We have all understood the technology of titanium alloy welding before, so what is the welding technology of titanium alloy clad steel plate? So today, let's talk about the technology of clad steel plates in titanium alloy welding. Compared with titanium alloy welding technology, this technology is much more complicated. It will take some time to master it thoroughly. Next, please look at the welding technology of titanium alloy clad steel plate, as follows:

Titanium is known as the "third metal", with high specific strength, excellent plastic toughness and corrosion resistance, and has been widely used in aerospace, shipbuilding and chemical industries. It is precisely because of the particularity of the material itself and welding, as well as the fact that titanium alloy clad steel plates are also classified into a relatively new construction category, and the construction methods are not sophisticated enough and imperfect, resulting in frequent quality problems in on-site welding construction.

First, the choice of welding method

Because the bottom steel of titanium alloy clad steel plate is Q235 steel, the welding process is mature and stable, so a variety of welding methods can be used, such as electrode arc welding, CO2 gas maintenance welding and electrode arc welding/submerged arc welding. But now considering the actual construction problem on site, the power of electrode arc welding is relatively low, and the slag needs to be specially sorted out; the use of electrode arc welding/submerged arc welding method requires electrode arc welding to make a base, increase the process, and because of the submerged arc welding method The welding parameters are large and the bottom layer is easily broken down, so the welding quality is difficult to ensure, and the heat-affected zone is large, which will have a certain negative impact on the titanium plate in the nearby composite area; CO2 gas maintenance welding is a semi-automatic operation, and the central link is reduced, greatly The welding construction power is improved, which is beneficial to ensure the construction progress and welding quality. However, due to the large spatter caused by CO2 gas maintenance welding, it is recommended to use a mixture of ArCO2 gas.

The welding method of titanium alloy clad steel plate is argon tungsten arc welding. The key point of this construction is the welding of titanium plate. Generally, the site is lap welding of titanium filler, the thickness of titanium filler is 1.5mm, and the thickness of titanium plate is 1.2mm. Because titanium is a transition element in the periodic table, it has certain chemical activity. The bright titanium plate can react with oxygen in the air at room temperature, and its activity increases with the increase of temperature. When it reaches 250 °C, it begins to absorb hydrogen, when it reaches 400 °C, it begins to absorb oxygen, and it begins to absorb nitrogen at 600 °C. Hydrogen, oxygen and nitrogen elements react to form various titanium compounds. Or dissolved in the titanium grain structure, forming an interstitial solid solution, changing the metal lattice, and reducing the mechanical properties and performance of the titanium plate. For this reason, in the process of titanium plate welding, it is necessary to do a good job in the finishing of titanium plates, titanium filler strips, and titanium welding wires and protection operations during the welding process.

2. Selection of welding parameters

The selection of welding parameters will also have a great impact on the design of titanium welds and heat-affected zones. Because titanium metal has the characteristics of high melting point, large heat capacity and poor thermal conductivity, if the welding parameters are large and the heat input is large, the high temperature heat affected zone will be wider, and the high temperature residence time will be longer, resulting in the weld and heat affected zone grains. It is thick, and even the titanium plate and the underlying steel are miscible. The central compound produced by the mutual dissolution of the two is a brittle structure, which destroys and changes the original metal lattice, is the stress concentration point and weak link in the weld, increases the brittleness of the weld, and reduces the plastic toughness and yield strength of the weld. Tensile strength, the mechanical properties of titanium-steel composite plate welds drop sharply. The weld seam and heat-affected zone transform into needle-like arrangements during cooling, resulting in a decrease in the plasticity of the welded joint. If the heat input is too large, if the protection method is not appropriate, the welding seam and the heat-affected zone will be exposed to the air, which will cause oxidation and discoloration, which will decrease or fail to meet the application requirements; otherwise, the welding seam cannot be ensured if the current is too small. Zone hardening is not conducive to the escape of hydrogen, which increases the tendency of cold cracking, and the construction progress is relatively slow. Therefore, the selection of welding current must be reasonable and effective. The recommended current for on-site construction is 110-150A, and the argon gas flow is 10-14L/min. In the welding process of titanium filler rods, the oxidation discoloration of the weld and the heat-affected zone and the occurrence of cracks are frequent problems. Oxidative discoloration is mainly due to the high surface temperature of titanium, the increase in the activity of titanium element, and the reaction with oxygen in the air during the contact process. Because of the different degrees of oxidation, the appearance of the color is different. Different colors also mean whether the weldment can meet the application requirements and whether it needs to be processed. The color of the weld and heat-affected zone is mainly judged as shown in the table below. In the welding process of titanium metal, it is necessary to pay attention to the maintenance of the weld seam and the heat-affected zone. The air chamber formed by the drag hood can be used for maintenance, or the large nozzle argon arc welding torch can be used to expand the surrounding maintenance area.

3. The occurrence of cracks and countermeasures

Cracks are a common disadvantage in titanium plate welding. Titanium weld cracks are attributed to cold cracks, mainly caused by hydrogen in the weld. The origin of hydrogen mainly includes moisture and oil in the plate and welding wire, and the ambient humidity is the main reason for the increase of hydrogen in the weld. Under the effect of high temperature during welding, a large amount of hydrogen is dissolved in the molten pool. During the cooling and condensation process of the weld, hydrogen is easily escaped due to the rapid decrease in solubility. If the weld cooling rate is too fast, the hydrogen will not escape and remain in the weld, which will make the hydrogen in the weld supersaturated, so the hydrogen will try to disperse and promote further embrittlement in this area. If there is a notch effect in this area and the hydrogen concentration is high enough, cracks may occur. Especially in winter construction, the ambient temperature is low, and the water vapor adheres to the titanium plate, which creates conditions for the hydrogenation of the weld. Because the titanium plate is too thin, the steel plate is relatively "warm", the temperature rises slowly, and the cooling rate of the corresponding titanium alloy clad steel plate welding seam is too fast. During the cooling process, the remaining hydrogen in the welding seam cannot escape in time. It exists in the form of supersaturation, which eventually leads to the appearance of cracks.

Therefore, in the welding process of titanium alloy clad steel plate, the surface of the base metal and welding wire should be carefully arranged, and the ambient temperature should not be lower than 5 ℃. In winter construction, use flame to preheat the bottom steel surface, one is to remove the moisture around the weld; the other is to increase the temperature of the weldment and reduce the cooling rate of the weld.

Fourth, the problems that should be paid attention to in the welding of titanium alloy composite steel plate

In tungsten argon arc welding, if the tungsten electrode touches the weld metal, that is, the tungsten electrode touches the tungsten. The welding operation should be stopped immediately, the pollution source should be removed, and the tungsten electrode should be replaced before the operation. When welding, the weld should be as long as possible, and the center should stop welding. When re-welding, the weld should be stacked about 10mm. During welding, arcing should not be started at will. After welding, self-inspection should be carried out, and problems should be dealt with in time. After welding, the weld bead, welding slag, spatter and other dirt on the surface of the weldment should be carefully sorted out, and the weld should be partially trimmed if necessary. When dealing with the defects of the welding seam, it should be repaired with a grinding wheel first, then wiped with a white cloth dipped in acetone, and then repaired after finishing. The number of repairs on the same part should not exceed two times. If it exceeds twice, it should be approved by the person in charge of the unit's technical skills before repairing.

5. Inspection of welds

The welding seam should be formed uniformly, finely, and with smooth transition. There should be no defects such as cracks, pores, tungsten inclusions, lack of fusion, oxidation overrun undercuts, and arc craters. Significant scratches are not allowed on the surface of titanium welds. When it is necessary to weld the lifting lugs or reinforce the steel bottom layer, the welding current should be small, and the next welding should be carried out after a period of time after each welding, so as to avoid the thermal oxidation of the titanium alloy composite layer due to the excessive heat input. discoloration. In winter construction, attention should be paid to maintaining the ambient temperature, because titanium metal is relatively brittle. If the temperature is too low, the cooling rate is fast, and cracks are easy to appear. The ambient temperature should be raised in time, and the temperature should be properly preheated within 80mm around the weld area, and the temperature should not be lower than 15 °C, and preheated from the bottom of the steel. It is forbidden for the weld to only melt the base metal without increasing the welding wire, resulting in lower strength of the weld and cracking when cooling.

After reading the welding technology of titanium alloy clad steel plate, do you think it is a bit complicated? In fact, it is not difficult to master it slowly and use a little time. The technology of titanium alloy welding clad steel plate is becoming more and more common now. I hope everyone Master this skill early, and then apply it to your life.