Select Lamination Steel: Steel Grade Specifications

There are two types of electrical steels used for rotor laminations, semi processed and fully processed. Both are non-oriented steel grades. More detailed information about these two types of steels can be found in The Metals Handbook.

Many organizations around the world have adopted specifications to characterize and describe the various steel grades used for rotor laminations. Information on some of these specifications is also described below.

3.1.1 Semi Processed Electrical Lamination Steels

Semi-processed electrical steels are delivered in the cold rolled, un-annealed condition, and must be annealed after punching the laminations to develop optimum magnetic properties. There are several advantages of supplying the steel in the cold rolled condition finish, including providing the best stamping characteristics, acceptable flatness and minimum burr. After stamping, the laminations are typically annealed at temperatures between 790 and 845oC (1450 and 1550oF) for about one hour in a decarburizing atmosphere. The objectives of the annealing treatment include:

  • Eliminating punching stresses
  • Promoting and controlling grain growth
  • Further reducing impurities, particularly carbon, nitrogen and sulfur.

After annealing, the microstructures of laminations punched from semi-processed steels will be fully recrystallized.

Characteristics of semi-processed lamination steels are shown in Table 3.1.1.1.

Table 3.1.1.1: Properties of semi processed, flat-rolled electrical steels.
0.0185-inch (0.47 mm ) Thickness0.025-inch (0.64 mm) Thickness
Core-Loss TypeMaximum Core Loss*Core-Loss TypeMaximum Core Loss*
W/lbW/kgW/lbW/kg
47S155 1.55 3.42 64S200 2.00 4.41
47S165 1.65 3.64 64S210 2.10 4.63
47S175 1.75 3.86 64S220 2.20 4.85
47S190 1.90 4.19 64S230 2.30 5.07
*At 60 Hz and B = 1.5 T (note that maximum core loss values at 50 Hz and 1.5T are 0.79 times maximum core losses at 60 Hz.

Extracted, with permission, from ASTM A 683/A 683M - 99, "Standard Specification for Nonoriented Electrical Steel, Semiprocessed Types", copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. A copy of the complete standard may be obtained from ASTM ( www.astm.org).

3.1.2 Fully Processed Electrical Lamination Steels

Fully processed electrical steels are intended for applications where the laminations can be punched and placed into service without an additional annealing treatment. The desirable magnetic characteristics are produced during the manufacturing of the steel, so an additional heat treatment by the rotor manufacturer is generally not required. The steel manufacturer anneals these fully processed grades in a moist hydrogen atmosphere at about 825°C (1520°F) to decarburize the steel (reduce the carbon concentration of the steel). The final annealing operation by the steel manufacturer is carried out at a higher temperature (up to 1100°C, or 2010°F) to promote grain growth and develop magnetic properties. The strip is then supplied to the stamper in the fully annealed condition.

Obviously during the punching of the laminations, the material adjacent to the outside diameter and adjacent to the slots becomes deformed, but the laminations are used with this less-than-optimum microstructure.

Characteristics of semi-processed lamination steels are shown in Table 3.1.2.1.

Table 3.1.2.1: Properties of fully processed, flat-rolled electrical steels.
0.0140-inch (0.36 mm) Thickness0.0185-inch (0.47 mm) Thickness0.0250-inch (0.64 mm) Thickness
Core-Loss TypeMaximum Core Loss*Core-Loss TypeMaximum Core Loss*Core-Loss TypeMaximum Core Loss*
W/lbW/kgW/kgW/lbW/kgW/lb
36F145 1.45 3.20 -- -- -- -- -- --
36F155 1.55 3.42 47F165 1.65 3.64 64F200 2.00 4.41
36F165 1.65 3.64 47F180 1.80 3.97 64F210 2.10 4.63
36F175 1.75 3.86 47F190 1.90 4.19 64F225 2.25 4.96
36F185 1.85 4.08 47F200 2.00 4.41 64F235 2.35 5.18
36F195 1.95 4.30 47F210 2.10 4.63 64F250 2.50 5.51
36F205 2.05 4.52 47F240 2.40 5.29 64F275 2.75 6.06
-- -- -- 47F280 2.80 6.17 64F320 3.20 7.05
-- -- -- 47F400 4.00 8.82 64F500 5.00 11.02
-- -- -- 47F450 4.50 9.92 64F550 5.50 12.13
*At 60 Hz and B = 1.5 T (note that maximum core loss values at 50 Hz and 1.5T are 0.79 times maximum core losses at 60 Hz.

Extracted, with permission, from ASTM A 667/A 667M - 99, "Standard Specifications for Nonoriented Electrical Steel Fully Processed Types", copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. A copy of the complete standard may be obtained from ASTM ( www.astm.org).

3.1.3 Specifications used for Lamination Steels

The two most common specifications used in the USA for laminations were developed by AISI (American Iron and Steel Institute) and ASTM International ( www.astm.org). These are described below. There are many other designations used around the world. Information about Japanese specifications can be found at www.jsa.or.jp/default_english.asp, and Chinese specifications can be found at ww.sac.gov.cn/sacen/.

The specifications adopted by the AISI were first introduced in 1946 to eliminate the wide variation in nomenclature formally used. There are several grades included in the AISI specification, such as M-47, M-45, M-36, M-27, M-22, M-19 and M-15, all of which are nonoriented silicon-steels. When originally adopted, the AISI designation number approximated ten times the maximum core loss in watts per pound, exhibited by 29 gauge (0.014-inch, or 0.36 mm) samples when tested at 60 Hz and at a magnetic flux density of 1.5 Tesla. For example, a M-47 steel would have a maximum core loss value of about 4.7 W/lb. However, over the years this rule-of-thumb has changed, and doesn't necessarily hold true. For example, today a fully processed M-36 strip (at 0.014-inch thickness) now has a maximum allowable core loss of 1.9 W/lb, (not 3.6 W/lb as suggested by its AISI designation).

Although the AISI designations are still in use, newer specifications developed by ASTM International provide more specific information about each of the different grades. There are two types of ASTM standards, using either imperial or metric units. An example of an ASTM designation is 47S200. The first two numbers represent the thickness of the lamination in millimeters (x100). Following the numbers is a letter (C, D, F, S are used for nonoriented steels) that indicates the material type and test conditions (see Table 3.1.3.1). The final three digits provide an indication of the maximum allowable core loss in watts per pound (x100).

In summary, 47S200 is a nonoriented electrical (silicon) steel, 0.0185-inches (0.47 mm) thick, having a maximum core loss value of 2.00 W/lb (or 4.40 W/kg). ASTM standards are available on the Internet at www.astm.org.

Table 3.1.3.1: Summary of the ASTM code letter designations for the nonoriented electrical steels.
Letter CodeASTM SpecificationGradeCondition
C A 840 Low-carbon lamination steel Fully processed
D A 726 Low carbon lamination steel Semi-processed
F A 667 Nonoriented electrical silicon-steel Fully processed
S A 683 Nonoriented electrical silicon-steel Semi-processed
Extracted, with permission, from ASTM A664-06, "Standard Practice for Identification of Standard Electrical Steel Grades in ASTM Specifications", copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. A copy of the complete standard may be obtained from ASTM ( www.astm.org).