What are the welding materials? General principles for selecting welding materials

Date：2021-10-12 13:00:00Views：2370

In order to obtain high-quality welded joints, it is necessary to reasonably select welding materials. Because the working conditions of welded parts are very different in operation, the material properties and components of base metal are very different, and the manufacturing process of parts is complex, it is necessary to comprehensively consider all aspects to determine the corresponding welding materials. What are the welding materials? Next, let's take a look at the principles that should be followed in selecting welding materials.

welding material: general term of materials consumed during welding (including welding rod, welding wire, flux, shielding gas, electrode, flux, etc.).

Welding rod: coated melting electrode for power arc welding.

Welding wire: metal wire used as filler metal during welding or for conducting electricity at the same time.

flux: a granular material that can melt to form slag (some also have gas) during welding and plays a protective and metallurgical role in molten metal.

Shielding gas: gas used to protect metal droplets, weld pool and high-temperature metal in the welding area during welding, and prevent external harmful gases from entering the welding area.

electrode: metal wire (welding wire, welding rod), rod (graphite rod, tungsten rod), tube, plate, etc. used to conduct current and melt the filler material and base metal or itself as filler material during fusion welding. In resistance welding, it refers to the metal pole used to conduct circuits and transmit pressure.

flux: powder material used in gas welding to remove oxides formed during welding and improve the wettability of molten pool.

General principles for selecting welding materials:

1. Welding rod

Basic requirements for welding rod:

(1) The deposited metal of welding rod shall have good mechanical properties

(2) The deposited metal of the welding rod shall have the specified chemical composition to meet the requirements of its service performance

(3) The welding rod shall have good process performance

(4) The welding rod is required to have good air hole and crack resistance

(5) The welding rod shall have good appearance (skin) quality

Composition of welding rod:

The electrode is composed of welding core and coating. The metal core covered by the coating in the electrode is the welding core, which is mainly used to conduct electricity and form an arc at the end of the electrode. At the same time, the welding core is melted by the arc and cooled to form a deposited metal with a certain composition. The coating applied on the surface of the welding core in the welding rod is called coating. Its main functions are mechanical protection, metallurgical treatment and improvement of welding process performance.

Classification of welding rods:

According to the basicity of slag, it is divided into acid electrode and alkaline electrode; According to the main components of the drug skin, it is divided into titanium type, titanium calcium type, ilmenite type and iron oxide type; It is classified into structural steel electrode (J), molybdenum and chromium molybdenum heat-resistant steel electrode (R), stainless steel electrode (chromium stainless steel g, chromium nickel stainless steel a), surfacing electrode (d), low temperature electrode (W), cast iron electrode (z), nickel and nickel alloy electrode (Ni), copper and copper alloy electrode (T), aluminum and aluminum alloy electrode (L) and special purpose electrode (TS).

Model and brand of welding rod:

The brand of welding rod shall include the following meanings: welding rod, type of welding rod, characteristics of welding rod (such as tensile strength of deposited metal, service temperature, type of welding core metal, chemical composition type of deposited metal, etc.), coating type and welding power supply.

According to the provisions of carbon steel electrodes (GB / T 5117-1995) and alloy steel electrodes (GB / T 5118-1995), the main structure of the electrode model consists of the letter "e" and four digits, and its structure and meaning are as follows:

E x1x2x3x4 e: electrode

X1x2: welding rod series, that is, the minimum tensile strength of deposited metal

X3: welding position of welding rod

X4: electrode coating type and welding power supply type

E.g. e 5015 electrode

50: tensile strength of deposited metal σ b≥409Mpa

1: All position (0, 1 all position; 2 flat welding and flat fillet welding; 4: flat welding, vertical welding, overhead welding and vertical downward welding are only applicable to carbon steel electrodes)

Low alloy steel electrode:

E X1X2 X3 X4-□-□

E: Welding rod

X1x2: minimum tensile strength of deposited metal

X3: welding position of welding rod (0, 1 full position; 2 for flat welding and flat fillet welding)

X4: welding current type and coating type are expressed in numbers

1: Classification code of chemical composition of deposited metal, expressed in letters

2: Additional chemical components are represented by chemical element symbols

Stainless steel electrode:

E 308L-16

E: Indicates electrode

308L: chemical composition of deposited metal, l represents ultra-low carbon,

308 indicates the type of chemical composition of the deposited metal of the electrode

Other types of welding rods will not be repeated.

2. Welding wire

Basic requirements for welding wire:

The welding wire plays the role of conducting current, filler metal and transition alloy in the welding process, and the self protective flux cored wire also plays the role of protection or deoxidation and nitrogen removal in the welding process. Therefore, the welding wire is required to have the required chemical composition and mechanical properties, and clear technical requirements for its size and surface quality should be put forward.

Classification of welding wires:

It can be divided into flux cored wire and solid cored wire according to the structural form, and flux cored wire can be divided into many types according to the different structure and filler; It is divided into low-carbon steel welding wire, low-alloy steel welding wire (welding wire for high-strength steel, Cr Mo heat-resistant steel welding wire and low-temperature steel welding wire), stainless steel welding wire, hard alloy surfacing welding wire, copper and copper alloy welding wire, aluminum and aluminum alloy welding wire, cast iron welding wire, etc; According to the welding methods, it is divided into submerged arc welding wire, electroslag welding wire, CO2 gas shielded welding wire, argon arc welding wire, (TIG welding wire, MIG welding wire, MAG welding wire), self shielded welding wire, surfacing welding wire and gas welding wire.

Model or brand of welding wire

(1) Carbon steel, low alloy steel and stainless steel welding wire for welding

Except GB / T8110-95, the model or brand of welding wire is represented by letter h. The preparation method of gas brand is as follows: the letter H represents welding wire; One or two digits after H represent the carbon content (average approximate); The chemical element symbol and the number after it represent the approximate mass fraction of the element. When the mass fraction of the main alloy element is ≤ 1%, the number can be omitted and only the element symbol can be marked; When a or E is marked at the tail of the welding wire brand, it means high-quality product or high-quality product, indicating lower impurity contents such as s and P.

For example: H08Mn2SiA

H: Welding wire 08: carbon content, mass fraction about 0.08%

Mn2: mass fraction of Mn content is about 2% Si: mass fraction of Si content is ≤ 1%

A: For high-quality products, the mass fraction of S and P is about ≤ 0.03%

(2) Carbon steel and low alloy steel welding wires for gas shielded welding

According to GB / T8110-95, the representation method of welding wire model is erxx-x: the letter Er represents the welding wire, the two digits after Er represent the minimum tensile strength of deposited metal, and the letters or numbers after Er represent the classification code of chemical composition of welding wire. When other chemical components are added, they can be directly represented by element symbols and separated from the previous numbers with a dash.

For example: er55-b2-mn

Er: welding wire 55: the minimum tensile strength of deposited metal is 550MPa

B2: classification code of chemical composition of welding wire Mn: indicates that the welding wire contains Mn element

2. Flux

Basic requirements for flux:

(1) It has good metallurgical properties

(2) Good welding process performance

(3) It has low water content and good moisture resistance

(4) The mass fraction of mechanical inclusions in the flux shall not be greater than 0.3%

(5) The flux shall have low S and P content, s ≤ 0.06%; ≤0.08％

(6) The flux shall have a certain particle size, ordinary 8-40 mesh and fine particle size of 14-60 mesh

(7) For electroslag welding flux, in order to obtain a good welding joint, the flux is required as follows

The conductivity of slag shall be within the appropriate range; The viscosity of slag shall be appropriate; Control the evaporation temperature of flux.In addition, the flux shall also have good slag removal, crack resistance and pore resistance.

Classification of flux:

Flux is often divided into smelting flux and non smelting flux (bonding flux, sintering flux), etc.

For example: HJ431

HJ: melting flux for submerged arc welding and electroslag welding

4: The flux type is high manganese

3: The flux type is high silicon and low fluorine

1: Brand number, different numbers in the same type, arranged by 0, 1... 9

2、 Selection of welding materials

In order to obtain high-quality welded joints, it is necessary to reasonably select welding materials.

1. Meet the requirements for the service performance of welded joints

Including normal temperature, high temperature short-time strength, bending performance, impact toughness, hardness, chemical composition, etc., as well as special requirements for joint performance in some technical standards and design drawings, such as endurance strength, creep limit, high temperature oxidation resistance, corrosion resistance, etc.

2. Requirements for manufacturing process performance and welding process performance of welded joints

In the manufacturing process of welded components, it is inevitable to carry out various forming and cutting processes, such as stamping, rolling, bending, turning, planing and other processing procedures, which requires the welded joint to have certain plastic deformation ability, cutting performance, high temperature comprehensive performance and so on. According to the weldability difference of base metal, the welding process requires that the welding material has good process performance and corresponding ability to resist crack and other defects.

3. Reasonable economy

While meeting the minimum requirements of the above service performance and manufacturing performance, cheap welding materials shall be selected to reduce the manufacturing cost and improve the economic benefit. For example, when welding low carbon steel electrodes for important parts, alkaline coated electrodes should be preferred, because alkaline electrodes have sufficient deoxidation and desulfurization, low hydrogen content and good crack resistance and impact toughness of weld metal. For some non important parts, acid electrode can be selected, because acid electrode not only has good processability, but also meets the performance requirements of non important parts, and the price is cheap, which can reduce the manufacturing cost.

3、 Selection of welding materials for plain steel and low alloy steel

(1) Equal strength principle

As a part of components, the tensile strength of welded joints shall not be less than the lower limit of the standard tensile strength of base metal. At the same time, it should be noted that the tensile strength of the deposited metal of the welding material should not be too much higher than that of the base metal, otherwise it will reduce the plasticity of the weld and increase the hardness, which is not conducive to the subsequent manufacturing and forming.

When selecting welding materials for welded joints under high temperature operation, it shall also be considered that the high-temperature short-time tensile strength or endurance strength is not lower than the corresponding value of the base metal.

When welding general carbon steel and ordinary low alloy steel, the selection of welding materials mainly considers the tensile strength of welding materials, but does not consider the matching of chemical composition of deposited metal with base metal; However, when welding Cr Mo heat-resistant steel materials, the selection of welding materials should consider not only the chemical composition of deposited metal and the matching of base metal, but also the matching of alloy elements, so as to ensure that the comprehensive properties of welded joints are consistent with the base metal.

In special cases, when the allowable stress of components is calculated according to the yield strength of materials, the equal strength of yield strength must be considered as an important factor.

(2) Equal toughness principle

When selecting welding materials, ensure that the impact toughness of the weld meets the requirements of relevant standards. Due to the different operating conditions of components, brittle failure often occurs due to insufficient toughness in operation, especially for components working at low temperature or high-strength thick wall components. Therefore, the relevant standards put forward clear requirements for the impact toughness index of welded joints. However, different standards have different requirements for impact toughness of joints. According to the regulations on safety supervision of steam boilers, the impact toughness of welded joints shall not be lower than the lower limit of the specified value of impact toughness of base metal. When the base metal has no impact toughness requirements, it shall not be lower than 27j. GB 150 steel pressure vessels stipulates that the impact toughness value of the joint shall be determined according to the minimum tensile strength of the steel. See table 3-40 for the minimum impact toughness requirements of carbon steel and low alloy steel joints.

The impact toughness value of low-temperature vessel shall not be lower than the lower limit of the specified value of base metal, while ASME code VIII-1 determines whether the joint should ensure the impact toughness performance according to the strength grade, thickness, working temperature and the ratio of design stress to allowable stress of the material. If the joint has impact toughness requirements, the minimum guarantee value of impact toughness shall be specified according to the strength level and thickness of the material.

(3) Consider the requirements and influence of manufacturing process

After welding, parts often go through various forming processes, such as rolling, pressing, bending, calibration and so on. Therefore, the welded joint and base metal must have certain processing deformation ability, among which the main cold deformation ability is measured by the bending test of the joint

4、 Selection of welding materials for austenitic stainless steel

The equal strength principle of welding material and base metal is not fully applicable to austenitic stainless steel. If austenitic stainless steel is used in corrosion-resistant working conditions, it has no specific requirements for strength, and the corrosion resistance of welds is mainly considered. If it is used under high temperature and high pressure conditions, it is required to have a certain high temperature and short-time strength for short-time work, and ensure that the weld metal has sufficient endurance strength and creep limit for long-term work. For example, when sa213-tp304h pipe is used under high temperature and high pressure conditions, e308h electrode with high carbon content shall be selected for arc welding.

a) Consider the chemical composition of the deposited metal

For austenitic stainless steel welding, when selecting welding materials, it is more important to consider that the chemical composition of the deposited metal should be equivalent to that of the base metal. As long as the chemical composition of the clad metal of the welding material is equivalent to that of the base metal, the service performance of the weld metal can be equivalent to that of the base metal, including mechanical properties, corrosion resistance, etc. in addition, Special attention shall also be paid to the special requirements of manufacturing technical conditions or drawings for corrosion resistance. In order to prevent intergranular cracks during welding, it is best to select stainless steel welding materials with low carbon (ultra-low carbon) and Ti and Nb. If the content of SO2 in the electrode coating or flux is too high, it is not suitable for the welding of austenitic steel with high nickel content. In order to prevent weld hot crack (solidification crack), the content of P, s, Sb and Sn impurities shall be controlled to avoid the formation of single-phase austenite structure in weld metal as far as possible.

b) Consider the ferrite content in the weld

Although many data show that the ferrite content in austenitic stainless steel weld is beneficial to reduce the crack tendency of weld metal, a large number of pure austenitic weld metal in production and application has been used for many years, and the joint runs well. In addition, proper ferrite content in some media is beneficial to corrosion resistance, but harmful to the impact toughness of weld metal under low temperature conditions. In general, the ferrite content of austenitic stainless steel is 4-12%, because the satisfactory intergranular corrosion resistance can be obtained by 5%.

c) Consider the influence of welding method

When selecting austenitic stainless steel welding materials, attention should be paid to the influence of welding methods on the chemical composition of deposited metal. Tungsten argon arc welding has the least effect on the change of chemical composition of weld metal. In the undiluted weld metal, except C and N, there is little change. Among them, the loss of C is the largest. The welding wire with C content of 0.06%, the content of C in the undiluted deposited metal of argon arc welding is 0.04%, while the content of N in the weld metal increases by about 0.02%. The contents of Mn, Si, Cr, Ni and Mo in GMAW may change slightly, while the loss of C is only 1 / 4 of that in argon arc welding, while the content of n increases more. The increase varies with different welding processes, up to 0.15%. In electrode arc welding and submerged arc welding, the alloy elements of weld metal are affected by the coating, flux, core and welding wire, especially those welding materials with alloy element transition through coating or flux. It is impossible to estimate the chemical composition of weld metal by the chemical composition of core and welding wire. Of course, the ferrite content of the weld can be estimated by the alloy content in the weld metal, but this estimated value has a certain deviation from the actual value, because the cooling rate of the welding process also affects the ferrite content. It is agreed that if the alloy element content in the weld metal is exactly the same and the welding methods are different, the ferrite content is also different. The strip surfacing is the highest, followed by submerged arc welding, electrode arc welding, CO2 gas shielded welding, MAG welding, MIG welding and argon arc welding. The ferrite content of the weld is the lowest. However, even with the same strip electrode surfacing, the ferrite content of welds in different parts is also different. In the measurement, it is found that the ferrite content at the arc ending and arc starting is about 2-3% lower than that in the middle section. With the standardization of stainless steel materials and welding materials, the selection of austenitic stainless steel welding materials becomes simple. The corresponding welding material brand can be selected through the brand of stainless steel. For example, E316 electrode can be directly selected for sa-240-316 stainless steel welding.

5、 Selection of welding materials for stainless steel

When welding martensitic stainless steel, it is better to use welding materials of the same quality as the base metal. For example, e410 series welding materials shall be selected when welding 1Cr13 steel, and the brand of electrode arc welding materials is G217. However, the weld metal structure of common 1Cr13 corresponding welding material is coarse martensite and ferrite, which is hard and brittle and easy to form cracks. Moreover, the weldment must be preheated at 250-350 ℃. In order to improve the performance, it is necessary to limit the content of S and P in the welding material, control the content of Si (≤ 0.30%), reduce the content of C, and add a small amount of Ti, Al and Ni to refine the grain and reduce the hardenability, Some data show that the single-phase ferrite structure can be obtained by increasing the Nb content in the welding material (up to about 0.8%). In CO2 gas shielded welding, the content of Ti and Mn in welding wire should be increased to achieve the purpose of deoxidation.

Austenitic stainless steel welding material can also be used for martensitic stainless steel. At this time, the influence of base metal dilution on the composition of weld metal must be considered. Through appropriate Cr and Ni content, martensitic structure can be avoided in weld metal. For example, A312 (E309Mo) electrode is used to weld 1Cr13 martensitic steel during electrode arc welding.

6、 Selection of welding materials for ferritic stainless steel

Ferritic stainless steel usually adopts the same welding material as the base metal, but the ferrite structure of the weld is coarse and the toughness is very poor. The toughened ferrite structure can be improved by increasing the Nb content in the welding material. At the same time, the toughness of the weld metal can be improved by heat treatment.

7、 Selection of welding materials for dissimilar steels

The welding between low carbon steel and low alloy steel and the welding between low alloy steels of different materials belong to the welding of the same kind of different materials. For the welding between these steels, the welding materials can be selected according to the low-grade materials, and the materials with low strength grade or low alloy element content. Choosing low-grade materials has better welding performance and cheaper price than high-grade materials, which is conducive to reducing manufacturing costs.

1. Definition of welding materials, including which materials?

Answer: general name of materials consumed during welding.Welding materials include welding rod, welding wire, flux, shielding gas, electrode, solvent, etc.

2. What are the selection principles of welding materials for carbon steel and low alloy steel?

Answer: 1) equal strength principle

2) Equal toughness principle

3) Consider the requirements and influence of manufacturing process

3. In general, for the welding of low carbon steel and low alloy steel, shall the welding materials be selected according to low-grade materials or high-grade materials? What electrode shall be selected for 20g and diwa353 electrode arc welding?

A: select welding materials according to low-grade materials.

Select J507 welding rod. (GB E5015 or AWS e7015 are acceptable)

4. What is the meaning of "e" in GB e5515-b2? What does "55" mean? When you see this brand, can you tell what steel it is used for welding?

Answer: "e" stands for welding rod

"55" represents the tensile strength of deposited metal, with a minimum value of 540 MP.

For welding Cr Mo heat resistant steel. You can also answer 13CrMo44, 15CrMo, 15CrMoR, 15CrMoG, sa-335p12, sa213t12, sa213t11, sa387gr12cl1, sa387gr11cl1, sa387gr11cl2, etc.

5. In H08Mn2SiA, what are the meanings of "H", "08", "Mn2", "Si" and "a" respectively?

Answer: "H" stands for welding wire

"08" means that the C content is about 0.08%

"Mn2" means that the Mn content is about 2%

"Si" means that the content of Si is ≤ 1%

"A" means high-quality product

6. What is the meaning of "50" and "70" in GB E5015 and AWS 5.1 e7015?

Answer: "50" means the minimum tensile strength of deposited metal is 490mpa

"70" represents the tensile strength of deposited metal. The minimum value is 70ksi, i.e. 485mpa

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