Analysis of weldability of 316L stainless steel pipe
316L welding crack. Under normal circumstances, the austenitic 316L stainless steel pipe has only half of the parameters of heat conduction, but the corresponding coefficient of linear expansion is relatively large, so it can be seen that there is a large welding stress at the position of the welding head. The austenitic 316L stainless steel tube has a large boundary between liquid and solid, and it takes a long time for recrystallization. Due to the strong directionality of the austenite crystal, there is a serious impurity segregation phenomenon.

Welding process of austenitic 316L stainless steel pipe . In the welding of austenitic 316L stainless steel pipe, the following methods are generally used: electrode arc welding, argon arc welding, gas welding, submerged arc automatic welding, and the like. Austenitic 316L stainless steel pipe in order to make the welded joint can meet the performance needs, generally need to select the corresponding welding consumable according to the principle of "component". At the same time, in order to improve the welding resistance of the welding head and the corresponding intergranular corrosion ability, it is often selected as H00Cr19Ni2Mo2.

First, the carbon content of this welding consumable is relatively low, generally around 0.03%. Since C is the main element causing intergranular corrosion of steel, when the carbon content is less than 0.03%, the amount of carbon precipitated is relatively small, and above this range, the amount of carbon precipitation is greatly increased. At the same time, carbon is prominent in causing weld hot cracks. From this point of view, it should be used in this type of welding material with a relatively high carbon content.

Second, since the electrode contains Nb element, it can react with carbon to form a stable carbide, which can effectively avoid the phenomenon of chromium depletion in the austenite grain boundary, thereby improving the resistance to intergranular corrosion.

Third, the chromium content of the electrode is generally about 8.5%. The chromium element can form the corresponding ferrite in the weld, mainly because the diffusion rate of chromium in the austenite is lower than that of the ferrite. It can be seen that the chromium element can effectively reduce the chromium deficiency phenomenon in the austenite grain boundary when it diffuses in the ferrite, so that the intergranular corrosion can be effectively prevented.

At the same time, the ferrite produced in the weld and the corresponding austenite can effectively prevent welding hot cracks. If about 5% of ferrite is present in the weld, the grain expansion of the austenite can be effectively prevented, so that the grains are refined, so that the weld impurities can be uniformly dispersed. Fourth, the electrode is an alkaline low-hydrogen type drug, which has high thermal crack resistance and can effectively prevent welding hot cracks.

Welding process of 316L stainless steel pipe

Prepare the 316L stainless steel tube before welding. In order to effectively prevent carbon and impurities from entering the weld during the welding process, it is generally necessary to use acetone to wipe the surface of the weld from 20 mm to 30 mm. At the same time, the oxide layer should be brushed off with a stainless steel wire brush and cleaned with acetone.

Welding process for 316L stainless steel tubes . Generally, the welding process needs to pay attention to the following aspects: First, since the most remarkable feature of austenite is that it is very sensitive to overheating, it is necessary to use a small current and a fast welding method for welding, and the corresponding welding current is generally lower than the average. 20% of carbon steel, which can effectively prevent intergranular corrosion and corresponding welding deformation. Second, in order to ensure stable arc combustion, argon arc welding mainly uses DC positive connection, while manual arc welding uses DC reverse connection method. Thirdly, when argon arc welding is used for bottoming, the corresponding weld thickness should be as low as possible, so that it can form a good fusion with the root. When the arc is closed, a gentle slope should be formed. For example, hand arc welding needs to be short. Arc welding, in the arc should be slowly carried out, so that the crater can be filled, so as to prevent crater cracks. Fourth, forced cooling should be performed after welding.

Post-weld treatment of 316L stainless steel tubes . When surface treatment is performed, defects such as nicks, dents, and rough spots appear on the surface of the stainless steel weldment, which accelerates the corrosion rate of the weldment. Generally, the surface of the stainless steel can be polished, which can effectively improve the corrosion resistance.