Surface reactions occurring on Fe-based alloys submitted to heat treatments under protective or reactive atmospheres

Abstract

Surface condition control is particularly important in industrially processed materials, because apparently minor surface phenomena involving selective oxidation or low concentration element segregation can modify the surface reactivity and alter the material's response to downstream treatments. These phenomena, therefore, must be investigated by the most sophisticated simulation and surface analysis techniques, to ensure that accidental contamination is avoided. The paper reports on combined XPS, AES and SIMS spectroscopy to assess quantitatively the surface modifications taking place in Fe-based alloys during annealing treatments under various atmospheres.A new method has been developed from the equations initially put forward by Seah to assess element and compound surface coverage, based on experimental XPS peak intensities, computed inelastic mean free paths and atom densities. It has been applied successfully to annealed specimens made of Fe, Fe-0.5%Si binary alloy and ultralow carbon (ULC) deep-drawing steel.

Effect of the presence of alloying elements in interstitial-free and low-carbon steels on their surface composition after annealing in reducing atmospheres (dew point=−30 °C)

“…This binding energy is typical of silicon as SiO 2 . [9,10] Figure 8 compares the Mn2p 3/2 high-resolution spectra obtained on the outer surface of the various IF and LC steels after the annealing process (continuous line) with those obtained after cold rolling (dotted line). The Mn2p 3/2 highresolution spectra contain one single component with a binding energy of 641.5 eV.…”

“…The presence of hydrogen together with nitrogen in the formulation of the annealing atmosphere usually reduces the slight oxidation that takes place on the steel surface during rolling, but often fails to prevent the segregation of alloying elements or more active impurities present in the bulk steel and the possibility of precipitation in oxide form during annealing. [1][2][3][4][5][6][7][8][9][10][11][12] Numerous studies have considered the segregation of Si [2,[8][9][10][13][14][15][16][17] and P [1][2][3][18][19][20][21][22][23][24][25][26][27][28][29] during the annealing process and the effect that the presence of these elements on the steel surface has on the subsequent growth of the zinc coating in hot-dip galvanizing and galvannealing processes. [12,[30][31][32][33] Other elements such as Mn have received less attention, as is noted by Mintz.…”

“…These long annealing times are necessary to obtain a sufficient amount of precipitates on the steel surface in order for their characterization by conventional techniques: scanning electron microscopy (SEM)/energy-dispersive X-ray (EDX) analysis or transmission electron microscopy (TEM). Far fewer researchers [8][9][10][11][12] use annealing cycles that are similar (close to 1 minute) to those used during galvanizing in commercial lines. [6] In recent years, highly promising results are being obtained with the Auger electron spectroscopy (AES) technique.…”

“…[2,6,7,[17][18][19][21][22][23][24][25][26][27][28][29]37] The X-ray photoelectron spectroscopy (XPS) technique is also proving to be an efficient and convincing tool for studying the segregation phenomena that take place on steel surfaces during annealing processes. [2,4,[8][9][10][11][21][22][23]38] A notable advantage of this last technique is that it provides information on the chemical state of the elements present, though it presents the limitation of its low lateral resolution. This work seeks to establish possible relationships between the bulk composition of the IF and LC steels and the contents of segregated alloying element observed by XPS on the surface of the annealed steels.…”

In situ surface analysis of annealed Fe-1.5%Mn and Fe-0.6%Mn low alloy steels

“…To accurately reproduce the surface chemistry of the steel sheets after a typical annealing, it is necessary to work in situ [2,3,4,5]; this means the use of analytical facilities directly attached to the reactor in which the annealing treatments are performed. In this way, the annealed surfaces do not suffer any kind of contamination (hydrocarbons) or oxidation (native oxide formation) as a result of air contact after the annealing, and the conditions present in the industrial devices are accurately reproduced.…”