Types and characteristics of flux-cored welding wire
According to the structure of the welding wire, flux-cored welding wire can be divided into two types: seamed welding wire and seamless welding wire. Seamless welding wire can be plated with copper, which has good performance and low cost and has become the direction of future development.
According to whether there is a shielding gas, flux-cored welding wire can be divided into gas shielded welding wire and self-shielded welding wire; the composition of the powder in the core of the flux-cored welding wire is similar to that of the electrode coating, including arc stabilizer, deoxidizer, slag-forming agent and alloying agent, etc. According to whether there is a slag-forming agent in the inner filler powder of flux-cored welding wire, it can be divided into "flux type" welding wire and "metal powder type" welding wire; according to the basicity of slag, it can be divided into titanium type, titanium calcium type and calcium type welding wire.
Titanium slag-based flux-cored wire has beautiful bead formation, good all-position welding process performance, stable arc, and small spatter, but the toughness and crack resistance of the weld metal are poor. In contrast, calcium slag-based flux-cored wires have excellent weld toughness and crack resistance, but poor bead formation and welding process performance. Titanium calcium type slag is between the above two.
The welding process performance of "metal powder type" flux-cored wire is similar to that of solid core welding wire, and its deposition efficiency and crack resistance are better than that of "flux type" welding wire. Most of the powder core is metal powder (iron powder, deoxidizer, etc.), and special arc stabilizer is added to ensure less slag formation, high efficiency, small spatter, stable arc, and low diffusible hydrogen content in the weld during welding. Crack resistance is improved.
The cross-sectional shape of the flux-cored wire has a great influence on the welding process performance and metallurgical performance. According to the cross-sectional shape of the flux-cored welding wire, it can be divided into two types: simple O shape and folded shape with complex cross-section.
The more complex and symmetrical the cross-sectional shape of the flux-cored wire, the more stable the arc, and the more sufficient the metallurgical reaction and protection of the flux-cored wire. However, as the diameter of the welding wire decreases, this difference gradually narrows. When the diameter of the welding wire is less than 2mm, the effect of the cut shape is not obvious.
Flux-cored wire has good welding performance, good weld quality and strong adaptability to steel, and can be used for welding various types of steel structures, including low-carbon steel, low-alloy high-strength steel, low-temperature steel, heat-resistant steel, stainless steel and Wear-resistant surfacing, etc. The protective gases used are CO2 and Ar+CO2. The former is used for ordinary structures and the latter is used for important structures. Flux-cored wire is suitable for automatic or semi-automatic welding, both DC and AC arcs are required.
1) Flux cored wire for low carbon steel and high strength steel
Most of these welding wires are titanium slag systems, which have good welding processability and high welding productivity. They are mainly used in shipbuilding, bridges, construction, and vehicle manufacturing. There are many varieties of flux-cored welding wires for low-carbon steel and high-strength steel. From the level of weld strength, flux-cored welding wires with tensile strength of 490MPa and 590Mpa have been widely used; from the perspective of performance, some focus on process performance, and some It focuses on the mechanical properties and crack resistance of welds, and some are suitable for all-position welding including downward vertical welding, and some are dedicated to fillet welds.
2) Stainless steel flux cored wire
There are more than 20 kinds of stainless steel flux-cored welding wires, in addition to chromium-nickel stainless steel flux-cored welding wires, there are also chromium-based stainless steel flux-cored welding wires. The diameter of the welding wire is 0.8, 1.2, 1.6mm, etc., which can meet the welding needs of stainless steel thin plate, medium plate and thick plate. Most of the protective gas used is CO2, and a mixed gas of Ar+ (20%~50%) CO2 can also be used.
3) Flux-cored wire for wear-resistant surfacing
In order to increase wear resistance or obtain some special properties on the metal surface, it is necessary to transfer a certain amount of alloying elements from the welding wire, but the welding wire is difficult to process and manufacture due to its high carbon content and alloying elements. With the advent of flux-cored welding wire, these alloying elements can be added to the flux core, and the processing and manufacturing are convenient, so the use of flux-cored welding wire for submerged arc surfacing wear-resistant surface is a common method and has been widely used. In addition, by adding alloying elements into the sintered flux, a surfacing layer with corresponding components can also be obtained after surfacing.
Commonly used flux-cored wire CO2 surfacing and flux-cored wire submerged arc surfacing methods are as follows.
Thin wire CO2 flux-cored wire surfacing This method has high welding efficiency, and the production efficiency is 3 to 4 times that of hand arc welding; the welding process performance is excellent, the arc is stable, the spatter is small, the slag is easy to remove, and the surfacing is beautiful. This method can only transfer alloying elements with flux-cored wires, and is mostly used for surfacing layers with low alloy composition.
Flux-cored wire submerged arc surfacing welding adopts large-diameter (3.2, 4.0mm) flux-cored welding wire, the welding current is large, and the welding productivity is obviously improved. When the flux is used, the alloy elements can also be transferred through the flux, so that the surfacing layer can obtain a higher alloy composition, and the alloy content can be changed between 14% and 20% to meet different application requirements. This method is mainly used for surfacing welding rolls, feed rolls, continuous casting rolls and other wear-resistant and corrosion-resistant parts.
