304 304 l-data-sheets-1-28-13

gggdgdg

TECHNICAL DATA SHEET AISI 304 AISI 304L

s t a i n l e s s - s t r u c t u r a l s . c o m P a g e | 1

Stainless Steel Structural Shapes: 304 and 304L Austenitic (Chromium-Nickel)

INTRODUCTION There are many grades of austenitic stainless steels, the most popular of which are 304 and 304L. Those

two account for about half of the total stainless steel production in the United States. Those are the two

grades we will address on this data sheet. Other grades include 316 316L, 317, 317L, 321, 347. Stainless

Structurals can manufacture shapes in almost any of the austenitic grades, plus nickel, duplex and exotic

alloys. If you need a particular grade, ask your sales representative.

Stainless Structurals’ shapes are stripped from plate with lasers, laser fused together, straightened,

ground, de-twisted and passivated. They are produced to ASTM-A-1069, which also includes a number of

other specifications.

Austenitic (18-8) stainless steel alloys possess significant beneficial properties. They are strong, light,

ductile, aesthetically pleasing and readily available in a variety of forms. They resist corrosion and

oxidation; fabricate and clean easily; and prevent contamination of products. They have also exhibited

good strength and toughness when exposed to cryogenic conditions.

Stainless Structurals offers two variations of the 18-8 stainless steels:

§ AISI 304 (S30400)

§ AISI 304L (S30403)

Of the two types, 304 is the most widely used alloy, followed by 304L. 304L is typically used for welded

applications that must resist intergranular corrosion. The essential difference is in the carbon content,

which is required to be lower in 304L than 304. These two grades are frequently supplied dual certified as

304/304L. This means that the carbon content, which is expressed as a maximum in both grades, is in

compliance with the maximum carbon content called for by each specification. In addition the dual

certified material meets the minimum mechanical properties, which are required to be higher in 304.

Therefore, the dual certification means the material is in full compliance with both specifications, providing

the higher minimum strength requirements for one grade along with the better intergranular corrosion

resistance of the other.

gggdgdg



Some popular applications of these two grades are in food processing, appliances and dairy. Standards

and specifications have been developed to guide the manufacture, construction and use of these grades.

The guidelines are listed herewith.

SPECIFICATIONS AND CERTIFICATIONS The following table provides the list of US specifications for the two popular grades.

Table 1: ASTM and ASME Specifications

Product Form Specification

ASTM ASME Plate, Sheet and

Strip A 240 SA-240

Laser Fused Structural Shapes

A1069

The specifications stipulate allowable stresses for the various product forms of the alloys. Within the

ASME Boiler and Pressure Vessel Code (Section II, Part D), the allowable stresses are given for 304 for

use up to a maximum temperature of 1500°F (816°C); and 304L up to 800°F (426°C).

In addition to ASTM and ASME, the National Sanitation Foundation accepts all alloy variations for food

preparation and storage; and the Dairy and Food Industries Supply Association (Sanitary Standards

Committee) approves all variations for contact with dairy products.

gggdgdg



PROPERTIES This section outlines the chemical composition, physical and mechanical properties of 304 amd 304L.

1.0 Chemical Composition ASTM A240 provides the typical chemical compositions for the 18-8 stainless steel variations. Refer to

Table 2 below. Table 2: Typical Chemical Compositions

Periodic Element

Percentage (%) Weight1

304 304L

Chromium

17.5 19.5

17.5 19.5

Nickel

8.0 10.5

8.0 12.0

Manganese 2.00 2.00

Silicon 0.75 0.75

Carbon 0.07 0.030

Nitrogen 0.10 0.10

Phosphorus 0.045 0.045

Sulfur 0.030 0.030 1 Maximum value, unless range is specified

2.0 Physical Properties The physical properties of austenitic stainless steel alloys are given below.

2.1 General

The following are accepted general physical properties of austenitic stainless steel alloys:

§ Density - 0.285 lb/in3 (7.90 g/cm3)

§ Melting Range - 2550 - 2590°F (1399 - 1421°C)

§ Modulus of Elasticity - 29 Mpsi (200 GPa)

(in Tension)

gggdgdg



2.2 Thermal

The following are accepted thermal properties of the alloys:

§ Specific Heat:

°F °C Btu/lb/°F J/kg.K

32 - 212 0 - 100 0.12 500

§ Linear Coefficient of Thermal Expansion:

Temperature Range Coefficients

°F °C in/in/°F cm/cm/°C

68 - 212 20 - 100 9.2 x 10-6 16.6 x 10-6

68 - 212 20 - 100 11.0 x 10-6 19.8 x 10-6

§ Thermal Conductivity

Temperature Range Btu/hr.ft.°F W/m.K

°F °C

212 100 9.4 16.3

932 500 12.4 21.4

Although other metals exhibit higher thermal conductivities, the stainless steel alloys are able to more

efficiently transfer heat through the maintenance of smooth, clean surfaces.

2.3 Electrical

Electrical resistivity properties include:

Temperature Range Microhm-in Microhm-cm

°F °C

68 20 28.3 72

212 100 30.7 78

392 200 33.8 86

752 400 39.4 100

1112 600 43.7 111

1472 800 47.6 121

1652 900 49.6 126

gggdgdg



2.4 Magnetic

Austenitic stainless steel alloys are not typically magnetic in the annealed condition (magnetic

permeability ≈ <1.02 at 200H). While cold work will increase the magnetic permeability, Stainless

Structurals’ shapes are manufactured from annealed material.

Percent Cold Work

Magnetic Permeability 304 304L

0 1.005 1.015

10 1.009 1.064

3.0 Mechanical Properties The mechanical properties of austenitic stainless steel alloys are as noted below.

3.1 At Room Temperature

ASTM A240 and ASME SA-240 require the following minimum properties for plate, sheet and strip forms

of the annealed alloy variations. A1069 laser fused structurals are in compliance. Table 3: Minimum Mechanical Properties

Property Minimum Mechanical Properties1

304 304L

0.2% Offset Yield Strength: psi

MPa

30,000

205

25,000

170

Ultimate Tensile Strength: psi

MPa

75,000

515

70,000

485

Percent Elongation in 2 in. or 51 mm

40.0 40.0

Hardness, Max.: Brinell

RB

201 92

201 92

1 In accordance with ASTM A240 and ASME SA-240

3.2 Cold Work As the alloys are cold worked (deformed) at room temperature or thereabout, partial transformation of

austenite (in the alloys) to martensite can occur. As this happens, the alloys tend to increase in yield and

gggdgdg



ultimate strength while decreasing in elongation. Austenitic stainless structural shapes are not supplied in

the cold worked condition. .

3.3 Properties at Low and Elevated Temperatures The effects of low and elevated temperatures on short-term tensile properties are displayed below. Creep

and stress ruptures should be considered at temperatures equivalent to or higher than 100°F (538°C).

Typical information is as follows.

Table 4: Tensile Properties at Varying Temperatures

Test Temperature 0.2%Yield Strength Tensile Strength Elongation

°F °C psi (MPa) psi (MPa) Percent in 2" or 51 mm

-423 -253 100,000 690 250,000 1725 25

-320 -196 70 000 485 230 000 1585 35

-100 -79 50 000 345 150 000 1035 50

70 21 35 000 240 90 000 620 60

400 205 23 000 160 70 000 485 50

800 427 19 000 130 66 000 455 43

1200 650 15 500 105 48 000 330 34

1500 815 13 000 90 23 000 160 46

3.4 Impact Resistance

Stainless steel, in the annealed condition, shows very high resistance to impact even at cryogenic levels.

This makes it a candidate for applications such as earthquake resistance, LNG facilities and cryogenics.

Typical results from Charpy V-notch impact tests are provided as follows:

Temperature Charpy V-Notch Energy Absorbed

°F °C Foot-pounds Joules

75 23 150 200

-320 -196 85 115

-425 -234 85 115

gggdgdg



3.5 Fatigue Strength

The fatigue strength, or endurance limit, represents the maximum amount of stress below which the

material is unlikely to fail after 10 million cycles in the air environment. For the austenitic stainless steels,

this figure is typically 35% of the tensile strength. A number of factors affect fatigue strength. A smooth

surface will provide greater strength than a rough or corroded surface. Fatigue strength is dependent on

many factors, so the quoted value can vary significantly.

4.0 Corrosion Resistance 4.1 General Corrosion

All variations of the austenitic stainless steel alloys show desirable resistance to corrosion within

moderately oxidizing and reducing environments. This resistance is due to the high chromium content in

these alloys, in which a microscopic layer of chromium oxide seals the surface.

As a consequence, the applicability of the alloys range from food processing equipment and utensils in

food, beverage and dairy industries, to heat exchangers, piping, tanks and other process equipment for

human consumables. The alloys are used to contain household and industrial chemicals; and are used in

non-marine environments as architectural and structural materials such as handrails and building

facades.

Examples of 304/304L resistance to oxidizing (acidic) environments is given below

% Nitric Acid Temperature

°F (°C) Corrosion Rate Mils/Yr (mm/a)

10 300 (149) 5.0 (0.13)

20 300 (149) 10.1 (0.25)

30 300 (149) 17.0 (0.43)

Other laboratory data for 304 and 304L in the table below illustrate that these alloys are also resistant to

moderately aggressive organic acids such as acetic, citric and even reducing acids such as phosphoric.

The relatively high nickel content of these alloys helps provide resistance to moderately reducing

environments. The more highly reducing environments such as boiling dilute hydrochloric and sulfuric

acids are too aggressive for these materials. Other grades such as 316/316L should be considered.

Boiling 50 percent caustic is likewise too aggressive for 304/304L. Consult your sales representative if

you need assistance.

gggdgdg



General Corrosion in Boiling Chemicals

Boiling Environment

Corrosion Rate, Mils/Yr (mm/a)

304 304L

20% Acetic Acid: Base Metal Welded*

0.1 1.0

(<0.01) (0.03)

0.1 0.1

(<0.01) (<0.01)

45% Formic Acid, Base Metal Welded*

55 52

(1.4) (1.3)

15 19

(0.4) (0.5)

10% Sulfamic Acid, Base Metal Welded*

144 144

(3.7) (3.7)

50 57

(1.3) (1.4)

1% Hydrochloric, Base Metal Welded

98 112

(2.5) (2.8)

85 143

(2.2) (3.6)

20% Phosphoric Acid, Base Metal Welded

<1.0 <1.0

(<0.03) (0.03)

-- --

-- --

65% Nitric Acid, Base Metal Welded

9.2 9.4

(0.2) (0.2)

8.9 7.4

(0.2) (0.2)

10% Sulfuric Acid, Base Metal Welded

445 494

(11.3) (12.5)

662 879

(16.8) (22.3)

50% Sodium Hydroxide, Base Metal Welded

118 130

(3.0) (3.3)

71 87

(1.8) (2.2)

*Autogenous weld on base metal sample.

In some cases, the low carbon 304L may show a lower corrosion rate than the higher carbon 304, as

shown by the data for formic acid, sulfamic acid and sodium hydroxides. Otherwise, the 304 and 304L

may be considered to perform equally in most corrosive environments. A notable exception is in

environments sufficiently corrosive to cause intergranular corrosion of welds and heat-affected zones on

susceptible alloys. 304L is preferred for use in such media in the welded condition since the low carbon

level resists carbide precipitation in the heat affected zone, and thereby enhances resistance to

intergranular corrosion.

4.2 Intergranular Corrosion

At high temperatures (800°F - 1500°F or 427°C to 816°C) during service conditions, these stainless steel

alloys may experience chromium carbide precipitation in the grain boundaries. This is typically referred to

‘sensitization’ and, when exposed to very harsh, aggressive conditions, the steel alloys may undergo

intergranular corrosion. It is the carbon content in 304 that causes sensitization under thermal processes;

as is the case for autogenous welds and heat-affected weld zones. Lower carbon content prolongs, but

does not eliminate, the likelihood for precipitation of harmful level of chromium carbides.

gggdgdg



Consequently, 304L with its lower carbon content is better suited for situations where the alloy is

commissioned in the as-welded condition. Dual certified 304/304L will have the same maximum carbon

limits as 304L, and is therefore allowable. Refer to the evidence provided below.

Intergranular Corrosion Tests

ASTM A 262 Evaluation Test

Corrosion Rate, Mils/Yr (mm/a)

304 304L

Practice B Base Metal Welded

20 (0.5) Intergranular 23 (0.6) Corrosion

20 (0.5) 20 (0.5)

Practice E Base Metal Welded

No Fissures on Bend Some Fissures on Weld

(unacceptable)

No Fissures No Fissures

PracticeA Base Metal Welded

Step Structure Ditched (unacceptable)

Step Structure Step Structure

4.3 Stress Corrosion Cracking (SCC)

The likelihood of stress corrosion cracking in the presence of halide ions is highest in 304 and 304L

alloys. This is due of their lower nickel content. Other conditions required for SCC include residual tensile

stress in the alloys and temperatures exceeding 120°F (49°C).

Residual stresses may occur from cold deformation during forming and thermal cycles during welding.

The stresses may be reduced via annealing or stress-relieving heat treatments following cold

deformation, although this is impractical for most shapes.

Refer to the table below for the behavior of the alloys during halide (chloride) stress corrosion testing.

Note that, although times are specified, failure is inevitable under these conditions.

Halide (Chloride) Stress Corrosion Tests

Test U-Bend (Highly Stressed) Samples

304, 304L

42% Magnesium Chloride, Boiling

Base Metal Welded

Cracked, 1 to 20 hours Cracked, ½ to 21 hours

33% Lithium Chloride, Boiling

Base Metal Welded

Cracked, 24 to 96 hours Cracked, 18 to 90 hours

26% Sodium Chloride, Boiling

Base Metal Welded

Cracked, 142 to 1004 hours Cracked, 300 to 500 hours

40% Calcium Base Metal Cracked, 144 Hours

gggdgdg



Halide (Chloride) Stress Corrosion Tests

Test U-Bend (Highly Stressed) Samples

304, 304L Chloride, Boiling --

Ambient Temperature Seacoast Exposure

Base Metal Welded

No Cracking No Cracking

4.4 Pitting/ Crevice Corrosion

Although SCC occurs in concentrated halide conditions, the alloys are suitable for fresh water and low

halide applications. 304 has been successfully used in surface condensers for cooling water with

concentrations of 1000 ppm chloride in power plants. Careful maintenance, cleaning and constant flow

were necessary.

Therefore, the halide concentration limit is typically taken as 100 ppm chloride; especially when crevices

may be present in the alloys. Evidence for this stems from 304 and 304L alloys showing no signs of

rusting or staining after the 100 hour, 5 percent neutral salt spray tests (ASTM B117). However, 304

stainless building facades, when exposed to sea blast or salt mists, exhibit pitting, crevice corrosion and

discoloration. So, at concentrations higher than 100ppm, crevice corrosion and pitting may occur; which is

why these alloys are not suitable for marine environments. Alloys containing molybdenum, e.g.,

316/316L, 317/317L, AL-6XN® or 254SMOare better suited for high chloride, acidic or heated

environments. . Stainless Structurals can provide all these grades, and more.

5.0 Weldability Of all the high-alloy steels, the austenitic stainless steel alloys have been found to be the most weldable;

and all fusion and resistance welding processes may be used. However, care during welding must be

shown to prevent cracking and preserve the corrosion resistant properties of the alloys.

During welding, temperature gradients occur in the alloys. The temperatures range from the melting

temperature in the molten pool to the ambient temperature in the extremities. Higher carbon content in

the alloys means there is a greater chance that the welding thermal cycles will cause chromium carbide

precipitation. And this will reduce the corrosion resistant properties. To counteract precipitation, 304 or

304/304L dual should be used for applications in the welded condition. Conversely, full annealing can be

done to remove the precipitant and improve the corrosion resistance. In most cases, however, full

annealing is not practical for a structural shape or construct. Laser fused stainless structurals are not

generally susceptible to the temperature gradient problems as noted above. That is because the fusion is

gggdgdg



very quick, the heat affected zone is much smaller than a conventional weld, and the joint cools much

more quickly.

304 and 304L grades will typically re-solidify with a small amount of post-weld ferrite. This is to minimize

the cracking susceptibility that austenitic steels show during welding.

308 (20% Cr-11% Ni) alloy is the preferred filler metal for welding 304/304L as it does not produce

martensite following multi-pass welds. And, to decrease to the tendency for hot cracking, the welding

environment is controlled in order to ensure the formation of a small amount of ferrite. 309 alloy (23%

chromium, 13.5% nickel) or nickel based filler metals are recommended in joining the austenitic alloys to

carbon steel. No filler metal is used in the production of A1069 laser fused structurals. The joints are

autogenous.

6.0 Heat Treatment Heat treating these alloys may be performed in order to remove the negative effects of cold forming

and/or to remove precipitated chromium carbides from their surfaces. To get both results, the alloys are

annealed, which occurs in the range of 1850°F (1010°C) to 2050°F (1121°C). To prevent the chromium

carbides from re-precipitating, cooling from these temperatures must be accomplished at high rates

through 1500-800°F (816°C – 427°C). As previously mentioned, heat treating is not practical for most

structural shapes due to their configuration and due also to their propensity for warping.

304 and 304L, like other austenitic grades, are not hardenable by heat treatment.

7.0 Cleaning Special care must be undertaken when these stainless steel alloys are fabricated. Likewise, routine

maintenance must be conducted while in use to ensure the alloys remain aesthetically pleasing and

corrosion resistant.

Fabrication:

During fabrication, the following cleaning habits should be employed:

§ Use inert gas processes in welding.

§ Use only stainless steel wire brushes to remove scale and slag, as carbon steel brushes can lead

to rusting of the surface.

§ Use passivating (descaling) solutions (e.g. mixture of nitric and hydrofluoric acids) for more

severe scale build-up during welding. The solutions should be quickly washed off after

application. This removes free iron from the surface, which could lead to surface corrosion.

gggdgdg



Use:

§ Pressure washing is recommended for normal maintenance on inland, light industrial and mild

applications.

§ More frequent washing should be used for heavy industrial application to prevent deposits that

could lead to corrosion and dullness.

§ Use non-abrasive cleaners, fiber brushes, sponge, or stainless steel wool to scrub off spots and

other deposits. If the material is polished, or if the appearance is important, limit the force used

with the stainless steel wool as it can leave permanent scratches on the stainless steel.

§ Clean and sterilize surfaces accordingly for critical applications. Use specially designed caustic

soda, organic solvent or mild acid solutions for additional cleaning in areas such as food

processing or pharmaceutical manufacturing. All such solutions must be washed off quickly.

Note that the products’ designs can impact on cleaning of the stainless steel alloys. Having equipment

free from sharp corners, crevices and rough welds can make cleaning. Polishing the surface of the

product also has a similar impact on cleanliness.

8.0 Surface Finishes Surface finishes for stainless steel structural shapes are noted below.

§ #1 Finish – hot rolled, annealed, and de-scaled surface. This is the standard;

– available in plate and sheet and all structural applications

– used in applications where smooth, bright finishes are not mandatory.

§ Polished finishes on structurals are available but may be costly Consult your Stainless Structurals

sales person for the most economical solution for your end use.

304 304 l-data-sheets-1-28-13

Engineering