1.What are stainless steel and stainless acid resistant steel?
The content of chromium (nickel, molybdenum and other elements should be added) in the metal material can make the steel in the passivation state, steel with stainless properties.Acid - resistant steel refers to corrosion - resistant steel in acid, alkali, salt and other strong corrosive media.
2.What is austenitic stainless steel? What are the commonly used brands?
Austenitic stainless steel is the most widely used and the most varieties. Such as:
Series 18-8:0Cr19Ni9 (304) 0Cr18Ni8 (308)
Series 18-12:00Cr18Ni12Mo2Ti (316L)
Series 25-13:0Cr25Ni13 (309)
Series 25-20:0Cr25Ni20, etc
3.Why do we say that welding stainless steel has certain process difficulty?
The main technological difficulties are:
< 1 > stainless steel material has strong thermal sensitivity, and stays in the temperature zone of 450-850 ℃ for a little longer, and the corrosion resistance of weld and heat-affected zone is seriously reduced.
< 2 > is prone to thermal cracking.
< 3 > poor protection and severe high temperature oxidation.
< 4 > linear expansion coefficient is large, resulting in large welding deformation.
4. Why should effective process measures be taken for welding austenitic stainless steel?
General process measures include:
< 1 > shall strictly select welding materials according to the chemical composition of the base material.
< 2 > small current., fast welding;Small line energy, reducing heat input.
< 3 > fine diameter wire, electrode, no swing, multilayer multipass welding.
< 4 > weld and heat affected zone forced cooling, reduce the residence time of 450-850℃.
5. Why should 25-13 series wires and electrodes be used for austenitic stainless steel and carbon steel and low alloy steel welding (dissimilar steel welding)?
Welding joint of different steels connected with austenitic stainless steel, carbon steel and low alloy steel, the weld deposit metal must be made of 25-13 series welding wire (309, 309L) and welding rod (Ao312, Ao307, etc.).If other stainless steel welding materials are used, martensite structure will be generated on the fusion line of carbon steel and low alloy steel, and cold crack will be generated.
6. Why should solid stainless steel wire use 98%Ar+2%O2 as protective gas?
During MIG welding of solid stainless steel wire, if pure argon is used, the surface tension of molten pool is large, resulting in poor weld molding and "hunchback" weld shape.Only 1-2% oxygen is needed to reduce the surface tension of the weld pool, and the weld can be smooth and beautiful.
7. Why is the surface of solid stainless steel MIG weld blackened?
The MIG welding speed of solid stainless steel wire is relatively fast (30-60cm/min). The shielding gas nozzle has been running to the front-end molten pool area. The welding seam is still in the red-hot and high-temperature state, which is oxidized by air, and the surface generates oxides, and the welding seam turns black.Pickling passivation can remove the black skin and restore the original surface color of stainless steel.
8. Why should a pulsed power supply be used for solid stainless steel wire to achieve jet transition and no splash welding?
When solid stainless steel welding wire MIG welding, 1.2 welding wire, when current I≥260-280A, to achieve the injection transition;Droplet less than this value for short - circuit transition, large spatter, generally can not be used.Only with pulsed MIG power supply, pulse current greater than 300A, can achieve the pulse emitter transition of 80-260A welding current, no splash welding.
9. Why is flux-cored stainless steel wire protected with CO2 gas?No pulsed power supply?
At present, the flux cored stainless steel welding wire (such as 308, 309, etc.) is commonly used. The flux formula in the welding wire is developed according to the chemical metallurgical reaction of welding under the protection of CO2 gas body, so it cannot be used for MAG or MIG welding.Do not use pulsed arc welding power source.
2020-12-03 
