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Chemical Properties
The chemistry offered is derived from the parent AISI 200
series, with suitable technical modifications to achieve the
final properties in a cost effective manner as compared to
the existing 304 Grade SS.
Literature survey reveals that AISI 200 series
were developed in 1950's in the United States, that development
was strictly by the nickel shortage which was prevalent at
that time.
The composition of these Steels varied widely
with carbon ranging from 0.08 to as high as 0.25% ,nickel
from 0.3 to around 7% ,Nitrogen from 0.10 to 0.4% with a chromium
level of 14 to 18%.The technical theme behind development
of these grades was mainly to substitute the costly nickel
with manganese and nitrogen to achieve the austenitic structure
by controlling the ratio of austenite forming elements and
ferrite forming elements ( Ferrite Factor )
The drawbacks with these steels were higher
carbon ( > 0.1%) and higher nitrogen resulting into poor cold
formability characteristics. With these back ground a new
chemistry was designed in which the carbon is controlled to
a maximum level of 0.09% and nitrogen upto 1700ppm to aid
in formability addition of Copper is made so that the work
hardening rate is controlled.
Thus the optimized chemistry offered by us
is
| Grade |
SI4 |
S |
0.015 |
| C |
0.07-0.09 |
Ni |
0.75-0.95 |
| Mn |
9.2 - 9.4 |
Cr |
14.8-15.2 |
| Si |
0.4 -0.6 |
Cu |
1.7-1.9 |
| P |
0.075 |
N2 |
1550-1750 |
Top
Physical Properties -
| Physical properties
of annealed AISI 200 Series |
| Density |
gr/cu.cm |
7.74 |
| lb/cu.in |
0.28 |
| Thermal
Conductivity |
20-100°C Cal/cm/sec/°C/cm |
0.039 |
| 68-212°C Btu/ft2/hr/°F/ft |
9.4 |
| Specific
Heat |
0-100°C Cal/gm/°C |
0.122 |
| 32-212°F Btu/lb/°F |
0.12 |
| Coefficient
of Thermal Expansion |
20-100°C cm/cm/°C |
16.6*10^-6 |
| 68-212°F in/in/°F |
9.2*10^-6 |
| 20-316°C cm/cm/°C |
18.0*10^-6 |
| 68-600°F in/in/°F |
10.0*10^-6 |
| 20-538°C cm/cm/°C |
19.6*10^-6 |
| 68-1000°F in/in/°F |
10.0*10^-6 |
| 20-871°C cm/cm/°C |
203*10^-6 |
| 68-1600°F in/in/°F |
11.3*10^-6 |
Top
Mechanical Properties -
| |
200 Series |
300 Series |
0.2% proof
stress (kg/mm2)
|
35.5 |
26.7 |
| Tensile Strength (kg/mm2)
|
77.2 |
59 |
| Elongation |
50.0 |
55.6 |
| GSN |
8-9 |
7.8 |
| Hv |
208 |
157 |
| Erchsen value |
12.5 |
12.9 |
| Limited Drawing Limit |
2.0 |
2.3 to 2.5 |
Top
Corrosion Properties
-
Considering that the components manufactured
out of these sheets are used in normal atmospheric conditions
chromium level 14.5% to 15.5% is quiet to resist pitting corrosion.
Experiments carried out showed
the following result
- Kitchen utensils and cutleries retained their surface
finish and luster similar to 304 Grade
- Laboratories scaled experiments carried out under different
media revealed the following data:
Corrosion Rates of the Stainless Steels
Fully Immersed in
3% Sodium Chloride
Stainless
Steel
|
Temperature |
Duration |
Corrosion
Rate |
Visual
Observation |
| °K |
°C |
(Hour) |
x 10^-2
mmpy |
| J |
303±2 |
30±2 |
720 |
2.58 |
Localised
Attack |
| S |
303±2 |
30±2 |
720 |
3.29 |
Localised
Attack |
| J |
371±2 |
98±2 |
100 |
0.25 |
Material Remained Same |
| S |
371±2 |
98±2 |
100 |
0.43 |
Material Remained Same |
Corrosion Rates of the Stainless Steels Fully
Immersed in Organic Acid Mixture(0.5%
Citric Acid+0.5% Tartaric Acid)
Stainless
Steel
|
Temperature |
Duration |
Corrosion
Rate |
Visual
Observation |
| °K |
°C |
(Hour) |
x10^-2
mmpy |
| J |
303±2 |
30±2 |
720 |
0.44 |
Fungal growth |
| S |
303±2 |
30±2 |
720 |
0.38 |
Fungal growth |
| J |
371±2 |
98±2 |
100 |
0.34 |
Material Remained Same |
| S |
371±2 |
98±2 |
100 |
0.17 |
Material Remained Same |
Dissolution Behaviour of the three stainless
steels in 3% NaCl on total Immersion
| SS |
Temp
°C |
Duration
(hours) |
Elements estimated
by AAS (ppm) |
| Fe |
Cr |
Cu |
Mn |
Ni |
Ti |
| J |
30±2 |
720 |
0.177 |
0.011 |
0.003 |
0.508 |
- |
- |
| S |
30±2 |
720 |
0.157 |
0.048 |
0.024 |
0.048 |
- |
- |
| J |
98±2 |
100 |
0.057 |
0.007 |
0.015 |
0.829 |
- |
- |
| S |
98±2 |
100 |
0.010 |
0.012
|
0.028 |
0.035 |
- |
- |
The above data suggest that the corrosion resistant as good
as 304 Grade SS under normal atmospheric conditions
Top
Formability
The blanks cut from the annealed sheets respond
favorably to the commonly fabrication operations such as deep
drawing ,spinning, welding ,bidding ,rib formation, embossing,
electro deposition of metals like Copper and necking of cylindrical
parts.
The quantified data on formability is given
below: Limited Drawing Ration
- 2
Percentage Stretch in Spinning
- 30%
Erichsen Value - 12.5
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