Application and Prospects of Stainless Steel Materials in Automotive Manufacturing

With the development of the national economy and the improvement of people’s consumption, the consumption of stainless steel is showing an increasing trend. The application of stainless steel in the automotive industry is one of the fastest growing application fields. By using high-strength stainless steel casting, the vehicle body can greatly reduce its weight and enhance the strength of the paint structure. Using stainless steel as the vehicle’s panels and decorative components can reduce maintenance costs. In addition, utilizing the advantages of stainless steel’s resistance to chloride ion corrosion and heat resistance, it is applied to the exhaust system of automobiles. The automotive industry is a key development focus for stainless steel applications.

Stainless steel not only has corrosion resistance, but also has good physical properties and surface quality. It is widely used in automotive manufacturing. According to different parts, the automotive industry has different requirements for the surface characteristics, mechanical properties, and physical properties of stainless steel, which can be roughly classified into five categories: stainless steel for automotive exhaust systems, stainless steel for automotive fuel tanks, stainless steel for automotive frames Stainless steel parts for automobiles and stainless steel for automotive decoration.

1. Stainless steel for automotive exhaust systems

With the improvement of the performance of automotive engines and the strictness of exhaust regulations, the temperature of the gases emitted by the engine is getting higher and higher. Recently, some automotive exhaust temperatures have reached as high as 900 ℃, and there is a tendency to become high-temperature (up to 950 ℃). Correspondingly, the automotive industry requires exhaust system components to have excellent heat and corrosion resistance, while also requiring lightweight as much as possible. Heat-resistant cast steel and heat-resistant steel have now been used to replace past cast steel and ordinary steel components. According to the different parts of the exhaust system, there are significant differences in gas temperature, component structure, and corrosion environment. Therefore, automotive exhaust systems not only require manufacturing materials to have high-temperature oxidation resistance and high-temperature strength, but also require them to have thermal fatigue characteristics, high-temperature corrosion resistance, and other properties. In the high-temperature area near the engine, the required material properties mainly include high-temperature strength, thermal fatigue characteristics, oxidation resistance, and high-temperature salt corrosion resistance; In areas far from the engine, the material is required to have good salt resistance and condensation water corrosion resistance; The end pipe material at the rear of the vehicle body should not only have good corrosion resistance, but also be aesthetically pleasing.

The amount of stainless steel used in the exhaust system accounts for more than half of the total amount of stainless steel used in automobiles, with 80% being ferritic stainless steel. 409L, 436L, etc. are commonly used stainless steel grades. From the perspective of economy and practicality, some European and American countries choose 0Cr11Ti type ferritic stainless steel for their exhaust systems, while Japan uses 13Cr-17Cr ferritic stainless steel and its improved versions.

2. Stainless steel for automotive fuel tanks

The fuel tank is an important safety and functional component in automobiles. The steel plate material of the fuel tank must possess various excellent properties, including excellent stamping forming performance, excellent welding performance, and high corrosion resistance (internal fuel corrosion resistance and external corrosion resistance to harsh environments). Stainless steel is another choice of steel for automotive fuel tanks, in addition to being coated with plain carbon steel, and is currently used worldwide. Fuel tanks made of stainless steel not only have no risk of fuel leakage, but also have excellent corrosion resistance and good formability. They also have the advantage of saving or simplifying the coating process and are easy to recycle.

At present, austenitic stainless steel, such as SUS304L, is commonly used in automotive fuel tanks. Considering the issues of stress corrosion cracking and cost, many steel companies are striving to develop ferritic stainless steel for fuel tanks. JFE announced in July 2003 that it had successfully developed a ferritic stainless steel 18Cr-1.45Mo-Ti (trade name JFE-SX1) with high corrosion resistance and formability for use in automotive fuel tanks and other components of fuel systems. Due to its corrosion resistance being closer to SUS304 than other ferritic stainless steels, and its excellent stamping formability, it is the only designated ferritic stainless steel by the Steel Fuel Tank Strategic Alliance (SASFT) under the American Iron and Steel Association (AISI).

3. Stainless steel for car frames

High stiffness is the biggest characteristic of composite frames made of stainless steel, as stainless steel not only ensures sufficient strength and weight ratio, but also has good plasticity, toughness, formability, and weldability. By combining the design of a modular car frame with the excellent performance of stainless steel materials, a car can be manufactured that is particularly lightweight, has good impact resistance, high safety and reliability, and has a long lifespan. Such a frame can also be fully recycled. Japanese stainless steel companies are working hard to research high-strength stainless steel for automobiles, and stainless steel containing 12% chromium has been successfully applied to high-speed passenger vehicles. The overall body shell made of AISI409 ferritic stainless steel has a service life of generally 15-20 years.

The low alloy double stabilized stainless steel containing 12% chromium developed abroad has overcome the shortcomings of poor workability. The structure of the steel is ferrite and a small amount of martensite. The weldability is good, and the yield strength is better than that of austenitic stainless steel, but the price is only half of that of austenitic stainless steel. At present, countries such as South Africa, the United Kingdom, Australia, Belgium, etc. have successively adopted 3Cr12 stainless steel to manufacture large buses, coal transportation vehicles, urban subway vehicles, and various specifications of cleaning vehicles (including airport large cleaning vehicles, sprinklers, and trailers), or to combine 3Cr12 and 304L stainless steel.

4. Automotive stainless steel components

Stainless steel is also widely used in various components. Metal sealing rings represented by stainless steel sealing rings have become the main substitute for traditional asbestos sealing rings. A metal sealing ring made of rubber and covered with stainless steel as the substrate. SUS301 is commonly used as the stainless steel substrate, which has the advantages of high temperature resistance, corrosion resistance, and good elasticity. In addition, when the engine is working, a series of faults may occur due to the increase in oil temperature, decrease in oil viscosity, and deterioration of oil quality. The automotive industry has always used tubular heat exchangers to cool the oil. In order to improve cooling efficiency and compact structure, some production enterprises have switched to stainless steel plate heat exchangers, mostly using SUS304, SUS430, and SUS409L materials. In terms of automotive fasteners, although low alloy cold heading steel materials are traditionally used, stainless steel is not uncommon in some parts of the automotive engine system and transmission system where environmental conditions are extremely harsh, and the usage is on the rise. The commonly used stainless steels for automotive fasteners include SUS410, SUS304, SUS316, SUS430J1L, SUH660, etc.

5. Stainless steel for automotive decoration

The use of stainless steel as a decorative material for both the interior and exterior of automobiles has a long history and is increasingly expanding its scope of use. To make cars look beautiful, production companies use stainless steel inserts, antennas, and wheel covers on sedans, as well as stainless steel on handrails, safety railings, and suspension rods on large passenger cars and vehicles. Other exterior components on cars are not only equipped with their own functions, but also endowed with decorative functions. In order to reduce costs, the rearview mirrors mainly use SUS430J1L series stainless steel, and some high-end sedans use SUS436J1L series stainless steel for rearview mirrors; Car wipers often use SUS430, SUS304, SUS301, etc; The headlight retainer is made of steel grades such as SUS430. The safety devices on cars also use stainless steel. For example, the seat belt tensioner uses SUS301 stainless steel, the sensor and booster pump of the airbag mainly use SUS304 and SUS304L stainless steel, and the ABS sensing ring uses steel grades such as SUS434 and SUS444.

The automotive industry is currently one of the fastest developing areas for stainless steel applications. Taking into account the costs of manufacturing, maintenance, and energy consumption, stainless steel cars are significantly lower than aluminum alloy cars and carbon steel cars, making them the most economical vehicles with great development prospects