Abstract
Q&P steels as a "Third Generation" of (AHSS) exhibit excellent tensile properties, which enable producing lightweight sections for the automotive industry and at the same time keep safety requirements. This research aims to predict the proper processing conditions for developing ultra-high-strength Q&P steel with a novel chemical composition of 0.37 C-3.65 Mn- 0.65Si- 0.87 Al- 1.5 Ni- 0.05P, wt. %. To design and optimize proper heat treatment conditions, the phase diagram, CCT curve, and critical temperatures of these alloys were first implemented using THERMO-CALC and JMATE PRO software and Gleeble 3500 machine. The heat treatment process included full austenitization, then quenching at 120°C followed by partitioning at 450°C for different times. The tensile properties, microstructure, and retained austenite volume fraction of heat-treated steel was studied at room temperature by tensile testing machine, optical microscope, and XRD. The finding summarized that partitioning of this steel for 100 s during processing had developed Q&P steel with ultra-high-strength of 1104 MPa with maximum total elongation and strength elongation balance 8.1 % and 8932 MPa %, respectively. The optical micrograph showed that heat-treated specimens at different partitioning times have had a microstructure of tempered martensite, carbide free bainite, and retained austenite. Besides, the retained austenite volume fraction has decreased with increasing partitioning time, which may be due to carbide precipitation during partitioning.
Highlights
Researchers are working hard to find solutions for reducing vehicle sectors' emissions, contributing to a high percentage of greenhouse gases (GHG) and possibilities for decreasing energy consumption
The optical micrographs indicated that increasing partitioning time from the 20 s to 100 s displayed a small change in the morphology and size of fine coexisted phases
The optical micrographs of this investigated Q&P steel demonstrated a general overview of the microstructure, but scanning electron microscopy will be performed for more identification of phases
Summary
Researchers are working hard to find solutions for reducing vehicle sectors' emissions, contributing to a high percentage of greenhouse gases (GHG) and possibilities for decreasing energy consumption. This can be achieved by developing new advanced material with excellent mechanical properties that enable producing lightweight sections and, at the same time, keep passengers safe. The second-generation AHSS has outstanding strength, strength-elongation balance, and formability compared to first generation. This generation's problem is the high content of alloying elements, which increases their alloys' cost. The third generation of AHSSs have developed to overcome the high cost of the second generation and simultaneously fulfill high mechanical properties compared to the first generation [2][3]
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