1‐Step “Quenching and Partitioning” of the Press‐Hardening Steel 22MnB5

Abstract

In recent years, high strength steels, particularly press‐hardening steel, have been more extensively employed for manufacturing safety‐relevant structural components in vehicle bodies. These applications require contrasting material properties such as extremely high strengths as well as high forming ductility. Owing to the purely martensitic microstructure, the residual ductility of the conventional press hardened steels is low. Quenching and partitioning heat treatments can fulfil the requirement of an increased residual ductility by stabilizing the retained austenite. Moreover, if the quenching and partitioning heat treatments are carried out after intercritical annealing treatment, then the steel's mechanical properties can be tailored by defining the volume fraction of ferrite in the microstructure. In order to determine the potential of an 1‐step quenching and partitioning heat treatment combined with intercritical annealing processes, elevated contents of retained austenite are produced in ferritic‐martensitic microstructures using the low‐alloyed 22MnB5 steel grade. In addition to a tempered martensitic microstructure, secondary martensite, and a low fraction of retained austenite, the microstructure consists of remaining fractions of ferrite; thus, providing an additional increase in ductility. For this optimized microstructure, a yield stress of 513 MPa and a tensile strength of 1045 MPa are measured with a total elongation of 10.8%.

Tailoring Soft Local Zones in Quenched Blanks of the Steel 22MnB5 by Partial Pre-cooling with Compressed Air

“…Hence, such parts feature both sections suited for mechanical joining operations as well as high-strength areas needed to improve the safety of the vehicles. In the same context, material zones with a locally reduced strength and increased ductility can be used to increase the energy absorption capacity and thus crash performance (Ref [7][8][9][10][11].…”

Effect of Annealing Process on Microstructure, Texture, and Mechanical Properties of a Fe-Si-Cr-Mo-C Deep Drawing Dual-Phase Steel

“…This is mainly ascribed to the fact that the diffusion of alloying elements is slow at low temperatures, thus requiring a long time for the phase transformation to complete. For martensitic transformation, its starting temperature Ms can be estimated using an empirical model, which is influenced by the concentrations of alloying elements in wt % [48]:…”

Effect of Different Intercritical Annealing Treatments without and with Overaging on the Mechanical Material Behavior

“…For manufacturing of components that feature microstructures with mechanical properties adapted to given load scenarios, intercritical annealing treatments with subsequent over critical cooling are attractive . Because of the incomplete austenitization during intercritical annealing between the A c 1 (austenite formation starts) and A c 3 temperatures (austenite formation is completed), a broad variation of the resulting material properties by adjusting the ferrite/austenite ratio can be realized, as only the austenite phase fraction transforms into martensite upon quenching. The ferrite of the initial microstructure remains besides the new formed martensite areas.…”

“…The metastable retained austenite in the mix of tempered primary martensite and secondary martensite can increase the uniform elongation through the TRIP effect . The Q&P process can also be used from intercritical annealing temperature . Moreover, because of a very low solubility of alloying elements in the ferrite, the content of austenite‐stabilizing alloying elements in the austenite is enlarged .…”

“…Moreover, because of a very low solubility of alloying elements in the ferrite, the content of austenite‐stabilizing alloying elements in the austenite is enlarged . This in turn facilitates the stabilization of the retained austenite during the overaging …”