JPH11279654A - Manufacture of titanium-containing ferritic stainless steel strip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of glistening marks (intergranular corrosion) due to sensitization at the time of cold rolling of a Ti-containing ferritic stainless steel strip. SOLUTION: The ferritic stainless steel strip is manufactured by subjecting a cast slab, having a composition containing, by weight, <=0.08% C, 10.50-20.00% Cr, and <=1.0% Ti, after heating or in a state of as-cast hot slab, to hot rolling and then applying a repetition of annealing, pickling, and cold rolling at least one or more times. In this case, Ti addition is regulated so that Ti/(C+N)>=0.006 T-0.4 is satisfied from the highest allowable temperature (T) selected from allowable design annealing temperatures at the annealing of one or plural times performed in the course of cold rolling, followed by refining.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a production method for preventing grain boundary corrosion flaws (hereinafter referred to as "glitter flaws") generated in a cold-rolled steel strip by appropriately adjusting components in steel, The present invention also relates to a method for producing a ferritic stainless steel containing Ti in which the cost of Ti is reduced.

[0002]

2. Description of the Related Art Ferrite stainless steel sheets containing Ti are used for home appliances and the like, and have improved workability, weldability, and corrosion resistance as compared with SUS430.

[0003] When producing a cold-rolled steel strip of ferritic stainless steel containing Ti, continuous annealing or batch-type annealing is performed in a cold-rolling step (hereinafter, these are referred to as annealing). During this annealing, depending on the annealing temperature or cooling conditions,
The material becomes sensitized, and the grain boundaries near the surface layer of the steel strip are eroded in the pickling process performed after annealing, and after the cold rolling process and the final annealing process, the crystal grains that have eroded the grain boundaries fall off. Then, a surface defect called a glitter flaw occurs.

[0004] When this glittering flaw occurs, there is a problem that the appearance is remarkably impaired. In addition, when this glittering flaw occurs, it is necessary to remove it by polishing, and an extra step is required.

[0005] In order to prevent the generation of glittering flaws due to the sensitization of ferritic stainless steel containing Ti, a method of reducing C and N is conventionally known. However, if the C and N content levels that can be reached industrially cannot completely suppress the intergranular corrosion susceptibility, which is the cause of glittering defects, stabilization that can fix C and N such as Ti or Nb. It is known that the harmful effects of C and N on intergranular corrosion can be eliminated by adding elements alone or in combination, and this is disclosed in Japanese Patent Application Laid-Open No. Hei 5-271880 by the same applicant as the present invention. .

In general, in the production of a ferritic stainless steel strip containing Ti, various components are designed in consideration of the processing conditions at the customer, and the required properties of the material such as mechanical properties are obtained. It is manufactured so that the annealing temperature range and the cooling rate range are determined.

[0007]

However, it is difficult to completely prevent brilliant flaws depending on the annealing temperature and cooling conditions with the addition of Ti which is stoichiometrically about the amount of Ti required to fix C and N. Met. Also, as described above, even if the components are manufactured under predetermined conditions such as the component design specified by the customer, temperature and cooling conditions, manufacturing disturbances, such as variations in cooling conditions after annealing, threading in the manufacturing process, etc. Due to variations in the speed and the like, the actual situation was that the glittering flaws of the ferritic stainless steel strip containing Ti were not completely prevented. Therefore, the present invention provides a method for producing a Ti-containing ferritic stainless steel strip which can prevent the occurrence of glittering flaws due to the sensitization of the Ti-containing ferritic stainless steel strip under all production conditions.

[0008]

According to the present invention, the weight%
And C: 0.08% or less, Cr: 10.50 to 20.0
A ferritic stainless steel strip in which a slab consisting of 0% and Ti: 1.0% or less is directly hot-rolled while being heated or cast, and then annealing, pickling and cold rolling are repeated at least once. In the cold rolling process
From the highest allowable temperature (T) selected from the allowable design annealing temperatures of one or more annealings, Ti / (C
+ N) ≧ 0.006T−0.4, and is melted by adjusting the addition of Ti. According to the present invention, after the predetermined component design and the annealing temperature design, the steel weight can be further finely adjusted based on the maximum allowable temperature (T) to design the steel component, so that it is possible to surely prevent glittering flaws.

Further, the present invention is a method of adding Ti into molten steel in the final stage of the smelting process in which the Ti addition adjustment is performed. According to the present invention, since the amount of Ti added can be adjusted after measuring the components in the steel in the final step of the smelting process, it is possible to accurately take into account the unavoidable N weight% that is inevitably contained in the components. It is possible to surely prevent glittering flaws.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted intensive investigations on glittering flaws that sometimes occur in SUS430LX, which is a ferritic stainless steel strip containing Ti, and as a result, predetermined manufacturing conditions are satisfied. In addition, glittering flaws have occurred. In order to surely prevent this, it has been found that the component design is re-examined from the maximum allowable temperature of the annealing step under the manufacturing conditions, and that the production can be surely prevented from glittering defects.

The evaluation of the glittering flaws is a visual evaluation, in which a gum tape is attached to the surface of the final cold-rolled steel strip, and thereafter, the evaluation is performed by observing the peeled-off strip. The surface after peeling is shattered and is seen as glitter when viewed visually, which is called a glitter flaw. In addition, when the surface roughness of the steel strip is severe, the flaw can be observed as a white streak-like flaw even when the gum tape is not attached.

Hereinafter, the alloy components and the contents of the Ti-containing ferritic stainless steel used as the base material will be described.

C: Element inevitably contained in stainless steel. When the C content is reduced, the material becomes soft, the workability is improved, and the generation of carbides is reduced. Further, as the C content is reduced, the weldability and the corrosion resistance of the welded portion are also improved. Therefore, the upper limit of the C content is set to 0.08% by weight.

Cr: a main element that enhances the corrosion resistance of stainless steel, and significantly improves corrosion resistance such as weather resistance and pitting corrosion resistance. The effect of Cr on improving corrosion resistance is 10.50.
Less than weight% is not sufficient. However, when the Cr content is 2
If the content exceeds 0.00% by weight, embrittlement is likely to occur,
Difficulty is involved in product processing. Therefore, the Cr content is set in the range of 10.50 to 20.00% by weight.

Ti: Ti has an effect of fixing C and N, and is an alloy element effective for improving corrosion resistance. However, 1.
When the content exceeds 0% by weight, a surface defect called Ti streak tends to be strengthened, and the surface quality of the material is deteriorated.

Next, from the highest allowable temperature (T) selected from the allowable design annealing temperature of one or more annealings performed in the cold rolling step, Ti / (C + N) ≧ 0.006T The reason why the addition of Ti is adjusted so as to satisfy −0.41 will be described below.

This is because, from the above-mentioned investigation results, the cause of the generation of this glittering flaw is that the predetermined Ti weight% is close to the lower limit, so that TiN is preferentially precipitated during cooling after heating such as annealing. As a result of a decrease in the stabilizing effect on C due to the amount of residual Ti, Cr carbide precipitates and becomes sensitized as shown in FIG. Further, the intergranular corrosion surface on which the Cr carbide was precipitated by repeating the subsequent pickling or cold rolling and annealing pickling was advanced to (b), (c), (d) and (e) in FIG. is there. That is, variations in manufacturing conditions are disturbances that are inevitably generated. In consideration of these, in order to reliably prevent glittering flaws, the above-described preferential precipitation of TiN and the resulting precipitation of Cr carbide are performed during annealing. It was found that it was easy to be influenced by the maximum temperature, and it was convinced that the creation of a countermeasure was effective.

If, after the predetermined component design and annealing temperature design, the steel weight component is further finely reviewed from the maximum allowable temperature according to the formula 1 to design the steel component, glittering defects can be reliably prevented. Furthermore, in order to perform the process reliably, the molten steel component is checked in the degassing process, which is the final component adjustment process of the smelting process, and the amounts of C and N, which are inevitable components, are surely grasped to adjust Ti. is there.

An experiment conducted to confirm the present invention will be described below. As test materials, C: 0.001% by weight
0.030%, Si: 00% or less, Mn: 1.00% or less, Cr: 10.50 to 20.00%, Mo: 2.20
% Or less, a sample of the cold-rolled steel strip using Ti-containing ferritic stainless steel cold-rolled steel strip consisting of 0.01 to 1.00%, other unavoidable impurities and Fe, and changing the amounts of Ti and C + N. May be collected, and glittering flaws may be generated under normal manufacturing conditions, and the surface is polished and then annealed in a laboratory in order to keep the conditions of the investigation and research constant. The temperature was changed in the range of 1100 ° C. and the cooling rate in the range of 0.53 to 27000 ° C./min, and the presence or absence of sensitization after cooling was examined. The range of annealing temperature is Ti
This is the normal annealing temperature range determined by the material properties of the ferritic stainless steel containing steel, and the cooling rate range is the normal cooling rate range of 30,000 ° C./m determined by the specifications of the annealing equipment.
in is assumed.

FIGS. 2 to 6 show the results of this experiment.
FIG. 1 shows the results obtained by arranging the values at the maximum annealing temperature that does not increase sensitivity regardless of the Ti / (C + N) ratio and the cooling rate. FIGS. 2 to 6 show the results of investigating the occurrence of glittering flaws while fixing Ti / (C + N) and changing the annealing temperature and the cooling rate. FIG. 1 summarizes the annealing temperature at which no glittering flaws occur over the entire cooling rate in relation to the Ti / (C + N) ratio. As a result, at an annealing temperature of 850 ° C. or more, Ti / (C + N) ≧ 0.00
It can be seen that by adjusting the Ti weight percentage to 6T-0.4, glittering flaws can be reliably prevented even when the cooling conditions change.

[0021]

As described above, according to the present invention,
When producing a ferritic stainless steel containing Ti, by re-adjusting the Ti content at the maximum allowable temperature, it is possible to reliably prevent the occurrence of glittering flaws in the cold-rolled steel strip. In addition, regardless of fluctuations in the cooling rate during annealing, there is an effect that the amount of Ti for fixing C and N can be minimized, and the manufacturing cost can be reduced.

[Brief description of the drawings]

FIG. 1 illustrates Ti / (C + N) for explaining manufacturing conditions of the present invention.
FIG. 4 is a relationship diagram between the maximum annealing temperature.

FIG. 2 is an experimental result when Ti / (C + N) = 0.0% by weight.

FIG. 3 is an experimental result of Ti / (C + N) = 5.3% by weight.

FIG. 4 is an experimental result of Ti / (C + N) = 5.6% by weight.

FIG. 5 is an experimental result of Ti / (C + N) = 5.9% by weight.

FIG. 6 is an experimental result of Ti / (C + N) = 6.2% by weight.

FIG. 7 is a schematic diagram illustrating a glitter flaw generation mechanism.

Claims (2)

[Claims] (1) C: 0.08% or less by weight, Cr:
10.50 to 20.00%, Ti: 1.0% or less is directly hot-rolled while being heated or cast as a hot piece.
Then, in the method for producing a ferritic stainless steel strip repeating annealing, pickling and cold rolling at least once or more,
From the highest allowable temperature (T) selected from the allowable design annealing temperatures of one or more annealings performed in the cold rolling process, Ti / (C + N) ≧ 0.006T−0.4. A method for producing a ferrite-based stainless steel strip containing Ti, characterized by adjusting the addition of Ti and smelting. 2. The method for producing a ferritic stainless steel strip containing Ti according to claim 1, wherein the addition of Ti is adjusted by adding Ti into the molten steel at the final stage of the smelting process.