U.S. patent application number 10/928551 was filed with the patent office on 2005-02-10 for high aluminiferous ferritic stainless steel sheet for weight sensor substrate, method for producing the same, and weight sensor.
Invention is credited to Fukaya, Masuhiro, Komori, Tadashi.
Application Number | 20050028903 10/928551 |
Document ID | / |
Family ID | 33301844 |
Filed Date | 2005-02-10 |
United States Patent
Application |
20050028903 |
Kind Code |
A1 |
Fukaya, Masuhiro ; et
al. |
February 10, 2005 |
High aluminiferous ferritic stainless steel sheet for weight sensor
substrate, method for producing the same, and weight sensor
Abstract
The present invention provides a stainless steel most suitable
as a metal base material for the weight sensor substrate of an
automobile airbag, a method for producing said stainless steel and
said weight sensor; and the stainless steel sheet comprises a high
aluminiferous ferritic stainless steel containing Al of 2.5 to 8
mass % and comprising, in mass, C: 0.025% or less, N: 0.025% or
less, the sum of C and N being 0.030% or less, and Nb: 0.05 to
0.5%, with the balance consisting of Fe and unavoidable impurities.
Further, said stainless steel sheet may further contain, in mass,
one or more of V: 0.05 to 0.4%, Ti: 0.02 to 0.2%, and Zr: 0.02 to
0.2%. The present invention makes it possible to control the
difference in the average linear expansion coefficient between said
stainless steel sheet and crystallized glass for a weight sensor to
less than 10% in the temperature range from 20.degree. C. to
900.degree. C. and thus to improve the adhesiveness of said
stainless steel sheet with said crystallized glass.
Inventors: |
Fukaya, Masuhiro; (Tokyo,
JP) ; Komori, Tadashi; (Tokyo, JP) |
Correspondence
Address: |
Robert T. Tobin
KENYON & KENYON
One Broadway
New York
NY
10004
US
|
Family ID: |
33301844 |
Appl. No.: |
10/928551 |
Filed: |
August 26, 2004 |
Current U.S.
Class: |
148/605 ;
420/62 |
Current CPC
Class: |
C22C 38/02 20130101;
C22C 38/06 20130101; C22C 38/26 20130101; C22C 38/04 20130101 |
Class at
Publication: |
148/605 ;
420/062 |
International
Class: |
C22C 038/26 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 2003 |
JP |
2003-052263 |
Nov 20, 2003 |
JP |
2003-391292 |
Claims
1. A high aluminiferous ferritic stainless steel sheet for a weight
sensor substrate, characterized by comprising a high aluminiferous
ferritic stainless steel containing, in mass, Cr: 12 to 30%, Al:
2.5 to 8%, Nb: 0.05 to 0.5%, C: 0.025% or less, and N: 0.025% or
less, the sum of C and N being 0.030% or less, with the balance
consisting of Fe and unavoidable impurities.
2. A high aluminiferous ferritic stainless steel sheet for a weight
sensor substrate according to claim 1, characterized in that said
high aluminiferous ferritic stainless steel further contains, in
mass, one or more of V: 0.05 to 0.4%, Ti: 0.02 to 0.2%, and Zr:
0.02 to 0.2%.
3. A high aluminiferous ferritic stainless steel sheet for a weight
sensor substrate according to claim 1 or 2, characterized in that
the average linear expansion coefficient of said stainless steel is
13.5 to 15.5.times.10.sup.-6/.degree. C. in the temperature range
from 20.degree. C. to 900.degree. C.
4. A high aluminiferous ferritic stainless steel sheet for a weight
sensor substrate according to claim 1 or 2, characterized in that
the difference in the average linear expansion coefficient between
said stainless steel sheet and crystallized glass for a weight
sensor is less than 10% in the temperature range from 20.degree. C.
to 900.degree. C.
5. A high aluminiferous ferritic stainless steel sheet for a weight
sensor substrate according to claim 1 or 2, characterized in that
the thickness of the oxide film of said stainless steel sheet is
less than 0.38 .mu.m.
6. A method for producing a high aluminiferous ferritic stainless
steel sheet for a weight sensor substrate, characterized by
stamping said high aluminiferous ferritic stainless steel sheet
according to claim 1 or 2 into a desired shape and successively
applying heat treatment for 20 to 120 minutes in the temperature
range from 800.degree. C. to 900.degree. C.
7. A weight sensor characterized by being composed of: a weight
sensor substrate comprising said high aluminiferous ferritic
stainless steel sheet according to claim 1 or 2; a crystallized
glass layer with which the surface of said substrate is covered;
strain sensitive resistive elements formed on the surface of said
crystallized glass layer; and a pair of electrodes for detecting
the change of the electric resistance of said strain sensitive
resistive elements.
Description
TECHNICAL FIELD
[0001] The present invention relates to a high aluminiferous
ferritic stainless steel sheet for the weight sensor substrate of
an automobile airbag, a method for producing the ferritic stainless
steel sheet, and a weight sensor.
BACKGROUND ART
[0002] An automobile is equipped with seatbelts and airbags as
devices for securing the safety of occupants. In recent years, in
order to further improve the performance of a seatbelt and an
airbag, there has been a tendency to control the movement of such
safety facilities in conformity with an occupant's weight (body
weight). For example, the expansion gas volume and expansion speed
of an airbag and the pretensioning of a seatbelt are adjusted in
conformity with an occupant's weight. For that purpose, it is
necessary to know the weight of an occupant in a seat by some sort
of means. As an example of such means, a means of disposing load
sensors (load cells) at the four corners of a seat rail assembly,
adding up the loads in the vertical direction imposed on the load
cells, and by so doing measuring the weight of a seat including an
occupant's weight has been proposed (Japanese Unexamined Patent
Publication No. H11-304579).
[0003] With regard to a mechanical quantity sensor for detecting
load, pressure, etc., various sensors has been proposed in
accordance with the kind of a substrate and the kind of a strain
sensitive material used for a resistive element. Typical proposed
examples are: (1) a sensor produced by using a film comprising a
resin such as polyester, epoxy, polyimide or the like as a
substrate and forming on the surface of the substrate a lamellar
resistive element comprising Cu--Ni alloy, Ni--Cr alloy or the like
by vapor deposition or sputtering, (2) a sensor produced by using a
glass plate instead of the aforementioned resin film (Japanese
Examined Patent Publication No. H3-20682), and (3) a sensor
produced by using a metal base material the surface of which is
covered with a crystallized glass layer as a substrate and forming
a resistive element on the surface thereof by coating it with paste
and baking it (Japanese Unexamined Patent Publication No.
H5-93659).
[0004] The magnitude of a mechanical quantity is measured in the
following way. When a force or a load is imposed on a mechanical
quantity sensor from outside, a resistive element formed on the
surface of a substrate deforms together with the substrate. The
imposed mechanical quantity is detected by measuring the change of
an electric resistance between a pair of electrodes formed by
connecting the resistive element, the change of the electric
resistance being caused by the change of the length and sectional
area of the resistive element. A mechanical quantity sensor that
uses a metal base material on the surface of which a crystallized
glass layer is formed as a substrate is most suitable as a sensor
used under a harsh environment because, unlike other types of
sensors, each of the component elements interdiffuses between the
metal base material and the crystallized glass layer and also
between the crystallized glass layer and a resistive element, and
thus the adhesiveness between them is very strong. As a resistive
element of a mechanical quantity sensor of this type, an element
formed by being coated with resistive paste containing ruthenium
oxide that functions as a resistive material, then dried and baked
is known.
[0005] As metal base materials used for mechanical quantity
sensors, a vitreous enamel steel, a stainless steel, a silicon
steel, various alloy materials such as nickel-chromium-iron,
nickel-iron, Kovar, Invar, etc., clad materials of those alloy
materials and the like can be selected. Japanese Unexamined Patent
Publication No. 2000-180255 discloses a technology that uses a
stainless steel sheet as a metal base material. Japanese Unexamined
Patent Publication No. H10-38733 discloses a technology that uses
SUS 430 as a metal base material from the viewpoint of the
adhesiveness with an insulating glass layer. Japanese Unexamined
Patent Publication No. H5-93659 discloses a technology that uses
SUS 430 concretely as a metal base material from the viewpoint of
the necessity of coordinating the expansion coefficient thereof
with that of a glass layer.
[0006] However, with a metal base material based on the
aforementioned existing technologies, glass adhesiveness and high
temperature oxidation resistance during baking are insufficient and
therefore the metal base material has not been put into practical
use. It is preferable that a sensor substrate is made of a
stainless steel sheet and that an insulating glass layer and the
layers of a resistive element and electrodes are solidified by
baking (the schematic illustration is shown in FIG. 1). In this
light, a stainless steel that has a high thermal resistance and an
excellent glass adhesiveness so that sensor members may be baked
together when each of the layers is baked at a high temperature has
strongly been longed for.
[0007] When a crystallized glass layer functioning as an insulating
layer, a strain sensitive resistive element and electrodes are
baked and resultantly solidified in the form of layers onto a
stainless steel sheet functioning as the substrate of a sensor, it
is necessary to coordinate the linear expansion coefficients of a
metal base material and a glass layer with each other in order to
improve the adhesiveness between them. Since the baking is applied
at a temperature of 900.degree. C. or lower, it is necessary for
the linear expansion coefficients of the metal base material and
the glass layer to approximate each other, not only in the vicinity
of room temperature but also in the temperature range from
20.degree. C. to 900.degree. C. If the difference in the average
linear expansion coefficient is large between a metal base material
and a crystallized glass layer, the adhesiveness between them
deteriorates considerably and therefore they do not function as the
substrate of a resistive element. Whereas the average linear
expansion coefficient of generally used crystallized glass is 13 to
16.times.10.sup.-6/.degree. C., that of a conventionally used
stainless steel is about 13.times.10.sup.-6/.degree. C.
Accordingly, the difference in the average linear expansion
coefficient is too large between the stainless steel substrate and
the glass layer, and thus sufficient glass adhesiveness cannot be
obtained.
SUMMARY OF THE INVENTION
[0008] The object of the present invention is, by providing a
stainless steel most suitable as a metal base material for the
weight sensor substrate of an automobile airbag, to improve high
temperature oxidation resistance when the stainless steel substrate
is sintered with a crystallized glass layer and thus to enhance the
adhesiveness thereof with the glass layer.
[0009] The present invention has been established as a result of
studying components, production methods, linear expansion
coefficients and high temperature oxidation resistance in order to
attain the above object, and it has been found that the object can
be achieved by applying to a metal base material a steel sheet
produced containing Nb, preferably further V, Ti and Zr, in a high
aluminiferous ferritic stainless steel sheet. The gist of the
present invention is as follows.
[0010] Specifically, the object of the present invention is
attained by a high aluminiferous ferritic stainless steel sheet and
a method for producing the stainless steel sheet according to the
following points (1) to (7).
[0011] (1) A high aluminiferous ferritic stainless steel sheet for
a weight sensor substrate, characterized by comprising a high
aluminiferous ferritic stainless steel containing, in mass,
[0012] Cr: 12 to 30%,
[0013] Al: 2.5 to 8%,
[0014] Nb: 0.05 to 0.5%,
[0015] C: 0.025% or less, and
[0016] N: 0.025% or less,
[0017] the sum of C and N being 0.030% or less, with the balance
consisting of Fe and unavoidable impurities.
[0018] (2) A high aluminiferous ferritic stainless steel sheet for
a weight sensor substrate according to the item (1), characterized
in that said high aluminiferous ferritic stainless steel further
contains, in mass, one or more of
[0019] V: 0.05 to 0.4%,
[0020] Ti: 0.02 to 0.2%, and
[0021] Zr: 0.02 to 0.2%.
[0022] (3) A high aluminiferous ferritic stainless steel sheet for
a weight sensor substrate according to the item (1) or (2),
characterized in that the average linear expansion coefficient of
said stainless steel is 13.5 to 15.5.times.10.sup.-6/.degree. C. in
the temperature range from 20.degree. C. to 900.degree. C.
[0023] (4) A high aluminiferous ferritic stainless steel sheet for
a weight sensor substrate according to the item (1) or (2),
characterized in that the difference in the average linear
expansion coefficient between said stainless steel sheet and
crystallized glass for a weight sensor is less than 10% in the
temperature range from 20.degree. C. to 900.degree. C.
[0024] (5) A high aluminiferous ferritic stainless steel sheet for
a weight sensor substrate according to the item (1) or (2),
characterized in that the thickness of the oxide film of said
stainless steel sheet is less than 0.38 .mu.m.
[0025] (6) A method for producing a high aluminiferous ferritic
stainless steel sheet for a weight sensor substrate, characterized
by stamping said high aluminiferous ferritic stainless steel sheet
according to the item (1) or (2) into a desired shape and
successively applying heat treatment for 20 to 120 minutes in the
temperature range from 800.degree. C. to 900.degree. C.
[0026] (7) A weight sensor characterized by being composed of: a
weight sensor substrate comprising said high aluminiferous ferritic
stainless steel sheet according to the item (1) or (2); a
crystallized glass layer with which the surface of said substrate
is covered; strain sensitive resistive elements formed on the
surface of said crystallized glass layer; and a pair of electrodes
for detecting the change of the electric resistance of said strain
sensitive resistive elements.
[0027] The high aluminiferous ferritic stainless steel sheet of the
present invention is a substrate material excellent in glass
adhesiveness and high temperature oxidation resistance and is
inevitable technology for sensor substrate material with which an
insulating layer is adhered.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a schematic illustration showing a mechanical
quantity sensor according to the present invention.
[0029] FIG. 2 is a graph showing the distribution of average linear
expansion coefficients in the range from the room temperature
(20.degree. C.) to 900.degree. C. in relation to the contents of Cr
and Al of the stainless steel.
[0030] FIG. 3 is a graph showing the relationship between an Al
content and an average linear expansion coefficient of the
stainless steel in the range from the room temperature (20.degree.
C.) to 900.degree. C.
THE MOST PREFERRED EMBODIMENT
[0031] The present invention is hereunder explained in detail.
[0032] The present invention has been established as a result of
studying the components of stainless steels, production methods,
linear expansion coefficients and high temperature oxidation
resistance, and provides a material excellent in glass adhesiveness
used for a weight sensor substrate of an automobile airbag by
adopting as the metal base material a stainless steel sheet
produced containing Nb in a high aluminiferous ferritic stainless
steel sheet and preferably further containing V, Ti and Zr
therein.
[0033] Firstly, the reasons for limiting the ranges of the
components in a stainless steel according to the present invention
are explained.
[0034] Cr: Cr is the most fundamental element in securing the
thermal resistance or high temperature oxidation resistance of a
stainless steel. In the present invention, when a Cr content is
less than 12 mass %, such properties are secured insufficiently and
in contrast, when Cr is contained in excess of 30 mass %,
particularly the toughness and ductility of a hot-rolled steel
strip deteriorate considerably and the producibility of the
material also deteriorates. For these reasons, a Cr content is
limited in the range from 12 to 30 mass %, preferably from 14.5 to
16 mass %.
[0035] Al: Al is an element that remarkably improves the high
temperature oxidation resistance and specific resistance of a
ferritic stainless steel. In addition to that, as an Al content
increases, a linear expansion coefficient increases. Therefore, in
the present invention, it is possible to make the linear expansion
coefficient of a ferritic stainless steel coordinate with and
approximate various linear expansion coefficients of various
crystallized glass layers by alloy design wherein mainly an Al mass
% is adjusted. FIG. 2 shows the distribution of average linear
expansion coefficients in the range from room temperature
(20.degree. C.) to 900.degree. C. in relation to the contents of Cr
and Al of the stainless steel. It is understood that an average
linear expansion coefficient depends not on a Cr content but on an
Al content. FIG. 3 shows the relationship between an Al content and
an average linear expansion coefficient of the stainless steel. The
approximate expression of an average linear expansion coefficient a
in the range from the room temperature (20.degree. C.) to
900.degree. C. is 12.8+0.28.times.(Al mass %) when an Al content is
about 8 to 9 mass % or lower, and 2.9+1.4.times.(Al mass %) when an
Al content exceeds about 9 mass %. As stated above, the average
linear expansion coefficient of generally used crystallized glass
is 13 to 16.times.10.sup.-6/.degree. C., and therefore it becomes
possible to control the difference in the linear expansion
coefficient between a stainless steel substrate and employed
crystallized glass within an allowable range by adjusting an Al
content in the range of 8 mass % or less. Further, with regard to
the influence of Al on high temperature oxidation resistance,
whereas the high temperature oxidation resistance is insufficient
with an Al content of 2.5 mass % or less, when Al is contained in
excess of 8 mass %, not only the average linear expansion
coefficient increases rapidly but also the toughness of a
hot-rolled steel strip deteriorates considerably and thus the
producibility of the material also deteriorates. For these reasons,
an Al content is limited in the range from 2.5 to 8 mass %,
preferably 4 to 6 mass %.
[0036] A stainless steel sheet according to the present invention
is a high aluminiferous stainless steel sheet and the toughness
thereof lowers after hot rolling. Therefore, it is necessary to
secure toughness in order to improve workability. The present
invention is aimed at securing the toughness of a steel sheet by
regulating components as follows.
[0037] C and N: C and N, when they are contained in excess of 0.025
mass % respectively, deteriorate the toughness of a hot-rolled
steel strip which is the raw material of a cold-rolled steel sheet
and the producibility of the material, namely cold-rolling
operability. Therefore, the contents of C and N are limited to
0.025 mass % or less respectively and the sum of C and N is limited
to 0.030 mass % or less. Preferably, the contents of C and N are
0.010 mass % or less respectively and the sum of C and N is also
0.010 mass % or less.
[0038] Nb: Nb is an element that forms carbonitride, thus prevents
Cr carbide from precipitating at grain boundaries, refines crystal
grains, enhances the toughness of a hot-rolled steel strip, and
thus improves the producibility of the material. Therefore, it is
possible to enhance the toughness of a hot-rolled steel strip by
containing Nb in a stainless steel according to the present
invention. When an Nb content is less than 0.05 mass %, the effect
is insufficient. In contrast, when an Nb content exceeds 0.5 mass
%, workability deteriorates considerably at cold rolling. For those
reasons, a Nb content is limited in the range from 0.05 to 0.5 mass
%, preferably 0.1 to 0.3 mass %.
[0039] V: V can be added selectively in the present invention. V
further enhances the toughness of a hot-rolled steel strip by the
same effect as Nb. When a V content is less than 0.05 mass %, the
effect is insufficient. In contrast, when a V content exceeds 0.4
mass %, workability deteriorates considerably at cold rolling. For
those reasons, a V content is limited in the range from 0.05 to 0.4
mass %.
[0040] Ti: Ti can be added selectively in the present invention. Ti
is an element that is effective in improving the high temperature
oxidation resistance of a ferritic stainless steel and improves the
adhesiveness of an oxide film. With a Ti content of 0.02 mass % or
more, the effect can show up. However, an excessive addition of Ti
deteriorates the toughness of a hot-rolled steel strip and also the
producibility of the material. When a Ti content exceeds 0.2 mass %
in particular, the deterioration of toughness is conspicuous. For
these reasons, a Ti content is limited in the range from 0.02 to
0.2 mass %, preferably from 0.04 to 0.10 mass %.
[0041] Zr: Zr can be added selectively in the present invention. Zr
exhibits the same effect as Ti does and is an element that is
effective in improving the high temperature oxidation resistance of
a ferritic stainless steel and improves the adhesiveness of an
oxide film. With the addition of Zr by 0.02 mass % or more, the
effect can be exhibited. In contrast, an excessive addition of Zr
deteriorates not only oxidation resistance but also the toughness
of a hot-rolled steel strip and thus the producibility of the
material. When a Zr content exceeds 0.2 mass % in particular, the
deterioration of toughness is conspicuous. For these reasons, a Zr
content is limited in the range from 0.02 to 0.2 mass %, preferably
0.05 to 0.15 mass %.
[0042] A preferable method for hot rolling a high aluminiferous
ferritic stainless steel sheet of low carbon and low nitrogen, to
which Nb or Nb, V, Ti, and Zr are added in appropriate amounts
according to the present invention, is described. Toughness can be
enhanced remarkably by: finishing hot rolling a stainless steel
slab containing components stipulated in the present invention in
the recovery temperature range from 700.degree. C. to the
recrystallization temperature; controlling the sum of the reduction
ratios in the recovery temperature range not exceeding a
recrystallization temperature to 15% or higher; successively
coiling the hot-rolled steel strip in the temperature range from
higher than 500.degree. C. to lower than 850.degree. C.; and
thereafter cooling it mandatorily. It is estimated that, by
applying the final stage rolling in the recovery temperature range
not exceeding the recrystallization temperature Ts (.degree. C.) in
hot rolling, the dislocations introduced during the rolling paths
form sub-boundaries as an energetically stable rearranged structure
and sub-grains are formed in the crystal grains of the structure
after hot rolling.
[0043] Next, the characteristics of a stainless steel intended in
the present invention are described. In the present invention, the
difference in the average linear expansion coefficient between a
high aluminiferous ferritic stainless steel sheet and crystallized
glass for a weight sensor substrate is less than 10% in the
temperature range from 20.degree. C. to 900.degree. C. When a
crystallized glass layer functioning as an insulating layer, a
strain sensitive resistive element and electrodes are baked and
resultantly solidified in the form of layers onto a stainless steel
sheet functioning as the substrate of a sensor, it is necessary to
coordinate their linear expansion coefficients with each other in
order to improve the adhesiveness between the metal base material
and the glass layer. Baking is applied at 900.degree. C. or lower
and therefore it is desirable that the linear expansion
coefficients are close to each other not only in the vicinity of
the room temperature but also in the temperature range from
20.degree. C. to 900.degree. C. When the difference in the average
linear expansion coefficient is more than 10%, the adhesiveness
between a metal base material and a crystallized glass layer
deteriorates considerably and therefore they do not function as the
base of a resistive element. The average linear expansion
coefficient of generally used crystallized glass is 13 to
16.times.10.sup.-6/.degree. C.
[0044] In the present invention, an appropriate average linear
expansion coefficient of a high aluminiferous ferritic stainless
steel sheet is 13.5 to 15.5.times.10.sup.-6/.degree. C. in the
temperature range from 20.degree. C. to 900.degree. C. A linear
expansion coefficient a is defined by the expression
L.sub.T=L.sub.20(1+.alpha.T). Here, L.sub.20 is a length at
20.degree. C. and L.sub.T is a length at a temperature T. If the
average linear expansion coefficient of a high aluminiferous
ferritic stainless steel sheet according to the present invention
is less than 13.5.times.10.sup.-6/.degree. C. or more than
15.5.times.10.sup.-6/.degre- e. C. in the temperature range from
20.degree. C. to 900.degree. C., the adhesiveness of the stainless
steel sheet with a crystallized glass layer is not secured.
[0045] It is possible to control the difference in the linear
expansion coefficient between a stainless steel sheet and
crystallized glass to 10% or less by regulating an Al content of
the stainless steel sheet in the range from 2.5 to 8 mass %.
[0046] A high aluminiferous ferritic stainless steel sheet
according to the present invention is a cold-rolled annealed steel
sheet produced by descaling and thereafter cold rolling a
hot-rolled steel strip and successively applying annealing and
descaling.
[0047] A cold-rolled steel sheet of a high aluminiferous ferritic
stainless steel sheet according to the present invention is stamped
into a desired shape and thereafter baked together with a glass
layer. The baking is applied for 20 to 120 minutes at 800.degree.
C. to 900.degree. C. When a baking temperature is lower than
800.degree. C., the interdiffusion between a stainless steel sheet
and a glass layer is insufficient and therefore the adhesiveness is
also insufficient. On the other hand, when a baking temperature
exceeds 900.degree. C., the thermal resistance of a glass layer
cannot withstand the temperature. Note that, a baking time here is
defined by the total hours spent in plural heat treatments. When a
baking time is shorter than 20 minutes, interdiffusion is
insufficient and thus adhesiveness is also insufficient. On the
other hand, when a baking time exceeds 120 minutes, an oxide film
having the thickness of submicron order is formed due to the
progress of oxidation, resulting in discoloration, so-called temper
color, and the deterioration of resistance against temper color.
The temper color does not directly affect the functions as a sensor
but a color tone intrinsic to a stainless steel surface is
lost.
[0048] In the present invention, the thickness of an oxide film
formed on the surface of a stainless steel sheet in the baking
treatment that is applied to the stainless steel sheet as well as a
crystallized glass layer is less than 0.38 .mu.m. When an oxide
film thickness is 0.38 .mu.m or more, it corresponds to the
wavelength of visible light (0.38 to 0.78 .mu.m) and therefore an
interference color such as blue-green appears. When an oxide film
thickness is less than 0.38 .mu.m, such an interference color does
not form and excellent temper color resistance is obtained.
[0049] An automobile airbag weight sensor according to the present
invention is, as shown in FIG. 1, a weight sensor characterized by
being composed of: a substrate 1 comprising a metal base material
of a high aluminiferous ferritic stainless steel sheet; a
crystallized glass layer 2 with which the surface of the substrate
is covered; strain sensitive resistive elements 4 formed on the
surface of the crystallized glass layer; and a pair of electrodes 3
for detecting the change of the electric resistance of the strain
sensitive resistive elements. Note that, in the weight sensor, volt
holes 5 used for putting the weight sensor in place are provided.
Since the adhesiveness of the substrate of a high aluminiferous
ferritic stainless steel sheet with a crystallized glass layer 2 is
good, it is possible to simultaneously apply baking treatment to a
metal substrate 1, a crystallized glass layer 2, electrodes 3 and
strain sensitive resistive elements 4, or to reduce the frequency
of the baking treatment.
EXAMPLES
[0050] Next, the present invention is concretely explained on the
basis of examples.
Example 1
[0051] High aluminiferous ferritic stainless steels shown in Table
1 were melted and refined by the converter AOD method or the vacuum
melting method. These steels were subjected to surface
conditioning, thereafter hot rolled at a hot-rolling finishing
temperature in the range from 880.degree. C. to 900.degree. C.,
coiled at a hot-rolling coiling temperature in the range from
400.degree. C. to 750.degree. C., and cooled by water cooling, and
thus hot-rolled steel strips 5 mm and 3.8 mm in thickness were
produced. Successively, the hot-rolled steel strips were subjected
to shot blasting and descaling by pickling, and thereafter cold
rolled to the thickness of 3 mm and 2 mm. Successively, the
cold-rolled steel strips were annealed at 920.degree. C. and then
subjected to salt treatment and descaling by pickling, and thus
cold-rolled steel sheets were produced. With regard to crystallized
glass, crystallized glass having the average linear expansion
coefficient of 14.5.times.10.sup.-6/.degree. C. was used.
[0052] Here, evaluation tests were carried out by the following
methods.
[0053] Contents of steel sheets were measured by sampling test
pieces from the steel sheets and subjecting them to element
analysis. C, S and N were measured by the gas analysis method (the
method of melt in inert gas and thermal conduction measurement in
the case of N, and the method of combustion in oxygen stream and
infrared-absorbing analysis in the case of C and S), and the other
elements were measured with a fluorescent X-ray analyzer (SHIMAZU,
MXF-2100).
[0054] The producibility (cold workability) was evaluated by
sampling a V-notched Charpy test piece of sub-size (5 mm or 3.8 mm
in thickness) conforming to the JIS Standard in the direction
parallel to the rolling direction, subjecting the test piece to an
impact test, and measuring the temperature at which the impact
value was 2 kgf/cm.sup.2 (vT2:.degree. C.). In the case where a vT2
value exceeded 80.degree. C., even though heating by warm water was
applied beforehand, the risk of sheet breakage increased extremely
due to an impact and the like when cold rolling was applied, thus
it was substantially impossible to apply cold rolling, and
therefore the case was evaluated as X. Any of the examples
according to the present invention showed good producibility. The
contents of C and C+N were beyond the upper limits in the case of
the comparative example No. 11, the Cr content was beyond the upper
limit in the case of the comparative example No. 12, the Al content
was beyond the upper limit in the case of the comparative example
No. 14, the contents of N and C+N were beyond the upper limits in
the case of the comparative example No. 16, the Nb content was
beyond the upper limit in the case of the comparative example No.
17, the Ti content was beyond the upper limit in the case of the
comparative example No. 18, the Zr content was beyond the upper
limit in the case of the comparative example No. 19, and the V
content was beyond the upper limit in the case of the comparative
example No. 20, and resultantly the producibility was poor in any
case of the comparative examples.
[0055] The high temperature oxidation resistance was evaluated by
using a sample the surface of which was polished to #400 in mesh
and measuring the increment of oxidation amount after the heating
for 120 minutes at 900.degree. C. in the atmosphere. A case where
the increment of the oxidation amount was not more than 0.2
mg/cm.sup.2 was indicated as .largecircle. and a case where the
increment of the oxidation amount exceeded 0.2 mg/cm.sup.2 was
indicated as X. The Cr content was lower than the lower limit
stipulated in the present invention in the case of the comparative
example No. 13 (sample No. 13) and the Al content was lower than
the lower limit stipulated in the present invention in the case of
the comparative example No. 15 (sample No. 15), and resultantly the
oxidation resistance was inferior in either case of the comparative
examples.
[0056] The linear expansion coefficient was evaluated by adopting
the test method stipulated in the ISO Standard and measuring an
average linear expansion coefficient in the range from the room
temperature (20.degree. C.) to 900.degree. C. A case where an
average linear expansion coefficient was in the range from 13.5 to
15.5.times.10.sup.-6/.degree. C. was indicated as .largecircle. and
a case where it was lower than 13.5.times.10.sup.-6/.degree. C. or
higher than 15.5.times.10.sup.-6/.deg- ree. C. was indicated as X.
In the examples according to the present invention, the difference
in the average linear expansion coefficient between a high
aluminiferous ferritic stainless steel sheet and crystallized glass
for a weight sensor substrate was within 10% in the temperature
range from 20.degree. C. to 900.degree. C. In the case of the
comparative example No. 15, the Al content was lower than the lower
limit stipulated in the present invention and also the average
linear expansion coefficient in the range from the room temperature
to 900.degree. C. was lower than the lower limit stipulated in the
present invention.
[0057] The glass adhesiveness was evaluated by the tape peeling
test JIS H8504 (a method for testing the adhesiveness of plating).
A case where a crystallized glass layer exfoliated was indicated as
X and a case where it did not exfoliate was indicated as
.largecircle.. The glass adhesiveness of the metal base materials
containing the components stipulated in the present invention
improved considerably. In the case of the comparative example No.
15, the Al content was lower than the lower limit stipulated in the
present invention and resultantly the glass adhesiveness was
poor.
1TABLE 1 Clas- Sam- sifi- ple Chemical components (mass %) cation
No. No. C Si Mn P S Cr Al N Nb V Ti Zr C + N In- 1 1 0.006 0.21
0.15 0.020 0.0021 15.09 4.71 0.0058 0.108 0.0118 vented 2 2 0.003
0.21 0.14 0.020 0.0003 14.95 4.54 0.0042 0.204 0.0072 steel 3 3
0.004 0.20 0.15 0.020 0.0003 14.94 4.46 0.0044 0.298 0.0084 4 4
0.006 0.21 0.15 0.020 0.0023 13.51 4.11 0.0061 0.213 0.249 0.0121 5
5 0.003 0.20 0.14 0.020 0.0006 18.01 3.21 0.0040 0.301 0.044 0.0070
6 6 0.005 0.21 0.14 0.019 0.0004 14.99 4.52 0.0040 0.100 0.08
0.0090 7 7 0.003 0.20 0.14 0.020 0.0006 15.20 4.69 0.0040 0.211
0.049 0.0070 8 8 0.005 0.21 0.14 0.019 0.0004 14.99 4.52 0.0040
0.100 0.153 0.143 0.0090 9 9 0.004 0.20 0.14 0.020 0.0003 15.00
4.51 0.0047 0.200 0.102 0.0087 10 10 0.003 0.21 0.14 0.021 0.0007
15.01 4.48 0.0048 0.128 0.191 0.0078 Com- 11 11 0.034* 0.21 0.14
0.020 0.0007 15.08 4.57 0.0041 0.252 0.154 0.0381* parative 12 12
0.006 0.21 0.15 0.020 0.0006 32.12* 4.69 0.0061 0.212 0.066 0.0121
example 13 13 0.005 0.21 0.15 0.020 0.0005 11.23* 3.55 0.0055 0.198
0.0105 14 14 0.005 0.21 0.14 0.019 0.0004 15.20 9.55* 0.0040 0.108
0.161 0.0090 15 15 0.004 0.21 0.15 0.020 0.0004 15.19 2.44* 0.0045
0.154 0.0085 16 16 0.003 0.20 0.14 0.020 0.0006 14.99 4.52 0.0410*
0.299 0.113 0.0440* 17 17 0.005 0.21 0.14 0.019 0.0004 15.20 4.69
0.0040 0.608* 0.0090 18 18 0.003 0.22 0.15 0.020 0.0004 14.95 4.54
0.0050 0.155 0.253* 0.0080 19 19 0.003 0.20 0.14 0.020 0.0006 14.99
4.52 0.0040 0.210 0.241* 0.0070 20 20 0.003 0.21 0.14 0.020 0.0006
15.02 4.46 0.0043 0.192 0.451* 0.0073 Evaluation Linear expansion
Sheet coefficient at thickness Producibility High temperature room
temp. to Glass Overall Classification No. Sample No. (mm) (Cold
workability) oxidation resistance 900.degree. C. adhesiveness
judgment Invented steel 1 1 2 .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. 2 2 2 .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle. 3 3 3
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. 4 4 3 .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. 5 5 3 .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. 6 6 3 .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle. 7 7 3
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. 8 8 2 .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. 9 9 3 .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. 10 10 3 .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle. Comparative
11 11 3 X -- -- -- X example 12 12 3 X -- -- -- X 13 13 3
.largecircle. X .largecircle. .largecircle. X 14 14 3 X -- -- -- X
15 15 3 .largecircle. X X X X 16 16 3 X -- -- -- X 17 17 2 X -- --
-- X 18 18 2 X -- -- -- X 19 19 3 X -- -- -- X 20 20 3 X -- -- -- X
The marks * show the figures are outside the relevant ranges
stipulated in the present invention.
Example 2
[0058] The steel sheets of sample Nos. 7 and 3 shown in Table 1
were subjected to baking heat treatment under the conditions shown
in Table 2. The crystallized glass having the average linear
expansion coefficient of 14.5.times.10.sup.-6/.degree. C., which
was the same as used in EXAMPLE 1, was used.
[0059] A coating film thickness was measured by GDS (Glow Discharge
Emission Spectrometry). The measuring device was JY500ORF-PSS type
made by JOBIN YVON (France) and the measurement area was 4 mm in
diameter. A sputter speed was measured by the depth formed after
subjecting a Japanese Iron and Steel Certified Reference Material
JSS652-13 to the discharge for 250 seconds. As the samples for
calibration, four kinds of specimens including Japanese Iron and
Steel Certified Reference Materials JSS652-13, JSS171-1, JSS1001-1
and the like were used.
[0060] The resistance to temper color was judged by visually
observing the existence of color development at visible
wavelengths.
[0061] The invention example Nos. 7 and 19 to 21 were the cases
where the baking conditions stipulated in the present invention
were adopted and were excellent in both the glass adhesiveness and
temper color resistance. In the case of the comparative example No.
22, the baking temperature was higher than the upper limit and thus
all the glass adhesiveness, film thickness and temper color
resistance were inferior. In the case of the comparative example
No. 23, the baking time was longer than the upper limit and thus
both the film thickness and temper color resistance were inferior.
In the case of the comparative example No. 24, the baking time was
shorter than the lower limit and thus the glass adhesiveness was
poor. In the case of the comparative example No. 25, the baking
temperature was lower than the lower limit and thus the glass
adhesiveness was poor.
2 TABLE 2 Baking condition Evaluation Sample Temperature Time Glass
Film Temper color Overall Classification No. No. (.degree. C.)
(min.) adhesiveness thickness resistance judgment Invention 7 7 850
110 .largecircle. .largecircle. .largecircle. .largecircle. example
19 7 850 40 .largecircle. .largecircle. .largecircle. .largecircle.
20 3 850 110 .largecircle. .largecircle. .largecircle.
.largecircle. 21 3 850 40 .largecircle. .largecircle. .largecircle.
.largecircle. Comparative 22 7 950* 100 X X X X example 23 7 850
150* .largecircle. X X X 24 7 850 15* X .largecircle. .largecircle.
X 25 7 750* 100 X .largecircle. .largecircle. X The marks * show
the figures are outside the relevant ranges stipulated in the
present invention.
* * * * *