Application and Weldability of Stainless Steel Materials in Automobiles
Abstract: Stainless steel is a general term for a kind of alloy steel with high chemical stability, so it is often used in the manufacture of parts or equipment with special requirements for corrosion resistance, oxidation resistance and high temperature resistance. Up to now, the average amount of stainless steel material per car has reached 20-30kg. In the future, with the development of lightweight automobiles and the continuous improvement of the performance requirements of automobile anticorrosion and high temperature resistant parts, the types of parts made of stainless steel materials will continue to increase. Based on this, this paper studies the application and weldability of stainless steel materials in automobiles.
Key words: stainless steel material; automobile; weldability
Introduction
In the process of making stainless steel materials into assemblies or separate parts from original plates and pipes through suitable processes, various welding processes will inevitably be used to achieve reliable connections between different components. For stainless steel materials, the changes in physical and chemical properties of materials brought about by higher alloying element content make the material weldability, welding process characteristics and requirements significantly different from those of low carbon steel materials. Based on this, this paper expounds the main applications of stainless steel materials in automobile manufacturing, and systematically analyzes the welding characteristics of the materials.
Overview of Stainless Steel Materials
The application of stainless steel in automobiles has a long history, but the use of stainless steel as a lightweight material for automobile structural parts has only been developed in recent years. It is generally believed that stainless steels with lightweight potential are mainly high-strength stainless steels, such as ASI200 and AIS300 series of high-strength austenitic stainless steels. At present, high-performance stainless steel has been used in the manufacture of automotive parts such as bumpers, front crash beams, engine mounts, and tailgates. The use of high-performance stainless steel can reduce the quality of auto parts by about 30%. However, the high production cost of stainless steel severely restricts the application of stainless steel in automobiles. At present, there are two main ways to reduce the production and use costs of stainless steel: one is to develop cheap stainless steel materials; the other is to optimize the design and processing technology of stainless steel auto parts.
Typical applications of stainless steel materials in automobiles
1 Stainless steel for exhaust system
With the continuous improvement of the exhaust temperature of the automobile engine and the lightweight design level of the whole vehicle, in order to meet the relevant requirements of the anti-chlorine atomic corrosion and high temperature use of the automobile exhaust system, up to now, the selection and use of materials have basically been realized by cast iron and aluminum plating. The conversion of materials such as steel pipes to stainless steel materials. Automobile exhaust system is the area with the largest amount of stainless steel in current automobile production, accounting for more than 50% of its total use. It should be pointed out that more than 80% of the stainless steel used in the automobile exhaust system is ferritic stainless steel. The reason for choosing ferritic stainless steel is that it has better high temperature resistance than austenitic stainless steel. At the same time, because its manufacturing raw materials do not contain or only contain a small amount of precious metal Ni, it also has obvious price advantages. 2 Stainless steel for body and frame
The density of aluminum alloy is about 2.7g/cm3, which is about 1/3 of steel material. Due to the characteristics of low density, light weight, high strength and excellent corrosion resistance, aluminum alloys are increasingly used in automotive body parts. The tensile strength of aluminum alloy is high, and it can completely replace some steel outer covers with lower strength requirements of automobile body. Temperature has a great influence on the plasticity and formability of aluminum alloys. In order to avoid defects such as cracking, springback, wrinkling and stacking of the aluminum alloy sheet during the forming process, the sheet or mold is generally heated to a certain temperature and then stamped, that is, warm forming. According to the different heating temperature, it is divided into warm forming and hot forming. Converting and upgrading the traditional cold stamping process technology, directly heating the aluminum alloy sheet, the technology is simple and fast; in terms of equipment, it is only necessary to increase the heating equipment for the aluminum alloy sheet, and the equipment investment is small. Therefore, the warm forming process of directly heating the aluminum alloy sheet is the main process currently used in the research and development stage of the trial production of aluminum alloy parts.
3 Stainless steel for fuel tank
As a core safety and functional component of an automobile, the fuel tank should not only have good mechanical properties, formability, weldability, and high and low temperature resistance, but also good fuel resistance and external environmental corrosion resistance. With the continuous tightening of automotive environmental regulations, fuel tank manufacturing materials have transformed from traditional coated plain carbon steel, lead-tin steel sheet to aluminized steel, galvanized-tin steel and stainless steel. At present, SUS340L stainless steel is the most used material for automobile fuel tanks. Considering the high cost of SUS340L stainless steel and a certain tendency of stress corrosion cracking, the research and development of low-cost ferritic stainless steel materials for automobile fuel tanks has become the focus of the next development.
Strategies for Improving Welding Quality of Stainless Steel Materials for Automobiles
1 Do the preparatory work before welding
Before the actual welding operation, four operation steps need to be done: the selected shielding gas is mainly argon, and its purity needs to be controlled above 99.99%; the welding groove is processed and the welding group is aligned (wrong side, gap, etc. ) requirements must fully meet the corresponding quality standards, for example, the inner, outer and peripheral slopes of 25mm need to be polished to make them appear metallic luster. At the same time, in order to fully control welding deformation, stress, etc., U-shaped groove can be used to implement welding treatment; a temperature and humidity meter should be placed at the corresponding welding position, and real-time monitoring of the humidity at the welding position should be carried out, and the standard should be controlled within the range of ≤85% , and effectively ensure that the welding process will not be disturbed by strong moisture from the outside world; it is required to take appropriate wind and rain protection measures in the welding site, so as to fully ensure the smooth and steady progress of the welding work.
2 Welding process control
During the welding process, attention should be paid to the welding process and welding temperature. First of all, the corners of the stainless steel should be fixed before welding to ensure the accuracy of the welding. After the welding is completed, it can be cut off with a cutting machine, but the original size of the base metal must not be damaged. After cutting, an acidic solution should be used for cleaning and passivation. . Secondly, use a small current when welding, high temperature will destroy the corrosion resistance of steel. The swing range of the welding torch is small, which can effectively avoid the formation of cross welds. The welding torch can use a large-diameter nozzle. While increasing the welding speed, the ejection amount of the shielding gas is increased, so that the welding at the weld is tighter and the protection effect is more obvious. Thirdly, the welding of the steel surface should be completed at one time as much as possible to ensure the uniform and fine welding seam, making it more flat and beautiful. When the temperature of the weld gradually decreases, but has not yet dropped to the freezing point, use a wire brush to wash off the residues of oxidation and splashing during the welding process to ensure the integrity of the weld surface.
In recent years, with the continuous improvement of automobile lightweight, long life and the continuous improvement of the user's perceived quality requirements, coupled with the current stricter requirements for automobile emission regulations, stainless steel materials have been rapidly developed and applied in my country's automobile industry. Many people in the industry believe that the demand and amount of stainless steel materials in the automotive industry will be further increased in the next step, especially for some in terms of oxidation resistance, corrosion resistance, thermal fatigue resistance, high temperature resistance, welding and formability. There is a demand for high-performance stainless steel materials with good performance. Therefore, in order to keep up with the rapid development and application of these high-performance stainless steel materials in automobiles, it is necessary and urgent to increase the development, precipitation and accumulation of advanced stainless steel materials for automobiles in the next step.
