| Alloy
303
Sandmeyer Steel offers Alloy 303 in thicknesses
from 3/16" through 2".
303 合金（UNS S30303）是无磁性的、奥氏体、可自由切削的不锈钢产品，这个
产品在基10%铬、8%镍的不锈钢产品基础上稍作变化，它的机械切削性更强，同
时还保持了良好的机械和抗腐蚀特性。
Specs:
304 Free-Machining Grade
General Properties
Typical Analyses
Resistance to Corrosion
Resistance to Oxidation
Physical Properties
Mechanical Properties
Fabricating Properties
General Properties
The Alloy 303 is a free-machining stainless steel specifically
designed to exhibit improved machinability. Sulfur is
added to produce the free-machining characteristics
while maintaining good mechanical and corrosion-resistant
properties.
Alloy 303 is a non-magnetic, austenitic
stainless steel which is not hardenable by heat treatment.
It is the free-machining modification of the basic 18%
chromium – 8% nickel stainless steel.
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Typical
Anlayses
| Element |
Percent |
| Carbon |
0.15 max |
| Manganese |
2.00 max |
| Silicon |
1.00 max |
| Chromium |
17.00 - 19.00 |
| Nickel |
8.00 - 10.00 |
| Phosphorous |
0.20 max |
| Sulfur |
0.15 min |
| Molybden |
0.60 max* |
| Iron |
Balance |
*Optional
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Resistance
to Corrosion
The addition of certain elements to stainless
steels to impart better machining characteristics also
slightly lowers corrosion resistance. For dry conditions,
and in most mildly corrosive environments, the free-machining
grade is practically comparable with its corresponding
unmodified type. Where moist atmospheres are involved,
some free-machining grades may tend to form a rust film,
and in certain severe environments, they may show somewhat
increased corrosion as a result of the free-machining
additions. In a majority of cases, they will perform
nearly the same as the basic parent composition.
Because the free-machining grades have
a slightly reduced corrosion resistance compared with
unmodified basic stainless steel, bright machined parts
may be susceptible to surface dulling or etching by
final treatment with nitric acid solutions. Caution
in the use of such treatments is suggested. For mild
action, mixtures containing as little as one or two
percent by volume nitric acid, with additions of an
inhibitor, may be allowable for short periods of time
at 120 to 140°F (49-60°C). A solution of 12
percent nitric acid and 4 percent copper sulfate is
also satisfactory where mild action is required. In
some instances, the complete elimination of treatment
with nitric acid solutions may be desirable.
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Resistance
to Oxidation
Alloy 303 has good resistance to oxidation at temperatures
up to 1700°F (927°C). In extreme oxidizing atmospheres,
irregular scaling may be encountered, particularly above
1400°F (760°C).
The rate of oxidation of all stainless
steels is greatly affected by the service atmosphere,
by heating and cooling cycles, and by design considerations.
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Physical
Properties
| Melting
Point |
2552°F
(1400°C) |
| Density |
0.290 lb/in3
or 8.03 g/cm3 |
Coefficient of Thermal Expansion
| Temperature Range |
|
| °F |
°C |
Per °F x 10-6 |
Per °C x 10-6 |
| 68 - 212 |
20 - 100 |
9.2 |
16.6 |
| 68 - 932 |
20 - 500 |
10.4 |
18.8 |
| 68 - 1450 |
20 - 787 |
10.9 |
19.6 |
Thermal Conductivity at 212°F (100°C)
| W/m•K |
Btu•in/hr•ft2•°F |
| 16.4 |
113.2 |
Electrical Resistivity
| Temperature |
|
| 糉 |
糃 |
Microhm-in |
Microhm-cm |
| 68 |
20 |
28.3 |
72.0 |
| 212 |
100 |
30.7 |
78.0 |
| 392 |
200 |
33.8 |
86.0 |
| 752 |
400 |
39.4 |
100.0 |
| 1112 |
600 |
43.7 |
111.0 |
| 1472 |
800 |
47.6 |
121.0 |
Magnetic Permeability
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Mechanical
Properties
The mechanical properties of these steels are functions
of their carbon, nickel and chromium, or chromium plus
manganese contents. Within the range of composition
for these steels, as furnished in the annealed condition,
the properties will vary within the following limits.
Room Temperature Properties - Annealed
Condition
Yield Strength
0.2% offset |
30 - 40 ksi
207 - 276 MPa |
| Tensile Strength |
75 - 90 ksi
517 - 621 MPa |
| Elongation in 2 in., % |
35 - 50 |
| Reduction in Area, % |
50 - 60 |
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Fabricating
Properties
Welding
Although the free-machining grades are not recommended
for welding, they may be welded with some difficulty.
Alloy 303 may be welded with Alloy 310 electrodes and
should be annealed after welding to redissolve precipitated
carbides, thereby increasing the resistance of the material
to intergranular corrosion.
Machining
The same machining methods commonly used for mild steel
are applicable to Alloy 303. High machining rates can
be obtained for these materials in the annealed condition
with hardnesses in the range of 200 to 240 Brinell.
However, modifications in machining techniques are necessary
to adjust to the special characteristics of each type
of stainless steel.
Since Alloy 303 will work harden, it should be machined
at reduced surface feet per minute and heavier feeds
to prevent glazing at the tool interface.
Annealing Temperatures
For maximum ductility, Alloy 303 should be annealed
near the upper limit of the 1800 - 2000°F (982-1043°C)
range. The material should be water quenched from the
annealing temperature to prevent harmful carbide precipitation.
For the same reason, heating within the 800 - 1500°F
(427 - 816°C) temperature range should be avoided
unless the material can be subsequently annealed.
Hardening Temperature
Alloy 303 is austenitic and cannot be hardened by heat
treatment.
Structure
Alloy 303 is austenitic at all temperatures. When heated
within the range 800 - 1500°F (427 - 816°C),
carbides will precipitate at the grain boundaries. Upon
reannealing, the carbides will be redissolved.
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