M-6 Steel Laminations

M6 29 ga. Grain Oriented Electrical Transformer Steel Lamination.

All of EDCOR Electronics Corporation's transformers that have steel core lamination are made with M6 29 Gauge - 0.014" (0.355 mm) Grain Orientated Electrical Transformer Steel Lamination, unless otherwise specified by customer, and is RoHS compliant. This steel is used in audio amplifiers, current, output, power transformers; chokes and saturable reactors; and ferro-resonant regulators. The squared hysteresis loop iron-silicon alloy was expressly developed to provide lower core loss with higher permeability in the rolling direction. Grain oriented laminations are supplied in the stress relief annealed condition. The elementary patterns of the crystals in the material are "oriented", or so arranged that the axis of easiest magnetization is nearly parallel and aligned in the direction of rolling. The alignment is accomplished by special cold-rolling and annealing processes. This allows the product to withstand more severe vibration and shock and enables the following:

  1. Lower core losses as a consequence of design.

  2. Higher initial permeability.

  3. Higher permeability at higher inductions.

  4. More stable VA/Temperature relationship over a wide range of ambient temperatures.

Our "EI" laminations are tested under standards set up by the ASTM A-346.

Technical Specs.

Specific Gravity
Grams per cu. cm. (A.S.T.M.)
Vol. Resistively
Microhms per cm. cube
Saturation Induction (Gauss) 20.300
Max. aging - Core Loss % 5
Coercive Force - (Oersteds) Annealed 0.12
Hysteresis Loss at 10 Kilogauss
(Ergs/cycle/cu. cm.)
Typical DC Permeability Value
Max. 16,000 Gauss
10,000 Gauss
1,000 Gauss
100 Gauss



Core Loss

Epstein-based core loss values for grain oriented steels are usually reported in the 100% with-grain (parallel to the rolling direction) condition. For lamination applications, particularly for E and I configurations, reference should also be made to core loss values with 5% with-grain, 25% cross-grain condition. Maximum core loss limits are shown in the following table.

Maximum Core Loss Limits for Grain Oriented M-6
(After Stress Relief Anneal)
Condition 29 Gauge - .0140"
100% with grain 0.66



Permeability refers to the relative ease with which a material will accept a magnetic field, compared to air with a permeability of 1.

One of the major advantages of laminations that are annealed after stamping is that the highest possible permeability is achieved. This translates into the lowest possible exciting powers (volt-amps per pound) for AC applications.

Typically, minimum peak permeability is 2000 for semi-processed, annealed last grades (measured at 1.5 Tesla, 60 Hertz) for cold rolled and non-oriented silicon grades.

Minimum peak permeability for fully processed grades is significantly less than 2000 and is a function of both gauge and grade.

As a general rule, permeability increases as thickness increases, and decreases with increasing alloy content or higher grades. As a result, some thin high alloy grades; e.g., 29 gauge M19, may exhibit permeability values less than 2000 for semi-processed, and less than 800 for fully processed grades.

The units for permeability are dimensionless because they represent a relative value. Some practices refer to gauss/oersted as the units for permeability.

Saturation Induction

Saturation induction can be important and can limit overall performance in some applications. As a general rule, saturation induction decreases with increasing alloy content, or grade. For magnetic steels, pure iron has the highest saturation induction (2.3 Tesla). The lowest saturation induction levels (2.10 Tesla) are found in the highest alloy grades M19 and M15, while grain oriented M6 exhibits saturation induction levels of 2.03 Tesla.

Surface Roughness

Surface roughness is measured by a probe which records and averages the height-to-height variations within a fixed sample length, generally in accordance with ANSI/ASME B46. The average of the surface profile heights is the arithmetic average AA).

Peak counts can also be used in some applications to describe surface textures and roughness.

Surface Roughness
Grade Surface Roughness
Micro inches AA* Microns AA*
Cold Rolled Motor Lamination Grades 50 to 90 1.27 to 2.25
Grain Oriented and Non-Oriented Silicon Grades 5 to 40 0.13 to 1.02
*AA =arithmetic average


Burr Tolerances

Most high quality laminations use tungsten carbide dies with tight tolerances to ensure that all aspects of the punched edges have minimum burrs.

Laminations are usually wired so that all of the burrs follow the same direction, allowing for nesting of laminations and maximum stacking factor without gaps. Assemblers who reverse (rather than rotate) lamination stacks to compensate for gamma should be aware that mismatch of burr directions can lead to gaps in the stack which may be undesirable.

Examples of burr tolerances are shown in the following table.

Examples of Burr Tolerances
Nominal Thickness of Steel, Inches Burr Tolerance (Max), Inches
0.0140 0.0020
0.0185 0.0025
0.0250 0.0030

Stacking Factors

The stacking factor is the ratio of the actual volume of steel in a stack, not including air or insulating materials, compared to the measured dimension of the stack. The stacking factor is affected not only by the surface roughness of the laminations, but also by the pressure applied to the stack and the method of assembly. Examples of typical stacking factors are found in the following table:

Typical Stacking Factors
Type of Material Surface Roughness, micro inches AA Butt Stacked 1:1 Interleaved
Grain Oriented 5 to 40 0.95 to 0.99 0.94 to 0.98
Non-Oriented Silicon 5 to 40 0.95 to 0.99 0.94 to 0.98

Surface Insulation

Description of Coatings

The primary function of a coating on a lamination is to provide interlaminar resistance for reduction of stray losses. The resistance of the coating normally depends on both the thickness of the coating and its chemical composition. Variation can be expected in coating resistance primarily due to variation of coating thickness, usually in the range 0.5 to 1.5 microns.

Typically, better performance (higher resistance) coatings are required for higher field strength applications or where elevated temperatures and/or higher efficiencies may be required. Applications using higher frequency (400-1000 Hertz) also usually require higher resistance coatings.

A summary of coating types used for electrical applications based on ASTM A976 is shown in the following table:

Classification of Insulation Coating for Electrical Steels
Compiled From: ASTM A-976
Name Classification
C-0 -Oxide that is formed naturally on the steel surface during mill processing. Essentially bare steel with some residual mill-related oxide from processing.
C-1 -User-formed oxide that is created on the steel surface by contact with an oxidizing furnace atmosphere at the end of the heat treating cycle. Commonly referred to as Steam Blue Oxide. It is a blue-gray iron oxide formed by reaction on the surface of the steel.
C-2 -Inorganic insulation coating predominantly comprised of magnesium silicate and used on grain oriented electrical steels. A glass film (fosterite) formed by the reaction of the steel with MgO.
C-3 -Organic varnish/enamel coating that is applied to the steel surface and cured by heating.
C-4 -Coating formed by the chemical treating or phosphating of the steel surface followed by an elevated temperature curing treatment.
C-4-AS anti-stick -Thin film of C-4 type coating used primarily for preventing sticking of semi- processed non oriented electrical steel or cold rolled motor lamination during quality anneals.
C-5 -Inorganic or mostly inorganic coating, similar to C4, to which ceramic fillers or film-forming inorganic components have been added to increase the insulating ability of the coating.
C-6 -Organic-based coating to which inorganic fillers have been added to increase the insulating ability of the coating. The coating is applied to the steel surface and cured by heating. C-6 is typically used on fully processed non oriented electrical steels.

C-3 varnish coatings should not be used in conjunction with annealed laminations.

Usually, C-2 and C-5 coatings are considered to be more difficult to weld consistently because of their higher surface resistance and the potential for variations in coating thickness. Special attention to ground current paths, particularly through the edges of the lamination, is recommended when welding laminations with these coatings.

- Steam Blue Oxide -

All of the steel that EDCOR Electronics use has a steam blue oxide on the surfaces and edges. This oxide, often in combination with the rough surface gives an insulating medium to minimize stray losses between laminations. Steam blue oxide is used primarily for fractional, subfractional, and small integral motors, low power, and audio transformers and power supplies.

In addition to its insulating characteristics, steam blue oxide reduces rust and corrosion, and is compatible with a variety of welding processes and secondary powder, epoxy or E-coat processes.

In applications involving high efficiency, high pressure, high power densities or large surface areas, higher value insulating coatings should be used.

Typical Coatings Available for Annealed Laminations (Semi-Processed) Grades:

Typical Lamination Coatings
Semi-Processed Annealed Grades
Grade Type of Steel Typical Coating
M6 Grain Oriented Steam blue C1 and C5
M6 Grain Oriented Glass film C2 with C1 and C5
M25 CRNO C4 anti-stick and steam blue C1
M19 CRNO C4 anti-stick and/or steam blue C1
M22 CRNO C4 anti-stick and/or steam blue C1
M27 CRNO C4 anti-stick and/or steam blue C1
M36 CRNO C4 anti-stick and/or steam blue C1
M50 CRML Steam blue C1
M55 CRML Steam blue C1
M56 CRML Steam blue C1
M67 Full Hard Steam blue C1


Basic Design Formulas:

Math Chart
Math Key