Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Patent
1989-10-12
1991-11-05
Willis, Jr., Prince
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
148 3, 148110, 148120, H01F 104
Patent
active
050629069
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method of making non-oriented electrical steel sheets.
BACKGROUND OF THE INVENTION
As important factors of governing magnetic properties of electrical steel sheets, sizes and dispersing conditions of AlN and MnS precipitated in steels are taken up. This is why these precipitates themselves become to obstacles to movements of magnetic domain walls and deteriorate not only the magnetic flux density under a low magnetic field but also the iron loss, and in addition, they hinder grain growth during recrystallization annealing, and immature grain growth thereby of ferrite grains give bad influences to developments of recrystallization texture preferable to the magnetic properties.
It is known that coarser precipitates are preferable for the movements of the magnetic domain walls during magnetization. Based on such background, there has been disclosed prior art trying to provide the precipitations and coarsenings of AlN or MnS before the recrystallization annealing in the processes of making the electrical steel sheets. For example, Japanese Patent Laid-Open Specification 38814/74 checks di-solution of the coarse AlN during a slab soaking by lowering the soaking temperature thereof; Japanese Patent Laid-Open Specification 22,931/81 lowers amounts of S and O which precipitates as non-metallic inclusions; Japanese Patent Laid-Open Specification 8,409/80 controls formation of sulphides by addition of Ca or REM; Same 108,318/77, 41,219/79 and 123,825/83 coasen AlN by brief soaking in the slab before the hot rolling; and Same 76,422/79 utilizes selfannealing effect by coiling at super high temperature after hot rolling for coarsening AlN and accelerating growth of ferrite grain.
From a viewpoint of saving the energy in the process, it is advantageous to carry out a hot direct rolling from the continuous casting of a slab when performing the hot rolling. However, if depending upon this process, a problem occurs that the coarse precipitations of AlN and MnS are made insufficient, and for solving the problem, the slab is subjected to a brief soaking before the hot rolling.
However, although the soaking time is short, such a process which once transfers the slab into the heating and soaking furnaces, could not enjoy merits of saving energy brought about by the hot direct rolling, and further for providing precipitation of AlN, if the soaking time is short, the precipitation will be non-uniform at the inside and outside of the slab.
DISCLOSURE OF THE INVENTION
In view of these problems of the prior art, in the invention the slab is directly sent to the hot rolling without the brief soaking, whereby others than AlN inevitably precipitated check the precipitation of AlN, and a delay time is taken between the roughing and the finish rolling, the temperature of which is performed at not more than Ar.sub.3, so that precipitating nuclei of AlN are effectively introduced into the steel, and uniform and coarse AlN precipitation is formed by a coiling at temperature of higher than 700.degree. C., thereby to enable to provide uniform and satisfied ferrite grain growth during the recrystallization annealing.
That is, the invention comprises roughing a slab immediately after continuously casting thereof to thickness of more than 20mm at reduction rate of more than 10% without brief soaking at specified temperature range, said slab containing C: not more than 0.005 wt %, Si: 0.1 to 1.5 wt %, Mn: 0.1 to 1.0 wt %, P: 0.01 to 0.15 wt %, and S: not more than 0.005 wt %; having a time interval of more than 30 sec at temperature range where the surface temperature of the roughed bar is higher than 950.degree. C. till a following finish rolling; performing a finish rolling at lower than Ar.sub.3 and at reduction rate of more than 25% and coiling at temperature of higher than 700.degree. C.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows influences of the roughing reduction rate on sizes of precipitating nuclei;
FIG. 2 shows influences of the waiting time of the roughed bar on sizes of the
REFERENCES:
patent: 4116729 (1978-09-01), Katoh et al.
patent: 4666534 (1987-05-01), Miyoshi et al.
Hosoya Yoshihiro
Jitsukawa Masaharu
Nishimoto Akihiko
Tomita Kunikazu
Urabe Toshiaki
Flatter R. D.
Nields Henry C.
NKK Corporation
Willis Jr. Prince
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