Why aren't cars made of stainless steel
The stainless steel we usually talk about does not actually never rust, but its "corrosion resistance" is relatively outstanding.
For example, the stainless steel spoons and washbasins in our homes are made of "austenitic" 304 stainless steel, which will rust after being used for a long time.
Many high-end watches are made of 316L stainless steel, which is fine if soaked in sea water. The more advanced Rolex uses 904L stainless steel, which has better "corrosion resistance".
1: Current anti-corrosion technology is sufficient
The usage conditions of a car are much more complicated than that of a washbasin watch, and stainless steel will not be used directly on the car just because it has good "corrosion resistance".
Moreover, the current automobile anti-rust technology can fully meet the demand. The performance of stainless steel is a bit excessive for cars.
(1) Galvanized steel sheet itself has certain anti-rust ability
The steel plate used in modern cars is called "galvanized steel plate", and the purpose of galvanizing is to prevent corrosion. When the galvanizing amount is 350g/m², the service life of galvanized steel sheets outside the house is 15 to 18 years in rural areas and 3 to 5 years in industrial areas. This lifespan is already several times, even more than ten times, that of ordinary steel plates.
(2) The spraying process can also play a role in preventing rust.
In addition to the rust prevention of the material itself, the coating process is also helpful for rust prevention. What is the first step in painting? Electrophoresis rust prevention.
After the car body is cleaned, it is placed in an electrified bath and immersed in it like a steamed bun. The paint ions will form a layer of electrophoretic paint on the car body under the action of the electric field force.
This layer of paint is what we call primer in vernacular. It mainly plays the role of isolating water and air. It is similar to vacuum packaging.
Usually, if the paint surface is scratched, whether or not to touch it up depends on whether the primer is damaged or not.
After the primer is sprayed, it must go through intermediate coating, color paint, and varnish, which can also play a certain isolation role.
Just like girls when they go out, they don’t just put on sunscreen. They have many things: face cream, eye cream, BB cream, etc.
(3) Wax injection into the cavity can prevent rust inside the car body.
Car paint mainly targets the surface of the car body. For the interior of the car body, manufacturers also have anti-rust methods - wax injection into the cavity.
The car body is actually not solid. For parts with cavities, holes have been reserved during the design.
First heat the car body, then inject liquid anti-rust wax from the reserved hole, and finally pour out the excess wax, forming a wax film with a thickness of several hundred microns on the inner wall of the cavity.
The purpose of the wax film is also to isolate air, and the principle of electrophoresis is actually similar.
2: The cost of making stainless steel cars is too high
(1) Stainless steel is more expensive, 3 times the price of galvanized steel plate
In fact, in history, some manufacturers did use stainless steel to build cars, and Porsche did it before.
In 1967, Porsche produced an all-stainless steel 911S, which is still stored in the Deutsche Museum in Munich.
The reason why this stainless steel 911 was produced was because at that time, the car body anti-corrosion technology was not as developed as it is now, and it was an experimental product. However, because stainless steel was very expensive, its cost was twice that of the ordinary 911 at that time.
For current manufacturers, galvanized steel sheets are easy to use and cheaper. There is no need to use stainless steel to build cars, right?
(2) Heavier, not conducive to energy saving, emission reduction and fuel consumption reduction
In addition, today's cars are developing towards lightweighting, using large areas of aluminum alloys and other advanced materials, as well as carbon fiber, which are used by Audi, Jaguar, etc., and they also use all-aluminum bodies, right?
The density of aluminum alloy is about 2.7g/cm³, and the density of stainless steel is 7.64 to 8g/cm³, which is nearly three times heavier than aluminum alloy. Even compared with current automobile steel, it has no advantage.
For manufacturers, in the context of energy conservation, emission reduction, and fuel consumption reduction, it is not cost-effective to use stainless steel that is three times heavier to make the body, and the fuel consumption is also high, right?
3: Insufficient strength of stainless steel
In addition to cost reasons, the strength of stainless steel is not enough for the frame.
(1) The yield strength is not enough and is not suitable for the frame
Steel is divided into low-strength steel, high-strength steel, ultra-high-strength steel and hot-formed steel according to the yield strength range.
For key parts such as A-pillar and B-pillar, manufacturers use hot-formed steel with a strength of about 1000MPa. Some manufacturers use boron steel with a strength of up to 1800MPa.
In the stainless steel family, the most widely used 304 stainless steel is already relatively high in strength. Its yield strength is about 205 to 400MPa. It is a high-strength steel, but it still cannot reach the level of ultra-high strength and hot-formed steel.
(2) Automotive steel also depends on tensile strength
Moreover, automotive steel cannot only look at yield strength, tensile strength is also very important.
Most car body parts are made by stamping steel plates into the required shape. Stainless steel is actually not suitable for stamping processing.
When stainless steel is cold worked, the greater the deformation, the higher the microscopic dislocation density, the more serious the internal stress and lattice distortion. Although the strength increases with deformation, the plasticity decreases.
It doesn’t matter if you don’t understand. It means that stainless steel will become brittle after stamping. At this time, the annealing process must be used to eliminate the hardening phenomenon before pressing can continue, otherwise it will easily crack.
Ordinary automobile steel plates are not that troublesome to get.
Therefore, there are actually not many stainless steel accessories on current cars, mainly exhaust pipes and some decorative accessories.
4: Expensive, which is an important reason why stainless steel is not used to build cars.
In general, the most important reason why manufacturers do not use stainless steel to build cars is that it is expensive. If it is purely for anti-corrosion, it is completely unnecessary.
Sinosteel Stainless Steel Pipe is one of largest Stainless Steel Pipe and Special Alloy Pipe manufacturer in china.
More info: https://www.sinosteel-pipe.com/en/blog-5677849774744585.html