Development trend of special steel welding materials and welding technology

1 Introduction

In the past 10 years, special steel has been stepping up to respond to drastic changes in market internationalization and environmental protection. The current financial crisis has led to a decline in the world economy, while major domestic steel producers in Japan are also cutting production. In this context, the situation in the field of special steel welding has also undergone great changes, with fierce cost competition and the pursuit of individualization of welding materials and welding techniques in order to enable companies to continue to survive. This paper summarizes the recent developments in welding materials and welding and joining techniques in conjunction with specific examples.

2. Welding materials

2.1 Overview

Due to the slow development of construction steel, automobile, shipbuilding, construction machinery, industrial machinery and other industries in the country and the rapid development in foreign countries, the production and sales of welding materials have been growing strongly in the past 10 years.

Tubular wire production has been stagnant until 2003, but recently due to the recovery of the shipbuilding industry, production began to increase, close to the level of solid wire production. In addition, there has been a decrease in the output of coated electrodes, and there has been a slight increase in solid wire and submerged arc welding materials.

Affected by the international market, after 2003, the import volume of solid wire in Japan showed an increasing trend. In 2007, the import volume was about 50,000 tons, which is equivalent to the export volume of welding materials. Among them, South Korea has the largest import volume, accounting for about 70%, and most of the rest comes from Taiwan and China.

Research topics for welding materials include: "Study on high-quality and high-performance welding of welding zones", "high-efficiency welding", and "improvement of welding environment" which has recently attracted attention.

2.2 Solid steel wire for mild steel and high strength steel

The research on the solid welding wire not only studies the welding wire itself, but also combines the welding wire with the shielding gas and the welding power source for research. The pulse active gas shielded arc welder and the mild steel 490MPa grade high strength steel developed by Datong Company are combined with a pulse active gas shielded arc welding wire to suppress the splash of the weld. The reason is that, since the falling speed of the peak current of the pulse wave is increased, the pulse frequency is increased (the skin effect is enhanced, the current is concentrated on the surface of the wire, so that the electromagnetic contraction force is increased, the droplet is moved smoothly), and the alkali metal is mainly contained. The application of grease on the surface of the wire produces a splash-preventing effect. The use of such a wire also improves the environment for the welding operation.

In an automobile production line that performs automatic welding of thin steel sheets, it is required to reduce welding defects such as welding fumes, weld burnouts, and weld line breaks in addition to the above-described weld spatter. Therefore, it is an important task to continue to develop welding wire in the future.

2.3 Ferritic stainless steel welding materials

In the automotive industry, due to the strictening of the world's exhaust regulations and the improvement of fuel utilization requirements, the demand for lightweight vehicles is increasing. In terms of exhaust system components, components requiring better corrosion resistance and heat resistance are required. .

The exhaust manifold of the automobile exhaust system has been changed from casting to more use of thin-plate welded structural parts, thus promoting the research and development of ferritic welding wire.

Datong Company has developed a ferritic welding wire which has good high temperature strength and corrosion resistance and good welding workability. Among them, the "WSR series" welding wire for Cu plating on the surface of the welding wire has been commercialized and is suitable for many parts. Welding. Table 1 lists the brand and chemical composition of the newly developed wire. The "WSR series" welding wire is based on WSR42K, and is a series of products with WSR42KM for improving high-temperature performance, WSR35K for improving corrosion resistance, and WSR42KF with good weld metal grain refinement resistance to weld cracking.

The WSR series is manufactured in batches on Datong's unique ferritic stainless steel coated wire production equipment. The device automatically performs operations such as wire stripping, plating, smoothing, and winding. After the bus bar is removed by H2SO4 electrolytic pickling to remove the scale, in order to improve the adhesion of the Cu-plated layer, a Ni plating treatment is performed, and then Cu is plated on one side, and the wire is smoothed and wound up by a bobbin.

2.4 welding wire for titanium

The arc welding methods for welding Ti materials include TIG welding (tungsten inert gas shielded arc welding), MIG welding (melting inert gas shielded welding), and plasma welding. Among them, the TIG welding method is the most commonly used method. However, its disadvantage is that it is inefficient in production. Therefore, Datong Company has developed a welding wire suitable for the welding method based on the Ti metal MIG welding method which ensures high production efficiency.

The original Ti material welding wire was studied. A Ti-cored wire "G-coat" suitable for MIG welding was developed by forming an oxygen-rich layer on the surface of the wire and adjusting the tensile strength of the wire.

2.4.1 Wire transportability

The wire feed load of the newly developed wire is smaller than that of the conventional wire, and the wire feeding can be stably performed. In addition, due to the increased tensile strength of the newly developed wire itself, the longitudinal bending of the wire also disappears.

2.4.2 Stability of arc and weld droplet movement

Newly developed welding wire can achieve a directional stable arc compared to conventional welding wire. Moreover, the newly developed welding wire is completely detached in one pulse, and almost all the droplets of the conventional welding wire are pulsed multiple times (2 to 10 times) to be discontinuously separated, thereby causing the droplet to grow.

Due to the above problems, a well-developed welding wire can be used to obtain a good narrow bead. The welded joints have good mechanical properties and are comparable to TIG welded materials. Thanks to the well-developed welding wire, the wire can be used for welding robots with strict feeding paths and complicated movements, and good weld bead can be obtained in various welding orientations. In addition, for thick plate welding of 4 mm or more, fillet welds and the like can be completed under one pulse, which greatly shortens the welding time. Therefore, the use of newly developed welding wire is expected to be further expanded.

Driven by the smooth development of the automotive and semiconductor industries, there has been a hybrid welding method using a combination of laser welding and arc welding. It is expected that the newly developed welding wire will be applied in the hybrid welding method because it further increases the welding speed. .


3. Welding joint technology

There are many types of solder joint technology. When classified according to the phase formed during welding and joining, it can be classified into three types: a fusion bonding method, a liquid phase-solid phase reaction bonding method, and a solid phase bonding method. Each method can be further categorized into more methods. In addition, the welding and joining technology is closely related to various welding and joining equipment, simulation technology and inspection technology.

3.1 Liquid-solid phase reaction bonding technology and solid phase bonding technology

3.1.1 Overview

The liquid-solid phase reaction bonding process has brazing and liquid phase diffusion bonding. The solid phase bonding process includes friction crimping, friction stir welding, normal temperature crimping, forging, explosive crimping, and ultrasonic crimping. This section introduces the development trend of liquid phase diffusion bonding and the ever-expanding friction stir joining in recent years.

3.1.2 Liquid phase diffusion bonding

The liquid phase diffusion bonding method is a method in which a workpiece is inserted into a joint surface, and the workpiece is joined in a state where the insert is melted and the base material is not melted. Liquid phase diffusion bonding is suitable for joining precision parts, complex shapes, special material parts, and dissimilar materials.

The liquid phase diffusion bonding method can be joined at a relatively low temperature, which has an advantage in that the adhesion of the joint surface is improved due to the action of the liquid phase. This method is suitable for the joining of some components in gas turbines and jet engines. The liquid phase diffusion bonding method is a very effective joining method for joining of dissimilar materials, and can be used for joining of Ti alloy and steel which are difficult to melt-weld. This combination of Datong's technology has been used in the manufacture of automotive turbine turbines.

3.1.3 friction stir welding

The friction stir welding method is: when the cylindrical member as a tool is rotated, the joint portion is pressed into the joint portion, and the joint portion is softened by the generated friction heat and the heat of processing, and at the same time, the joint material is plastically flowed due to the rotation of the tool. Engage. The tool is usually made of tool steel. Due to the plastic flow, the joints are finer than the base material, and the mechanical properties are improved. In addition, since it is non-melt welding, the maximum heating temperature is relatively low, so the heat affected zone is small. This is a feature of this method. This method has been applied to low-melting materials such as Al alloys, and can be used in many fields such as railway vehicles and aerospace. In the automotive industry, cars with Al alloy girders have been replaced with improved friction stir joining-friction stir point bonding technology instead of resistance spot welding. Recent research reports indicate that improvements in tool materials are improved, and friction stir joining can be used to join carbon steel, stainless steel, Ti, and Ti alloys.

3.2 Surface modification technology

3.2.1 Overview

In addition to surfacing (arc, plasma, laser) and vacuum coating (PVD, CVD), thermal spray technology is also being studied in changing surface materials. This section introduces surfacing technology and recent thermal spray technology.

3.2.2 surfacing

In recent years, in order to be able to be used in a harsh environment, parts are required to have abrasion resistance, corrosion resistance, and heat resistance. Surfacing is a method that can meet these requirements inexpensively. At the same time, surfacing is an indispensable welding method for repairing component damage. The surfacing welding process includes: arc welding surfacing, powder plasma arc surfacing, powder laser surfacing and the like. Arc welding surfacing is used for the repair of soil sanding parts and metal molds. Powder plasma arc surfacing, because it can produce a variety of functional powders, can be used in many aspects besides powder plasma arc surfacing for engine valve surfacing and petroleum refining cracker tubes. Powder laser surfacing, because of the laser as a heat source, is suitable for surfacing in small parts, and is expected to be used in many aspects such as precision product mold repair and jet engine repair.

3.2.3 Thermal spraying

Surface modification techniques include techniques such as nitriding and carburizing to change the structure and properties of the surface of the component itself, and techniques such as plating and ion plating to attach other high-performance materials to the surface of the component. The thermal spraying method belongs to the second technique and is suitable for improving the corrosion resistance of the boiler pipe fittings and improving the wear resistance of the rolls and the cold working die. Recently, according to the requirement of improving the fuel utilization rate of automobile lightweighting, the method of using thermal spraying technology instead of pressing the casting cylinder sleeve into the engine cylinder has attracted people's attention.

The thermal spraying method is a technique in which a thermal spray material (filament, powder, or bar) such as a metal or ceramic in a molten or semi-molten state is impacted on a base material at a high speed by an energy source (heat source) to deposit a film on the base material ( See Figure 2). The energy sources for thermal spraying are: chemical energy generated by fuel combustion or explosion, spark discharge, and electrical energy generated by plasma. In addition, recently, cold spray technology that uses only particle motion to form a film has attracted attention. The characteristics of the thermal spraying method are: (1) a wide selection range of thermal spraying materials; (2) no limitation on the material and size of the base material; (3) rapid film formation; (4) thick film formation; (5) A porous film is produced; (6) construction can be carried out on site.

3.3 Welding related technology

3.3.1 Overview

For welding materials, various evaluation experiments after welding are generally performed. Mainly include: microstructure observation, hardness test, tensile test, Charpy impact test, welding crack test and so on. In addition, evaluation and analysis during the welding process play an important role in the development of welding materials in the future. Here, an introduction to the analysis technique of the welding arc phenomenon is given.

3.3.2 Analytical technique of welding arc phenomenon

Taking a picture of the welding arc phenomenon with a high-speed camera can not only judge the movement pattern of the welding droplet, but also accurately understand the arc shape and the welding pool generated during the welding process. The development of higher precision welding materials and welding techniques is made possible by the analysis of these images. Datong Company has developed a unique analysis technique for welding arc phenomenon, which can quickly and quickly determine the vibration of the front end of the wire, the size of the droplet, the length of the arc, the angle of the front end of the wire when the droplet is detached, the wire feeding speed, the number of splashes, etc. And can perform high-precision analysis work.

It can be expected that the analytical results obtained by the technique are fed back to the welding process, and welding with higher quality and higher precision can be realized.

4 summary

The market situation in the field of welding will be further changed in the future, and the application range, welding materials and welding processes of welding technology will be further developed. Therefore, while predicting the changes of the times, it is becoming more and more important to fully understand the functions required for the end use, go beyond the traditional model, and propose and develop the welding materials and welding process solutions.