JP2012081670A - Organic resin coated steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide organic resin coated steel of which a life can be prolonged further as compared with steel manufactured by a conventional technology.SOLUTION: The organic resin coated steel includes an iron phosphate chemical conversion treatment layer, an aluminum phosphate chemical conversion treatment layer, and an organic resin layer laminated on a surface of the steel in this order from a steel side. An average thickness of the iron phosphate chemical conversion treatment layer is 0.1-1 μm. The aluminum phosphate chemical conversion treatment layer contains metal M selected from P, Al, B, and Mg or Ca. A composition of the aluminum phosphate chemical conversion treatment layer includes a binder giving AlO/PO=0.2-0.6, BO/PO=0.01-0.1, MO/PO=0.01-0.2 at a molar ratio in terms of anhydrous oxide, and inorganic extender pigment.

Description

  The present invention relates to an organic resin-coated steel material. More specifically, the present invention relates to an organic resin-coated steel material having an organic-coated base treatment layer.

  It is widely practiced that steel materials used in applications where corrosion protection performance is important (for example, marine steel structures) are protected by resin coating. Usually, in order to improve corrosion resistance and adhesiveness, a chemical conversion treatment is performed on the surface of the steel material, and a resin coating is performed thereon. The steel material coated with the resin exhibits anticorrosion performance until the resin coating is peeled off. However, by performing the chemical conversion treatment, the peeling of the resin coating can be suppressed and the anticorrosion life can be extended.

  Conventionally, chromate treatment has been used as this chemical conversion treatment, but recently, chemical conversion treatment not using chromate has been developed for environmental measures. However, it has not been easy to achieve the same level of corrosion resistance, adhesion, cathode peel resistance, etc. required for offshore structures as steel materials using chromate treatment. For this reason, various attempts have been made in the past to improve these performances.

  For example, Patent Document 1 discloses an aluminum phosphate non-chromate resin-coated steel material having a coating life comparable to a chromate-treated material.

  However, recently, since it has been demanded to extend the life of steel materials exceeding chromate, further development is desired.

Patent Publication 2007-313885

  An object of the present invention is to provide an organic resin-coated steel material capable of further extending the life compared to steel materials in the prior art.

  As a result of diligent research, the present inventors have improved the above-mentioned purpose by appropriately improving the “chemical conversion treatment layer” that should constitute the organic resin-coated steel material (even if the conventional resin type and configuration are not significantly changed). Has been found to be achievable.

The organic resin-coated steel material of the present invention is based on the above discovery, and more specifically,
(A copy of "Claim 1")

  According to the knowledge of the present inventors, the reason why the organic resin-coated steel material can be extended in the present invention is estimated as follows.

  That is, according to the knowledge of the present inventors, the problem that hinders the extension of the life of marine steel structures is caused by the fact that the resin coating is “stripped” by collision with drifting objects such as driftwood and ships in the tidal zone. It was estimated to be. If the resin coating is stripped, the corrosion resistance and film durability will deteriorate, even if the steel material is not exposed, even if the steel material is not exposed. is there.

  On the other hand, in the conventional impact resistance test that has been used in the past, that is, in a method of observing cracks / peeling of the coating film or coating by dropping and colliding the weight vertically with a horizontally placed test piece. The coating resin layer is subjected to a strong compressive stress, and the resin is destroyed. However, the present inventors have found that such a conventional impact resistance test is not necessarily suitable for the evaluation of the corrosion resistance and film durability of the steel material for marine steel structures described above.

  According to the knowledge of the present inventors, it is rare that a driftwood, a drifting object, a ship, etc. actually collide with a steel material (to be evaluated) perpendicularly, but rather with an angle other than “vertical”. It was estimated that there were more cases. Based on such a hypothesis, the present inventors predicted that “rubbing fracture”, which occurs when a large shear stress is applied in addition to compressive stress, is extremely important for the coating resin.

  From this point of view, the present inventors believe that if the "rubbing resistance" of the resin coating is weak, the actual "anticorrosion life" will rather be reduced even if a chemical conversion treatment having excellent adhesion and corrosion resistance is used. It was. Therefore, the present inventors considered that the conventional test of “falling a normal weight vertically” is not appropriate as an evaluation test of “rubbing resistance”.

  Based on the above consideration, the present inventors have devised a new “rubbing fracture test method” as shown in the examples described later. According to the “rubbing fracture test method” devised by the present inventors, it has been found that the “rubbing fracture resistance” of the resin coating can be appropriately evaluated as described later. This new “rubbing resistance” evaluation (compared to the conventional impact resistance test), especially when the coating thickness of the resin coating is several millimeters, the difference is significant. However, it has been proved by experiments of the present inventors.

  Based on the above findings (new “rubbing fracture test method”), the present inventors have further researched on “resin coating that hardly causes rubbing fracture”, and further obtained the following findings.

  According to the above new “rubbing fracture” test, it was found that the molecular cohesive force of the organic resin has an important influence on the “rubbing breakability” when the organic resin layer breaks.

  As a result of further earnest research based on the above findings, the present inventors have found that the chemical conversion treatment layer can be obtained without increasing the molecular cohesion, that is, without significantly changing the type and configuration of conventional resins. The present inventors have found that the improvement of the above can extend the life of the organic resin-coated steel material and can improve the rubbing fracture of the resin layer.

  The organic resin-coated steel material of the present invention has excellent “rubbing resistance”. Therefore, the organic resin-coated steel material of the present invention has a suitable long life in applications where the “rubbing resistance” is effective (for example, steel materials for marine structures for marine areas where there are many ship traffic and drifting objects). Can be achieved.

  The organic resin-coated steel material of the present invention can have the following aspects.

[1]
An organic resin-coated steel material in which an iron phosphate chemical conversion treatment layer, an aluminum phosphate chemical conversion treatment layer, and an organic resin layer are laminated on the steel material surface in this order from the steel material side;
The aluminum phosphate-based chemical conversion treatment layer contains P, Al, B, and a metal M selected from Mg or Ca;
The composition of the aluminum phosphate-based chemical conversion treatment layer is Al ₂ O ₃ / P ₂ O ₅ = 0.2 to 0.6 and B ₂ O ₃ / P ₂ O ₅ = 0 in terms of a molar ratio in terms of anhydrous oxide. An organic resin-coated steel material comprising a binder giving 0.01 to 0.1 and MO / P ₂ O ₅ = 0.01 to 0.2 and an inorganic extender pigment.

[2]
The organic resin-coated steel material according to [1], wherein the iron phosphate chemical conversion treatment layer has an average film thickness of 0.1 to 1 μm.

[3]
The organic resin-coated steel material according to [1] or [2], wherein the inorganic pigment is added in an amount of 10 to 50 vol% with respect to the dry film of the aluminum phosphate chemical conversion treatment layer.

[4]
The organic resin layer according to any one of [1] to [3], wherein the organic resin layer includes a primer layer formed immediately above the chemical conversion treatment layer and a top layer made of a urethane elastomer resin. Coated steel.

[5]
The organic resin-coated steel material according to [4], wherein the primer layer is made of an epoxy resin.

[6]
The organic resin-coated steel material according to [4] or [5], wherein the primer layer has a thickness of 100 to 500 μm.

[7]
The organic resin-coated steel material according to any one of [4] to [6], wherein the top layer has a thickness of 2 to 4 mm.

[8]
The organic resin-coated steel material according to any one of [1] to [7], wherein the aluminum phosphate chemical conversion treatment layer has a thickness of 5 to 40 μm.

[9]
The organic resin-coated steel material according to any one of [1] to [8], wherein the metal M is Mg.

[10]
The organic resin-coated steel material according to any one of [1] to [9], wherein the inorganic extender pigment in the aluminum phosphate-based chemical conversion treatment layer is alumina.

(Organic resin coated steel)
The organic resin-coated steel material of the present invention includes a steel material, an iron phosphate chemical conversion treatment layer disposed thereon (in order from the surface of the steel material), and an aluminum phosphate chemical conversion treatment layer disposed thereon. And an organic resin layer disposed thereon. Thus, in the organic resin-coated steel material of the present invention, it is important that the chemical conversion treatment layer has a “two-layer structure”.

(Steel grade)
The steel type is not particularly limited. From the viewpoint of cost, it is preferable to use a steel type that is a general-purpose steel for structural materials such as SS400.

(Steel)
The steel material (that is, the shape of the steel type) is not particularly limited. From the point of shape, a steel pipe, a steel pipe sheet pile, a steel sheet pile, a thick board, etc. can be illustrated. In order to remove rust, scale, contaminants, etc. from the surface of these steel materials, it is extremely preferable to perform a ground treatment such as sand blasting, grid blasting, and shot blasting to expose a clean metal surface.

(Iron phosphate chemical conversion treatment layer)
The iron phosphate chemical conversion treatment layer (that is, iron phosphate coating) to be disposed on the steel surface is not particularly limited. From the point of resistance to rubbing and rubbing, a dense and thin microcrystalline film composed of a mixture of FePO ₄ .2H ₂ O and Fe ₂ O ₃ and the aforementioned additive ions inevitably mixed is preferable. Such a suitable iron phosphate chemical conversion treatment layer can be obtained using, for example, a commercially available chemical conversion solution for iron phosphate. The thickness of the iron phosphate chemical conversion layer is usually about 0.1 to 0.4 μm at most. In the present invention (for example, in a mode in which the surface of the substrate is blasted and the surface is severely uneven), the film thickness is preferably 0.1 to 1 μm in consideration of variations in film formation. The film thickness is preferably 0.1 to 0.5 μm (particularly 0.2 to 0.5 μm). When this film thickness is thinner than 0.1 μm, the uniformity of the film is lost and the effect of the invention tends to be reduced. On the other hand, when the film thickness exceeds 1 μm, it tends to be difficult to form the film.

  In the present invention, the iron phosphate chemical conversion treatment layer described above can sufficiently improve the rubbing breakability of the organic resin layer due to a synergistic effect with the aluminum phosphate chemical conversion treatment layer described later.

  As phosphate treatments other than iron phosphate treatment, zinc phosphate treatment and manganese phosphate treatment are known and are used more widely than iron phosphate treatment. Are inferior to iron phosphate treatment.

(Aluminum phosphate chemical conversion treatment layer)
The structure of the aluminum phosphate chemical conversion treatment layer to be disposed on the iron phosphate chemical conversion treatment layer is not particularly limited. From the viewpoint of water-resistant adhesion, the aluminum phosphate chemical conversion treatment layer is preferably one in which an inorganic extender pigment (as will be described later) is dispersed in the binder phase. When alumina is used as the inorganic extender pigment, aluminum is contained in both the binder phase and the solid phase of the pigment. In such an embodiment, for example, when the cross section is observed with EPMA (Electron Probe Microanalyzer), P (phosphorus) is contained in the binder, but P is not contained in alumina. It is easy to distinguish.

  The adhesion amount of the aluminum phosphate chemical conversion treatment layer is preferably 5 to 40 μm from the viewpoint of initial adhesion and water-resistant adhesion. The adhesion amount is more preferably 10 to 30 μm (particularly 15 to 25 μm). When the adhesion amount is less than 5 μm, the blast surface cannot be uniformly wetted, unevenness is generated, and the rubbing fracture property tends to vary. When the amount of adhesion exceeds 40 μm, the rubbing breakability tends to decrease.

(Oxide composition formula)
Before the description of the composition of the binder phase, the “oxide composition formula” used in the composition notation will be described. In the case of hydrous inorganic oxides, the oxide composition formula is expressed by the sum of oxide and water equal to the composition, and is often used in the field of ceramics and mineralogy. Further, in the “claims” of the present application, each composition is expressed by a molar ratio with respect to P ₂ O _5, but the balance is divided into P ₂ O ₅ , water (hydrogen ions and hydroxide ions). Inevitable impurity oxide).

(binder)
The constituent elements of the binder are preferably Al, P, B, M, O, and H from the viewpoint of an element that achieves both adhesion and durability comparable to chromate treatment and a low environmental load. Of these elements, O and H usually exist as oxide ions or hydroxide ions (although they are usually expressed together as H ₂ O in the oxide composition formula), It constitutes an indefinite proportional compound with a cation. That is, the chemical conversion treatment binder of the present invention is usually a compound that does not have an element ratio as originally indicated by an integer ratio. This is one of the reasons for using the above "oxide notation".

(Rin)
P is a main salt of anion of the chemical conversion treatment layer as a phosphate, and phosphorus is H ₂ PO ₄ ⁻ , HPO ₄ ²⁻ , phosphate ion, or an n-mer (metaphosphate ion, polyphosphate) in the film. Ions) and serves to connect aluminum (III) ions, boron (III) ions, and metal M ions. In addition, trivalent boron and metal M ions, like aluminum, form complex indefinite proportional compounds with phosphate ions.

(aluminum)
Al plays a major role in improving the cathode peel resistance and water adhesion resistance, but usually exists as Al (III). In the present invention, the molar ratio is Al ₂ O ₃ / P ₂ O ₅ = 0.2 to 0.6 (more preferably 0.3 to 0.5, particularly preferably 0.38 to 0.41). . In the present invention, in the range of Al ₂ O ₃ / P ₂ O ₅ = 0.2 to 0.6 in terms of molar ratio, there is no (substantially) a defect in the network in which phosphate ions and aluminum ions are bonded, Good film formability and durability can be exhibited. If this molar ratio exceeds 0.6, the water-resistant adhesion and film-forming properties tend to deteriorate. On the other hand, when the molar ratio is less than 0.2, the cathode peel resistance tends not to be improved sufficiently.

In the present invention, after all, the main components of the binder are trivalent aluminum and HPO ₄ ²⁻ , and it is a hybrid containing some H ₂ PO ₄ ⁻ , trivalent boron and M divalent ions. Preferably. These molar ratios are non-stoichiometric compounds that usually do not have an integer ratio. According to the estimation of the present inventors, the aluminum phosphate in the aluminum phosphate-based chemical conversion treatment layer is located between AlPO ₄ and Al ₂ (HPO ₄ ²⁻ ) ₃ (if it is positioned imagewise). ing. The relationship (difference) between AlPO ₄ and Al ₂ (HPO ₄ ²⁻ ) ₃ is that when H ₃ PO ₄ is removed from Al ₂ (HPO ₄ ²⁻ ) ₃ , it becomes AlPO ₄ . The exact positioning tends to change slightly due to dehydration during curing and reaction with the iron substrate. Examples No. If the form of aluminum phosphate in the case of 4 to 9 is expressed by a simple average chemical composition formula, it becomes approximately H _1.2 PO ₄ ^1.8− .

(Boron)
B has the property of improving the film-forming property at the time of baking of the film. In the present invention, B ₂ O ₃ / P ₂ O ₅ = 0.01 to 0.1 is excellent in terms of molar ratio. This molar ratio is more preferably 0.05 to 0.1 (more preferably 0.08 to 0.1). When this molar ratio is less than a specified value (that is, 0.01), the film forming property tends to be deteriorated. On the other hand, even if the amount is larger than the specified value (that is, 0.1), the effect is saturated and does not further improve. B is usually present as a trivalent boron, and, like Al (III), forms a complex non-proportional compound with phosphate ions.

(Mg or Ca)
The metal M (Mg or Ca) has an effect of improving the film forming property by increasing the film density when forming the inorganic ionic film, increasing the adhesion of the base, and reducing the structural defects. In the present invention, MO / P ₂ O ₅ = 0.01 to 0.2 is effective. This molar ratio is more preferably 0.05 to 0.15 (more preferably 0.07 to 0.12). If this ratio (MO / P ₂ O ₅ ) is less than the specified amount (ie 0.01), the effect tends to be weakened. On the other hand, when the amount is larger than the specified amount (ie 0.2), the adhesiveness is lowered, and the coating tends to choke or the coating liquid rapidly gels, making it difficult to manufacture at the stage of the processing liquid. . 3. The resin coating structure according to claim 2 (that is, “the organic resin layer is composed of a primer layer made of an epoxy resin formed immediately above the chemical conversion treatment layer and a top layer made of a urethane elastomer resin, and the thickness of the primer layer” Is 100 to 500 μm and the thickness of the top layer is 2 to 4 mm ”), Mg is more suitable than Ca.

(Inorganic extender pigment)
The inorganic extender pigment may be added as necessary to improve the film formability of the aluminum phosphate chemical conversion coating. From the viewpoint of water-resistant adhesion, it is preferable to add an inorganic extender pigment. Since the phosphoric acid aluminum chemical conversion treatment liquid is acidic, it is not particularly limited as long as it is insoluble in acid and well dispersed in the treatment liquid. From the viewpoint of dispersibility and coatability, it is preferable to use alumina, titania, silica or the like having a particle size of 5 to 15 μm. A surface treatment for improving dispersibility and insolubility can be applied to the surface of these particles as necessary.

  The addition amount of the inorganic extender pigment is preferably 10 to 50 vol% (based on the coating film after drying and curing). This addition amount is more preferably 10 to 20 vol% (more preferably 10 to 16 vol%). When the amount of the inorganic extender pigment is less than 10 vol%, the film formability tends to be difficult to improve. On the other hand, when the added amount is larger than 50 vol%, the rubbing resistance tends to deteriorate.

(Organic resin layer)
The organic resin layer to be disposed on the aluminum phosphate chemical conversion treatment layer has a function of blocking corrosion factors such as water, oxygen, and electrolyte from the steel material, and remarkably improving the corrosion resistance of the steel material. The total thickness of the organic resin layer is preferably 1 to 5 mm from the viewpoint of balance between cost and durability. This thickness is further preferably 1 to 3 mm (particularly 2 to 3 mm).

(Organic resin layer for offshore structures)
In particular, an organic resin layer used for an offshore structure needs to have excellent adhesion, corrosion resistance, and durability. For this reason, it is general that the organic resin layer has a two- to three-layer structure, the chemical conversion treatment layer side is provided with one or two layers as a resin primer layer, and the protective layer having a thick film thickness is provided on the atmosphere side.

  In addition, when a steel surface having a large protrusion or curvature such as a steel pipe sheet pile is present, the coating method is suitable for the organic resin coating, and therefore the desirable resin configuration that can be manufactured by the coating method is the aspect of claim 2 (that is, organic The resin layer is composed of a primer layer made of an epoxy resin formed immediately above the chemical conversion treatment layer and a top layer made of a urethane elastomer resin, and the thickness of the primer layer is 100 to 500 μm, and the thickness of the top layer Is an aspect of 2 to 4 mm.

(Primer layer)
The primary purpose of the primer layer is to improve the adhesion between the metal and the resin layer and the water resistance of the adhesive surface, and if necessary (in the present invention, between the metal and the iron phosphate chemical conversion treatment layer). ) Can be provided. An epoxy resin or the like is suitable for a coating resin for offshore structures. In this case, the thickness of the epoxy resin is excellent from 100 to 500 μm, and the steel material and the top layer can be firmly bonded. The film thickness of the epoxy resin is further preferably 200 to 500 μm (particularly 300 to 500 μm). When the film thickness is less than 100 μm, there are many coating defects that become the starting point of corrosion, and the corrosion resistance tends to deteriorate. On the other hand, even if the film thickness is thicker than 500 μm, the adhesion effect of the primer layer tends to be saturated.

(Protective layer)
The protective layer is a resin layer mainly responsible for anticorrosion, excellent in durability, and blocking electrolyte, water and oxygen, and is preferably provided (as the outermost layer) if necessary. From the viewpoint of high durability, formability, and economical efficiency, the protective layer is preferably a urethane resin type, a polyolefin resin type, or an epoxy resin type. These modified products and those suitably added with a curing agent and an inorganic pigment may be used as necessary.

  If it is a coating resin for marine structures (for a protective layer), a urethane elastomer can be suitably used. The urethane elastomer layer has a film thickness range of 2 to 4 mm, which makes it easy to achieve both rubbing resistance and durability. If the film thickness is thinner than 2 mm, the water resistance tends to be inferior. On the other hand, when the film thickness is thicker than 4 mm, the rubbing resistance tends to be inferior.

  The steel material was 75 × 150 × 4 mm plain steel, and the surface was 3a blasted with grid blasting.

(Iron phosphate treatment)
A commercially available iron phosphate treatment solution (Nippon Parker Rising Co., Ltd., Parphos 3454) was spray-coated and dried on the surface of the steel material. Although the film thickness was changed depending on the spray amount and the treatment time, a film having a thickness of 1 μm or more could not be obtained. As a comparison, a sample not subjected to iron phosphate treatment (film thickness 0 μm) was also prepared. Further, as a phosphate-treated sample (for comparison) different from the iron phosphate treatment, Enares 20 manufactured by Nippon Parker was spray-coated under the recommended conditions in the same manner as the zinc phosphate treatment.

(Aluminum phosphate chemical conversion treatment)
For aluminum phosphate-based chemical conversion treatment, 100 wt% water, 1.8 wt% magnesium oxide, surface to improve dispersibility, with respect to 50 mass% primary aluminum phosphate aqueous solution containing 1.5 wt% boron oxide. A solution prepared by adding and mixing 15 wt% of the treated alumina pigment or titania pigment was used. The inorganic composition molar _{ratio, Al 2 O 3 / P 2} O 5 = 0.4, B 2 O 3 / P 2 O 5 = 0.05, a _{MgO / P 2 O 5 = 0.2} , inorganic filler The pigment accounts for 16 vol% in the dry film.

  Samples for comparison (composition) were prepared by adjusting the mixed wt% of each substance.

  For comparison of the chemical conversion treatment configuration, the sample treated with zinc phosphate treatment instead of the iron phosphate treatment, or the sample obtained by removing the iron phosphate treatment from the invention product and the sample excluding the aluminum phosphate chemical treatment, respectively. Produced. Samples for comparison (film thickness) were prepared in the same manner.

  The adjusted aluminum phosphate chemical conversion solution was wetted with a brush. The film thickness of the aluminum phosphate chemical conversion film was changed by changing the amount of the treatment liquid attached (0 μm for the untreated film). After coating, it was dried for about 2 minutes with warm air of about 80 ° C.

  The film thickness was determined by SEM and EPMA observation of the coating cross section. First, the thickness of a chemical conversion treatment film is measured from SEM observation of a steel material cross section subjected to iron phosphate treatment or observation of EPMA phosphorus distribution. Since the thickness varies, 10 points selected at random were averaged. The aluminum distribution was observed with EPMA for the cross section of these iron phosphate-treated steel materials subjected to aluminum phosphate conversion treatment, and the thickness of the aluminum phosphate conversion treatment layer was determined. Since the thickness varies, 10 points selected at random were averaged.

(Organic resin coating)
The organic resin coating is spray-applied and cured as a primer with an epoxy resin paint so as to have a predetermined film thickness, and then a two-component cured urethane elastomer containing kaolin clay powder is spray-coated to a predetermined thickness. A polyurethane resin layer was formed as described above.

  A sample coated with 3 mm of polyurethane elastomer without the primer coating process was also prepared for comparison.

(Evaluation methods)
The evaluation method (rubbing fracture test) is described below. A sample is placed and fixed under a 10 kg iron ball at an angle of 30 degrees with respect to the vertical direction, and the iron ball is allowed to freely fall and collide with the center of the sample. The fall height was increased from a minimum of 20 cm in steps of 10 cm and allowed to fall freely, and the minimum height at which the resin coating peeled off by rubbing the iron ball was recorded. Here, if a part of the resin coating was detached from the sample, it was judged as peeling.

  In addition, general performance was also evaluated. The adhesiveness of the resin coating was evaluated by a JIS-K5600-5-7 pull-off method, and 30 kg / cm 2 or more was regarded as acceptable (◯). The water resistance is obtained by stripping a 1 cm wide resin from one side of the 75 mm side sample of 75 × 150 mm, polishing with a belt sander or the like to expose the steel surface, and immersing it in a 3% sodium chloride aqueous solution at 50 ° C., It was taken out after half a year. Since the peeling progressed from the resin coating end to the back, the chisel blade was inserted into the gap at the resin coating end, and the resin coating was peeled off with a hammer. The area where the metal surface was exposed was defined as a peeled area, and the distance from the end was measured with a caliper at four points and averaged. Peeling less than 10 mm was rated as ◯, and 10 mm or more and less than 15 mm as △.

  The results obtained as described above are shown in Table 1 below.

  The organic resin-coated steel material of the present invention reduces the resin coating detachment due to the collision of drifting objects and ships on the sea, and the steel material is well protected against corrosion. Therefore, the organic resin-coated steel material of the present invention can be used particularly suitably for a steel structure foundation to be placed in the ocean.

Claims (10)

An organic resin-coated steel material in which an iron phosphate chemical conversion treatment layer, an aluminum phosphate chemical conversion treatment layer, and an organic resin layer are laminated on the steel material surface in this order from the steel material side;
The aluminum phosphate-based chemical conversion treatment layer contains P, Al, B, and a metal M selected from Mg or Ca;
The composition of the aluminum phosphate-based chemical conversion treatment layer is Al ₂ O ₃ / P ₂ O ₅ = 0.2 to 0.6 and B ₂ O ₃ / P ₂ O ₅ = 0 in terms of a molar ratio in terms of anhydrous oxide. An organic resin-coated steel material comprising a binder giving 0.01 to 0.1 and MO / P ₂ O ₅ = 0.01 to 0.2 and an inorganic extender pigment.   The organic resin-coated steel material according to claim 1, wherein the iron phosphate chemical conversion treatment layer has an average film thickness of 0.1 to 1 μm.   The organic resin-coated steel material according to claim 1 or 2, wherein the inorganic pigment is added in an amount of 10 to 50 vol% with respect to the dry film of the aluminum phosphate chemical conversion treatment layer.   The organic resin-coated steel material according to any one of claims 1 to 3, wherein the organic resin layer includes a primer layer formed immediately above the chemical conversion treatment layer and a top layer made of a urethane elastomer resin. .   The organic resin-coated steel material according to claim 4, wherein the primer layer is made of an epoxy resin.   The organic resin-coated steel material according to claim 4 or 5, wherein the primer layer has a thickness of 100 to 500 µm.   The organic resin-coated steel material according to any one of claims 4 to 6, wherein the top layer has a thickness of 2 to 4 mm.   The thickness of the said aluminum phosphate chemical conversion treatment layer is 5-40 micrometers, The organic resin-coated steel material in any one of Claims 1-7 characterized by the above-mentioned.   The organic resin-coated steel material according to any one of claims 1 to 8, wherein the metal M is Mg.   The organic resin-coated steel material according to any one of claims 1 to 9, wherein the inorganic extender pigment in the aluminum phosphate-based chemical conversion treatment layer is alumina.