Search

There are many industrial processes that require intimate contact between an alloy and a corrosive gaseous environment at high temperatures. The alloys used under these conditions are designed to form [...]

Isothermal heat treatments below the martensite start temperature are carried out in a 0.25C‐1.4Mn‐1.4Si‐0.32Mo steel (in wt%). The microstructural observation reveals a combination of tempered lath and plate martensite, accompanied by bainite and retained austenite. The temperature variation of the austenitic carbon content under different constrained equilibrium models is calculated and compared with experimental measurements. Neither of the existing models seems to predict the behavior of the measured austenitic carbon content in the temperature range studied. The results suggest that the diffusional formation of bainite governs the carbon content of austenite at temperatures nearby the MS. [ABSTRACT FROM AUTHOR]

The influence of order phenomena on the electrical and magnetic properties of a series of Fe-Si alloys is analyzed. Electrical resistivity and hysteresis loop measurements are performed on alloys after different thermal treatments, including annealing and quenching from several temperatures. Mossbauer spectroscopy and differential scanning calorimetry were used to characterize both the type of order existing in the alloys and the order-disorder transition temperature. For the highest quenching temperature, the highest magnetic losses are measured due to internal stresses and disordering induced during quenching. High electrical resistivity is obtained by high-temperature quench only when the Si content was over 10.6 at.%. This occurred due to an order-disorder transition, which reduces the B2 degree of order present in the alloy. On the other hand, disordering appears to be detrimental for the excess losses due to the creation of antiphase domain boundaries. Index Terms--Calorimetry, electrical and magnetic properties, electrical steel, high-Si steel, Mossbauer spectroscopy, order-disorder.

Hot dipping and diffusion annealing is an alternative production process to obtain steel with high silicon contents while avoiding rolling problems. Surface alloying with Si and Al is achieved on a low-Si steel substrate ([approximately equal to] 3%Si) by hot dipping in a hypereutectic Al-27%Si molten bath. To obtain a sufficient amount of Al and Si in solid solution over the thickness, a diffusion annealing treatment is performed after hot dipping. A diffusion annealing at 1250 [degrees]C allows the homogenization of the composition obtaining a concentration of 6.3% Si and 4.5% Al over the thickness. The evolution of microstructure, crystallographic texture, and magnetic properties in each step of the process is reported. After dipping and annealing, the losses decreased proportionally with the total Si-Al concentration achieved during the process. Values as low as 0.6 W/kg at 50 Hz (1T) and 10 W/kg at 400 Hz (1T) have been obtained in the experimental materials with high Si + Al content and 0.35-mm thickness. Index Terms--Alloys, annealing, diffusion process, ferromagnetic materials, materials processing.

A study is conducted to assess the influence of order phenomena on the magnetostriction of high Fe-Si alloys for electrical applications. The magnetostriction of high silicon electrical steels in the range of 4 to 6 wt. % Si is studied with regards to the effect of processing and thermal treatment.

Isothermal heat treatments below the martensite start temperature are carried out in a 0.25C‐1.4Mn‐1.4Si‐0.32Mo steel (in wt%). The microstructural observation reveals a combination of tempered lath and plate martensite, accompanied by bainite and retained austenite. The temperature variation of the austenitic carbon content under different constrained equilibrium models is calculated and compared with experimental measurements. Neither of the existing models seems to predict the behavior of the measured austenitic carbon content in the temperature range studied. The results suggest that the diffusional formation of bainite governs the carbon content of austenite at temperatures nearby the MS. [ABSTRACT FROM AUTHOR]