JP2006274331A - Architecture member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stainless steel which can be worked into an architecture member to be installed in a part exposed to the atmosphere such as a hood of an exhaust fan, a mailbox and a nameplate, has excellent appearance and corrosion resistance, and is economical. <P>SOLUTION: This architecture member employs a ferritic stainless steel including ≤0.015% C, ≤0.5% Si, 11.0-25.0% Cr, ≤0.020% N, 0.05-0.50% Ti, 0.10-0.50% Nb and ≤0.0100% B; further including one or more of ≤3.0% Mo, ≤2.0% Ni, ≤2.0% Cu and ≤4.0% Al; and having an rmin value of 1.3 or higher. The architecture member does not have cracks due to working in a forming process and keeps the excellent corrosion resistance for a long period of time. The architecture member can be corrosion-protected by coating a clear lacquer thereon. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an architectural member made of stainless steel that is installed in a portion exposed to the atmosphere, such as a ventilation fan hood, a post box, or a nameplate.

Due to the recent trend toward higher-grade building structures, cases in which stainless steel having a metallic luster has been used in building members that have conventionally been made of plastic, wood, painted steel, or the like have increased. SUS304 is the mainstream as the most widely used stainless steel.
Since SUS304 is austenitic stainless steel, it can be easily bent and drawn as compared with ferritic stainless steel. On the other hand, because it contains expensive Ni, the price of the raw material increases due to the increase in raw material costs, which is not economical. In addition, in austenitic stainless steel, sea salt particles adhere to portions where stress is applied by processing, and stress corrosion cracking may occur due to corrosion when the temperature rises in summer. The occurrence of cracks may impair the function as a structure and is fatal.

Due to the diversification of the shape of building materials in recent years, more severe processing is performed on the material, so when using inexpensive ferritic stainless steel for these building members, depending on the steel type, bending and drawing can be used. It was difficult to obtain a desired shape.
Therefore, in the present invention, an inexpensive ferritic stainless steel that has been devised to solve these problems, and that can be drawn and bent easily as a building structure material and that does not cause stress corrosion cracking. The purpose is to provide.

  The present invention has been devised to solve such problems, and by using stainless steel whose base material is specified, it can be processed into a complicated shape, and has a beautiful appearance unique to stainless steel. Can have a long term.

  As ferritic stainless steel in the present invention, C: 0.015% or less, Si: 0.5% or less, Cr: 11.0-25.0%, N: 0.020% or less, Ti: 0.05 Steel types including ˜0.50%, Nb: 0.10 to 0.50%, and B: 0.0100% or less are used. Furthermore, one or more of Ni: 2.0% or less, Mo: 3.0% or less, Cu: 2.0% or less, and Al: 4.0% or less can be contained.

  The ferritic stainless steel of the present invention can be rigorously processed and formed, can make the shape of a building structure complicated, and does not cause perforation due to corrosion, so that it can have a aesthetic appearance unique to stainless steel.

  Hereinafter, the matter which specifies this invention is demonstrated. “%” Indicating the content of each element means “% by mass” unless otherwise specified.

  C forms carbides, which serve as recrystallization nuclei for randomization of recrystallized ferrite in the final annealing. However, C is an element that increases the strength after cold rolling annealing, and if it is too high, the ductility is lowered.

  Si is usually used for the purpose of deoxidation, but it has a high solid solution strengthening ability, and if its content is too high, the material is hardened and the ductility is lowered, so the content was made 0.5% or less.

  In order to provide corrosion resistance as stainless steel, Cr needs to be contained at 11.0%. However, when the amount of Cr increases, the toughness and workability decrease, so the upper limit of the content is made 25.0%.

   N forms a nitride, and like C, it acts as a recrystallization nucleus for randomizing the crystal orientation of the recrystallized ferrite in the final annealing. However, N is an element that increases the strength of the cold-rolled annealed material, and if it is too high, the ductility is lowered.

  Ti is an element that fixes C and N and improves workability and corrosion resistance, and its minimum amount is 0.05%. However, when Ti is added, the steel material cost increases, and surface defects caused by Ti inclusions become a problem. Therefore, the upper limit of the Ti content is set to 0.50%.

  Nb is an element that fixes C and N and improves impact resistance and secondary workability, and the minimum amount of these effects is 0.05%. However, when Nb is added too much, the material is cured and the workability is adversely affected. Further, since the recrystallization temperature is raised, the upper limit is made 0.5%.

  B is an alloy component that has the effect of fixing N and improving the corrosion resistance and workability, and is added as necessary. In order to exert the above action, it is desirable to add 0.0005% or more. However, if added excessively, hot workability and weldability are deteriorated, so the upper limit was set to 0.0100%.

  Mo is an element effective for improving the corrosion resistance, but excessive addition causes a decrease in hot workability due to solid solution strengthening at high temperature and delay of dynamic recrystallization, so it is made 3.0% or less. . Preferably 0.5% or more is added.

Ni is an austenite forming element, and addition over 2.0% leads to hardening and cost increase, so 2.0% was made the upper limit.

Cu is an element that improves the pitting corrosion resistance of ferritic stainless steel. Cu is inevitably contained such as mixing from scrap during melting, but excessive addition reduces the hot workability and corrosion resistance, so it was made 2.0% or less.
Preferably 0.5% or more is added.

  Al is an effective element for deoxidation and oxidation resistance, but excessive addition causes surface defects, so the upper limit was made 4.0%. Preferably 0.1% or more is added.

  Mn: It is an element usually contained in steel materials, and the content is not particularly limited in the present invention. It is an austenite-forming element, has a low solid solution strengthening ability and little adverse effect on materials. However, if the content is large, Mn fume is generated during melting, and the manufacturability is lowered. Therefore, the component range is desirably set to 2.0% or less.

The following two elements are impurities inevitably mixed from raw materials.
P: An element harmful to hot workability. In particular, if it exceeds 0.050%, the effect becomes remarkable, so it is desirably limited to 0.050% or less.

S: An element that easily segregates at grain boundaries and promotes a decrease in hot workability due to grain boundary embrittlement.
If it exceeds 0.020%, the effect becomes remarkable, so it is preferably 0.020% or less.

  In addition to these, Ca, Mg, Co, REM, etc. may be contained in the raw material scrap during melting, but it does not affect the shape freezing property of the molded product unless it is contained in large amounts. Absent.

  Some buildings are on the waterfront, and sea salt particles come in from the sea, causing corrosion and detracting from the beauty of stainless steel. Therefore, in the present invention, it is possible to use stainless steel even in a salt damage area by applying clear coating. An acrylic or epoxy paint can be used for clear coating.

  A stainless steel plate having a thickness of 0.8 mm having the components and compositions shown in Table 1 is used as a raw material (Steel Nos. A to E in Table 1 are steels of the present invention whose chemical component values are within the scope of the present invention, F to H are Other steels (comparative steels) and rmin values were measured. The r value is measured by applying a 15% tensile strain using a JIS No. 13B test piece, and then rolling direction (L direction), 45 deg. direction (D direction) with respect to the rolling direction, and perpendicular direction with respect to rolling (T direction). The r value at was determined. The lowest r value among the values obtained in the above three directions was defined as rmin. The r value was calculated by measuring the plate thickness and the plate width, and dividing the natural logarithm of the width shrinkage rate by the natural logarithm of the plate thickness reduction rate.

Further, a stainless steel plate having a thickness of 0.8 mm having the components and compositions shown in Table 1 was processed into a cup shape. Processing was performed by cylindrical drawing with an initial blank diameter of φ76 mm (punch 1 stage = φ40, 2 stages = φ31.5, 3 stages = φ24.5). In order to evaluate the corrosion resistance test and workability of the processed product, an impact resistance test was performed. SUS304 was used as a comparative material.

  The corrosion resistance test was carried out by a combined salt / wet cycle test. One cycle of the test is salt spray (5% NaCl for 15 minutes) → drying (60 ° C., 35% RH, 60 minutes) → wet (60 ° C., 95% RH, 180 minutes), and surface corrosion after 300 cycles Corrosion resistance was evaluated by the rate of rusting from the state. The eruption rate was calculated by the grid pattern method. In the impact resistance test, φ2 mm beads were sprayed for 1 hour at a pressure of 5 kg / mm2 (← required to be described in SI unit system), and the temperature was controlled at 5 ° C. at that time. When necking or the like occurs in the processed part, cracks occur after the impact resistance test, so the workability was evaluated based on the presence or absence of cracks. Table 2 shows the results of the corrosion resistance test and the workability evaluation by the impact test.

  In the impact resistance test, no cracks occurred in the steel of the present invention. The rmin value was 1.3 or more. The comparative steel F having a C content higher than the claimed range and the comparative steel H having a Nb content lower than the claimed range had an rmin value lower than 1.3, so that the workability was not sufficient and cracking occurred in the impact test.

Regarding corrosion resistance, the steel of the present invention did not show significant corrosion even in the processed part. On the other hand, in SUS304 which is a comparative steel, stress corrosion cracking was observed in the processed part. Although the H steel could be processed, the overall concentration of red rust was remarkable due to the low Cr concentration. It was found that the steel of the present invention has good corrosion resistance even in the processed part.
In addition, when clear coating was applied to steel A, no cracking occurred. It was found that glazing resistance was improved by clear coating.

  According to the present invention, it is possible to provide a ferritic stainless steel having formability necessary for processing into a building member and capable of maintaining corrosion resistance over a long period of time in a severe corrosive environment. Compared with austenitic stainless steel, it is advantageous in terms of cost.

Claims (4)

In mass%, C: 0.015% or less, Si: 0.5% or less, Cr: 11.0 to 25.0%, N: 0.020% or less, Ti: 0.05 to 0.50%, Nb : 0.10 to 0.50%, B: 0.0100% or less, made of a ferritic stainless steel having an rmin value of 1.3 or more. Furthermore, Mo: 3.0% or less is contained, The structural member of Claim 1 characterized by the above-mentioned. Furthermore, 1 or more types of Ni: 2.0% or less, Cu: 2.0% or less, Al: 4.0% or less are contained, The structural member of Claim 1 or 2 characterized by the above-mentioned. A building material, wherein the ferritic stainless steel according to claim 1 is clear-coated.