Welding rod (covered electrode)
[Edit this paragraph] Composition of welding rod
Welding rod consists of two parts: welding core and coating. The welding rod applies coating (coating) evenly and centripetally on the outside of the metal welding core. Different types of welding rods have different welding cores. The welding core is the metal core of the welding rod. In order to ensure the quality and performance of the weld, there are strict regulations on the content of each metal element in the welding core. In particular, the content of harmful impurities (such as sulfur, phosphorus, etc.) should be strictly regulated. limitations, better than the parent material. The composition of the welding core directly affects the composition and performance of the weld metal, so the harmful elements in the welding core should be as small as possible. The C content should be less than 0.10%. For example, H08A contains S less than or equal to O. 03%, P less than or equal to 0.03%, C less than or equal to 0.1%.
The welding core for welding carbon steel and low alloy steel generally uses low carbon steel as the welding core, and is filled with manganese, silicon, chromium, nickel and other ingredients (see the national standard for welding wire GB1300-77 for details) . The reason for using low carbon is that on the one hand, the steel wire has good plasticity when the carbon content is low, and it is easier to draw the welding wire. On the other hand, it can reduce the CO content of the reducing gas, reduce spatter or pores, and increase the temperature of the weld metal when it solidifies. Good for overhead welding. Adding other alloying elements is mainly to ensure the comprehensive mechanical properties of the weld. It also has a certain effect on the welding process performance and the removal of impurities.
For high-alloy steel and other metal materials such as aluminum, copper, cast iron, etc., in addition to requiring the composition of the welding core to be similar to that of the metal to be welded, the content of impurities must also be controlled, and certain additives are often added according to process requirements. Specific alloying elements.
The welding rod is a molten electrode coated with a coating for arc welding. It is composed of a coating and a welding core. The coating on the front end of the electrode is 45. The left and right chamfers are for the convenience of arc starting. There is a section of exposed welding core at the tail, which accounts for about 1/16 of the total length of the electrode, which is convenient for holding the welding clamp and conducts electricity. The diameter of the welding rod (actually refers to the diameter of the welding core) is usually 2, 2.5, 3.2 or 3, 4, 5 or 6mm. The commonly used ones are small 3.2, small 4 and small 5. species, its length "L" is generally between 250^-450 mm.
1. Welding core
The metal core covered by the coating in the welding rod is called the welding core. The welding core is generally a steel wire with a certain length and diameter. When welding, the welding core has two functions: first, it conducts the welding current and generates an arc to convert electrical energy into heat energy; second, the welding core itself melts as a filler metal and fuses with the liquid base metal to form a weld.
When welding with electrodes, the core metal accounts for part of the entire weld metal. Therefore, the chemical composition of the welding core directly affects the quality of the weld. Therefore, the grade and composition of the steel wire used as the core of the welding rod are individually specified. If it is used as filler metal in fusion welding methods such as automatic submerged arc welding, electroslag welding, gas shielded welding, and gas welding, it is called welding wire. (1) The influence of various alloying elements in the welding core on welding
1) Carbon (C) Carbon is the main alloying element in steel. When the carbon content increases, the strength and hardness of the steel increase significantly. , and the plasticity decreases. During the welding process, carbon plays a certain deoxidizing role and reacts with oxygen under the high temperature of the arc to generate carbon monoxide and carbon dioxide gases, which removes the air around the arc area and molten pool to prevent harmful oxygen and nitrogen gases in the air. Adverse effects on the molten pool, reducing the oxygen and nitrogen content in the weld metal. If the carbon content is too high, the reduction effect will be violent, which will cause larger splashes and pores. Considering the effect of carbon on the hardenability of steel and its increased susceptibility to cracks, the carbon content of low carbon steel welding cores is generally around 0.1%.
2) Manganese (Mn) Manganese is a good alloying agent in steel. As the manganese content increases, its strength and toughness will increase. During the welding process, manganese is also a good deoxidizer, which can reduce the oxygen content in the weld. Manganese combines with sulfur to form manganese sulfide floating in the slag, thereby reducing the tendency of hot cracking in the weld. Therefore, the manganese content of the general carbon structural steel welding core is 0.30% to 0.55%. The manganese content of some special-purpose steel wires can be as high as 1. 70% to 2.10%.
3) Silicon (Si) Silicon is also a good alloying agent. Adding an appropriate amount of silicon to steel can improve the yield strength, elasticity and acid resistance of the steel; if the content is too high, it will reduce Plasticity and toughness. During the welding process, silicon also has good deoxidizing ability and forms silica with oxygen, but it will increase the viscosity of the slag and easily promote the formation of non-metallic inclusions.
4) Chromium (Cr) Chromium can improve the hardness, wear resistance and corrosion resistance of steel. For mild steel, chromium is an accidental impurity. The main metallurgical characteristic of chromium is that it is prone to rapid oxidation to form the refractory oxide chromium trioxide (Cr203), thereby increasing the possibility of weld metal inclusions. After chromium trioxide transitions to slag, it can increase the viscosity of the slag and reduce its fluidity.
5) Nickel (NO) Nickel has a significant effect on the toughness of steel. Generally, when the low temperature impact value is required to be high, some nickel should be appropriately mixed in.
6) Sulfur (S ) Sulfur is a harmful impurity. As the sulfur content increases, the tendency of hot cracking of the weld will increase. Therefore, the sulfur content in the weld core shall not exceed 0. 04%. When welding important structures, the sulfur content shall not exceed 0.03%.
7) Classification of phosphorus (2) welding core
Welding core is classified according to the national standard "Steel Wire for Welding" (GB 1300-77) and is used for welding Special steel wire can be divided into three categories: carbon structural steel, alloy structural steel, and stainless steel.
2. Coating
The coating applied on the surface of the solder core is called coating. The coating of the welding rod plays an extremely important role in the welding process. If uncoated light electrodes are used for welding, during the welding process, a large amount of oxygen and nitrogen in the air will invade the molten metal, oxidizing and nitriding the metallic iron and beneficial elements carbon, silicon, manganese, etc. to form various oxides and Nitride remains in the weld, causing slag inclusions or cracks in the weld. The gas melted into the molten pool may cause a large number of pores in the weld. These factors can greatly reduce the mechanical properties (strength, impact value, etc.) of the weld and make the weld brittle. In addition, when welding with light electrodes, the arc is very unstable, the spatter is serious, and the welding seam formation is poor.
People have found in practice that if a layer of coating composed of various minerals is applied to the outside of the bare welding rod, the arc burning can be stabilized and the quality of the weld can be improved. This kind of welding rod is called a coating welding rod. . With the continuous development of industrial technology, people have created high-quality thick-coated welding rods that are now widely used.
[Edit this paragraph] Requirements for welding rods
(1) It is easy to strike the arc, ensuring arc stability and small spatter during the welding process.
(2) The melting speed of the coating should be slower than the melting speed of the welding core to create a trumpet-shaped sleeve (the length of the sleeve should be smaller than the diameter of the welding core), which is conducive to the transfer of droplets and the creation of a protective atmosphere;
(3) The specific gravity of the molten slag should be less than the specific gravity of the molten metal, the solidification temperature should also be slightly lower than the metal solidification temperature, and the slag shell should be easy to remove;
(4) It has With alloying and metallurgical treatment functions;
(5) Suitable for welding in various positions.
[Edit this paragraph] Welding rod model and grade
(1) Welding rod grade
Take structural steel as an example: grade and preparation method. The knot is XXX. The knot is a structural steel welding rod. The third number represents the type of coating and the welding current requirement. The first and second numbers represent the tensile strength of the weld metal.
(2) Model of welding rod
The model of welding rod is determined according to relevant national standards and international standards. EXXX, taking structural steel as an example, the model numbering method is the letter "E" represents the welding rod, the first and second digits represent the minimum tensile strength of the deposited metal, the third digit represents the welding position of the welding rod, the third and fourth digits represent Welding current type and coating type.
4. Classification of welding rods
According to different situations, there are three classification methods for welding rods: classification according to the purpose of the welding rod, classification according to the main chemical composition of the coating, and classification after the coating is melted. Characteristic classification of slag.
According to the use of welding rods, there are two forms of expression. One is compiled by the former Ministry of Machinery Industry. Welding rods can be divided into: structural steel welding rods, heat-resistant steel welding rods, stainless steel welding rods, and surfacing welding rods. , low temperature steel electrodes, cast iron electrodes, nickel and nickel alloy electrodes, copper and copper alloy electrodes, aluminum and aluminum alloy electrodes and special purpose electrodes. The second is the national standard, which is carbon steel electrodes, low alloy electrodes, stainless steel electrodes, cladding electrodes, cast iron electrodes, copper and copper alloy electrodes, aluminum and aluminum alloy electrodes. There is no principle difference between the two. The former is represented by a commercial brand, and the latter is represented by a model.
If classified according to the main chemical composition of the electrode coating, welding electrodes can be divided into: titanium oxide type electrodes, titanium calcium oxide type electrodes, ilmenite type electrodes, iron oxide type electrodes, cellulose Type welding rod, low hydrogen welding rod, graphite welding rod and salt-based welding rod.
If classified according to the characteristics of the slag after the electrode coating is melted, the welding electrodes can be divided into acidic electrodes and alkaline electrodes. The main components of acidic electrode coating are acid oxides, such as silica, titanium dioxide, ferric oxide, etc. The main components of alkaline electrode coating are alkaline oxides, such as marble, fluorite, etc.
According to different uses, welding rods can be divided into structural steel welding rods, heat-resistant steel welding rods, stainless steel welding rods, cast iron welding rods, copper and copper alloy welding rods, aluminum and aluminum alloy welding rods, etc.
Welding rods can be divided into two categories according to the chemical properties of the slag: acidified welding rods and alkalized welding rods. The weld produced by alkaline electrode contains less hydrogen, sulfur and phosphorus. Welds have good mechanical properties, but are sensitive to oil, water, and rust, and are prone to pores. When welding with acidic electrodes, the arc is stable, there is less spatter, and the slag removal is good. Therefore, alkaline electrodes are used for important welding structural parts, while acidic electrodes are used for general structural parts.
The grade of structural steel welding rods is represented by the Chinese pinyin followed by three digits. For example, the grade of structural steel welding rods used in our internship is J422 (or Jie 422). "J" represents the "knot" character for structural steel welding rods. The last two numbers "42" mean that the tensile strength of the weld metal is not less than 420MPa; the last number "2" represents titanium-calcium type coating, which can be used with either AC or DC power supply.
Acid carbon steel welding rod
Type: J421, J421Fe, J422, J423, J425, J502, J501Fe15
Brand GB model AWS model coating type current type Main application specifications
J421 E4313 E6013 Titanium oxide type AC/DC welding low carbon steel structure, especially suitable for intermittent welding of small thin plates and short welds and cover welding that requires a smooth surface Φ2.0— Φ5.0
J421Fe E4313 E6013 Iron powder titanium type AC/DC welding of general low carbon steel structures, especially suitable for intermittent welding of small thin parts and short welds and cover welding that requires a smooth surface Φ2. 5—Φ5.0
J422 E4303 - Calcium titanium AC/DC used for welding more important low carbon steel structures and strength grade low alloy steels, such as 09Mn2, etc. Φ2.0—Φ5.0
J423 E4301 - Titanium ferrotype AC/DC can be welded to the more important low carbon steel structure Φ3.0-Φ5.0
J425 E4311 E6011 Cellulose potassium type AC/DC Suitable for butt, corner and lap welding of thin plate structures.
Such as power station flue, air duct, transformer fuel tank, ship hull and vehicle outer plate low carbon steel structure Φ3.2-Φ5.0
J502 E5003 - Calcium titanium AC/DC mainly used for 16Mn Welding of low alloy steels Φ2.0—Φ5.0
J501Fe15 E5024 E7024 Iron powder titanium type AC/DC is suitable for welding of rolling stock, shipbuilding, boilers and other structures Φ2.5—Φ5.0
Chemical composition of deposited metal Mechanical properties of deposited metal
Grade C Mn Si S P Tensile strength (Mpa) Yield strength (Mpa) Elongation () Impact value
℃ J
J421 ≤0.12 0.3～0.6 ≤0.35 ≤0.035 ≤0.040 ≥420 ≥330 ≥22 0 ≥47
J421Fe ≤0.12 0.3～0.6 ≤0.35 ≤0.035 ≤ 0.040 ≥420 ≥330 ≥17 0 ≥47
J422 ≤0.12 0.3～0.6 ≤0.25 ≤0.035 ≤0.040 ≥420 ≥330 ≥22 -20 ≥47
J423 ≤0.20 0.3 ~0.6 ≤0.20 ≤0.035 ≤0.040 ≥420 ≥330 ≥22 0 ≥27
J425 ≤0.12 0.3～0.6 ≤0.30 ≤0.035 ≤0.040 ≥420 ≥330 ≥22 -30 ≥27
J502 ≤0.12 ≤1.60 ≤0.30 ≤0.035 ≤0.040 ≥420 ≥400 ≥20 0 ≥27
J501Fe15 ≤0.12 0.8～1.4 ≤0.90 ≤0.035 ≤0.040 Mo≤0.30 V≤0.08 ≥42 0 ≥400 ≥17 0 ≥27
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Basic carbon steel welding rod
Type: J426, J427, J506, J507, J506Fe
Brand GB model AWS model coating type current type main application specifications
J426 E4316 E6016 low hydrogen potassium AC/DC is used for welding important low carbon steel and low alloy steel structures.
Such as O9Mn2, etc. Φ2.5-Φ5.0
J427 E4315 - low hydrogen sodium type DC(R) is used to weld important low carbon steel and low alloy steel, such as O9MnSi, etc. Φ2.5-Φ5 .0
J506 E5016 E7016 Low hydrogen potassium AC/DC used for welding medium carbon steel and low alloy steel such as 16Mn, O9MnSi, etc. Φ2.5-Φ5.0
J507 E5015 E7015 Low hydrogen sodium type DC(R) can weld medium carbon steel and some low alloy steels such as 16Mn, O9Mn2Si, O9Mn2V, etc. Φ2.5—Φ5.0
J506Fe E5018 E7018 Iron powder low hydrogen potassium Type AC/DC is suitable for welding carbon steel and low alloy steel, such as 16Mn, etc. Φ2.5-Φ5.0
Chemical composition of deposited metal Mechanical properties of deposited metal
Grade C Mn Si S P Tensile strength (Mpa) Yield strength (Mpa) Elongation () Impact value
℃ J
J426 ≤0.12 ≤1.25 ≤0.90 ≤0.035 ≤0.040 ≥420 ≥330 ≥22 -30 ≥27
J427 ≤0.12 ≤1.25 ≤0.90 ≤0.035 ≤0.040 ≥420 ≥330 ≥22 -30 ≥27
J506 ≤0.12 ≤1.6 ≤0.75 ≤0.035 ≤0.040 ≥490 ≥400 ≥22 -20
-30 ≥47
≥27
J507 ≤0.12 ≤1.25 ≤0.75 ≤0.035 ≤0.040 ≥490 ≥400 ≥22 -20
-30 ≥47
≥27
J506Fe ≤0.12 ≤1.6 ≤0.75 ≤0.035 ≤0.040 ≥490 ≥400 ≥22 -30 ≥27
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