Sep 26 2012
Topics Covered
Introduction
Chemical Composition
Physical Properties
Mechanical Properties
Thermal Properties
Other Designations
Fabrication and Heat Treatment
Machinability
Welding
Forging
Hot Working
Cold Working
Annealing
Applications
Introduction
Stainless steels are known as high-alloy steels. They have excellent
corrosion resistance in comparison with other steels as they contain
more chromium.
Based on their crystalline structure, stainless steels are divided
into three groups, namely, martensitic, austenitic and ferritic steels.
A combination of martensitic and ferritic steels forms a fourth group
known as precipitation-hardened steels.
The grade 446 stainless steel is a ferritic, non-heat treatable
stainless steel that provides good resistance to high temperature
oxidation and corrosion. The following datasheet provides more details
of grade 446 stainless steel.
Chemical Composition
The chemical composition of grade 446 stainless steel is outlined in
the following table.
| Element |
Content
(%) |
| Iron, Fe |
73 |
| Chromium, Cr |
23.0 - 27.0 |
| Manganese, Mn |
1.50 |
| Silicon, Si |
1.0 |
| Nickel, Ni |
0.25 |
| Carbon, C |
0.20 |
| Phosphorous, P |
0.040 |
| Sulfur, S |
0.030 |
Physical Properties
The following table shows the physical properties of grade 446
stainless steel.
| Properties |
Metric |
Imperial |
| Density |
7.80 g/cm3 |
0.282 lb/in³ |
Mechanical Properties
The mechanical properties of grade 446 stainless steel are displayed
in the following table.
| Properties |
Metric |
Imperial |
| Tensile strength |
550 MPa |
79800 psi |
| Yield strength (@strain 0.200%) |
345 MPa |
50000 psi |
| Elastic modulus |
200 GPa |
29000 ksi |
| Poisson's ratio |
0.27-0.30 |
0.27-0.30 |
| Elongation at break |
20% |
20% |
| Hardness, Brinell (estimated from
Rockwell B) |
159 |
159 |
| Hardness, Knoop (estimated from
Rockwell B) |
173 |
173 |
| Hardness, Rockwell A (estimated
from Rockwell B) |
51.1 |
51.1 |
| Hardness, Rockwell B |
83 |
83 |
| Hardness, Vickers (estimated from
Rockwell B) |
159 |
159 |
Thermal Properties
The thermal properties of grade 446 stainless steel are given in the
following table.
| Properties |
Metric |
Imperial |
| Thermal expansion co-efficient
(@0-100°C/32-212°F) |
10.4 µm/m°C |
5.78 µin/in°F |
| Thermal conductivity |
21.6 W/mK |
150 BTU in/hr.ft².°F |
Other Designations
Equivalent materials to grade 446 stainless steel are:
- AISI 446
- ASTM A176
- ASTM A268
- ASTM A276
- ASTM A314
- ASTM A473
- ASTM A511
- ASTM A815
- DIN 1.4762
- QQ S763
- QQ S766
- ASME SA268
- ASTM A580
- FED QQ-S-763
- FED QQ-S-766
- MIL SPEC MIL-S-862
- SAE J405 (51446)
Fabrication and Heat Treatment
Machinability
Machinability of the grade 446 stainless steel is possible at slow
speeds with positive feeds, rigid mounts and sharp tooling surfaces.
Welding
The grade 446 stainless steel can be easily welded using most of the
traditional methods except oxyacetylene welding. Type 308 welding
material can be used if required, but it will not exhibit scaling
resistance equal to the base metal. Differences in coefficient of
thermal expansion of base and weld metal has to be taken into
consideration.
Forging
Forging can be started at 1149°C (2100°F) and completed at 871°C
(1600°F). The last 10% of forging has to be performed below 871°C
(1600°F) to gain grain refinement and room temperature embrittlement.
Hot Working
The hot working of grade 446 stainless steel is performed in between
the ranges 1093- 1177°C (2000-2150° F). The last 10% of hot working has
to be performed below 871°C (1600°F) to gain grain refinement
Cold Working
The grade 446 stainless steel is more difficult to cold work than
other stainless steels due to the high level of chromium content.
Annealing
Annealing of the grade 446 stainless steel has to be soaked at 816°C
(1500°F) and then water quenched. The temperature should not exceed
900°C (1650°F) at any time and slow cooling below 649°C (1200°F) can
cause loss of ductility.
Applications
The grade 446 stainless steel can be used in the following products:
- X-ray tube bases
- Boiler baffles
- Oil burner components
- Annealing boxes
- Industrial mufflers
- Kiln linings
- Glass molds
- Furnace parts