Thread Content
Compared to ordinary carbon steel, stainless steel requires stricter welding procedures and higher technical skills from welders; moreover, there is a question as to what color the weld should have to be considered optimal. Below, I will share my personal opinions and views with everyone. Through welding experiments (manual welding, automatic welding, TIG welding), it has been verified that welds can be classified by color as follows: 1 silver-white, 2 golden-yellow, 3 multicolored (golden-yellow + blue), 4 blue, 5 dark blue, 6 gray-black (with a glossy finish), 7 pitch black. The quality of the weld color is closely related to the welding process parameters and the skill level of the welder. The main issues include: 1. The cleanliness of the groove before welding; 2. The purity and flow rate of the shielding gas; 3. The magnitude of the welding current; 4. The quality of the welding material; 5. The number of passes and layers in the weld; 6. The welding speed; 7. The control of the interpass temperature; 8. The control of the heat input. When all the welding process conditions are met, the weld should be silver-white, and its various physical and chemical properties should also be optimal. For automated submerged arc welding equipment, it is essential to strictly control the welding parameters and heat input; in other words, the thickness of each weld piece determines the appropriate values for welding current and voltage, welding speed, and wire feed speed. In fact, welding is like acting; the lead actors and supporting actors need to have perfect coordination in order to achieve the best results. For example, for workpieces made of the same material but with different wall thicknesses, the welding parameters must vary. If these parameters are too high, intergranular corrosion will occur, leading to a reduction in chromium content; in severe cases, cracks may form as well, and the appearance of the surface will be unsightly. Based on experience, the silver-white and yellow grades mentioned above are both acceptable; silver-white is the best choice. Welds that are multicolored have already suffered from intergranular corrosion and chromium depletion, in other words, chromium carbide formation, which renders the stainless steel unable to maintain its corrosion-resistant properties. Colors beyond blue and dark blue are irrelevant to welding quality. In actual welding work, welding process parameters cannot be applied rigidly; due to differences in ambient temperature, the thickness and size of the weldment, as well as the welding speed, the appropriate parameters also vary. When welding large workpieces with thick walls, the current level must naturally be higher; when necessary, multi-layer and multi-pass welding should be employed, along with control of the interpass temperature. Otherwise, although the appearance of the weld may be good, the internal quality may not meet the actual requirements for welding. When multi-layer, multi-pass welding is used, it is better to cool the previous layer of welds before proceeding with the next layer of weld passes. During automatic welding, the welding speed and wire feeding speed must also be adjusted to match the corresponding current and voltage. To achieve the best weld quality for the same workpiece, if the welding speed changes, it is necessary to adjust the current, voltage, or the speed of the wire feeder. The faster the welding speed, the higher the voltage; the faster the wire feeding speed. However, taking into account metal melting and welding quality, an optimal welding speed as well as optimal current, voltage, and heat input must be selected to ensure weld quality. 1. Cleaning before welding must be carried out strictly in accordance with the welding procedure specifications. 2. The argon gas must meet the requirements for welding stainless steel. 3. Increase the nozzle diameter appropriately to ensure an effective shielding effect. 4. Use a low current and short arc for rapid welding. 5. After establishing the arc, wait until the weld pool has completely cooled before removing the welding torch. 6. Strictly control the heat input. Secondly, the working environment is also a very important factor; factors such as the wind and dust in the welding area, the cleanliness of the weld surface, the skill level of the welder, and the quality of the welding wire all affect the quality of the welds.