Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Reexamination Certificate
2001-08-07
2003-09-02
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
C148S111000
Reexamination Certificate
active
06613160
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method to produce a grain-oriented electrical steel sheet having crystal grains whose orientations are aligned in the {110}<001> orientations in terms of the Miller index. The grain-oriented electrical steel sheet is used as a soft magnetic material for the cores of electrical equipment such as transformers.
2. Description of the Related Art
A grain-oriented electrical steel sheet is a steel sheet containing 4.8% or less of Si and consisting of crystal grains the orientations of which are aligned in the {110}<001> orientations (the so-called Goss orientations). The steel sheets are required to have good excitation performance and core loss performance with regard to their magnetic properties. The magnetic flux density B8 under the magnetic field intensity of 800 A/m is commonly used as an indicator of the excitation performance, and the core loss at W17/50 per 1 kg of a steel sheet when it is magnetized to 1.7 T at the frequency of 50 Hz is commonly used as an indicator of the core loss performance. The magnetic flux density B8 is the most significant factor governing the core loss property: the higher the value of the flux density B8, the better the core loss property becomes. In order to raise the flux density B8, it is important to properly align the crystal orientation. Control of the crystal orientation is achieved by taking advantage of a grain growth phenomenon called secondary recrystallization.
To control the secondary recrystallization, it is necessary to control the structure of the primary recrystallization prior to the secondary recrystallization and of fine precipitates called inhibitors. The inhibitors have a function to suppress the growth of ordinary crystal grains in the primary recrystallization structure and selectively allow the grains having the {110}<001> orientations to grow with priority.
As typical examples of the precipitates, MnS was proposed by M. F. Littmann (Japanese Examined Patent Publication No. S30-3651), J. E. May and D. Turnbull (Trans. Met. Soc. AIME 212 (1958) p769) and others; AlN by Taguchi et al. (Japanese Examined Patent Publication No S40-15644); and MnSe by Imanaka et al. (Japanese Examined Patent Publication No. S51-13469).
A normal practice is that these precipitates are completely dissolved as solid solutions during the slab heating prior to hot rolling and then precipitate as fine deposits during the processes of hot rolling and subsequent annealing. The slabs have to be heated to a temperature as high as 1,350 to 1,400° C., or even higher, in order to turn these precipitates into complete solid solutions. However, since this heating temperature is higher than that of plain carbon steel slabs by roughly 200° C., the following problems are brought about; 1) a specially designed reheating furnace is required; 2) the unit energy consumption of the reheating furnace is high; and 3) molten scale is formed in a great amount and deslagging, and other extra work for furnace maintenance, are necessary.
Facing these problems, research and development in search of a production method using low temperature slab heating were carried out. As a production method using the low temperature slab heating, Komatsu et al. proposed a method to form (Al, Si)N through a nitriding process and use it as an inhibitor.(see Japanese Examined Patent Publication No. S62-45285). Kobayashi et al. disclosed, as a method of the nitriding, a method to nitride the steel sheet in the form of an uncoiled strip after decarburization annealing (see Japanese unexamined Patent Publication No. H2-77525), and Ushigami et al, reported the behavior of the nitrides thus formed (Materials Science Forum, 204-206 (1996) pp593-598).
With regard to the production method of a grain-oriented electrical steel sheet by low temperature slab heating, the control of a primary recrystallization structure during decarburization annealing is important for controlling the secondary recrystallization, because no inhibitor is formed during the decarburization annealing. As far as the research into a production method of a grain-oriented electrical steel sheet by the conventional high temperature slab heating is concerned, few reports have been presented regarding the control of the primary recrystallization structure prior to the secondary recrystallization, and the inventors of the present invention disclosed its importance in Japanese Examined Patent Publication No. H8-32929, Japanese Unexamined Patent Publication No. H9-256051, etc.
They disclosed in Japanese Examined Patent Publication No. H8-32929 that, if the primary recrystallization grain structure became uneven with a variation coefficient of its grain size distribution larger than 0.6, the secondary recrystallization would become unstable. Then, as a result of studies of the primary recrystallization structure and the inhibitors, which are control parameters for secondary recrystallization, they made it clear in Japanese unexamined Patent Publication No. H9-256051, further, that the flux density of final products could be enhanced by controlling the ratio I{111}/I{411}, namely the ratio of the grains aligned in the {111} orientations to those aligned in the {411} orientations, of the primary recrystallization grain structure, which grains are considered to accelerate the growth of the Goss orientation grains in the texture after decarburization annealing (where, I means diffraction intensity). Here, I{111} and I{411} are the proportions of the grains with their {111} and {411} planes, respectively, aligned in parallel to the surface of the steel sheet, and they are measured in terms of the diffraction intensity values by the X-ray diffraction measurement at a plane {fraction (1/10)} of the sheet thickness from the surface.
The primary recrystallization structure after the decarburization annealing is influenced not only by annealing cycle factors of the decarburization annealing such as heating rate, soaking temperature, soaking time, etc., but also by process conditions prior to the decarburization annealing such as the application or otherwise of annealing to a hot-rolled steel sheet, the reduction ratio at cold rolling (cold reduction ratio), etc.
The primary recrystallization after the decarburization annealing can be controlled, for example, by properly changing the annealing cycle parameters of the decarburization annealing such as the heating rate, soaking temperature, soaking time, etc. Among these, the control of the heating rate is a significant measure to control the primary recrystallization. It was found out, however, that, although the flux density increased basically when the heating rate was raised, if it was raised to 40° C./sec. or higher, the secondary recrystallization might become unstable even when the primary recrystallization structure after the decarburization annealing was sound.
With respect to the influence of the cold reduction ratio over the primary recrystallization, it is necessary to set the reduction ratio at 80% or higher in order to have the crystal grains having the orientation aligned in the {111} and {411} orientations develop in the primary recrystallization structure, and this is very important for making the ratio of I{111}/I{411} equal to or less than 3, which ratio is an indicator in obtaining a high magnetic flux density.
It has been found out, however, that, although the flux density of final products was basically enhanced when the cold reduction ratio was raised, if it exceeded a certain limit, the secondary recrystallization became unstable and the flux density of the final products would be deteriorated even when the value of I{b
111
}/I{411} was kept equal to or less than 3.
Besides the above measures to control the secondary recrystallization through the control of the primary recrystallization texture and th
Fujii Hiroyasu
Murakami Ken-ichi
Nakamura Shuichi
Ushigami Yoshiyuki
Yamamoto Norihiro
Kenyon & Kenyon
Nippon Steel Corporation
Sheehan John
LandOfFree
Method to produce grain-oriented electrical steel sheet... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method to produce grain-oriented electrical steel sheet..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method to produce grain-oriented electrical steel sheet... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3076985