JP4041781B2 - Steel material with excellent corrosion resistance - Google Patents

Description

  The present invention belongs to the technical field related to steel materials having excellent corrosion resistance.

  In general, steel used in a corrosive environment is subjected to any of measures such as plating, painting, thermal spraying, and anticorrosion. However, surface coatings such as plating, painting, and thermal spraying always have some fine defects, and when the corrosion progresses in that part, the reaction proceeds locally and is often not always safe in terms of reliability. In addition, the anticorrosion is not a complete problem because it goes without saying that the problem is economical, and if the reliability and setting conditions of the apparatus are wrong, corrosion may be caused.

  In recent years, the use of Cr-containing steels and stainless steels for the purpose of improving the corrosion resistance of steel bodies from the viewpoint of improving reliability, simplifying manufacturing and construction processes, making maintenance-free, economically demanding, saving resources, etc. It is increasing. However, in consideration of an increase in material cost, weldability, mechanical characteristics, economy, etc., materials that satisfy corrosion resistance cannot be used, and these are often not a drastic measure.

  As a steel material for improving the corrosion resistance of the steel substrate, there is a weather-resistant steel material in which an appropriate amount of chemical components such as Cr, Cu, Ni, and P is added to the steel. As this weather-resistant steel material, JIS has a weather-resistant hot-rolled steel material for welded structures. Two types are specified: (SMA: JIS G 3114) and high weatherability rolled steel (SPA: JIS G 3125). Weatherproof steel is steel that blocks the progress of permanent corrosion by a dense stable rust layer formed on the surface of the steel material, and has been used in mild corrosive environments such as inland areas.

  Among the conventional means for improving corrosion resistance, surface treatment has problems in terms of reliability due to the progress of local corrosion, electrocorrosion etc. has problems of equipment and conditions, and economic problems. Cr-containing steel and stainless steel are In consideration of weldability, mechanical properties, material cost increase, and economic efficiency, it is often impossible to use a material that satisfies corrosion resistance, which is not a drastic measure.

  In weathering steel, a long period of about 10 years or more is required until a stable rust layer is formed, and in practical use, initial corrosion and accompanying outflow of red rust are problematic. This tendency is particularly strong in Japan, which has a hot and humid climate. Rust stabilization treatment is generally performed for the purpose of preventing contamination of surrounding structures by rust juice until rust stabilization when using weatherproof steel bare. However, this method also has a problem that the formation of a dense rust layer is inhibited and the expected effect cannot be obtained in an environment where a lot of salt comes in just like preventing bare rust soup.

Means for solving such problems have been proposed. For example, JP-B 53-22530, JP-B 56-33991, JP-B 58-39915, JP-B 58-17833, JP-A 02-133480, JP-B 06-21273, etc. Then, a method has been proposed in which a resin is coated on the surface of weathering steel to prevent the invasion of incoming salt from the external environment and promote the generation of stable rust. JP-A No. 02-133480 discloses a surface treatment solution that promotes the formation of stable rust with a scaly crystal structure of Fe ₃ O ₄ , phosphoric acid, butyral resin and the balance being a solvent. In the above Japanese Patent Publication No. 06-21273, one or more compounds of P, Cu, Cr, Ni, Si and Mo, Fe ₂ O ₃ , Fe ₃ O ₄ , phosphoric acid, bisphenol-based epoxy resin and the balance are solvent and paint. A rust-stabilized surface treatment method for applying a coating liquid as an auxiliary agent is disclosed.

  However, none of these methods improve the steel material itself, and there is a problem in promoting the generation of good rust. That is, the resin coating usually has a minute defect, and the effect of the coating film cannot be expected at the defective portion. Furthermore, the progress of the corrosion at the coating film defect part causes crevice corrosion at the coating film-substrate interface, and the coating film itself may be peeled off or dropped before the stable rust layer is formed. Therefore, the use of weathering steel in a severe environment where salt content cannot be avoided is limited, which is a serious problem.

As an improvement of the steel material itself, there are those described in JP-A-10-330881 (Patent Document 1) and JP-A-11-71632 (Patent Document 2). The former described in JP-A-10-330881 is that excellent weather resistance can be obtained by adding Cr-free, Cu, Ni, Ti or the like. However, the amount of alloy addition is limited in consideration of mechanical properties, weldability, and cost, which limits the improvement in weather resistance, and there is a problem that the weather resistance is not sufficient in a severe environment. The latter described in JP-A-11-71632 defines a range in which weldability is ensured while obtaining weather resistance by adding Cr-free, Cu, Ni, Ti, etc., and specifying a carbon equivalent. However, sufficient corrosion resistance cannot be obtained as a result of limiting the amount of alloy addition in consideration of mechanical properties, weldability, and cost.
JP-A-10-330881 Japanese Patent Laid-Open No. 11-71632

  In order to improve the corrosion resistance of iron, the addition of elements for improving corrosion resistance such as Cr, Cu and Ni is commonly used. In general, the higher the added amount, the higher the corrosion resistance of these elements. However, as the added amount increases, mechanical properties and weldability often decrease, and the material cost also increases. It is desirable to keep the element addition amount as low as possible.

  In this way, improving corrosion resistance and improving steel properties and cost performance are trade-offs, and many studies have been conducted to fully satisfy the two, but there is a compromise between some balance points. Absent.

  The present invention has been made paying attention to such circumstances, and its purpose is to have excellent corrosion resistance without causing deterioration of mechanical properties and weldability due to excessive addition of an element for improving corrosion resistance. It is intended to provide a steel material that can be used.

  In order to achieve the above-mentioned object, the present inventors have conducted intensive studies and have completed the present invention. According to the present invention, the above object can be achieved.

The present invention thus completed and capable of achieving the above object relates to a steel material having excellent corrosion resistance, and is a steel material having excellent corrosion resistance according to claim 1 (excellent corrosion resistance according to the present invention). It has the following structure.

That is, the steel material excellent in corrosion resistance according to the present invention is C: 0.20 mass% or less (excluding 0%), Si: 0.10 to 1.0 mass%, Mn: 2.5 mass% or less. (Excluding 0%), Al: 0.03-0.50 mass%, Zn: 0.0001-3 mass%, Cr: 0.2 mass% or less (excluding 0%), Cu: 0.05 to 3.0% by mass, Ni: 0.05 to 6.0% by mass, Ti: 0.01 to 1.0% by mass, the balance being excellent in corrosion resistance consisting of iron and inevitable impurities It is a steel material .

  The steel material excellent in corrosion resistance according to the present invention can have excellent corrosion resistance without causing deterioration of mechanical properties and weldability due to excessive addition of an element for improving corrosion resistance.

The present invention relates to a steel material excellent in corrosion resistance. Basically, Cr, Cu, Ni having an effect of improving corrosion resistance is suppressed to a small concentration as a whole steel material, and Cr, Cu, Ni is added to the surface contributing to corrosion resistance. It is concentrated to give a large concentration on the surface.

The above may be achieved by the combined addition of Zn Cr, Cu, and Ni. Zn is electrochemically base and is solid-dissolved in a wide composition range in iron, and therefore has an effect of promoting the dissolution of Fe in a corrosive environment. This means that the corrosion resistance of the steel material is temporarily reduced. However, Zn and Fe preferentially dissolve in the early stage of corrosion, so that Cr, Cu, and Ni are left behind on the steel material surface. The concentration of Cr, Cu, Ni increases.

That is, the steel material excellent in corrosion resistance according to the present invention contains Zn, and Cr: 0.2 mass% (wt%) or less, Cu: 0.05 to 3.0 mass%, Ni: 0.05 to It is made to contain 6.0 mass% (henceforth%) . Thus Cr, Cu, the addition amount of Ni is small, has low concentration as a whole steel, by Zn and Fe is preferentially dissolved in the corrosion early, Cr in the steel material surface, Cu, Ni is concentrated in type left behind And the concentration of Cr, Cu, and Ni on the steel surface increases.

Since the Cr in the steel material surface, Cu, Cr in Ni are concentrated to the surface of the steel material, Cu, the concentration of Ni becomes higher, thereby improving the corrosion resistance, it can have excellent corrosion resistance. Further, the added amount of Cr, Cu, and Ni is small, and the concentration of the steel material as a whole is low. This amount is not an excessive amount that causes deterioration of mechanical properties and weldability.

Therefore, the steel material excellent in corrosion resistance according to the present invention can have excellent corrosion resistance without causing deterioration in mechanical properties and weldability due to excessive addition of the corrosion resistance improving elements (Cr, Cu, Ni ) . That is, the addition amount of the corrosion resistance improving element (Cr, Cu, Ni ) is a small amount that does not cause deterioration of mechanical properties and weldability, but can have excellent corrosion resistance.

Oite excellent steel in corrosion resistance according to the present invention, the content of Zn is generally steel, it is necessary that the scrap level or more. When the Zn content is at a general steel or scrap level, the concentration of Cr, Cu, Ni on the steel material surface hardly occurs, and the corrosion resistance is insufficient.

Zn is essential for improving the corrosion resistance of steel, and not only improves the corrosion resistance of the base metal of the steel, but also has a function of forming a protective rust by densifying and refining the generated rust. Furthermore, zinc has an effect of facilitating dissolution of the Fe base material, concentrating elements for improving corrosion resistance, and zinc corrosion products covering the surface of the steel material and acting as an environmental barrier film.
By making the Zn content 0.0001% or more, the above-described effect of Zn can be obtained more reliably, and by making the Zn content 3% or less, the corrosion resistance of the base material is made high. Can be maintained. When the Zn content is more than 3%, the Fe base material is dissolved and the corrosion resistance of the base material is lowered.
Therefore, the Zn content is set to 0.0001 to 3%.
In order to obtain the effect of Zn as described above more reliably and to maintain the corrosion resistance of the base material at a higher level, the Zn content is preferably 0.0008 to 3%, and more preferably 0.002 It is preferable to set it to -3%, and it is further more preferable to set it as 0.02-1.0%. In order to achieve a higher level of corrosion resistance in the atmospheric chloride environment as described above, the Cr content is desirably 0.02% or less.

Cr becomes an element for improving corrosion resistance in the air and seawater. Cr is an effective element for strengthening steel. However, if added in a large amount, the weldability is reduced. By setting the Cr content to 0.2% or less, the corrosion resistance under atmospheric chloride environment (such as a place close to the sea), particularly the perforation resistance, can be further improved. That is, in the atmospheric chloride environment, Cr may have an adverse effect, and reducing the Cr content improves the corrosion resistance, particularly the perforation resistance. By setting the Cr content to 0.2% or less, such an effect can be obtained, and the corrosion resistance in the atmospheric chloride environment, particularly the perforation resistance can be further improved. From the above points, although Cr is contained, Cr is 0.2% by mass or less (excluding 0%).

Cu and Ni are both an element having a corrosion resistance improving effect and weldability improving effect, by containing these, these effects can be exhibited. Among them, Cu is an element electrochemically noble than iron and has the effect of densifying the rust generated on the steel surface, promoting the formation of a stable rust layer, and improving the corrosion resistance such as weather resistance. It also contributes to improved weldability. If the Cu content is less than 0.05%, this effect is not obtained, and even if it exceeds 3.0%, no further effect is obtained, and conversely, processing such as hot rolling for the production of steel is not possible. In some cases, the material may become brittle (hereinafter also referred to as hot work brittleness). Therefore , Cu: 0.05 to 3.0%. In order to more reliably suppress the occurrence of hot work brittleness, the Cu content is preferably 0.5% or less. That is, Cu: 0.05 to 0.5% is desirable.

  Similar to the case of Cu, Ni has the effect of densifying the rust generated on the steel surface, promoting the formation of a stable rust layer, and improving corrosion resistance such as weather resistance. It also contributes to improved weldability. Furthermore, Ni also has an effect of suppressing hot work brittleness when Cu is added. Therefore, when Ni is contained together with Cu, a synergistic effect of improving corrosion resistance and suppressing hot work brittleness can be expected.

When the Ni content is less than 0.05%, the excellent effects as described above cannot be obtained. On the other hand, the excessive content of Ni widens the solid-liquid solidification temperature range in the complete austenite structure, promotes the segregation of low melting point impurity elements to the dendrite grain boundaries, and reacts with S to the grain boundaries of the weld metal. A NiS compound having a low melting point is precipitated and the ductility of the grain boundary of the solidified metal is deteriorated. Thus, excessive content of Ni adversely affects the resistance to welding hot cracking, so the upper limit content should be 6.0%. Therefore , Ni: 0.05-6.0%.

  When Cu and Ni are added together with Zn, Cu and Ni are concentrated in a portion where Zn is preferentially dissolved, so that the effect of improving corrosion resistance is greater than that at the normal rust-iron interface.

Excellent steel in corrosion resistance according to the present invention, as described above, containing Zn, further Cr: (not inclusive of 0%.) 0.2% or less, Cu: 0.05 to 3.0%, Ni : it is necessary to contain 0.05 to 6.0%, the Zn, Cr, Cu, also contain elements other than Ni. That is, containing Zn, further Cr: (not inclusive of 0%.) 0.2% or less, Cu: 0.05 to 3.0% Ni: with containing 0.05 to 6.0%, It contains elements other than these (C, Si, Mn, Al, Ti) , and the balance consists of Fe and inevitable impurities .

In the steel material according to the present invention , Ti: 0.01 to 1.0% by mass is contained . Thereby , corrosion resistance etc. improve further.

  That is, Ti is an element having an effect of improving corrosion resistance, and has a beneficial effect of densifying the generated rust and promoting the formation of a stable rust layer, as well as Cr, Cu, and Ni, and is extremely excellent. Has the effect of imparting corrosion resistance. In particular, it has the effect of suppressing and miniaturizing the formation of β-FeOOH rust that is characteristically produced in chloride environments and adversely affects the corrosion resistance of steel. It also has the advantage of cleaning the steel. Furthermore, the corrosion product of zinc is refined, densified, and has a function of further improving the function of improving corrosion resistance by blocking the environment with the corrosion product. Therefore, the above effects can be obtained by adding Ti.

Such an effect is obtained by addition of Ti amount: 0.01% or more. When Ti is added in excess of 0.03%, the effect is remarkably increased, and the addition of Ti amount: 0.05% or more. More desirable. However, even if excessive addition is performed, the effect tends to saturate and is not preferable economically. From this point, the Ti content is preferably 1.0% or less. Therefore , the addition amount of Ti is set to 0.01 to 1.0%. By adding such an amount (0.01 to 1.0%) of Ti, the above-described effects can be obtained, and the corrosion resistance and the like are further improved.

  Ti also has the effect of improving toughness and weldability. In other words, the inclusion of Ti causes TiC, TiN, and the like, which are strong ferrite transformation nuclei, to be dispersed and precipitated in the steel during the cooling process of the welded portion, greatly contributing to the refinement of the ferrite structure in the weld heat affected zone. If the Ti content is less than 0.01%, this effect is not obtained, and if it exceeds 1.0%, the effect is saturated and not economical. In order to exert the effect of Ti more, it is preferable to contain 0.05% or more of Ti, and when Ti exceeds 0.5%, the embrittlement of steel may become a problem. Not right. From such a point, the Ti content is desirably 0.05 to 0.5%.

C is an element effective for the strength of steel, and is an element effective for securing a strength of 390 to 630 N / mm ² grade or higher, but when C: more than 0.2%, the weldability and bareness of steel Deteriorates the weather resistance. From this point, C: 0.20% or less (not including 0%) .

Si is an element for deoxidation and solid solution strengthening of molten steel, and also has an effect of promoting the formation of a dense stable rust layer and improving corrosion resistance such as bare weather resistance. However, when the Si content is less than 0.10%, these effects are insufficient. On the other hand, if it is too much and Si: more than 1.0%, the weldability is lowered. From such a point, Si: 0.10 to 1.0% .

Mn is an element effective for the strength of steel, and is an element effective for securing a strength of 390 to 630 N / mm ² grade or higher in place of C. However, when Mn is more than 2.5%, MnS is It may be produced in a large amount in steel and may cause deterioration of corrosion resistance such as bare weather resistance. From this point, Mn: 2.5% or less (not including 0%) .

When Al is added in combination with Ti, the formation of a stable rust layer is further promoted, and the corrosion resistance is further improved. Al also has an effect of improving weldability. Furthermore, Al is an effective element for improving the toughness of steel by capturing solid solution oxygen as a deoxidizing element of molten steel and preventing the occurrence of blowholes. If the Al content is less than 0.03 %, these effects cannot be obtained sufficiently. On the other hand, if the Al content exceeds 0.50%, the effect of improving the corrosion resistance by promoting the formation of the stable rust layer is On the contrary, it deteriorates the toughness of the steel by degrading the weldability and increasing the number of alumina inclusions. From such points, Al: 0.03 to 0.50% .

Therefore, the steel according to the present invention, C: 0.20 wt% or less, Si: 0.10 to 1.0 mass%, Mn: 2.5 wt% or less, Al: 0.03 to 0.50 wt% Is also included.

Ca is an element that further improves corrosion resistance, and also has an effect of improving weldability. One of the effects of improving the corrosion resistance of Ca is to fix S, which is harmful to corrosion resistance, and to clean the steel matrix. Further, as another effect, Ca dissolved in a small amount in the steel is dissolved in a small amount along with the corrosion reaction of iron in the progress of corrosion on the steel surface or on the microscopic defect portion, and exhibits alkalinity. For this reason, it has a solution pH buffering effect at the tip of corrosion (anode), and has an effect of suppressing corrosion at the tip of corrosion. These have a completely opposite action to the action of an element that lowers the pH when dissolved, such as Cr. When Ca is used in combination with Ti, a synergistic effect of improving corrosion resistance such as bare weather resistance is produced in combination with the effect of reducing Cr and the effect of promoting the formation of a stable rust layer such as Ti. Such an effect is not exhibited when Ca is less than 0.0001%, but even if Ca is excessively contained, the effect is saturated and is not economical. In particular, when Ca is contained excessively, the cleanliness of the steel is deteriorated, and there is a possibility of damaging the furnace wall during steelmaking, especially during the production of weathering steel. From the above points, Ca: 0.0001 to 0.01% may be further added.

La and Ce are dissolved in a small amount in accordance with the corrosion reaction of iron in the progress of corrosion on the steel surface or microscopic defects, and exhibit alkalinity. For this reason, it has a solution pH buffering effect at the tip of corrosion (anode), and has an effect of suppressing corrosion at the tip of corrosion. These have a completely opposite action to the action of an element that lowers the pH when dissolved, such as Cr. When combined with the effect of reducing Cr and the effect of promoting the formation of a stable rust layer such as Ti, a further synergistic effect of improving corrosion resistance can be expected. Such an effect is not exhibited when La: less than 0.0001% or Ce: less than 0.0001%, but even if La or Ce is contained excessively, the effect is saturated and is not economical. It also deteriorates the mechanical properties. From the above points, La: 0.0001 to 0.05 mass% or Ce: 0.0001 to 0.05 mass% may be further added.

Therefore, the steel material according to the present invention, further Ca: 0.0001 to 0.01 wt%, La: 0.0001 to 0.05 wt%, Ce: 0.0001 to 0.05 one or more of the weight% May be added.

Nb, V, and Zr have the same effect as Ti. Amorphous rust is generated and the proportion of α-FeOOH is increased to form fine and dense rust, and β-FeOOH is suppressed. A stable rust layer is formed. However, the effect is inferior to Ti. For this reason, when these elements are contained, it is preferable to selectively contain them as a supplement to the effect of Ti. Even if these elements are added in a large amount, the effect is saturated, and since they are expensive elements, Nb: 0.10% or less, V: 0.10% or less, and Zr: 0.05% or less are further added. You may do it.

Mo prevents chlorine ions from entering, so it is useful for preventing corrosion in a chloride environment. However, even if added in a large amount, the effect is saturated, and since it is an expensive element, 0.25% or less. Further, it may be added. Mg is an element that suppresses the pH drop associated with the dissolution of the steel material and suppresses the corrosion of the steel and contributes to the improvement of the corrosion resistance. However, the effect is saturated even if added excessively, so 0.010% The following may be further added.

Therefore, the steel material according to the present invention, further Nb: 0.10 mass% or less, V: 0.10 wt% or less, Zr: 0.05 mass% or less, Mo: 0.25 wt% or less, Mg: 0. One or more of 010% by mass or less may be added.

  If S exceeds 0.02%, FeS and MnS, which are the starting points of corrosion, are produced in large amounts in the steel, which may inhibit the formation of the stable rust layer and lead to deterioration of corrosion resistance. There is. Further, when Ni or the like is excessively contained, a NiS compound having a low melting point is precipitated at the grain boundary of the weld metal due to the reaction with S, and the ductility of the grain boundary of the solidified metal tends to be deteriorated. In this respect, if the S content is 0.02% or less, it becomes possible to contain a larger amount of Ni without precipitating the low melting point NiS compound. Therefore, the S content is preferably 0.02% or less. Furthermore, S: 0.01% or less is desirable, and 0.005% or less is even more desirable.

  The form of application of the steel material according to the present invention is not particularly limited, for example, a hot-rolled steel sheet, a cold-rolled steel sheet, or a steel sheet subjected to annealing after hot rolling or cold rolling, It is also possible to use by performing plating such as chemical conversion treatment, hot dipping, electroplating, and vapor deposition, various coatings, coating base treatment, organic coating treatment, and the like.

  In the case of coating, chemical conversion treatment such as phosphate treatment or electrodeposition coating may be performed according to various applications. A known resin can be used as the paint, and an epoxy resin, a fluororesin, a silicon acrylic resin, a polyurethane resin, an acrylic resin, a polyester resin, a phenol resin, an alkyd resin, a melamine resin, and the like can be used together with a known curing agent. In particular, from the viewpoint of corrosion resistance, it is recommended to use epoxy, fluorine, or silicon acrylic resin. In addition, known additives added to the paint, such as coloring pigments, coupling agents, leveling agents, sensitizers, antioxidants, UV stabilizers, flame retardants, and the like may be added.

  Also, the form of the paint is not particularly limited, and can be appropriately selected according to the use such as solvent-based paint, powder paint, water-based paint, water-dispersed paint, and electrodeposition paint.

  In order to form a desired coating layer on the steel material using the coating material, a known method such as a dipping method, a roll coater method, a spray method, or a curtain flow coater method may be used. The thickness of the coating layer may be a known appropriate value depending on the application.

  Examples of the present invention and comparative examples will be described below. The present invention is not limited to this embodiment, and can be implemented with appropriate modifications within a range that can be adapted to the gist of the present invention, all of which are within the technical scope of the present invention. include.

  Steel plates having chemical components shown in Tables 1 and 2 were used as test materials. A test piece was prepared from the test material, and a corrosion resistance evaluation test and a perforation resistance evaluation test were performed using the test piece to evaluate the corrosion resistance and the perforation resistance.

  As a corrosion resistance evaluation test, a test was conducted to expose a specimen at an exposure test site in Hyogo Prefecture. More specifically, this test is a test in which the surface of the test piece is subjected to sandblasting and then exposed southward for one year (plus forced spraying of salt water once a week). After this corrosion resistance evaluation test, the rust on the surface of the test piece was removed, and the corrosion resistance was evaluated from the reduction in thickness.

  For the perforation resistance evaluation test, the test piece was subjected to phosphate treatment, followed by cationic electrodeposition (20-micron target), cross-cut reaching the steel substrate, and CCT test (saline spraying → drying → Wet cycle test was conducted. After this perforation resistance evaluation test, the evaluation surface was divided into 16 sections at equal intervals, the maximum perforation depth was measured for each section, the average value was calculated, and the perforation resistance was evaluated.

  The standard for the evaluation of the test results is based on the corrosion amount B of No. 1 (Comparative Steel 1), where the corrosion amount is less than 70% of the corrosion amount B (excellent level), and the corrosion amount is the corrosion amount. B (70% or more and less than 80%) of B (excellent level), corrosion amount of 80% or more and less than 90% of corrosion amount B (good), corrosion amount of 90% or more of corrosion amount B X (defect). In addition, the said corrosion amount is a plate | board thickness reduction | decrease amount in the case of a corrosion resistance evaluation test, and is the average value of the maximum hole depth of each division in the case of a hole resistance evaluation test.

The test results are shown in Table 1 . As can be seen from Table 1 , the steel materials No. A to F are Zn-free and are steel materials according to comparative examples. The steel materials No. A to F all have a corrosion resistance and a hole resistance of x (defect).

On the other hand, the steel materials No. G to P are according to the examples of the present invention, and are superior in corrosion resistance and perforation resistance to the steel materials according to the comparative examples. That is, the corrosion resistance and perforation resistance are Δ (good), ○ (excellent level), or ◎ (excellent level).

Among the steel of the No.G～P, steel No.G~J is (are varied), respectively, Zn different amounts in the range of from 0.01 to 3.0%. All of these steel materials have excellent corrosion resistance (excellent level). Porosity resistance is ○ (excellent level) or ◎ (very excellent level). Among these, Zn content: 0.03 to 0.3% is ◎, and particularly excellent in resistance to porosity. Yes.

Steel materials No. K to L correspond to examples of the present invention, and are excellent in corrosion resistance and perforation resistance .

Steel materials No. M to P correspond to the examples of the present invention, and are excellent in corrosion resistance and perforation resistance .

  In the above Examples and Comparative Examples, the corrosion resistance evaluation test and the perforation resistance evaluation test were performed by the above test methods, and the above results were obtained. However, the test method was different from this test method. Even in the case of, although the absolute value is different, the result of the same tendency as described above is obtained.

The steel materials of No. G to P described above have a small content of Cr, Cu, Ni, etc. as shown in Table 1, and the concentration of the steel material as a whole is low. This amount deteriorates the mechanical properties and weldability. Since it is not such an excessive addition amount, it has sufficient mechanical properties and weldability.

  The steel material according to the present invention can have excellent corrosion resistance without deteriorating mechanical properties and weldability due to excessive addition of an element for improving corrosion resistance. That is, it can have excellent corrosion resistance while ensuring sufficient mechanical properties and weldability. Therefore, the steel material according to the present invention can be suitably applied to uses such as bridges, ships, marine structures, other steel structures, building materials, home appliances, automobile steel plates and the like. More specifically, the steel materials according to the present invention are (1) various corroded steel structures, concrete corrosive environments such as supports, alkaline corrosive environments, (2) seawater corrosive environments such as ships, bridges, piles, and sheet piles, (3) Water tanks, water supply pipes, hot water supply pipes, can containers, various containers, tableware, cooking equipment, bathtubs, pools, bathroom vanities, etc., (4) Bridge cables, various containers, low temperature heat exchangers, bathroom components, etc. (5) Soil corrosive environment such as various storage tanks, columns, piles, sheet piles, piping, etc., (6) Bridges, columns, exterior / interior materials for buildings, roofing materials, fittings, kitchen members, various handrails, roofs It can be suitably used in various corrosive environments such as atmospheric corrosive environments such as drains, home appliances, automobiles, and railway vehicles.

Claims (1)

C: 0.20 mass% or less (not including 0%), Si: 0.10 to 1.0 mass%, Mn: 2.5 mass% or less (not including 0%), Al: 0.0. 03 to 0.50 mass%, Zn: 0.0001 to 3 mass%, Cr: 0.2 mass% or less (excluding 0%), Cu: 0.05 to 3.0 mass%, Ni: 0 Steel material excellent in corrosion resistance, containing 0.05 to 6.0 mass%, Ti: 0.01 to 1.0 mass%, with the balance being iron and inevitable impurities .