Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2003-01-28
2004-11-02
McNeil, Jennifer (Department: 1775)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S469000, C428S472000, C428S472200, C148S113000, C148S307000, C148S308000, C204S192150
Reexamination Certificate
active
06811900
ABSTRACT:
TECHNICAL FIELD
This invention relates to an ultra-low iron loss grain-oriented silicon steel sheet and a method of producing the same, and is to more improve the iron loss property by effectively improving properties and adhesion property of a first coating layer when a plurality of ceramic coating layers are formed on a surface of a silicon steel sheet after finish annealing.
BACKGROUND ART
In the production of the grain-oriented silicon steel sheets, there is recently proposed a method of producing an ultra-low iron loss grain-oriented silicon steel sheet by forming a thin ceramic tension coating such as TiN, TiO
2
, CrN, TiC, Ti(C, N), Si
3
N
4
, SiO
2
, AlN, Si system (Si—N—O—C) or the like on a surface of a grain-oriented silicon steel sheet having no forsterite undercoating (hereinafter referred to as a non-coating sheet) through a PVD process. A longtime pending issue in such a production method lies in a point that a ceramic tension coating having an adhesion property and bending properties durable to a stress relief annealing at a high temperature for a long time and capable of attaining an ultra-low iron loss without the deterioration of the iron loss feared in the stress relief annealing is effectively formed.
When the ceramic coating is formed on the surface of such a noncoating sheet through the PVD process, especially when a ceramic coating such as TiN, TiO
2
, CrN, TiC, Ti(C, N) or the like is formed, a hollow cathode discharge process (HCD) having a low voltage-high current characteristic and an excellent ionization ratio on deposit particles is said to be optimum.
On the other hand, a magnetron sputtering process is said to be optimum in the formation of a ceramic coating such as Si
3
N
4
, SiO
2
, AlN, Si system (S—N—O—C) or the like.
However, when the ceramic tension coating is directly formed on the non-coating sheet by using the conventional process as mentioned above, it is very difficult to obtain a ceramic coating keeping a sufficient adhesion property even after the stress relief annealing at a high temperature.
This is mainly considered due to the fact that since the ceramic coating formed by the PVD process is unstable as compared with naturally existing ceramics, the peeling is easily caused through the progress of reaction between the formed ceramic coating and the surface of the non-coating sheet in the high-temperature stress relief annealing.
The invention advantageously solves the above problems and is to propose an ultra-low iron loss grain-oriented silicon steel sheet provided with a ceramic tension coating having excellent adhesion property and bending properties even after the stress relief annealing at a high temperature for a long time and causing no deterioration of iron loss feared in such a stress relief annealing as a first object.
It is a second object of the invention to propose an advantageous method of producing an ultra-low iron loss grain-oriented silicon steel sheet provided with the ceramic tension coating as mentioned above.
DISCLOSURE OF THE INVENTION
The inventors have made various studies in order to achieve the above objects and obtained knowledge as mentioned below.
(1) The adhesion property is most important at an interface between the surface of the non-coating sheet and the ceramic tension coating formed by the PVD process. As a first coating layer (precoat), therefore, it is advantageous to form a ceramic coating having a very thin thickness and a somewhat large thermal expansion coefficient.
(2) In the formation of such a precoat ceramic coating, it is advantageous for enhancing the adhesion property to apply a large bias voltage to a substrate to adopt a coating process in which large and an ionization ratio is high.
(3) Upon said precoat ceramic coating, it is advantageous to use a ceramic tension coating having a small thermal expansion coefficient and serving as a diffusion barrier in the high-temperature stress relief annealing for effectively applying tension to a silicon steel sheet without deteriorating the adhesion property.
Further, it has been elucidated that it is effective to form a thin ceramic tension coating of TiN by a HCD process in order to satisfy the above requirement (1), and to apply a high bias voltage of not less than −100 V at this HCD process in order to satisfying the requirement (2), and to form SiN, by a magnetron sputtering process in order to satisfy the requirement (3), respectively.
As to the requirement (2) among the above requirements, however, it has been revealed that when a high bias voltage of not less than −100 V is directly applied to a substrate of a grain-oriented silicon steel sheet through rolls or the like in a high plasma atmosphere of the HCD process, abnormal discharge is frequently caused to spirally upheave the TiN coating and also many cracks are created on the upheaved TiN coating and hence the sufficient adhesion property is not obtained.
In order to solve the above problem, it is considered that the application of the bias voltage to the substrate of the grain-oriented silicon steel sheet is desirable to be a non-contact system.
Now, the inventors have made studies with respect to a method and an apparatus for attaining the application of the high bias voltage at a non-contact state and obtained the following knowledge.
a) The high bias voltage can be applied to the grain-oriented silicon steel sheet as a material to be treated at a non-contact state by arranging positive and negative electrodes in proximity to the material to be treated and disposing a magnetic field generating means in the vicinity of such positive and negative electrodes so that electrons generated between the positive and negative electrodes focus. Also, the high bias voltage can be applied to the substrate of the grain-oriented silicon steel sheet without causing abnormal discharge or the like by using such a non-contact type high bias voltage applying method.
b) The composition of the ceramic coating formed by the above method is not the conventional TiN but is TiNO. Also, the TiNO coating epitaxially grows and is formed on the steel sheet substrate in a good consistency, so that a further improvement of the adhesion property and hence tension applying effect is attained.
The invention is based on the above knowledge.
That is, the construction of the invention is as follows.
1. An ultra-low iron loss grain-oriented silicon steel sheet having a plurality of ceramic coating layers formed on a surface of a grain-oriented silicon steel sheet after finish annealing, characterized in that said steel sheet has a TiNO coating formed by a hollow cathode discharge process as a first coating layer.
2. An ultra-low iron loss grain-oriented silicon steel sheet having a plurality of ceramic coating layers formed on a surface of a grain-oriented silicon steel sheet after finish annealing, characterized in that said steel sheet has a TiNO coating formed by a hollow cathode discharge process as a first coating layer and further a SiN
x
, coating formed by a magnetron sputtering process on the TiNO coating.
3. A method of producing an ultra-low iron loss grain-oriented silicon steel sheet by forming a plurality of ceramic coating layers on a surface of a grain-oriented silicon steel sheet after finish annealing without forming a forsterite undercoating on a surface of the steel sheet, characterized in that a TiNO coating is formed on a surface of the as finish annealed steel sheet as a first coating layer by a hollow cathode discharge process under an application of a high bias voltage of not less than −100 V to the steel sheet.
4. A method of producing an ultra-low iron loss grain-oriented silicon steel sheet by forming a plurality of ceramic coating layers on a surface of a uni-directional silicon steel sheet after finish annealing without forming a forsterite undercoating on a surface of the steel sheet, characterized in that a TiNO coating is formed on a surface of the as finish annealed steel sheet as a first coating layer by a hollow cathode discharge process under an application
JFE Steel Corporation
McNeil Jennifer
Piper Rudnick LLP
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