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Products and solutions, 2010-06-25, 12:20 PM

ThyssenKrupp Steel Europe: Breakthrough for tailored tempering

The tailored tempering process, developed on the basis of hot forming technology and patented by ThyssenKrupp Steel Europe, has made its industrial breakthrough. ThyssenKrupp Umformtechnik GmbH, a subsidiary of the Duisburg-based steel producer, has received an order from a German auto manufacturer to produce B-pillars for more than 100,000 cars annually by tailored tempering. The safety-relevant components are to be used in a compact car. ThyssenKrupp Umformtechnik, a manufacturer of car body and chassis components, developed the process to industrial maturity.

Use of hot forming in car manufacture is currently on the increase. The process permits weight savings of up to 30 percent in car components. Hot forming uses special manganese-boron steels. The sheet material is heated to 880 - 950 degrees Celsius, then formed into a component and cooled rapidly in the die. This produces components with strengths of up to 1,500 Megapascals (MPa)– These strengths are significantly higher than those produced even with the strongest steels used for cold stamping. The components are lighter because the high strength of the material means they can be designed with thinner walls and without additional reinforcements.

While conventional hot forming only allows production of components with the same strength throughout, tailored tempering produces parts which are not only very strong but also able to yield in specific areas. These properties are needed in crash-relevant components for instance, which have to protect vehicle occupants and absorb impact energy in a controlled way. The B-pillar, for example: This component, a vertical structural member extending from the door sill to the roof frame, has to be able to yield in the lower third to absorb crash energy. The upper part has to stabilize the passenger cell and to protect the occupants in a side impact. With the process patented by ThyssenKrupp Steel Europe, parts with differing local strength and elongation properties can be produced in a single step from a homogeneous steel sheet.

This is made possible by a newly developed die with flexible heating. The targeted heating of specific zones of the die gives the finished component elongation properties exactly where they are needed. Because the heated blank cools more slowly in these zones, the steel hardens less. The technology is highly cost-efficient because it eliminates several process steps.

The ThyssenKrupp Steel Europe hot forming process offers both precision and flexibility. Depending on sheet thickness, the area of transition between hard and soft zones is extremely narrow – just 15 – 60 millimeters – and this level of accuracy is reproducible. This means that the properties at every point of the finished component can be accurately predicted.

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