Effect of Grain Refinement on Cold Formability Behavior on Medium C-Boron Steel

Abstract:

The effect of grain refinement on cold formability behavior on medium C-Boron steel has been studied. In particular a 30MnB4 steel long product has been considered to be used for screw production as final application. One of the issues during the cold forming of screw heads is given by the possible material failure in the most strained area, like the flange tip in the head. The probability of having a high scrap rate is strictly linked to the material cold formability limits. The study focused on the comparison between steel with conventional and ultrafine microstructure. Relationships between steel microstructure and plastic deformation behavior of the material were investigated by FEM modeling. Calibration of the model was carried out by analyzing the ultrafine grained steel, produced in pilot mill whose grain size was about 2-3 μm and the conventional steel industrially produced (grain size about 12 μm). Specific laboratory tests to characterize the material formability have been carried out. Finite element simulations have been performed to characterize the strain and stress state both in the forming process and in experimental tests to determine the material ductile fracture locus. Mechanical tests allowed to build the ductility curves related to the different microstructures to be used to simulate cold forming taking into account the material damage. Results put in evidence a significant improvement in the forming behavior of UFG steel, meaning that the refinement of grain size should produce a more evident effect in scrap reduction during the cold forming process.

• Periodical: Materials Science Forum (Volumes 783-786)
• Pages: 2677-2682
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.783-786.2677
• Online since: May 2014
• Authors: Ilaria Salvatori*, Claudio Guarnaschelli, Tommaso Coppola
• Keywords: Cold Formability, Ferrite Grain Refinement , Plastic Damage, Ultrafine Grain Steel (UFG)

References

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[3] ASM Handbook, Forming and forging, Vol. 14, 1993, ASM International.