Stainless steels

The build-up alloys are not designed to resist wear but to return a worn part back to, or near, its original dimensions and to provide adequate support for subsequent layers of true hardfacing materials. However, these alloys are sometimes used as wear-resistant materials under mild wear conditions.

The build-up alloys fall into two categories: alloy steels and austenitic manganese steels. The alloy steel build-up materials are used with carbon steel and alloy steel substrates; the austenitic manganese steels are used for the joining, repair, and/or protection of manganese steel components. Specific build-up alloy compositions and properties are given in Table 37. Typical examples of applications where build-up alloys are used include tractor rails, railroad rail ends, steel mill table rolls, and large slow-speed gear teeth.

Table 37 Composition, hardness, and abrasion data for build-up alloys and metal-to-metal wear alloys

Alloy

Composition, wt%

Hardness, HRC

Abrasion, volume loss

Low-stress(c)

High-stress(d)

Fe

Cr

C

Si

Mn

Mo

Ni

mm

in.3 x 10-3

mm

in.3 x 10-3

Build-up weld overlay

EFe1(a)

bal

2

0.1

1.0

1

1.5

37

88

5.4

49

3.0

EFeMn-C(a)

bal

4

0.8

1.3

14

4

18

65

4.0

57

3.5

EFeMn-Cr(a)

bal

15

0.5

1.3

15

2.0

1

24

93

5.7

46

2.8

Metal-to-metal weld overlay

EFe2(a)

bal

3

0.2

1.0

1

1.0

1

48

54

3.3

66

4.0

EFe3(b)

bal

6

0.7

1.0

1

1.0

59

60

3.7

68

4.1

(a) Two-layer SMA deposit process.

(b) Two-layer SAW deposit process.

(c) Dry sand/rubber wheel test (ASTM G 65, Procedure B): Load 13.6 kg (30 lb); 200 rev.

(d) Slurry/steel wheel test (ASTM B 611, modified): load 22.7 kg (50 lb); 250 rev

Alloys in the metal-to-metal category (commonly referred to as machinery hardfacing alloys) are martensitic, air-hardening steels that can be applied several layers thick and can be finish machined (although with some difficulty) if adequate equipment is used. They are recommended for wearing, industrial, heavy-duty, nonlubricated parts. These materials are also sometimes referred to as "super build-up" alloys. If a machined finish is required, three layers are generally applied, with the assumption that the top layer will be removed during machining. A single layer is usually adequate because of the effects of substrate/overlay intermixing (dilution).

Typical compositions and properties of metal-to-metal wear alloys are listed in Table 37. In hostile environments, a higher chromium content is beneficial. ER420 (American Welding Society, AWS, classification), and modified versions containing nickel, molybdenum, and niobium (or vanadium), are therefore the natural choice when high temperatures and mildly corrosive environments are encountered. For applications using steel mill hot-work rolls (which demand considerable hot hardness, resistance to oxidation, and resistance to thermal fatigue) both ER420 and EFe3 have been found suitable. Other applications for the metal-to-metal wear alloys in Table 37 include tractor rollers and crane wheels (EFe2), pincer guide shoes (EFe3), and blast furnace bells (ER420).

Most of the materials in the metal-to-earth, carbide, and nonferrous alloy categories consist of hard particles within a metallic matrix, and, for many, it is the hard constituent that provides resistance to wear. The primary function of the metal-to-earth abrasion alloys and tungsten carbides is abrasion resistance. The metal-to-earth alloys are high-chromium white irons in which chromium carbides are formed during alloy solidification. The tungsten carbides are actually composite materials, and their use involves the transfer of discrete tungsten carbide particles (which in the welding consumable forms are encased in a steel tube) across the welding arc and into the molten weld pool, where they are subsequently "frozen" into the overlay structure by the matrix formed from the melting of the steel tube. Typical applications for these material types include shovel teeth, rock crusher parts, plowshares, and auger flights.

The nonferrous hardfacing alloys are used in environments that are too aggressive for the ferrous hardfacing alloys or where high resistance to a specific type of wear (other than abrasion) is required. They are classified as follows:

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