Components with Optimised Properties due to Advanced Thermo-mechanical Process Strategies in Hot Sheet Metal Forming

Abstract

The increasing demand for car body structures with optimised energy absorption capacity and the ability to maintain their structural integrity even under the highest dynamic load has stimulated the development of new thermo-mechanical process routes for the production of pressed and roll-formed sheet metal parts in order to combine both extreme formability and a highest level of strength for the final product. These process routes offer a high potential for further improvements in the field of strength-strain correlation and load adapted property distribution of the components, as well as an enhanced process productivity. A new type of thermo-mechanical tailored processing of sheets and profiles is presented, based on the adequate application of differential heating and cooling strategies. By the control of local microstructural effects, the components develop a property distribution adapted to complex load situations. New tooling concepts complement these developments in order to ensure high process efficiency and reliability.

Hydrogen Embrittlement of Hardened Low-carbon Sheet Steel

“…1) However, recently steel parts with martensitic microstructures and more complicated shapes are being produced by hot stamping at temperatures where austenite is stable, followed by die quenching. [2][3][4][5][6] A systematic study of the effect of tempering on sheet tensile specimens of AISI 10B22, a 0.22 wt% C steel, alloyed with boron for hardenability and which corresponds to European grade 22MnB5, has shown that strengths between 1 200 MPa and 1 600 MPa can be produced with little changes in ductility, about 6 to 8 % in sheet tensile specimens, after tempering martensite between 150 to 350°C. 7,8) Tempering at higher temperatures causes extensive discontinuous yielding, greatly reduced strain hardening, and lower strengths.…”

Research on hot stamping for a typical part of B1500HS boron steel using experiment and numerical simulation methods

“…The curves in Figure 10 and the data in Table 3 show that, the lower austenitization temperature is helpful for manufacturing the structural components with distributed properties by introducing a thin air gap between the tools and steel plate [26], or using the tool materials with the lower thermal conductivity [27], as the austenite attained at the lower austenitization temperature is particularly susceptible to the cooling rate [28]. The fracture morphology of sample austenitized at 870 °C, 900 °C, 930 °C or 960 °C is shown in Figure 11.…”

Artificial Neural Network (ANN) based microstructural prediction model for 22MnB5 boron steel during tailored hot stamping

“…On the other hand, the high tensile strength of the fully hot stamped parts leads to them having low ductility and poor energy absorption characteristics. Such hot stamped parts therefore are not fully optimized for crash performance and light weighting [6][7][8]. Researchers have come up with an innovative solution to this problem where local sheet metal cooling rates are varied by dividing the tooling into heated and cooled zones.…”

“…The final microstructure produced in boron steel after tailored hot stamping is a complex mixture of martensite, bainite and ferrite phases depending on the thermal and mechanical processing conditions [1,[6][7][8][9]20]. Metallography and microhardness measurements are well suited for a qualitative assessment of such complex microstructures generated during tailored hot stamping but these techniques are not suitable for quantification of different phases present in the final microstructure.…”