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501-25-19 Body Repairs - General Information 501-25-19 DESCRIPTION AND OPERATION processes used in body manufacturing. As well as very good reshaping properties, the panels also have a relatively high rigidity. High strength steels The strength of the material and the nature of the surface can be changed as required by different engineering processes. In order to achieve suitable configuration and a good match between construction specifications and what is possible in production, a large range of high strength panels is available. The range of the minimum yield strength is from 180 N/mm× to 460 N/mm×. High strength thin steel panels usually have a surface finish. Electrolytic surface sealing is preferred. Within the group of high strength steels, various types of steel are used in body construction: ‡ Micro-alloyed high strength steels for very difficult drawn components such as fenders, the internal components of doors, hoods and luggage compartment lids or load bearing components such as sidemembers, crossmembers etc. ‡ Bake-hardening steels and phosphorus alloyed steels for external panel components with higher draw depth and subject to higher operational demands. ‡ Isotropic materials for flat shaped outer steel panels on doors, hoods, luggage compartment lids, roofs. Ultra-high-strength steels These steels are predominately used for body structural components which are relevant to safety. Despite the reduced thicknesses of the panels used, weight reduction is often achieved together with greater strength. As with high-strength steels, special types of steel are used in the ultra-high-strength steels group: ‡ Complex phase steels are used for door side impact carriers, bumper carriers and body components relevant to crashes. Besides high strength, they have good cold reshaping properties and are easily welded. ‡ Dual phase steels have the same properties as complex phase steels. Because of their high strengthening properties they are suitable for body reinforcements. ‡ Residual austenite steels and martensite phase steels have very high strength levels of up to 1200 N/mm× and are mostly used in body structures relevant to crashes. ‡ Manganese-boron steels have ultra high strength levels of up to 1600 N/mm× and are mostly used in body structures relevant to crashes. Due to the use of Ultra-high-strength steels, some special points must be taken into account during body repair: ‡ Increased force required during straightening. ‡ Strong springback tendency during alignment work. ‡ Cutting tools have a shorter useful life. CAUTION: High-strength and ultra-high-strength steel panels must not be heated during straightening work. Work without applying heat when carrying out straightening work. Losses of strength will occur at temperatures as low as 250 °C. The basic working methods and the tools to be used are the same however. Coated steel panels In a similar way to high-strength steel panels, coated steel panels are finding more applications because of the better corrosion protection which they offer. There are basically two different process which are used to apply a zinc layer: ‡ Hot dip zinc coating. ‡ Electrolytic zinc plating. The following points must be noted when welding: NOTE: Welding fumes are harmful to health. Make certain that the workspace is well ventilated and use welding fume extraction. ‡ Zinc starts to melt at about 420 °C. ‡ The zinc vaporizes at a temperature of about 900 °C. ‡ The amount of heating determines the damage to the zinc coating, and therefore to the corrosion protection.