Advances in Metallic Coated Advanced Steels: On-Demand Oral Presentations
Sponsored by: AIST: Metallurgy Processing Products and Applications Technology Committee , AIST: Galvanizing Technology Committee
Program Organizers: Joseph McDermid, McMaster University; Frank Goodwin, ILZRO
Friday 8:00 AM
October 22, 2021
Room: On-Demand Room 8
Location: MS&T On Demand
Liquid Metal Embrittlement of 3rd Generation Advanced High Strength Steel Driven by Nano-intermetallic Phase Formation Along Grain Boundaries: Yuki Ikeda1; Anirban Chakraborty2; Hassan Ghassemi-Armaki2; Robert Maass1; 1Federal Institute for Materials Research and Testing (BAM); 2ArcelorMittal Global Research and Development
Despite the high strength and ductility of advanced high-strenght streels (AHSS), the Zinc (Zn) coating typically applied to increase its corrosion resistance can be the origin of significant mechanical property degradation if, for example, joined with spot welding. This property degradation is a manifestation of the well-known Liquid Metal Embrittlement (LME) phenomena, during which liquified Zn infiltrates into the steel substrate along grain boundaries (GBs). In order to shed more light on the early stages of LME in AHSS, we pursue here the approach to study infiltrated but uncracked GBs. We use scanning transmission electron microscopy (STEM) to investigate these boundaries and conclude that prior to cracking nucleation and growth of intermetallic phases occurs inside the uncracked GBs. We discuss these findings in the context of resulting local strain heterogeneities that may eventually trigger microcracking in LME.
Insight into the Mechanism of Liquid Metal Embrittlement in Resistance Spot Welding of Zn-coated Dual Phase Steel: The Role of Boron and Silicon: Elahe Akbari1; Philipp Kürnsteiner1; Peter Oberhumer1; Günter Hesser1; Heiko Groiss1; Martin Arndt2; Martin Gruber2; Robert Sierlinger2; 1Christian Doppler Laboratory for Nanoscale Phase Transformations, Center of Surface and Nanoanalytics, Johannes Kepler University Linz; 2Voestalpine Stahl GmbH
Despite numerous studies on liquid metal embrittlement (LME) during welding of Zn-coated 3rd generation advanced high strength steels (AHSS), a conclusive mechanism demonstrating how different alloying elements such as boron and silicon influence LME behavior, is still missing.In the present study, hot tensile tests were conducted to study LME susceptibility in high ductility dual phase (DP-HD) steel. Results indicated that the presence of boron, as well as decreasing silicon-content from 1.5% to 0.9%, mitigate LME sensitivity at elevated temperatures. Electron backscatter diffraction in conjunction with transmission electron microscopy verified the intergranular penetration of Zn along prior austenite grain boundaries, where Zn as a ferrite stabilizer promotes the formation of α-Fe(Zn). Those Zn- wetted grain boundaries present a promising path for LME crack propagation. LME cracks in resistance spot welded DP-HD steels were investigated and the grain boundaries that are prone to LME crack propagation were analyzed in detail.
Optimal Wavelength Selection for Improved Multi-wavelength Pyrometry of Advanced High Strength Steel: Fatima Suleiman1; Kaihsiang Lin1; Kyle Daun1; 1University of Waterloo
Accurate pyrometry during thermal processing of advanced high strength steels (AHSS) requires detailed knowledge of the spectral emittance of the steel, which varies with the as-received state of the coil and evolves during annealing due to oxidation. Multi-wavelength pyrometers, which use irradiance measurements at an increased number of detection wavelengths, have proven effective at capturing some of these complex wavelength-dependent variations in emissivity. However, multi-wavelength pyrometry estimates are also prone to over-fitting due to their increased degrees of freedom, which may lead to large errors in the inferred temperature. This study employs the Bayesian methodology to determine the optimal combination of detection wavelengths that minimizes the posterior covariance on the temperature estimates. Using in-situ measurements from annealed DP980 coupons, the expected temperature variance is compared for various wavelength combinations in the near-infrared range. This paper presents a generalized framework for optimizing multi-wavelength pyrometers for accurate temperature estimates on high-performance steels.