First, let’s say that of the whole set of steel rolling factories in the world, only a few produced such steel grades. In order to make high quality spring steel with a minimum amount of impurities, it is necessary to special, expensive equipment.
The spring steel has a number of features — durability, a very high yield strength, an acceptable level of corrosion resistance, surface quality of the material, the absence of non-metallic impurities.
The most important parameter for spring steel is durability. To measure the tensile strength, a piece of wire is stretched until the wire is broken. In the production of lesjöfors springs, a wire with a strength of 1800 to 2100 N / mm2 is used, which almost 2 times the similar indicator in inexpensive springs. This means that, with other things being equal, the lesjöfors spring will break in the case of an application 2-fold load.
The yield strength reflects the ability of the material to maintain its shape during bending and twisting. In steel, which uses Lesjöfors, it reaches 90% of the strength limit. And this, in turn, speaks of high fatigue properties. With long-term operation, the lesjöfors spring will also save its shape and maintain the car body at the required height.
High rates of strength and flowability are achieved by heat treatment (hardening, vacation) and adding special alloying elements to steel: silicon, manganese, chrome. Alloying additives also positively affect the high level of corrosion resistance.
The quality of the material surface has a big impact on the spring indicators. Silvering, exfoliation and other metal surface defects significantly reduce the quality of the finished springs. They reduce strength and lead to premature breakdown.
The absence of non-metallic impurities directly affects the strength of the spring, because The more such particles are contained in steel, the greater the likelihood that they concentrate at one point and will cause the earnest breakdown of the part. Therefore, such steel for lesjöfors springs is not suitable.
In spring wire, which uses Lesjöfors, surface defects and non-metallic impurities reach no more than 0.7% of the diameter, which is more than three times higher than spring steel rates of inexpensive brands. Lesjöfors seriously refers to the choice of steel supplier and uses for automotive springs only spring steel steel with a minimum number of foreign inclusions.