JP4207942B2 - Steel material for construction with excellent weather resistance and method for producing the same - Google Patents

Description

  The present invention relates to a steel material for construction having excellent weather resistance, the surface of which is stable in an atmospheric corrosive environment and covered with an oxide having high anticorrosion properties, and a method for producing the same.

Generally, by adding elements such as phosphorus (P), copper (Cu), chromium (Cr), nickel (Ni) to steel, the corrosion resistance (that is, weather resistance) of the steel in the atmosphere can be improved. it can. These low-alloy steels are called weathering steels, and rust that protects against corrosion (hereinafter referred to as “weathering rust”) is formed on the surface outdoors in a few years. This is so-called maintenance-free steel that eliminates the need for anticorrosion treatment such as painting.
However, since it takes several years for the weather-resistant rust to form, floating rust and flow rust such as red rust and yellow rust are generated during the period up to that time, which is not preferable in appearance but also contaminates the surrounding environment. The problem of becoming the cause of this is left.

About this problem, for example, a surface treatment that forms a phosphate film after treating the steel surface with an acidic aqueous solution containing Fe ions and one or more of P, Cu, Cr, Ni, and Mn ions. A method has been proposed (see Patent Document 1). However, there is a problem that the treatment content is complicated, for example, it is necessary to pre-treat with an acidic aqueous solution before forming the phosphate film.
In addition, in order to prevent the formation of floating rust and flow rust, surface treatment methods such as a method of coating the surface of weathering steel and a method of coating after forming a phosphate film have been conventionally performed. However, there are problems such as the generation of weather-resistant rust is delayed by coating, and the coating film itself is deteriorated to remarkably deteriorate the appearance.
Furthermore, there are many environments where it is difficult to form weatherable rust even in weathering steel, such as in coastal areas, and in such areas, weathering rust is not formed even if the treatment described in the above publication is performed. is there.

Japanese Patent Laid-Open No. 1-142088

  The problem of the present invention is that the steel surface has a stable and high anticorrosion property in an atmospheric corrosive environment, and has an oxide layer that suppresses the generation of floating rust and flow rust such as red rust and yellow rust, and has excellent weather resistance. Another object of the present invention is to provide a method for producing a steel material having excellent weather resistance by generating such an oxide layer by a simple treatment.

The gist of the present invention resides in (1) the construction steel material having excellent weather resistance and (2) the production method thereof.
(1) On the surface of the base steel, the layer thickness is 0.1 to 50 μm, and one or both of chromium as the oxide and nickel as the oxide is contained in a total of 0.3% by mass or more. And a steel material for construction having excellent weather resistance, having a transformed magnetite layer and / or hematite layer (hereinafter, these layers are also referred to as “oxide layers”).
(2) After applying an aqueous solution containing 0.3 to 5% by mass of chromium (III) ions and / or 0.3 to 6% by mass of nickel (II) ions to the surface of the base steel, 450 to 720 ° C. And the surface of the base steel has a layer thickness of 0.1 to 50 μm, and contains one or both of chromium as an oxide and nickel as an oxide in a total amount of 0.3% by mass or more. The manufacturing method of the steel material for construction excellent in the weather resistance as described in said (1) which forms the magnetite layer and / or hematite layer to perform.

The above-mentioned “base steel” is steel as a base material for building steel having excellent weather resistance according to the present invention, such as carbon steel, so-called weather resistant steel containing Cr, Cu, P, Ni, etc. It refers to low-alloy steel, and further alloy steel (steel that generates so-called “rust” described later), and does not include steel that does not generate “rust” such as stainless steel and Ni-based alloy. The “carbon steel” mentioned here is, for example, a specific chemical composition: C: 0.1 to 0.4%, Si: 0.1 to 0.4%, Mn: 0.2 to 0 .6%, P: 0.03% or less, S: steel containing 0.03% or less.
The “low alloy steel” is a steel containing about 5% or less of the total content of alloy elements such as C, Si, Mn, P, Cr, Ni, Mo, Cu, and Ti in carbon steel. Yes, “alloy steel” is a steel whose total alloy content exceeds 5%. For example, steel containing Cr: 10% or less, Ni: 10% or less, Ti: 10% or less, etc. is also used as a base steel. Included in alloy steel.

In addition, the base steel may have “rust” formed on the surface. Furthermore, not only those in the state of the material before being used for a building or the like, but also those already used for a building or the like are included in the base steel.
If the rust formed on the steel surface is chemically stable, the elution of Fe ions from the steel surface is suppressed, and if the chemically stable rust is physically dense, it breaks into rust. And structural defects such as voids are difficult to generate, and oxygen, water, and even corrosive substances are prevented from entering the base steel surface. The elution of Fe ions, which is the cause of the formation of, is more significantly suppressed or prevented.

  The present inventors transform the products generally called “rust” (α-FeOOH, γ-FeOOH, amorphous rust, etc.) that are formed on the steel surface in the presence of water at a high temperature, thereby stabilizing the steel surface. When the oxide layer made of magnetite or hematite is covered, and the oxide contains Cr or Ni, the weather resistance of the steel is found to be extremely good. It came to an eggplant.

  In the steel for building construction of the present invention, the base steel surface is shielded from the atmospheric corrosive environment, and oxygen, water and even corrosive substances are prevented from entering the base steel surface. Excellent in properties. This building steel can be easily produced by the method of the present invention in which a chemically stable and dense oxide layer is formed on the surface of the base steel by a simple treatment.

Hereinafter, the steel material for construction excellent in the weather resistance of the present invention and the manufacturing method thereof will be described in detail. The above-mentioned “rust”, “%” of Cr and Ni contained in the magnetite layer and hematite layer, and “%” of Cr and Ni in the aqueous solution all mean “mass%”.
The steel material of the present invention has a layer thickness of 0.1 to 50 μm on the surface of the base steel, and a total of 0.3% by mass of either or both of chromium as an oxide and nickel as an oxide. It is a steel material for construction having excellent weather resistance, having a magnetite layer and / or a hematite layer (hereinafter, these layers are also referred to as “oxide layers”) which have been contained and transformed.

  Although Cr and Ni existing in the oxide layer exist as those oxides, they will not be referred to as “Cr as oxide” or “Ni as oxide”, but simply “Cr”, “Ni. ".

  The reason for having a magnetite layer and / or a hematite layer on the surface is that these layers are very stable in the atmosphere, do not undergo phase transformation, and do not dissolve in the presence of moisture.

Furthermore, if either or both of Cr and Ni are contained in these oxide layers, the magnetite and hematite will be dense and will have a structure with few cracks and pores. When each is contained alone, the content is 0.3% or more, and when both Cr and Ni are contained, the total content of both needs to be 0.3% or more.
If the content of Cr and / or Ni is too large, the magnetite or hematite layer deteriorates in adhesion to the base steel and collapses and peels from the interface with the base steel. Alternatively, the upper limit of the Ni content is desirably 50%. The oxide layer has a thickness of 0.1 to 50 μm.

  The steel for construction of the present invention having such a configuration is such that the base steel surface is shielded from the atmospheric corrosive environment and oxygen, water, and further corrosive substances are prevented from entering the base steel surface. Is difficult to elute and the generation of floating rust and flow rust is prevented or suppressed.

The architectural steel material of the present invention, after applying an aqueous solution containing 0.3-5% chromium (III) ions and / or 0.3-6% nickel (II) ions on the surface of the base steel, It can manufacture by heating to 450-720 degreeC.
An aqueous solution containing 0.3 to 5% Cr (III) ions and / or 0.3 to 6% Ni (II) ions is applied to the surface of the base steel in the heating step after the application. This is because the magnetite and hematite formed on the surface of the steel material are made dense so that the structure has few cracks and fine pores.

  When an aqueous solution containing Cr (III) ions and Ni (II) ions is applied to the surface of the base steel, these ions and Fe ions eluted from the base steel are mixed, and when dried in this state, Fe So-called “rust” containing Cr and Ni is formed on the surface of the base steel, and when this is further heated to a high temperature, the “rust” transforms into magnetite or hematite. If Cr and Ni are contained at this time, when the “rust” is formed, the “rust” becomes finer, and the structure of the interface between the “rust” and the base steel becomes dense. , Magnetite and hematite are dense and have a structure with few cracks and pores.

Further, after applying an aqueous solution containing Cr (III) ions and Ni (II) ions, it may be directly heated to a high temperature without drying. In the process of heating, the so-called “rust” in which Cr and Ni are contained in Fe is first generated by drying, and then “rust” is transformed into a dense magnetite or hematite similar to the above in which Cr and Ni are contained. Become.
Such an effect is also seen when an aqueous solution containing Cr (III) ions and Ni (II) ions alone is applied.

The lower limit of the concentration of Cr (III) ions and Ni (II) ions in the aqueous solution applied to the surface of the base steel is set to 0.3% respectively for either Cr (III) ions or Ni (II) ions. However, if it is less than 0.3%, the effect of making the above-described magnetite or hematite dense and having few cracks and pores is not sufficiently exhibited.
Further, the upper limits of the concentration of Cr (III) ions and Ni (II) ions are 5% and 6%, respectively. When the upper limit is exceeded, the magnetite layer and hematite layer formed in the heating process described below This is because the (oxide layer) becomes too thick and collapses and peels from the interface between the oxide layer and the base steel. This is presumably because the internal stress acting on the oxide layer exceeds the adhesion between the oxide layer and the base steel.
Application of an aqueous solution containing Cr (III) ions or Ni (II) ions to the surface of the base steel is carried out using any method such as an air spray method, an airless spray method, or a brush coating method, as in ordinary coating. May be.

There is no particular limitation on the amount (or thickness) of the aqueous solution to be applied. However, if the coating amount is too small, it may not be applied to the entire surface of the base steel, and even if the coating amount is increased, it does not contribute to the interfacial reaction and is economically inappropriate. Therefore, the coating amount is preferably 2 to 50 μm.
As described above, the application of the aqueous solution containing Cr (III) ions or Ni (II) ions can be carried out simply and without being limited to any place, and since it is effective in one application, it is economical. Are better.

  After applying an aqueous solution containing Cr (III) ions and / or Ni (II) ions to the surface of the base steel, heat treatment is performed, but after the application, a drying process is naturally incorporated before heating. . That is, when the application area is large and application takes time, it results in natural drying in the air before performing the drying process, and after application, it is heated directly to a high temperature without drying in the air. Even in this case, as described above, drying is performed in the course of heating.

  From the viewpoint of elution rate of Fe ions from the base steel and mass transfer of Cr ions and Ni ions, at least 5 minutes at room temperature, for example, at 50 ° C. for at least 1 minute, It is desirable that the surface is wet. However, if the wet state is too long, the elution amount of Fe ions increases, and the amount of Cr and Ni in the oxide layer formed on the surface of the base steel decreases. Time is desirable.

  When forming a dense magnetite or hematite oxide layer on the surface of the base steel, as an advantage of using an aqueous solution containing Cr (III) ions and Ni (II) ions, as described above, the construction is simple, In addition to being excellent in economic efficiency, it has a role of improving the adhesion of the oxide layer generated on the surface of the base steel. Since the mobility of ions in the solution is much larger than that in solids, the “rust” that first forms on the steel surface contains a large amount of Fe ions eluted from the base steel, The “rust” generated later includes only Fe ions that have passed through the first “rust” layer, and the content of Cr (III) ions and Ni (II) ions increases.

  As a result, the oxide layer formed on the surface of the base steel becomes a Cr or Ni-rich layer as it goes to the outer surface side, whereas the base steel side becomes rich in Fe and the adhesion is improved. .

After applying an aqueous solution containing Cr (III) ions or Ni (II) ions, heating to 450 to 720 ° C. is because the so-called “rust” generated after application is very stable in an atmospheric corrosive environment. It is for making it transform into. If the heating temperature is less than 450 ° C., a dense magnetite or hematite that is sufficiently adhered to the base steel is not formed, and a defective portion is formed.
On the other hand, when the temperature exceeds 720 ° C., the oxidation to the inside of the base steel proceeds, the oxide layer easily peels off during cooling, the base steel is exposed at that portion, and the weather resistance is remarkably lowered. In some cases, the mechanical properties near the surface of the steel deteriorate.

  As a heating method, it is possible to heat the entire steel material after applying an aqueous solution containing Cr (III) ions or Ni (II) ions. However, in a high temperature range of 450 ° C. or more, as a normal structural steel When low alloy steel is used, the base steel itself is in a heat-treated state, and properties such as strength may be significantly deteriorated. Therefore, it is preferable to employ a method in which only the surface of the steel material is heated by an induction heating device or a gas burner.

  Since the so-called “rust” generated by applying an aqueous solution containing Cr (III) ions or Ni (II) ions is relatively fast, the reaction to be transformed into magnetite or hematite is relatively high. It is preferable that the temperature be at least 5 minutes at 600 ° C. and at least 1 second at 720 ° C. In addition, since the effect does not change even if the time for maintaining the high temperature is long, the upper limit is not particularly limited, but it is desirable that the upper limit is 10 minutes at 450 ° C, 30 seconds at 600 ° C, and 10 seconds at 720 ° C.

After the heat treatment, it may be allowed to cool in the atmosphere. During cooling, among the oxide layers formed on the surface of the base steel, a porous (porous) oxide layer in the vicinity of the surface may be peeled off. Since a strong oxide layer with good adhesion is formed at the interface of the base steel, there is no problem with regard to weather resistance. However, when aesthetics are important, the porous oxide layer on the surface may be removed with a brush, nylon brush or the like.
According to the method of the present invention, a chemically stable and dense oxide layer can be generated on the surface of the base steel by a simple treatment, and a steel material for construction having excellent weather resistance can be obtained.

  A steel material (test piece) having a chemical composition shown in Table 1 and having an oxide layer formed on the surface by the method of the present invention using a weather resistant steel and a normal steel having the chemical composition shown in Table 1 as a base steel is exposed to the atmosphere. The surface condition and thickness reduction amount of the test pieces were investigated.

表２に、基材鋼の表面に塗布したＣｒ（ＩＩＩ）イオンおよび／またはＮｉ（ＩＩ）イオンを含む水溶液（以下、「処理液」という）の組成、および加熱処理条件を示す。なお、「基材鋼」の欄の符号は、表１の「基材鋼」の欄の符号に対応する。

Table 2 shows the composition of an aqueous solution containing Cr (III) ions and / or Ni (II) ions applied to the surface of the base steel (hereinafter referred to as “treatment solution”), and heat treatment conditions. In addition, the code | symbol of the column of "base steel" respond | corresponds to the code | symbol of the column of "base steel" of Table 1.

まず、上記の基材鋼から１５０ｍｍ×６０ｍｍ×３ｍｍの寸法の試験用鋼片を切り出し、その表面をエメリー紙で研磨し、さらにバフ研磨した後、処理液をスプレーにより塗布し、表面が濡れた状態で自然乾燥させた。その後、誘導加熱装置で試験用鋼片の表面温度が表２に示した温度になるように加熱し、大気中で放冷して表面に酸化物層を形成させた試験片とした。各試験片の表面は、黒色ないしは黒褐色を呈し、表面を手で触ると、表層のポーラスな粉状のものは容易にとれるが、基材鋼との界面には手ではとれない酸化物層が形成されていた。

First, a test steel piece having a size of 150 mm × 60 mm × 3 mm was cut out from the above-mentioned base steel, the surface was polished with emery paper, further buffed, and then the treatment liquid was applied by spraying to wet the surface. It was naturally dried in the state. Then, it heated so that the surface temperature of the steel piece for a test might become the temperature shown in Table 2 with the induction heating apparatus, it was left to cool in air | atmosphere, and it was set as the test piece which formed the oxide layer on the surface. The surface of each test piece is black or black-brown, and when the surface is touched by hand, a porous powdery surface can be easily removed, but an oxide layer that cannot be removed by hand is present at the interface with the base steel. Was formed.

Each of the above test specimens was exposed for 365 days (1 year) or 730 days (2 years) under the same conditions in an industrial zone at a distance of 4 km from the coast. About the test piece which passed 1 year after exposure and the test piece which passed 2 years, while examining the external appearance and the density | concentration of Cr and Ni in a surface oxide layer, plate thickness reduction amount was calculated | required. The appearance was examined by visual observation, and the concentrations of Cr and Ni were examined by EDX (energy dispersive microanalyzer).
Also, the thickness reduction amount is measured in advance by measuring the mass of the test steel piece before applying the treatment liquid using a blank material, and after removing the oxide layer on the surface after applying the treatment liquid and heat treatment. The thickness of the test steel slab was measured, and the thickness (ie, blank value) decreased by applying the treatment solution and heat treatment was determined from both measured values, and this blank value was determined from the thickness reduction after exposure. By subtracting, the reduction in plate thickness due to exposure was determined.

  As a result of the appearance investigation, the appearance of the test pieces used in Examples 1 to 3, 5, 6, 8, and 9 of the present invention shown in Table 2 was not much different from that before the exposure, and was black or blackish brown. . On the other hand, the appearance of the test pieces used in Examples 4, 7, 10 and 11 of the present invention was partially observed as flowing rust. When the surface after removing the flowing rust and the oxide layer was observed, corrosion occurred in some places. Some thinning was observed, but the depth was slight.

On the other hand, in the test pieces of Comparative Examples 1 and 2, the appearance before exposure was blackish brown, which was indistinguishable from the test piece of the present invention example. After about 1 year, almost half of the exposed surface disappeared, and the black-brown portion disappeared. After 2 years, the entire surface was covered with rust, and the appearance was completely different from that before the exposure.
In addition, as a result of analysis of the oxide layer on the surface of the test piece before exposure by EDX, in any of the test pieces used in the examples of the present invention, Cr and / or Ni is 0.3% or more in the entire area of the test piece, Concentration of Cr and Ni was observed. However, in the test piece used in the comparative example, despite the use of weathering steel as the base steel, the content of Cr and Ni is very low overall, locally 0.3% or more Although there was a portion, it was less than 0.3%.

  Table 3 shows the results of the investigation of the reduction in the thickness of the test piece after exposure. From this result, it can be seen that the thickness of the test piece of the present invention is much smaller than that of the test piece used in the comparative example. In addition, that the thickness reduction amount is 1 to 2 μm, in other words, indicates that there was almost no corrosion during the exposure period of 2 years.

In the steel for building construction of the present invention, the base steel surface is shielded from the atmospheric corrosive environment, and oxygen, water, and further corrosive substances are prevented from entering the base steel surface. Excellent in properties. This steel material can be easily manufactured by the method of the present invention in which a chemically stable and dense oxide layer is formed on the surface of the base steel by a simple treatment. Thereby, it can utilize widely as a steel material for construction excellent in a weather resistance, and its manufacturing method.

Claims (2)

  The surface of the base steel has a layer thickness of 0.1 to 50 μm, and contains one or both of chromium as oxide and nickel as oxide in a total amount of 0.3% by mass or more, and transformation. A structural steel material having excellent weather resistance, characterized by having a magnetite layer and / or a hematite layer. After applying an aqueous solution containing 0.3 to 5% by mass of chromium (III) ions and / or 0.3 to 6% by mass of nickel (II) ions to the surface of the base steel, it is heated to 450 to 720 ° C. A magnetite layer having a layer thickness of 0.1 to 50 μm on the surface of the base steel and containing one or both of chromium as an oxide and nickel as an oxide in total of 0.3% by mass or more The method for producing a steel material for building having excellent weather resistance according to claim 1, wherein a hematite layer is formed.