Professional paper
The performances of advanced high strength steels in personally motor vehicle manufacturing
Igor Župančić
; Javna vatrogasna postrojba grada Zagreba, Zagreb, Hrvatska
Abstract
The use of advanced high-strength-steels (AHSS) is increasing in populary for almost every vehicle manufactures. They are result of a never-ending quest for material that allows different increases. AHSS vehicle panels are thinner, lighter and stronger that mild and many high-strength steel panels and accomplish the same desired effect for collision energy management. However the addition of AHSS used in vehicle construction has raised some concerns about the identity and characteristics of these steels, where they are commonly located, and to what extent they can be repaired. The best method to determine a steel type on a vehicle is to look at the vehicle-specific body repair information. High strength steel are generally defined as having tensile strengths between 270 and 700 MPa. Ultra high strength steels (UHSS) sre defined as steels with tensile strength greather than 700 MPa. Steel hardness is dependent on the alloying elements used during the manufacturing process. Carbon is the primary hardening element in steels, and is used varying percentages depending on the desired strength. However, many AHSS steels derive their strength from a combination of ferrite (more commonly known as iron) bainite, martensite, and retained austenite. AHSS grades have unique combinations of material and mechanical properties. Most have carefully selected chemical compositions and multiphase microstructures resulting from precisely controlled heating and cooling processes. Various strengthening mechanisms are employed to achieve a range of strength, ductility, toughness, and fatigue properties. Improved manufacturing processes have, in many cases, been key contributors to the implementation of these technologies. Conventional mild steel has a relatively simple ferritic microstructure; it typically has low carbon content and minimal alloying elements, is readily formed, and is especially sought for its ductility. Widely produced and used, mild steel often serves as a baseline for comparison of other materials. Conventional low- to high-strength steels include IF (interstitial free), BH (bake hardened), and HSLA (high-strength low-alloy). These steels generally have yield strength of less than 550 MPa and ductility that decreases with increased strength.
Medium carbon steel 0,3 % C to 0,6 % C are selected for uses were higher mechanical properties are needed. All these medium carbon steels are suitable for wide variety of automotive application. Borron is an interstitial element and has a very low solubility in α-solid solution (≤ 0,003 %). The primary function of borron additions to heat teratablesteels is to increase their hardness. In addition to the benefits of economy ond alloy conservation borron steel offer significan adventages of better extradability and machinability compared with borron-free steelsof equivalent hardness. Moreover steels containig borron are also less susceptible to quench cracking and distortion heat treatment. Consequently, borron-containing carbon and alloy steels are widely used in automotive, constructional, and various other application. Some investigators have reported that a small beneficial effect of borron on toughness after tempering to high hardness levels and a slightly adverse effect at lower hardness. On the other hand, for steels partialy hardened or unhardened, borron either did not have a beneficial effect on impact properties or apparently had an adverse effect. The maintain the desired B-hardness effect, strong nitrade-forming elements, such as Ti, Al, Zr and even B (at high levels) can be added to combine with the available nitrogen in B-treated steels. TiN is one of the stronest stable niitride. When using Ti to protect B, common steelmaking practice is to add at least the stoichiometric amount of Ti to precipitate any available N before B addition. The type of borron steel used on vehicle today has extremely high strength. Borron steel can have a yield point of about 1.350 to 1,400 N/mm2. That’s about for times stronger than average high-strength steel. The application of borron steel to strengthen the weaker areas of the motor vehicle is obviously for the motor industry that is the correct path for them to take. Not only are there many other new steels all with differing strengths, there are also many new coatings whitch the steel has been treated with. Coatings such as Zinc, Bonazinc, Granocoating, aluminated sheet metals etc. USIBOR-BTR-Borron are also the same grade of steel, just with a different name, depending which country it comes from. It is very strong but light in weight. In general it is used to provide extra strength in the sill area, roof and centre posts, chassis areas, door strengthening bars, dash cross-members and roll over bars.
Keywords
Hrčak ID:
150853
URI
Publication date:
15.12.2015.
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