Investigation into the surface selective oxidation of dual‐phase steels by XPS, SAM and SIMS

Abstract

Surface selective oxides created during continuous annealing (MnO, SiO 2 , etc.) can have a deleterious effect on coating adhesion after hot-dip galvanizing. Earlier research works have made it clear that increasing the annealing atmosphere oxidizing potential can alleviate the problem by reducing external surface selective oxidation. In the present study, increasing the water vapour content of the nitrogen-hydrogen protective gas mixture was used to raise its oxidizing potential. The technique was applied to a classical dual-phase steel (0.15% C, 1.5% Mn, 0.45% Si, 0.05% Al. . .) that was annealed for 60 s at 800-810• C in protective atmospheres of nitrogen and 5% hydrogen with water vapour contents ranging from 10 to 6000 ppm.Post-annealing surfaces were characterized by x-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS) and scanning Auger microscopy (SAM). In situ XPS analyses were carried out right after simulation annealing in the preparation chamber connected to the spectrometer, never returning the specimens to air. This made it possible to identify in a reliable way the elements that segregated to the surface during the treatment, and to determine their corresponding oxidation states. On the other hand, the high sensitivity of SIMS was taken advantage of to assess oxide in-depth concentration profiles (SiO 2 , Al 2 O 3 , FeO) as a function of the annealing conditions, and SAM was used to characterize the corresponding oxide particle morphology.External selective oxidation was thus shown to decrease with increasing water vapour contents in the atmosphere (from 80 to 6000 ppm), whereas internal oxidation increases drastically to ∼4 µm below the free surface. At 10 ppm of H 2 O the oxygen partial pressure is very low and the external selective oxidation results in a thin, but almost complete, coverage of the steel surface. Consequently, metallic iron cannot be observed at the surface, thus hampering hot-dip galvanizability, unless the water vapour content is raised to 6000 ppm. Various surface morphologies were observed and discussed.In the authors' opinion, basic investigations of this type are an indispensable first step to improving the response of highly alloyed steels (dual-phase, TRIP) to hot-dip galvanizing.

Internal Oxidation during Intercritical Annealing of CMnSi TRIP Steel

“…1,2) The external oxides on the surface and internal oxides in the subsurface of intercritically annealed TRIP steels have been studied previously by Scanning Electron Microscopy (SEM), X-ray Photo-electron Spectroscopy (XPS), Secondary Ion Mass Spectroscopy (SIMS), Energy Dispersive Spectrometry (EDS) and Glow Discharge Optical Emission Spectroscopy (GDOES). [3][4][5] A review of the observed oxides using these various micro-analytical methods is reported in Table 1. These micro-analysis techniques used for oxide characterization on TRIP steels usually give an average oxide layer composition at the macro scale.…”

Formation of Surface and Subsurface Oxides during Ferritic, Intercritical and Austenitic Annealing of CMnSi TRIP Steel

“…Internal selective oxides have been studied by means of XPS, SIMS and Glow Discharge Optical Emission Spectroscopy (GDOES). 3,4) A review of the oxides observed on TRIP steels using these various micro-analytical methods are reviewed in Table 1. The methods used for oxides characterization usually give the average composition on a macro scale.…”

Efeito Do Ponto De Orvalho Da Atmosfera Dos Fornos De Recozimento Da CGL Na Qualidade Do Revestimento Ga Em Aço Bake Hardenable

“…Este resultado está de acordo com a teoria de Wagner (1) para oxidação seletiva interna/ externa, uma vez que, em POs mais elevados, a quantidade de oxigênio na atmosfera é maior, resultando em maior concentração deste elemento no interior do aço e, consequentemente, a sua oxidação interna. Após deconvolução e indexação dos picos Mn2p3/2, verificou-se que, exceto para o PO = -30°C, o manganês encontra--se na superfície desse aço sob a forma de óxidos simples (MnO ou Mn 3 O 4 ), (2)(3)(4)(5)(6)(7)(8) assim como formando óxidos mistos com outros elementos, (5,7,8) conforme as proporções da Figura 1b. Assim, para o aço recozido com PO = -60°C tem-se a maior presença de manganês na forma de óxidos mistos.…”

“…Em POs elevados, a difusão de manganês para a superfície é inferior, possibilitando sua oxidação mais intensa em regiões mais internas (0,06 µm a partir da superfície). Estas observações estão de acordo com Eynde, Servais e Lamberigts, (4) que constataram que a oxidação externa de manganês é desfavorecida em altos POs.…”