No abstract

The microstructures were observed in C-Mn steel and statistical analysis of the inclusions produced when trace amounts of rare earth were added to the steel. The results show that the content of intragranular acicular ferrite decreased in the order of being treated with La þ Ce/La/Ce in C-Mn steel after the treatment of different kinds of rare earths. The optimum mass ratio of La and Ce for La þ Ce combined treatment is 3:1.The best incubation time after Le þ Ce (3:1) treatment is 5 min. The size of inclusion nuclei favouring intragranular acicular ferrite nucleation concentrates in the range of 1-4 mm. The disregistries between rare earth inclusions and a-Fe are small, which plays an important role in rare earth inclusions inducing intragranular acicular ferrite nucleation.

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.

No abstract

No abstract

The effect of different Ce content on the hot ductility of C-Mn steel containing arsenic was investigated at the temperature ranging from 700 to 1100°C conducting Gleebel-1500 thermal-mechanical simulator. The reduction of area (RA%) was used to evaluate the hot ductility. The 0.16 mass% As widened the ductility trough range and especially, decreased the RA value at 850-950°C. Conversely, adding Ce in the steel could remedy the arsenic-induced hot ductility deterioration. Moreover, with the increase of Ce content from 0 to 0.035 mass%, the RA value at 800-950°C significantly increased, compared to that of the arsenic steel. When the content of Ce reached 0.027-0.035 mass%, the RA value at 800-850°C was even higher than that of steel without As. Besides, the corresponding fracture morphology was changed from intergranular feature to ductile and/or interdendritic feature. Grain refinement by Ce addition, the formation of arsenious rare earth inclusions and grain boundary segregation of Ce were considered to improve the hot ductility of the steel containing As.Keywords: arsenic and cerium / hot ductility / austenite grain refinement / arsenious rare earth inclusions / grain boundaries *

No abstract

No abstract