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The use of hot formed 22MnB5 steel with an aluminium-silicon (AS) coating is well established for high strength automotive parts to combine weight reduction and passenger safety. Recent developments aim to increase the material strength for further weight saving and to improve the ductility. Especially an improved ductility makes hot formed parts suitable for additional applications, such as parts with higher energy absorption or even axially loaded parts. thyssenkrupp Steel Europe AG has developed new hot stamping grades. With an increased strength of about 1900 MPa, the MBW-K 1900 allows the application of even lighter parts compared to 22MnB5. Due to the increased strength level, delayed fracture has to be evaluated. Furthermore, the recommended parameters for processing MBW-K 1900 are regarded. A high crash performance of a material implies a high strength, while the material still shows no cracking during folding or heavy bending of the automotive part. This is the basis for the development of tribond 1200 and tribond 1400. As a new concept for hot stamping, tribond 1200/1400 are composite materials, which bond two outer layers of a ductile 500 MPa steel grade with a high strength 1500 MPa steel core layer. Both grades are already well known as monolithic steels MBW 500 and MBW 1500 for hot stamping. An aluminium-silicon coating allows tribond 1200/1400 to be processed in the same way as AS coated 22MnB5. Nevertheless tribond 1200/1400 show a reduced susceptibility to hydrogen embrittlement in the 4-point bending test compared to 22MnB5. By their improved crash behaviour, tribond 1200/1400 enable the manufacturing of more kinds of hot formed parts such as longitudinal beams. An advanced simulation method takes the composite structure of tribond 1200/1400 into account to evaluate the crash behaviour.

In comparison with other high-strength concepts, high-strength IF steel has a particularly high forming capacity with increased strength, while the sheet thickness reduction through forming is, on the whole, smallest with high-strength IF steel. Solid-solution hardening through Si, Mn and P is particularly suitable as a mechanism for increasing strength, as this leads to comparatively low formability losses with increased strength values. An additional increase in strength is possible using the bake-hardening effect. This can be achieved with an incomplete C and N binding through Ti and/or Nb, or through stoichiometric microalloying with V. The effect is basically caused by the relatively low thermodynamic stability of VC. V-alloyed, vacuum degassed steel combines in this way good forming behaviour with an increase in strength through bake-hardening.Through an increasing segregation of P at grain boundaries, solid solution hardening with this element can lead to unfavourable embrittlement in higher strength IF steel and to intercrystalline fracture. B-addition to the amount of 0.002% (mass content) greatly reduces the tendency to become brittle without leading to any remarkable losses with regard to formability. Examinations concerning the precipitation behaviour of Ti-IF steel with P show that a formation of iron titanium phosphate (FeTiP) in the hot strip only occurs where there is an excess ofTi and high coiling temperatures are used. For a P-alloyed IF steel with stoichiometrical Ti-content no precipitation of FeTiP takes place in hot band, nor is the thermal activation in continuous annealing simulation sufficient to achieve a transformation of existing Ti-precipitates into FeTiP, which might occur according to literature. Hoherfeste vakuumentkohlte Stahlemit Mikrolegierung unter besonderer Berucksichtigung von IF·Stahlen. Hohertsster IF-Stahl weist im Vergleich mit anderen Hohertest-Konzepten ein besonders hohes Umformvermogen bei erhohtsr Festigkeit auf, wobei die Blechdickenreduzierung durch Umformen beim hohertesten IF-Stahl insgesamt am geringsten ist. Ais MechaniSmus der Festigkeitssteigerung eignet sich besonders eine Mischkristallhartung durch Si, Mn und P, die bei angehobenen Festigkeitswerten zu vergleichsweise geringen EinbuBen in der Umformbarkeit tuhrt. Ein zusatztlcher Festigkeitszuwachs ist unter Ausnutzung des Bake-Hardeninq-Effektes moglich. Dieser kann mit einer unvollstandlqen C-und N-Abbindung durch Ti und/oder Nb oder durch eine stochiometrische Mikrolegierung mit V erreicht werden. Der Effekt ist im Wesentlichen auf die verhaltnismaBig geringe thermodynamische Stabilltat von VC zurOckzufOhren. V-Iegierter, vakuumentkohlter Stahl kombiniert auf diese Weise ein gOnstiges Umformverhalten mit einem Festigkeitszuwachs durch Bake-Hardening. Eine Mischkristallverfestigung mit P kann durch eine steigende Segregation dieses Elementes an den Korngrenzen zu einer ungOnstigen VersprOdung bei hOherfestem IF-Stahl und zu interkristallinem Bruchverhalten fOhren. B-Zusatze in Massengehalten von ca. 0.0...