Boiler Steel Tubes According To The Composition Can Be Divided Into
Boiler Steel Tubes According to the composition can be divided into
Stainless steel can be divided into three kinds according to the composition. Namely: 13 chrome stainless steel, 18 chrome stainless steel, 18-8 stainless steel. The numbers represent the chromium content of the steel, and 18-8 represents the mass fraction of chromium of 18% and the mass fraction of nickel is 8%. Can be said from the previous three grades of stainless steel features: cheap, general, expensive. Their carbon mass fraction is very small, probably only 0.1% or less. According to its organization state, 13 chrome stainless steel is martensitic, 18 chrome stainless steel is ferrite type, 18-8 stainless steel is austenitic type. And the more anti-rust ability later. But according to the strength, the highest martensitic, followed by ferrite, austenite type of the weakest.
Above is a very rough division of the American standard steel pipe, layman is difficult to distinguish them. But there are very simple distinctions, 13 chrome stainless steel and 18 chrome stainless steel will be attracted by the magnet, while the 18-8 stainless steel will not. However, the type of stainless steel increased to the extent that the rough division method was not applicable. For example, there can be hardened, there can be carburizing and nitriding, there can be solution treatment, with rapid processing, and improve the corrosion resistance, heat resistance and solderability and so on. In order to cope with this wide variety of requirements, little by little to change the chemical composition of stainless steel, made with different uses of stainless steel materials, these numbers are countless materials have been standardized, see JIS standards. Corner slot connector (JC)
First, the premise will be polished
But must be welded at the galvanized layer polished, otherwise it will produce bubbles, trachoma, false welding and so on. But also make the weld brittle, rigid decline.
Second, the welding characteristics of galvanized steel
Galvanized steel is generally plated in a low-carbon steel layer of zinc, galvanized layer is generally 20um thick. Zinc has a melting point of 419 ° C and a boiling point of about 908 ° C. In welding, zinc melts into a liquid floating on the surface of the bath or at the root of the weld. Zinc in the iron has a large solid solubility, zinc liquid will penetrate deep along the grain boundary weld metal, low melting point zinc to form a "liquid metal embrittlement."
At the same time, zinc and iron can form intermetallic brittle compounds, these brittle phase to weld metal plasticity reduction, under the action of tensile stress cracks.
If the fillet welds, especially the fillet welds of the T-joints, are most prone to penetrating cracks. Galvanized steel welding, the groove surface and the edge of the zinc layer, under the arc heat, resulting in oxidation, melting, evaporation and evaporation of white dust and steam, easily lead to weld pores.
ZnO, which is formed by oxidation, has a higher melting point of about 1800 ° C or more. If the parameters are small during the welding process, it will cause ZnO to be slag. Since Zn becomes a deoxidizer. Produce FeO-MnO or FeO-MnO-SiO2 low melting point oxide slag. Second, due to the evaporation of zinc, volatile a lot of white smoke, the human body to stimulate, hurt the role, therefore, must be welded at the galvanized layer polished out.
Third, the welding process control
Galvanized steel pre-welding preparation and the general low-carbon steel is the same, need to pay attention to is to carefully handle the groove size and the nearby galvanized layer. For the penetration, the groove size should be appropriate, generally 60 ~ 65 °, to leave a certain gap, usually 1.5 ~ 2.5mm; in order to reduce the penetration of zinc on the weld, before welding, the groove can be galvanized Layer after cleaning and then welding.
In the actual supervision work, the use of a centralized groove, leaving no blunt edge technology for centralized control, two welding process, reducing the possibility of not penetrating.
The electrode should be based on galvanized pipe base material selection, the general low-carbon steel due to consider easy to operate, the choice of J422 is more common.
Welding method: welding the first layer of welding in the weld, try to make the zinc layer melting and vaporization, evaporation and escape the weld, can greatly reduce the liquid zinc to stay in the weld.