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Product Description

Grain oriented electrical steels (GOES) are iron-silicon alloys that were developed to provide the low core loss and high permeability required for efficient and economical electrical transformers. GOES is the most energy efficient electrical steel and used in transformers where energy conservation is critical.

We have been a global innovator in the most efficient GOES products, since first inventing and introducing them in 1926. GOES is a critical material to the well-being of our electric grid. As the only domestic producer of GOES, we have the dedicated equipment, advanced manufacturing processes, and experienced employees to keep our homes and businesses powered.

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Product Applications

Available Grades

Grain-Oriented Electrical SteelDownloads

LITE CARLITE® and Mill Anneal

CARLITE®

TRAN-COR® H

TRAN-COR® X

Product Details

CARLITE 3 Surface Insulation

AK Steel’s TRAN-COR H products are supplied with CARLITE 3 insulative coating, an inorganic coating equivalent to ASTM A976 C-5. CARLITE 3 insulation is ideal for materials that will be used in the form of sheared laminations for power transformers and other apparatus with high volts per turn. In addition to supplying all the benefits of C-5 insulation, CARLITE 3 provides other important advantages which include:

  • Potential for reduced transformer building factor from added resistance to elastic strain damage.
  • Potential for reduction of magnetostriction related transformer noise.
  • High stacking factor.
  • Easy assembly due to smoothness of coating (low coefficient of friction).

LITE CARLITE Surface Insulation

AK Steel's LITE CARLITE GOES products are supplied with CARLITE 3 insulative coating, an inorganic coating equivalent to ASTM A976 C-5. LITE CARLITE is ideal for materials that will be used in distribution transformers and other magnetic apparatus with low to moderate volts per turn where the cores are stress-relief annealed. In addition to supplying the basic benefits of C-5 insulation, LITE CARLITE provides other important advantages which include:

  • Potential for reduced transformer building factor from added resistance to elastic strain damage after core or lamination annealing.
  • Potential for reduction of magnetostriction related transformer noise.
  • High stacking factor.
  • Easy assembly due to smoothness of coating (low coefficient of friction).

Stress-Relief Annealing of CARLITE 3/LITE CARLITE Products

In wound or formed cores, there is a substantial amount of both plastic and elastic strain which degrades the magnetic properties of the electrical steel. When the strain is low, the strain will be elastic and removal of the load or restraining force will permit the steel to return to essentially a stress-free condition. However, if the steel is plastically deformed, it will retain stresses even after the load is removed. In these circumstances, stress-relief annealing is needed to return the material to a stress-free condition.

While a thermal flattening treatment is part of the process for application of CARLITE 3 insulation, CARLITE 3 insulated GOES products require stress-relief annealing to fully develop the magnetic properties. The annealing should be conducted for a suitable time and temperature in a protective atmosphere to prevent adverse changes to the steel chemistry. Conditions that create excessive thermal gradients should be avoided since these can reintroduce stress and/or distort the shape of the steel.

While a soaking temperature of 1450 - 1500 °F (790 - 820 °C) for a time of at least 15 minutes is recommended, stress-relief annealing should be conducted for the shortest time possible without producing excessive thermal gradients. It is recommended that higher stress-relief annealing temperatures be employed only after experimentation shows it is clearly beneficial. Higher annealing temperatures can result in "sticking" and/or "flaking" of the CARLITE coating.

Proper specification of annealing time must take into account the size and weight of the finished cores being annealed, the degree of exposure to heating and cooling during annealing and the amount of plastic deformation imparted on the core during fabrication. The furnace heat input should be adjusted so that the heating rate is not too great when approaching the soaking temperature. Forcing cores to heat rapidly to soak temperate should be avoided because incomplete annealing and/or thermal distortion is likely. If the cores are not well exposed, the length of the soaking period should be extended.

Proper specification of the cooling time requires similar consideration. It is recommended that the rate of cooling after annealing does not exceed 185 °F (100 °C) per hour from soaking temperature 1400 °F (750 °C) and not exceed 330 °F (180 °C) per hour to a temperature of 1200 °F (650 °C). Steel cores or laminations can usually be removed from the protective atmosphere at 600 - 700°F (325 - 375 °C) without ill effect.

The qualities of the CARLITE 3 coating are best maintained or enhanced when stress-relief annealing is conducted in an atmosphere that is neutral or slightly oxidizing to iron. An oxygen-free atmosphere or a nitrogen-hydrogen mixture containing 5% hydrogen or less is recommended for batch annealing where exposure times in excess of one hour are typical. Vacuum annealing of CARLITE 3 insulated materials is not recommended.

Domain Refinement

TRAN-COR H CARLITE high permeability electrical steels offer an outstanding degree of grain orientation. This combination of higher permeability with low residual stress offers the potential for lower core losses and less noisy transformer core structures, particularly at higher operating inductions, when compared to conventional grain oriented electrical steels. The core loss characteristics are further enhanced in the TRAN-COR H CARLITE DR (Domain Refined) products where laser scribing is employed. In this process, a precisely focused laser beam is rapidly scanned across the steel surface. The micro-strain imparted into the material forces the pre-existing magnetic domains to subdivide. The finer domain structure reduces the distance that the domain walls must move during AC magnetization, thereby reducing eddy current losses. The result is far lower core loss than possible with conventional grain oriented electrical steels of comparable thickness.

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