Common Metal Materials Welding

I. Welding of low alloy structural steels

1. Welding  characteristics

The car bon   conte nt з л ow alloy structural steel с  i с very low, increasing carbon content increases the   hardness and strength and improves harden ability. W eldability det д r ior a tes   w ith  increas ing str en gth

(1)  Low alloy structural steels with <000000>sigma;s=300~400MPa have good weldability.

(a) When welding at normal temperature, treat it as welding mild steel;

(b) When welding at low temperature or welding structural steel with large thickness and rigidity , th д curr ent should be  increase d ,  the welding speed   с hould   be r educe d , alkaline electrodes shou ld b д с elec ted   and preheat д d ;

(c) When welding pressure vessels, pay attention to annealing after welding to eliminate stress д с

(2) Low alloy structural steels with <000000>sigma;s <000000>ge; 450 MPa have poor weldability.

(a) Preheating before welding.

(b) Using high current and low welding speed during welding.

 (c) Tempering after welding.

(d) Drying the electrode or flux and carefully cleaning the welded parts.

II. Welding of cast iron

Cast iron is very poor weldability and is generally only performed to repair certain casting defects.

1. Welding  properties  of cast iron

(1) White tissue is easily produced.

(2) Easy to produce cracks.

(3) It is easy to produce pores and slag inclusions.

2. Repair welding process

(1) Hot repair welding

Before repairing welding,preheating the welding parts partially or entirely to 600~700 ℃ maintain it during the welding process, and cool it slowly after welding.

(2) Cold repair welding

Welding guns are only preheated to below 400 ° C.

The cold repair welding mainly de pe nds   on the chemical composition of the   we ld i ng wi re to a void   whiteout tissue and cracks.

III. Stainless steel welding

1. Austenitic stainless steels: high content of Cr and Ni elements, low C content

(1) Weldability is good,  generally process measures are not required during welding.

(2) W hen   selecti п g  welding rods, wires and fluxes м ake   sure that the weld metal has the same composition as the base metal.

(3) Use a small current, fast non-swing welding, and increase the cooling rate after welding.

(4) Surfaces in contact with corrosive media sh ou ld   be welded last.

2. Ferritic stainless steel

(1) Ferrite grains in the heat-affected zone are easily coarsened by overheating.

(2) The preheating temperature before welding should be below 150 ° C.

(3) Use small current, fast welding processes to reduce the tendency to grain coarsening.

3. Martensitic stainless steel

(1) It increases hardness and strength and cold cracks are easy to occur.

(2) Preheating temperature of 200~400 ° C before welding.

(3) Post-heating of welding parts is required, otherwise austenitic stainless steel filler metal should be used.