I-Steel
Future-oriented light weight construction in the automotive industry with I-Steel
Bodyshop in car manufacturing
In order to reduce the fuel consumption and therefore the carbon-dioxide emissions from passenger cars measures for reducing the weight in vehicle construction are becoming more and more significant. Particularly the reduction of the sheet metal thickness in the area of the car body can provide a significant contribution to mastering this problem. In this case maintenance of the body stability and passenger safety make the use of high-strength steel grades necessary.
The high-strength I-Steels (isotropic steels) developed especially for such requirements by Salzgitter AG are distinguished by their excellent formability with simultaneously high strength. Demanding interior components as well as large outdoor panels can be produced with these high-strength I-Steel grades.
The potentials for weight reduction by reducing the sheet metal thickness have been proven in comprehensive studies including FEM simulation (finite element method). FEM simulation offers the possibility of calculating the material properties in terms of processing characteristics and component characteristics before production of the parts. Within the usual sheet metal thickness range (0,70 mm to 0,90 mm) the possibility of reducing the thickness by 10 to 20% using I-Steel in comparison to conventional deep drawing sheet was proven on various components without any loss of strength properties.
Forming characteristics
Deep drawn cups of
conventional deep drawing
steel grade (r.) and I-Steel (l.)
The excellent forming characteristics of I-Steels are achieved by their special flow properties. This is distinguished by a uniform flow regardless of the position in relation to the rolling direction (isotropic flow). For production of rotation symmetrical parts this means that the earing which occurs when conventional deep drawing steel grades are used leading to a nonuniform distribution of the wall thickness, does not occur with I-Steel.
The excellent forming characteristics of I-Steels are achieved by their special flow properties. This is distinguished by a uniform flow regardless of the position in relation to the rolling direction (isotropic flow). For production of rotation symmetrical parts this means that the earing which occurs when conventional deep drawing steel grades are used leading to a nonuniform distribution of the wall thickness, does not occur with I-Steel.
The properties of I-Steel can be described as follows:
- High guaranteed minimum yield strength of 220, 260, 300, 340 MPa
- High plasticity during forming process
- High elongation values
- Resulting in high strengthening
- Unlimited applicability for outdoor panels
- Low variation of mechanical values
- Available as cold-rolled sheet metal, electro-zinc coated, hot-dipped galvanised and/or organically coated
- Unlimited applicability for car body construction
- All familiar methods can continued to be used for forming, joining and painting when processing I-Steel.
All familiar methods can continued to be used for forming, joining and painting when processing I-Steel.
Production and processing
Ladle treatment for
adjustment of micro-alloying
and temperatureProduction
and processing
Following the oxygen blowing process in the converter the I-Steel is subjected to an alloying treatment in the secondary metallurgical centre. Here defined microalloying is accomplished with titanium. Continuously cast slabs are rolled to the technologically required hot strip thickness on the hot strip mill. A particularly important step in the process is adjustment of the exactly defined hot rolling and coiling temperatures.
In the cold wide strip mill the as-rolled initial product for the I-Steel is produced. The required recrystallisation annealing for high strength and good formable material is performed in the hydrogen high-convection annealing plant. The energy is transferred by the hydrogen resulting in rapid and uniform warming all the way through. In the subsequent operation a defined roughness is processed onto the strip surface. I-Steel is available with PRETEX® surface structure if desired.
The I-Stahl can also be provided with corrosion protection corresponding to the desired application. In addition to electrozinc coated on one or both sides passivation by phophating and various organic coatings are available to increase the corrosion protection even more. A hotdipped galvanised version has been developed.
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Conditions of delivery
I-Steels are available as cold-rolled steel sheet up to a thickness of 2,5 mm (up to 3,0 mm on request). The minimum thickness is 0,5 mm (below 0,5 mm on request). The coil width depends on the strip thickness and is max. 1.860 mm.
Steel production process
The steel is produced using the oxygen blowing process.
Applications
I-Steels can be used for various applications with high demands on cold-formed components:
Cold-pressed parts, large outdoor panels, cold-shaped parts. It is the responsibility of the processor to ensure that his calculation, design and processing methods are suitable for the material. The forming technology used must be suitable for the intended purpose and correspond to the state-of-the-art.
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Welding
I-Steels can be welded using all electric manual and automatic processes when the general rules of technology are observed. Embrittlement does not occur in the heat affected zone. Preheating is not necessary. Soft wires and electrodes are recommended as welding filler. The recommendations of the specific manufacturer have to be observed with selecting the welding filler.
Surface coatings
I-Steels are available with an electro-zinc coating according to DIN EN 10152 as well as organically coated. I-Steels are also available as hot-dipped galvanised version.
Weitere Informationen sind dem Salzgitter Flachstahl Werstoffblatt 11-110 zu entnehmen.
Delivery
Delivery according to our product line regarding dimensions, versions and order quantities.
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