JP2001073079A - Extra-low carbon thin steel sheet for deep drawing and extra-low carbon thin steel sheet for deep drawing applied with galvanizing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain excellent deep drawability, in an extra-low carbon thin steel sheet for deep drawing contg. C and Ti respectively by specified amounts, by controlling the concn. ratio of precipitated N expressed by (the concn. of precipitated N in the surface layer part from the surface of the steel sheet to a specified depth of the sheet thickness)/(the concn. of precipitated N in the center part of the steel sheet) to the value equal to or below the specified one. SOLUTION: This extra-low carbon thin steel sheet for deep drawing contains, by mass, <=0.005% C and 0.01 to 0.1% Ti, and in which the concn. ratio of precipitated N expressed by (the concn. of precipitated N in the surface layer part from the surface of the steel sheet to 1/100 of the sheet thickness)/(the concn. of precipitated N in the center part of the steel sheet) is <=3.0. It is also preferable that, as to the crystal grains in the position of 100 μm in the sheet thickness direction from the surface of the steel sheet, the shape ratio expressed by (the grain size in the rolling direction)/(the grain (BR) size in the sheet thickness direction) is <=3.0. It is also suitable that the steel sheet is incorporated with at least one kind among Sn, Pb, As, Bi, Te, Se and Sb respectively by 0.001 to 0.10%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin steel sheet (hot-rolled steel sheet, cold-rolled steel sheet) mainly used for automobiles or home appliances and suitable for deep drawing, and a zinc-based plating applied to the surface of the steel sheet. The present invention relates to thin steel sheets (such as galvanized steel sheets, galvanized steel sheets, and galvannealed steel sheets).

[0002]

2. Description of the Related Art Thin steel sheets used for automobiles and home appliances are usually subjected to press forming to produce products. In recent years, in order to reduce the production costs of these products, so-called integral forming of larger thin steel sheets has been promoted, and thin steel sheets have been required to have better deep drawability. Was. In general, as a steel sheet for deep drawing,
A so-called IF (Intersticial free) steel in which a carbonitride forming element such as Ti or Nb is added to a very low carbon steel. In such a steel sheet for deep drawing, in particular, an ultra-low carbon steel sheet to which Ti is added, when the slab is heated under the conventional atmosphere, a phenomenon in which the surface layer of the steel sheet is nitrided is observed.
When a thin steel sheet is nitrided, it hardens, and the deep drawing properties deteriorate. Therefore, in order to maintain good deep drawability, a thin steel sheet in which nitriding is suppressed as much as possible is required.

[0003] By the way, several proposals have been made so far for suppressing nitriding. For example, JP
No. 48318, Sn, Pb, As, Bi, T
A method of adding e, Se, and Sb is disclosed. Particularly, in the case of silicon steel sheet with Si added to steel,
No. 31366, the technique of adding Sn and Sb, and in Japanese Patent Application Laid-Open No. Hei 2-240214, Se, Te, Sb, Bi, Pb, Sn, As are applied to a hot-rolled sheet, and the non-oxidizing atmosphere is applied. And the like are disclosed. In producing an alloyed hot-dip galvanized steel sheet, Japanese Patent Application Laid-Open No. 2-38550 discloses a method for removing a surface layer of a nitrided steel sheet.

[0004]

However, of the above-mentioned known techniques, Japanese Patent Application Laid-Open No.
The method disclosed in Japanese Patent No. 48318 is a technique developed exclusively for low-carbon thin steel sheets.
The technology disclosed in Japanese Patent Application Laid-Open Publication No. H11-163873 relates to a silicon steel sheet.
On the other hand, thin steel sheets used for automobiles and home appliances in recent years have extremely low carbon (C: 0.005%) with improved ductility by reducing the carbon in the steel to a very small amount.
Below) It is a thin steel plate. In such ultra-low carbon steel sheets, the effect of addition of Sb or the like is low carbon steel sheets (C: 0.02 to 0.10).
%) And different behaviors such as silicon steel sheets, so far, no reports have been found on ultra-low carbon steel sheets. In addition, methods involving the application of elements such as Sb and the removal of the nitride layer on the surface of steel sheets not only complicate the manufacturing process, but also require the introduction of new equipment such as coating equipment and removal equipment, thus increasing costs. Cannot be denied.

SUMMARY OF THE INVENTION An object of the present invention is to overcome the above-mentioned problems of the prior art and to provide an ultra-low carbon thin steel sheet (including a zinc-plated steel sheet) having excellent deep drawability.
Is to provide.

[0006]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have suppressed nitriding during slab heating and annealing, and suppressed the amount of precipitated N in the surface layer of a thin steel sheet. That the deep drawability can be improved,
Further, it was found that if the amount of precipitated N is controlled in an appropriate range, the crystal grains in the surface layer of the thin steel sheet do not become abnormal grains, and this has a favorable effect on the deep drawability. Further, it was confirmed that a similar effect could be obtained when the surface of the thin steel sheet was plated with zinc. The gist configuration of the present invention completed based on such knowledge is as follows. (1) In mass%, C: 0.005% or less, Ti: 0.01 to 0.1%
In the ultra-low carbon thin steel sheet for deep drawing containing, the ratio of the precipitated N concentration expressed by (precipitated N concentration in the surface layer from the steel sheet surface to 1/100 of the sheet thickness) / (precipitated N concentration in the central part of the steel sheet) Is an ultra-low carbon steel sheet for deep drawing characterized by having a value of 3.0 or less. (2) The crystal grains at a position of 100 μm in the thickness direction from the surface of the steel sheet have a shape ratio represented by (grain size in the rolling direction) / (grain size in the thickness direction) of 3.0 or less. ,
The ultra-low carbon thin steel sheet for deep drawing according to the above (1). (3) In a steel sheet, at least one of Sn, Pb, As, Bi, Te, Se, and Sb is 0.001 to 0.10% by mass%.
The ultra-low carbon steel sheet for deep drawing according to the above (1) or (2), characterized in that it is contained. (4) An ultra-low carbon thin steel sheet for deep drawing, wherein the thin steel sheet according to any one of the above (1) to (3) is used as a material and zinc-plated by electroplating or hot-dip metal plating. Ultra-low carbon thin steel sheet with alloyed hot-dip galvanized steel sheet surface, Sn, Pb, As,
At least one of Bi, Te, Se, and Sb in mass%;
The zinc-plated ultra-low-drawing ultra-low carbon thin steel sheet according to the above (4), characterized by containing 0.0001 to 0.01% each. (6) An ultra-low carbon thin steel sheet whose surface is subjected to alloying hot-dip galvanizing, wherein the X-ray diffraction intensity ratio D of the alloy phase in the plated layer is 0.2 or less. ) Or an ultra-low carbon thin steel sheet for deep drawing, which has been subjected to the zinc plating according to (5). However, the X-ray diffraction intensity ratio D = (Γ
X-ray diffraction intensity of phase (222) plane + X-ray diffraction intensity of Γ1 phase (444) plane / (X-ray diffraction intensity of δ1 phase (330) plane)

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the reason why the gist of the present invention is limited to the above-described range, including the history of completing the present invention, will be described. The inventors have determined the mass% (hereinafter, represented by%).
When manufacturing a Ti-containing ultra-low carbon thin steel sheet for deep drawing containing C: 0.005% or less and Ti: 0.01 to 0.1%,
The surface layer before and after slab heating was investigated, and the nitriding behavior during slab heating was examined. In this experiment, the heating condition of the slab was set at 1250 ° C. for 2 hours on an actual line, and after removing the oxide film mainly composed of iron oxide, the precipitate on the surface layer was observed with a TEM (transmission electron microscope). And identification. As a result, a small amount of precipitate was observed on the slab surface layer before heating,
While most of them were Ti sulfides, precipitates composed of a large amount of Ti-based nitride and small amounts of Nb, Al, and B-based nitride were observed in the surface layer after slab heating. Degradation of the deep drawability of the thin steel sheet due to nitriding is caused by precipitates such as Ti nitrides generated during slab heating, and the strain generated by rolling etc. is sufficiently reduced by the dislocation movement inhibiting action of the precipitates. It was presumed that they did not disappear.

[0008] Therefore, as a result of studying various conditions of the slab heating and annealing conditions, it was found that the concentration of precipitated N in the surface layer (the concentration of N existing in the precipitated state as a nitride in the steel, the same applies hereinafter) was reduced in press formability. Turned out to be involved. In FIG. 1, the precipitation expressed by the ratio of the precipitation N concentration in the surface layer portion of the thin steel sheet (at a position 1 / 100th of the plate thickness from the plate thickness surface) to the precipitation N concentration in the central portion (the center position of 1/3 of the plate thickness) is shown. N concentration ratio is r of hot rolled steel sheet
The effect on the value is shown. From FIG. 1, the deposition N concentration ratio is
It can be seen that when the value exceeds 3.0, the r value decreases, and when the value is less than 3.0, a good r value can be obtained. The concentration of precipitated N in the surface layer of the thin steel sheet is determined by dissolving the portion from the surface of the steel sheet to 1 / 100th of the sheet thickness by electrolysis, extracting only the nitride, and measuring the N content of the nitride. Was divided by the total weight of the dissolved N to determine the precipitated N concentration. On the other hand, the N
The amount is determined by electrolyzing 1/100 of the original sheet thickness from the surface of the center 1/3 of the sheet thickness obtained by grinding 1/3 of the sheet thickness from both surfaces of the thin steel sheet. I asked. The precipitation N concentration ratio was calculated from the obtained ratio of both precipitation N concentrations.

[0009] The inventors have also set the above-mentioned N concentration ratio to 3.0.
In the following, it was confirmed that when each element of Sn, Pb, As, Bi, Te, Se, and Sb was added to steel, the amount of nitriding during slab heating was reduced, and it could be advantageously achieved. FIG. 2 shows the relationship between the amount of Sn added and the amount of nitriding during slab heating. here,
The method for measuring the amount of nitriding is to remove an oxide film formed on the surface of the slab, grind the surface layer 1 mm, collect an analysis sample,
The nitrogen concentration was measured. The amount of nitriding was determined from the difference in nitrogen concentration before and after heating in the surface layer of 1 mm. From FIG. 2, Sn
It can be seen that the addition of 0.001% or more results in a nitriding suppression effect. However, when Sn was added excessively in excess of 0.1%, deterioration of deep drawability was observed. For this reason
The range of Sn addition is preferably 0.001 to 0.1%. Pb, As, Bi, Te, Se, and Sb other than Sn also have the same effect as Sn by adding 0.001 to 0.1%. When two or more of these elements are added, it is desirable to add them so that the total amount of these elements is 0.001 to 0.1%.

[0010] If nitriding occurs during slab heating or recrystallization annealing, fine precipitates are formed, and these precipitates hinder the movement of dislocations and tend to generate abnormal crystal grains. Fig. 3 (a) shows the case where there are few fine precipitates and no abnormal crystal grains.
Is a microstructure of a cross section in the rolling direction when abnormal crystal grains are generated due to fine precipitates. As a result of examining such a cross-sectional structure for various steel sheets, it was found that the ratio of the grain size in the rolling direction of the crystal grains to the sheet thickness direction affected the r-value. Then, from the steel sheet surface in the thickness direction 100
A good r-value is obtained when the crystal ratio of the surface layer of the thin steel sheet at the position of μm is 3.0 or less in terms of the shape ratio expressed by (grain size in the rolling direction) / (grain size in the thickness direction). I understood. The shape ratio was determined from the surface of a thin steel sheet in a rolling direction of 20 μm by using an optical microscope.
With respect to crystal grains existing in an arbitrary range (20000 μm ² ) having a length of 0 μm, the diameter in the crystal grain thickness direction and the diameter in the rolling direction were measured, and the ratio was obtained from the average of the ratio between the two.

The tendency of the above-mentioned ratio of the concentration of precipitated N and the shape ratio of crystal grains closely related to the r value to the r-value is not only in hot-rolled steel sheets but also in cold-rolled steel sheets. The same was true for galvanized steel sheets, hot-dip galvanized steel sheets, and galvannealed steel sheets made from steel sheets (hot-rolled steel sheets and cold-rolled steel sheets). That is, a good deep drawn thin steel sheet can be obtained by controlling the precipitation N concentration ratio of the surface layer, and a higher quality deep drawn thin steel sheet can be obtained by controlling the crystal grain size ratio of the surface layer. And the above-mentioned thin steel sheet is made of Sn, Pb, As, Bi, Te, Se, Sb
By adding at least one of them in the range of 0.001 to 0.1%, a decrease in the concentration of precipitated N in the surface layer of the thin steel sheet and a decrease in the ratio of the concentration of precipitated N can be advantageously achieved.

Further, the present inventors have investigated the alloyed hot-dip galvanized steel sheet among the thin steel sheets, and found that at least one of Sn, Pb, As, Bi, Te, Se, and Sb was contained in the coating layer. The inventors also grasped the fact that when the content is 0.0001 to 0.01%, excellent deep drawability and excellent surface appearance can be obtained. In order to contain such Sn, Pb, As, Bi, Te, Se, Sb, etc. in the plating layer, these elements may be manufactured using a material in which the surface layer of a thin steel sheet is concentrated, and these elements are thin. This is performed by supplying the steel sheet to the plating layer. In the case where a thin steel sheet containing no such element is used as a raw material, it can be achieved by adding at least one element selected from the above elements to a hot-dip galvanizing bath.

Although the mechanism for improving the surface appearance described above is not always clear, Sb, Sn, etc.
It is considered that the segregation element segregates at the interface between the steel sheet and the plating during plating and alloying, thereby suppressing local alloying. That is, in a portion where alloying is fast, such as a grain boundary, diffusion of Fe and Zn is suppressed by the segregation element, and uniform alloying is achieved, thereby improving the surface appearance. In addition, according to the investigation by the inventors, in the case of a galvannealed steel sheet, the X-ray diffraction intensity ratio D of the alloy phase in this galvanized layer was determined.
[= (X-ray diffraction intensity of Γ phase (222) plane + X-ray diffraction intensity of Γ1 phase (444) plane) / (X-ray diffraction intensity of δ1 phase (330) plane)]
Was adjusted to be 0.2 or less, the deep drawability was further improved. Here, the X-ray diffraction intensity ratio D is
It can be controlled by the temperature and time during alloying.

The composition of the thin steel sheet to which the present invention is applied may be a normal deep drawing thin steel sheet except that it contains C: 0.005% or less and Ti: 0.01 to 0.1%. As preferable ranges of other elements, Si: 0.1% or less, Mn: 0.
40% or less, Al: 0.050% or less, Nb: 0.05% or less, B: 0.
0015% or less. In addition, in order to suppress nitriding at the time of slab heating and to reduce the precipitation N in the surface layer portion of the steel sheet,
It is also important to control the heating temperature and time during slab heating and the oxygen concentration in the atmosphere. Specifically, as conditions for achieving the scope of the present invention, for example, it is preferable that the slab heating temperature is 1150 ° C., the heating time at 1150 ° C. is 60 minutes, and the oxygen concentration in the atmosphere at that time is 5%. . In addition, in order to control the shape ratio of crystal grains within the range of the present invention, it is desirable to consider the oxygen concentration in the atmosphere during slab heating.
The production of a thin steel sheet by controlling such slab heating conditions can be performed without complicating the process and increasing the cost, since there is no need to apply elements such as Sb or remove the nitride layer on the surface of the steel sheet. .

[0015]

EXAMPLES Ultra low carbon steel shown in Table 1 was melted in a converter and made into a slab by a continuous casting line. This slab is heated in a heating furnace while changing the heating conditions (temperature, time, oxygen concentration),
Hot rolling was performed to a thickness of 3 mm. Thereafter, an oxide layer mainly composed of iron was removed in a pickling line to obtain a hot-rolled steel sheet. This steel sheet was cold-rolled into a cold-rolled steel sheet having a thickness of 0.6 mm, and recrystallization annealing was performed in a continuous annealing line. For electroplating,
Using a hot-rolled steel sheet after pickling or a cold-rolled steel sheet after continuous annealing, electro-galvanizing or electro-zinc-nickel plating was performed. For hot-dip galvanizing, a hot-rolled steel sheet after pickling and a cold-rolled steel sheet which is not subjected to annealing while being cold-rolled were used for annealing, plating and alloying in a continuous hot-dip galvanizing line.

With respect to the obtained thin steel sheets, the ratio of the concentration of precipitated N, the shape ratio of crystal grains, and the r value were measured. The concentration ratio of precipitated N was determined by the same method as described above. For example, plate thickness 3
mm hot-rolled steel sheet, the concentration of precipitated N in the surface layer is 30 μm, which is 1 / 100th of the plate thickness from the surface, dissolved by electrolysis,
The amount of precipitated N by taking out only the nitride (N as nitride
Amount), and this was determined by dividing the total weight by the dissolution. On the other hand, the concentration of precipitated N at the center of the plate thickness was 1% at the center of the plate thickness.
30 μm from the surface of the ３ thick part (1 mm thick at the center) was dissolved by electrolysis, and the concentration of precipitated N was determined in the same manner. The precipitated N concentration ratio was determined from the former and the latter concentration ratio. Similarly, 0.6 mm
In the case of the cold rolled steel sheet, the concentration of precipitated N element in the surface layer is 1% of the sheet thickness.
/ 100 is electrolyzed at 6 μm, and that at the center is 0.2 mm
Was electrolyzed to a surface of 6 μm. The precipitation N concentration ratio in the plated steel sheet was determined in the same manner as in the case of the hot-rolled steel sheet or the cold-rolled steel sheet except that the plating layer was dissolved with hydrochloric acid to which antimony trioxide was added.

The shape ratio of the crystal grains was determined by the following method. For each of the hot-rolled steel sheet, cold-rolled steel sheet, and plated steel sheet (after removing the plating layer), the cross section in the rolling direction is polished with a diamond buff, and etched with 1% nital liquid, and the grain boundaries are reduced. Observable. Observe this cross section at 400x magnification with an optical microscope and measure
The grain size in the thickness direction and the rolling direction was measured for crystal grains existing at 0 μm and in the rolling direction of 200 μm, and the average value of the ratio was determined. The measurement of the particle size was performed so as to pass through substantially the center of the crystal grain. The r-value is measured by pulling a JIS No. 5 test piece from the rolling direction of each of the hot-rolled steel sheet, cold-rolled annealed sheet, and plated steel sheet (having the plating layer removed with hydrochloric acid-antimony) after pickling, and measuring by pulling did.

The surface appearance of the galvannealed steel sheet is as follows:
The surface was visually observed, and was evaluated as x when there was poor appearance due to uneven alloying, and as o when there was no appearance failure. X-ray diffraction intensity ratio D of the alloy phase in the plating layer, that is, (X-ray diffraction intensity of (Γ) phase (222) plane + ΓX-ray diffraction intensity of Γ1 phase (444) plane) / (δ1 phase (3
30) The X-ray diffraction intensity of the surface) was measured by an X-ray diffractometer (RINT 1500) manufactured by Rigaku Corporation with a tube: Cu, a tube voltage: 50 kV, a tube current: 250 mA, a scan speed: 4.00 degree / min, and scanning. Axis: Under the condition of 2θ / θ, the ratio is determined by using the intensity of the peak of the {phase (222) plane + the {1} phase (444) plane at the plane interval of 2.60} and the peak of the δ1 phase (330) plane at the plane interval of 2.135}. X-ray diffraction intensity ratio D was obtained from

The slab heating conditions and annealing conditions are shown in the table.
The other conditions were as follows. Hot rolling condition Final rolling temperature: 900 ° C Coil winding temperature: 600 ° C Finished sheet thickness: 3mm Cold rolling condition Sheet thickness: 0.6mm Annealing condition Temperature × time: 820 ° C × 60 seconds Atmosphere: 2 vol% hydrogen-nitrogen, dew point -30 ° C Plating conditions Electrogalvanizing: Coating weight 25g / m²  Electric zinc nickel plating: Adhesion amount 20g / m², Ni10% hot-dip galvanizing: 80 g / m coating weight²  Alloyed hot-dip galvanizing: 40 g / m coating weight², Fe11-12% Alloying treatment conditions Temperature x time: 500-550 ° C x 10-30 seconds

Table 2 shows the measurement results of the precipitation N concentration ratio, the crystal grain shape ratio, and the r value obtained for each of the steel sheets manufactured using the components of steels 1 and 2 in Table 1 together with the manufacturing conditions. In addition, Tables 3 to 5 show the results of thin steel sheets obtained by adding an additive element such as Sn to the composition of Steel 2 in Table 1. Table 2 and Table 3
From Examples 5 to 5, the invention examples in which the precipitation N concentration ratio is within the range of the present invention are as follows:
It can be seen that an excellent r value can be obtained. Further, when the shape ratio of the crystal grains in the surface layer satisfies the range of the present invention, one layer of r
An improvement in the value is observed. Inventive examples in which Sn and Sb are contained in the plating layer in a predetermined amount and the X-ray diffraction intensity ratio D is appropriate have excellent appearance without alloy unevenness.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

[Table 3]

[0024]

[Table 4]

[0025]

[Table 5]

[0026]

As described above, according to the present invention,
By controlling the precipitation N concentration ratio, a thin steel sheet having excellent deep drawability can be provided. Further, by further controlling the shape ratio of the surface layer crystal grains, it is possible to further improve the deep drawability. In addition, this precipitation N concentration ratio is
It can be controlled by adding elements such as Sb and slab heating conditions (temperature, time, atmosphere). Furthermore, in the case of a thin steel sheet subjected to alloyed hot-dip galvanizing, the above Sn
By further containing an element such as the above, or by limiting the X-ray diffraction intensity ratio of the alloy phase in the plating layer, better quality can be obtained. Therefore,
INDUSTRIAL APPLICABILITY The present invention greatly contributes to improvement of workability, particularly deep drawability, of various thin steel sheets such as hot-rolled steel sheets, cold-rolled steel sheets, galvanized steel sheets, hot-dip galvanized steel sheets, and galvannealed steel sheets.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of the concentration of precipitated N on the r value of a hot-rolled steel sheet.

FIG. 2 is a graph showing the effect of adding Sn on the nitriding amount of a slab.

FIG. 3 is a diagram showing a typical metal structure in a surface layer portion of a thin steel plate.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // C23C 2/06 C23C 2/06 2/28 2/28 (72) Inventor Chiaki Kato Kurashiki City, Okayama Prefecture Mizushima Kawasaki-dori 1-chome (without address) Kawasaki Steel Corporation Mizushima Works

Claims (6)

[Claims] (1) In mass%, C: 0.005% or less, Ti: 0.01
Ultra-low carbon steel sheet for deep drawing containing up to 0.1%
A deep drawing wherein a ratio of a precipitated N concentration represented by (precipitated N concentration in the surface layer portion from the steel sheet surface to 1/100 of the sheet thickness) / (precipitated N concentration in the central part of the steel sheet) is 3.0 or less. Ultra-low carbon steel sheet. 2. The method according to claim 1, wherein the crystal grains at a position of 100 μm in the thickness direction from the surface of the steel sheet have a shape ratio represented by (particle size in the rolling direction) / (particle size in the thickness direction) of 3.0 or less. The ultra-low carbon thin steel sheet for deep drawing according to claim 1, wherein: 3. The steel sheet contains Sn, Pb, As, Bi, Te, Se, and Sb.
At least one of them is 0.001
3. The composition according to claim 1, wherein the content is 0.10%.
2. An ultra-low carbon steel sheet for deep drawing according to item 1. 4. An ultra-low carbon steel sheet for deep drawing, wherein the thin steel sheet according to claim 1 is used as a material and zinc-plated by electroplating or hot-dip metal plating. 5. An ultra-low carbon thin steel sheet having a steel sheet surface subjected to alloyed hot-dip galvanizing, wherein Sn,
The zinc-plated deep drawing according to claim 4, characterized in that at least one of Pb, As, Bi, Te, Se, and Sb is contained in an amount of 0.0001 to 0.01% by mass. Ultra-low carbon steel sheet. 6. An ultra-low carbon thin steel sheet having a surface of a steel sheet subjected to alloyed hot-dip galvanizing, wherein an X-ray diffraction intensity ratio D of an alloy phase in the plating layer is 0.2 or less. Item 7. An ultra-low carbon thin steel sheet for deep drawing, wherein the zinc-based plating according to item 4 or 5 is applied. However, the X-ray diffraction intensity ratio D =
(X-ray diffraction intensity of Γ phase (222) plane + X-ray diffraction intensity of Γ1 phase (444) plane) / (X-ray diffraction intensity of δ1 phase (330) plane)