JP2007302970A - Steel material with film having excellent corrosion resistance and corrosion fatigue resistance, and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a steel material with a film which which has a stable and dense rust layer in an atmospheric corrosive environment, is free from deterioration in hydrogen embrittlement and material strength, is easily and inexpensively produced and is excellent in corrosion resistance and corrosion fatigue resistance. <P>SOLUTION: In the steel material with a film having excellent corrosion resistance and corrosion fatigue resistance, the surface is coated with a film mainly composed of FeOOH, and the region from the outermost surface to 100 μm in a depth direction is provided with a layer in which, according to infrared spectroscopy, provided that the absorption peak intensity near 920 cm<SP>-1</SP>corresponding to α-FeOOH is defined as A, the absorption peak intensity near 840 cm<SP>-1</SP>corresponding to β-FeOOH is defined as B, and the absorption peak intensity near 740 cm<SP>-1</SP>corresponding to γ-FeOOH is defined as C, the α-FeOOH ratio defined by [äA/(A+B+C)}×100%] is ≥10%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a film having high corrosion resistance in an atmospheric corrosive environment, specifically to a steel material with a film having a stable and dense rust layer on the surface and excellent corrosion resistance and corrosion fatigue resistance, and a method for producing the same.

  As is well known, steel materials used in atmospheric corrosive environments have their material compositions adjusted to prevent deterioration of static and fatigue strength properties due to corrosion thinning or formation of corrosion pits, and deterioration of appearance due to rusting. Alternatively, the corrosion resistance is often improved by forming a reaction product having a high corrosion resistance on the surface by surface treatment or the like.

  By the way, as a material composition adjustment, a small amount of Cu, Ni, Cr, P or the like is added, and a rust layer containing α-FeOOH having high corrosion resistance is formed on the base material surface by corrosion of the base material. Weatherproof steel with a function to suppress the progress is used for bridge materials and building materials. However, in a relatively mild environment such as an industrial zone or a rural area, it usually takes 5 to 10 years for the corrosion-resistant rust to form. There was a problem of deteriorating the appearance. In general, α-FeOOH is formed by phase transformation of γ-FeOOH (γ-FeOOH and β-FeOOH in a Cl-containing environment) generated at the initial stage of corrosion after a long period of time. Therefore, the base material in a period in which at least one of γ-FeOOH and β-FeOOH is formed on the surface is inferior in corrosion resistance, and corrosion progresses before α-FeOOH is formed. As a result, since deep and sharp corrosion pits are formed, there is a problem that static and fatigue strengths are lowered.

  Furthermore, when used in a stationary state such as a bridge material or a building material, α-FeOOH is likely to be formed over a long period of time. Even when α-FeOOH was formed over time, destruction due to corrosion did not occur. That is, an interval until α-FeOOH formation was allowed. However, when repeated stress fluctuations are applied, such as in drive train mechanism parts, the generated rust falls off due to stress fluctuations before transforming into α-FeOOH, and again β-FeOOH, which has corrosion progress, There was a problem that the formation of γ-FeOOH was repeated and the destruction was accelerated by thinning the base material.

  Further, in the conventional weathering steel and the like, the structure of the rust layer when α-FeOOH is formed is mainly composed of β-FeOOH and γ-FeOOH on the outermost surface side, α-FeOOH on the base material side, and α -It is known that a rust layer containing a large amount of FeOOH is formed to a depth of 100 μm or more from the outermost surface (Shunhei Misawa, “Iron and Steel”, Vol. 79. No. 1 (1992) p. 69). ing. The weather-resistant steel with the characteristic that α-FeOOH is formed on the base metal side has been used for a long time in environments such as beaches with a large amount of incoming salt and cold regions where snow melting agents are sprayed in winter. Corrosion proceeds remarkably fast before α-FeOOH is formed, or corrosion progresses shortly before α-FeOOH is formed, and the load cannot be supported due to thinning of the base material, making it difficult to use for convenience. Up to now, steel materials with an increased amount of the above-mentioned additive elements have been proposed, but there has been a problem that raw material costs and manufacturing costs are remarkably higher than the effect of improving corrosion resistance. That is, the conventional steel material (weather-resistant steel) in which the rust layer containing α-FeOOH is formed over a long period of time cannot obtain sufficient corrosion resistance and corrosion resistance work. A method that can be formed and a steel material that already holds α-Fe00H have been desired.

  On the other hand, as the anticorrosive surface treatment, there is a method of providing a zinc coating for the purpose of so-called sacrificial anticorrosion, in which a corrosion sacrificial layer is provided on the steel material to delay the corrosion of the base material. However, for example, when forming a zinc film by electroplating, it is caused by the management of construction conditions to prevent pinholes and uneven plating, and the hydrogen generated on the surface of the steel to be treated of the cathode penetrates into the steel. The manufacturing process is complicated and the cost is high, for example, a separate process for preventing hydrogen embrittlement is required. Moreover, in the phosphoric acid type film | membrane process (zinc phosphate chemical conversion process) containing zinc, although construction is possible comparatively easily, compared with the plating film, the corrosion resistance of the film | membrane was inadequate. Furthermore, as a surface-treated steel material that has both a sacrificial anticorrosive action of Zn and a self-repairing action of Al, Zn-Al-Si-based molten alloy plated steel (trade name: galvanium steel, manufactured by Nippon Steel Sheet Co., Ltd.) Are known. However, since the temperature of the plating bath is 400 ° C. or higher, the plating bath cannot be used when the mechanical strength is lowered due to heating of the steel material during bath immersion. In addition, there is a problem that the manufacturing cost becomes high.

Conventionally, as publications related to the proposed steel material, for example, Patent Documents 1 to 3 shown below are known.
Patent Document 1 discloses a surface-treated steel material that improves the weather resistance by converting eluted iron ions to α-FeOOH by coating the surface with an organic resin paint containing chromium sulfate and / or copper sulfate. . However, in Patent Document 1, since sulfate ions stabilize β-FeOOH, the protection and stability of the formed rust are unclear, and the processing content is complicated and the processing cost is high. was there.

  Patent Document 2 discloses a rust stabilization treatment steel material and a rust stabilization treatment method in which a steel material is exposed to the atmosphere to form rust on the surface, and then an aqueous alkaline solution is applied to convert the steel material into α-FeOOH. However, in Patent Document 2, the amount of α-FeOOH produced is small, and a layer having an α-FeOOH ratio of 10% or more cannot be obtained as in the present invention. Therefore, for example, in an environment where corrosion is likely to be accelerated such as a beach with a large amount of incoming salt, corrosion prevention may not always be obtained. In addition, since it takes 30 days or more for exposure to the atmosphere, there are problems that processing takes time, and static strength characteristics and fatigue strength characteristics deteriorate due to corrosion pits generated during the exposure.

Patent Document 3 discloses an organic coated steel sheet having corrosion resistance in which a chemical conversion treatment belly is formed on a zinc-based plated steel sheet and an organic film containing aluminum phosphate is formed thereon. However, in Patent Document 3, the content of the treatment is complicated and the treatment cost is high, for example, it is necessary to perform a chemical conversion treatment before forming an organic film containing aluminum phosphate.
Japanese Patent No. 2666673 Japanese Patent No. 2827669 Japanese Patent No. 3381647

  The present invention has been made to solve the above-described problems, and has a stable and dense rust layer in an atmospheric corrosion environment, without hydrogen embrittlement and a decrease in material strength, and at low cost and easy to manufacture. An object of the present invention is to provide a coated steel material excellent in corrosion fatigue resistance and a method for producing the same.

The features of the present invention for solving the above-described problems are as follows.
(1). The surface is covered with a film mainly composed of FeOOH, and in the region from the outermost surface to 100 μm in the depth direction, the absorption peak intensity around 920 cm ⁻¹ corresponding to α-FeOOH is represented by A, β in the infrared spectroscopy. When the absorption peak intensity near 840 cm ⁻¹ corresponding to —FeOOH is B and the absorption peak intensity near 740 cm ⁻¹ corresponding to γ-FeOOH is C, the definition is “{A / (A + B + C)} × 100%”. A coated steel material excellent in corrosion resistance and corrosion fatigue resistance, characterized by having a layer having an α-FeOOH ratio of 10% or more.

(2). The coated steel material having excellent corrosion resistance and corrosion fatigue resistance according to (1), wherein the thickness of the layer having the α-FeOOH ratio of 10% or more is 20 to 100 μm.
(3) Corrosion resistance and corrosion fatigue resistance as set forth in (1) or (2), characterized in that one or more of Cu, Ni, Cr and Mo are contained in a total amount of 1.7 to 3.0 wt%. Steel with excellent coating.

(4). A steel material whose surface is covered with a film having an amorphous structure of A1, P, O, and H and having a thickness of 1 to 5 μm is subjected to a salt spray treatment at an ambient temperature of 30 to 40 ° C. and a salt water concentration of 3 to 5 wt% NaCl. , A spraying amount of 50 to 200 mL / min / mm ² , a cycle in which the spraying time is 5 to 30 minutes and then maintained in an atmosphere of a temperature of 25 to 85 ° C. and a relative humidity of 30 to 95% for 10 to 24 hours. Is repeated 1 to 10 times, a method for producing a coated steel material excellent in corrosion resistance and corrosion fatigue resistance.

(Five). The surface of the steel material is covered with a film having a thickness of 1 to 5 μm composed of A1, P, O, and H by bringing the steel material into contact with an aqueous solution containing 40 to 50 ° C. containing Al ions and PO ₄ ions for 30 seconds or more. The method for producing a coated steel material having excellent corrosion resistance and corrosion fatigue resistance as described in (4).
(6). The surface of the steel material is covered with a film having a thickness of 1 to 5 μm made of Al, P, O, and H by bringing the steel material into contact with an aqueous solution containing Al ions and PO ₄ ions for 180 seconds or longer. (4) The method for producing a coated steel material having excellent corrosion resistance and corrosion fatigue resistance.

(7). After contacting the steel material with a room temperature aqueous solution containing Al ions and PO ₄ ions, the steel material is heated in an atmosphere of 300 ° C. or less to make the surface of the steel material a thickness of Al, P, O and H 1 The method for producing a coated steel material having excellent corrosion resistance and corrosion fatigue resistance according to (4), characterized by covering with a film of ˜5 μm.

  According to the present invention, a film having a stable and dense rust layer in an atmospheric corrosive environment, without hydrogen embrittlement or a decrease in material strength, and having excellent corrosion resistance and corrosion fatigue resistance that is easy to manufacture at low cost. The attached steel material and the manufacturing method thereof are obtained.

Hereinafter, the present invention will be described in more detail.
As a result of earnest research on the corrosion behavior, corrosion fatigue mechanism, and chemical conversion treatment method of steel materials, the present inventors have invented a steel material that has excellent corrosion resistance and corrosion fatigue resistance, and a method for producing the same, which is not found in the prior art. It came. Hereinafter, the present invention will be described in detail.

The steel material according to the present invention has a surface mainly covered with a film made of FeOOH, and corresponds to α-FeOOH by microscopic IR (infrared spectroscopy) in a region from the outermost surface to 100 μm in the depth direction. Assuming that the absorption peak intensity near ⁻¹ is A, the absorption peak intensity near 840 cm ⁻¹ corresponding to β-FeOOH is B, and the absorption peak intensity near 740 cm ⁻¹ corresponding to γ-FeOOH is C, “{A / (A + B + C)} × 100% ”is a structure having a layer having an α-FeOOH ratio of 10% or more.

The rust component formed under the atmospheric corrosion ring containing Cl component and moisture includes Fe oxides and hydroxides such as α-FeOOH, β-FeOOH, γ-FeOOH, Fe ₃ O _4. Since FeOOH consists of fine particles and is dense, it has an environment blocking function that suppresses the entry of elements such as C1, O, and H that cause corrosion from the outside environment. That is, the steel material on which rust containing α-FeOOH is formed on the surface is prevented from subsequent corrosion and has improved corrosion resistance. A typical example is weather resistant steel. However, in the case of weathering steel, as described above, a considerable time is required until α-FeOOH is formed, and during that time, corrosion proceeds and deeply dull corrosion pits are generated, so that the fatigue strength is significantly reduced.

  The steel material according to the present invention is characterized by having a layer having an α-FeOOH ratio of 10% or more in a region from the outermost surface to 100 μm in the depth direction. Further, the feature of the formation process is that β-FeOOH, γ-FeOOH and the like are phase-transformed to α-FeOOH at an early stage. Corrosion proceeds from the surface and follows the process of early transformation of β-FeOOH and γ-FeOOH formed on the surface to α-FeOOH in the initial corrosion, so the outermost surface (environment) side is rich in α-FeOOH. It takes the form covered with the containing layer. When the α-FeOOH ratio is 10% or more, the subsequent corrosion is substantially suppressed and the corrosion resistance is improved. Further, since this layer is formed in a region from the outermost surface to 100 μm in the depth direction, no significant corrosion thinning is involved. Therefore, since α-FeOOH is formed in a form that covers the outermost surface side at an early stage, the subsequent corrosion of the steel material is suppressed, and the shape of the corrosion pits is relatively shallow and smooth. Very small.

  Moreover, as for the thickness of the layer whose (alpha) -FeOOH ratio which concerns on this invention is 10% or more, 20-100 micrometers is desirable. Here, if the thickness is less than 20 μm, the environmental barrier function is inferior, so that sufficient corrosion resistance cannot be obtained. On the other hand, when the thickness exceeds 100 μm, the thickness of the base material is reduced, that is, the base material thinning is increased, so that the static strength and the fatigue strength are lowered.

  Furthermore, the steel material according to the present invention desirably contains a total of 1.7 to 3.0 wt% of one or more of Cu, Ni, Cr, and Mo. For example, Cu uniformly contained in the steel material is electrochemically noble than Fe, which is the main component of the steel material, and therefore promotes uniform dissolution of the steel material as a stable cathode, and β-FeOOH and γ-FeOOH are α -Increase the rate of phase transformation to FeOOH. As additive elements having the same action as Cu, there are Ni, Cr, and Mo. The Cu, Ni, Cr, and Mo may be one or more, and the total is preferably 1.7 to 3.0 wt%. Here, if it is less than 1.7 wt%, the effect is small and insufficient, and if it exceeds 3.0 wt%, the effect does not increase, and conversely the material cost increases, which is not preferable.

Next, a method for forming a layer having an α-FeOOH ratio of 10% or more according to the present invention will be described.
The film according to the present invention is a steel material whose back surface is covered with a film having an amorphous structure with a thickness of 1 to 5 μm made of Al, P, O, and H. A salt spray treatment is performed at an ambient temperature of 30 to 40 ° C. and a salt water concentration of 3 to 3. 5 wt% NaCl, spray amount 50-200 mL / min / mm ² , spraying time 5-30 minutes after each condition, temperature 25-35 ° C., relative humidity 30-95% atmosphere 10-24 hours The holding cycle can be obtained by repeating 1 to 10 times.

P that is uniformly distributed in the Al—P—O—H-based film results in uniform dissolution of the steel material in the above cycle and subsequent uniform formation of β-FeOOH and γ-FeOOH in the presence of O and H, Furthermore, since it has an effect of promoting the phase transformation to α-FeOOH, the formation of a uniform α-FeOOH film is promoted as a result. These actions of P are characterized in that P easily forms H ₂ PO ₄ ⁻ ions with O and H. This H ₂ PO ₄ ⁻ ion has a high complexing ability with Fe ³⁺ ions, and has an action of increasing the oxidation rate of Fe ²⁺ ions (Shunhei Misawa, “Anticorrosion Technology”, Vol. 23, 17-27 (1974). )).
Al is considered necessary for the Al—P—O—H-based film to have an amorphous structure. It is considered that the fact that this film has an amorphous structure serves as a soil for nucleation of α-FeOOH having a form of an aggregate of ultrafine particles and promotes the formation of α-FeOOH.

Next, a method of forming an Al—P—O—H-based film having an amorphous structure and having a thickness of 1 to 5 μm on the surface of the steel material will be described.
The Al—P—O—H-based film is obtained by bringing a steel material into contact with an aqueous solution containing 40 to 50 ° C. containing Al ions and PO ₄ ions for 30 seconds or more, or with the same aqueous solution at 30 ° C. for 180 seconds or the same aqueous solution at room temperature. After making it contact with, it can produce by heating at 300 degrees C or less.

The aqueous solution is obtained by first adding aluminum phosphate (AlPO ₄ ) to water. Since AlPO ₄ is hardly soluble in water, it is obtained by further adding phosphoric acid (H ₃ PO ₄ ) to dissolve them. The weight concentration of AlPO ₄ is preferably in the range of 1 to 10%. Here, when the weight concentration exceeds 10%, the concentration of H ₃ PO ₄ added for dissolution increases, which may cause acid erosion to the steel material. On the other hand, when the weight concentration is less than 1%, AlPO ₄ is frequently replenished, so that workability is lowered. Moreover, the water used for a solvent can use industrial water, tap water, distilled water, etc. However, when Cl which may accelerate corrosion is contained in water, it is preferable to remove this as much as possible. In order to bring the aqueous solution into contact with the steel material, any method such as dipping, air spraying or brush coating may be used.

The formation mechanism of the film has not been fully elucidated, but is considered as follows.
In this treatment solution, aluminum primary phosphate (Al (H ₂ PO ₄ ) ₃ ), H ₃ PO ₄ , and AlPO ₄ are in an equilibrium state represented by the following formula (1). Contacting the steel in the processing solution, the _H 3 PO ₄ as shown in the following formula (2) by acting on Fe, the solution ((1)) in _H 3 PO ₄ concentration in the vicinity of its surface is reduced. For this reason, it is considered that the reaction proceeds to the right in the equilibrium formula (1), and hardly soluble AlPO ₄ is deposited on the surface of the steel material to form an Al—PO film.
A1 (H ₂ P0 ₄ ) ₃ (soluble) ⇔ 2H ₃ PO ₄ (liquid) + AlPO ₄ (slightly soluble) (1)
Fe + 2H ₃ PO ₄ → Fe (H ₂ PO ₄ ) ₂ + H ₂ ↑ (2)
That is, it is considered that the formation of the Al—P—O-based film is based on the formation and deposition of hardly soluble AlPO ₄ due to the decomposition of Al (H ₂ PO ₄ ) ₃ , triggered by the steel material corrosive action of H ₃ PO ₄ . Therefore, in order to promote the formation of such a film, it is better to raise the temperature of the aqueous solution in order to increase the reaction rate of the formula (2).

  When the temperature of the aqueous solution is 30 ° C. and 40 to 50 ° C., respectively, the contact time with the steel material requires 180 seconds or more and 30 seconds or more, respectively. Below this, the reaction rate is slow, and an Al—PO film is formed. Difficult to do. The upper limit temperature of the aqueous solution is preferably 300 ° C. or lower because the higher the temperature, the more difficult the maintenance and the higher the maintenance cost. In addition, when the temperature of the aqueous solution is room temperature, it is difficult to form a film only by contact. Therefore, the film can also be obtained by heating in an atmosphere of 300 ° C. or less after contact to evaporate water. When the heating temperature exceeds 300 ° C., the evaporation rate of moisture is too high, the film density decreases, and the film strength decreases, which is not preferable. Moreover, since there exists a possibility that the static strength and fatigue strength of steel materials may fall, it is not preferable.

  The thickness of the Al—P—O—H film thus formed is preferably 1 to 5 μm, and if it is less than 1 μm, the effect of the P or amorphous structure is small, and the α-FeOOH ratio according to the present invention is 10%. The above film cannot be obtained. Further, even if the thickness exceeds 5 μm, these effects hardly increase, and conversely, the formation of the film is costly and undesirable.

  The above-mentioned aqueous solution can be easily produced using inexpensive aluminum phosphate, phosphoric acid, or distilled water, and can be easily processed, so that an Al—P—O—H film can be formed at low cost. . Moreover, since this aqueous solution is a weak acid, the amount of hydrogen generated from the steel material is extremely small, and there is no fear of hydrogen embrittlement. Furthermore, since all processes are performed at 300 ° C. or lower, there is almost no decrease in material strength.

Next, a method for early forming α-FeOOH from a steel material whose surface is covered with an Al—P—O—H film will be described.
The salt spray treatment is performed to impart Cl, O, H to a steel material whose surface is covered with an Al—P—O—H film to promote the elution of the steel material. The treatment conditions are preferably 30 to 40 ° C., a salt water concentration of 3 to 5 wt% NaC1, a spray amount of 50 to 200 mmL / min / mm ² , and a treatment time of 5 to 30 minutes. If the temperature is less than 30 ° C., the elution rate is small, and even if it exceeds 40 ° C., the elution rate does not change greatly. When the salt water concentration is less than 3 wt%, the supply amount of Cl, O, H is small and the elution rate is small, and when the salt water concentration exceeds 5 wt%, the elution rate hardly increases. When the spraying amount is less than 50 mL / min / mm ² , the supply amount of Cl, O, H is small and the elution rate is small, and when it exceeds 200 mL / min / mm ² , the elution rate hardly increases and the spraying is reversed. Since the cost of a liquid increases, both are not preferable. If the treatment time is less than 5 minutes, the supply amount of Cl, O, H is small and the elution rate is small, and if it exceeds 30 minutes, the elution rate hardly increases and the cost of the spray solution increases. Both are not preferable.

  However, only the salt spray treatment increases the cumulative supply amount of Cl and stabilizes β-FeOOH, so that early formation of α-FeOOH is difficult. Therefore, after the salt spray treatment, exposure to a stable environment containing no Cl component and oxygen and moisture coexisting, and supplying O and H to the steel material surface enables early formation of α-FeOOH.

  As processing conditions after spraying this salt water, it is desirable to hold | maintain for 10 to 24 hours in the atmosphere of temperature 25-35 degreeC, and relative humidity 30-95%. Here, when the temperature is less than 25 ° C., the formation rate of α-FeOOH is small, and when it exceeds 35 ° C., the formation rate of α-FeOOH does not change greatly, and conversely, the cost for temperature management and temperature maintenance is high. Both are not preferable. If the relative humidity is less than 30%, the supply rate of O and H is small and inefficient, and if the relative humidity exceeds 95%, maintenance and management are difficult and the cost becomes high, which is not preferable. If the treatment time is less than 10 hours, the formation amount of α-FeOOH is small, and even if it exceeds 24 hours, the formation amount of α-FeOOH does not increase greatly.

  Moreover, formation of α-FeOOH can be further accelerated by repeating the treatment such as salt spray. The number of repetitions is preferably in the range of 1 to 10 times, and exceeding 10 times is not preferable because the amount of α-FeOOH formed does not increase greatly. Both the salt spray treatment and the constant temperature and humidity treatment can use commercially available apparatuses that can be obtained at low cost, and the coating according to the present invention can be formed at low cost.

(Example)
Examples are shown below, but the present invention is not particularly limited to these Examples.
Steel for springs having a diameter of 4 mm and a length of 20 to 80 mm (steel type 1: 0.4C-1.4Si-0.8Mn-0.7Cr-Fe, steel type 2: 0.4C-1.8Si-0.2Mn-1 0.0Cr-0.5Ni-0.08Ti-0.18V-Fe, Steel type 3: 0.4C-2.5Si-0.7Mn-0.8Cr-1.8Ni-0.2V-0.4Mo-Fe ( wt%)) after forming an Al—P—O—H-based film under the conditions shown in Tables 1 to 6 below, followed by treatment such as salt spraying under the conditions described in Tables 1 to 6 provided. As a test material, corrosion resistance evaluation and corrosion fatigue durability evaluation were performed. Moreover, about the test material, the thickness of the Al-P-O-H type | system | group film | membrane and the film thickness whose (alpha) -FeOOH ratio and (alpha) -FeOOH ratio are 10% or more were evaluated. Here, an Al—P—O—H-based film was formed using a 5 wt% -AlPO ₄ aqueous solution. The formed Al—P—O—H-based film had an amorphous structure as a result of X-ray diffraction.

The thickness of the Al—P—O-based film was evaluated by embedding a steel material in a resin, polishing it to a mirror surface, and observing the cross section using an optical microscope or an electron microscope.

The α-FeOOH ratio is obtained by embedding a sample in a resin and using microscopic FT-IR (Fourier transform infrared spectroscopy). From the obtained spectrum, the absorption peak intensity around 920 cm ⁻¹ corresponding to α-FeOOH is expressed as A , the absorption peak intensity at around 840 cm ^-1 corresponding to the β-FeOOH B, γ-FeOOH corresponding to 740 cm ^-1 an absorption peak intensity in the vicinity of the case where the C "{a / (a + B + C)} × 100% " The thickness of the layer having an α-FeOOH ratio of 10% or more was also determined using the same method. In this microscopic FT-IR analysis, in addition to α-FeOOH, β-FeOOH, and γ-FeOOH, no hydroxide or oxide of Fe was detected.

  In the corrosion resistance evaluation test, the test material was left in a thermostatic chamber (26 ° C., 95% RH) for 500 hours. The evaluation was performed by embedding the test material after standing for 500 hours in a resin and measuring the cross-sectional area by an optical microscope and image processing. When the cross-sectional area before the test is D and the cross-sectional area after the test is E, “{(D−E) / D} × 100%” is defined as the cross-sectional reduction rate, and the cross-sectional area reduction rate of the steel material as a reference X is X, and the cross-sectional area reduction rate is less than 60% of X is “best” (level of excellent corrosion resistance), 60% to less than 90% is “good” (level of excellent corrosion resistance), and 90% or more is “bad” "(Corrosion resistance is inferior level).

The corrosion fatigue resistance test was carried out by subjecting a specimen left for 0.5 hours under salt spray at an atmospheric temperature of 35 ° C., a salt water concentration of 5 wt% NaC1, and a spray amount of 180 mL / min (min) / mm ² to shear stress in the atmosphere. The process of oscillating 3000 times under the condition of τ = 735 ± 441 MPa (0.5 hours) and then letting it stand in a constant temperature and humidity chamber (26 ° C., 95 ° C. RH) for 23 hours is repeated until the specimen is broken. It was. The evaluation is based on the standard steel durability number Y, where the durability number is 120% or more of Y is “best” (level of excellent corrosion fatigue resistance), and 110% or more and less than 120% is “good” (corrosion resistance) The level of excellent fatigue properties) and less than 110% were defined as “bad” (the level of poor corrosion fatigue resistance).

  The steel material of Comparative Example 1 has a chemical composition of 0.4C-1.4Si-0.8Mn-0.7Cr-Fe (steel type 1, Cu, Ni, Cr, Mo total 0.7 wt%). Therefore, it was used as a standard for evaluation of corrosion resistance and corrosion fatigue resistance of Examples 1 to 15, 18 to 37 and Comparative Examples 2 to 10 and 13 to 20. Note that the mechanical properties of the base material are the same for both the untreated material and the treated material.

In the steel materials of Examples 1 to 5 and Comparative Examples 2 and 3, the temperature of the aqueous solution was set to 50 ° C., and the contact time was changed in the range of 10 to 360 seconds (no heating after contact), Al—P—O—H. The steel material on which the system film was formed was sprayed with salt water under conditions of a temperature of 35 ° C., a salt water concentration of 5 wt%, a spray amount of 200 mL / min / mm ² , and a spray time of 30 min, and then a temperature of 30 ° C. and a relative humidity of 95%. A cycle in which the atmosphere is kept for 24 hours is repeatedly produced 10 times. In Examples 1 to 3 in which the contact time is in the range of 120 to 360 seconds, the thickness of the Al—P—O—H film is 3 to 5 μm, and α-FeOOH is in the region from the outermost surface to the depth method of 100 μm. There is a layer having a ratio of 10% or more, the thickness of the layer is 60 to 100 μm, and both the corrosion resistance and the corrosion fatigue resistance are “best” (very excellent level). Further, in Examples 4 and 5 in which the contact times are 60 seconds and 30 seconds, respectively, the Al—P—O—H-based film has a thickness of 1 to 2 μm and a region from the outermost surface to 100 μm in the depth direction. There is a layer having an α-FeOOH ratio of 10% or more, the thickness of the layer is 20 to 30 μm, and both corrosion resistance and corrosion fatigue resistance are “good” (excellent level). However, in Comparative Example 2 and Comparative Example 3 in which the contact times are 20 seconds and 10 seconds, respectively, the thickness of the Al—P—O—H film is less than 1 μm and the region from the outermost surface to 100 μm in the depth direction. There is no layer having an α-FeOOH ratio of 10% or more, and the corrosion resistance and corrosion fatigue resistance are both “bad” (inferior level).

In the steel materials of Examples 6 to 9 and Comparative Examples 4 and 5, the temperature of the aqueous solution was set to 40 ° C., and the contact time was changed in the range of 10 to 180 seconds (no heating after contact), Al—P—O—H. The steel material on which the system film was formed was sprayed with salt water under conditions of a temperature of 35 ° C., a salt water concentration of 5 wt%, a spray amount of 200 mL / min / mm ² , and a spray time of 30 min, and then a temperature of 30 ° C. and a relative humidity of 95%. A cycle in which the atmosphere is kept for 24 hours is repeatedly produced 10 times. In Example 6 and Example 7 in which the contact times are 180 seconds and 120 seconds, respectively, the thickness of the Al—P—O—H-based film is 3 to 5 μm, and α in the region from the outermost surface to 100 μm in the depth direction. There is a layer having a FeOOH ratio of 10% or more, the thickness of the layer is 50 to 70 μm, and both the corrosion resistance and the corrosion fatigue resistance are “best” (very high level). In Examples 8 and 9 where the contact times are 60 seconds and 30 seconds, respectively, the Al—O—P—H film thickness is 1 to 2 μm, and the region from the outermost surface to 100 μm in the depth direction. There is a layer having an α-FeOOH ratio of 10% or more, the thickness of the layer is 20 to 30 μm, and both corrosion resistance and corrosion fatigue resistance are “good” (excellent level). However, in Comparative Example 4 and Comparative Example 5 in which the contact times are 20 seconds and 10 seconds, respectively, the thickness of the Al—P—O—H-based film is less than 1 μm, and the region from the outermost surface to the depth method is 100 μm. There is no layer having an α-FeOOH ratio of 10% or more, and the corrosion resistance and corrosion fatigue resistance are both “bad” (inferior level).

In the steel materials of Examples 10 and 11 and Comparative Example 6, the temperature of the aqueous solution was set to 30 ° C., and the contact time was changed in the range of 120 to 360 seconds (no heating after contact), and an Al—P—O—H film After the salt water spray was performed on the steel material having a temperature of 35 ° C., a salt water concentration of 5 wt%, a spray amount of 200 mL / min / mm ² , and a spray time of 30 min, an atmosphere of 30 ° C. and 95% relative humidity was obtained. A cycle for 24 hours was repeatedly produced 10 times. In Example 10 and Example 11 in which the contact time is 360 seconds and 180 seconds, respectively, the thickness of the Al—P—O—H-based film is 1 to 2 μm, and α is in the region from the outermost surface to 100 μm in the depth direction. A layer having a FeOOH ratio of 10% or more exists, the thickness of the layer is 20 μm, and both corrosion resistance and corrosion fatigue resistance are “good” (excellent level). However, in Comparative Example 6 in which the contact time is 120 seconds, the α-FeOOH ratio is 10% or more in the region where the thickness of the Al—P—O—H-based film is less than 1 μm and from the outermost surface to 100 μm in the depth direction. There is no layer, and the corrosion resistance and corrosion fatigue resistance are both “bad” (inferior level).

In the steel materials of Comparative Examples 7 to 9, the temperature of the aqueous solution was set to room temperature, the contact time was changed in the range of 5 to 900 seconds (no heating after contact), and the steel material on which the Al—P—O—H film was formed was formed. On the other hand, a cycle in which salt spray is performed under conditions of a temperature of 35 ° C., a salt water concentration of 5 wt%, a spray amount of 200 mL / min / mm ² , and a spray time of 30 min, and then maintained in an atmosphere of a temperature of 30 ° C. and a relative humidity of 95% for 24 hours. It was produced repeatedly 10 times. In all of Comparative Examples 7 to 9 in which the contact time is 5 to 900 seconds, the α-FeOOH ratio is in a region where the thickness of the Al—P—O—H film is less than 1 μm and from the outermost surface to 100 μm in the depth direction. No 10% or more layer exists, and the corrosion resistance and corrosion fatigue resistance are both “bad” (inferior level).

In the steel materials of Comparative Example 10 and Examples 12 and 13, the temperature of the aqueous solution was room temperature, the contact time was 5 seconds, the heating temperature after contact was changed in the range of 200 to 400 ° C., and the Al—P—O—H system was used. The steel material on which the film was formed was sprayed with salt water under conditions of a temperature of 35 ° C., a salt water concentration of 5 wt%, a spray amount of 200 mL / mim / mm ² , and a spray time of 30 min, and then an atmosphere at a temperature of 30 ° C. and a relative humidity of 95%. The cycle for 24 hours is repeatedly produced 10 times. In Comparative Example 10 where the heating temperature after contact is 400 ° C., the thickness of the Al—P—O—H film is 3 μm, and the α-FeOOH ratio is 10% or more in the region from the outermost surface to 100 μm in the depth direction. The corrosion resistance is "good" (excellent level), but the corrosion fatigue resistance is "poor" (inferior level). In Examples 12 and 13 where the heating temperatures after contact are 300 ° C. and 200 ° C., respectively, the thickness of the Al—P—O—H film is 3 μm, and the region from the outermost surface to 100 μm in the depth direction is used. There is a layer having an α-FeOOH ratio of 10% or more, the thickness of the layer is 50 to 80 μm, and the corrosion resistance and corrosion fatigue resistance are both “good” (excellent level).

In the steel materials of Examples 14 and 15, the temperature of the aqueous solution was set to room temperature, the contact time was changed in the range of 3 seconds and 1 second, respectively (heating temperature after contact 200 ° C.), and the Al—P—O—H-based film was formed. The formed steel material is sprayed with salt water under conditions of a temperature of 85 ° C., a salt water concentration of 5 wt%, a spray amount of 200 mL / min / min ² , and a spray time of 30 min, and kept in an atmosphere of a temperature of 30 ° C. and a relative humidity of 95% for 24 hours. The cycle is repeated 10 times. In Examples 14 and 15 in which the contact times are 3 seconds and 1 second, respectively, the thickness of the Al—P—O—H-based film is 2 to 3 μm, and α in the region from the outermost surface to 100 μm in the depth direction. A layer having a FeOOH ratio of 10% or more exists, the thickness of the layer is 10 to 30 μm, and both corrosion resistance and corrosion fatigue resistance are “good” (excellent level).

  The steel material of Comparative Example 11 has a chemical composition of 0.4C-1.8Si-0.2Mn-1.0Cr-0.5Ni-0.08Ti-0.18V-Fe (steel type 2, Cu, Ni, Cr, Mo And a non-processed spring steel material, which was used as a standard for evaluating the corrosion resistance and corrosion fatigue resistance of Example 16.

In the steel material of Example 16, the temperature of the aqueous solution was 50 ° C. in the steel type 2 and the steel material was formed with an Al—P—O—H film at a contact time of 30 seconds (no heating after contact). ° C., brine concentration 5 wt%, spray volume 200mL / min / mm ^2, after each condition spraying time 3min, temperature 30 ° C., which cycle to hold 24 hours to an atmosphere of 95% relative humidity was repeated produced 10 times It is. In Example 16 of steel type 2, there is a layer having an α-FeOOH ratio of 10% or more in a region where the thickness of the Al—P—O—H film is 1 μm and the depth from the outermost surface to 100 μm. The thickness of the layer is 50 μm, and the corrosion resistance and corrosion fatigue resistance are both “best” (very good level).

  The steel of Comparative Example 12 has a chemical composition of. Spring of 0.4C-2.5Si-0.7Mn-0.8Cr-1.8Ni-0.2V-0.4Mo-Fe (steel grade 3, Cu, Ni, Cr, Mo total is 3.0 wt%) This was a non-treated steel material, and was used as a standard for evaluating the corrosion resistance and corrosion fatigue resistance of Example 17.

In the steel material of Example 17, the temperature of the aqueous solution was 50 ° C. on the steel type 3 and the steel material was formed with an Al—P—O—H film at a contact time of 30 seconds (no heating after contact). A cycle in which the temperature was maintained at 30 ° C. and the relative humidity was 95% for 24 hours was repeated 10 times after being performed under the conditions of ° C., salt water concentration 5 wt%, spray amount 200 mL / min / mm ² and spray time 30 min. It is. In Example 17 of steel type 3, there is a layer with an α-FeOOH ratio of 10% or more in a region where the thickness of the Al—P—O—H film is 1 μm and the depth from the outermost surface to 100 μm. The thickness of the layer is 60 μm, and both the corrosion resistance and the corrosion fatigue resistance are “best” (very excellent level).

The steel materials of Examples 18 to 20 and Comparative Example 13 are salt water with respect to a steel material having an Al—P—O—H film formed with an aqueous solution temperature of 50 ° C. and a contact time of 180 seconds (no heating after contact). Spraying was performed under conditions of 25 to 45 ° C., a salt water concentration of 5 wt%, a spray amount of 200 mL / min / mm ² , and a spraying time of 30 min, and then a cycle of maintaining in an atmosphere of a temperature of 30 ° C. and a relative humidity of 95% for 24 hours. It was produced repeatedly. In Example 18 in which the temperature of the salt spray is 45 ° C., a layer in which the thickness of the Al—P—O—H film is 3 μm and the α-FeOOH ratio is 10% or more in the region from the outermost surface to the depth direction of 100 μm. The layer thickness is 120 μm, the corrosion resistance is “best” (very good level), and the corrosion fatigue resistance is “good” (excellent level).

  In Example 19 in which the temperature of the salt spray is 40 ° C., the thickness of the Al—P—O—H film is 3 μm, and the α-FeOOH ratio is 10% or more in the region from the outermost surface to 100 μm in the depth direction. There is a layer, the thickness of the layer is 90 μm, and the corrosion resistance and corrosion fatigue resistance are both “best” (very good level). In Example 20 in which the temperature of the salt spray is 30 ° C., the thickness of the Al—P—O—H film is 3 μm, and the α-FeOOH ratio is 10% in the region from the outermost surface to 100 μm in the depth direction. The above layers exist, the thickness of the layer is 40 μm, and both the corrosion resistance and the corrosion fatigue resistance are “good” (excellent level). However, in Comparative Example 13 in which the temperature of the salt spray is 25 ° C., the thickness of the Al—P—O—H film is 3 μm, and the α-FeOOH ratio is 10% in the region from the outermost surface to the depth method of 100 μm. The above layers do not exist, and the corrosion resistance and corrosion fatigue resistance are both “bad” (inferior level).

The steel materials of Examples 21 and 22 and Comparative Example 14 are salt water with respect to steel materials in which the temperature of the aqueous solution is 50 ° C. and the contact time is 180 seconds (no heating after contact) and an Al—P—O—H film is formed. A cycle in which spraying is performed under conditions of a temperature of 85 ° C., a salt water concentration of 1 to 7 wt%, a spray amount of 200 mL / min / mm ² , and a spray time of 30 min, and then maintained in an atmosphere of a temperature of 30 ° C. and a relative humidity of 95% for 24 hours. Was repeated 10 times. In Example 21 in which the salt water concentration of the salt spray is 7 wt%, the thickness of the A1-P—O—H film is 3 μm, and the α-FeOOH ratio is 10% or more in the region from the outermost surface to 100 μm in the depth direction. The thickness of the layer is 90 μm, and both the corrosion resistance and the corrosion fatigue resistance are “best” (very excellent level). In Example 22 where the salt water concentration of the salt spray is 3 wt%, the thickness of the Al—P—O—H film is 3 μm, and the α-FeOOH ratio is 10 in the region from the outermost surface to 100 μm in the depth direction. % Of the layer exists, the thickness of the layer is 30 μm, and the corrosion resistance and corrosion fatigue resistance are both “good” (excellent level). However, in Comparative Example 14 in which the salt water concentration of the salt spray is 1 wt%, the thickness of the Al—P—O—H film is 3 μm, and the α-FeOOH ratio is 10 in the region from the outermost surface to 100 μm in the depth direction. % Or more layers do not exist, and the corrosion resistance and corrosion fatigue resistance are both “bad” (inferior level).

The steel materials of Examples 23 to 25 and Comparative Example 15 are salt water with respect to the steel materials in which the temperature of the aqueous solution is 50 ° C. and the contact time is 180 seconds (no heating after contact) to form an Al—P—O—H film. Spraying is performed under the conditions of a temperature of 35 ° C., a salt water concentration of 5 wt%, a spray amount of 30 to 250 mL / min / mm ² , and a spraying time of 30 min, and then kept in an atmosphere of a temperature of 30 ° C. and a relative humidity of 95% for 24 hours. The cycle was repeatedly produced 10 times. In Example 23 and Example 24 in which the spray amount of the salt spray is 100 to 250 mL / min / mm ² , the thickness of the Al—P—O—H-based film is 3 μm, and from the outermost surface to 100 μm in the depth direction. There is a layer having an α-FeOOH ratio of 10% or more in the region, the thickness of the layer is 70 to 100 μm, and both the corrosion resistance and the corrosion fatigue resistance are “best” (very excellent level). Further, in Example 25 in which the spray amount of the salt spray is 50 mL / min / mm ² , the thickness of the Al—P—O—H film is 3 μm, and α − in the region from the outermost surface to 100 μm in the depth direction. A layer having an FeOOH ratio of 10% or more exists, the thickness of the layer is 30 μm, and both corrosion resistance and corrosion fatigue resistance are “good” (excellent level). However, in Comparative Example 15 in which the spray amount of the salt spray is 30 mL / min / mm ² , the thickness of the Al—P—O—H-based film is 3 μm, and α− in the region from the outermost surface to the depth method of 100 μm. There is no layer having a FeOOH ratio of 10% or more, and both the corrosion resistance and the corrosion fatigue resistance are “bad” (inferior level).

The steel materials of Examples 26 and 27 and Comparative Example 16 are salt water with respect to a steel material in which an Al—P—O—H film was formed with an aqueous solution temperature of 50 ° C. and a contact time of 180 seconds (no heating after contact). A cycle in which spraying is carried out under conditions of a temperature of 35 ° C., a salt water concentration of 5 wt%, a spray amount of 200 mL / min / mm ² and a spray time of 1 to 60 min, and then left in an atmosphere of a temperature of 30 ° C. and a relative humidity of 95% for 24 hours. Was repeated 10 times. In Example 26 in which the spray time of the salt spray is 60 min, the thickness of the Al—P—O—H film is 3 μm, and the α-FeOOH ratio is 10% or more in the region from the outermost surface to 100 μm in the depth direction. There is a layer, the thickness of the layer is 90 μm, and the corrosion resistance and corrosion fatigue resistance are both “best” (very good level). Further, in Example 27 in which the spray time of the salt spray is 5 min, the thickness of the Al—P—O—H film is 3 μm, and the α-FOOH ratio is 10% in the region from the outermost surface to 100 μm in the depth direction. The above layers exist, the thickness of the layer is 30 μm, and both the corrosion resistance and the corrosion fatigue resistance are “good” (excellent level). However, in Comparative Example 16 in which the spray time of the salt water spray is 1 min, the Al—P—O—H film thickness is 3 μm, and the α-FeOOH ratio is 10% in the region from the outermost surface to 100 μm in the depth direction. The above layers do not exist, and the corrosion resistance and corrosion fatigue resistance are both “bad” (inferior level).

The steel materials of Examples 28 to 30 and Comparative Example 17 are salt water with respect to the steel materials in which the temperature of the aqueous solution is 50 ° C. and the contact time is 180 seconds (no heating after contact) to form an Al—P—O—H film. Spraying is performed under conditions of a temperature of 35 ° C., a salt water concentration of 5 wt%, a spray amount of 200 mL / min / mm ² , and a spraying time of 30 min, and then the temperature is maintained in an atmosphere of 20 ° C. to 40 ° C. and a relative humidity of 95% for 24 hours. The cycle was manufactured 10 times. In Example 28 where the retention temperature after spraying with salt water is 40 ° C., the thickness of the Al—P—O—H film is 3 μm, and the α-FeOOH ratio is 10% in the region from the outermost surface to 100 μm in the depth direction. The above layers are present, the thickness of the layer is 110 μm, the corrosion resistance is “best” (very excellent level), and the corrosion fatigue resistance is “good” (excellent level). In Example 29 where the holding temperature after spraying with salt water is 35 ° C., the thickness of the Al—P—O—H film is 3 μm, and the α-FeOOH ratio is 10% in the region from the outermost surface to 100 μm in the depth direction. The above layers exist, the thickness of the layer is 90 μm, and both the corrosion resistance and the corrosion fatigue resistance are “best” (very excellent level).

  In Example 30 where the holding temperature after spraying with salt water is 25 ° C., the Al—P—O—H film thickness is 3 μm, and the α-FeOOH ratio is in the region from the outermost surface to 100 μm in the depth direction. There is a layer of 10% or more, the thickness of the layer is 50 μm, and both corrosion resistance and corrosion fatigue resistance are “good” (excellent level). However, in Comparative Example 17 in which the holding temperature after spraying with salt water is 20 ° C., the Al—P—O—H film thickness is 3 μm, and the α-FeOOH ratio is in the region from the outermost surface to 100 μm in the depth direction. There is no layer of 10% or more, and the corrosion resistance and corrosion fatigue resistance are both “bad” (inferior level).

In the steel materials of Examples 31 and 32 and Comparative Example 18, the temperature of the aqueous solution was 50 ° C., the contact time was 180 seconds (no heating after contact), and the steel material on which the Al—P—O—H film was formed was salt water. After spraying at a temperature of 35 ° C., a salt water concentration of 5 wt%, and a spray amount of 200 mL / min / mm ² under each condition of a spray time of 30 min, the temperature is 30 ° C. and the relative humidity is 10% to 60% in an ambient atmosphere for 24 hours. The holding cycle was repeatedly produced 10 times. In Example 31 and Example 32 in which the relative humidity after spraying with salt water is 60% and 30%, respectively, the Al—P—O—H film thickness is 3 μm, and the region from the outermost surface to 100 μm in the depth direction. There is a layer having an α-FeOOH ratio of 10% or more, the thickness of the layer is 20 to 40 μm, and both the corrosion resistance and the corrosion fatigue resistance are “good” (excellent level). However, in Comparative Example 18 where the relative humidity after spraying with salt water is 10%, the thickness of the Al—P—O—H film is 3 μm, and the α-FOOH ratio is in the region from the outermost surface to 100 μm in the depth direction. There is no layer of 10% or more, and the corrosion resistance and corrosion fatigue resistance are both “bad” (inferior level).

The steel materials of Examples 33 and 34 and Comparative Example 19 are salt water with respect to a steel material having an Al—P—O—H film formed with an aqueous solution temperature of 50 ° C. and a contact time of 180 seconds (no heating after contact). A cycle in which spraying is carried out under conditions of 35 ° C., salt water concentration 5 wt%, spray amount 200 mL / min / mm ² and spray time 30 min, and then kept in an atmosphere of 30 ° C. and 95% relative humidity for 5 to 48 hours. This was produced 10 times repeatedly. In Example 33 where the retention time is 48 h, a layer with an Al-P-O-H film thickness of 3 μm and a α-FeOOH ratio of 10% or more exists in a region from the outermost surface to 100 μm in the depth direction. The thickness of the layer is 130 μm, the corrosion resistance is “best” (very excellent level), and the corrosion fatigue resistance is “good” (excellent level). Further, in Example 34 in which the holding time is 10 h, a layer in which the thickness of the Al—P—O—H film is 3 μm and the α-FeOOH ratio is 10% or more in the region from the outermost surface to the depth method of 100 μm. The thickness of the layer is 40 μm, and both corrosion resistance and corrosion fatigue resistance are “good” (excellent level). However, in Comparative Example 19 in which the holding time is 5 h, a layer in which the thickness of the Al—P—O—H film is 3 μm and the α-FeOOH ratio is 10% or more in the region from the outermost surface to 100 μm in the depth direction. The corrosion resistance and corrosion fatigue resistance are both “bad” (inferior level).

The steel materials of Examples 35 to 37 and Comparative Example 20 are salt water with respect to a steel material having an Al—P—O—H film formed with an aqueous solution temperature of 50 ° C. and a contact time of 180 seconds (no heating after contact). Spraying was performed under the conditions of a temperature of 35 ° C., a salt water concentration of 5 wt%, a spray amount of 200 mL / min / mm ² , and a spraying time of 30 min, and then a cycle of maintaining in an atmosphere of a temperature of 30 ° C. and a relative humidity of 95% for 24 hours is 0. It was produced by changing the range of ~ 15 times. In Example 35 in which the number of cycles was 15, a layer with an Al-P-O-H film thickness of 3 μm and an α-FeOOH ratio of 10% or more in the region from the outermost surface to 100 μm in the depth direction. The layer thickness is 150 μm, the corrosion resistance is “best” (very good level), and the corrosion fatigue resistance is “good” (excellent level). In Examples 36 and 37, in which the number of cycles is 5 and 1, respectively, the thickness of the Al—P—O—H-based film is 3 μm, and the inclination is up to 100 μm from the outermost surface to the depth direction. There is a layer having a -FeOOH ratio of 10% or more, the thickness of the layer is 20 to 50 μm, and both corrosion resistance and corrosion fatigue resistance are “good” (excellent level).
However, in Comparative Example 20 in which the number of cycles is 0, the thickness of the Al—P—O—H yarn film is 3 μm, and the α-FeOOH ratio is 10% or more in the region from the outermost surface to 100 μm in the depth direction. There is no layer, and the corrosion resistance and corrosion fatigue resistance are both “bad” (inferior level).

  In addition, this invention is not limited to the said Example as it is, It can implement by modifying a component in the range which does not deviate from the summary in an implementation stage. Specifically, although the spring steel has been described in the above embodiments, the contents of these implementations can also be used for bolts and various iron-based structures. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiments. Furthermore, the constituent elements in different embodiments may be appropriately combined.

Claims (7)

The surface is covered with a film mainly composed of FeOOH, and in the region from the outermost surface to 100 μm in the depth direction, the absorption peak intensity around 920 cm ⁻¹ corresponding to α-FeOOH is represented by A, β in the infrared spectroscopy. When the absorption peak intensity near 840 cm ⁻¹ corresponding to —FeOOH is B and the absorption peak intensity near 740 cm ⁻¹ corresponding to γ-FeOOH is C, the definition is “{A / (A + B + C)} × 100%”. A coated steel material excellent in corrosion resistance and corrosion fatigue resistance, characterized by having a layer having an α-FeOOH ratio of 10% or more. 2. The coated steel material having excellent corrosion resistance and corrosion fatigue resistance according to claim 1, wherein the thickness of the layer having the α-FeOOH ratio of 10% or more is 20 to 100 μm. The film excellent in corrosion resistance and corrosion fatigue resistance according to claim 1 or 2, characterized by containing a total of 1.7 to 3.0 wt% of at least one of Cu, Ni, Cr, and Mo. With steel. A steel material whose surface is covered with a film having an amorphous structure having a thickness of 1 to 5 μm made of A1, P, O and H is subjected to a salt spray treatment at an ambient temperature of 30 to 40 ° C., a salt water concentration of 3 to 5 wt% NaCl, and a spray amount of 50. A cycle that is maintained in an atmosphere at a temperature of 25 to 35 ° C. and a relative humidity of 30 to 95% for 10 to 24 hours after being performed under conditions of ˜200 mL / min / mm ² and a spraying time of 5 to 30 minutes, A method for producing a coated steel material excellent in corrosion resistance and corrosion fatigue resistance, characterized by repeating 10 times. The surface of the steel material is covered with a film having a thickness of 1 to 5 μm composed of A1, P, O, and H by bringing the steel material into contact with an aqueous solution containing 40 to 50 ° C. containing Al ions and PO ₄ ions for 30 seconds or more. The method for producing a coated steel material having excellent corrosion resistance and corrosion fatigue resistance according to claim 4. The surface of the steel material is covered with a film having a thickness of 1 to 5 μm made of Al, P, O, and H by bringing the steel material into contact with an aqueous solution containing Al ions and PO ₄ ions for 180 seconds or longer. The method for producing a coated steel material having excellent corrosion resistance and corrosion fatigue resistance according to claim 4. After contacting the steel material with a room temperature aqueous solution containing Al ions and PO ₄ ions, the steel material is heated in an atmosphere of 300 ° C. or less to coat the surface of the steel material with a thickness of 1 to 5 μm made of Al, P, O and H. The method for producing a coated steel material having excellent corrosion resistance and corrosion fatigue resistance according to claim 4.