JPH08253848A - Production of ultrahigh weatherability chromium-iron alloy steel - Google Patents

Abstract

PURPOSE: To produce a Cr-Fe alloy steel extremely excellent in weatherability with high productivity by subjecting a Cr-Fe alloy steel having a specified componental compsn. to specified hot rolling and annealing, thereafter executing cold rolling and moreover subjecting the same to specified finish annealing. CONSTITUTION: A Cr-Fe alloy steel having a compsn. contg., by weight, 60 to 80% Cr, <=15ppm C, <=15ppm S, <=30ppm N, <=50ppm O and 0.05 to 1% Si, and the balance Fe with inevitable impurities is subjected to hot rolling so as to regulate the rough rolling starting and finish rolling starting temp. to 1100 to 1300 deg.C. After that, this hot rolling stock is annealed in the temp. range of 1100 to 1300 deg.C for 30sec to 10min and is thereafter subjected to cold rolling. At this time, it is rolled by a dulled roll subjected to dull working and having 1.0 to 25μm surface roughness Ra by cold rolling according to necessary. Next, this cold rolling stock is subjected to finish annealing at 500 to 1000 deg.C for 1 to 200sec while the dew point is regulated to -50 to -30 deg.C in an atmospheric gas constituted of gaseous H2 of 1 to 25vol.%, and the balance inert gas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to buildings in the coastal area where particularly high weather resistance is required and temples and shrines where long life is required.
The present invention relates to a method for producing ultra-high weather resistance Cr-Fe alloy steel used for building members such as Buddhist temples.

[0002]

2. Description of the Related Art Utilizing the high weather resistance and excellent aesthetics of Cr-Fe alloy steel, Cr-Fe alloy steel is increasingly used as a building member. However,
In recent years, due to the development of coastal (gulf) areas, the expansion of the use of steel for buildings that require long life, such as temples and shrines, and the demand for longer life for the entire building, higher weather resistance. Is required.

In order to meet the demand for such high weather resistance, it is impossible to obtain satisfactory weather resistance by the method of surface treatment such as painting or plating. On the other hand, as a method of improving the weather resistance of the steel material itself, it is known to increase the content of Cr. In addition, JP-A-5
8-199848 discloses a method for improving the weather resistance of Fe-Cr alloy steel by increasing the contents of Cr and Mo.

However, if the Cr content is high, the production is difficult. Therefore, the Cr-F is increased by increasing the Cr content.
There was a limitation in improving the weather resistance of the e-alloy steel. On the other hand, with regard to the Cr and Mo-added steels, if the addition amounts of both exceed a certain region, a precipitation phase appears and conversely the weather resistance deteriorates, and there is a problem that productivity is very poor. However, the contents of Cr and Mo can be increased only to some extent, and a steel material having sufficient weather resistance cannot be obtained. That is, with the conventional technology, although it is possible to realize a Cr-Fe alloy steel excellent in weather resistance to some extent,
Satisfactory weather resistance cannot be realized as a building material used for applications requiring particularly severe weather resistance such as in coastal areas or for applications requiring long life such as temples and shrines.

In recent years, a dull processed material has been widely used as a building material, but the dull processed material of Fe-Cr alloy steel is disclosed in JP-A-5-163528 and 5-163.
As disclosed in Japanese Patent No. 587, there is a problem that the manufacturing process is extremely complicated, such as pickling and acid dipping after dulling.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and even in applications where the conventional technology cannot achieve, particularly severe weather resistance and long life are required. Provided is a method for producing an ultra-high weather resistance Cr-Fe alloy steel capable of producing Cr-Fe alloy steel having extremely excellent weather resistance capable of more than 20 minutes with excellent productivity. Especially.

[0007]

The present inventors have found that Cr-F
As a result of systematically investigating and studying the influence of the components in the steel for e-alloyed steel, it was found that it is more effective to further increase the Cr content than the addition of Mo etc. from the viewpoint of weather resistance and productivity. Heading out, we tried to further increase the amount of Cr in the steel. As a result, the contents of C, N, S and O as components in the steel are reduced as much as possible, the content of Si is set within a specified range, and the hot rolling conditions and the annealing conditions after hot rolling are set to predetermined values. It has been found that not only excellent weather resistance can be realized, but also Cr-Fe alloy steel having a Cr content of 60% by weight or more, which has hitherto been impossible to manufacture, can be manufactured by setting the range to be in the range. It has been found that, by this, further improvement in weather resistance can be realized.

Moreover, in addition to this, as a result of studying the surface structure of the steel sheet having excellent weather resistance by making full use of various surface analysis instruments, the conditions at the time of finish annealing of the alloy steel produced under the above-mentioned prescribed conditions were set within the prescribed range. By limiting, an oxide film having extremely excellent weather resistance is formed on the surface of the Cr-Fe alloy steel,
They have also found that superior weather resistance can be realized, and have completed the present invention.

Further, as mentioned above, the conventional Cr--Fe
When manufacturing dull processed materials with alloy steel, after dull processing,
Although steps such as pickling and acid dipping are required, it is possible to perform dull processing by simply incorporating dull rolling into a normal cold rolling process by satisfying the above-mentioned predetermined conditions, and various buildings can be constructed. It is also possible to provide a dull processed material having excellent anti-glare properties, which can be widely used, with high productivity.

That is, the present invention uses chromium (Cr) 6
0 wt% to 80 wt%, carbon (C) 15 ppm
Below, sulfur (S) is 15 ppm or less, nitrogen (N) is 30
ppm or less, oxygen (O) 50 ppm or less, silicon (S
Cr-Fe alloy steel containing i) in an amount of 0.05% by weight or more and 1% by weight or less and the balance iron (Fe) and inevitable impurities has a rough rolling start and finish rolling start temperature of 1100.
Hot rolling at ℃ or more and 1300 ℃ or less, then 11
30 seconds or more 10 in the temperature range of 00 ° C to 1300 ° C
After annealing for less than a minute, cold rolling is performed, and then,
The dew point is −50 ° C. or higher in an atmosphere gas composed of 1% by volume to 25% by volume of hydrogen gas and the balance of inert gas.
In a furnace adjusted to 30 ° C or lower, 500 ° C or higher and 10
Ultra-high weather resistance Cr-Fe characterized by performing finish annealing for 1 second or more and 200 seconds or less at an annealing temperature of 00 ° C or less.
A method for manufacturing alloy steel is provided.

The present invention further relates to the method for producing the ultra-high weather resistance Cr-Fe alloy steel of the present invention, further comprising the cold rolling wherein the surface average roughness (Ra) is 1.0 μm or more and 25 μm or less. Provided is a method for producing an ultrahigh weather resistance Cr-Fe alloy steel, which includes a rolling step using a machined dull weighted roll.

[0012]

The method for producing the ultra-high weather resistance Cr-Fe alloy steel of the present invention will be described in detail below.

The ultra-high weather resistance Cr-Fe alloy steel of the present invention (hereinafter referred to as Cr-Fe alloy steel of the present invention) contains 60% of Cr.
Weight% to 80% by weight, C 15 ppm or less, S 15 ppm or less, N 30 ppm or less, O 50 ppm
Hereinafter, Si is contained in an amount of 0.05 wt% or more and 1 wt% or less
The balance has a composition of Fe and inevitable impurities. When the content of Cr is less than 60% by weight, sufficient corrosion resistance cannot be obtained in the field where the material according to the present invention is used, and a precipitation phase is likely to appear, resulting in deterioration of weather resistance and productivity. Conversely, the Cr content is 8
When it exceeds 0% by weight, melting becomes difficult, which is not preferable in manufacturing. The Cr content is preferably 65% by weight.
~ 75% by weight. Conventionally, it is said that when the Cr content is high, cracks are likely to occur during processing such as rolling,
In the present invention, this problem is overcome by defining the above composition and the conditions of hot rolling and annealing after hot rolling as described later.

It is desirable to reduce the contents of C, S, N and O as much as possible, but C is 15 ppm or less and S is 15
ppm or less, N is 30 ppm or less, and O is 50 ppm or less. If the content of any of the above components exceeds this range, a precipitation phase is likely to appear, and weather resistance and productivity decrease. Further, if the Si content is less than 0.05% by weight, sufficient weather resistance cannot be obtained.
If it is contained in excess of 1, the mechanical properties are adversely affected.

In the present invention, the Cr-Fe alloy steel further contains one or two kinds of Ti and Nb, so that the Cr-Fe alloy steel is further excellent in corrosion resistance, workability and toughness. Can be obtained. Ti and N
When b is added, the addition amount of Ti is 0.1% by weight to 0.5% by weight, and Nb is 0.1% by weight to 0.5% by weight.
Is preferred.

The manufacturing method of the present invention uses such Cr-F.
e alloy steel is used, and in addition to such an alloy composition, it has the following characteristics under the conditions of hot rolling, annealing after hot rolling, cold rolling and finish annealing. Therefore, other conditions and steps are not particularly limited.

In the production method of the present invention, steel is melted and refined by a usual method, and the alloy steel obtained has a rough rolling start temperature and a finish rolling start temperature of 1100 ° C to 13 ° C.
Hot rolling is performed at 00 ° C. If the rough rolling start temperature and finish rolling start temperature of hot rolling are less than 1100 ° C, cracks are likely to occur during rolling, and conversely, if it exceeds 1300 ° C, the effect of further improving the properties is small. The rough rolling start temperature and finish rolling start temperature of hot rolling are preferably 1150 ° C to 1250 ° C.

After such hot rolling, 1100 ° C. to 1 ° C.
Annealing is performed for 30 seconds to 10 minutes in a temperature range of 300 ° C.
If the annealing temperature is less than 1100 ° C., the crystal grains are not uniform and workability and other problems occur. Conversely, if it exceeds 1300 ° C., the crystal grains become too coarse and corrosion resistance and other problems occur. . Further, if the annealing time is less than 30 seconds, the effect of performing the annealing cannot be obtained, and conversely, if the annealing is performed for more than 10 minutes, the crystal grains are coarsened, which causes a problem in terms of corrosion resistance and the like. The annealing condition after hot rolling is preferably 11
It is 30 seconds to 150 seconds in the temperature range of 50 ° C to 1250 ° C.

In the method for producing Cr-Fe alloy steel of the present invention, cold rolling is performed after such annealing. The method of cold rolling is not particularly limited, and known methods such as tandem rolling using a tandem mill and Sendzima rolling may be used.

Further, in the present invention, during such cold rolling, a dull is applied to the surface of the steel sheet by using a dull-processed rolling roll (dull roll). It may be applied to make a cold-rolled sheet with dull marks. Here, in the manufacturing method of the present invention, when the dull processing is performed, the surface average roughness (Ra) is 1.0 μm to 25 μm.
Dulling is performed using a roll with a dull weight of μm. Ra
Is less than 1.0 μm, the dullness transferred to the steel sheet is not clear, and the effect of dulling cannot be sufficiently obtained. Conversely, Ra is 25 μm
If a roll having a dull weight exceeding the above is used, the unevenness of the dullness becomes too large, and it becomes impossible to obtain sufficient weather resistance due to falling. In addition, R of the roll with dull weight
a is preferably 1 μm to 20 μm. Moreover, it is preferable to incorporate the dull weighted roll in the latter half of the cold rolling roll.

In the method for producing Cr-Fe alloy steel of the present invention, the cold-rolled sheet thus obtained has a volume ratio of 1% by volume to
Using an atmosphere gas composed of 25% by volume of hydrogen gas and an inert gas, the dew point was adjusted to −50 ° C. to −30 ° C., and the annealing temperature was 500 ° C. to 1000 ° C. for 1 second to 200 ° C.
Finish annealing for seconds. By subjecting the cold-rolled sheet to such finish annealing, an oxide film having extremely excellent weather resistance is formed on the surface of the Cr-Fe alloy steel sheet, and a Cr-deficient phase does not occur immediately below the oxide film. Therefore, it is possible to obtain a Cr-Fe alloy steel having extremely excellent weather resistance.

For finish annealing, an atmosphere gas composed of 1% by volume to 25% by volume of hydrogen gas and an inert gas is used.
When the content of hydrogen gas in the atmosphere gas is less than 1% by volume,
The hydrogen gas does not reduce the surface of the Cr-Fe alloy steel,
The oxide film formed on the surface of this alloy becomes too thick, which causes problems in terms of corrosion resistance, and on the contrary, even if the hydrogen gas content exceeds 25%, further improvement in corrosion resistance can be obtained. Absent. The concentration of hydrogen gas in the atmosphere gas is preferably 5% by volume to 20% by volume in terms of equipment and cost. Further, as the inert gas, it is preferable to use nitrogen gas, argon gas or the like.

Further, in finish annealing, the dew point in the furnace is -50 ° C to -30 ° C, and the annealing temperature is 500 ° C to 1000 ° C.
The temperature and the annealing time are set to 1 second to 200 seconds for the following reasons. When the dew point is less than -50 ° C, the annealing temperature is 500
When the temperature is lower than 0 ° C. or when the holding time is shorter than 1 second, the oxide film formed is too thin and sufficient weather resistance cannot be obtained. In addition, when the dew point exceeds −30 ° C., the annealing temperature exceeds 1000 ° C., or the holding time exceeds 200 seconds, the oxide film becomes too thick, so that a Cr-deficient phase occurs immediately below the oxide film. , Cannot obtain sufficient weather resistance.

The manufacturing method of the present invention basically has the above configuration. Here, in the production method of the usual alloy steel, after annealing, a pickling step is required to remove the oxide film formed on the alloy steel surface, but in the production method of the present invention,
Since an oxide film having excellent weather resistance is formed from the composition of the alloy steel and the annealing conditions, there is no need for pickling and the steps can be omitted, so that a significant cost reduction can be achieved.

Although the method for producing the ultra-high weather resistance Cr-Fe alloy steel of the present invention has been described above in detail, the present invention is not limited to the above examples, and various kinds are possible within the scope not departing from the gist of the present invention. Of course, it is possible to improve and change.

[0026]

EXAMPLES The present invention will be described in more detail with reference to specific examples of the present invention.

Specimens of various Cr-Fe alloy steels were manufactured as follows. First, a steel having the composition shown in Table 1 below was melted and refined by a usual method. Steel No. 1 to 5 are alloy steels according to the present invention, and steel N
o. 6 to 11 are alloy steels according to comparative examples.

[0028]

[Table 1]

The Cr-Fe alloy steel thus obtained was hot-rolled under the conditions shown in Table 2 below and annealed after the hot-rolling. The annealing time was 100 seconds. After annealing, cold rolling was performed using a tandem mill. In addition, when performing dull processing, incorporate a dull weighted roll that has been subjected to electrical discharge machining in the final stage of the cold rolling roll,
Dull weight was applied. Surface average roughness of dull roll (R
a) is shown in Table 2 below.

The various cold-rolled steel sheets thus obtained were subjected to finish annealing to produce various Cr-Fe alloy steel sample materials. The finish annealing was performed on a continuous annealing line for ordinary steel. The atmosphere gas is hydrogen gas 5% -nitrogen gas 95% ... A hydrogen gas 20% -nitrogen gas 80% ... B hydrogen gas 10% -argon gas 90% ... C hydrogen gas 20% -argon gas 80. % ... D was used. The atmosphere gas used, the dew point in the finish annealing furnace, the temperature and the holding time are shown in Table 2 below.

Each of the obtained Cr-Fe alloy steel test materials was subjected to the following weather resistance test. [Piting potential] 80 ° C measured according to JIS G 0577 3.
10 μA in anodic polarization curve in 5% NaCl solution
The electric potential (mV vs. SEC) when showing / cm ² was measured. [Atmospheric exposure test] An atmospheric exposure test according to JIS Z 2381 was performed at a position 5 m from the sea where the corrosive environment is considered to be severe. In the rusting investigation after 3 years, the case where rust was generated was evaluated as ×, the case where spots were formed was evaluated as Δ, and the case where neither rust nor stains were formed was evaluated as ○. Furthermore, the initial glossiness of each test material and the glossiness after 3 years of exposure to the atmosphere described above were measured with a gloss meter, and the gloss retention rate ([glossiness after 3 years of atmospheric exposure / initial glossiness] x 100) was calculated. It was calculated. The above results are shown in Table 2 below.

[0032]

[Table 2]

[0033]

[Table 3]

As is clear from the results shown in Table 2,
The Cr-Fe alloy steel according to the present invention is 800 even in the pitting potential measurement under the severe condition of the solution temperature of 80 ° C.
It shows a high pitting corrosion resistance of mV or more, and from the result of the exposure test in the coastal environment, it is found that not only rust and spots are not observed, but also the gloss retention of the material itself is extremely high at 70% or more. On the other hand, even if the composition of the steel is within the range of the present invention, the temperature at the start of rough rolling and the start of finish rolling during hot rolling, the annealing conditions after hot rolling, and the finish annealing conditions, and further, the unit weight When performing, if any of the roll roughness of the dulled roll is outside the present invention, sufficient weather resistance cannot be obtained. On the contrary, the temperature at the start of rough rolling during hot rolling and at the start of finish rolling, the annealing conditions after hot rolling, and the finish annealing conditions, and the roll roughness of dull weighted rolls when performing dull weight Even if is within the range of the present invention, if the steel composition is out of the range of the present invention, it is still impossible to obtain sufficient weather resistance. From the above results, the effect of the present invention is clear.

[0035]

As described above in detail, according to the present invention, regarding the production of Cr-Fe alloy steel, in addition to Cr, C, S, N, O and Si are made to have a steel composition within a predetermined range. , Performing hot rolling under the above-mentioned predetermined conditions and annealing after hot-rolling, and then performing cold-rolling, and then performing finish annealing treatment under the above-mentioned predetermined conditions; Due to the synergistic effect of finish annealing conditions and the like, it is possible to manufacture an ultra-high weather resistance Cr-Fe alloy steel having extremely excellent weather resistance. Moreover, according to the present invention, when performing dull basis weight, dull processing during cold rolling is possible, and the pickling step can be omitted. Therefore, the manufacturing cost can be significantly reduced.

Claims (2)

[Claims] 1. Chromium (Cr) is 60% by weight or more and 80% by weight or less, carbon (C) is 15 ppm or less, and sulfur (S) is 1%.
Cr- containing 5 ppm or less, nitrogen (N) 30 ppm or less, oxygen (O) 50 ppm or less, silicon (Si) 0.05 wt% or more and 1 wt% or less, and the balance iron (Fe) and unavoidable impurities. Fe alloy steel is hot-rolled at a rough rolling start and finish rolling start temperature of 1100 ° C. or higher and 1300 ° C. or lower, and then 3 in a temperature range of 1100 ° C. or higher and 1300 ° C. or lower.
After annealing for 0 seconds or more and 10 minutes or less, cold rolling is performed, and then, in a gas atmosphere consisting of 1% by volume or more and 25% by volume or less of hydrogen gas and the balance inert gas, a dew point is -50.
500 ℃ in the furnace adjusted to -30 ℃ or more below ℃
Ultra-high weather resistance C characterized by performing finish annealing for 1 second or more and 200 seconds or less at an annealing temperature of 1000 ° C. or more and 1000 ° C. or less
Method for producing r-Fe alloy steel. 2. The method for producing an ultra-high weather resistance Cr-Fe alloy steel according to claim 1, further comprising the cold rolling in which the surface average roughness (Ra) is 1.0 μm or more and 25 μm or less. Of a super-high weather resistance Cr-Fe alloy steel, including a rolling process using a dull weighted roll that has been subjected to.