Abstract
To improve the weld zone properties of Advanced High Strength Steel (AHSS), quenching and partitioning (Q&P) has been used immediately after laser welding of a low-carbon steel. However, the mechanical properties can be affected for several reasons: (i) The carbon content and amount of retained austenite, bainite, and fresh martensite; (ii) Precipitate size and distribution; (iii) Grain size. In this work, carbon movements during the partitioning stage and prediction of Ti (C, N), and MoC precipitation at different partitioning temperatures have been simulated by using Thermocalc, Dictra, and TC-PRISMA. Verification and comparison of the experimental results were performed by optical microscopy, X-ray diffraction (XRD), Scanning Electron Microscop (SEM), and Scanning Transmission Electron Microscopy (STEM), and Energy Dispersive Spectroscopy (EDS) and Electron Backscatter Scanning Diffraction (EBSD) analysis were used to investigate the effect of martensitic/bainitic packet size. Results show that the increase in the number density of small precipitates in the sample partitioned at 640 °C compensates for the increase in crystallographic packets size. The strength and ductility values are kept at a high level, but the impact toughness will decrease considerably.
Highlights
The automotive industry focuses on increasing the use of advanced high-strength steels (AHSS)in order to satisfy the current demand for decreasing the fuel consumption by reduced weight and increasing vehicle safety by using these steels in different energy-absorbing components [1]
V notch samples were specimens prepared according to the Results showed that all the samples that were partitioned at had very low impact
The aim of this work was to investigate the reason for brittle fracture of the samples from
Summary
In order to satisfy the current demand for decreasing the fuel consumption by reduced weight and increasing vehicle safety by using these steels in different energy-absorbing components [1]. These AHSS are produced by thermomechanical processes, which control the microstructure and grain size as well as the precipitation hardening of micro-alloyed steels. During welding of AHSS, the weld area will be completely changed and the excellent properties (i.e., tensile strength, toughness) will be lost. This means that the welded area could be the best area for crack propagation [2]. The final structure will contain tempered martensite (which increases the yield strength) with retained austenite (which improves the ductility), and, depending on the Metals 2018, 8, 747; doi:10.3390/met8100747 www.mdpi.com/journal/metals
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