Cold rolled non-oriented electrical steel sheet

A cold rolled non-oriented electrical steel sheet having a low iron loss is disclosed. The steel sheet consists of not more than 0.02% of C, 0.1-3.5% of Si, not more than 1.0% of Al, 0.1-1.0% of Mn, 0.03-0.40% of Sn and the remainder being substantially Fe.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention relates to a non-oriented electrical steel sheet, and 
more particularly relates to a cold rolled non-oriented electrical steel 
sheet having a low iron loss. 
(2) Description of the Prior Art 
Non-oriented electrical steel sheets are graded by their iron loss. For 
example, in the JIS, non-oriented electrical steel sheets having a 
thickness of 0.050 mm are graded as follows. In the S-30 grade steel 
sheet, W.sub.10/50 must be not higher than 3.70 W/kg and W.sub.15/50 must 
be not higher than 8.00 W/kg; and in the S-10 grade steel sheet, 
W.sub.10/50 must be not higher than 1.25 W/kg and W.sub.15/50 must be not 
higher than 3.10 W/kg. 
The iron loss of non-oriented silicon steel sheets is occupied by the 
hysteresis loss rather than by the eddycurrent loss contrary to the iron 
loss of oriented electrical steel sheets, and the hysteresis loss occupies 
generally 60-80% of the total iron loss. The hysteresis loss is in inverse 
proportion to the crystal grain size. It is an effective means to promote 
the normal grain growth of recrystallized grains at the final annealing in 
order to decrease the iron loss, and this means has hitherto been always 
used in order to lower the iron loss. 
The inventors have newly found out that the alloying of Sn to non-oriented 
silicon steel sheet is effective for lowering the iron loss thereof, and 
have accomplished the present invention. 
SUMMARY OF THE INVENTION 
The feature of the present invention is the provision of a cold rolled 
non-oriented electrical steel sheet having a low iron loss, which consists 
of not more than 0.02% by weight of C, 0.0-3.5% by weight of Si, not more 
than 1.0% by weight of Al, 0.1-1.0% by weight of Mn, 0.03-0.40% by weight 
of Sn and the remainder being substantially Fe.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention will be explained in more detail. 
There has hitherto been hardly known the influence of Sn upon the magnetic 
property of non-oriented electrical steel sheet. After various 
investigations, the inventors have found out that Sn is remarkably 
effective for lowering the iron loss of non-oriented electrical steel 
sheet as illustrated in the following data. 
The single FIGURE of the drawing shows the results of measurement of iron 
losses of Epstein samples produced by subjecting hot rolled sheets having 
different contents of each of Si and Sn as shown in the following Table 1 
to a one-stage cold rolling to prepare cold rolled sheets having a final 
gauge of 0.5 mm, and then subjecting the cold rolled sheets to a 
continuous annealing under a dry hydrogen atmosphere kept at 950.degree. 
C. 
It can be seen from Table 1 and the Figure that the addition of Sn to 
silicon steel sheet is effective for the production of electrical steel 
sheet having a low iron loss. 
TABLE 1 
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Sample C Si Mn S Al Sn 
No. (%) (%) (%) (%) (%) (%) 
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1 0.002 1.01 0.29 0.004 0.27 0.01 
2 0.004 1.02 0.29 0.003 0.28 0.04 
3 0.002 1.01 0.29 0.004 0.27 0.13 
4 0.004 1.02 0.29 0.005 0.28 0.38 
5 0.004 1.85 0.30 0.003 0.28 0.01 
6 0.005 1.85 0.30 0.003 0.29 0.04 
7 0.004 1.85 0.30 0.003 0.28 0.13 
8 0.005 1.85 0.30 0.003 0.29 0.38 
9 0.006 3.20 0.29 0.002 0.29 0.01 
10 0.007 3.20 0.29 0.003 0.29 0.04 
11 0.006 3.20 0.29 0.003 0.29 0.12 
12 0.007 3.20 0.29 0.002 0.29 0.40 
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The reason of the limitation of the composition of the non-oriented 
electrical steel of the present invention will be explained hereinafter. 
When a silicon steel sheet contains less than 0.03% of Sn, the effect of Sn 
for lowering the iron loss of the resulting electrical steel sheet does 
not appear. While, when a silicon steel sheet contains more than 0.40% of 
Sn, the Steel sheet cracks during the cold rolling. Therefore, the Sn 
content in the silicon steel sheet of the present invention should be 
within the range of 0.03-0.40%. 
When, the C content in a silicon steel sheet is more than 0.02%, the 
magnetic property of the resulting electrical steel sheet is poor. 
Therefore, the C content in a silicon steel sheet of the present invention 
should be not more than 0.02%. 
Si serves to increase the specific resistivity and to lower the iron loss 
of steel sheet. When the Si content in a steel sheet is more than 3.5%, 
the steel sheet is brittle and cannot be cold rolled. In rimmed steel, the 
effect of Sn does not appear. When, a steel sheet contains not less than 
0.1% of Si, the steel sheet has an improved aggregation texture. 
Therefore, the Si content in the steel sheet of the present invention 
should be within the range of 0.1-3.5%. 
Al serves to improve the magnetic property of silicon steel sheet. When a 
silicon steel sheet contains more than 1.0 % of Al, the steel sheet is apt 
to crack. Therefore, the Al content in the silicon steel sheet of the 
present invention should be not more than 1.0%. 
Mn serves to prevent the crack of silicon steel sheet during the hot 
rolling. When the Mn content in a silicon steel sheet is less than 0.1%, 
the above described crack cannot be prevented. While, when the Mn content 
exceeds 1.0%, the magnetic property of the resulting electrical steel 
sheet is poor. Therefore, the Mn content in the silicon steel sheet of the 
present invention should be within the range of 0.1-1.0%. 
Then, a method of producing the cold rolled non-oriented electrical steel 
sheet of the present invention will be explained. 
The starting steel to be used in the present invention can be produced by 
means of any of commonly known open hearth furnace, converter and 
electrical furnace. Then, the starting steel may be subjected to a vacuum 
degassing treatment or a ladle refining treatment. Sn may be added to the 
molten steel in a ladle or to the molten steel at the pouring thereof into 
a casting mold or into a continuous casting system mold. However, it is 
necessary that the solidified steel ingot or slab has the above described 
composition. A steel ingot or slab obtained in the above described method 
is hot rolled by a commonly known hot rolling method. The hot rolled sheet 
is pickled, after annealing or without annealing, to remove oxide scale 
and then cold rolled. The cold rolling may be carried out by an one-stage 
cold rolling or a two-stage cold rollings with an intermediate annealing, 
whereby a cold rolled sheet having a final gauge is produced. The cold 
rolled sheet is then subjected to a continuous annealing to produce a 
final product. Alternatively, the cold rolled sheet is sold in the market 
as a semi-processed product. An electric apparatus manufacturer punches 
the cold rolled sheet into a desired shape and then carries out a 
stress-relief annealing to produce a final product. 
The following example is given for the purpose of illustration of this 
invention and is not intended as a limitation thereof. 
EXAMPLE 
A hot rolled sheet having a thickness of 2 mm, which consists of 0.004% of 
C, 0.32% of Si, 0.31% of Mn, 0.005% of S, 0.27% of Al, 0.04% of Sn and the 
remainder being substantially iron, was pickled, and subjected to a 
one-stage cold rolling to produce a cold rolled sheet having a final gauge 
of 0.5 mm. The cold rolled sheet was continuously annealed for 3 minutes 
under a dry hydrogen atmosphere kept at 950.degree. C. An Epstein test 
piece was cut out from the finally annealed sheet, and the electromagnetic 
property of the test piece was measured. The steel sheet had a very 
excellent electromagnetic property of W.sub.10/50 of 2.65 W/kg, 
W.sub.15/50 of 5.90 W/kg and B.sub.50 of 1.76 T.