Cast iron is W (c) ≥ 2.14 of the iron-carbon alloy, cast iron and steel, although the intensity is lower than, less plastic, but it has good wear resistance, shock absorption, casting and cutting, etc. can be. As the cast iron with high carbon content, organization uneven, low plasticity, the material is poor Welding Materials, the welding process can easily produce white, defects such as cracks and pores, so the cast iron welding process should pay attention to choose the appropriate welding methods and welding materials.
To ensure the welding effect recommended the following measures for welding, welding and repair welding of cast iron as a reference when;
1 First, remove the welded parts of the oil, sand, water, dirt, rust and oxidation layer, and depending on the type of defect, groove, playing only the hole and weld pool shape and other preparatory measures.
2 for thermal Welding Wire China, welding parts first preheated to about 500-600 ℃, choose the appropriate current, continuous welding, the welding process always preheat temperature, solder while red hot state immediately after the cover asbestos or other insulation material to ensure slow cooling, which will help graphite fold, in order to improve its crack and processing performance.
3 for cold welding workpiece, melting the base metal in order to avoid too much, reduce the chilling tendency, welding process, maximize the use of low current, short-arc, a narrow bead (each bead length is generally less than 50mm), after welding immediately to hammer weld stress relaxation, to prevent cracking when the temperature dropped to below 60 ℃ under a re-welded.
4 close attention to fill the crater when the arc, to prevent the arc pit cracks.
High temperature, high pressure and the presence of hydrogen under the conditions of operation of the pressure vessel, in order to avoid the desulfurization reaction of a large number of H2S on the surface of the reactor wall corrosion and stops when the reactor is running, by the even more sulfuric acid (H2SXO6)-induced stress corrosion cracking, usually in the reactor wall cladding corrosion resistant material. Of molybdenum as the main strengthening element niobium solid solution hardening nickel-base wrought superalloy 625 has excellent resistance to corrosion and oxidation resistance, low temperature to 980 ℃ are from high strength, toughness, fatigue strength and oxidation resistance. In the atmosphere, natural water, water, salt and alkali and other weak neutral medium, essentially non-corrosive, in a more demanding medium, both the capability of oxidizing acids, and resistance to reducing acid media. Resistance to intergranular corrosion, stress corrosion, pitting and crevice corrosion fine. Because both applications that require high corrosion resistance, but also to meet the high temperature corrosion resistant alloys used and has been widely used in the manufacture of pressure vessels. For the container wall can be used with a very large area of ??welding technology, welding small diameter over the inner wall, due to flux-cored welding process (FCAW) with a high deposition efficiency, productivity has improved significantly, economic good; to adapt the scope of current and voltage large, relatively easy to achieve welding conditions, easy to carry semi-automatic and automatic welding; off the residue in good weld appearance; spatter is small, excellent arc stability, pass rates, etc. are widely used in production. Based on 625 nickel-based cored Welding Wires Manufacturer characteristics, by welding test to determine the effects and properties of flux-cored welding layer forming the main welding parameters, in order to take over the inner wall of small-diameter flux-cored wire welding using nickel-based hardfacing provide scientific basis. A welding equipment and welding materials 1.1 Welding Equipment This test uses ESAB LAH 500 flux cored wire welding equipment, which by the welding (including the power supply wire feeder, the control system) water-cooled welding torch and walking systems, cooling systems, gas supply system. Stainless steel flux-cored arc welding equipment, DC power supply with flat characteristics, by changing the wire feed speed to adjust the welding current, therefore, more convenient to adjust the welding specifications. When the arc length changes, can cause a large current changes, there is a strong self-regulation; the same time, due to short-circuit current is large, arc relatively easy. 1.2 Welding According to technical requirements of surfacing products, the use of nickel-based 625-type nickel-base alloy welding, according to wire the components and specifications, use the WEL FCW 625 surfacing materials. Wire diameter φ1.2mm, the thickness of 50mm of 2.25Cr-1Mo material on the nickel-based cored wire welding, welding the first layer when the strict control of the preheating temperature, interpass temperature and post-heat temperature, Layer 2 surfacing layer temperature should be controlled below 100 ℃. 1.3 Ni-base alloy 625 welding characteristics Since nickel-base alloy 625 austenitic weld metal structure into a single organization, the liquid weld metal, poor mobility, melting depth, easy to produce hot welding cracks and pores, so should be thoroughly cleaned before welding the workpiece; welding use a smaller heat input, so that joint residence time to reduce the high temperature, to control and reduce the hot cracking and improve corrosion resistance are favorable; and should choose the right welding speed; between the nickel-base alloy welding without preheating, interpass temperature should be controlled at 100 ℃. Welding procedure test 2 Affect the performance of flux-cored welding layer forming and welding process parameters are: welding current, welding voltage, welding speed, stem elongation, amount of overlap and so on. 2.1 welding current Welding current and weld bead shape, penetration, dilution rate, mechanical properties have a great relationship, welding current is too large, a large welding spatter, weld overlay surface oxidation and prone to hot cracking; the welding current is too prone to defects and weld slag bad. After testing, the diameter of φ1.2mm flux-cored welding current to determine the 180 ~ 200A weld surfacing between the best shape. 2.2 Welding voltage For the flux-cored welding, welding voltage and welding current match is very important. In the welding current under certain conditions, if the voltage is too low, narrow weld surfacing is prone to the phenomenon of slag, and the surfacing thickness, resulting in a waste of welding consumables; if the welding voltage is too high, compared weld surfacing wide, making the surfacing thickness can not meet the requirements, after several tests, the diameter of φ1.2mm flux-cored welding voltage to determine the 28 ~ 32V surfacing weld between the best shape. Welding speed of 2.3 Welding flux cored Cast Iron Electrodes speed on the greatest impact, there are two main aspects: ① surfacing weld geometry; ② surfacing dilution rate. If the welding speed is too fast, weld surfacing too narrow, too thin, then the next one lap welding, easily lead to overlap. On the contrary, easy to form heap tall, heap width of the weld will cause nozzle clogging, easily lead slag, for nickel-based cored wire diameter φ1.2mm welding speed to determine the best in the 250 ~ 300mm/min. 2.4 out of wire length and wire locations Extending the length of the arc welding stability, penetration, etc affect the arc energy, the length of wire stretched out too long, make the arc unstable, erratic, and the big splash. Too short length of wire out, could easily lead to excessive spatter nozzle clogging, the bad gas, welding is easy to produce pores. After testing, the length of wire out of the range should be 15 ~ 20mm. Welding, torch angle θ of about 40 °, well, if θ is too large or too small, will reduce the CO2 gas protective effect. 2.5 weld surfacing amount of overlap between Surfacing weld between the amount of overlap (wire weld surfacing with a distance between a) directly affect the surfacing layer thickness and roughness, and the surfacing layer of scoliosis greater impact on performance, in order to solve these problems, the nickel-based cored wire weld surfacing amount of overlap between the series of tests done, and to determine the weld surfacing have access to good shape, excellent performance of the process parameters, namely, wire relative to the previous one edge of the 0 ~ 1mm of the surfacing weld forming beautiful, good mechanical properties. 2.6 CO2 gas flow Nickel-based cored wire welding, the gas flow 15 ~ 20L/min, if the gas flow less is not enough to protect the gas stiffness, reducing the effect of gas; if the welding current is larger, faster welding speed, wire out length is longer, are required to increase the gas flow. 2.7 optimum welding parameters After the large number of welding test to determine the nickel-based cored wire welding, the get a good shape, excellent performance surfacing welding parameters (Table 1). Assessment process for the next welding and product components to provide a scientific basis. 3 welding procedure qualification In the process, based on the test, press the "internal pressure vessel nickel-base alloy 625 welding technology conditions" requirements, the use of welding parameters in Table 1, a welding procedure qualification test plate thickness of 50mm in the 2.25Cr-1Mo material on the assessment of nickel-based cored wire welding, welding the first layer when the strict control of the welding preheat temperature, interpass temperature and post-heat temperature, the first cladding layer 2 layer between the temperature control below 100 ℃ . Surfacing of the test results (chemical composition, surfacing bending test, hardness measurement and corrosion test)