Rapid annealing effects on microstructure, texture, and magnetic properties of non-oriented electrical steel

Abstract

This paper presents a classic process-structure-properties approach for optimizing the magnetic properties of electrical steels. Cold-rolled non-oriented electrical steel (Fe; 0.001 wt% C; 0.2 wt.% Mn; 1.3 wt% Si) was subjected to extremely short 3-30 seconds annealing cycles in a range from 880°C to 980°C with a heating rate varying from 15°C to 300°C/sec. The resulting microstructure was studied by means of optical microscopy and X-ray orientation distribution function analysis. Recrystallized grains were refined with increased heating rate, caused by the nucleation rate increase, which is faster than the growth rate due to rapid heating. The optimal grain size of 60 to 80 mm in terms of magnetic properties was obtained by increasing the annealing temperature range to 920°C to 940°C with a higher heating rate of 300°C/sec and an annealing time of 6 to 9 seconds. With the heating rate increase, the characteristic {111} recrystallization fiber of cold-rolled steel was depressed, but the beneficial {110}<001> Goss texture component was significantly strengthened. The recrystallized grain size and texture were enhanced by rapid annealing, and, as a result, the magnetic properties of non-oriented electrical steel improved.

Improving the Magnetic Properties of Non-Oriented Electrical Steels by Secondary Recrystallization Using Dynamic Heating Conditions

“…In contrast to the scientific works [26,27,28], addressing the use of unconventional cold rolling schemes (e.g., with different rolling angles to the rolling direction) and subsequent conventional heat treatment with low heating rate, we have proposed a combination of a conventional temper rolling process for the steel after primary recrystallization with a subsequent final, unconventional second annealing treatment at dynamic heating conditions, i.e., using extraordinary high heating rate. On the other hand, other research studies [29,30] have clearly indicated a beneficial effect of rapid annealing on the increase of average grain size and significant improvement of crystallographic texture of electrical steel after strip-casting and cold rolling process.…”

Diffusion behavior of 3.2% Si-grain-oriented steel coated with Al by plasma vapor deposition

“…Owing to the difference in the diffusion coefficients between Fe and Al, additional vacancies are generated, producing Kirkendall voids by their coalescence. The formation of voids in different steels has been observed by other groups [2,[5][6][7] after annealing at different temperatures and durations. To reduce the formation of Kirkendall voids, we controlled the holding time and heating rate because both of these annealing parameters control the diffusion behavior of Fe and Al.…”

“…Because of the world energy crisis, research on electrical steels has recently been focused on the improvement of energy efficiency, and this research has demonstrated that the addition of Si, Al, or both to conventional Fe-3.2% Si steel can increase the steel's resistivity and reduce its energy loss (i.e., increases its energy efficiency) [1][2][3][4][5][6][7][8][9][10][11].…”

“…When Al-Si alloy was used as the coating material, several intermetallic phases such as Fe x Si y Al z were formed [17,18]. Furthermore, it has been reported that during diffusion annealing, Kirkendall voids were horizontally formed near the surface, and in the case of intermetallic-phase formation, Kirkendall voids were formed among the intermetallic phases of Fe and Al [2,[5][6][7]. These phenomena increase core loss because they interrupt the movement of magnetic domains as the magnetic field changes, but little is known about the formation of intermetallic phases or Kirkendall voids during diffusion annealing.…”

A novel laboratory set-up for investigating surface and interface reactions during short term annealing cycles at high temperatures

“…Hence, the necessity to study short term metal/gas reactions at high temperatures under welldefined atmospheres mainly results from these industrial demands and still represents an important research discipline. 7 Consequently, an accurate definition of the reaction conditions is vitally important to generate a well-defined environment for materials testing and to meet the interests of modern steel research by exactly reproducing industrial process conditions.…”