17-7 - UNS S17700:
Type 17-7 PH is a semi-austenitic precipitation hardening alloy that provides high strength and hardness, excellent fatigue properties, good corrosion resistance, and minimum distortion upon heat treatment. Corrosion resistance is similar to AISI Type 304 stainless steel; having good resistance to staining and pitting under normal atmospheric conditions with a Pitting Resistance Equivalent Number (PREN) of 17. These properties make it an ideal material choice for aerospace applications and products requiring high strength and good corrosion resistance. It retains remarkable mechanical and physical properties at high temperatures.
17-7 precipitation hardening alloy 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 the soft austenitic annealed condition, 17-7 is highly formable and ideal for operations such as tube drawing, bending, and end forming. 17-7 is readily weldable in both the annealed and heat treated conditions.
- Melting Point: 2550 - 2640°F (1400 – 1450°C)
- Density: 0.282 lbs/in3 / 7.8 g/cm3
- Modulus of Elasticity in Tension (RH 950 & TH 1050): 29.6 X 106 psi / 204 GPa
- Tensile Strength Minimum (psi): 130,000
- Yield Strength Minimum 0.2% offset (psi): 40,000
- % Elongation in 2” Typical: 35%
- Hardness: Rockwell B85
Condition: Hardened + Aged (TH1050)
- Tensile Strength Typical (psi): 200,000
- Yield Strength Typical 2% offset (psi): 185,000
- % Elongation in 2": 9%
- Hardness: Rockwell C40
Condition: Hardened, Cryogenic Quench + Aged (RH950)
- Tensile Strength Typical (psi): 235,000
- Yield Strength Typical 2% offset (psi): 220,000
- % Elongation in 2": 6%
- Hardness: Rockwell C48
Condition: Cold Rolled/Worked + Aged (CH900)
- Tensile Strength Typical (psi): 265,000
- Yield Strength Typical 2% offset (psi): 260,000
- % Elongation in 2": 2%
- Hardness: Rockwell C49
- Carbon: 0.09 max
- Manganese: 1.00 max
- Phosphorus: 0.040 max
- Sulfur: 0.030 max
- Silicon: 1.00 max
- Chromium: 16.00 - 18.00
- Nickel: 6.50 - 7.75
- Aluminum: 0.75 - 1.50
- Iron: Balance
17-7 requires three essential steps in heat treating:
- Austenite conditioning.
- Cooling to transform the austenite to martensite
- Precipitation hardening to Condition TH 1050 or RH 950
- Alternatively, to obtain the highest mechanical properties from the alloy, Condition A material is transformed to martensite at the mill by cold reduction to Condition C. Hardening to Condition CH 900 is accomplished with a single, low-temperature aging heat treatment.
Corrosion resistance in Conditions TH 1050 and RH 950 is generally superior to that of the standard hardenable chromium types of stainless steels such as Types 410, 420 and 431. Corrosion resistance in Condition CH 900 approaches that of Type 304 in most environments.