Evolution of Power Losses in Bending Rolled Fully Finished NO Electrical Steel Treated under Unconventional Annealing Conditions

Abstract

Currently, the non-oriented (NO) iron-silicon steels are extensively used as the core materials in various electrical devises due to excellent combination of their mechanical and soft magnetic properties. The present study introduces a fairly innovative technological approach applicable for fully finished NO electrical steel before punching the laminations. It is based on specific mechanical processing by bending and rolling in combination with subsequent annealing under dynamic heating conditions. It has been revealed that the proposed unconventional treatment clearly led to effective improvement of the steel magnetic properties thanks to its beneficial effects involving additional grain growth with appropriate crystallographic orientation and residual stress relief. The philosophy of the proposed processing was based on employing the phenomena of selective grain growth by strain-induced grain boundary migration and a steep temperature gradient through the cross-section of heat treated specimens at dynamic heating conditions. The stored deformation energy necessary for the grain growth was provided by plastic deformation induced within the studied specimens during the bending and rolling process. The magnetic measurements clearly show that the specimens treated according to our approach exhibited more than 17% decrease in watt losses in comparison with the specimens treated by conventional heat treatment leading only to stress relief without additional grain growth.

Neighbor-Affected Orientation Rotation in the Grain Boundary Region

“…Non-oriented silicon steel is an important magnetic material widely used in electrical equipment cores. The λ texture (<001>//ND, normal direction) is beneficial for magnetic properties of non-oriented silicon steel [ 7 , 8 ], but it is not a stable ending orientation in rolling [ 9 , 10 , 11 ] due to the divergent rotation of scattered λ orientations. Therefore, controlling the rotation of scattered λ orientations at grain boundary regions is always a challenge to optimize λ texture for non-oriented silicon steel.…”

Analysis of the Reasons for the Tearing of Strips of High-Strength Electrical Steels in Tandem Cold Rolling

“…To obtain a suitable texture and microstructure, precise control of the process is necessary during all the individual manufacturing steps. This involves adjusting the chemical elemental composition during the steel making, tuning the appropriate temperature and reduction control during hot rolling, controlling the temperature during hot band annealing, controlling the temperature and deformation during cold rolling, and controlling the heating rate and temperature during final annealing [ 12 , 13 , 14 ].…”

Joining of the Laminated Electrical Steels in Motor Manufacturing: A Review

“…The addition of silicon to iron results in a decrease in coercivity and an increase in resistivity [ 12 , 18 , 19 , 20 , 21 , 22 ]. Furthermore, the reduction of the sheet thickness results in the reduction of the eddy current loss in the electrical steel when put in the alternating magnetic field environment [ 14 , 23 , 24 ]. The stator and rotor in a motor are made of hundreds of laminated and joined thin electrical steel sheets [ 25 ], which could reduce the eddy current loss and improve efficiency.…”