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Stainless Steel - Grade 431 (UNS S43100)

Chemical Formula

Fe, <0.20% C, 15-17% Cr, 1.25-2.50% Ni, <1.00% Mn, <1% Si, <0.040% P, <0.03% S

Topics Covered

Background

Key Properties

Composition

Mechanical Properties

Physical Properties

Grade Specification Comparison

Possible Alternative Grades

Corrosion Resistance

Heat Resistance

Heat Treatment

Welding

Machining

Applications

Background

This heat treatable martensitic, nickel-bearing grade has the best corrosion resistance properties of all the martensitic grades. It has excellent tensile and torque strength, and good toughness, making it ideally suited to shafting and bolt applications. It can be hardened to approximately 40HRC. Because of its high yield strength, this grade is not readily cold worked and is therefore not recommended for use in operations such as cold heading, bending, deep drawing or spinning.

Martensitic stainless steels are optimised for high hardness, and other properties are to some degree compromised. Fabrication must be by methods that allow for poor weldability and usually also allow for a final harden and temper heat treatment. Corrosion resistance is lower than the common austenitic grades, and their useful operating temperature range is limited by their loss of ductility at sub-zero temperatures and loss of strength by over-tempering at elevated temperatures.

Key Properties

These properties are specified for bar product in ASTM A276. Similar but not necessarily identical properties are specified for other products such as plate and forgings in their respective specifications.

Composition

Table 1. Composition ranges for 431 grade of stainless steels.

Grade

C

Mn

Si

P

S

Cr

Mo

Ni

N

431

min.

max.

-

0.20

-

1.00

-

1.00

-

0.040

-

0.030

15.00

17.00

-

1.25

2.50

-

Mechanical Properties

Table 2. Mechanical properties of 431 grade stainless steels.

Tempering Temperature (°C)

Tensile Strength (MPa)

Yield Strength 0.2% Proof (MPa)

Elongation (% in 50mm)

Hardness Brinell (HB)

Impact Charpy V (J)

Annealed *

862

655

20

285 max

-

204

1345

1055

20

388

50

316

1295

1035

19

375

53

427

1350

1080

19

388

#

538

1140

965

19

321

#

593

1015

770

20

293

64

650

960

695

20

277

84

Grade 431 is frequently stocked and supplied in "Condition T", with specified tensile strength of 850 - 1000MPa.

* Annealed tensile properties are typical for Condition A of ASTM A276; annealed hardness is the specified maximum. Grade 431 is only rarely stocked in annealed Condition A.

# Due to associated low impact resistance this steel should not be tempered in the range 425-600°C

Physical Properties

Table 3. Typical physical properties for 431 grade stainless steels.

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

431

7750

200

10.2

12.1

-

20.2

-

460

720

Grade Specification Comparison

Table 4. Grade specifications for 431 grade stainless steels.

Grade

UNS No

Old British

Euronorm

Swedish SS

Japanese JIS

BS

En

No

Name

431

S43100

431S29

57

1.4057

X17CrNi16-2

2321

SUS 431

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

Table 5. Possible alternative grades to 431 stainless steel.

Grade

Why it might be chosen instead of 431

410

Only a lower hardened strength is needed.

416

High machinability is required, and the lower hardened strength and lower corrosion resistance of 416 is acceptable.

440C

A higher hardened strength or hardness than can be obtained from 420 is needed.

Corrosion Resistance

Excellent resistance to a wide variety of corrosive media. Reasonable resistance to salt water in cold southern waters but less resistant than Grade 316 in tropical waters. Overall the corrosion resistance of 431 is approximately the same as or slightly below that of grade 304.

Performance is best with a smooth surface finish, in the hardened and tempered condition.

Heat Resistance

Resists scaling in intermittent service to 925°C and in continuous service to 870°C, but is generally not recommended for use in temperatures above the relevant tempering temperature, because of reduction in mechanical properties.

Heat Treatment

Full anneal - not practical for this grade - it hardens even when cooled slowly.

Process Anneal - heat to 620-660°C and air cool.

Hardened by heating to 980-1065°C, holding for about 1/2 hour then quenching in air or oil. Pre-heating at 760-790°C may be useful for complex parts or those already hardened. Temper to suit mechanical requirements, at temperatures as indicated in the accompanying table.

The tempering range 425-600°C should be avoided due to reduced impact toughness, although the effect is less marked than in most other martensitic grades.

Welding

Welding is difficult due to cracking. A pre-heat of 200-300°C is recommended prior to welding. Grade 410 filler rod can be used, but Grades 308L, 309 or 310 will provide more ductile welds, so long as matching properties are not required. Post-weld heat treat at 650°C.

Machining

In the annealed condition this grade is relatively easily machined, but if hardened to above 30HRC machining becomes more difficult.

Applications

Typical applications include:

         Nuts and bolts

         Propeller shafting

         Pump shafts

         Beater bars

         Marine hardware

         Laboratory benches & equipment

 

Source: Atlas Steels Australia

 

For more information on this source please visit Atlas Steels Australia

 

Date Added: Nov 7, 2001 | Updated: Jul 12, 2013
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