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Stainless Steel - Grade 409 (UNS S40900)

Chemical Formula

Fe, <0.08% C, 10.5-11.75% Cr, <0.5% Ni, <1.0% Mn, <1.0% Si, <0.045% P, <0.03% S, 6x%C-0.75% Ti

Topics Covered

Background

Key Properties

Composition

Mechanical Properties

Physical Properties

Grade Specification Comparison

Possible Alternative Grades

Corrosion Resistance

Heat Resistance

Heat Treatment

Welding

Applications

Background

409 is a titanium stabilised ferritic stainless steel. Although regarded as a general-purpose chromium stainless steel the primary application for Grade 409 is automotive exhaust systems. Its applications are those where appearance is a secondary consideration to mechanical properties and corrosion resistance and where some weldability is required.

More highly stabilised versions of 409 are useful where 409 has been proven marginal - these grades S40910, S40920 and S40930 are stabilised with titanium, niobium or both titanium and niobium.

Key Properties

These properties are specified for annealed tubing in ASTM A268. Similar but not necessarily identical properties are specified for other products such as coil and bar in their respective specifications.

Composition

Typical compositional ranges for grade 409 stainless steels are given in table 1.

Table 1. Composition ranges for 409 grade stainless steel

Grade

C

Mn

Si

P

S

Cr

Ni

Ti

409

min.

max.

-

0.08

-

1.00

-

1.00

-

0.045

-

0.030

10.5

11.75

-

0.50

6x%C

0.75

Mechanical Properties

Typical mechanical properties for grade 409 stainless steels are given in table 2.

Table 2. Mechanical properties of 409 grade stainless steel

Grade

Tensile Strength (MPa) min

Yield Strength 0.2% Proof (MPa) min

Elongation (% in 50mm) min

Hardness

Rockwell B (HR B) max

Brinell (HB) max

409

380

207

20

95

207

Physical Properties

Typical physical properties for annealed grade 409 stainless steels are given in table 3.

Table 3. Physical properties of 409 grade stainless steel in the annealed condition

Grade

Density (kg/m3)

Elastic Modulus (GPa)

Mean Coefficient of Thermal Expansion (μm/m/°C)

Thermal Conductivity (W/m.K)

Specific Heat 0-100°C (J/kg.K)

Electrical Resistivity (nΩ.m)

0-100°C

0-315°C

0-538°C

at 100°C

at 500°C

409

7600

208

11.0

11.7

12.4

25.8

27.5

460

600

Grade Specification Comparison

Approximate grade comparisons for 409 stainless steels are given in table 4.

Table 4. Grade specifications for 409 grade stainless steel

Grade

UNS No

Old British

Euronorm

Swedish SS

Japanese JIS

BS

En

No

Name

409

S40900

409S19

-

1.4512

X6CrTi12

-

SUH 409

These comparisons are approximate only. The list is intended as a comparison of functionally similar materials not as a schedule of contractual equivalents. If exact equivalents are needed original specifications must be consulted.

Possible Alternative Grades

Possible alternative grades to grade 409 stainless steels are given in table 5.

Table 5. Possible alternative grades to 409 grade stainless steel

Grade

Why it might be chosen instead of 409

3CR12

Similar corrosion resistance, easier welding and more readily available than 409, particularly in heavy sections. (409 may have better drawability than 3CR12.)

304

Better corrosion resistance and heat resistance but at higher cost.

321

Higher heat resistance than 409 or 304.

Aluminised steel

Lower resistance to exhaust gases, but at lower cost than stainless steel grade 409.

Corrosion Resistance

Grade 409 resists atmospheric and exhaust gas corrosion. A light surface rust will form in most atmospheres; this rust retards further corrosion but makes the surface undesirable for decorative applications. The corrosion resistance is about the same as that of 3CR12 and the 12% chromium martensitic grades such as 410, and inferior to the 17% chromium grade 430.

Heat Resistance

Generally 409 is classified as resistant to scaling in intermittent service up to 815°C and up to 675°C in continuous service, but these temperatures are dependent upon the exact service environment.

Heat Treatment

Annealing - heat to 790-900°C and air cool. This grade cannot be hardened by thermal treatment.

Welding

Readily welded but a pre-heat of 150-260°C is recommended. Grade 409 or Grade 430 electrode or filler rods can be used, but AS 1554.6 pre-qualifies welding of 409 with Grade 309 rods or electrodes. These austenitic fillers result in a more ductile weld.

Post-weld annealing at 760-815°C improves weld ductility.

Post-weld annealing is not required when welding thin sections. Automotive exhaust tubing is typically welded without filler metal (autogenously).

All welding must be carried out with minimum heat input to reduce grain growth effects.

Applications

Typical applications include:

         Automotive exhaust systems

         Catalytic converters

         Mufflers

 

Source: Atlas Steels Australia

 

For more information on this source please visit Atlas Steels Australia

 

Date Added: Oct 23, 2001 | Updated: Jul 12, 2013
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