In order to depress the embrittlement induced by grain boundary segregation of arsenic in steel, the effect of Ce addition on the formation of arsenious inclusions and arsenic concentration at grain boundaries were systematically investigated in iron melts. The results showed that different types of arsenious rare earth inclusions were formed with different Ce content. As Ce content increased from 0.037 to 0.095 wt%, the dominant inclusion in the melt was changed from the Ce-S-O inclusion fully coated by Ce-S-As inclusion to the Ce-S-As inclusion completely covered by Ce-As inclusion. Simultaneously, the single Ce-S-As and Ce-As inclusions were also detected when Ce content was more than 0.055 wt%. The amount and average size of inclusions increased with increasing Ce content. Transmission electron microscope analysis indicated that the Ce-As inclusion was the CeAs phase, which was formed during solidification process. Furthermore, concentration of arsenic on grain boundaries after adding Ce was decreased to the level of the matrix.

Effect of Cerium on Characteristic of Inclusions and Grain Boundary Segregation of Arsenic in Iron Melts

Medium-energy ion scattering study of arsenic and sulfur segregation to the Fe-9% W(100) surface

High-resolution medium-energy ion scattering (MEIS) was used to investigate the segregation of arsenic and sulfur on the (100) oriented surface of a body-centered cubic Fe-9 wt %W(100) single crystal containing 53 wt-ppm As and 10 wt-ppm S. At temperatures ranging from 800 to 1100 °C, both segregants compete for the available surface sites. Arsenic segregation dominates at temperatures around 800 °C where maximum As surface concentrations of θAsmax=0.40 were found. S segregation is most pronounced at temperatures around 1000 °C with θSmax=0.43. MEIS shows the segregated As (S) atoms to be arranged 1.27 A (1.22 A) above the topmost metal layer. The metal-to-metal layer distances show an oscillatory behavior with an expansion of the first to second metal layer (+0.05 A). With As and S on the surface, there is a strong W depletion of the topmost three metal layers.

Competition of arsenic and sulfur segregation on Fe-9%W(100) single crystal surfaces

The surface of polycrystalline iron covered by segregated arsenic, phosphorus and sulphur was analysed in a combined electron spectroscopic study by means of Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The saturation coverage of arsenic at 1033 K was determined as 0.33±0.02 monolayer. Sulphur, arsenic and phosphorus segregate in competition. A relation giving the surface coverage from the XPS intensity of adsorbed element is deduced from the experiments and is also calculated. Experimental and calculated values are found to be in relatively good agreement.

Surface segregation of arsenic in iron

The segregation kinetics of surface-active, residual elements are investigated in an in situ study of annealing scrap-based silicon electrical steel sheet where the arsenic (As) surface segregation is highlighted. During annealing in the temperature range of 300–950 °C, different kinds of interactions between the segregated residual elements were observed. Attractive interactions between the segregands produced co-segregation, e.g., between Sn and Sb, whereas repulsive interactions resulted in site competition, e.g., between Sn and As. These competing interactions are strongly time dependent. In spite of there being twice as much Sn compared to As in the bulk material, the As prevailed in the surface enrichments of the polycrystalline silicon steel at 950 °C. The intensity of the As surface segregation in the temperature range 800–950 °C is proportional to the calculated amount of γ-austenite phase in the (α + γ) steel matrix. The detected phenomenon of the As versus Sn site competition could be valuable for the texture design and surface engineering of silicon steels with a thermodynamically stable two-phase (α + γ) region.

A. Carraretto

Papers

Evidence of arsenic segregation in iron