For Hardfacing

Introduction of Hard-faced Wear-resistant Welding Materials

 

1.Introduction of base metal properties:

  As the base metal for hard surface surfacing welding, there are usually general carbon steel, medium and high carbon steel, tool steel, cast iron, high manganese steel, stainless steel and other materials, so several levels of problems must be considered in welding:

 

Carbon equivalent of base metal: Carbon equivalent of base metal will affect the effectiveness of welding, and also determine the setting of preheating and inter-track temperature. Therefore, evaluation before welding should be carried out.

 

The use environment state of the workpiece: Evaluate the hard-faced welding material according to whether there are friction, impact, high temperature, corrosion and other factors in the use environment of the workpiece.

 

Expected service life: It will affect the type of welding material selected and the number of welding layers

 

Selection of transition layer: If high carbon-high alloy hard surface welding material is directly welded on the base metal, there will be serious risk of cracking and peeling. It is recommended to weld the transition layer welding material before welding the hard surface layer.

 

Selection of hard surface layer: Appropriate hard surface welding material shall be selected according to the hardness requirements of engineering design, allowable welding thickness, workpiece type, whether heat treatment is required, workpiece use environment state (temperature & corrosivity & wear type, etc.), whether weld bead is allowed to have cracks, etc.

 

 

2.Welding method and characteristics

  The main consideration of hard surface welding is that the hard surface layer can be effectively attached to the workpiece, and the degree of cracks is reduced to the lowest or no cracks, so as to give full play to the maximum function of hard surface welding. In order to achieve this goal, welding procedure, temperature management and selection and matching of welding materials are very important. The following suggestions are made on several welding points:

 

①The surface condition of the base metal:

  Before welding, determine whether the base metal is a repeated welded workpiece or a new workpiece? If it is a workpiece repaired repeatedly, the residual welding layer before should be evaluated whether it should be processed or backed with welding material of transition layer (buffer layer); If it is a new workpiece, check the oxide layer, pit condition and surface residue on the surface of the base metal before welding.

 

 Preheating and channel temperature control

  Preheating and control of weld temperature can effectively prevent or reduce weld crack. The following suggestions are made on various common base metal types and welding temperature

 

 

 

Base metal steel grade

Carbon equivalent%

Preheating and inter-channel temperature

Carbon steel

Low alloy steel


0.3

0.3~0.4

0.4~0.5

0.5~0.6

0.6~0.7

0.7~0.8

0.8

100

100

150

200

250

300

350

High manganese steel (13% Mn)

No preheating, channel temperature ≤ 200 ℃ or workpiece for water cooling

Austenite iron series stainless steel

150

High alloy steel (high carbon-high chromium series, etc.)

 

Note: Carbon equivalent (%) = C + Mn + Si + Cr + Mo + Ni

 

③Post-heating:

For thick plate welding, high carbon equivalent, high carbon and high chromium materials, it is recommended to carry out post-heating treatment at 200 ~ 350 ℃ * 0.5 ~ 1 hour after welding, so as to slow down the cooling rate of weld bead and avoid the risk of excessive cracks or peeling of weld bead.


④Post-heat treatment:

Post-welding heat treatment is carried out at 550 ℃ ~ 750 ℃ to prevent cold cracks, eliminate internal stress and quenching and tempering treatment, but the influence of heat treatment conditions on hardness must be evaluated.


⑤Selection of welding materials for transition layer:

The commonly used transition layer will use welding materials of "carbon steel low hydrogen system" or "Vostian iron stainless steel system". Generally, carbon steel-low alloy steel base metal will use carbon steel welding materials as backing transition, while high manganese steel-Vostian iron stainless steel-high alloy steel will use Vostian iron stainless steel welding materials as backing transition.

 

The selection of transition welding material is not only based on the type of base metal, but also the matching with the material of hard surface welding layer. For example, if 410NM grade welding material is selected in hard surface layer, 309L or 309MoL grade welding material is recommended as transition layer.

 

⑥Consideration of dilution rate and welding thickness:

The material of hard surface welding is usually different from the composition of base metal, so considering the dilution rate, welding cost, the limitation of welding layer thickness, crack degree and other factors, the design of welding procedure is very important.

 

 

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