Q235 carbon steel (pearlite steel) and stainless steel SUS304 (austenitic steel -0Cr 18Ni9) can be welded. However, in welding, we should not only pay attention to the influence of the physical and chemical properties of the metal itself on the weldability, but also pay attention to the influence of the differences in composition and microstructure of the two metals on the performance of the joint.

The problem of two kinds of parent materials:

Pearlite steel: cold cracking, embrittlement, etc.

Austenitic steel: hot cracks, etc.

Special problems:

(1) Dilution of the parent metal to the weld leads to changes in the microstructure and properties of the weld.

The dissolution of pearlite steel matrix will dilute the filler metal and cause its composition and structure changes.

(2) forming a solidified transition layer

In the weld metal near the fusion line on one side of pearlite steel, a transition layer with different composition from the internal weld metal will be formed. The high hardness martensite structure in the transition layer will increase brittleness, significantly reduce plasticity and form a low plasticity zone, thus reducing the reliability of the welded structure.

(3) forming a carbon migration transition layer

In the process of welding or post-welding heating (heat treatment or high temperature operation), carbon diffuses from the pearlite base material to the weld through the fusion zone, forming a softened decarburized layer on the pearlite base material near the fusion zone and a carburized layer with higher hardness in the austenitic weld near the fusion zone.

(4) The stress state of the joint is complicated.

Thermal stress caused by local heating, residual stress caused by different thermal expansion coefficients of two steels (this stress cannot be eliminated by heat treatment).

Welding material: covered electrode model -E3 10- 16 or E3 10- 15.

Welding process requirements:

1, welding method

The welding method with small fusion ratio can reduce the dilution of base metal. Covered electrode surfacing, non-MIG welding and covered electrode arc welding are all acceptable.

2. Welding parameters

Small diameter covered electrode or welding wire, low current, high voltage, fast welding.

3, surfacing transition layer

When welding thick and large weldments, the transition layer can be surfacing on the groove surface of pearlite steel, and the transition layer is made of high chromium nickel austenitic covered electrode or nickel and nickel alloy covered electrode (such as Ni307). The thickness of the transition layer is generally 6 ~ 9mm.

4. Welded joints are generally not subjected to post-weld heat treatment.