CRNGO Non-Oriented Silicon Steel: Quality Standards, Grades and Core Loss

Non-oriented silicon steel, also called CRNGO electrical steel, is the standard material for rotating machines because its crystal grains are randomly oriented and its magnetic behaviour is nearly isotropic. This article explains how CRNGO quality is defined, which standard systems govern it, and which parameters a buyer must verify before ordering.

What CRNGO Non-Oriented Silicon Steel Is

CRNGO steel is a very pure iron-silicon alloy whose grains have no preferred orientation after final annealing. Unlike grain-oriented (CRGO) steel it shows almost the same permeability in every direction, which is why it is selected for motors, generators and other equipment in which the flux path rotates or changes direction.

Random grain orientation with isotropic magnetic properties.

Low hysteresis loss and low total core loss after proper final annealing.

Stable permeability at higher frequencies, suitable for inverter-driven machines.

Good punching behaviour for high-volume lamination production.

Standards That Define CRNGO Quality

Quality requirements for non-oriented electrical steel are described in national and international standard systems. The most frequently referenced are GB/T 2521 (China), IEC 60404-8-4 (international), ASTM A677/A677M (United States) and JIS C 2552 (Japan). These documents fix the designation rules, the test method and the guaranteed limits for a given grade family, but they do not necessarily use identical test conditions for every parameter.

For that reason a mill certificate must be read against the standard required by the destination market, and the guaranteed values must be checked at the test frequency that the standard specifies. Comparing a loss value measured at one polarisation and frequency with a value measured at another is the most common source of disagreement between suppliers and users.

How Grades Are Designated

Non-oriented grades are designated by thickness and by guaranteed maximum core loss, so the grade number itself states the quality level.

In this system the leading number is one hundred times the nominal thickness in millimetres, while the trailing number states the maximum core loss per kilogram measured at 50 Hz. A 35WW250 sheet is therefore 0.35 mm thick with a maximum loss of 250 units, and a 50W800 sheet is 0.50 mm thick with a maximum loss of 800 units. Thinner material of the same loss class costs more but lowers loss in high-frequency operation.

Key Quality Parameters to Verify

Core loss at the specified polarisation and frequency, normally stated as W/kg at 50 Hz.

Magnetic induction, given as a flux density at a defined field strength, which sets the torque capability of a given stack size.

Lamination factor, the proportion of the stack that is actually steel, which determines how much flux the core can carry.

Thickness tolerance and flatness, which control stacking factor and air gap uniformity.

Insulation coating type, typically C3 for punching, C4 for corrosion protection, C5 for annealing resistance and C6 for high insulation resistance.

Surface insulation resistance and coating adhesion after punching.

Mechanical properties such as yield strength and ductility, which influence burr formation and die life.

Selection and Inspection Guidance

During inquiry the buyer should state the grade and thickness, the applicable standard, the coating type, the target application, the coil width and the order quantity, because slitting width and coil weight affect yield and price. On delivery, the mill test report should be compared with the ordered grade, and a sample should be checked for thickness tolerance, surface condition and coating continuity.

For high-end equipment such as inverter-fed motors, a thinner gauge in a lower loss class usually gives a better system result than a thicker sheet of the same nominal grade, because loss rises steeply with frequency and thickness. For general-purpose motors and compressors a medium or standard grade at 0.50 mm remains the most economical choice.

Frequently Asked Questions

Q: What does CRNGO stand for?
It stands for cold rolled non-grain-oriented electrical steel, the type whose crystal grains are randomly distributed so that magnetic properties are nearly the same in all directions.

Q: Which standard should a CRNGO order reference?
Reference the standard that applies in the destination market: GB/T 2521 in China, IEC 60404-8-4 internationally, ASTM A677/A677M in the United States and JIS C 2552 in Japan.

Q: How is a non-oriented grade identified?
The designation combines thickness and guaranteed maximum core loss, so 35WW250 is a 0.35 mm sheet and 50W800 is a 0.50 mm sheet, each with a defined loss class at 50 Hz.

Q: Why is core loss the main grading indicator?
Because it directly determines the efficiency and temperature rise of a motor or transformer, and it is the parameter that distinguishes one quality level from another within the same thickness.

Q: Which coating types are available?
Organic, inorganic and semi-organic coatings are supplied, commonly specified as C3, C4, C5 or C6 according to the required punching, corrosion, annealing or insulation performance.

Q: Does thinner steel always give lower loss?
Not on its own. A thinner high-grade sheet lowers eddy current loss, but the final result also depends on induction, coating quality, stack building factor and the actual operating frequency.