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Microalloyed, vacuum degassed high‐strength steels with special emphasis on IF steels
Author(s) -
Engl Bernhard,
Gerber Thomas
Publication year - 1996
Publication title -
steel research
Language(s) - English
Resource type - Journals
eISSN - 1869-344X
pISSN - 0177-4832
DOI - 10.1002/srin.199605515
Subject(s) - materials science , formability , embrittlement , metallurgy , hardening (computing) , brittleness , precipitation hardening , high strength steel , solid solution strengthening , brittle fracture , fatigue limit , solid solution , composite material , microstructure , fracture (geology) , layer (electronics)
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 of Ti and high coiling temperatures are used. For a P‐alloyed IF steel with stoichlometrical 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.