JP2006104547A - Highly corrosion resistant steel coated with zinc-rich primer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly corrosion resistant steel in which the properties of preventing the generation of iron rust by interaction between the surface of a matrix and a zinc-rich primer are improved, and rust prevention effect is further improved. <P>SOLUTION: The highly corrosion resistant steel is obtained by coating the surface of a matrix freed from scale with a zinc-rich primer, and the matrix has a composition comprising, by mass, 0.01 to 0.2% C, 0.05 to 1.0% Si, 0.1 to 3.0% Mn, 0.02 to 1.0% Ni, and the balance Fe with inevitable impurities, and the vicinity of the surface of the matrix is provided with an Ni-concentrated layer having a thickness of ≥1 μm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a high corrosion resistance steel material in which a zinc rich primer is applied to the surface of a steel base (such as a thick steel plate), and particularly to a high corrosion resistance steel material having excellent iron rust resistance.

  Steel materials such as thick steel plates have the advantages of high strength and excellent workability, and are inexpensive and easy to obtain. Therefore, large transport equipment (for example, ships), steel buildings (for example, buildings) Etc.) or steel structures (eg bridges, steel towers, tanks, etc.). Since steel materials used for these applications are used outdoors, they are painted to prevent corrosion.

  However, the steel manufacturing process involves heating a steel slab produced by casting molten steel, and then hot rolling to finish it to a predetermined size. A product is inevitably generated, and a scale remains on the surface of the steel after hot rolling.

  In order to coat steel, it is necessary to remove the scale (so-called surface treatment) by previously cleaning the surface of the metal phase of the steel (hereinafter referred to as “base metal”). The surface treatment is roughly classified into a primary surface treatment and a secondary surface treatment.

  The primary surface treatment is performed to prevent the occurrence of iron rust during the processing or assembling of the steel material. In other words, after removing scale and iron rust on the ground surface at a steelworks, shipyard, processing factory, etc., a primer is applied.

  The secondary surface treatment is a treatment in which iron rust generated from the pinholes and damaged parts of the primer applied in the primary surface treatment is removed during the processing or assembling of the steel material, and the primer is applied again.

  As a means for removing scale and iron rust, shot blasting is common in primary surface treatment. In the secondary surface treatment, a sandblast treatment and a power tool (for example, a grinder) are mainly used. In order to completely remove the metal layer, a considerable thickness of the metal layer on the surface of the ground iron is removed at the same time. As a primer, a wash primer or a zinc rich primer is used for both the primary surface treatment and the secondary surface treatment. However, zinc-rich primers having excellent corrosion resistance are widely used.

After performing the surface treatment (that is, the primary surface treatment and the secondary surface treatment) in this way, the surface of the ground iron is coated. As the paint used for painting, resin-based paints such as butyral resin, polyester resin, and epoxy resin are used.
Rust / Corrosion Technology Overview Editorial Board: Rust / Corrosion Technology Overview, 2000

  As explained above, the secondary surface treatment removes the iron rust generated from the pinholes and damaged parts of the primer film formed by the primary surface treatment during the processing or assembling of the steel material, and reapply the primer. It is processing. Therefore, if the antirust effect of the primer formed by the primary surface treatment is improved, the load of the secondary surface treatment can be reduced.

  The present invention improves the property of preventing the occurrence of iron rust (hereinafter referred to as iron rust resistance) by the interaction between the surface of steel and the zinc rich primer, further improving the rust prevention effect. It aims at providing corrosion-resistant steel materials.

The anti-corrosion function of steel coated with zinc rich primer is
(1) Zinc rich primer coating prevents water, oxygen, chloride, and other corrosive factors from entering the base iron from the environment.
(2) Zn contained in the zinc rich primer coating binds to environmental corrosion factors (so-called sacrificial protection) to suppress the occurrence of iron rust.
(3) Corrosion products in which Fe contained in the base iron and Zn contained in the zinc rich primer coating are combined with the corrosion factor are exerted by suppressing the invasion of the corrosion factor from the environment into the base iron.

  The effect of the anticorrosion function (1) is improved as the ion permeation resistance of the zinc rich primer increases. The higher the sacrificial anticorrosive ability of Zn, the better the anticorrosive function of (2). The effect of the anticorrosion function (3) increases as the corrosion resistance of the corrosion product increases.

  Of these, the anticorrosion function of (1) varies depending on the characteristics of the zinc rich primer, but the anticorrosion functions of (2) and (3) depend on the characteristics of the zinc rich primer and the components of the iron. The effect varies. The background and results of the research on anticorrosion function (2) and (3) are explained below.

  Steel slabs were manufactured by casting molten steel to which alloying elements such as Ni, Cu, Cr, and Mo were added, and the steel slabs were hot rolled to form thick steel plates. Next, the scale of the thick steel plate was removed by shot blasting, and a zinc rich primer was further applied to produce a small exposure test piece. The test piece was exposed for 6 months to an environment (that is, a coastal area) where salt content comes in, and an exposure test was conducted.

  After the exposure test was completed, the surface of the test piece was visually observed, and the number of iron rusts that appeared in the form of dots was measured. As a result, it was found that the number of dotted iron rusts was significantly reduced in the test pieces collected from the thick steel plates to which Ni was added compared to the test pieces to which other elements were added. That is, in order to improve the iron rust resistance of a steel material having a zinc rich primer coating, it is necessary to add Ni to the base iron.

  However, since Ni is an expensive element, adding Ni causes an increase in the manufacturing cost of the steel material. However, if concentrated near the surface of the ground iron, the amount of Ni used can be reduced without impairing the iron rust resistance. Then, this inventor examined the technique which concentrates Ni to the surface vicinity of a ground iron from a viewpoint of suppressing the raise of the manufacturing cost of steel materials.

  A steel slab containing 2.9% by mass of Ni (thickness 210 mm) was heated at 1120 ° C. for 2 hours, and then hot rolled to obtain a thick steel plate (thickness 20 mm). A sample was taken from a thick steel plate and subjected to EPMA analysis to investigate the concentration distribution of O, Fe, and Ni near the surface of the ground iron. A typical example is shown in FIG. A region where Ni is concentrated (hereinafter referred to as a Ni-enriched layer) is observed near the surface of the base iron. The thickness of the Ni-enriched layer is about 5 μm, and the maximum Ni concentration in the Ni-enriched layer is about 5 times that of the ground iron.

  That is, when a steel material containing Ni is heated, Fe oxide called scale is generated on the surface, while Ni is concentrated near the surface of the ground iron. At that time, Ni does not concentrate in the scale, but remains in the ground iron near the surface to form a Ni concentrated layer. Therefore, the Ni added to the steel is concentrated near the surface of the steel to form a Ni-enriched layer, and the Ni-enriched layer remains even when used as a steel structure, thereby further enhancing the corrosion resistance of the steel. Can be increased.

  In addition, the vicinity of the surface of the ground iron means within 1000 μm from the surface of the ground iron. The Ni-enriched layer refers to a layer that is at least 1.2 times the Ni content inside the base material.

  However, conventional thick steel plates (for example, marine steel plates) are subjected to shot blasting in the manufacturing process, mechanically removing the scale on the surface, and further coated with a zinc rich primer. In the shot blasting process, a steel ball having a diameter of about 1 mm is usually sprayed, so that the roughness of the surface of the steel after the scale is removed is about 60 μm in Rmax. Therefore, the Ni concentrated layer having a thickness of about 5 μm is removed together with the scale by the shot blasting process.

  In order to produce the highly corrosion resistant steel material of the present invention in which the Ni concentrated layer is formed in the vicinity of the surface of the base iron, it is necessary to remove the scale while leaving the Ni concentrated layer. However, mechanical means such as shot blasting and cutting usually inevitably remove the Ni-enriched layer together with the scale. Therefore, in the present invention, it is desirable to remove only the scale using chemical means. That is, if only the scale is chemically removed by pickling, it is advantageous to leave the Ni concentrated layer in the vicinity of the surface of the base iron. Although it is not necessary to limit a pickling liquid to a specific component density | concentration, the hydrochloric acid aqueous solution generally used widely is preferable.

  Further, by adding an inhibitor to the pickling solution, it is possible to prevent elution of the base iron by pickling and leave the Ni concentrated layer. It should be noted that only scales may be removed using mechanical means such as shot blasting or cutting, with appropriate conditions.

  The present invention has been made based on the above findings.

  That is, the present invention is a highly corrosion-resistant steel material obtained by applying a zinc rich primer to the surface of the base iron from which scale has been removed, wherein the base iron is C: 0.01 to 0.2% by mass, Si: 0.05 to 1.0% by mass, Mn: 0.1 to 3.0% by mass, Ni: 0.02 to 1.0% by mass, with the balance being composed of Fe and inevitable impurities, and having a Ni concentrated layer with a thickness of 1 μm or more near the surface of the base iron High corrosion resistance steel.

  In the highly corrosion-resistant steel material of the present invention, it is preferable that the ground iron contains one or two of Cu: 0.1 to 1.0 mass% and Mo: 0.01 to 0.5 mass% in addition to the above-described composition. Furthermore, it is preferable to contain 1 type (s) or 2 or more types in Nb: 0.005-0.1 mass%, Ti: 0.005-0.1 mass%, and V: 0.005-0.1 mass%.

  In the highly corrosion resistant steel material of the present invention, the maximum value of Ni concentration in the Ni concentrated layer is preferably 0.1% by mass or more.

  According to the present invention, it is possible to obtain an inexpensive high corrosion-resistant steel material in which a Ni concentrated layer is formed in the vicinity of the surface of the base iron and the iron rust resistance is remarkably improved.

  First, the reason why the components of the ground iron of the high corrosion resistant steel material of the present invention are limited will be described.

C: 0.01-0.2 mass%
C is an element that increases the strength of the high corrosion-resistant steel, and it is necessary to contain 0.01% by mass or more in order to obtain a desired strength. On the other hand, if it exceeds 0.2% by mass, the toughness of the high corrosion resistance steel will deteriorate. Therefore, C in the ground iron needs to satisfy the range of 0.01 to 0.2% by mass.

Si: 0.05-1.0 mass%
Si is an element that acts as a deoxidizing agent in the melting stage of molten steel and increases the strength of the high corrosion resistant steel material. In order to obtain a desired strength, it is necessary to contain 0.05% by mass or more. On the other hand, if it exceeds 1.0 mass%, the toughness and weldability of the high corrosion resistance steel will deteriorate. Therefore, Si in the ground iron needs to satisfy the range of 0.05 to 1.0 mass%.

Mn: 0.1-3.0 mass%
Mn is an element that increases the strength of the high-corrosion-resistant steel, and it is necessary to contain 0.1% by mass or more in order to obtain a desired strength. On the other hand, if it exceeds 3.0% by mass, the toughness and weldability of the high corrosion resistance steel will deteriorate. Therefore, Mn in the ground iron needs to satisfy the range of 0.1 to 3.0 mass%.

Ni: 0.02 to 1.0 mass%
Ni is the most important element among the elements added to the highly corrosion-resistant steel material of the present invention. Ni improves the sacrificial anticorrosive property of Zn by making the eclectic potential with Zn in the zinc rich primer noble, refines the Zn corrosion product, and reduces the corrosion factor due to the Zn corrosion product to the iron It works to increase the permeation resistance and suppress the corrosion of the railway. In addition, the action of making the Fe corrosion product finer and the action of negativeizing the charge of the Fe corrosion product suppress the permeation of chloride ions to the surface of the steel, increasing the pH near the surface of the steel, Inhibits corrosion.

  The above effects are more remarkable as the Ni concentration increases. However, when the Ni concentration in the vicinity of the surface of the ground iron is about 5% by mass, for example, the iron rust on the surface of the steel material coated with the zinc rich primer disappears for 6 months, which is the shipbuilding period. Therefore, it is unnecessary to concentrate more Ni in the vicinity of the surface of the base iron, which only increases the raw material cost.

  As already explained, when a steel material containing Ni is heated, a Ni concentrated layer is formed in the vicinity of the surface of the ground iron. Ni does not concentrate in the scale, but in the iron bar near the surface. At this time, the Ni concentration of the Ni-enriched layer is about 5 times the Ni concentration of the base iron.

  According to the studies by the present inventors, the Ni concentration layer has a maximum Ni concentration of 0.1% by mass or more in order to suppress the occurrence of iron rust in the steel material coated with the zinc rich primer. Is preferable. Therefore, the Ni concentration of the ground iron needs to be 0.02 mass% or more. Therefore, the Ni concentration in the ground iron needs to satisfy the range of 0.02 to 1.0 mass%.

  The thickness of the Ni concentrated layer may be 1 μm or more. The reason is that the steel material to which the zinc rich primer is applied has a very small amount of corrosion reduction in 6 months.

  In the high corrosion resistance steel material of the present invention, in addition to C, Si, Mn, and Ni, the following elements may be added as necessary.

Cu: 0.1 to 1.0 mass%
Cu refines the Fe corrosion product, thereby increasing the permeation resistance of corrosion factors to the ground iron and suppressing the corrosion of the ground iron. If the Cu content in the base iron is less than 0.1% by mass, the effect cannot be obtained sufficiently. On the other hand, if it exceeds 1.0 mass%, hot workability in the production process of the high corrosion resistance steel is impaired. Accordingly, when Cu is added to the ground iron, it is preferably in the range of 0.1 to 1.0 mass%.

Mo: 0.01-0.5 mass%
Mo forms molybdate ions in Zn corrosion products and Fe corrosion products, thereby preventing chloride ions from passing through the corrosion products and reaching the base iron. If the Mo content in the ground iron is less than 0.01% by mass, the effect cannot be obtained sufficiently. On the other hand, when it exceeds 0.5 mass%, the effect is saturated. Therefore, when adding Mo to the ground iron, the range of 0.01 to 0.5 mass% is preferable.

Nb: 0.005 to 0.1 mass%, Ti: 0.005 to 0.1 mass%, V: 0.005 to 0.1 mass%
Nb, Ti, and V are elements that increase the strength of the high corrosion-resistant steel, and one or more of them can be added as necessary. Nb, Ti, and V are all effective when contained in amounts of 0.005% by mass or more. However, if each content exceeds 0.1% by mass, the toughness and weldability of the high corrosion-resistant steel materials deteriorate. For this reason, it is preferable that all of Nb, Ti, and V be 0.005 to 0.1% by mass.

  Next, the manufacturing method of the high corrosion resistance steel material of this invention is demonstrated.

  A molten steel having a predetermined composition is melted by a conventionally known technique such as a converter method or an electric furnace method, and then a steel slab is manufactured by a continuous casting method or an ingot forming method. In addition, at the smelting stage of molten steel, refining technology (so-called primary refining) mainly using decarburization such as the converter method and electric furnace method, followed by refining technology mainly using degassing such as vacuum degassing method (so-called primary refining). Secondary refining) may be used in appropriate combination.

  Next, the steel slab is heated to 900 to 1200 ° C. and further hot-rolled to obtain a steel material having a predetermined shape (ie, steel plate, section steel, etc.), and then cooled by air cooling or accelerated cooling.

  Since the steel material produced in this way has a scale formed on the surface, it is advantageous to perform pickling to chemically remove only the scale. As the pickling solution, conventionally known ones such as dilute hydrochloric acid (ie, an aqueous solution of hydrochloric acid), dilute sulfuric acid (ie, an aqueous solution of sulfuric acid), dilute phosphoric acid (ie, an aqueous solution of phosphoric acid) can be used. However, it is preferable to use dilute hydrochloric acid in consideration of pickling efficiency and dissolution characteristics of the scale.

  Further, by adding an inhibitor to the pickling solution, it is possible to prevent elution of the base iron by pickling and leave the Ni concentrated layer. Inhibitors are appropriately selected and used according to the components of the base iron, the type of pickling solution, and the like.

  In addition, mechanical means such as shot blasting and cutting can be used if only the scale removal is performed and the metal layer on the surface of the ground iron is not removed or the Ni-enriched layer can be left in a necessary amount.

  After removing the scale, a zinc rich primer containing Zn is applied to the surface of the base iron to form a film. The application method is not limited to a specific means, and conventional techniques such as spraying, brushing, and roll coater can be used.

  The highly corrosion resistant steel material of the present invention can be manufactured by the above procedure. In the highly corrosion-resistant steel material of the present invention, a Ni concentrated layer is formed in the vicinity of the surface of the ground iron. Therefore, the iron rust resistance is remarkably improved by the interaction between the zinc rich primer coating and the Ni concentrated layer. In addition, since Ni is concentrated near the surface of the ground iron, it is not necessary to increase the Ni concentration of the entire ground steel. Therefore, the amount of expensive Ni used can be reduced, and an increase in manufacturing cost of the high corrosion resistant steel material can be suppressed.

  Molten steel having the components shown in Table 1 was melted using a converter, and a steel slab having a thickness of 210 mm was obtained by continuous casting. Steel number 1 in Table 1 is an example in which Ni is not added (that is, comparative example), and steel numbers 2 to 11 are examples (that is, invention examples) that all satisfy the components of the high corrosion resistance steel of the present invention. These steel slabs were heated to 1120 ° C and then hot rolled to form thick steel plates with a thickness of 20 mm and a width of 2500 mm. The thick steel plate thus obtained was pickled and the surface scale was chemically removed. Dilute hydrochloric acid was used for the pickling solution.

  Further, the steel plate (steel numbers 1 to 11) produced in the same manner as above was subjected to shot blasting by spraying a steel ball having a diameter of about 1 mm to mechanically remove the surface scale.

  As shown in Table 2, the steel plate symbols 1A to 11A, in which the steel plates obtained from the steel slabs with steel numbers 1 to 11 were subjected to shot blasting and mechanically scaled, are compared regardless of the components of the steel slab. It is an example. Among the steel plate symbols 1B to 11B, 2C, 3C, and 3D obtained by subjecting the thick steel plates obtained from the steel slabs having the steel numbers 1 to 11 to the pickling treatment, the steel plate symbol 1B is out of the scope of the present invention. Therefore, the steel plate symbols 2B to 11B and 3D are comparative examples, and the steel slab components satisfy the scope of the present invention, the scale is chemically removed, and the thickness of the Ni concentrated layer is 1 μm or more. It is an example. On the other hand, in 2C and 3C, the components of the steel slab satisfied the scope of the present invention and the scale was chemically removed, but because of the strong pickling conditions, the thickness of the Ni concentrated layer is less than 1 μm. It is a comparative example.

  For the inventive example and the comparative example, the maximum value (% by mass) of the Ni concentration in the Ni concentrated layer, the thickness of the Ni concentrated layer (μm), and the occurrence of dotted iron rust were investigated.

  When investigating the maximum value of Ni concentration in the Ni-enriched layer and the thickness of the Ni-enriched layer, an analytical test piece (10 mm x 10 mm) is taken from the surface layer of each thick steel plate from which the scale has been removed, and EPMA Analysis was performed. The maximum value of Ni concentration in the Ni concentrated layer is as shown in Table 2. Note that the maximum value of the Ni concentration in the Ni-concentrated layer was calculated by Ni concentration (mass%) inside the base material × maximum Ni detection strength of the Ni-concentrated layer ÷ average Ni detection strength inside the base material. Table 2 shows the thickness of the region where the Ni concentration is 1.2 times or more of the inside of the base metal (that is, the thickness of the Ni concentrated layer).

  Next, in order to investigate the occurrence of dotted iron rust, corrosion test pieces (thickness 5 mm, width 50 mm, length 100 mm) including the steel plate surface were collected from each thick steel plate, and then inorganic zinc rich primer Was applied to form a film. The thickness of each coating was 15 μm. These corrosion test pieces were subjected to an exposure test for 6 months in a beach environment (amount of incoming salt: 1.5 mdd). After the exposure test was completed, the surface of the corrosion test piece was visually observed, and the number of dotted iron rusts was measured.

  As is apparent from Table 2, in the invention examples (steel symbols 2B to 11B, 3D), a Ni concentrated layer is formed near the surface of the thick steel plate, and the thickness of the Ni concentrated layer is 1 μm or more. On the other hand, in the comparative examples (steel symbols 1A to 11A and 1B), there is no Ni concentrated layer near the surface of the thick steel plate. In the comparative examples (steel symbols 2C and 3C), a Ni concentrated layer is formed near the surface, but the thickness of the Ni concentrated layer is less than 1 μm.

  For the comparative example (steel symbols 2A to 11A, 2C, 3C) and the invention example (steel symbols 2B to 11B, 3D) The inventive example is significantly reduced.

  From this, it can be seen that the presence of the Ni concentrated layer exhibits a great effect in reducing the amount of iron rust generated in the high corrosion resistant steel material coated with the zinc rich primer.

It is a graph which shows concentration distribution of Fe, Ni, and O.

Claims (4)

  A highly corrosion-resistant steel material obtained by applying a zinc rich primer to the surface of the base iron from which scale has been removed, wherein the base iron is C: 0.01 to 0.2% by mass, Si: 0.05 to 1.0% by mass, Mn: 0.1 to 3.0% by mass, Ni: 0.02 to 1.0% by mass, with the balance being composed of Fe and inevitable impurities, and having a Ni concentrated layer having a thickness of 1 μm or more in the vicinity of the surface of the base iron High corrosion resistance steel.   The high corrosion resistance steel material according to claim 1, wherein the base iron contains one or two of Cu: 0.1 to 1.0 mass% and Mo: 0.01 to 0.5 mass% in addition to the composition. .   The base iron contains one or more of Nb: 0.005-0.1% by mass, Ti: 0.005-0.1% by mass, and V: 0.005-0.1% by mass in addition to the composition. The highly corrosion-resistant steel material according to claim 1 or 2. The high corrosion resistant steel material according to claim 1, 2, or 3, wherein the maximum value of Ni concentration in the Ni concentrated layer is 0.1 mass% or more.