JPH075984B2 - Method for producing Cr-based stainless steel thin plate using thin casting method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a Cr-based stainless steel thin plate using a thin casting method.

(Prior Art) A stainless steel thin plate is obtained by directly rough rolling a slab with a thickness of about 200 mm obtained by a continuous casting process, as disclosed in, for example, JP-A-55-97430.
After heating to a temperature of about 200 ° C, it is hot-rolled to form a hot-rolled sheet, which is then annealed in a bell-type annealing furnace.
The product is cold rolled and finish annealed.

However, when the Cr-based stainless steel cold-rolled steel sheet produced in this manner is subjected to forming such as pressing, surface irregularities called ridging occur in parallel with the rolling direction.
This phenomenon is considered to be caused by the solidification structure of the slab, that is, coarse columnar crystals, and as a method of preventing this, the solidification structure is improved by means such as component composition, casting temperature, electromagnetic stirring, or hot rolling. Methods such as controlling the conditions and heat treatment conditions have been used.

For example, JP-A-58-32568 proposes a method of completing solidification while maintaining the growth rate of the solidified shell at 0.8 mm / sec or more in the casting process.

On the other hand, a method has been proposed in which the solidified structure is made finer by reducing the thickness of the cast plate to prevent the occurrence of ridging.

For example, in Japanese Patent Laid-Open No. 62-54017, it is proposed to improve the ridging property of Cr-based stainless steel by casting a plate having a thickness of 30 mm or 10 mm or less, and then subjecting it to predetermined cooling or working, heat treatment. ing.

Further, in Japanese Laid-Open Patent Publication No. 62-176649, ferritic stainless steel without roping is obtained by casting a sheet having a thickness of 5 mm or less using a single roll or twin roll method, and then annealing, cold rolling and annealing. A method of manufacturing has been proposed.

(Problems to be Solved by the Invention) In the conventional technique, since the cooling rate is slow when forming a slab by continuous casting, it is not possible to sufficiently suppress coarsening of columnar crystals and equiaxed crystals. It was difficult to suppress the occurrence of ridging when using a slab with a plate thickness of about 200 mm.

On the other hand, in the method of suppressing the ridging by thinning the slab, if the plate thickness is simply reduced, the solidification structure becomes difficult to break because the reduction ratio is lowered, and the ridging property is rather deteriorated.

The present invention has an object to provide a method for producing a Cr-based stainless steel sheet having excellent workability by solving the problems of the conventional method in producing a Cr-based stainless steel sheet using a thin casting method. It is a thing.

(Means for Solving the Problems) That is, the present invention is Cr: 8 to 30%, C: 0.001 to 0.5%, Si: 5.0% or less, Mn: 5.0% or less, Al: 0.001 to 0.5%, N: 0.001 ~ 0.5% as the main component, the balance is composed of molten alloy steel consisting essentially of Fe.
After being cast into a band of mm or less, it is rolled at a rolling reduction rate of 20% or more at the γ-phase precipitation start temperature or more, held for 3 seconds or more and 5 minutes or less in the temperature range, wound into a coil, and then cold rolled. And a method for manufacturing a Cr-based stainless steel thin plate using a thin casting method characterized by annealing, and in the method,
When coiling into a coil, a thin-wall casting method characterized by winding at less than 700 ° C, annealing after winding or in a temperature range of 700 ° C to 1000 ° C, or winding at 700 ° C to 1000 ° C. The gist is the method of manufacturing the Cr-based stainless steel thin plate used.

The present invention will be described in detail below.

An object of the present invention is to provide a method for manufacturing a Cr-based stainless steel thin plate using a thin wall casting method.

As described above, in the production of a Cr-based stainless steel thin plate by the conventional continuous casting method, the cooling rate is slow when forming a slab by continuous casting, so that the coarsening of columnar crystals and equiaxed crystals is sufficient. Uncontrollable, plate thickness 200m
It was difficult to suppress the occurrence of ridging when using a slab of about m.

On the other hand, in the method of suppressing the ridging by thinning the slab, if the plate thickness is simply reduced, the solidification structure becomes difficult to break because the reduction ratio is lowered, and the ridging property is rather deteriorated.

The present inventors, as a result of repeated research on a method for producing a Cr-based stainless steel thin plate using a thin casting method, in order to improve the ridging characteristics of the Cr-based stainless steel thin plate, a colony of a product plate (approx. It is necessary to disperse the size of the crystal grains) having a small size and at random, and to make the crystal grain size relatively small. For that purpose, a slab cast to a plate thickness of 10 mm or less is formed by ferrite-austenite transformation. It was found that it is necessary to carry out rolling processing of 20% or more and holding for 3 seconds or more and 5 minutes or less in the temperature range above the temperature.

That is, in the thin casting process, since a large reduction ratio cannot be obtained during hot rolling, the solidification structure is not sufficiently destroyed by recrystallization. Therefore, it is intended to promote recrystallization by holding the material after hot rolling.

By setting the thickness of the slab to 10 mm or less, the solidification structure can be made relatively fine-grained, and further recrystallization by hot rolling and retention can achieve sufficient fine-graining, but the slab thickness exceeds 10 mm. As the solidification structure becomes coarse and the energy consumed for hot rolling becomes large, the merit becomes smaller.
mm or less is desirable. The cast thickness should be determined from the desired product thickness and the required hot and cold rolling reductions. Further, the hot rolling rate is set to 20% or more, and the lower limit is set to 20% or less because sufficient recrystallization does not occur at a hot rolling rate lower than that.

The reason why the hot rolling temperature and the holding temperature are set to the γ-phase precipitation start temperature or higher is that the strain introduced by processing is not consumed by the transformation and contributes to recrystallization entirely, and also in such a high temperature range. The reason for this is that recrystallization proceeds very quickly.

The retention time after hot rolling was set to 3 seconds or more and 5 minutes or less,
If it is less than 3 seconds, recrystallization is not sufficiently performed, and if it exceeds 5 minutes, grain growth occurs and the grains become coarse.

The thin-walled slab that has undergone rolling processing and retention in such a predetermined temperature range may be wound up at a low temperature of less than 700 ° C to be used for cold rolling, and the coiled coil may be annealed at 700 ° C or more and 1000 ° C or less. After that, it may be subjected to cold rolling. Instead of annealing, the material may be wound in a temperature range of 700 ° C. or higher and 1000 ° C. or lower and then subjected to cold rolling.

Usually, Cr-based stainless steel has two phases, an α phase and a γ phase, in a high temperature region, and when cooled as it is, the γ phase remains as a hard phase in the α phase. If this hard phase is present during cold rolling, the structure is randomized during annealing recrystallization and the ridging property is improved. On the other hand, when the hard phase is decomposed and softened by annealing or winding at high temperature, a texture preferable for deep drawability is formed during cold rolling and annealing recrystallization, and the deep drawability is improved.

The reason for winding at a low temperature of less than 700 ° C is to improve the ridging property rather than the deep drawability,
On the contrary, the reason for annealing at 700 ° C or more and 1000 ° C or less is to improve the deep drawability rather than the ridging property. The reason for winding at 700 ° C or higher and 1000 ° C or lower is to omit the annealing step. In this case, if the annealing temperature is lower than 700 ° C, it takes a long time to decompose the hard phase, so there is no economic merit, and if it exceeds 1000 ° C, the temperature range where the γ phase precipitates is reached. This is what you do.
For the same reason, the winding is performed at 700 ° C or higher and 1000 ° C or lower.

Next, the reasons for limiting the components of the starting material of the present invention will be described.

The reason why the Cr content is 8% or more is that the corrosion resistance is inferior when the Cr content is less than this. Corrosion resistance is improved as the amount of Cr added increases, but if it exceeds 30%, the effect is small, and cold rolling property deteriorates. Considering economical efficiency, the Cr amount beyond this is not preferable, so 30% was made the upper limit.

Si is necessary as a deoxidizing agent, but if added in excess of 5.0%, the hot workability is significantly impaired, so the content was made 5.0% or less.

Mn is required as a desulfurizing and deoxidizing agent, but even if added in excess of 5.0%, its effect is saturated and it is not economical.
% Or less.

The C content is set to 0.001% or more because it is difficult to melt a starting material having a C content less than 0.001% by the usual method.
% And above. Although the ridging property is improved as the amount of C added increases, if it exceeds 0.5%, the cold ductility and r value deteriorate, so the upper limit was made 0.5%.

Although the γ value improves as the amount of Al added increases, the effect saturates even if added over 0.5%, and it is not economical, so the upper limit is set to 0.
Which was set to 5% of the lower limit was made 0.001 percent, O ₂ increases significantly the amount of Al is less than this, the lower limit since undesirable 0.
It is 001%.

The larger the amount of N added, the better the ridging property, but 0.5
%, The upper limit was set to 0.5%, and the lower limit was set to 0.001%.
The smaller the amount of N added, the better the r value, which is preferable.
Since less than 001% cannot be melted by the usual method, the lower limit is 0.001%.

Next, examples of the present invention will be described.

Example 1 Cr-based stainless steel having the components shown in Table 1 was cast into a thin-walled slab with a thickness of 3 mm using a twin roll made of copper, hot-rolled at 1280 ° C, and immediately placed in a soaking furnace. I entered it and held it. Further, a part of the samples was subjected to winding treatment at 750 ° C. for 1 hour or annealing at 840 ° C. for 4 hours. The obtained hot-rolled sheet was pickled, cold-rolled at 80% and annealed at 875 ° C for 1 minute, and then subjected to a tensile test, an r value and a ridging test. Table 2 shows the hot rolling conditions.

Table 3 shows the test results. Steels A to D, which are the steels of the present invention, showed excellent tensile, r-value and ridging characteristics, but E steel which was not hot-rolled had poor r-value and ridging characteristics, and was retained after hot-rolling. The F steel, which was not present, was slightly improved as compared with the E steel, but the r value and the ridging property were still poor.

Example 2 A Cr-based stainless steel having the components shown in Table 4 was cast into a thin-walled slab having a plate thickness of 4 to 10 mm using a cast iron mold, hot-rolled at 1280 ° C., and then immediately leveled. It was charged into a heating furnace and retained. Then, a winding treatment was performed at 600 ° C. for 1 hour or 750 ° C. for 1 hour. The obtained hot-rolled sheet was pickled, cold-rolled at 80% and annealed at 875 ° C for 1 minute, and then subjected to a tensile test, an r value and a ridging test. Table 5 shows the hot rolling conditions.

Table 6 shows the test results. The present invention steels G to J showed excellent tensile, r-value and ridging characteristics, but K and L steels which were not retained after hot rolling had poor r-value and ridging characteristics.

(Effects of the Invention) As described in detail above, according to the present invention, a Cr-based stainless steel thin plate having good tensile properties, ridging properties, and deep drawability,
It can be manufactured very easily and at low cost using the thin-wall casting method, and has a great industrial effect.

Claims (4)

[Claims] 1. A main component of Cr: 8 to 30%, C: 0.001 to 0.5%, Si: 5.0% or less, Mn: 5.0% or less, Al: 0.001 to 0.5%, N: 0.001 to 0.5%. Is a molten alloy steel consisting essentially of Fe with a thickness of 10
After being cast into a band of mm or less, it is rolled at a rolling reduction rate of 20% or more at the γ-phase precipitation start temperature or more, held for 3 seconds or more and 5 minutes or less in the temperature range, wound into a coil, and then cold rolled. And a method for manufacturing a Cr-based stainless steel thin plate using a thin-wall casting method, which comprises annealing. 2. A method for producing a Cr-based stainless steel thin plate using a thin wall casting method according to claim 1, wherein the coil is wound up at a temperature of less than 700 ° C. 3. Winding into a coil, then 700 ° C. or more 1000
The annealing is performed in a temperature range of ℃ or less.
Alternatively, a method for producing a Cr-based stainless steel thin plate using the thin-wall casting method described in 2. 4. The method for producing a Cr-based stainless steel thin plate using a thin casting method according to claim 1, wherein the coil is wound at a temperature of 700 ° C. or more and 1000 ° C. or less.