# US 4,394,192 A · Method for producing low silicon steel electrical lamination strip

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- Number: US 4,394,192 A
- Document ID: US4394192A
- Status: Granted
- Kind: A
- Application number: 06/279,830
- Filed: 1981-07-02
- Granted: 1983-07-19
- Earliest claimed: 1981-07-02
- Assignees: Inland Steel Company
- Inventors: Prabhat K. Rastogi
- Web page: https://patentgrep.com/patent/US4394192A

## CPC

- H01F 1/14775: {in the form of sheets}
- C21D 8/12: during manufacturing of articles with special electromagnetic properties
- C21D 8/1222: {Hot rolling}
- C21D 8/1233: {Cold rolling}
- C21D 8/1266: {between cold rolling steps}
- H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B)

## Abstract

The chemical composition and processing of a cold rolled steel strip are controlled. Laminations for the core of an electric motor are stamped from the strip and decarburized to produce a lamination having a 1.5 T (15 kG) average core loss value less than about 5.70 W/kg (2.60 W/lb.) and average peak permeability substantially more than about 2000 G/Oe. for a sample thickness of about 0.018 in. (0.46 mm.).

## Claims

### Claim 1

In a method for producing cold rolled steel strip for use in electric motor laminations, the steps of:
providing a steel consisting essentially of the following composition in wt.% before cold rolling:
______________________________________ carbon .06 max. manganese .55-.75 silicon .15-.25 aluminum .15-.25 phosphorus .12 max. sulfur .025 max. iron essentially the balance; ______________________________________
hot rolling said steel into steel strip;
coiling said hot rolled steel strip while the steel is at a coiling temperature in the range 1250.degree.-1400.degree. F. (682.degree.-760.degree. C.) and then allowing said coiled strip to cool;
cold rolling said steel strip;
continuously annealing said steel strip at a strip temperature in the range 1250.degree.-1400.degree. F. (682.degree.-760.degree. C.) for about 2-5 minutes, and then allowing said strip to cool;
and temper rolling said strip to produce a reduction of about 5-7.5%;
whereby said steel strip, after said temper rolling step, has a grain size and crystallographic orientation which, upon subsequent magnetic annealing at a temperature in the range 1400.degree.-1550.degree. F. (760.degree.-843.degree. C.) for about 1-2 hours in a decarburizing atmosphere, produces an average ferritic grain size of about 3.5-5.0 ASTM and a preponderance of crystallographic planes containing the easiest direction of magnetization.

### Claim 2 (depends on 1)

In a method as recited in claim 1 wherein:
said steel consists essentially of the following composition in wt.% before cold rolling:
______________________________________ carbon .05 max. manganese .60-.70 silicon .18-.22 aluminum .18-.22 phosphorus .7-.10 sulfur .020 max. iron essentially the balance. ______________________________________

### Claim 3 (depends on 1)

In a method as recited in claim 1 wherein:
said coiling step is performed at a temperature in the range 1300.degree.-1350.degree. F. (704.degree.-732.degree. C.).

### Claim 4 (depends on 1)

In a method as recited in claim 1 wherein:
said cold rolling step produces a cold reduction of about 65-80%.

### Claim 5 (depends on 1)

In a method as recited in claim 1 wherein:
said steel strip is continuously annealed at a strip temperature in the range 1300.degree.-1350.degree. F. (704.degree.-732.degree. C.).

### Claim 6 (depends on 5)

In a method as recited in claim 5 wherein:
said steel strip is continuously annealed at said strip temperature for about 2.5-3.5 minutes.

### Claim 7 (depends on 1)

In a method as recited in claim 1 wherein:
said temper rolling step produces a reduction of about 6-7%.

### Claim 8 (depends on 1)

In a method as recited in claim 1 wherein:
said steel consists essentially of the following composition in wt.% before cold rolling:
______________________________________ carbon .05 max. manganese .60-.70 silicon .18-.22 aluminum .18-.22 phosphorus .07-.10 sulfur .020 max. iron essentially the balance; ______________________________________
said coiling step is performed at a temperature in the range 1300.degree.-1350.degree. F. (704.degree.-732.degree. C.);
said cold rolling step produces a cold reduction of about 65-80%;
said steel strip is continuously annealed at a strip temperature in the range 1300.degree.-1350.degree. F. (704.degree.-732.degree. C.);
said steel strip is continuously annealed at said strip temperature for about 2.5-3.5 minutes; and
said temper rolling step produces a reduction of about 6-7%.

### Claim 9 (depends on 1)

In combination with the method steps recited in claim 1, the additional steps for producing said electric motor laminations, said additional steps comprising:
stamping electric motor laminations from said steel strip after the latter has been temper rolled;
and then magnetic annealing said laminations at a temperature in the range 1400.degree.-1550.degree. F. (760.degree.-843.degree. C.) for about 1-2 hours in a decarburizing atmosphere to reduce the carbon content to less than about 0.006 wt.% and produce an average ferritic grain size of about 3.5-5.0 ASTM and a preponderance of crystallographic planes containing the easiest direction of magnetization.

### Claim 10 (depends on 9)

The combination of steps recited in claim 9 wherein:
said magnetic annealing step is conducted at a temperature substantially below 1550.degree. F. (843.degree. C.).

### Claim 11 (depends on 9)

The combination of steps recited in claim 9 wherein:
said laminations have a 1.5 T (15 kG) average core loss value less than about 5.70 W/kg (2.60 w/lb.) and average peak permeability substantially more than about 2000 G/Oe. for a sample thickness of about 0.018 in. (0.46 mm.).