Sep 26 2012
Topics Covered
Introduction
Chemical Composition
Physical Properties
Mechanical Properties
Thermal Properties
Other Designations
Fabrication and Heat Treatment
Machinability
Welding
Heat Treatment
Hot Working
Cold Working
Annealing
Applications
Introduction
Stainless steels are high-alloy steels which have high corrosion
resistance when compared to other steels due to the presence of large
amounts of chromium. They contain about 4-30% of chromium. Based on
their crystalline structure, they are further divided into ferritic,
austenitic, and martensitic steels. Another group of stainless steels
are known as precipitation-hardened steels. They are the combination of
martensitic and austenitic steels.
Grade 15-7 stainless steel is a semi-austenitic precipitation
hardening stainless steel. It has high strength and moderate corrosion
resistance. The following datasheet gives an overview of grade 15-7
stainless steel.
Chemical Composition
The following table shows the chemical composition of grade 15-7
stainless steel.
| Element |
Content
(%) |
| Iron, Fe |
74.9 |
| Chromium, Cr |
15 |
| Nickel, Ni |
7 |
| Molybdenum, Mo |
2 |
| Aluminum, Al |
1.1 |
Physical Properties
The physical properties of grade 15-7 stainless steel are given in
the following table.
| Properties |
Metric |
Imperial |
| Density |
7.81 g/cm3 |
0.282 lb/in³ |
Mechanical Properties
The mechanical properties of grade 15-7 stainless steel are
displayed in the following table.
| Properties |
Metric |
Imperial |
| Tensile strength |
900 MPa |
131000 psi |
| Yield strength (@ strain 0.200%) |
380 MPa |
55100 psi |
| Elastic modulus |
190-210 GPa |
27557-30458 ksi |
| Poisson's ratio |
0.27-0.30 |
0.27-0.30 |
| Elongation at break |
30% |
30% |
| Hardness, Rockwell B (converted
from Brinell hardness) |
88 |
88 |
Thermal Properties
The following table outlines the thermal properties of grade 15-7
stainless steel.
| Properties |
Metric
|
Imperial
|
Thermal expansion (@21-93ºC/199ºF)
|
9 µm/mºC |
5 µin/in°F |
Thermal conductivity (@21ºC/70ºF)
|
15.1 W/mK |
105 BTU in/hr.ft².°F |
Other Designations
Other designations that are equivalent to grade 15-7 stainless steel
include:
- AMS 5520
- AMS 5657
- ASTM A564 (632)
- ASTM A579 (632)
- ASTM A693 (632)
- ASTM A705 (632)
- DIN 1.4532
- DIN 1.4574
- MIL S-8955
- AMS 5812
- AMS 5813
Fabrication and Heat Treatment
Machinability
Grade 15-7 stainless steel has good machinability in the hardened
condition.
Welding
Grade 15-7 stainless steel can be welded using common arc and
resistance methods. Inert gas shielding is avoided in order to prevent
oxidation of aluminum.
Heat Treatment
Solution treated material is cold worked which results in condition
C material. The condition C material is heated at 482°C (900°F) for 1 h
followed by cooling.
Solution treated material is heated at 955°C (1750°F) for 10 min in
A1750 condition followed. In R100 condition, it is cooled at -73°C
(-100°F) for 8 h with in 1 h of treating to A1750 condition. It is
again heated at 510°C (950°F) for 1 h in the RH 950 condition. After
fabrication, it is heated at 760°C (1400°F) for 90 min in the condition
T. It is again cooled at 13°C (55°F) for 0.5 h with in 60 min. It is
heated at 565°C (1050°F) for 90 min in TH1050 condition followed by
cooling in air.
Hot Working
Grade 15-7 stainless steel has good hot working capacity. This
process should be followed by annealing in order to respond heat
treatment.
Cold Working
Grade 15-7 stainless steel is limited to cold working.
Annealing
Grade 15-7 stainless steel is annealed at 1038°C (1900°F) followed
by cooling rapidly.
Applications
Grade 15-7 stainless steel is used in the following applications:
- Diaphragms
- Welded and brazed honeycomb panels
- Retaining rings
- Aircraft bulkheads
- Springs
- Other applications requiring high strength at elevated
temperatures