Sep 26 2012
Topics Covered
Introduction
Chemical Composition
Physical Properties
Mechanical Properties
Thermal Properties
Other Designations
Fabrication and Heat Treatment
Machinability
Forming
Welding
Heat Treatment
Forging
Annealing
Hardening
Applications
Introduction
Stainless steels are called as high-alloy steels. They have high
corrosion resistance than other steels due to the presence of large
amounts of chromium in the range of 4-30%. Based on their crystalline
structure, stainless steels are divided into martensitic, ferritic and
austenitic. They are divided into another group known as
precipitation-hardened steels, which are a combination of martensitic
and austenitic steels.
The following datasheet will provide more details about grade 21-6-9
stainless steel, which has excellent toughness and high temperature
oxidation resistance.
Chemical Composition
The following table shows the chemical composition of grade 21-6-9
stainless steel.
| Element |
Content
(%) |
| Iron, Fe |
64 |
| Chromium, Cr |
20 |
| Manganese, Mn |
9 |
| Nickel, Ni |
6 |
| Silicon, Si |
1 |
| Nitrogen, N |
0.23 |
| Carbon, C |
0.080 |
| Phosphorous, P |
0.060 |
| Sulfur, S |
0.030 |
Physical Properties
The physical properties of grade 21-6-9 stainless steel are given in
the following table.
| Properties |
Metric |
Imperial |
| Density |
7.83 g/cm3 |
0.283 lb/in³ |
Mechanical Properties
The mechanical properties of grade 21-6-9 stainless steel are
displayed in the following table.
| Properties |
Metric |
Imperial |
| Tensile strength, ultimate |
883 MPa |
128000 psi |
| Tensile strength, yield (@0.2%) |
745 MPa |
108000 psi |
| Elongation at break (in 50 mm) |
56% |
56% |
| Modulus of elasticity (typical for
stainless steel) |
200 GPa |
29000 ksi |
| Machinability (based on 100
machinability for AISI 1212 steel) |
30 |
30 |
Thermal Properties
The following table outlines the thermal properties of grade 21-6-9
stainless steel.
| Properties |
Metric |
Imperial |
| Thermal expansion co-efficient (@
25-95°C/77-203°F) |
16.7 µm/m°C |
9.28 µin/in°F |
| Thermal conductivity
(@-180°C/-292°C) |
7.80 W/mK |
54.1 BTU in/hr.ft².°F |
Other Designations
Other designations that are equivalent to grade 21-6-9 stainless
steel include the following:
- AMS 5561
- AMS 5562
- AMS 5656
- ASTM A269 (XM-10)
- ASTM A276 (XM-10)
- ASTM A312 (XM-10)
- ASTM A314 (XM-10)
- ASTM A412 (XM-10)
- ASTM A479 (XM-10)
- ASTM A580 (XM-10)
- ASTM A813 (XM-10)
- ASTM A814 (XM-10)
Fabrication and Heat Treatment
Machinability
Grade 21-6-9 stainless steel is difficult is machine due to its high
work hardening rate. Hence, ample cutting fluids, positive feeds and
slow speeds are preferred to overcome work hardening.
Forming
The yield strength of grade 21-6-9 stainless steel is double that of
other conventional stainless steels. This has to be taken into
consideration while choosing required forming pressures and techniques.
Welding
Grade 21-6-9 stainless steel can be welded using SMAW, MIG and TIG
methods. Post-weld annealing can be performed on these steels to
improve corrosion resistance.
Heat Treatment
Grade 21-6-9 stainless steel can be stress-relieved at temperatures
below 705°C (1300°F). However, stress relieving of this steel below
(900 to 1250°F) would affect the mechanical properties of the steel.
Forging
Forging of grade 21-6-9 stainless steel can be performed at 927 to
982°C (1700 to 1800°F) followed by water or air quenching.
Annealing
Grade 21-6-9 stainless steel can be annealed at temperature ranging
from 982 to 1177°C (1800 to 2150°F) and then air cooled.
Hardening
Grade 21-6-9 stainless steel is unresponsive to heat treatment. It
can be hardened only through cold reduction.
Applications
The following are the major applications of grade 21-6-9 stainless
steel:
- Aircraft components
- Steam and autoclave parts
- Chemical and pollution control equipment