Welding Wire Selection: A Solid Versus Flux Cord Guide

I. Critical Points in Welding Wire Selection

The selection of welding wire should be based on the type of steel to be welded, the quality requirements of the welding parts, the welding construction conditions (plate thickness, groove shape, welding position, welding conditions, treatment thermal post-welding and welding operation, etc.) and cost considerations.

The order of consideration for welding wire selection is as follows:

① Select the welding wire based on the steel type of the structure to be welded.

For carbon steel and low-alloy, high-strength steel, the principle of “equal strength matching” is mainly followed, selecting the welding wire that meets the mechanical performance requirements.

For heat-resistant steel and weather-resistant steel, the emphasis is mainly on the consistency or similarity of the chemical composition of the weld metal and the parent material to meet the heat and corrosion resistance requirements.

② Select welding wire based on the quality requirements of the part to be welded (especially impact resistance).

Regarding welding conditions, groove shape, shielding gas proportions and other technical conditions, welding materials that achieve maximum welding efficiency and reduce welding cost while ensuring the performance of the welded joint should be selected.

③ Select the welding wire based on the welding position at the site.

Corresponding to the plate thickness of the workpiece to be welded, select the diameter of the welding wire used, determine the value of the current used, and refer to the product introduction materials and use experience of various manufacturers to select the brand of welding wire Suitable for welding position and current use.

Welding process performance includes arc stability, spatter particle size and quantity, slag removal, weld appearance and shape. For the welding of carbon steel and low-alloy steel (especially semi-automatic welding), the welding method and welding materials are mainly selected based on the performance of the welding process.

The performance comparison of gas shielded welding welding process using solid wire and flux cored wire is shown in Table 1.

Table 1 Comparison of welding process performance between solid core welding wire and flux core welding wire in gas shielded welding

Welding process performance			Solid Core Welding Wire		CO 2 Welding, flux-cored welding wire.
			CO 2 Welding	Air+CO 2 Welding	Slag Mold	Type of metal powder
Operation Difficulty	Flat welding	Ultra-thin sheet (δ≤2mm) Thin sheet (δ<6mm) Medium sheet (δ>6mm) Thick sheet (δ>25mm)	A little poor Average Good Good	Higher Higher Good Good	A little poor Great Good Good	A little poor Great Good Good
	Horizontal angle welding	Single layer Multilayer	Generally Generally	Good Good	Higher Higher	Good Good
	Vertical welding	Down Down	Sugarplum	Great Great	Higher Higher	A little lower A little lower
Weld seam appearance		Flat welding Horizontal angle welding Vertical welding Aerial welding	Average Below average Average Below average	Higher Higher Higher Good Higher	Higher Higher Higher Higher Higher	Great Good Average Below average
Other		Arc Stability Melting depth Splashes Slag Detachability Edge bite	In general Great A little poor – Great	Great Great Great – Great	Higher Higher	Higher Higher Higher A little lower Higher

II. Solid Core Welding Wire Selection

1. Submerged Arc Welding Wire

Welding wire and flux are consumable materials in submerged arc welding. Welding with a wide range of metallic materials, from carbon steel to high nickel alloys, can be accomplished using welding wire and flux.

The selection of submerged arc welding wire should consider the influence of flux components and base material.

To obtain different weld bead compositions and mechanical properties, a combination of one type of flux (mainly molten flux) with several types of welding wire can be used, or one type of welding wire can be combined with several types of flux (mainly sintered flux). ).

For a certain welding structure, the welding wire and flux to be used should be decided after a comprehensive analysis of the steel grade composition, welding seam performance requirements and changes in welding process parameters.

During submerged arc welding, the flux has two purposes: to protect the weld metal and to conduct the metallurgical treatment. Welding wire acts as filler metal, while alloying elements are also added to the weld to participate in metallurgical reactions.

(1) Welding wires for low carbon steel and low alloy steel

There are three welding wires commonly used for submerged arc welding of low carbon steel and low alloy steel:

• Low manganese welding wire (such as H08A): This type of welding wire is often used for welding low carbon steel and low alloy steel with high manganese flux.
• Medium manganese welding wire (such as H08MnA, H10MnS): This type of welding wire is mainly used for welding low alloy steel, and can also be used for welding low carbon steel with low manganese flow.
• High manganese welding wire (such as H10Mn2, H08Mn2Si): ​​This type of welding wire is used for welding low alloy steel.

(2) High strength steel wire

This type of welding wire contains more than 1% manganese and between 3% to 0.8%, such as H08MnMoA and H08Mn2MoA. It is used to weld low-alloy, high-strength steel with high strength.

To improve welding performance, Ni, Cr, V and Re can be added to the welding wire, based on the composition and performance requirements of high-strength steel. MN-MO welding wire is mainly used for welding metals with tensile strength of 590MPa such as H08MnMoA.

Welding metal with a strength level of 590MPa generally uses Mn-Mo series welding wire, such as H08MnMoA, H08Mn2MoA, H10Mn2Mo, etc.

Welding seams with a strength level of 690 to 780MPa generally use Mn-Cr-Mo series, Mn-Ni-Mo series or Mn-Ni-Cr-Mo series welding wire.

When higher toughness is required for the weld seam, a Ni-containing welding wire can be used, such as H08CrNi2MoA, etc.

When welding steel grades with a strength level of less than 690MPa, molten flux and sintered flux can be used.

When welding high-strength steel with a strength level of 780MPa, sintered flux must be used to obtain high toughness, in addition to selecting the appropriate welding wire.

See Table 2 for the mechanical properties, characteristics and uses of solid wire for submerged arc welding.

Table 2: Mechanical properties, characteristics and uses of solid wire for submerged arc welding

Welding Wire Class	Diameter /mm	Features and applications	Mechanical properties of the metal surface.
			Tensile strength σb /MPa	Yield resistance σS /MPa	Stretch rate δ5 /%	AkV Impact Energy /J
H08A	2.0~5.0	Low carbon structural steel welding wire is most commonly used in submerged arc welding, in conjunction with welding fluxes such as HJ430, HJ431 and HJ433. It is used to weld low carbon steel structures and certain low alloy steels (such as 16Mn).	410~550	≥330	≥22	≥27(0℃)
H08MnA	2.0~5.8	Carbon steel welding wire, used in conjunction with flux for submerged arc welding, results in weld bead metal with excellent mechanical properties. It is used for submerged arc welding of carbon steel and low alloy steel with corresponding strength levels (such as 16Mn, etc.) in boilers and pressure vessels.	410~550	≥330	≥22	≥27(0℃)
H10Mn2	2.0~5.8	Copper coated submerged arc welding wire, combined with HJ130, HJ330 and HJ350 welding fluxes, produces weld beads with excellent mechanical properties. It is used for submerged arc welding of carbon steel and low alloy steel structures (such as 16Mn, 14MnNb, etc.).	410~550	≥330	≥22	－
H10MnSi	2.0~5.0	Copper-plated welding wire, when used with corresponding flux, can produce weld metal with good mechanical properties. Provides high welding efficiency and reliable welding quality. It is used to weld important low carbon steel and low alloy steel structures.	410~550	≥330	≥22	≥27(0℃)
HYD047	3.0~5.0	The welding wire, combined with HJ107 flux, provides a molten metal with excellent resistance to extrusion and granular abrasion. Its anti-cracking performance is excellent and there is no cracking in cold welding. The surface of the welding wire is perfect and can be copper coated, simplifying the welding operation. The arc is stable, with strong resistance to net voltage fluctuations and good process performance. It is commonly used to coat the surface of the rolling mill extrusion roll.	－	－	－	－

(3) Welding wire for stainless steel

The composition of the welding wire used for stainless steel must be similar to that of the stainless steel to be welded. For chromium stainless steel, welding wires such as HoCr14, H1Cr13 and H1Cr17 should be used.

For chromium-nickel stainless steel, welding wires such as H0Cr19Ni9, HoCr19Ni9 and HoCr19Ni9Ti should be used. For ultra-low carbon stainless steel, corresponding ultra-low carbon welding wire such as HOOCr19Ni9 should be used.

The flux used in submerged arc welding can be of the casting or sintering type. The oxidizability of the flux must be low to reduce loss from burning of the alloy elements.

Currently, sintered flux is mainly used abroad for welding stainless steel, while casting flux remains the main method in China, although sintered flux is being developed and gaining popularity.

2. Welding wire for gas shielded welding

Gas shielded welding is categorized into three types: inert gas shielded welding (such as tungsten inert gas (TIG) welding and metal inert gas (MIG) welding), active gas shielded welding (tungsten inert gas welding) active metal (MAG)) and self-shielded welding.

Related Reading: MIG vs TIG Welding

Pure argon (Ar) is used for TIG welding, while argon mixed with 2% oxygen (Ar + 2% O2) or argon mixed with 5% carbon dioxide (Ar + 5% CO2) is commonly used for welding MIG. Carbon dioxide gas (CO2) is mainly used for MAG welding.

To improve the performance of the CO2 welding process, a mixture of CO2 + Argon or CO2 + Argon + Oxygen, or flux-cored wire, can also be used.

(1) TIG welding wire

TIG welding may or may not include filler wire. If filler wire is not used, the base metal will be directly connected after being melted by the heat of welding.

In cases where filler wire is used, the composition of the welding wire remains unchanged after melting due to the pure argon shielding gas that prevents oxidation.

As a result, the composition of the welding wire is the same as that of the solder. Some welders also use the base metal composition as the welding wire composition to ensure consistency between the base metal and the weld.

TIG welding offers low welding energy, high welding strength, plasticity and toughness, and is easy to meet performance requirements.

(2) MIG and MAG welding wires

The MIG method is mainly used for welding high-alloy steels such as stainless steel. To improve the characteristics of the arc, an appropriate amount of oxygen gas (O2) or carbon dioxide (CO2) is added to the argon gas, which is known as the MAG method. When welding alloy steels, adding 5% CO2 to argon can improve the antiporosity of the weld.

However, when welding ultra-low carbon stainless steel, only argon mixed with 2% oxygen can be used to prevent carburization of the weld. Currently, MIG welding of low alloy steels is being replaced by MAG welding with Argon mixed with 20% CO2.

During MAG welding, the presence of oxidation in the shielding gas requires an increase in deoxidizing elements such as Silicon (Si) and Manganese (Mn) in the welding wire.

Other components of the welding wire may be the same or different from the base metal. When welding high-strength steel, the carbon (C) content in the weld is generally lower than that of the base metal and the manganese (Mn) content must be higher for both deoxidation requirements and alloy composition.

To improve toughness at low temperatures, the silicon (Si) content in the solder should not be too high.

(3) CO2 welding wire

CO2 is an active gas with strong oxidation, therefore the welding wire used for welding with CO2 must contain highly deoxidizing elements such as Manganese (Mn) and Silicon (Si). Mn-Si welding wire, such as h08mnsia, H08Mn2SiA, h04mn2sia, etc., is generally used for CO2 welding.

The diameter of the CO2 welding wire varies from 0.89mm to 2.0mm, with wire diameters less than or equal to 2mm being considered CO2 welding with fine wire and wire diameters greater than or equal to 1.6mm being considered CO2 welding with wire thick.

H08Mn2SiA welding wire is a commonly used CO2 welding wire with good process performance, suitable for welding low alloy steel with strength grade below 500MPa.

For steels with higher strength grade requirements, welding wire containing Molybdenum (Mo) such as H10MnSiMo should be used.

3. Electroslag welding wire

Electroslag welding is a suitable method for welding medium and thick plates. Electroslag welding wire mainly serves as filler metal and alloying purposes.

Wire types commonly used for submerged arc welding of low-carbon steel and high-strength low-alloy steel can be seen in Table 3.

Table 3 Wire grades commonly used for submerged arc welding of low-carbon steels and low-alloy, high-strength steels.

Welding Steel Number	Commonly used welding wire models
Q235,Q255 15,20,25 16Mn,09Mn2 15MnV,15MnVCu 15MnVN,14MnMoV,18MnMoNb	H08MnA H08MnA,H10Mn2 H08Mn2Si,H10MN2,H10MnSi,H08MnMoA H08MnMoA,H08Mn2MoVA H10Mn2MoVA,H10Mn2Mo

4. Non-ferrous metal and cast iron welding wire

The first two letters of the brand, “HS”, represent welding wires for non-ferrous metals and cast iron. The first digit of the mark indicates the academic composition of the type of welding wire, and the second and third digits indicate different brands of the same type of welding wire.

(1) Surface welding wire

There are currently two main types of carbide welding wires for cladding: high chromium alloyed cast iron (Solmait) and cobalt based alloy (Stellite).

High chromium alloy cast iron offers good resistance to oxidation and cavitation, high hardness and good wear resistance. Cobalt-based alloys maintain high hardness and good corrosion resistance at high temperatures of up to 650 degrees.

Low carbon and low tungsten welding wires have good toughness, while high carbon and high tungsten welding wires have high hardness but low impact resistance.

Hard alloy cladding welding wire can be overlapped using oxygen, acetylene, gas electric welding and other methods.

Although oxygen and acetylene surface has low production efficiency, its equipment is simple, the welding depth is shallow, and the amount of melted base metal is small, resulting in high surface quality. As a result, it is widely used.

The composition, characteristics and applications of commonly used hard alloy welding wires are shown in Table 11.

Table 11: Composition, characteristics and applications of commonly used hard alloy welding wires

Note	Name	Chemical composition /%	The hardness of the surface layer at room temperature is HRC.	Key Features and Applications
HS101	High Chrome Cast Iron Overlay Welding Wire	C2.5~3.3 Cr25~31 Ni3~5 Si2.8~4.2 Fe Excess material	48~54	The overlay has excellent resistance to oxidation and gas corrosion, high hardness and good abrasion resistance. However, it should not be used above 500°C as it will reduce hardness. It is suitable for overlap welding applications that require wear resistance, oxidation resistance or gas corrosion resistance, such as excavator teeth, pump bushings, diesel engine valves, exhaust blades, etc.
HS103	High Chrome Cast Iron Overlay Welding Wire	C3~4 Cr25~32 Co4~6 B0.5~1.0 Fe Excess material	58~64	The overlay has excellent oxidation resistance, high hardness and good wear resistance, but low impact resistance. It is difficult to cut and can only be ground. It is used in applications that require strong wear resistance, such as gear drill shafts, coal excavators, crusher rollers, pump frames, mixing blades, etc.
HS111	Cobalt-Based Overlap Welding Wire (AWSRCoCr-A Equivalent)	C0.9~1.4 Cr26~32 W3.5~6.0 Fe≤2.0 Excess material	40~45	Co-Cr-W alloy with the lowest C and W content has the best toughness, can withstand impacts under cold and hot conditions, has a small tendency to crack, and has good resistance to corrosion, heat and wear. It is used in situations that require good wear resistance and corrosion resistance at high temperatures, such as high pressure and high temperature valves, hot shear blades, hot forging dies, etc.
HS112	Cobalt-Based Overlap Welding Wire (AWSRCoCr-B Equivalent)	C1.2~1.7 Cr26~32 W7~9.5 Fe≤2.0 Excess material	45~50	This Co-Cr-W alloy has medium hardness, better wear resistance than HS111, but slightly lower plasticity. It has good corrosion, heat and wear resistance and can maintain these properties at temperatures up to 650℃. It is used for overlap welding of high pressure and high temperature valves, internal combustion engine valves, synthetic fiber scissor blades, high pressure pump bushings and inner lining sleeves, hot rolling mill rolls, etc.
HS113	Cobalt Based Overlay Welding Wire	C2.5~3.0 Cr27~33 W15~19 Fe≤2.0 Excess material	55~60	The coating has high hardness and excellent wear resistance, but low impact resistance and a high tendency to crack during welding of the coating. It has good strength, heat resistance and wear resistance, and can maintain these properties at temperatures up to 650 ℃. It is mainly used for overlap welding of gear drill bearings, boiler rotating blades, crusher blades, screw feeders and other wear parts.
HS114	Cobalt Based Overlay Welding Wire	C2.4~3.0 Cr27~33 W11~14 Fe≤2.0 Excess material	≥52	Co-Cr-W high carbon alloy overlay welding wire has good wear resistance and corrosion resistance, but poor impact resistance. It is mainly used for overlap welding of high temperature working gas turbines, aircraft engine turbine blades, gear drill bearings, boiler rotating blades and other wear parts.
HS115	Cobalt-Based Overlap Welding Wire (Equivalent to AWSSRCoCr-E)	C0.15~0.35 Cr25.5~29 Mo5~6 Ni1.75~3.25 Excess material	≥27	Mo reinforced low carbon Cr-Mo welding wire has good high temperature corrosion resistance, impact resistance and high temperature resistance. It is used for overlap welding of various valves, valve seats, turbine blades, casting molds and extrusion molds.
HS116	Cobalt-Based Overlap Welding Wire (AWSRCoCr-C Equivalent)	C0.70~1.20 Cr30~34 W12.5~15.5 Excess material	46~50	The overlay has higher wear resistance and high temperature resistance, but low toughness. It has good corrosion resistance under sulfuric acid, phosphoric acid and nitric acid conditions. It is used for overlay welding of hot pressing molds of copper and aluminum base alloys, etc.
HS117	Cobalt Based Overlay Welding Wire	C2.30~2.60 Cr31~34 W16~18 Excess material	≥53	The overlay has strong wear and corrosion resistance and can maintain these characteristics at temperatures up to 800℃. It is used for pump bushings and rotary seal rings, wear panels, etc.

(2) Copper and copper alloy welding wire

Copper and copper alloy welding wires are commonly used for welding copper and copper alloys, and brass welding wires are also widely used for brazing carbon steel, cast iron and carbide tools.

A variety of welding methods can be used to weld copper and copper alloys, and correct filler metal selection is crucial to obtaining high-quality welds. When using oxygen acetylene gas welding, it must be used in conjunction with gas welding flux.

The types and chemical composition of copper and copper alloy welding wires can be seen in Table 5. The commonly used grades, models and applications of copper and copper alloy welding wires are listed in Table 6.

Table 5: Types and chemical composition of copper and copper alloy welding wires

Type

Model Number

Chemical composition / %

Ass

Zn

Sn

Yes

Mn

No

Faith

P

Pb

Al

You

s

Total amount of other elements

Copper

HSCu

≥98.0

*

≤1.0

≤0.5

≤0.5

*

*

≤0.15

≤0.02

≤0.01

－

－

≤0.05

Brass

HSCuZn-1

57.0~60.0

Margin

0.5~1.5

－

－

－

－

－

≤0.05

≤0.01

－

－

≤0.05

HSCuZn-2

56.0~60.0

0.8~1.1

0.04~0.15

0.01~0.5

－

0.25~1.20

HSCuZn-3

56.0~62.0

0.5~1.5

0.1~0.5

≤1.0

≤1.5

≤0.5

HSCuZn-4

61.0~63.0

－

0.3~0.7

－

－

－

Nickel silver

HSCuZnNi

46.0~50.0

－

－

≤0.25

－

9.0~11.0

－

≤0.25

≤0.05

≤0.02

－

－

≤0.50

HSCuNi

Margin

－

*

≤0.15

≤1.0

29.0~32.0

0.40~0.75

≤0.02

≤0.02

0.20~0.50

≤0.01

Bronze

HSCuSi

Margin

≤1.5

≤1.0

2.8~4.0

≤1.5

*

≤0.5

*

≤0.02

*

－

－

≤0.5

HSCuSn

*

6.0~9.0

*

*

*

*

0.10~0.35

≤0.01

HSCuAl

≤1.0

－

≤0.10

≤2.0

－

－

*

7.0~9.0

HSCuAlNi

≤1.0

－

≤0.10

0.5~3.0

0.5~3.0

≤2.0

*

7.0~9.0

Note: The total amount of impurity elements includes the sum of elements marked with an asterisk

.

Table 6: Make, model and purpose of commonly used copper and copper alloy welding wires.	Note	Model Number	Name Chemical composition	/% Fusion point	/℃
Forms:	HS201	HSCu	Custom Made Special Purple Copper Welding Wire Sn1.1 Si0.4 Mn0.4	remaining ass	1050
Used as filler material in argon arc welding and red copper oxy-acetylene gas welding.	HS202	－	Low Phosphorus Copper Welding Wire P0.3	remaining ass	1060
It serves as a filler material in oxyacetylene gas welding and red copper carbon arc welding.	HS220	HSCuZn-1	Tin Brass Welding Wire Cu59 Sn1	remaining Zn	860
Used as a filler material in oxy-acetylene welding and brass welding with inert gas shielding. Also suitable for brazing copper, copper alloys and cupronickel alloys.	HS221	HSCuZn-3	Tin Brass Welding Wire Cu60 Sn1 Si0.3	remaining Zn	890
Functions as a filler material in oxyacetylene gas welding and carbon arc welding of brass. It is also widely used in brazing copper, steel, cupronickel alloys, gray cast iron and for embedding hard alloy tools.	HS222	HSCuZn-2	Iron Brass Welding Wire Cu58 Sn0.9 Si0.1 Fe0.8	remaining Zn	860
Used as filler material in oxy-acetylene gas welding and carbon arc welding of brass. It can also be used for brazing copper, steel, cupronickel alloys, gray cast iron and for embedding hard alloy tools.	HS224	HSCuZn-4	Silicone Brass Welding Wire Cu62 Si0.5	remaining Zn	905

Used as a filler material in oxy-acetylene gas welding and carbon arc welding of brass. It can also be used in brazing copper, cupronickel and gray cast iron.

(3) Aluminum and aluminum alloy welding wire

Aluminum and aluminum alloy welding wires are used as filler materials for aluminum alloy argon arc welding and oxygen and acetylene gas welding. The selection of welding wire is mainly based on the type of base metal, crack resistance, mechanical properties and corrosion resistance of the butt joint.

In general, welding wires with the same or similar brand as the base metal are used for welding aluminum and aluminum alloys to achieve better corrosion resistance.

However, when welding heat-treated reinforcing aluminum alloys with a high tendency to hot cracking, the selection of welding wire mainly focuses on solving crack resistance. In this case, the composition of the welding wire is significantly different from that of the base metal.

Common types and applications of aluminum and aluminum alloy welding wires are shown in Table 8.

Table 7: Types and chemical compositions of aluminum and aluminum alloy welding wires.

Type

Model Number

Chemical composition/%

Yes

Faith

Ass

Mn

mg

Cr

Zn

You

V

Zr

Al

Total amount of other elements

Pure Aluminum

SAl-1

Fe+Si≤1.0

0.05

0.05

－

－

0.10

0.05

－

－

≥99.0

0.15

SAl-2

0.20

0.25

0.40

0.03

0.03

0.04

0.03

≥99.7

SAl-3

0:30

0:30

－

－

－

－

－

≥99.5

Aluminum Magnesium

SAlMg-1

0.25

0.40

0.10

0.50~1.0

2.40~3.0

0.05~0.20

－

0.05~0.20

Margin

SAlMg-2

Fe+Si≤0.45

0.05

0.01

3.10 ~ 3.90

0.15~0.35

0.20

0.05~0.15

SAlMg-3

0.40

0.40

0.10

0.50~1.0

4:30 pm ~ 5:20 pm

0.05~0.25

0.25

0.15

SAlMg-5

0.40

0.40

－

0.20~0.60

4.70~5.70

－

－

0.05~0.20

Aluminum Copper

SAlCu

0.20

0:30

5.8~6.8

0.20~0.40

0.02

0.10

0.10~0.20

0.05~0.15

0.10~0.25

Aluminum Manganese

SAlMn

0.60

0.70

－

1.0~1.6

－

－

－

－

－

aluminum silicon

SAlSi-1

4.5~6.0

0.80

0:30

0.05

0.05

0.10

0.20

SAlSi-2

11.0~13.0

0.80

0:30

0.15

0.10

0.20

－

Note: Except where specified, a single number represents the maximum value.

Table 8: Composition and uses of common aluminum and aluminum alloy welding wires.	Note	Chemical composition/%	Melting point ℃
Forms:	HS301 (Thread 301) Al≥99.5% Si≤0.3%	Fe≤0.3%	660
Welding pure aluminum and aluminum alloys that do not require high welding performance.	HS311 (Thread 311) Si4.5~6.0% Fe≤0.6%	rest Al	580~610
Welding of aluminum alloys other than aluminum-magnesium alloys, especially heat-treated reinforced aluminum alloys that are prone to hot cracking.	HS321 (Thread 321) Mn1.0~1.6% Si≤0.6% Fe≤0.7%	rest Al	643~654
Welding aluminum-manganese and other aluminum alloys.	HS331 (Thread 331) Mg4.7~5.7% Mn0.2~0.6% Si≤0.4% Fe≤0.4% Ti0.05~0.2%	rest Al	638~660

Welding of aluminum-magnesium alloys and aluminum-zinc-magnesium alloys, repair welding of aluminum-magnesium alloy castings.

(4) Cast Iron Welding Wire

Cast iron welding wire is mainly used to repair cast iron through gas welding. The flame temperature of oxygen and acetylene (less than 3400°C) is much lower than the arc temperature (6000°C) and the hot spots are not concentrated, making it more suitable for repairing thin-walled cast iron castings Gray.

Furthermore, the lower flame temperature of gas welding reduces the evaporation of the spheroidizing agent, which is beneficial to preserving the microstructure of nodular cast iron in the weld.

Currently, there are two types of nodular iron welding wires for gas welding: rare earth magnesium alloy and yttrium-based heavy rare earth. Yttrium has a high boiling point and greater resistance to spheroidization decline than magnesium, making it more effective in ensuring weld spheroidization. As a result, it has been widely used in recent years.

For the model and chemical composition of cast iron welding wire, see Table 9. For the composition characteristics and uses of gas welding wires commonly used for cast iron repairs, see Table 10.

Table 9 Model and Chemical Composition of Cast Iron Welding Wire	Model or Brand
	Chemical composition/%	W	Yes	Mn	s	P	No	Mo	Ce
Spheroidizing Agent	RZC-1	3.2~3.5	2.7~3.0	0.60~0.75	≤0.10	0.50~0.75	－	－	－
－	RZC-2	3.5~4.5	3.0~3.8		0.30~0.80	≤0.05	－	－	－
－	RZCH	3.2~3.5	2.0~2.5		0.50~0.70	0.20~0.40	1.2~1.6	0.25~0.45	－
－	RZCQ-1	3.2~4.0	3.2~3.8	0.10~0.40	≤0.015	≤0.05	≤0.50	－	≤0.20
0.04~0.10	RZCQ-2	3.5~4.2	3.5~4.2	0.50~0.80	≤0.03	≤0.10	－	－	－
0.04~0.10	HS401Hot Welding Wire	3.0~4.2	2.8~3.6	0.30~0.80	≤0.08	Spheroidizing Agent	－	－	－
－	HS401 Cold Welding Wire	3.0~4.2	3.8~4.8			0.30~0.80	－	－	－
－ HS402	Rare Earth Heavy Welding Wire	3.8~4.2	3.0~3.6	0.50~0.80	≤0.05	≤0.50	－	－	－
Yttrium-Based Heavy Rare Earths 0.08-0.10	Light wire for rare earth welding	3.5~4.0	3.5~3.9	0.50~0.80	≤0.03	≤0.10	－	－	－

Rare Earth Magnesium 0.03-0.04

Note: The model (RZC×-×) and chemical composition of cast iron welding wire are formulated in accordance with GB 10044-1988; The brand (HS4××) and chemical composition of cast iron welding wire are included in the “Welding Material Product Sample”, those without brand are non-standard welding wires.

Table 10: Composition and use of commonly used cast iron gas welding wire.	Note	Model Number	Chemical composition / %
Forms:	HS401	RZC-2 C3.0~4.2 Si2.8~3.6	Mn0.3~0.8
Used for welding and repair of gray cast iron castings, such as restoration of certain gray cast iron parts and welding and coating of agricultural tools, with low cost.	HS402	RZCQ-2 C3.8~4.2 Si3.0~3.6 Mn0.5~0.8	RE0.08~0.15

Used for welding and coating of ductile iron parts. III.

Flux-cored wire selection

1. Types and characteristics of flux-cored wire

According to the structure of welding wire, flux cored wire can be divided into seam and seamless welding wire. Seamless welding wire, which can be coated with copper to improve performance and reduce cost, is the direction of future development. Flux cored wire can also be divided based on the presence of shielding gas into gas shielded wire and self shielded wire.

The core powder of flux-cored wire is similar to that of the electrode coating and contains arc stabilizers, deoxidizers, slag forming agents and alloying agents. Depending on the presence of slag-forming agents in the filler powder, it can be divided into “flux-type” and “metal powder-type” welding wire. The basicity of slag further categorizes welding wire into titanium, titanium-calcium and calcium types.

Titanium slag flux cored wire has attractive weld bead formation, good welding performance in all positions, stable arc and minimal spatter, but the toughness and crack resistance of the weld metal are low. Calcium slag flux cored wire has excellent welding toughness and crack resistance, but the weld bead formation and welding performance are slightly inferior. The titanium calcium slag system is a compromise between the two.

The welding performance of “metal powder type” flux-cored wire is similar to that of solid cored wire and has better deposition efficiency and crack resistance compared to “powder type” wire.

The core of most metal powder type wires contains metal powder (such as iron powder and deoxidizers) and a special arc stabilizer for reduced slag formation, high efficiency, minimal spatter, stable arc, low diffusible hydrogen content in the weld and better resistance to cracking. .

The section shape of the flux cored wire significantly impacts the welding process and metallurgical properties. It can be divided into simple O-shape and complex bendable shapes such as quincunx, T-shape, E-shape and intermediate wire filling shapes.

The more complex and symmetrical the shape of the wire section, the more stable the arc and the more sufficient the metallurgical reaction and protection provided by the flux-cored wire.

However, this difference decreases with decreasing wire diameter, and when the diameter is less than 2mm, the influence of shape is not significant.

Flux cored wire has excellent welding performance, good weld quality and strong adaptability to steel. It can be used to weld various types of steel structures, including low-carbon steel, high-strength low-alloy steel, low-temperature steel, heat-resistant steel, stainless steel and wear-resistant surfaces. _{Shielding gases used include CO} 2 _{and Ar + CO} 2 _{with CO} 2 _{used for common structures and Ar + CO} 2

used for important structures. The wire is suitable for automatic or semi-automatic welding and can be used with DC or AC arc welding.

2. Flux cored wire for low carbon steel and high strength steel

Most of these welding wires are part of the titanium slag system and are known for their good welding processability and high productivity. They are commonly used in various industries such as shipbuilding, bridge construction, vehicle manufacturing, etc. There are different types of flux cored wires available for both low carbon steel and high strength steel.

From the strength point of view, flux-cored wires with tensile strengths of 490MPa and 590MPa have gained widespread use.

In terms of performance, some focus on process performance, while others focus on weld mechanical properties and crack resistance. Some are suitable for welding in all positions, including vertical down welding, and some are designed specifically for fillet welds.

3. Stainless steel flux cored wire

There are more than 20 types of stainless steel flux cored wires, including those made from chromium-nickel stainless steel and chrome stainless steel. The diameter of these welding wires ranges from 0.8mm to 1.6mm, making them suitable for welding thin, medium and thick stainless steel plates. _{The most commonly used shielding gas for these wires is CO} 2 _{although a mixture of argon and CO} 2

(in a proportion of 20% to 50%) can also be used.

4. Hardfacing flux cored wire

To improve wear resistance or obtain specific properties on metal surfaces, a certain amount of alloying elements needs to be transferred from the welding wire. However, this can be challenging due to the high carbon content and alloying elements present in the welding wire.

With the introduction of flux-cored wires, these alloy elements can be added to the flux core, making the manufacturing process more convenient. As a result, the use of flux-cored wires for submerged arc coating of wear-resistant surfaces has become a common and widely used method.

By adding alloying elements to the sintered flux, it is also possible to obtain a coating layer with corresponding components after coating. This method can meet different coating requirements when used in combination with solid core or flux cored wires. _{The common methods for CO 2 flux cored wire}

Flux cored wire submerged arc surface and surface are characterized by high welding efficiency and excellent welding process performance, including a stable arc, minimal spatter, easy slag removal and a smooth surface. _{The method using CO 2 flux-cored wire}

Coating is mainly used to coat layers with low alloy composition and can only be used for the transition of alloy elements in flux-cored wire.

The flux-cored submerged arc surface, on the other hand, uses larger diameter flux-cored wires (3.2 mm to 4.0 mm) and results in significantly improved welding productivity. The use of flux allows the transfer of alloying elements, enabling a higher alloy composition in the surface layer, ranging from 14% to 20% to meet different application requirements.

This method is mainly used to coat wear-resistant and corrosion-resistant parts such as rolling mill rolls, feed rolls and continuous casting rolls.

5. Self-protective flux-cored wire

Self-shielded welding wire refers to welding wire that can conduct arc welding without the need for shielding gas or flux, resulting in qualified welds.

Self-shielded flux core welding wire contains dust and metal powder that serve as slag and gas production as well as deoxidation, whether inside the steel plate or coated on the surface of the welding wire.

During welding, the dust turns into slag and gas under the action of the arc, providing protection against slag and gas without the need for additional gas shielding.

Self-shielded flux-cored wire has higher deposition efficiency compared to electrodes.

In terms of flexibility and wind resistance, field welding with self-shielded flux-cored wire is better than gas-shielded welding and can typically be welded at wind speeds of up to four levels.

Due to the absence of the need for shielding gas and its suitability for field or high-altitude operations, self-shielded welding wire is commonly used on construction and installation sites.

However, the plasticity and weld metal toughness of self-shielded welding wire are generally lower compared with those of flux-cored welding wire with shielding gas.

At present, self-shielded welding wire is mainly used for welding low-carbon steel structures and is not recommended for welding important structures such as high-strength steel.