ASTM A677-16 Specification for Nonoriented Electrical Steel, Fully Processed Types

ASTM A677-16 Specification for Nonoriented Electrical Steel, Fully Processed Types Scope:

Electrical steel is usually manufactured in cold-rolled strips less than 2 mm thick. These strips are cut to shape to make laminations which are stacked together to form the laminated cores of transformers, and the stator and rotor of electric motors. Laminations may be cut to their finished shape by a punch and die or, in smaller quantities, maybe cut by a laser, or by wire EDM.

The primary use of this steel, which is produced to specified maximum core-loss values for magnetic devices, is commercial power frequency (50 and 60 Hz) applications. During mill processing, desirable core-loss and permeability characteristics are developed, therefore extra heat treatment by the user is typically not required.

In ASTM A677-16, electrical steel made without special processing to control crystal orientation, non-oriented steel, usually has a silicon level of 2 to 3.5% and has similar magnetic properties in all directions, i.e., it is isotropic. 

Non-grain-oriented electrical steel (NGOES) is mainly used in rotating equipment like electric motors, generators, and over-frequency and high-frequency converters. Grain-oriented electrical steel (GOES), on the other hand, is used in static equipment such as transformers.

For ASTM A677-16, the values in SI units are taken as standard.

Specification for Non Oriented Fully Processed Electrical Steel

Ordering Information 
As per ASTM A677-16, orders for material should include the following information to describe the desired material adequately:

1. ASTM number.
2. Core-loss type number.
3. Surface coating type.
4. Limitations in coil size or lift weights.
5. Thickness, width, length, and the total weight of the ordered item.
6. Application: The user should provide the producer with as much information as possible about the intended application so that the producer can fabricate the most suitable material.
7. Special requirements or exceptions to the specification.

Manufacture 

Typical Melting and Casting: 

Fully processed electrical steels can be made by basic-oxygen, electric-furnace, or other steelmaking practices as per ASTM A677-16.

The primary use of this steel, which is produced to specified maximum core-loss values for magnetic devices, is commercial power frequency (50 and 60 Hz) applications. During mill processing, desirable core-loss and permeability characteristics are developed, therefore extra heat treatment by the user is typically not required.

They have low carbon, usually less than 0.020 %. The main alloy used is silicon, but aluminum may be sometimes used in place of or in addition to silicon. Sulfur is less than 0.025 %; and is usually the lowest in the numbered types indicating the lowest core loss.

Other elements such as phosphorus, copper, nickel, antimony, and tin are present only in residual amounts except in the higher numbered core-loss types.

Typical Rolling and Annealing:

The processing sequence for fully processed steel includes hot-rolling, annealing, pickling, cold-rolling, and decarburizing annealing. 

Magnetic Properties 

The magnetic properties of electrical steel are dependent on heat treatment, as increasing the average crystal size decreases the hysteresis loss. In ASTM A677-16, hysteresis loss is determined by a standard Epstein tester and, for common grades of electrical steel, may range from about 2 to 10 watts per kilogram (1 to 5 watts per pound) at 60 Hz and 1.5 tesla magnetic field strength.

In ASTM 677-16, fully processed electrical steel is usually delivered with an insulating coating, full heat treatment, and defined magnetic properties, for applications where punching does not significantly degrade the electrical steel properties. Excessive bending, incorrect heat treatment, or even rough handling can adversely affect the electrical steel’s magnetic properties and may also increase noise due to magnetostriction. 

The size of magnetic domains in sheet electrical steel can be reduced by scribing the surface of the sheet with a laser, or mechanically. This greatly reduces the hysteresis losses in the assembled core.

Specific Core Loss: Each core-loss type of electrical steel is identified by a maximum core-loss limit. 

Permeability: The permeability at all inductions should be as high as possible, consistent with the required core-loss limits that govern the grade. 

Specific Exciting Power: The RMS exciting power required for the excitation of a particular type of electrical steel is frequently useful to the user. 

Magnetic Aging: Although steel sold with this specification is considered non-aging, the maximum core-loss values are based on tests of freshly sheared specimens. 

Surface Insulation Characteristics 

Nonoriented electrical steels usually have a smooth surface finish and a thin layer of surface oxide with sufficient insulating ability for most small cores. 

Applied Coatings:

Electrical steel is usually coated to increase electrical resistance between laminations, reducing eddy currents, providing resistance to corrosion or rust, and acting as a lubricant during die-cutting. There are various coatings, organic and inorganic, used in ASTM A677-16, and the coating used depends on the application of the steel. The type of coating selected depends on the heat treatment of the laminations, whether the finished lamination will be immersed in oil and the working temperature of the finished apparatus. 

Mechanical Requirements 

Lamination Factor: For ASTM A677-16, the lamination factor should be as high as possible. 

Ductility: The material should be as ductile as possible. 

Hardness: The hardness of these materials can be determined using Test Methods E18 or Test Method E92. Hardness is affected by chemistry and by the grain size and microstructure of the final product. 

Workmanship, Finish, and Appearance 

Flatness: No specific limits for flatness have been established. Flatness should be suitable for the intended application. The user should inform the producer of any requirements for a degree of flatness. Processes used to improve flatness may affect magnetic and mechanical properties. 

Surface Imperfections: The surface should be clean and free of manufacturing defects such as holes, blisters, slivers, indentations, and so forth, which would interfere with its functioning. 

Sampling  

The producer should assign a number to each test lot for identification. The test lot shall not exceed 20,000 lb (9100 kg) in weight. As per ASTM A677-16, test samples should be obtained after final mill heat treatment or other operations that can influence the magnetic properties of fully processed electrical steel. 

The values given in SI units should be taken as standard. Parenthetical values are mathematical conversions to (cgs-emu and inch-pound) units, which are solely presented for informational purposes and are not to be taken as standards.

Specimen Preparation

The Epstein test specimen should be in the as-sheared condition with one-half of the test strips sheared parallel to and one-half transverse to the rolling direction in accordance with Practice A34/A34M. 

Test Methods 

In ASTM A677-16, the required tests for core loss to determine the core-loss grade, and other magnetic tests when made, should be in accordance with the Test Method A343/ A343M. 

Certification  

Each package of coils should have attached to its outside wrappings, a tag showing the user’s order number, specification number, grade designation, coating or surface type-designation, thickness, width, weight, and test lot number. 

Each wide coil should have the specification number, grade designation, coating or surface-type designation, thickness, width, weight, and test lot number marked on the outer surface of the coil itself, as per ASTM A677-16.

In a lift of narrow coils, each narrow coil in the package should be tagged with the specification number, grade designation, coating or surface-type designation, thickness, width, and test lot number. 

Packaging 

Methods of packaging, loading, and shipping are done in accordance with the standard A700. 

Conclusion:

ASTM A677-16 covers specification which details all the requirements that flat-rolled nonoriented fully processed electrical steel must comply with.