Seven Major Problems in Welding Stainless Steel

1.Why is it difficult to weld stainless steel?

Answer：

(1) Stainless steel is highly thermally sensitive. If it stays in the temperature range of 450~850℃ for a long time, the corrosion resistance of the weld and heat-affected zone will be seriously reduced.

(2) It is easy to have thermal cracks;

(3) Poor protection, severe high-temperature oxidation;

(4) Large linear expansion coefficient, easy to produce large welding deformation

2. What effective process measures can be taken for welding austenitic stainless steel?

Answer：

(1) Strictly select welding materials according to the chemical composition of the base material;

(2) Fast welding with low current and low wire energy to reduce heat input;

(3) Thin diameter welding wire and electrode, no swing, multi-layer and multi-pass welding:

(4) Forced cooling of the weld and heat-affected zone to reduce the stay time at 450~850℃;

(5) Argon protection on the back of TIG weld:

(6) The weld in contact with the corrosive medium is finally welded;

(7) Passivation treatment of welds and heat-affected zones

3. Why should 25-13 series welding wires and electrodes be used for welding austenitic stainless steel and carbon steel and low alloy steel (dissimilar steel welding)?

Answer:

When welding dissimilar steel joints connecting austenitic stainless steel and carbon steel and low alloy steel, the weld deposited metal must use 25-13 series welding wires (309, 309L) and electrodes (austenitic 312, austenitic 307, etc.)

If other stainless steel welding materials are used, martensitic structure will be generated on the fusion line of carbon steel and low alloy steel, and cold cracks will appear.

4. Why should solid stainless steel welding wire use 98%Ar+2%02 shielding gas?

Answer:

When MIG welding solid stainless steel welding wire, if pure gas protection is used, the surface tension of the molten pool is large, the weld is poorly formed, and the weld is in the shape of a "hunchback" weld. Adding 1~2% oxygen can reduce the surface tension of the molten pool and make the weld smooth and beautiful.

5. Why does the surface of the MIG weld of solid stainless steel wire turn black? How to solve this problem?

Answer:

When the MIG welding speed of solid stainless steel wire is fast (30~60cm/min), the shielding gas nozzle has run to the front molten pool area, and the weld is still in a red-hot high-temperature state, which is easily oxidized by air, and oxides are generated on the surface, and the weld turns black. The pickling passivation method can remove the black skin and restore the original surface color of the stainless steel.

6. Why does solid stainless steel wire need a pulsed power supply to achieve jet transition and spatter-free welding?

Answer:

When MIG welding solid stainless steel wire, φ1.2 welding wire, when the current 1≥260~280A, jet transition can be achieved; less than this value, the molten droplet is short-circuited transition, the spatter is large, and it is generally not recommended. Only by using a pulsed MIG power supply can the pulsed droplet transition from small specifications to large specifications be achieved (select the minimum or maximum value according to the wire diameter), and spatter-free welding can be achieved.

7. Why is CO2 gas protection used for flux-cored stainless steel welding wire, and no pulsed power supply is used?

Answer:

The flux formula in the commonly used flux-cored stainless steel welding wire (such as 308, 309, etc.) is developed according to the welding chemical metallurgical reaction under CO2 gas protection, so generally, pulsed arc welding power supply is not used (pulsed power supply basically needs to use mixed gas). If you want to enter droplet transition in advance, you can also use pulsed power supply or conventional gas shielded welding machine with mixed gas welding.