“Welding Wear Resistant Steel”

Wear resistant steels are used extensively in the mining and aggregate industries for the manufacturing and refurbishment of shoots, buckets, bucket lips, box liners, and other equipment that sees regular exposure to hard and abrasive materials. 

Because of their unique properties, these steels have very specific requirements regarding their machining and welding. Welding procedures, in particular – if not performed appropriately – can cause damage and cracking, or a less obvious softening of the steel, resulting in significant increase in cost and decreased service life of the weldments.

As the reasoning behind the requirements listed in the WPS and WPDS may not always be obvious at first glance, the following tries to outline those reasons, and why it is important to educate everyone in the production process on the proper welding of wear resistant steel.

A Background on Wear Resistant Steel

Wear resistant steel comes in both wrought and cast form. Both wrought and cast forms are typically steels with sufficient hardenability (see Wikipedia article here for a definition) to allow them to be heat treated to produce a martensite or martensite/bainite structure that is subsequently tempered to the desired hardness level.

In the heat treatment process, these steels are typically treated to a desired Brinell hardness level which can range from as low as 350 up to 500.

The process is very sensitive to temperature, time, and the alloying of the steel itself. All wear-resistant steels are not the same, and therefore behave differently when welding and treating. In order to achieve the hardness levels desired when producing the steel, the chemical composition of these steels is typically increased with the thickness of plate being produced.

Table 1 presents maximum chemical compositions for wrought wear resistant steel and Table 2 presents actual data for a few cast alloys.

Table 1 Chemical Composition of Wear Resistant Wrought Steels

Name

C

 

Mn

Si

Cr

Ni

Mo

V

B

CEV

typ

UTS

(MPa)

Thickness

(mm)

Hardox

0.15

1.60

0.70

0.50

0.25

0.25

 

0.004

0.42

1250

8-20

400

0.18

1.60

0.70

1.00

0.25

0.25

 

0.004

0.48

1250

20-32

 

0.22

1.60

0.70

1.40

0.50

0.60

 

0.004

0.57

1250

32-45

 

0.32

1.60

0.70

1.40

1.50

0.60

 

0.004

0.73

1250

80-130

Dillidur

0.20

1.60

0.50

1.00

1.5

0.70

0.10

0.004

0.43

1200

10

400V

               

0.46

1200

25

                 

0.51

1200

40

                 

0.61

1200

80

                 

0.64

1200

120

AlgoTuf

0.17

1.50

0.45

0.20

 

0.20

 

0.003

0.37

1206

5-13

400F

0.17

1.50

0.45

0.25

 

0.20

 

0.003

0.41

1206

13-20

 

0.20

1.50

0.45

0.70

 

0.35

 

0.003

0.51

1206

20-25

 

0.26

1.50

0.45

0.60

 

0.65

 

0.003

0.57

1206

25-70

                       

Compositions are maximum values in wt%

CEV(IIW) = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15

Table 2 Chemical Composition of Wear Resistant Cast Steels

Name

C

 

Mn

Si

Cr

Ni

Mo

V

B

CEV

(act)

Hardness

(HB)

Thickness

(mm)

                       

A

0.198

1.01

0.50

1.04

1.95

0.25

0.02

 

0.67

400

50

                       

B

0.260

0.75

0.30

0.89

1.95

0.23

0.01

 

0.79

400

50

                       

C

0.285

0.94

0.39

0.286

0.514

0.188

   

0.56

400

25

                       

D

0.287

1.54

2.35

0.66

0.10

0.38

0.02

 

0.723

400

50

                       

 

Actual Analysis weight %

CEV(IIW) = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15

 

Producing a quality weld in wear resistant steel

The processes used for welding wear resistant steel typically include; SMAW, FCAW, MCAW, and SAW. Regardless of the process used, the primary objective of the resulting procedure is to ensure that the high hardness of the steel and joint be maintained, while avoiding cracking and weld defects. 

1 - Maintaining Hardness:

To maintain the hardness (and associated wear resistance) the aim of a weld procedure is to create a weld where the heat affected zone of the weld is as hard as the base metal but not significantly harder.

To achieve this result, weld procedures are written to limit the heat input during welding, with limits selected based on the thickness of the material. To ensure appropriate hardness levels in the weld deposit an alloyed filler metal is used. Welding with mild steel consumables will produce lower hardness levels in the joint. If this approach is used, the hardness in the joint is then controlled by the amount of dilution between weld metal and base metal.

2 – Avoiding Cracking:

A common defect when welding wear resistant steels is cracking of the base metal next to the joint. This is caused by a mechanism called Hydrogen Induced Cold Cracking (HICC). There are 3 primary components of a weld procedure (all are critical) used to avoid HICC:

  1. Preheat - To avoid the potential for hydrogen induced cold cracking, manufacturers typically will provide a recommended preheat temperature that is based on the hardness of the steel and thickness of the weld joint. This preheat is used to lower the cooling rate and help remove hydrogen. 

  2. Consumable Selection - Low hydrogen consumables should be specified by the weld procedure, which means proper storage is essential. Diffusible hydrogen levels can increase significantly in consumables stored in an open package out of an electrode oven, even over a period of a couple hours.

  3. Weld pass Selection - For multi-pass weld joints it is recommended that the last weld pass does not touch the base metal. A “temper bead” welding technique may be used as well to avoid HICC and still maintain high hardness values in the heat affected zone.

The Importance of Following Procedures

Unlike welding mild steels - a relatively forgiving process - wear resistant steel is highly sensitive to variations in the weld procedure. It is critical that welders, supervisors, and others involved in the production process be aware of and follows the approved procedures at all times. The investment in training will pay for itself in reduced rework, and longer service life.