Hardfacing

Hardfacing may be broadly defined as the application of a wear-resistant material, in depth, to the vulnerable (or worn) surfaces of a component by a weld overlay or thermal spray process. This discussion deals with the weld overlay materials used to resist wear; the thermal spray materials are covered in the previous section in this article. More detailed information on hardfacing process and alloy selection can be found in Ref 47 and 53.

Welding processes used to apply hardfacing materials range from the traditional (for example, oxyacetylene torch) to the new and sophisticated (for example, plasma-transferred arc, PTA, and laser methods). To accommodate these different overlay processes, the hardfacing materials are available in a variety of forms. The most popular processes, and the forms most commonly associated with each process, are listed in Table 36.

Table 36 Characteristics of welding processes used in hardfacing

Welding process

Mode of application

Form of hardfacing alloy

Weld-metal dilution,

Deposition

Minimum thickness(a)

Deposit efficiency, %

%

kg/h

lb/h

mm

in.

OAW

Manual

Bare cast rod, tubular rod

1-10

0.5-2

1-4

0.8

32

100

Manual

Powder

1-10

0.5-2

1-4

0.8

32

85-95

Automatic

Extra-long bare cast rod, tubular wire

1-10

0.5-7

1-15

0.8

32

100

SMAW

Manual

Flux-covered cast rod, flux-covered tubular rod

10-20

0.5-5

1-12

3.2

8

65

Open arc

Semiautomatic

Alloy-cored tubular wire

15-40

2-11

5-25

3.2

8

80-85

Automatic

Alloy-cored tubular wire

15-40

2-11

5-25

3.2

8

80-85

GTAW

Manual

Bare cast, tubular rod

10-20

0.5-3

1-6

2.4

32

98-100

Automatic

Various forms(b)

10-20

0.5-5

1-10

2.4

32

98-100

SAW

Automatic, single wire

Bare tubular wire

30-60

5-11

1025

3.2

8

95

Automatic, multiwire

Bare tubular wire

15-25

1127

2560

4.8

3 16

95

Automatic, series arc

Bare tubular wire

10-25

1116

2535

4.8

3 16

95

PAW

Automatic

Powder(c)

5-15

0.5-7

1-15

0.8

32

85-95

Manual

Bare cast rod, tubular rod

5-15

0.5-4

1-8

2.4

32

98-100

Automatic

Various forms(b)

5-15

0.5-4

1-8

2.4

32

98-100

GMAW

Semiautomatic

Alloy-cored tubular wire

10-40

0.9-5

2-12

1.6

1 16

90-95

Automatic

Alloy-cored tubular wire

10-40

0.9-5

2-12

1.6

1 16

90-95

Laser

Automatic

Powder

1-10

(d)

(d)

0.13

0.005

85-95

(a) Recommended minimum thickness of deposit.

(b) Bare tubular wire; extra-long (2.4 m, or 8 ft) bare cast rod; tungsten carbide powder with cast rod or bare tubular wire.

(c) With or without tungsten carbide granules.

(d) Varies widely depending on powder feed rate and laser input power

Hardfacing materials fall into six categories:

• Metal-to-metal wear alloys

• Metal-to-earth abrasion alloys

• Tungsten carbides (for extreme earth sliding and cutting wear)

• Nonferrous alloys

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