Surfacing Weld: Everything You Need to Know

What is surfacing weld?

Surfacing weld is a welding process in which a layer of wear-resistant, corrosion resistant, heat resistant metal layer is deposited on the surface or edge of the workpiece.

Surfacing weld can improve the service life of parts, reasonably use materials and improve product performance.

Different workpieces and surfacing electrodes need different surfacing processes.

Surfacing weld is usually used to repair worn and cracked parts.

Surfacing Weld: Everything You Need to Know 1

Related reading: The Ultimate Guide to Welding

Application scope of surfacing weld equipment:

Automatic surfacing of cement equipment, vertical mill, roller mill, screw conveyor, fan and rotary kiln.

Automatic surfacing of iron and steel equipment, converter, roll, blast furnace, continuous casting machine and conveyor wheel.

Automatic surfacing of power equipment, coal mill, grinding roller, boiler tube, turbine, drain pipe and gear.

Now I will explain the surfacing weld process to you through cases, let’s dive right into it.

Case:

As a key spare part of the rolling mill, the roll consumes a large amount of steel in the rolling process.

The annual steel output in China has exceeded 600 million tons, and the value of the roll consumed is more than 17 billion yuan.

Therefore, using surfacing method to repair old rolls and prolong the service life of rolls has become an important measure for steel rolling enterprises in China to reduce production costs and improve economic benefits.

When the original roll reaches the scrap period, it can be repaired by surfacing.

The roll repaired by surfacing welding has the characteristics of low cost, long service life and good use effect.

It is widely welcomed by steel rolling enterprises, and also conforms to the basic national policies of energy conservation, clean production and circular economy in China.

The figure below shows the old roll repaired by surfacing.

Surfacing Weld: Everything You Need to Know 2

Old roll repaired by surfacing weld

With the increasing progress of science and technology, the mechanical equipment of various products is gradually developing towards the direction of large-scale, high efficiency and high parameters, and the requirements for the reliability and use performance of products are getting higher.

As a branch of welding technology, material surface surfacing is an effective means to improve the performance of products and equipment and prolong the service life.

In addition to metals and alloys, ceramics, plastics, inorganic nonmetals and composites can be used as surfacing alloy materials.

Therefore, the surfacing technology can make the surface of parts obtain various special properties such as wear resistance, heat resistance, corrosion resistance, high temperature resistance, lubrication, insulation, etc.

At present, surfacing technology is widely used in mechanical manufacturing, metallurgy, electric power, mining, construction, petrochemical and other industrial sectors.

Surfacing Weld: Everything You Need to Know 3

Automatic submerged arc strip surfacing weld

Characteristics of surfacing weld

Surfacing weld is a process in which materials with certain properties are deposited on the surface of the workpiece by welding methods.

Related reading: 10 Different Types of Welding You Should Know

The purpose of surfacing weld is different from the general welding method.

It is not to connect the workpiece, but to modify the surface of the workpiece to obtain the cladding layer with special properties such as wear resistance, heat resistance, corrosion resistance, or to recover the insufficient size of the workpiece due to wear or processing errors.

The application of these two aspects in surface engineering is called repair and strengthening.

The following figure shows the surface of the component after surfacing.

Surfacing Weld: Everything You Need to Know 4

Surface of parts after surfacing weld

The advantages of surfacing weld over other surface treatment methods are:

1) The bonding between the surfacing layer and the base metal is metallurgical bonding, with high bonding strength and good impact resistance.

2) The composition and performance of the surfacing layer metal are easy to adjust, and the commonly used electrode arc welding surfacing electrode or flux cored electrode is convenient to adjust the formula.

Various alloy systems can be designed to adapt to different working conditions.

3) The thickness of the surfacing layer is large.

Generally, the thickness of the surfacing layer can be adjusted within 2~30mm, which is more suitable for severe wear conditions.

4) Cost saving, good economy.

When the substrate of the workpiece is made of ordinary materials and the surface is surfacing welded with high alloy, not only the manufacturing cost is reduced, but also a large number of precious metals are saved.

In the process of workpiece maintenance, reasonable selection of surfacing alloy and surfacing repair on the surface of damaged workpiece can greatly extend the service life of the workpiece, extend the maintenance cycle and reduce the production cost.

5) Because surfacing technology is to increase or restore the size of parts by welding, or to obtain alloy layer with special properties on the surface of parts, it is not difficult for those skilled in welding technology, and it is highly operable.

Surfacing Weld: Everything You Need to Know 5

Electroslag strip automatic surfacing weld

Classification of surfacing weld

Surfacing weld technology is a kind of fusion welding technology. All methods belonging to fusion welding can be used for surfacing weld.

The classification of common surfacing weld methods is shown in the table.

At present, the most widely used are electrode arc surfacing and oxyacetylene flame surfacing.

Classification of common surfacing methods

Table 9-1 Classification of Common Surfacing weld Methods

Surfacing weld

 method

Dilution ratio (%)

Deposition speed/(kg/h)

Minimum overlay thickness

Deposition efficiency (%)

Oxyethylene flame surfacing

Electrode wire feeding

1~10

0.5-1.8

0.8

100

Automatic wire feeding

1~10

0.5-6.8

0.8

100

Powder surfacing

1~10

0.5-18

0.2

85-95

Electrode arc surfacing

10-20

0.5-5.4

3.2

65

Tungsten electrode chlorine arc surfacing

10-20

0.5-4.5

2.4

98-100

Electrode arc surfacing

Tungsten electrode chlorine arc surfacing

10-40

0.9~5.4

3.2

90-95

15-40

2.3-11.3

3.2

80-85

Arc management surfacing

Monofilament

4.5-11.3

3.2

95

95

Multifilament

11.3-27.2

4.8

95

95

Series arc

11.3-15.9

4.8

4.8

95

Monopole

12-36

3.0

3.0

95

Multiband electrode

22-68

4.0

4.0

95

Plasma arc surfacing

Automatic powder feeding

0.5-6.8

0.25

0.25

85-95

Welding rod powder feeding

1.5-3.6

2.4

2.4

98-100

Automatic wire feeding

0.5-3.6

2.4

2.4

98-100

Double hot filament

13-27

2.4

2.4

98-100

ESW

10~14

15~75

15

95-100

Application of surfacing weld

As a branch of the welding field, the application scope of surfacing weld technology is very wide, and the application of surfacing weld technology is almost all over the manufacturing industry, such as mining machinery, transportation machinery, metallurgy machinery, power machinery, agricultural machinery, automobiles, petroleum equipment, chemical equipment, construction, and the manufacturing and maintenance of tool molds and metal structures.

The metal parts and products with unqualified appearance can be repaired by surfacing, or bimetal parts can be manufactured.

The use of surfacing weld can prolong the service life of parts, reduce costs, improve product design, especially for the rational use of materials (especially precious metals).

According to the application and working conditions of the workpiece, the application of surfacing weld technology is mainly shown in the following aspects:

(1) Restore the workpiece size for surfacing weld

It is a common problem for factories and mining enterprises that the workpiece size is insufficient due to wear or processing errors.

It is a common process method to repair the above workpieces by surfacing.

The repaired workpieces can not only be used normally, but also exceed the service life of the original workpieces in many cases.

Because the performance of the original parts can be greatly improved by using new processes and new materials for surfacing repair.

Such as surface surfacing repair of cold roll, hot roll and profiled roll, surfacing repair of worn parts of agricultural machinery (tractors, agricultural vehicles, transplanters, harvesters, etc.).

According to statistics, the amount of surfacing alloy used to repair old workpieces accounts for 72.2% of the total amount of surfacing alloy.

Surfacing Weld: Everything You Need to Know 6

Cold roll repaired by surfacing technology

Surfacing Weld: Everything You Need to Know 7

Roller tyre and roller skin repaired by surfacing technology

(2) Wear and corrosion-resistant surfacing

Wear and corrosion are the main factors causing the failure of metal materials.

In order to improve the wear resistance and corrosion resistance of the metal workpiece surface, meet the requirements of working conditions, and extend the service life of the workpiece, one or more layers of wear resistance or corrosion resistance can be deposited on the workpiece surface.

The materials with different properties are selected for the substrate and surfacing layer of the workpiece, which can produce bimetallic workpiece.

Because only the surface layer of the workpiece has the required special properties in terms of wear resistance and corrosion resistance, it gives full play to the role and potential of the material, and saves a lot of precious metals.

Hardfacing wear-resistant or anti-corrosion layer I on workpiece surface

(3) Make new parts

The bimetal machine parts with comprehensive properties can be made by surfacing an alloy on the metal substrate.

The substrate and surfacing alloy layer of this kind of parts have different properties, which can meet the different performance requirements of both.

This will give full play to the potential of materials.

For example, for the blades of hydraulic turbine, the base material is carbon steel, and a layer of stainless steel is welded on the parts (mostly on the lower part of the back of the blades) where cavitation may occur to make them cavitation resistant bimetallic blades;

In the manufacturing of metal abrasive tools, the matrix is required to be strong and tough, and the carbon steel and low alloy steel with relatively low price are selected for manufacturing.

The cutting edge mold requires high hardness and wear resistance.

The use of wear-resistant alloy surfacing on the cutting edge mold of the mold can save a lot of precious alloy consumption and greatly extend the service life of the mold.

Surfacing Weld: Everything You Need to Know 8

Hardfacing wear-resistant or corrosion resistant layer II on workpiece surface

Application field of surfacing

Mold manufacturing

  • The roughening of the plastic mold surface increases the aesthetic feeling and service life;
  • Repair the parting surface of helmet plastic mold by surfacing welding;
  • Surface strengthening of diffluent cone of aluminum alloy die casting die;
  • Repair and strengthen the mold cavity for out of tolerance, wear, scratch, etc.

Plastic rubber

Rubber and plastic mechanical parts repair, rubber, plastic parts mold out of tolerance, wear and repair.

Aerospace

  • Repair of aircraft engine parts, turbines and turbine shafts;
  • The surface of the rocket nozzle is strengthened and repaired, and the aircraft outer panel parts are repaired;
  • Enhancement or repair of artificial satellite shell;
  • Local carburizing strengthening of titanium alloy parts;
  • Local carburizing strengthening of iron base superalloy;
  • The surface of magnesium alloy is infiltrated with A1 and other anti-corrosion coatings;
  • Repair of local defects of magnesium alloy parts by surfacing welding;
  • Local surfacing repair of nickel base/cobalt base superalloy blade workpiece, such as wear of blade crown damping surface and blade tip and ablation of guide vane.

Manufacturing maintenance

In the automobile manufacturing and maintenance industry, it is used for the compensation and repair of cams, crankshafts, pistons, cylinders, brake discs, impellers, hubs, clutches, friction discs, exhaust valves, etc., as well as the repair of surface weld bead defects of automobile bodies.

Ship electric power

  • Repair of electric crankshaft, bearing sleeve, bearing bush, electrical components, resistor, etc;
  • Welding of connecting piece between electric railway locomotive wheel and bottom line track;
  • Production and welding of conductive roller and metal oxidation copper aluminum electrode in electroplating plant.

Manufacturing maintenance

In the automobile manufacturing and maintenance industry, it is used for the compensation and repair of cams, crankshafts, pistons, cylinders, brake discs, impellers, hubs, clutches, friction discs, exhaust valves, etc., as well as the repair of surface weld bead defects of automobile bodies.

Ship electric power

  • Repair of electric crankshaft, bearing sleeve, bearing bush, electrical components, resistor, etc;
  • Welding of connecting piece between electric railway locomotive wheel and bottom line track;
  • Production and welding of conductive roller and metal oxidation copper aluminum electrode in electroplating plant.

Machinery industry

Correction of out of tolerance workpieces and repair of machine tool guide rails, various shafts, cams, hydraulic presses, hydraulic press plungers, cylinder walls, journals, rolls, gears, pulleys, mandrels for spring forming, plug gauges, ring gauges, various rolls, rods, columns, locks, bearings, etc.

Foundry industry

Repair the defects such as sand hole and air hole of iron, copper and aluminum castings, and repair the wear of aluminum mold.

Technical skills and methods of surfacing weld

Surfacing Weld: Everything You Need to Know 9

1. Overview

Surfacing welding is a process of overlaying materials with certain properties on the surface of weldments by welding.

The purpose is not to connect the weldment, but to obtain a deposited metal layer with special properties such as wear resistance, heat resistance and corrosion resistance on the surface of the weldment, or to restore or increase the size of the weldment.

The surfacing method is widely used in manufacture and repair.

2. Metal for surfacing weld

Generally speaking, the deposited metal shall first meet the service conditions of the weldment;

Secondly, it is considered that the weldability of the surfacing metal is better, and then the more economical surfacing metal is properly selected.

The common surfacing metals used in the working environment are:

  • Hypoeutectic cobalt base alloy and cobalt base alloy containing intermetallic compound are selected for high stress intermetallic wear;
  • Low alloy steel for surfacing shall be selected for low stress inter metal wear;
  • Most cobalt based alloys or nickel based alloys are selected for wear+corrosion or oxidation between metals;
  • High alloy cast iron is selected for low stress abrasive wear, impact etching and abrasive etching;
  • Low stress, severe abrasive wear, carbide cutting edge;
  • Cobalt base alloy is selected for cavitation erosion;
  • High alloy manganese steel is selected for severe impact;
  • Hypoeutectic cobalt base alloy is selected for severe impact+corrosion+oxidation;
  • The hypoeutectic cobalt base alloy and cobalt base alloy containing intermetallic compound are selected for intermetallic wear at high temperature;
  • Austenitic manganese steel is selected for chiseling abrasive wear;
  • Thermal stability High temperature creep strength (540 ℃) Cobalt base alloy carbide cobalt base alloy is selected.

Iron base surfacing metal is widely used due to its many products, wide range of performance changes, good combination of toughness and wear resistance, and low cost.

There are roughly four categories:

(1) Pearlitic steel surfacing metal

This type of alloy has good weldability, strong impact resistance and low hardness, and is mainly used to repair mechanical parts like shafts.

(2) Austenitic steel surfacing metal

Austenitic manganese steel surfacing metal has the characteristics of high impact toughness and work hardening, but it is easy to produce hot cracks.

It is generally used to repair parts that are worn between metals and abrasives under severe impact load, such as mine skip cars, railway turnouts, etc.

Austenitic chromium manganese surfacing metal has better weldability than austenitic manganese steel, as well as better corrosion resistance, heat resistance and heat crack resistance.

It is mainly used to repair manganese steel and carbon steel parts that are severely impacted by metal to metal wear.

(3) Martensitic steel surfacing metal

The structure of this type of surfacing metal is mainly martensite.

The hardfacing layer has high hardness and yield strength, high wear resistance, and can withstand moderate impact, but its impact resistance is worse than that of pearlitic steel and austenitic steel.

It is mainly used to repair worn parts between metals, such as gears, tractor chassis, etc.

(4) Alloy cast iron surfacing metal

This kind of surfacing layer has high abrasive wear resistance, heat resistance, corrosion resistance, good oxidation resistance, and light impact resistance, but it is easy to crack during surfacing, so be careful when welding.

It is mainly used for surfacing agricultural machinery, mining equipment and other parts.

Nickel base surfacing metal

Among them, the nickel chromium boron silicon series alloy is the most widely used alloy.

It has excellent resistance to low stress abrasive wear and wear between metals.

It has good corrosion resistance, heat resistance and high temperature oxidation resistance, but its resistance to high stress abrasive wear and impact resistance are slightly poor.

It is usually used in corrosive media or occasions subject to low stress abrasive wear in high temperature environments.

Nickel base alloys containing intermetallic compounds, such as Ni-32Mo-15Cr-3Si, have high high temperature hardness, excellent resistance to intermetallic wear and moderate abrasive wear, but poor impact resistance;

This alloy is more suitable for gas tungsten arc surfacing or plasma arc surfacing, and is commonly used for surfacing valve sealing surfaces working in severely corrosive media.

The price of nickel base alloy containing carbide is much lower than that of cobalt base alloy.

From an economic point of view, it has been widely used as a substitute for cobalt base surfacing metal.

Cobalt based surfacing metals mainly refer to cobalt chromium tungsten alloys, which can maintain high strength and hardness at about 650 ℃, have certain corrosion resistance and excellent adhesion wear resistance.

Cobalt based alloys have the best comprehensive performance among various surfacing metals, and are commonly used for surfacing of parts under high-temperature working conditions.

Copper base surfacing metal

Generally, there are four types: bronze, brass, white copper and pure copper.

Copper based surfacing alloys have good corrosion resistance, cavitation resistance and wear resistance between metals.

They can be welded on iron based materials to make bimetallic parts, and can also be used to repair worn parts;

However, the copper base surfacing metal has poor resistance to sulfide corrosion, wear of wear-resistant materials and high temperature creep, low hardness, and is not easy to weld. It is only applicable to the environment below 200 ℃.

This type of surfacing metal is mainly used for the surfacing of bearing shells, low pressure valve sealing surfaces, etc.

Carbide surfacing metal

It is mainly used for surfacing welding of oil well bits and road construction machinery parts under severe wear conditions.

3. Welding process and method of surfacing

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Oxygen acetylene surfacing

It is mainly used for surfacing of parts with smooth surface and high quality requirements, mainly small and medium-sized weldments in small batches.

Such as surfacing of valves, oil well bits, ploughshares and other parts.

The oxygen acetylene equipment is simple, easy to operate, low cost, and can be used with gas welding equipment, but the hole diameter of the welding torch nozzle is larger than that of gas welding;

Hardfacing materials of almost all shapes can be used (including leftovers);

With high visibility, surfacing can be carried out on a small area, and a thin and smooth surfacing layer can be obtained;

The dilution ratio of this method is low, and the depth of melting layer can be controlled within 0.1mm, which is easy to ensure the quality of the surfacing layer;

The carburizing effect of reducing flame and carbonizing flame will reduce the toughness of the hardfacing layer, but can improve the wear resistance of the hardfacing layer with carbide as the main wear-resistant phase;

This method is characterized by high labor intensity, low production efficiency and certain technical requirements for welders.

Oxygen acetylene surfacing generally uses carbonization flame, and the flame property is related to the type of surfacing metal:

Nickel base alloys usually use neutral flame, but occasionally use carbonization flame to improve metal fluidity;

Double acetylene excess flame (the length ratio of inner flame to flame core is 2:1) shall be used for iron base alloy surfacing;

When surfacing with low melting point surfacing alloy with high carbon content (such as high chromium cast iron or cobalt base alloy), 3 times of acetylene excess flame shall be used.

The vast majority of steel parts can be overlayed without flux. Flux must be used when overlaying cast iron, and measures must be taken to prevent white microstructure and cracks.

Preheating and slow cooling can greatly reduce the possibility of cracking of the surfacing layer, and also help to reduce the dilution ratio;

Small workpieces can be directly heated by welding torch, while large workpieces are generally heated in the furnace, and enough time is guaranteed to make the temperature uniform.

The maximum thickness of each layer of surfacing welding is about 1.6mm, which can be multi-layer surfacing welding.

Self fusing alloy powder is used for oxygen acetylene spray welding (spray melting).

According to the order of powder spraying and remelting, the spray welding process can be divided into “one-step method” and “two-step method”;

“One step” spray welding is characterized by simultaneous powder spraying and remelting, that is, the method of spraying while melting.

Generally, the powder spraying is very fine, and its steps are preheating, pre spraying, spraying working powder and melting;

The “two-step” spray welding is characterized by two steps of powder spraying and remelting. The remelting gun is used for remelting.

Its steps are preheating, powder spraying and remelting.

The common defects of oxygen acetylene surfacing are lack of fusion of pores, which are caused by improper operation or poor quality of surfacing materials.

Electrode arc surfacing

Welding rod arc welding equipment is cheap and versatile, which is suitable for field surfacing.

Common power sources include arc welding transformer, arc welding rectifier, arc welding generator and arc welding inverter;

Especially suitable for surfacing parts with irregular shape and parts with poor accessibility;

The arc heat is concentrated, the deformation is small, and the productivity is high, but its penetration is large, the dilution rate is high, and the hardness and wear resistance of the surfacing layer are reduced.

Generally, 2 to 3 layers are welded, and multi-layer welding is easy to crack.

Electrode arc surfacing is mainly used for small batch production and repair of worn parts.

The surfacing electrodes in China are: D10 ×~ 24 ×; D25 ×~ 29 ×; D30 ×~ 49 ×; D50 ×~ 59 ×; D60 ×~ 69 ×; D70 ×~ 79 ×; D80 ×~ 89 × Etc.

The electrode with titania calcium type, ilmenite type and low hydrogen type coating should preferably adopt DC reverse connection for surfacing, and the electrode with graphite type coating should preferably adopt DC positive connection, or AC power supply.

Before surfacing, the electrode shall be dried at the temperature specified in the electrode manual.

Generally, the acid electrode shall be dried at 150 ℃ for 0.5~1h, and the alkaline electrode shall be dried at 250~350 ℃ for 1~2h.

The preheating temperature of surfacing is mainly determined according to the carbon equivalent.

For example, the carbon equivalent (%) is 0.4, 0.5, 0.6, 0.7 and 0.8, and the preheating temperature (℃) is 100, 150, 200, 250 and 300 respectively.

Slow cooling after surfacing can be carried out in the furnace or asbestos, or it can be cooled slowly by proper heating.

See Fig. 1 for process parameters of electrode arc surfacing.

Fig. 1 Surfacing welding process parameters of shielded metal arc welding

Thickness of surfacing layer mm<1.5<5≥5
Electrode diameter mm3.24-55~6
Number of surfacing layers11~2≥2
Surfacing  welding current A800~100140~200≥180~240

Submerged arc surfacing

Submerged arc surfacing is automatic production, high current and high efficiency;

No light radiation, good working conditions;

The submerged arc heat is too much and the dilution rate is too high.

Generally, 23 layers of surfacing can ensure the required performance. In order to avoid cracking, preheating and slow cooling measures are often taken;

It is mainly used for horizontal surfacing, and is most suitable for the surfacing of large parts that are not easy to deform, such as the surfacing of corrosion resistant layer on the inner wall of large diameter containers, and the surfacing of wear-resistant layer on the roll of the steel rolling mill.

It is not suitable for surfacing small parts.

DC power supply or AC power supply can be used for submerged arc surfacing.

From the perspective of improving surfacing quality and production efficiency, DC reverse connection is mostly used;

When welding current is increased, dilution ratio, penetration depth and overlay thickness will increase;

The influence of welding arc voltage on dilution ratio is not obvious.

Generally, the arc voltage is 30~35V, and the extension length of welding wire is 8 times of the welding wire diameter;

In order to reduce the dilution ratio and improve the deposition speed,

The electrode is improved by using multi wire and strip electrodes (in tandem).

Other surfacing methods

Other surfacing methods include gas metal arc surfacing, tungsten argon arc surfacing, plasma arc surfacing, electroslag surfacing, laser surfacing, friction surfacing, etc.

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