JP2002332550A - High chromium steel sheet excellent in press formability and method for producing the same - Google Patents

Abstract

[PROBLEMS] To provide a high chromium steel sheet excellent in press formability and a method for producing the same. SOLUTION: This steel sheet has a mass% of C: 0.000%.
5 to 0.005%, N: 0.0005 to 0.015%,
Cr: 16 to 18%, Si: 0.01 to 0.2%, M
n: 0.01-0.2%, P <0.02%, S <0.0
1%, Al: 0.005 to 0.1%, Ti: 96 × (C
/ 12 + N / 14) to 0.25% by adding 0.9Si + 0.
Steel containing 5Mn + 8.6P + 2Ti ≦ 0.75%, with the balance being iron and unavoidable impurities,
When the product plate is subjected to tensile tests in three directions of parallel, perpendicular and 45 ° to the rolling direction, the yield elongation is less than 0.05% and the yield strength or 0.2% proof stress is 260 MPa in any direction. Less than.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a high chromium steel sheet excellent in press formability and a method for producing the same.

[0002]

2. Description of the Related Art In many cases, high chromium steel sheets represented by ferritic stainless steels are used by press forming for kitchens, home appliances, and the like. However, when a high chromium steel sheet is formed, wear damage of the punch and the die is significantly faster than that of ordinary steel (carbon steel). The reason for this is that the strength of the high chromium steel sheet is significantly higher than that of ordinary steel. Therefore, if the strength of the high chromium steel sheet can be reduced, it is considered that wear damage during press forming can be suppressed. Studies on softening high chromium steel (ferritic stainless steel) have been made so far, and JP-A-62-30852 and JP-A-63-47353 are known.
However, none of the findings could reduce wear damage during pressing.

[0003]

SUMMARY OF THE INVENTION The present invention relates to a steel plate capable of suppressing abrasion damage of punches and dies during press forming.
It is an object to provide a high chromium steel sheet based on 7% Cr and a method for producing the same.

[0004]

Means for Solving the Problems SUS430, which is a representative steel type of high chromium steel sheet, contains about 17% of Cr. Since Cr is a solid solution strengthening element, it is considered that the strength can be reduced by reducing the amount of Cr, but it is an essential element for ensuring corrosion resistance. Thus, the present inventors
Investigating the effect of material properties on the wear damage of punches and dies for press forming based on 7% Cr steel,
The following findings were obtained. When the yield point elongation is high, the wear damage is large. If the yield stress or the 0.2% proof stress exceeds 260 MPa, the wear damage is significantly increased. If the elongation at yield point and the yield stress or the yield stress or the 0.2% proof stress in any of the three directions of parallel, perpendicular and 45 ° to rolling are low, wear damage is suppressed.

Further, the relationship between the material properties, the components and the production method was investigated, and the following findings were obtained. The yield point elongation can be reduced by fixing C and N as precipitates. The descending yield stress or 0.2% proof stress is largely affected by the solid solution strengthening elements Si, Mn, P, and Ti, and the larger the amount of addition, the greater the increase. When the rolling reduction of the temper rolling after the final annealing is high, the value of 0.1% is preferable.
2% yield strength greatly increases.

The present invention has been completed based on the above findings, and the gist thereof is as follows. (1) As a steel component, in mass%, C: 0.0005 to 0.005%, N: 0.0005 to 0.015%, Cr: 16 to 18%, Si: 0.01 to 0.2% , Mn: 0.01 to 0.2%, P: less than 0.02%, S: less than 0.01%, Al: 0.005 to 0.1%, Ti: 96 × (C / 12 + N / 14) ０．２0.25%, and the following formula (1) is satisfied, and the balance is iron and unavoidable impurities. The tensile test is performed on the product plate in three directions of parallel, perpendicular and 45 ° The yield elongation is less than 0.05% in any direction, and
A high chromium steel sheet excellent in press formability, characterized in that the yield strength or 0.2% proof stress is less than 260 MPa. 0.9Si + 0.5Mn + 8.6P + 2Ti ≦ 0.75% (1) (2) As a steel component, in addition to mass%, Mg: 0.
The high chromium steel sheet having excellent press formability according to the above (1), which contains 0001 to 0.01%. (3) As a steel component, B: 0.0
The high chromium steel sheet having excellent press formability according to the above (1) or (2), which contains 005 to 0.005%. (4) As a steel component, Co: 0.
1 to 3%, V: 0.1 to 3% of one or two of the above-mentioned (1) to (3), which is excellent in press formability. Chrome steel plate. (5) In producing the high chromium steel sheet according to any one of the above (1) to (4), after hot rolling, the grain size number is adjusted to 6 to 8 through a combination process of annealing and pickling. And then performing temper rolling at a rolling reduction of less than 0.5%, the method for producing a high chromium steel sheet having excellent press formability.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. In the following description,% indicates mass%. C, N: When C and N are added in large amounts, the amount of Ti required to fix them increases. Since Ti increases the yield stress or 0.2% proof stress, both C and N need to be kept low. The respective upper limits were set to C: 0.005% and N: 0.015% in consideration of the refining ability. On the other hand, the lower limit is 0.0005% in consideration of the cost in the refining stage.

[0008] Cr: The present invention considers the press formability of a high chromium steel sheet based on 17%. The allowable range of refining is ± 1%, and the range is 16 to 18%.

Si, Mn: Si and Mn are preferably low from the viewpoint of suppressing the yield stress or the 0.2% proof stress, and the upper limit is made 0.2%. The lower limit was set to 0.01% of the lowest level mixed as an impurity.

P: Since P is a strong solid solution strengthening element,
The lower one is preferred. However, the content was set to less than 0.02% because mixing from the Fe—Cr raw material is considered.

S: If S is added in a large amount, the corrosion resistance is degraded.

Al: Al is used as a deoxidizing element, but if it exceeds 0.1%, moldability and manufacturability are reduced. Therefore, the upper limit is set to 0.1%. However, since about 0.005% is mixed as an impurity level, the lower limit is set.

Ti: Ti is a level that can reliably fix C and N, and is twice the stoichiometric composition, ie, 96 ×
(C / 12 + N / 14) was made the lower limit. However, when the addition amount is large, the upper limit is set to 0.
25%.

In addition to the above basic components, the following components can be added as required. Mg: Mg has the effect of making the solidified structure finer and improving the formability. The effect is exhibited at 0.0001% or more, and the lower limit is set. Also, even if it is added in a large amount, the effect is saturated,
0.010% was made the upper limit. The amount of Mg in the present invention indicates the amount added during refining and remaining in the steel after the production of the steel sheet, and is not mixed as impurities from slag or the like. The preferred range is 0.0002 to 0.00.
3%.

B: An element that improves workability, particularly secondary workability. The effect appears by adding 0.0005% or more. However, the effect saturates at more than 0.005%.

Co, V: These are elements which, when added in small amounts to high chromium steel, improve workability without increasing the yield strength (or 0.2% proof stress). The lower limit at which the effect is exerted is 0.1%. However, the addition of more than 3% greatly increases the strength, so the upper limit is 3%.

Other elements: Elements other than the above are not added except to be mixed as unavoidable impurities. Especially Nb
Is preferably less than 0.02% in order to significantly increase the yield stress.

Si, Mn, P, Ti: Among the elements specified as above, solid solution strengthening elements Si, Mn, P,
Regarding the four elements of Ti, it is necessary to satisfy the following equation (1): 0.9Si + 0.5Mn + 8.6P + 2Ti ≦ 0.75 (1) The left side of the expression is 0.
If it exceeds 75, the descending yield stress increases, and the abrasion damage of the punch during molding increases.

Temper rolling ratio: Temper rolling is carried out after a hot rolling, a combination of annealing and pickling. This has the effect of suppressing the yield point elongation, but when the rolling reduction is 0.5% or more, the material has a lower yield stress or a lower 0.1%.
Since the 2% proof stress greatly increases, it is set to less than 0.5%.
The rolling ratio may be converted into an elongation ratio in the steel sheet rolling direction. Since the yield point elongation may not occur depending on the component,
There is no particular need to set a lower limit.

Grain size number: It is necessary to adjust the grain size number before temper rolling to 6-8. If the particle size number is larger than 8, the yield stress (0.2% proof stress) increases, so 8 was set as the upper limit. Conversely, if it is smaller than 6, the surface becomes rough at the time of press molding. In order to set the grain size number as described above, the cold rolling ratio and the annealing temperature may be appropriately adjusted. The crystal grain size number may be measured according to the method described in JIS.

Yield point elongation and falling yield stress or 0.2
% Yield strength: If the yield point elongation in any of the three directions parallel to, perpendicular to, and 45 ° with the rolling direction is 0.05% or more, the punch wear during forming becomes severe, so it was set to less than 0.05%. When the yield stress is less than 260 MPa in all three directions, wear and tear of the punch and die during molding can be reduced. It is considered that the lower the yield stress is, the more the wear damage can be suppressed.
It is preferable to be MPa. The yield point elongation and the downward yield stress may be measured by a method according to JIS. If there is no yield point, a 0.2% proof stress is used instead of the falling yield stress.

Further, the manufacturing process needs to go through a process in which annealing and cold rolling are combined after hot rolling. This means that one or more times of cold rolling and annealing are performed after the hot rolling, and hot rolled sheet annealing may or may not be performed, or annealing may be performed during cold rolling. However, it is necessary to perform annealing before temper rolling.

In the present invention, the above-mentioned components are limited, and the grain size number and the temper rolling ratio before the temper rolling are defined.
For the first time, a steel sheet satisfying the yield point elongation and the yield stress (0.2% proof stress) in three directions parallel, perpendicular and 45 ° to the rolling direction can be manufactured, and the abrasion damage of punches and dies during forming can be suppressed.

[0024]

Examples of the present invention will be described below. Example 1 A ferritic stainless steel shown in Table 1 was melted and hot-rolled, and the grain size number was adjusted to 6 to 8 by a combination of annealing and cold rolling. After subjecting this to temper rolling of 0.1%, a tensile test (3 directions parallel, perpendicular and 45 ° to the rolling direction) and a press forming test in a laboratory (10 times for the same steel type) were performed. . Table 2 shows the results of the tensile test and the investigation of the state of wear of the punch after the press test. In the steel of the present invention, the abrasion of the punch after press forming was extremely small, and was at a level not visually recognized.

[0025]

[Table 1]

[0026]

[Table 2]

Example 2 After hot rolling some of the ferritic stainless steels shown in Table 1, the grain size number was changed by a combination of annealing and cold rolling, and the temper rolling rate was changed to produce a product sheet. Was prepared. These steel sheets were subjected to a tensile test (three directions parallel, perpendicular and 45 ° to the rolling direction) and a press forming test in a laboratory (each of the same steel type ten times).
Table 3 shows the results of the tensile test, the state of wear of the punch after the press test, and the surface condition of the steel sheet. The steel of the present invention showed almost no abrasion of the punch after press forming and no roughening of the steel sheet surface.

[0028]

[Table 3]

[0029]

According to the present invention, the press formability of a high chromium steel plate can be improved by limiting the steel composition and the strength in three directions parallel, perpendicular and 45 ° to the rolling direction. In addition, the abrasion of the die can be suppressed. In addition, a method for producing a high chromium steel sheet having excellent press formability can be provided only by defining the crystal grain size number and the temper reduction ratio by ordinary equipment, and the industrial value is extremely high.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22C 38/32 C22C 38/32 (72) Inventor Masao Kikuchi 2-6-3 Otemachi, Chiyoda-ku, Tokyo New Inside Nippon Steel Corporation (72) Inventor Junichi Hamada 3434 Shimada, Hikari-shi, Nippon Steel Corporation Inside the Hikari Works (72) Inventor Yuji Koyama 1-1 1-1 Tobata-cho, Tobata-ku, Kitakyushu Inside Yawata Works (72) Inventor Hiroshi Sugano 1-1 Hibata-cho, Tobata-ku, Kitakyushu Nippon Steel Corporation Yawata Works F-term (reference) 4E002 AA07 AD06 BC05 BD09 BD10 CB01 4K037 EA01 EA02 EA04 EA10 EA12 EA14 EA15 EA18 EA23 EA25 EA27 EA31 EA32 EB01 EB02 EB03 FG01

Claims (5)

[Claims] 1. As steel components, in mass%, C: 0.0005-0.005%, N: 0.0005-0.015%, Cr: 16-18%, Si: 0.01-0. 2%, Mn: 0.01 to 0.2%, P: less than 0.02%, S: less than 0.01%, Al: 0.005 to 0.1%, Ti: 96 × (C / 12 + N / 14) a steel containing -0.25% and satisfying the following formula (1), with the balance being iron and unavoidable impurities;
When subjected to a tensile test in three directions, vertical and 45 °, in any direction, the yield elongation is less than 0.05%, and the yield strength or 0.2% proof stress is less than 260 MPa. High chromium steel sheet with excellent press formability. 0.9Si + 0.5Mn + 8.6P + 2Ti ≦ 0.75% (1) 2. The high chromium steel sheet having excellent press formability according to claim 1, wherein the steel composition further contains 0.0001 to 0.01% of Mg in mass%. 3. The high chromium steel sheet having excellent press formability according to claim 1, further comprising, as a steel component, B: 0.0005 to 0.005% by mass%. 4. The steel component according to claim 1, further comprising one or two of mass%, Co: 0.1 to 3%, and V: 0.1 to 3%. The high chromium steel sheet excellent in press formability according to any one of the above. 5. In producing the high chromium steel sheet according to any one of claims 1 to 4, after hot rolling, a grain size number is adjusted to 6 to 8 through a combined process of annealing and pickling. A method for producing a high chromium steel sheet having excellent press formability, wherein temper rolling is performed at a rolling reduction of less than 0.5%.