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Corporate name: Beijing Kefengshuo Trade Co.,Ltd.
Company address: Room 2307 A of Guorun Business Building,NO.46 South Road, Western of the Fourth Ring Road,Fengtai District of Beijing City.
Telephone:86-01-83650269
Company facsimile: 010-83650249 Handset: 86-15811565789
enterprise mailboxes：
kfsh@firm-trade.com
MSN: kefengshuo1@hotmail.com
MSN: kefengshuo2@hotmail.com |
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１． Introduction to Carbon Steel Electrode |
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Carbon steel electrodes apply to welding carbon steel and low strength low-alloy steel. |
When selecting welding electrodes, one should do according to the requirements of their chemical composition, mechanical properties, crack-resistance performance and, at the same time, analyze comprehensively all kinds of factors like welding structures, steel plate thickness, working conditions, stress status, welder performance, etc. If necessary, do some welding experiments, work out corresponding technical measures, and then decide and select the right kinds of welding electrodes. |
1.To weld carbon steel, the electrodes whose strength corresponds with the steel are generally selected. And if the steel is complex-structured, thick, rigid, dynamic-loaded and hard-to-weld, low-hydrogen electrodes with good plasticity, high impact toughness and good crack-resistance are generally selected. If the welding position has already been specified, special electrodes should be selected, such as electrodes for vertical down position welding, electrodes for backing weld, etc. In order to improve welding efficiency, iron powder electrodes can be selected. |
2.If the weld cools quickly, its strength increases and cracks easily appear, the electrodes whose strength is one degree lower than the base metal can be selected. For dissimilar steel welding between low-carbon steel and low-alloy steel, the electrodes corresponding with the steel at low strength grade are generally selected. And, to take low-alloy steel into consideration, low-hydrogen type is suitable. |
3.To weld medium-carbon steel, due to the high carbon content of steel, which increases the welding crack tendency, low-hydrogen electrodes are generally selected, with some measures like preheating and slow cooling and corresponding welding technology adopted. |
4.Cast steel is hard-to-weld, with high carbon content, thick and big, complex-structured, which easily leads to its high crack tendency, especially when there are quite a number of alloying elements in the cast steel. Low-hydrogen electrodes are generally selected, with some measures like preheating and slow cooling and corresponding welding technology adopted. |
5.In order to guarantee welding quality, weld bonds of work pieces should be cleaned and oil stains, rust, moisture, paint, smut and so on. Should not be left, which is especially significant for using low-hydrogen electrodes |
6.For low-hydrogen electrodes, they must be baked under 350℃ for an hour before welding and used as soon as baking is completed, or some flaws like blowholes, slag inclusions, cracks will appear. Generally cellulose type electrodes do not need baking. If they are affected with damp, they should be baked before welding under the temperatures specified in the specification. However, high temperatures will damage their welding performance. |
7.Generally low-hydrogen electrodes should not be baked over and over again so as to prevent the coating becoming crisp and falling off. |
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２．Introduction to Low-alloy Steel Electrode |
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Low-alloy steel electrode refers to low-alloy high strength steel electrode whose tensile strength is over 500MPa and which is used for structural welding. When selecting welding electrodes, one should do according to the requirements of their chemical composition, mechanical properties, crack-resistance performance and, at the same time, consider comprehensively all kinds of factors like shapes of welded structures, working conditions, stress status and so on. If necessary, do some welding experiments and take some technical measures so as to guarantee welding quality. |
1、Generally electrodes are selected according to the strength grade of the steel and, at the same time, dimensions, shapes, grooves, working conditions, stress status of the welded structures should also be analyzed comprehensively so as to select the needed electrodes and technical measures.
2、 If the weld cools quickly, its strength increases and cracks easily appear, the electrodes whose strength is one degree lower than the base metal can be selected.
3、For multi-layer welding on thick plates or normalizing treatment after welding, high weld strength should be prevented.
4、When selecting acid electrodes or basic electrodes at the same strength grade, shapes of work pieces, steel plate thickness, working conditions, etc. should be mainly considered. If good plasticity, high impact toughness and good crack-resistance are required, basic (low-hydrogen) electrodes should be selected.
5、For dissimilar steel welding between carbon steel and low-alloy steel or between low-alloy steel and low-alloy steel, the electrodes corresponding with the steel at lower strength grade are generally selected.
6、To weld medium-carbon steel, due to the high carbon content of steel, which increases the welding crack tendency, low-hydrogen type electrodes are generally selected, with some measures like preheating, slow cooling and postheating adopted.
7、To weld on cast steel, because it has high carbon content, large thickness and complex structures, which easily leads to its high crack tendency, especially when there are quite a number of alloying elements in the cast steel, low-hydrogen type electrodes are generally selected, with some measures like preheating and corresponding welding technology adopted.
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３． Introduction to Surfacing Electrode |
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Surfacing welding refers to a kind of welding technology that a metal layer resisting wear, corrosion, heat, etc. is deposited on the surface or the edge of a work piece. It has notable economic benefit on repairing parts, extending the service life of parts, using materials properly, improving the performance of products and reducing costs. |
The working process and working condition of surfacing welding are quite complicated. Appropriate electrodes must be selected according to different requirements in surfacing welding. Different work pieces and surfacing electrodes need different surfacing procedures to obtain satisfactory effects of surfacing welding.
The most frequent problem in surfacing welding is cracking. Some major methods to avoid cracking are as follows.
1.Preheating before welding, controlling interpass temperature and cooling slowly after welding.
2.Heat treatment to eliminate stress after welding.
3.To avoid cracking in multi-layer welding, low-hydrogen type surfacing electrodes should be selected.
4.If necessary, a transition layer between the surfacing layer and the base metal should be made by surfacing welding (using low-carbon and high toughness electrodes).
Cracking is related to work pieces and carbon content and alloying elements in the deposited metal. Therefore, the preheating temperature is generally estimated according to the carbon equivalent of the electrode selected.
The carbon equivalent formula is as follows.
Ceq=C+1/6Mn+1/24Si+1/5Cr+1/4Mo+1/15Ni
This estimation formula is suitable for low, medium and high-carbon steel materials and low-alloy steel materials.
Carbon Equivalent(%) |
Preheating Temperature |
Carbon Equivalent(%) |
Preheating Temperature |
≤0.40 |
100℃ are above |
≤0.70 |
250℃ are above |
≤0.50 |
150℃ are above |
≤0.80 |
300℃ are above |
≤0.60 |
200℃ are above |
≤0.90 |
350℃ are above |
Preheating of high-manganese steel and austenitic steel can be left out. The preheating temperature of high-alloy steel is higher than 400℃.
The effects of surfacing welding refers to the performance like layer hardness, wear-resistance, heat-resistance, etc. The performance is related to the following factors.
1.The strength of welding current and the length of arc. Strong current and long arc may easily make the alloying elements damaged. However, if the current is not too strong and the arc is not too long, it is good for the transition of the alloying elements.
2.The preheating temperature and the conditions of slow cooling decide the quality of the surfacing layer.
3.Different heat treatment methods given to the surfacing metal may produce different hardness.
The hardness and the chemical composition of the surfacing layer refer to those of the surfacing metal with three layers or more.
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４． Introduction to Cast Iron Electrode |
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Due to the high carbon content, the heterogeneous structures, the low strength and the bad plasticity, cast iron electrode has bad weldability and cracks can easily form in welding. The cooling speed after welding is extremely fast and white structure can easily form, which leads to difficult machine work. |
In order to make welding and repair welding on cast iron satisfactory, the method “ materials account for 30% while technology accounts for 70%” must be noticed. This means that not only selecting electrodes is important, adopting appropriate repair welding methods is also quite important.
The following welding technology is suggested as references for welding and repair welding on cast iron.
1. First clear away the impurities like fgreasy filth, sand, moisture, rust, etc. on the welded parts. For the cast iron pieces always working under high temperatures and steam environment, the carbon-poor layers and oxide layers on the surfaces should be cleared away too.
2. Some preparative measures like bevelling, stop hole punching, molten pool molding, etc. should be carried out according to the shapes and flaw types of the welded parts.
3. For the work pieces that need cold welding, they should be preheated under about 500-600℃ at first. Appropriate current should be selected. Continuous welding can be used. The preheating temperature can be kept in the whole process of welding. The weldments should be covered with some heat insulating materials like asbestos powder immediately after welding to make it cooled slowly so as to improve their crack-resistance and machinability.
4. For the work pieces that need cold welding, in order to prevent the base metal from melting excessively, decrease chilling tendency and prevent the heat from focusing excessively to form too much stress, weak current, short arc and stringer bead (the length of each bead is generally not higher than 50mm) had better be used. The weld should be hammered immediately after welding so as to loosen the stress and avoid cracking. Another bead should be made when the temperature decreases to below 60℃.
5. When ending arc, the crater should be filled so as to avoid cracking where the arc is ended. |
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５．Introduction to Pipe Welding Electrode |
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Pipe welding electrode, popular in China in recent years, is a kind of high cellulose type and low-hydrogen type structural steel electrode produced to get used to pipeline transportation engineering. One of its characteristics is that it is used for downward girth welding with high welding efficiency. The cellulose content of high cellulose type coating is very high. The arc is steady. When welding, organic substances are decomposed in arc region and a large quantity of gas is formed to protect the deposited metal. The arc has greater spray force. The penetration is deeper. The penetration power is strong. One-side welding with back formation. It has low blowhole sensitivity. The melting speed is high. The low-hydrogen type electrodes have higher mechanical properties, higher yield of deposited metal and excellent welding performance.
High cellulose type electrodes are suitable for backing weld on thick-walled vessels and bottom layers of steel pipes. Back chipping can be left out. Both the work efficiency and the labor conditions can be improved. All-position welding.
Low-hydrogen type electrodes are suitable for filling welding and cosmetic welding on thick-walled vessels and steel pipes, and also used for vertical downward welding on key steel structures. |
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