TY - JOUR A1 - Zhang, Lei A1 - Pittner, Andreas A1 - Michael, Thomas A1 - Rhode, Michael A1 - Kannengießer, Thomas T1 - Effect of cooling rate on microstructure and properties of microalloyed HSLA steel weld metals N2 - Two high strength Nb/Ti microalloyed S690QL steels were welded with identical filler material, varying welding parameters to obtain three cooling rates: slow, medium and fast cooling. As cooling rate increased, the predominantly acicular ferrite in Nb weld metal (WM) is substituted by bainite, with a consequence of obvious hardness increase, but in Ti WM, no great variation of acicular ferrite at all cooling rates contributed to little increment of hardness. The transition between bainite and acicular ferrite has been analysed from the point view of inclusions characteristics, chemical composition and cooling rate. Excellent Charpy toughness at 233 K was obtained with acicular ferrite as predominantly microstructure. Even with bainite weld of high hardness, the toughness was nearly enough to fulfill the minimal requirements. WM for Ti steel showed to be markedly less sensitive to the variations of cooling rate than that for Nb steel. KW - High strength steel KW - Weld metal KW - Cooling rate KW - Charpy toughness KW - Acicular ferrite PY - 2015 U6 - https://doi.org/10.1179/1362171815Y.0000000026 SN - 1362-1718 VL - 20 IS - 5 SP - 371 EP - 377 PB - Taylor and Francis CY - London, UK AN - OPUS4-36518 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Weczera, S. A1 - Rhode, Michael A1 - Sunderkoetter, C. A1 - Plath, A. A1 - Jüttner, S. T1 - Laboratory experiments on press hardened steels in different delivered states exposed to hydrogen N2 - The legal and economical demands in the automotive industry lead to increasing efforts reducing the CO2 emissions. A way to achieve that goal is to reduce the total weight of the car and therefore the fuel consumption. With the application of high strength steels in car body manufacturing it is possible to decrease the sheet thickness of the used materials and therefore the weight of the automobile. Components made of high strength steels can be produced by cold forming as well as by hot forming. In high strength steel the hydrogen content plays a crucial role for the component behavior. It is known that the hydrogen diffusivity and solubility are based on several factors, for example increasing dislocation density by cold working processes, vacancies, chemical composition and grain boundaries. The understanding and the control of the interaction between hydrogen and the high strength press hardened steels is an important factor for the application of the materials. The scope of this work is the determination of hydrogen diffusion and permeability kinetics in press hardened steel samples. An electrochemical hydrogen permeation method was applied on boron-manganese steel grades with different rolling reduction in initial ferrite/pearlite matrix as well as for the as-quenched martensite microstructure. The diffusible hydrogen contents of the specimens were measured using the carrier gas hot extraction technique (CGHE). T2 - CHS2 2015 - 5th International conference on hot sheet metal forming of high-performance steel CY - Toronto, Ontario, Canada DA - 31.05.2015 KW - Automotive KW - High strength steel KW - Hydrogen KW - Measurement KW - Carrier gas hot extraction KW - Press-hardened KW - Martensite KW - 22MnB5 KW - Permeation PY - 2015 VL - 5 SP - 45 EP - 54 PB - Verlag Wissenschaftliche Scripten CY - Auerbach, Germany AN - OPUS4-33468 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -