Before you start the process of welding stainless steel, it is necessary to explore all the possible features of such welding. Boil stainless steel - not the easiest exercise, the complexity of which depends on many nuances.
Scheme of welding semiautomatic device.
One of the most important is good weldability, in other words, the primary ability of the metal to create a welded joint.
Primary features that can necessarily affect the quality of welding:
Welding stainless steel semi-automatic.
- Linear expansion and casting shrinkage. If the shrinkage is high, then the chance of a possible deformation of the metal during work with welding electrodes and after increases. And if the parts to be welded are wide enough and there is no gap between them, then the possibility of large cracks increases.
- Thermal conductivity - in stainless steel, it is almost halved compared to other metals, therefore, when welding it, it is necessary to reduce the amperage by 15-20%.
- The electrical resistance is quite high, so welding with conventional electrodes is impossible due to their excessive heating. Therefore, special electrodes are made on the basis of nickel-chrome rods with a length of not more than 3.5 cm for welding stainless steel.
- Intergranular corrosion - stainless steel is inherent in the ability to lose anti-corrosion properties, if the thermal mode of welding is wrong or the wrong machine is chosen. The essence of this process is that when the temperature reaches more than 500 degrees Celsius, chromium and iron carbide appears on the edge of the metal, which leads to metal corrosion. However, there are methods to combat this, for example, rapid cooling in a variety of ways.
Features of stainless steel welding
Double pulse for perfect welding of aluminum and stainless steel.
In order to properly and accurately weld stainless steel, it is also necessary to take into account the fact that some of its physical properties differ from ordinary steel:
- electrical resistivity - 6 times higher;
- melting point - below 100 degrees Celsius;
- thermal conductivity - less by 2/3;
- thermal expansion is half as high.
There are completely different methods of welding their own steel. For example, arc welding using special tungsten electrodes, carried out in an inert environment, is used if the thickness of the metal exceeds 1.5 mm. If it is necessary to weld thin steel or pipes, then it is best to resort to welding with the help of melting electrodes in inert gas.
Pulsed arc welding should be applicable only to steel sheets whose thickness is 0.8 mm. Steel with a thickness of 0.8 to 3.0 mm is used to make a short arc using consumable electrodes, while steel with a sheet thickness over 3.0 mm is used for jet transfer of metal.
If, however, plasma welding is considered, then it can be concluded that it is suitable for a very wide variation in thickness, therefore, it is used much more often. Submerged arc welding is used for metal thicknesses greater than 10 mm. But the most popular welding methods are welding using coated electrodes, tungsten electrodes in an argon environment, and semi-automatic argon welding with stainless steel wire.Back to table of contents
Welding with coated electrodes
Modes of welding in inert gases.
If it doesn’t matter to you what kind of electrodes to weld and you do not have any special requirements for the welding joint, then the most acceptable way will be welding with coated electrodes (these include OZL-8, NIAT-1, TsL-11 electrodes). Of all the electrodes, it is best to choose those that will provide, after welding, corrosion resistance, heat resistance and good mechanical properties.
Welding should be carried out at a constant current with mandatory reverse polarity. Care must be taken to ensure that the seam is melted to a minimum, since the electrodes used when welding a stainless steel have a small diameter and they need a minimum of thermal energy. The strength of the current in the process of welding stainless steel must be strictly adjusted by 15-20% lower than when welding ordinary metal. With a high current due to low thermal conductivity and with high resistance of coated electrodes, significant overheating and even detachment of pieces can occur. Because of this, these electrodes have a high melting rate, so if you use them for the first time, then at first it may be unusual.
To preserve the corrosion characteristics of the weld, accelerated cooling should be arranged during welding. To do this, you can use copper gaskets or a certain air blowing. If the steel is chrome-nickel, you can cool it with water.Back to table of contents
Welding stainless steel with tungsten electrodes
Welding with tungsten electrodes in an inert environment is suitable when the metal to be welded is very thin or if the requirements for the quality of the welded joint are very high. For example, if you need to cook pipes that will later be used to transport gases or liquids under high pressure, this welding method is ideal. The procedure is carried out in an argon environment, the current can be both constant and variable, but of direct polarity. In the role of filler material is recommended to take the wire with a higher level of doping than the metal. During operation, oscillatory movements with electrodes should be avoided to avoid disturbing the cooking zone, which can lead to oxidation of the weld and increase the cost of the process itself.
On the reverse side of the air, the seam must be protected by blowing argon, but still stainless steel is not very critical to such protection, but it is necessary to eliminate even the slightest possibility of tungsten particles entering the weld pool in any case. In this case, the contactless ignition of the welding arc will help; you can also use a carbon or graphite plate for the same purpose.
After the work is completed, in order not to overuse the tungsten electrode, the gas should not be turned off immediately, but after a while (usually 10-15 seconds). This helps to avoid strong oxidation of heated electrodes, which increases their useful life.Back to table of contents
Welding stainless steel with their own hands.
When welding stainless steel, it is always necessary to take into account all its features - otherwise, after work, various undesirable weld defects may occur, for example, the formation of "knife" corrosion. Hot cracking may occur due to high temperatures, mainly due to the brittleness of the seams.
In order to avoid such incidents, it is best to use filler materials that will help in creating strong seams. However, such materials should not contain ferrite more than 2%. In addition, arc welding will also help in strengthening the seams, in which the arc length will be small. It should be remembered that craters on the base metal should not be displayed.
If you use automatic welding, you should remember that it is usually used to cook at lower speeds. But in order to reduce the risk of deformation, it is best to make fewer approaches, because welding at maximum speed contributes to better corrosion resistance.
Thus, before choosing which electrodes to weld a stainless steel, you should familiarize yourself with all its features and characteristics, know exactly what requirements will be placed on the welding seam and for what purposes the product will be used.