JP2001348650A - Stainless hot rolled steel strip for civil engineering and building structure excellent in initial rusting resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively and easily produce stainless steel for civil engineering and building structures excellent in initial rusting resistance, e.g. in the case of shipping and in the case of field operation in which the same is exposed to rain, while an oxide scale layer is left on the surface, by applying a proper amount of oil. SOLUTION: This stainless steel has a composition containing, by mass, >8 to <15% Cr, >0.0025 to <0.03% C, >0.0025 to <0.03% N, <0.03% S, >0.5 to <3.0% Mn, <0.5% Al, <0.04% P and >0.1 to <2.0% Si, and the balance substantially Fe with inevitable impurities, and in which, while an oxide scale layer formed on the surface is left, the surface of the oxide scale layer is coated with oil of 1 to 100 g/m2 to form an oil layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-rolled stainless steel strip for civil engineering and building structures having excellent initial rust resistance.

[0002]

2. Description of the Related Art Conventionally, as materials for civil engineering and building structures,
Mainly, ordinary steel such as SS400, high-strength steel such as SM490, and materials obtained by painting or plating these steels have been used.

However, in recent years, with the diversification of designs, the use of various materials has begun to be studied. Above all,
Stainless steel, which is excellent in corrosion resistance and design, requires little maintenance cost for rusting, and is therefore a very attractive material from the viewpoint of life cycle cost (LCC).

[0004] In particular, buildings constructed in coastal areas have problems that, in addition to having a short life, maintenance costs for controlling corrosion are increased, and welding is also required in promoting waterfront development. The role of stainless steel as a corrosion-resistant functional material for civil engineering and architectural structures with excellent resistance and corrosion resistance, especially initial rust resistance, is greatly expected.

[0005] Stainless steel is made of SUS4
Precipitation hardening represented by ferritic stainless steel represented by 30, martensitic stainless steel represented by SUS410 steel, austenitic stainless steel represented by SUS304, duplex stainless steel represented by SUS329 steel, and SUS630 Broadly classified into type stainless steel.

Among such various stainless steels, those which have been conventionally studied as materials for civil engineering and building structures are as follows:
It is an austenitic stainless steel with the highest use record including material strength, corrosion resistance, ease of welding, weld toughness and versatility.

Austenitic stainless steel has strength,
It has properties that sufficiently satisfy the properties required for civil engineering and building materials, such as corrosion resistance, fire resistance, and weld toughness.

However, this austenitic stainless steel 1) contains a large amount of alloying elements such as Ni and Cr.
It is much more expensive than ordinary steel, 2) causes stress corrosion cracking, and 3) has a larger coefficient of thermal expansion than ordinary steel, and has relatively low thermal conductivity, so it has a thermal effect during welding. Because it is easy to accumulate distortion due to the material and it is difficult to apply it to members that require accuracy, it is applied to general-purpose structural materials that used ordinary steel and painted or plated materials Is difficult,
There was a problem that the applicable range was limited.

For this reason, recently, as a substitute for plated or painted ordinary steel, low Cr having a Cr content of 15 mass% or less has been used.
The application of alloy steel containing steel and its coated steel sheet to steel materials for civil engineering and construction is being studied.

[0010] Generally, stainless steel used for civil engineering and building structural materials removes an oxide scale layer called a so-called black scale formed on a surface layer during hot rolling. Although it is common to perform a washing process,
Recently, in order to provide the stainless steel as inexpensively as possible, the use of the stainless steel in a state in which an oxide scale layer is adhered without performing a pickling treatment has begun to be studied. The advantages of using the oxide scale layer with the oxide scale layer attached are that the pickling process can be omitted, reducing the production cost. Sometimes the presence of a layer makes it less noticeable.

Regarding the improvement of corrosion resistance of stainless steel, for example, Japanese Patent Application Laid-Open Nos. 11-302796 and 11-3027
No. 97 is described. In all of the stainless steels described in these publications, the total content of carbon and nitrogen in the steel is limited to 0.1 mass% or less, and one or two of Ni and Cu alloying elements are reduced to 0.1 mass%. % Or more, 1.0 mass%
It is an essential component for improving corrosion resistance to be contained in less than the above.

[0012] However, the addition of alloying elements such as Ni and Cu to steel is not preferable because it causes an increase in product cost, and the improvement of the corrosion resistance of stainless steel described in the above-mentioned publications is not satisfactory. It is meant to improve the overall corrosion resistance of steel, and stainless steel for civil engineering and building structures is not intended to prevent initial rusting at the time of shipping or construction on site exposed to rain, for example. Did not.

Means for improving the corrosion resistance, weldability, and weld toughness of stainless steel include purifying the stainless steel to suppress the formation of inclusions in the steel, or adding Nb or It is effective to add Ti and fix carbon and nitrogen as carbides and nitrides.Various stainless steels produced by such means have been developed.For example, Japanese Patent Application Laid-Open No. 60-13060 discloses Nb, a carbon and nitrogen stabilizing element
Discloses a stainless steel in which the corrosion resistance is improved by adding an appropriate amount of Mo, Ni, and Cu, and the corrosion resistance is further improved by adding Mo, Ni, and Cu.

However, purifying the steel by reducing C, N, etc. in the steel or adding an alloying element leads to an increase in cost, and further pursuing the purifying. Required high-precision refining and had limitations in production.

[0015] Therefore, in the case of stainless steel for civil engineering and architectural structures, for example, at the time of shipping or on-site construction when exposed to rain, it is possible to reduce the cost of stainless steel without changing the steel composition, particularly by purifying it or adding alloying elements. It was necessary to develop a means that could easily prevent initial rusting.

[0016]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a stainless steel hot-rolled steel strip for civil and architectural construction which is excellent in initial rust resistance and solves the above-mentioned problems in the prior art. It is in.

[0017]

Means for Solving the Problems In order to achieve the above-mentioned object, the present inventors focused on a hot-rolled steel strip in which an oxide scale layer remained, and provided an appropriate oil on the upper layer of the oxide scale layer. By forming a layer, it was found that initial rusting was remarkably suppressed, especially at the time of shipping and on-site construction when exposed to rain, without strictly controlling production conditions such as components in steel and heat treatment. In addition, this means can be performed inexpensively and easily.

The present invention has been completed by further study based on the above findings. That is, the gist configuration of the present invention is as follows. 1. Cr: more than 8 mass%, less than 15 mass% C: more than 0.0025 mass%, less than 0.03 mass% N: more than 0.0025 mass%, less than 0.03 mass% S: less than 0.03 mass% Mn: more than 0.5 mass%, less than 3.0 mass% Al: Less than 0.5% by mass P: Less than 0.04% by mass Si: More than 0.1% by mass and less than 2.0% by mass, with the balance substantially composed of Fe and unavoidable impurities, and an oxide scale formed on the surface 1-100 g / m ² on this oxide scale layer while leaving the layer
A hot-rolled stainless steel strip for civil and building construction with excellent initial rust resistance, characterized by forming an oil layer by applying oil.

2. In the above item 1, the oil for forming the oil layer has a kinematic viscosity of 1.5 × 10 ⁻⁶ to 10 × at 40 ° C.
A stainless steel hot-rolled steel strip for civil and building construction with excellent initial rust resistance, characterized by a 10 ^-6 m ² / s.

3. In the above item 1 or 2, the composition further comprises one or more selected from Cu: less than 3.0 mass%, Mo: less than 3.0 mass% and Ni: less than 3.0 mass%. Stainless steel hot rolled steel strip for civil and building structures with excellent initial rusting properties.

4. In the above 1, 2 or 3, Co: 0.01 mass% or more, less than 0.5 mass%, V: 0.01 mass% or more, less than 0.5 mass%, and W: 0.001%
A hot-rolled stainless steel strip for civil and building construction with excellent initial rust resistance, characterized by having a composition containing one or more selected from mass% or more and less than 0.05 mass%.

5. In any one of the above items 1 to 4,
B: A hot-rolled stainless steel strip for civil and building construction having excellent initial rust resistance, characterized by having a composition containing 0.0002 to 0.002 mass%.

6. In any one of the above items 1 to 5,
Further, the composition is characterized by containing one or more selected from Ti: less than 0.7 mass%, Nb: less than 0.7 mass%, Ta: less than 0.7 mass%, and Zr: less than 0.5 mass%. Stainless steel hot rolled steel strip for civil and building structures with excellent initial rust resistance.

[0024] The concept of "stainless hot rolled steel strip" in the present invention includes a long hot rolled steel strip obtained by hot rolling stainless steel, and a hot rolled steel strip cut out of the steel strip. Steel plates shall be included.

[0025]

Next, the reason why the present invention is limited to the above-described configuration will be described.

Cr: more than 8 mass% and less than 15 mass% Cr is an element effective for improving corrosion resistance, but it is difficult to secure sufficient corrosion resistance when its content is 8 mass% or less. Since Cr is a ferrite phase (α phase) stabilizing element,
Addition of 15 mass% or more not only causes a decrease in workability,
Since the stability of the austenite phase (γ phase) is reduced and a predetermined amount of martensite phase cannot be secured at the time of quenching, the strength of the welded portion decreases. Therefore, in the present invention, the Cr content is set to be more than 8 mass% and less than 15 mass%. In addition, the range of the Cr content that is particularly preferable for having both rust resistance, workability, and weldability is 10.0 to 13.5 mass%.

C and N: Both exceed 0.0025 mass%, and
Less than 03 mass% To improve the toughness and workability of the heat-affected zone and to prevent weld cracking, it is effective to reduce C and N as conventionally known. Further, C and N not only have a great effect on the hardness of the martensite phase, but also (Fe, Cr) ₂₃ C ₆ , (F
(Fe, Cr) ₇ C ₃ , (Fe, Cr) ₃ C, (Fe, Cr) ₂ N, (Fe, Cr) and other Fe-Cr-based carbides and nitrides are formed, and in the Cr-deficient phase Since the formation of carbides and the like becomes remarkable when each of the contents of C and N is 0.03 mass% or more, the contents of C and N are each 0.03 mass%.
Less than. However, in the steel composition range of the present invention,
Although the reduction of C and N contents is effective for improving the properties of welds, workability, corrosion resistance, etc., reducing the contents of C and N to 0.0025 mass% or less increases the refining load. Therefore, the contents of C and N are set to be more than 0.0025 mass% and less than 0.03 mass%, respectively. Note that C
And the content of N is more preferably 0.005 to 0.02 mass%.

S: less than 0.03 mass% S combines with Mn to form MnS, and serves as an initial rusting starting point. In addition, S is a harmful element that segregates at crystal grain boundaries and promotes grain boundary embrittlement, so that it is preferable to reduce S as much as possible.
In particular, when the S content is 0.03 mass% or more, the adverse effect becomes remarkable. Therefore, the S content is suppressed to less than 0.03 mass%, and more preferably 0.006 mass% or less.

Mn: more than 0.5 mass% and less than 3.0 mass% Mn is an austenite phase (γ phase) stabilizing element and effectively contributes to the improvement of weld toughness by changing the structure of the weld heat affected zone to a martensite structure. Also, Mn is a useful element as a deoxidizing agent like Si, and if the Mn content is 0.5 mass% or less, a sufficient effect as a deoxidizing agent cannot be obtained.
The Mn content was set to exceed 0.5% by mass. On the other hand, an excessive addition of 3.0 mass% or more causes a reduction in workability and a reduction in corrosion resistance due to the formation of MnS. Therefore, the Mn content is limited to less than 3.0 mass%. It is more preferable that the Mn content be in the range of 0.7 to 1.5 mass%.

Al: less than 0.5% by mass Al is not only an element useful as a deoxidizing agent, but also effectively contributes to improving the toughness of a weld.
If the content is 0.5 mass% or more, the amount of inclusions increases and mechanical properties deteriorate, so the Al content is limited to less than 0.5 mass%. When a predetermined amount of Mn or Si is contained, deoxidation is sufficient, so that Al need not be particularly contained in steel.

P: less than 0.04 mass% P not only decreases the hot workability, formability and toughness, but also is a harmful element to corrosion resistance. Particularly, when the P content is 0.04 mass% or more. Since the effect becomes remarkable, the P content is controlled to be less than 0.04 mass%.
It is more preferable that the P content be 0.025 mass% or less.

Si: more than 0.1 mass% and less than 2.0 mass% Si is an element useful as a deoxidizing agent, but its content is
If the content is less than 0.1 mass%, a sufficient deoxidizing effect cannot be obtained.
Since excessive addition of 2.0 mass% or more causes reduction in toughness and workability, the Si content is set to exceed 0.1 mass% and less than 2.0 mass%. It is more preferable that the Si content be 0.3 to 0.5 mass%.

While the essential components contained in the stainless steel according to the present invention have been described above, other various elements described below can be appropriately contained in the present invention.

Cu: less than 3.0 mass% Cu is an element for stabilizing austenite, and is an element effective for improving corrosion resistance, forming an austenite phase, suppressing grain growth in a heat affected zone of welding, and improving toughness. is there. However, when the Cu content is 3.0 mass% or more, the susceptibility to embrittlement, particularly hot cracking, tends to increase. Therefore, the Cu content is preferably set to a range of less than 3.0 mass%. It is more preferable that the lower limit of the Cu content is 0.1 mass% at which the effect of improving the corrosion resistance is remarkably exhibited, and the upper limit is 0.6 mass% at which the sensitivity to hot cracking tends to increase.

Mo: less than 3.0 mass% Mo is an element effective for improving the corrosion resistance like Cu. However, when the Mo content is 3.0 mass% or more, the stability of the austenite phase is reduced, and the toughness and workability tend to be reduced. Therefore, the Mo content is preferably set to a range of less than 3.0 mass%. . From the viewpoint of the balance between corrosion resistance and workability, it is more preferable that the Mo content be in the range of 0.1 to 0.5 mass%.

Ni: less than 3.0 mass% Ni is an element for improving ductility and toughness. It is particularly preferable to add Ni when it is necessary to improve the toughness of the heat affected zone. However, if the Ni content is 3.0 mass% or more, the material tends to be hardened and its effect tends to be reduced, so that the Ni content is preferably in the range of less than 3.0 mass%. In addition, since Ni is concentrated in the oxide scale layer and has an effect of improving rust resistance, the Ni content should be 0.1 mass% or more when it is necessary to significantly exhibit the effect of improving rust resistance. preferable.

Co: 0.01 mass% or more, less than 0.5 mass%,
V: 0.01 mass% or more, less than 0.5 mass%, W: 0.001 mass
% Or more, but less than 0.05 mass% Co, V and W improve the initial rust resistance of steel without adding a large amount of expensive Cr, Ni, Mo, etc., or reducing C and N extremely. Is an element that is effective for water and can be added as needed. The contents of Co, V and W are respectively
0.01mass%, 0.01mass%, at which the above-mentioned improvement effect becomes apparent
It is preferably 0.001 mass%. V and W
The content of each is 0.5mass% or more and 0.05mass%
% Or more, the hardening of the material tends to be remarkable due to the precipitation of carbides, so it is preferable to limit the content to less than 0.5 mass% and less than 0.05 mass%, respectively, and the Co content is 0.5 mass% or more. However, it is preferable to limit the amount to less than 0.5 mass% because of the possibility of hardening the steel. still,
More preferably, the Co content is 0.03-0.2 mass%, the V content is 0.05-0.2 mass%, and the W content is 0.005-0.02 mass%.
mass%.

B: 0.0002 to 0.002 mass% B is an element effective for improving the hardenability of steel. However, if the B content is less than 0.0002 mass%, the above-mentioned improvement effect cannot be sufficiently obtained, and if the B content exceeds 0.002 mass%, the material tends to be hardened and the toughness and workability tend to be impaired. The content is preferably 0.0002 to 0.002 mass%. It is more preferable that the B content is 0.0005 to 0.001 mass%.

Ti: less than 0.7% by mass, Nb: less than 0.7% by mass, Ta: less than 0.7% by mass, Zr: less than 0.5% by mass Ti, Nb, Ta and Zr are all carbonitride forming elements. It suppresses grain boundary precipitation of Cr carbonitride during heat treatment and heat treatment, and effectively acts to improve corrosion resistance. Also, Ti is an element effective for improving hardenability. However, Ti,
Nb and Ta content is 0.7mass% or more, and Zr content is 0.5ma
If ss% or more, the material tends to harden,
Preferably, the contents of Ti, Nb and Ta are all less than 0.7 mass%, and the Zr content is less than 0.5 mass%. In addition, Ti, N
The preferred ranges of the contents of b, Ta and Zr are all 0.01 to 0.3.
mass%.

The balance Fe and inevitable impurities The balance other than the above-mentioned steel composition components is Fe and inevitable impurities. As the inevitable impurities, for example, it is accepted that the O content is in a range of 0.010 mass% or less.

The main feature of the constitution of the present invention is that the oxide scale is limited to the above steel composition and the oxide scale layer formed mainly on the surface in the hot rolling step is left. To form an oil layer by applying 1 to 100 g / m ² of oil on the layer. By adopting this configuration,
For example, at the time of shipping or on-site construction when exposed to rain, it is possible to effectively prevent initial rusting at low cost and simply without changing the steel composition particularly by adding high purity or alloying elements.

The oil layer is mainly composed of commercially available oils for rust prevention, hydraulic oils used for lubricating machines, lubricating oils, cutting oils,
It is preferably formed by applying wax, grease or the like, or a water-soluble rust inhibitor containing these. still,
The term “oil” as used in the present invention means a general term for mineral oils, organic carboxylate salts, organic amines, other inorganic substances, etc., and oils containing rust-preventive additives.

The rust preventive additives include polar groups (-NH ₂ , -OH, -CH = C
H ₂ -COOH, etc.) whose polar groups are densely arranged on the metal surface and the base oil (mineral oil, etc.) hydrocarbons overlap on it to form oxygen, chlorine ions, water, metal powder and other rust It is thought to inhibit the factors and suppress the generation of rust.

The reason why the oil layer is formed on the oxide scale layer is as follows.

That is, an object of the present invention is to effectively improve the initial rusting resistance without changing the composition of the steel composition or the production conditions while the oxide scale layer remains on the surface of the stainless steel. As a result of extensive studies by the inventors, it has been found that if an appropriate amount of oil is applied on the oxide scale layer to form an oil layer, the initial rusting resistance is significantly improved. Was.

In general, when rust-preventive oil is applied to the surface of stainless steel having a smooth surface from which an oxide scale layer has been removed by performing a pickling treatment after hot rolling, it is possible to prevent the steel surface from coming into direct contact with the outside. Because it can be avoided, the initial rusting resistance should naturally be improved, but in the case of the surface from which the oxide layer has been removed, even if oil is applied, the surface is smooth,
It is difficult for the oil to flow down from the surface to form an oil layer having a sufficient film thickness on the steel surface, and in order to form an oil layer having a sufficient film thickness, a large amount of oil must be applied.

On the other hand, in the case of stainless steel having an oxide scale layer remaining on the surface, the oxide scale has a certain degree of unevenness and porosity. It is difficult to flow down from, it is easy to form an oil layer of sufficient thickness,
Oil penetrates into porous portions and crack defect portions in the oxide scale layer, and sufficient rust resistance can be secured with a small amount of oil as described above. Since it was found that the initial rusting resistance of the oil layer and the oxide scale layer complemented each other, the initial rusting resistance could be effectively improved, and the present invention was completed. is there.

In addition, even if rust is formed on the surface of the steel plate, the stainless steel plate coated with oil on the oxide scale layer is combined with the scale color, and the (scale) acid is removed from the oxide scale layer. There is also an advantage that rust is less noticeable than a washboard.

The amount of oil applied to form the oil layer
Varies greatly depending on the type of oil (viscosity, rust prevention effect, etc.)
However, the coating amount of each type of oil layer is 1 g.
/ M^TwoIf it is above, sufficient initial rust resistance can be obtained,
The application amount is 100 g / m^Two If it exceeds the initial resistance
As the effect of improving rust properties is saturated, the applied oil flows,
Due to the disadvantage that the yield is significantly reduced,
Coating amount is 1 to 100 g / m ^Two Range.

FIG. 1 shows a rust-preventive oil having a surface on which an oxide scale layer remains and having different coating amounts (main components: acrylic-modified alkyd resin, alkanolamine, special fatty acid and Water, kinematic viscosity: 3.0 × 10 ^-6
The results obtained by measuring the rust generation rate (%) after performing an atmospheric exposure test for 20 days on various stainless steels coated with m ² / s) are shown. It can be seen that when the amount is 1 g / m ² or more, the generation of rust is sufficiently suppressed.

In consideration of actual workability and yield, it is preferable to consider the kinematic viscosity of the oil applied to form the oil layer. Specifically, the kinematic viscosity at the time of application is 40 ° C. It is preferably from 1.5 × 10 ⁻⁶ to 10 × 10 ⁻⁶ m ² / s.

When the kinematic viscosity is higher than 10 × 10 ⁻⁶ m ² / s, when the oil is applied on the oxide scale layer by spraying with a nozzle or the like, the nozzle is clogged, and the oil is applied. Work can be interrupted frequently,
In addition, when the oil is manually applied to the oxide scale layer using a roll or a brush, the oil does not spread evenly, and a large amount of oil is required to form an oil layer having a sufficient film thickness. This is not only costly, but also causes problems such as poor workability.

On the other hand, if the kinematic viscosity is lower than 1.5 × 10 ⁻⁶ m ² / s, the oil can be uniformly applied on the oxide scale layer, but the applied oil tends to flow without stopping at the same position. If you try to form an oil layer of sufficient thickness,
This is because a large amount of oil is required, which is expensive.

For this reason, the oil for forming the oil layer has a kinematic viscosity of 1.5 × 10 ⁻⁶ to 10 × at 40 ° C.
It is preferably 10 ⁻⁶ m ² / s.

Next, an example of a preferred method for producing the stainless steel of the present invention will be described. First, molten steel adjusted to the above-mentioned steel component composition is smelted in a commonly known smelting furnace such as a converter or an electric furnace, and then subjected to a vacuum degassing method (RH method) and a VOD method.
It is preferable that the steel material is refined by a known refining method such as an AOD method, and then cast into a slab or the like by a continuous casting method or an ingot-making method.

Next, the steel material is heated and turned into a hot-rolled steel sheet by a hot rolling process. The heating temperature in the hot rolling step is not particularly limited, but if the heating temperature is too high, the crystal grains become coarse and the toughness and workability deteriorate, so the heating temperature is preferably 1300 ° C. or lower.

In the hot rolling step, it is sufficient that a hot-rolled steel sheet having a desired thickness can be obtained, and the conditions for the hot rolling are not particularly limited. It is preferable from the viewpoint of securing strength and toughness.

However, when workability, ductility, and good surface properties are required, the finishing temperature in hot rolling is preferably 820 ° C. or more and 1000 ° C. or less.

The winding temperature is preferably in the range of 500 to 800 ° C.

After the completion of the hot rolling, it is preferable to perform hot rolled sheet annealing for softening. This hot rolled sheet annealing is performed at an annealing temperature of 600 to 1100 ° C. and a holding time of 0.01 to 20 hours.
It is preferable from the viewpoint of not only softening but also improving workability and securing ductility.

When a martensite structure is formed in a hot-rolled sheet, the temperature range of 600 to 730 ° C. after annealing of the hot-rolled sheet is set.
Slow cooling at a cooling rate of 50 ° C./h or less is more preferable from the viewpoint of softening.

Thereafter, after slow cooling, 1% of this oxide scale layer is left on the oxide scale layer while leaving the oxide scale layer formed on the surface.
An oil layer is formed by applying oil of 100 g / m ² by spraying using a nozzle or the like, and a stainless steel strip as a final product can be obtained. The above description is only an example of the embodiment of the present invention, and various changes can be made within the scope of the claims.

[0063]

EXAMPLE Molten steel having the composition shown in Table 1 was smelted in a converter-secondary refining process, formed into a slab by a continuous casting method, and then reheated to 1200 ° C to reduce the rolling reduction of the final rough rolling to 30 to 30 ° C. After performing 6-pass rough rolling at 45%, a 4.2-mm hot-rolled steel sheet was formed by 7-pass finish rolling at a final finishing temperature of 840 to 990 ° C.
After subjecting these hot-rolled steel sheets to hot-rolled sheet annealing at a temperature in the range of 650 to 950 ° C., a nozzle is coated with a solvent-diluted rust-preventive oil (main component is mineral oil) having a coating amount and a coating amount shown in Table 2. Apply by spraying used, perform air exposure test and salt spray test,
The initial rust resistance was evaluated. Table 2 shows the evaluation results.

The atmospheric exposure test was conducted in accordance with JIS Z 2381 under the conditions of exposing at a position 5 m from the revetment wall and at a slope of 36 degrees to the south-facing ground. In Table 2, when the red rust generation area was 5% or less, the initial rust resistance was determined to be good.

The salt spray test is based on JIS Z 2371 and
% NaCl solution, pH 6.5 to 7.2, temperature 35 ° C. ± 2 ° C.

The presence / absence of nozzle clogging and the fixation rate (%) of oil on the oxide scale layer were also examined.

[0067]

[Table 1]

[0068]

[Table 2]

From the results shown in Table 2, all of the invention examples are as follows.
Comparative example of pickled plate (white scale) (Sample Nos. 44 and 45)
It can be seen that it has almost the same initial rust resistance as that of. On the other hand, Comparative Examples in which the amount of oil applied is outside the proper range of the present invention, except for Samples Nos. 44 and 45, are inferior in initial rust resistance. Sample Nos. 44 and 45, which are comparative examples,
Since the pickling process is performed, workability and cost performance are inferior.

[0070]

According to the present invention, by applying an appropriate amount of oil while the oxide scale layer remains on the surface, for example, at the time of shipping or construction on site exposed to rain.
In particular, it has become possible to provide stainless steel for civil engineering and building structures with excellent initial rust resistance at low cost and easily without changing the steel composition or manufacturing conditions due to high purity or addition of alloying elements. .

[Brief description of the drawings]

FIG. 1 shows the results of measuring the rust generation rate (%) of various stainless steels coated with different amounts of rust-preventive oil on the oxide scale layer after conducting an atmospheric exposure test for 20 days. FIG.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Susumu Sato 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Research Institute Co., Ltd. F-term (reference) 4K062 AA01 BB09 BC01 CA02 DA10 FA12 FA16 GA01 GA10

Claims (6)

[Claims] 1. Cr: more than 8 mass%, less than 15 mass% C: more than 0.0025 mass%, less than 0.03 mass% N: more than 0.0025 mass%, less than 0.03 mass% S: less than 0.03 mass% Mn: more than 0.5 mass%, 3.0 Less than mass% Al: Less than 0.5 mass% P: Less than 0.04 mass% Si: Contains more than 0.1 mass% and less than 2.0 mass%, and the balance substantially has a composition of Fe and unavoidable impurities and is formed on the surface. 1 to 100 g / m ² on the oxide scale layer while leaving the oxide scale layer to be formed.
A hot-rolled stainless steel strip for civil and building construction with excellent initial rust resistance, characterized by forming an oil layer by applying oil. 2. An oil according to claim 1, wherein the oil for forming the oil layer has a kinematic viscosity at the time of application of 1.5 × 10 ⁻⁶ to 10 × at 40 ° C.
A stainless steel hot-rolled steel strip for civil and building construction with excellent initial rust resistance, characterized by a 10 ^-6 m ² / s. 3. The composition according to claim 1, further comprising one or more selected from Cu: less than 3.0 mass%, Mo: less than 3.0 mass%, and Ni: less than 3.0 mass%. A hot-rolled stainless steel strip for civil and building structures with excellent initial rust resistance. 4. The method according to claim 1, 2 or 3, further comprising: Co: 0.01 mass% or more, less than 0.5 mass%, V: 0.01 mass% or more, less than 0.5 mass%, and W: 0.001%
A hot-rolled stainless steel strip for civil and building construction with excellent initial rust resistance, characterized by having a composition containing one or more selected from mass% or more and less than 0.05 mass%. 5. The method according to claim 1, wherein:
B: A hot-rolled stainless steel strip for civil and building structures having excellent initial rust resistance, characterized by having a composition containing 0.0002 to 0.002 mass%. 6. The method according to claim 1, wherein:
Further, the composition is characterized by containing one or more selected from Ti: less than 0.7 mass%, Nb: less than 0.7 mass%, Ta: less than 0.7 mass%, and Zr: less than 0.5 mass%. Stainless steel hot rolled steel strip for civil and building structures with excellent initial rust resistance.