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

The main goals of the transport industry are lightweight and the increase in safety for passengers. Consequently, the choice of materials is very important. The materials adopted in recent years are lightweight alloys, such as aluminum and magnesium alloys, carbon fiber-reinforced polymers, and advanced highstrength steel (AHSS). In the automotive industry, five classes of AHSS are distinguished: dual-phase steel (DP), complex phase steel (CP), transformationinduced plasticity steel (TRIP), martensitic steel (MART), and press-hardened steel (PHS). [1,2] DP steels are ferritic-martensitic phase steels, which exhibit a strength between 450 and 1400 MPa depending on the amount of martensite. [3] Complex phase steels contain bainitic, martensitic, and ferritic phases and show higher formability than DP ones. [1] TRIP steels are characterized by a certain amount of retained austenite phase, which transforms into the martensite phase during the deformation. This effect helps the distribution of the strain and increases elongation, justifying the greater formability of TRIP steels compared to CP and DP steels. [1,4] Martensitic steels have high strength levels but show very low formability. Finally, the press-hardened steels are typically carbonmanganese-boron alloyed steels, [5] which are generally adopted in the press hardening (PH) process where the unformed blank is heated in a furnace up to the complete austenitization temperature, formed in the hot condition and finally quenched in the die. These steels are typically delivered in ferritic-pearlitic conditions and have, at the end of the PH process, almost doubled resistance levels due to the transformation into the martensitic phase due to the quenching phase. Among the PHS, the most common one is the 22MnB5; [5] however, other steel grades with higher carbon content are recently proposed to be used in the PH process. [6][7][8] PHS combined with the PH process allow to satisfy at the same time the requirements related to safety and those related to vehicle weight reduction, [9] therefore they are increasingly adopted in anti-intrusion applications of automotive structures (bumpers, doors, bodies-in-white).Current innovation trends are aimed at opportunities these AHSS offer in terms of tailored mechanical properties. [10][11][12][13][14] Currently, the stamped part designing with customized performances includes forming technologies that use tailor rolled blanks, tailor welded blanks, patchwork blanks, tailor tool tempering, tailor heating, and tailor cooling process. [15] A great deal of research has been carried out around the tool tempering approach in recent years. [12,13,16] With this approach, the tailored properties are achieved by exploiting different cooling conditions during the

Section: Influence Of Process Parameterssupporting

confidence: 85%

Analysis of Transition Zone on a Hot‐Stamped Part with Tailored Tool Tempering Approach by Numerical and Physical Simulation

Palmieri

Posa

Angelastro

et al. 2023

“…Similar microstructures were obtained in literature in previous studies of similar steel. [38][39][40] However, it is worth mentioning that previous studies were focused on much thinner sheets and on other cooling processes. Observations of the fracture surfaces of tensile tested specimens at 25, 60, and 85 mm additionally confirmed the transition to a more ductile state of B27 by revealing a transition from brittle to more ductile fracture behavior.…”

Section: Strength and Hardness: B27 And B38mentioning

confidence: 99%

Differential Microstructure and Properties of Boron Steel Plates Obtained by Water Impinging Jet Quenching Technique

Romanov,

Jahedi,

Bäckström

et al. 2023

Soil‐working tools in agriculture are made of boron containing steels with high wear resistance and hardenability. Nevertheless, these tools are subject to high impacts, abrasive wear, fatigue and therefore prone to failure. To combine varying levels of properties within one component in as‐quenched condition can be beneficial for such products. To obtain this property variation a component must undergo a complex and controllable cooling. Therefore, the aim of this work is to obtain a microstructure gradient along two 15 mm thick steel plates in a newly developed test rig by Water Jet Impingement Technique to confirm its controllability and flexibility. Furthermore, a quenching simulation model was created for hardness prediction using phase transformation data from a machine learning tool. Microstructure variation was observed using light optical microscopy and the electron backscatter diffraction technique. Mechanical properties were studied through tensile tests and hardness measurements, and also compared with simulation results. 0.27 mass‐% C steel sample obtained almost fully martensitic state transitioning to a softer ferritic/bainitic condition, while the 0.38 mass‐% C steel sample resulted predominantly in a fully hardened martensitic state slightly showing ferritic and bainitic features along the sample. The quenching simulation model showed promising hardness prediction for both steels.This article is protected by copyright. All rights reserved.

“…[26] The AP&T company designed a new TemperBox furnace in which a cooled mask, placed a few millimeters from the blank surface corresponding to the soft regions, protects these regions from thermal radiation and, at the same time, it absorbs their thermal energy. [27][28][29] In addition to industrial research, academic research is also proposing solutions for creating soft local zones through a precooling phase; for example, Golovko et al [30] proposed precooling by compressed air to obtain a bainitic microstructure (more ductile microstructure than the martensitic one) in the soft areas.…”

Section: Introductionmentioning

confidence: 99%

“…In addition to industrial research, academic research is also proposing solutions for creating soft local zones through a precooling phase; for example, Golovko et al [ 30 ] proposed precooling by compressed air to obtain a bainitic microstructure (more ductile microstructure than the martensitic one) in the soft areas.…”

Section: Introductionmentioning

confidence: 99%

Effects of the Intermediate Precooling Parameters on the Mechanical Properties of a Tailored Press‐Hardened Component in Advanced High‐Strength Steel

Palmieri,

Tricarico

2023

In recent years, several automotive companies have studied new tailored tempering technologies for press hardening process to produce structural components with tailored mechanical properties, that is, component with both soft zones to absorb energy and hard zones to avoid intrusion during an impact. One of these technologies involves a tailored tempering station interposed between the austenitization furnace and the press machine in which classical stamping and quenching phases occur. In the tailored tempering station, areas that are desired to be ductile are cooled, while areas with the final high mechanical properties remain at the complete austenitization temperature. This work investigates this new tailored tempering technology by means of finite‐element models and experimental lab‐scale tests. The aim is understanding the influence of cooling rate and the dwell time in the tempering station (precooling time) on the formability and mechanical and microstructural properties of the stamped part. Two different cooling ways of soft areas are explored: 1) by a cooled mask and 2) by a mask with compressed air. Results indicate that an increase in precooling time leads to greater softening in the ductile region but also leads to formability challenges. These effects are even more pronounced with a higher cooling rate.