JP3839946B2 - Manufacturing method of steel material with excellent rust-proofing property by rust prevention oil - Google Patents

Description

【００３２】
【発明の効果】
本発明によれば、戸建て住宅、集合住宅、大型建築物、ビルディングや橋梁等の建造物の構造部材として用いられるさび止め油の効果を充分に生かした耐食性に優れる鋼材を安価に供給することが可能となる。
【図面の簡単な説明】
【図１】塩水噴霧試験後のさび発生面積率とＣｒ添加量との関係を示した図である。[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a method for producing a steel material that is used after being subjected to a rust prevention treatment with a rust preventive oil used as a structural member of a detached house, an apartment house, a large building, a building or a bridge.
[0002]
[Prior art]
Due to stricter safety standards for buildings and the pursuit of functionality, steel materials for pillars and beams are required to have higher functionality. In particular, corrosion resistance is an important factor that affects the service life of a structure, and its improvement is required. The ultimate example is stainless steel for building structures that eliminates rust.
[0003]
For structural use, SUS304 (18Cr-8Ni), which is excellent in corrosion resistance and toughness, has many uses. However, since stainless steel requires a large amount of expensive elements such as Cr and Ni, the material cost and manufacturing cost are high, and although it is functionally superior, there is a problem in its economic efficiency.
[0004]
Therefore, although the occurrence of rust and corrosion is inevitable, steel materials have been developed that are inexpensive, suppress the progress of corrosion, and minimize the amount of corrosion.
For example, in JP-A-60-162507, the surface scale of a slab of ordinary steel is removed, glass paper is attached and rough-rolled, then this is removed and finish-rolled to achieve excellent adhesion and corrosion resistance. A method for producing a black skin scale coating is disclosed.
However, in this method, the number of processes increases with the attachment and peeling of glass paper, and these process capacities are generally the lowest in the process line in the production line, and the overall production capacity is limited. As a result, the production capacity of the entire process is reduced, resulting in an increase in manufacturing cost. As a result, although this method improves the corrosion resistance, there is a problem in economic efficiency.
[0005]
Japanese Patent Application Laid-Open No. 8-199289 discloses a steel containing 0.50 to 1.50% Cr, and an oxide scale having a thickness of 10 μm or less having a chromium oxide film between the base material and the scale in a hot rolling process. An H-section steel having is disclosed.
However, the present invention is a technique for generating an oxide layer having excellent corrosion resistance on the surface of ordinary steel that is inherently inferior in corrosion resistance. Therefore, when corrosion progresses through the oxide layer, the effect of improving corrosion resistance is lost. Therefore, in this method, it is impossible to maintain a low corrosion rate below that of ordinary steel for a long time in a humid environment, and it is considered impossible to improve the long-term durability of a building.
[0006]
[Problems to be solved by the invention]
By the way, when considering structural materials such as pillars and beams of buildings, the corrosive environment is roughly divided into two periods until the exterior material is completed.
The latter is not so severe as a corrosive environment because free inflow of outside air is regulated by the exterior material and interior material. Rather, although the time is short, the corrosiveness of the environment is more severe in the former period where it is directly exposed to wind and rain or dust.
[0007]
Further, if rust is generated on the surface of the steel material before the construction of the exterior material is finished, there is a problem that corrosion is likely to proceed under the rust layer even after the exterior material is formed. That is, it is the corrosion resistance against the occurrence of rust that dominates the durability of the structural material.
[0008]
Therefore, the most economical method for imparting corrosion resistance to the structure is most effective in improving only the anticorrosion performance during processing and construction of the material.
[0009]
As an initial rust prevention treatment for steel materials, it is widely performed to apply rust prevention oil.
However, simply applying rust-preventing oil to the metal surface can easily remove the oil film due to mechanical contact with foreign matter, and during drilling and bending of steel at the factory prior to construction. In addition, it is impossible to provide sufficient corrosion resistance in the actual construction stage.
[0010]
Therefore, in order to improve the rust resistance during the construction period at a low cost, it is necessary to develop a technique in which the effect of the rust prevention oil is maintained against contact with foreign matter, scratches, and the like.
[0011]
[Means for Solving the Problems]
The inventor has improved the properties of the oxide scale formed on the surface of the steel material in the hot rolling process, so that the rust-preventing oil can be easily impregnated and the oil remains even if it comes into contact with foreign matter. We have succeeded in finding a steel composition that can sufficiently exhibit corrosion resistance even with oil, and have found a method for producing a steel material that is excellent in rust-proofing property by rust prevention oil.
[0012]
The gist of the present invention is as follows.
(1) By weight%
C: 0.005% to 0.1%, Si: 0.05% to 1.5%,
Mn: 0.05% to 1.5%, P: 0.2% or less,
S: 0.05% or less, Cr: 5-18%
Slab is cast from a molten steel containing Fe and inevitable impurities, and then reheated to a temperature range of 1100 to 1300 ° C., and then hot-rolled and wound into a coil at 550 ° C. or more Then, after being held at 550 ° C. or more for 30 minutes or more, it is cooled, and is a method for producing a steel material excellent in rust prevention property by rust prevention oil,
(2) Molten steel is weight%
Mo: 0.1-2.5%, Cu: 0.1-2.5%,
Ni: one or more of 0.1 to 2.5%,
Furthermore, it contains, It is a manufacturing method of the steel materials excellent in the rust prevention property by the rust prevention oil as described in said (1) characterized by the above-mentioned.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Below, the component range of the molten steel of this invention and the reason for limitation of a manufacturing method are described.
C is an effective element for improving the strength of steel. However, if it is less than 0.005%, the strength required for structural steel cannot be obtained. Moreover, the excessive addition exceeding 0.1% reduces remarkably the base material toughness and the toughness of the heat affected zone. Therefore, the lower limit is set to 0.005% and the upper limit is set to 0.1%.
[0014]
Si needs to be added to molten steel as a deoxidizer in order to reduce the dissolved oxygen in the steel and ensure hot workability. If it is less than 0.05%, the deoxidation effect is weak. On the other hand, if added over 1.5%, the toughness of the base metal and the welded portion is impaired, so the lower limit was made 0.05% and the upper limit made 1.5%.
[0015]
Mn needs to be added to molten steel as a deoxidizer and desulfurizer. If it is less than 0.05%, a predetermined effect cannot be obtained. On the other hand, if added over 1.5%, the toughness and cracking properties of the base metal and the welded part are impaired, so the lower limit was made 0.05% and the upper limit made 1.5%.
[0016]
When P is present in a large amount, not only the weldability is impaired, but also a phenomenon that promotes the generation of rust appears. Therefore, it was limited to 0.2% or less.
[0017]
S is not only a starting point for rust as a sulfur-based inclusion such as MnS, but also increases the corrosion rate. Furthermore, it segregates at the grain boundaries and harms hot workability. Therefore, it is necessary to regulate to 0.05% or less. S is more preferable as an impurity.
[0018]
Cr has the effect of suppressing the occurrence of corrosion and reducing the corrosion rate in the atmospheric environment. In particular, regarding the suppression of rust generation, it exhibits a synergistic effect with rust prevention oil impregnated in oxide scale. Also, once corrosion occurs and a rust layer is formed, it has the effect of reducing the overall corrosion rate of the steel material under the rust layer. However, if the amount of Cr added is small, the effect is weak in terms of suppressing rust generation and reducing the corrosion rate.
On the other hand, if added excessively, raw material costs and smelting costs increase, so the economic efficiency decreases. In particular, when less than 5% is added, even if the oxidization scale is impregnated with rust-preventing oil, rust generation cannot be suppressed in the outdoor air environment. From the above points, the lower limit was set to 5% and the upper limit was set to 18%.
[0019]
Mo, Cu, and Ni have the effect of suppressing the occurrence of corrosion and reducing the corrosion rate in the atmospheric environment, like Cr. Therefore, when the effect of improving the corrosion resistance by adding Cr is weak, it is necessary to add one or more of Mo, Cu, and Ni. However, if the amount is small, the effect is weak, and if it is added excessively, raw material costs and manufacturing costs increase, and the economic efficiency decreases. Therefore, the lower limit is set to 0.1% and the upper limit is set to 2.5%.
[0020]
By the way, if the chemical components in the steel are restricted to the above-described range and only hot rolling is performed by a normal method, the steel material is not easily impregnated with rust prevention oil. In order to exhibit such unprecedented characteristics, it is necessary to control the properties of the oxide scale generated on the surface of the steel sheet in the manufacturing method described below, in addition to the chemical composition of the steel.
[0021]
In the present invention, first, molten steel having a chemical composition in the above-described range is cast, and then reheated to a temperature range of 1100 to 1300 ° C. The reason for limiting the reheating temperature to this temperature is that heating at 1100 ° C. or higher is necessary in order to generate a thick internal oxidation tank during heating and to facilitate rolling of the slab by hot working. In view of performance and economy, the upper limit was set to 1300 ° C.
[0022]
The heated slab is subjected to rough rolling and finish rolling. Although the hot rolling temperature is not particularly defined, the finish hot rolling finish temperature is preferably set to 800 to 1000 ° C. in terms of promoting the generation of oxide scale. Finishing above 1000 ° C. is not preferable because the crystal grains of the steel sheet are coarsened and the toughness required as a structural material is lowered.
[0023]
The reason why the coil is wound in a coil shape at 550 ° C. or higher after finish rolling is that the oxide scale becomes thicker as it is wound at a higher temperature, and the surface layer is pulverized. Since the predetermined effect cannot be obtained by winding below 550 ° C., the lower limit was set to 550 ° C. In addition, the reason why the temperature is maintained at 550 ° C. or higher for 30 minutes or more after winding is to make the oxide scale thick and porous. Since the effect is weak when the temperature is low or the time is short, the temperature is set to 550 ° C. or more and the time is set to 30 minutes or more.
[0024]
【Example】
Hereinafter, the present invention will be described in detail based on examples.
The prototype steel shown in Table 1 was melted in a converter and cast into a slab by continuous casting. Then, after reheating in a heating furnace, it was rolled to a thickness of 3 mm with a rough rolling mill and a finish rolling mill and wound into a coil. Thereafter, the coil was put in a heat insulation furnace and kept at a predetermined temperature.
[0025]
The impregnation amount of rust prevention oil was examined by the following method. Rust prevention oil is applied to the test piece weighed in weight with a brush and dried at room temperature for 3 hours. Thereafter, the surface was strongly wiped with tissue paper. This operation was repeated until no oil adhered to the tissue paper, and the amount of oil remaining per unit surface area of the steel was determined. In addition, the solvent dilution type rust prevention oil 3 type 1 described in JISK2246 was used as a rust prevention oil.
[0026]
The rust resistance was evaluated by the following method. The steel material cut into a size of 100 mm × 70 mm was coated with rust preventive oil by brush and dried at room temperature for 3 hours. Thereafter, the surface was strongly wiped with tissue paper. This operation was repeated until no oil adhered to the tissue paper, and then a 5% NaCl aqueous solution heated to 35 ° C. was sprayed for 100 hours. The extent of rust was measured by measuring the area ratio of rust with an image processing apparatus.
[0027]
Numbers 1 to 6 are obtained by changing the addition amount of Cr within the scope of the present invention with the heating temperature, the coiling temperature, and the holding conditions. FIG. 1 shows the relationship between rust resistance (rust generation area ratio after salt spray test) and Cr content. Numbers 1 and 2 are comparative examples in which the amount of Cr added is less than the range of the present invention. Although the amount of impregnation of rust prevention oil does not depend on the amount of Cr added, the degree of rust generation is large when the amount of Cr added is less than 5%.
[0028]
In addition, numbers 7 to 13 are obtained by changing the manufacturing conditions while keeping the components of the molten steel constant. It can be seen that the amount of impregnation of rust-preventing oil varies greatly as the production conditions change. In No. 7, the heating temperature is lower than the range of the present invention, the amount of impregnation of rust prevention oil is small, and the rust resistance is poor. Similarly, No. 9 is an example in which the winding temperature is lower than the range of the present invention, No. 11 is air-cooled after winding, and No. 12 is a short holding time after winding, both of which are rust resistant. Is bad.
[0029]
From the above, while controlling the amount of Cr added to an appropriate range and controlling the heating temperature, the coiling temperature, and the holding conditions together, it is possible to impart a high rust resistance to the rust prevention oil. It can be seen that the steel material can be manufactured.
[0030]
Next, numbers 14 to 26 are examples showing the effect of addition of Mo, Cu, and Ni. It can be seen that rust resistance is significantly improved by adding one or more of these elements to the molten steel.
[0031]
[Table 1]

[0032]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the steel material excellent in corrosion resistance which fully utilized the effect of the rust prevention oil used as a structural member of buildings, such as a detached house, an apartment house, a large building, a building, and a bridge, can be supplied at low cost. It becomes possible.
[Brief description of the drawings]
FIG. 1 is a graph showing a relationship between a rust generation area ratio and a Cr addition amount after a salt spray test.

Claims (2)

% By weight
C: 0.005% to 0.1%,
Si: 0.05% to 1.5%
Mn: 0.05% to 1.5%,
P: 0.2% or less,
S: 0.05% or less,
Cr: 5 to 18%
Slab is cast from a molten steel containing Fe and inevitable impurities, and then reheated to a temperature range of 1100 to 1300 ° C., and then hot-rolled and wound into a coil at 550 ° C. or more Then, after cooling for 30 minutes or more at 550 ° C. or higher, cooling is performed, and the method for producing a steel material excellent in rust prevention property by rust prevention oil. Molten steel is in weight percent
Mo: 0.1 to 2.5%,
Cu: 0.1 to 2.5%,
Ni: 0.1 to 2.5%
1 or more types of these are further contained, The manufacturing method of the steel materials excellent in the rust prevention property by the rust prevention oil of Claim 1 characterized by the above-mentioned.

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