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Stainless Steel - Grade 440 (UNS S44000)

By AZoM.com Staff Writers

Topics Covered

Introduction
Key Properties
    Composition
    Mechanical Properties
    Physical Properties
    Grade Specification Comparison
    Possible Alternative Grades
Corrosion Resistance
Heat Resistance
Heat Treatment
Welding
Machining
Applications

Introduction

Grade 440C stainless steels are high carbon steels, which attain the highest hardness, wear resistance and strength of all stainless steel grades after heat treatment. These properties make this grade suitable for applications such as valve components and ball bearings. Grade 440A and 440B stainless steels, on the other hand, have similar properties - except for a slightly lower percentage of carbon in grade 440A.

All three forms of grade 440 steels are commonly used. However, grade 440C is more readily available than the other standard grades. Grade 440F, a free-machining type of grade 440 series, is also available with a high carbon content similar to that of grade 440C. Martensitic steel grades are high-hardness steels, usually fabricated using techniques that require hardening and tempering treatments.

These grades have a corrosion resistance lower than that of other austenitic grades. The applications of martensitic steels are limited by the loss of strength caused by over-tempering at high temperatures, and loss of ductility at temperatures below zero.

Key Properties

The following section discusses the properties of grade 440 bar products covered under ASTM A276. These values may not be similar to that of other forms such as forgings and plates.

Composition

The chemical compositions of various elements of grade 440 stainless steels are tabulated below:

Table 1. Chemical composition ranges of grade 440 stainless steels

Grade

C

Mn

Si

P

S

Cr

Mo

Ni

N

440A

min.

max.

0.6

0.75

-

1

-

1

-

0.04

-

0.03

16

18

-

0.75

-

-

440B

min.

max.

0.75

0.95

-

1

-

1

-

0.04

-

0.03

16

18

-

0.75

-

-

440C

min.

max.

0.95

1.20

-

1

-

1

-

0.04

-

0.03

16

18

-

0.75

-

-

Mechanical Properties

Table 2. Mechanical properties of grade 440C stainless steels

Tempering Temperature (°C)

Tensile Strength (MPa)

Yield Strength 0.2% Proof (MPa)

Elongation (% in 50mm)

Hardness Rockwell (HR C)

Impact Charpy V (J)

Annealed*

758

448

14

269HB max#

-

204

2030

1900

4

59

9

260

1960

1830

4

57

9

316

1860

1740

4

56

9

371

1790

1660

4

56

9

* Annealed properties are typical for Condition A of ASTM A276# Brinell hardness is ASTM A276 specified maximum for annealed 440A, B and C.

Physical Properties

The following table outlines the physical properties of grade 440 stainless steels:

Table 3. Typical physical properties of grade 440 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

0-200°C

0-600°C

at 100°C

at 500°C

440A/B/C

7650

200

10.1

10.3

11.7

24.2

-

460

600

Grade Specification Comparison

Grade specifications for 440 stainless steels are given in the following table:

Table 4. Grade specifications of grade 440 stainless steels

Grade

UNS No

Old British

Euronorm

Swedish SS

Japanese JIS

BS

En

No

Name

440A

S44002

   

-

-

 

SUS 440A

440B

S44003

   

1.4112

X90CrMoV18

 

SUS 440B

440C

S44004

-

-

1.4125

X105CrMo17

-

SUS 440C

Possible Alternative Grades

Suitable alternatives to grade 440 stainless steels are listed in the table below:

Table 5. Possible alternative grades to 440 stainless steels

Grade

Reasons for choosing 440C

440A/B

Slightly softer and more corrosion resistant grade needed

440F

High machinability required, with same hardness and hardenability as 440C

420

Lower strength and hardness needed than any of the 440 grades

416

Higher machinability required, and the much lower hardness and strength is still adequate

Corrosion Resistance

Grade 440 stainless steels exhibit excellent resistance to mild acids, alkalis, foods, fresh water and air. A smooth polished surface also helps grade 440 steels resist corrosion in tempered, passivated and hardened conditions.

Grade 440C steels exhibit corrosion resistance similar to that of grade 304 steels.

Heat Resistance

Grade 440 stainless steels should not be used at temperatures below the relevant tempering temperature, due to loss of mechanical properties caused by over-tempering.

Heat Treatment

Annealing — Grade 440 stainless steels are full annealed at 850 to 900°C, followed by slow furnace-cooling at about 600°C and air-cooling. Sub-critical annealing is carried out at 735 to 785°C, followed by slow furnace-cooling.

Hardening — Grade 440 stainless steels are heated at 1010 to 1065°C, then quenched in air or oil. Oil quenching is usually carried out for heavy sections. Following this process, these steels are tempered at temperatures from 150 to 370°C, to achieve a high hardness and improved mechanical properties.

Tempering at temperatures between 425 and 565°C should be avoided as the corrosion and impact resistance properties of grade 440 tend to reduce in this range. Also, tempering of these grades at 590 to 675°C will result in high impact resistance and loss of hardness.

Welding

During welding, grade 440 stainless steels are pre-heated at 250°C, followed by full annealing. Grade 420 filler rods can be used to achieve a high hardness weld. Grade 309 or 310 filler rods will, however, provide soft welds, having high ductility.

Machining

Grade 440 stainless steels can be easily machined in their annealed state. Machining these grades after hardening is extremely difficult, or impossible in some cases.

Applications

Grade 440 stainless steels find applications in the following:

  • Chisels
  • Surgical equipment
  • High quality knife blades
  • Valve seats
  • Rolling element bearings
Date Added: Nov 7, 2001 | Updated: Apr 30, 2014
Comments
  1. Liew Thiam Soon Liew Thiam Soon Malaysia says:

    Can 440c steel be temper with charcoal fire? thanks.

  2. Liew Thiam Soon Liew Thiam Soon Malaysia says:

    Can 440C steel be temper with charcoal fire? Thanks.

  3. Yogesh K Verma Yogesh K Verma India says:

    Can 440c steel be used as punch for cutting and shearing of 0,5mm steel having a Tensile strength MPa - C1700-2050 (247-297)

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of AZoM.com.
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