluminum.
One of the desirable features of the alloy is the elimination of the need for preheating and postweld annealing procedures needed for conventional hardenable stainless steel materials. |
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One of the conditions in which 17-7 is furnished is the annealed condition, Condition A. In this condition, the material possesses an austenitic structure. As an austenitic material, the 17-7 alloy possesses a relatively low strength. This is the condition in which formability is easiest.
To develop the high precipitation hardened strength of the alloy by heat treatment, starting from Condition A, heat treatments are done to accomplish two necessary steps. The first is a heat treatment which alloys the relatively stable austenite of Condition A to transform to martensite (Austenite Conditioning and Transformation). The second is a precipitation hardening heat treatment to further strengthen the material. The austenite is easier to transform to martensite using a lower temperature heat treatment. For this reason, Condition TH 1050 uses a 1400° F (760° C) heat treatment to produce a martensite transformation around room temperature, and this is followed by a precipitation hardening heat treatment at 1050° F (565° C). If Condition RH 950 is desired, the austenite conditioning heat treatment is conducted at 1750° F (955° C). In this case, the martensite transformation is not complete until the material is held for some time at –100° F (-73° C). When transformation is complete, the material is precipitation hardened at 950° F (510° C) to Condition RH 950. Because the precipitation hardening reaction can be driven past peak strength by high temperature or excessive time at the aging temperature, higher temperature or longer time precipitation hardening heat treatments produce lower strength levels. When 17-7 with an austenitic structure is cold worked by substantial deformation, a transformation to martensitic structure results from the deformation. In this condition, Condition C, the material may be precipitation hardened directly by heat treatment at 900° F (482° C) to Condition CH 900. |