Welding of carbon steel and ordinary low alloy steel

1. What is carbon steel? What are the commonly used ones? Answer: Carbon steel is also called carbon steel. Commonly used welding ones include low carbon steel (containing C ≤ 0.25%) and medium carbon steel (containing C = 0.25%--0.60%); high-quality carbon structural steel (08, 10, 15, 20, 25, 30, 35, 40, 45).

2. Why is it called ordinary low alloy steel? How are they classified? Answer: In ordinary low alloy steel, in addition to carbon, it also contains a small amount of other elements, such as: manganese, silicon, vanadium, molybdenum, titanium, aluminum, niobium, copper, boron, phosphorus, rare earth, etc., and the performance changes, obtaining better performance than ordinary carbon steel, such as: high-strength steel, corrosion-resistant steel, low-temperature steel, heat-resistant steel, etc.

3. What are the mechanical properties of metal materials? Answer: Strength, hardness, deformability, endurance, fatigue resistance and creep performance, etc.

4. What are the process properties of steel? Answer: The ability of steel to withstand various hot and cold processing, such as machinability, forgeability, castability and weldability.

5. What is the weldability of metal? Answer: The difficulty of obtaining high-quality welding under certain welding process conditions. It includes two aspects: one is the joining performance, alternative process weldability; the other is the use performance, alternative use weldability.

6. Why does low-alloy high-strength steel crack? What are the influencing factors? Answer: With the increase of carbon content and alloying elements, the stress that produces cold cracks increases. The three factors that produce cold cracks are: 〈1〉 Hard quenched martensitic structure in the welded joint 〈2〉 High presence of diffusible hydrogen (H) in the welded joint 〈3〉 The welded joint has an upper interconnection joint.

7. Why should process measures be taken to prevent cold cracks? Answer: The process measures to prevent cold process are: 〈1〉 Establish a low-hydrogen welding environment 〈2〉 Formulate a reasonable welding sequence a, selection of welding method b, specification of welding heat input c, formulation of welding sequence 〈3〉 Preheating and control of interlayer temperature before welding (100--150℃) 〈4〉 Immediately perform dehydrogenation treatment after welding (300--400℃*2h) 〈5〉 Post-weld de-stressing heat treatment (600--650℃*2h)

8. Why do CO2 welding workers need to take windproof measures when working outdoors? Answer: When CO2 gas shielded welding is performed outdoors, when the wind force is ≤ level 2 (wind speed: 1.6-3.3 m/s), normal welding can be performed. When the wind force reaches level 3 (wind speed: 3.4-5.4 m/s), a large gas flow meter should be used, with a gas outlet pressure of 0.4-0.5 MPa and a flow rate of 60-70 L/min; normal welding can also be performed without welding defects such as pores. If a wind shield is installed at the upwind port, the welding quality can be better guaranteed.