JPH10298720A - High purity chromium steel sheet excellent in secondary working brittleness resistance after deep drawing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce deterioration in secondary working brittleness after deep drawin in a high purity chromium steel sheet by regulating the balance of P and B to be added. SOLUTION: This steel sheet is has compsn. by weight, <=0.010% C, <=0.5% Si, <=1.0% Mn, <=0.01% S, 9 to 25% Cr, <=0.6% Ti+Nb so as to also satisfy >=7.0 (Ti+Nb)/(C+N), 0.002 to 0.05% Al, <=0.0015% Ca and <=0.01% N, contg., at need, <=3% Mo, <=1% Cu and <=1% Ni and contg. P and B satisfying the range surrounded by the lines of (a), (b), (c), (d), (e) and (f) shown in the fig., and the balance substantial Fe. The expansion of the use for deep drawing of the high purity chromium steel sheet by the improvement of its usability can be expected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-purity chromium steel sheet having excellent secondary work brittleness resistance after deep drawing.

[0002]

2. Description of the Related Art A ferritic stainless steel sheet, a typical type of chromium steel sheet, is inexpensive and has excellent rust resistance compared to austenitic stainless steel sheet, and is therefore widely used in kitchen appliances and home appliances. I have. recent years,
With the improvement of decarburization and denitrification technologies in the steelmaking process, high-purity ferritic stainless steel sheets with further improved workability and rust resistance have been developed, and have been processed into complex shapes for use in a wider range of applications. Opportunities have increased.

[0003] Purification of decarburization and denitrification of ferritic stainless steel sheet increases elongation and r-value, so that deep drawing workability is remarkably improved. However, in the secondary processing in which the pipe expansion is further performed thereafter, there is a defect that the so-called secondary processing brittleness is inferior, for example, the forming ability is low, and grain boundary cracks are easily generated.

[0004] Regarding the improvement of the brittleness of secondary working of a high-purity ferritic stainless steel sheet, for example, Japanese Patent Publication No. 2-7391 and Japanese Patent Application Laid-Open No. 8-296000 disclose a technique of adding Ti and B. Also, Japanese Patent Application Laid-Open No. 8-20884
No. 3 proposes a technique for adding Ti, trace amounts of Nb and B. However, even in a high-purity ferritic stainless steel sheet in which these elements are controlled, secondary working cracks often occur depending on the balance of other elements, and further improvement has been desired.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a high-purity chromium steel sheet having high deep drawability due to high purification.
An object of the present invention is to provide a method for further improving the resistance to secondary working brittleness after deep drawing.

[0006]

Means for Solving the Problems The inventors of the present invention have made intensive studies to achieve the above object, and as a result, among various elements, in order to improve the brittleness resistance of a high-purity chromium steel sheet in secondary working, among other elements, And B
Found that the effect of the addition balance of
The invention has been reached.

That is, the present invention is based on the above findings, and the gist of the present invention is that C
: 0.010% or less, Si: 0.5% or less, Mn:
1.0% or less, S: 0.01% or less, Cr: 9 to 25
%, Ti + Nb: 0.6% or less, and (Ti + Nb)
/ (C + N) is 7.0 or more, Al: 0.002 to 0.0
5%, Ca: 0.0015% or less, N: 0.01% or less, Mo: 3% or less, Cu: 1% or less, Ni: 1% or less, and P and B Line ab shown in
A high-purity chromium steel sheet excellent in secondary work brittleness resistance after deep drawing, characterized in that the steel sheet satisfies the range surrounded by cdef and the balance consists of Fe and inevitable impurities.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the reasons for limiting the various elements of the present invention will be described in detail. C is restricted for the purpose of ensuring workability and corrosion resistance. In particular, although it is desirable to improve the deep drawing workability, it is desirable to lower the workability. As a condition for maintaining high elongation and high r value, the upper limit is set to 0.010%.

[0009] The amount of Si is limited. Si is an element effective for deoxidation and is recommended for some applications because it improves high-temperature oxidation resistance, but is limited in the processing applications used in the present invention, and its range is 0.5% Or less, preferably 0.25% or less.

[0010] The amount of Mn is limited. Mn is a useful element for eliminating the harm of the deoxidizing agent and S, but when added excessively, the cold workability is reduced. The upper limit of the range is 1.0%.

The amount of S is limited. S is a harmful element that segregates at crystal grain boundaries and promotes grain boundary embrittlement at high temperatures, so its upper limit is made 0.01%. Preferably, 0.0
06% or less.

[0012] Cr is added in a required amount. Cr is a basic element that imparts corrosion resistance to the product of the present invention. If the amount is less than 9%, the corrosion resistance is insufficient, and if it exceeds 25%, the cold workability is reduced and the productivity is deteriorated. Therefore, Cr is added in the range of 9 to 25%.

[0013] Ti and Nb are added in required amounts. Ti and Nb fix C and N, and are important elements for improving corrosion resistance and stabilizing the metallographic structure. To exhibit the effect, (Ti + Nb) / (C + N) needs 7.0 or more. It is. However, excessive addition impairs the surface properties of the slab and lowers manufacturability, so the upper limit is limited to 0.6% by the sum of Ti + Nb.

Al is added in a required amount. Al is an effective element as a deoxidizing agent, but if its amount is less than 0.002%, it has no effect, and if it exceeds 0.05%, it causes inconvenience such as deterioration of bending workability. Therefore, Al is 0.002 to
Limited to 0.05%.

The amount of Ca is limited. Ca is an element effective in suppressing nozzle clogging during casting,
It is selectively added according to the amount of Ti. However, an excessive addition increases the amount of Ca-based inclusions and lowers corrosion resistance and manufacturability. Therefore, the range is limited to 0.0015% or less. Preferably, it is 0.0010% or less.

N, like C, is restricted for the purpose of ensuring workability and corrosion resistance. It is desirable to lower the drawability to improve the drawability, but the cost is increased, so the upper limit is limited to 0.01% or less.

Mo is added as needed to improve corrosion resistance. Mo has an effect of suppressing the progress of pitting corrosion unique to stainless steel plates. However, the addition exceeding 3% saturates the effect and increases the cost, so the range is limited to 3% or less.

Cu is added as required. Cu has the effect of suppressing general corrosion in many corrosive environments when added in a small amount. However, if it exceeds 1%, the effect is saturated. Ni is added as needed. Ni improves the rust resistance by adding a small amount. If it exceeds 1%, the effect is saturated, so the range is limited to 1% or less.

P and B are important elements that have the greatest influence on the improvement of the secondary workability in the steel of the present invention, and are limited to the range surrounded by the line abcdef shown in the figure. In the range where B is lower than the line abcd, improvement in secondary work brittleness resistance is not exhibited. When P is higher than the line de, not only the secondary working brittleness is remarkably deteriorated, but also the hot workability is deteriorated, and surface flaws are frequently generated. In a range where B is higher than the line ef, the deep drawability is deteriorated and the slab cracks are easily generated. Therefore, the appropriate range is limited to the range surrounded by the line abcdef. For secondary work embrittlement resistance, preferably the line ghij
The range surrounded by ef is even better.

The effect of reducing the embrittlement of secondary working of a high-purity chromium steel sheet by reducing P and adding B is presumed as follows. Conventional steel has a high C and N content, and these elements segregate interstitially at crystal grain boundaries, contributing to stabilization of the grain boundary structure. However, in high-purity steels with low C and N, P, which is a substitutional element, is segregated at the grain boundaries instead of these elements, so that the electronic structure of the grain boundaries changes, and the grain boundary bonding force is reduced, resulting in brittleness. It is considered to be. On the other hand, B is an interstitial element like C and diffuses quickly. It is considered that the addition of B causes the penetration of B into the grain boundaries prior to the addition of P, thereby restoring the grain boundary bonding force.

In the production process of the steel sheet of the present invention, a steel having the above-mentioned composition is melted in an electric furnace, a converter, etc., the components are adjusted in a secondary refining furnace, and then cast into pieces by a continuous casting method. Then, it is manufactured through a normal manufacturing process of repeatedly performing hot rolling, annealing pickling (annealing is omitted depending on the situation), cold rolling, annealing pickling, and if necessary, further cold rolling, annealing pickling, and the like. Is done.

[0022]

EXAMPLE Steels of the present invention and comparative steels having the component compositions shown in Table 1 were melted in a converter-secondary refining furnace, continuously cast into CC slabs, and then heated to 1130 to 1200 ° C. Then, a hot-rolled sheet having a thickness of 3.0 mm was formed by hot rolling. This hot-rolled sheet was subjected to annealing pickling-cold rolling-anneal pickling to obtain a cold-rolled steel sheet having a thickness of 0.6 mm.

[0023]

[Table 1]

The steel sheet obtained by the above method was used as a test material, and the secondary work brittleness resistance was evaluated by the following method. That is, a cylindrical cup was produced as a primary processed product by deep drawing with a drawing ratio of 2.1. Then, after keeping the cups at a temperature of -10 to 30 ° C, a 3% pipe expansion strain was applied to the end of the cup by impact to examine the occurrence of brittle cracks on the side wall of the cup. The number of repetitions was three.

[0025]

[Table 2]

In the evaluation of the secondary working brittleness resistance in Table 2, the mark ◎ indicates no cracking at a test temperature of 0 ° C. or more, the mark 無 し indicates no cracking at 15 ° C or more, and the mark ● indicates cracking at 15 ° C or more. From the results in Table 2, it can be seen that the steel sheet of the present invention exhibits extremely excellent characteristics with respect to the brittleness resistance after secondary drawing after deep drawing.

[0027]

As described above, according to the present invention, the secondary workability brittleness which has been a problem in the conventional high-purity ferritic stainless steel sheet is greatly improved, and the chromium for high deep drawing can withstand severe processing. Steel sheet can be provided. By using the product of the present invention, it is possible to easily draw unprecedentedly complex objects in kitchens, home appliances, automobiles and other wide application fields, and its economic and social effects are extremely large.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between P and B with respect to the susceptibility of a high-purity chromium steel sheet to secondary working brittleness.

Claims (2)

[Claims] 1. In weight%, C: 0.010% or less, Si: 0.5% or less, Mn: 1.0% or less, S: 0.01% or less, Cr: 9 to 25%, Ti + Nb: 0.6% or less, and (Ti + Nb) / (C + N) 7.0 or more, Al: 0.002 to 0.05%, Ca: 0.0015% or less, N: 0.01% or less, And P and B satisfy the range surrounded by the line abcdef shown in the figure, and the balance is substantially made of Fe. . 2. The steel sheet according to claim 1, further comprising:
High purity chromium steel sheet having excellent secondary work brittleness resistance after deep drawing, characterized by containing one or more of Mo: 3% or less, Cu: 1% or less, and Ni: 1% or less. .