Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0226—Hot rolling

Definitions

• This disclosure relates to a steel material having excellent alcohol-induced corrosion resistance in particular, alcohol-induced pitting corrosion resistance and alcohol-induced SCC resistance.
• the disclosure relates to steel material having excellent alcohol-induced pitting corrosion resistance and alcohol-induced SCC resistance which is preferably applicable in parts which directly contact bio-alcohol, examples thereof including steel material used in tanks that store bio-alcohols such as bio-ethanol, tanks inside vessels or tanks for automobiles for the purpose of transportation, and steel material used for pipeline transportation.
• bio-alcohol for example, bio-ethanol is produced mainly by decomposing and purifying sugar content in corn, wheat, or the like. Recently, bio-ethanol is being used widely throughout the world, as an alternative fuel for petroleum (gasoline) or as fuel mixed with gasoline. The usage amount thereof is increasing every year.
• bio-ethanol has a drawback in that it can be safely handled only in facilities provided with ethanol resistance measures, for example, facilities using as tanks, organic coating material, stainless steel or stainless clad steel which have excellent ethanol-induced SCC resistance. Further, for transportation of bio-ethanol, conventional pipelines or the like for transporting petroleum could not be used.
• JP 2011-26669 A proposes as a measure to deal with biofuels a method of applying a zinc-nickel alloy containing 5% to 25% of Ni to the steel material for tanks for biofuels, and applying on the alloy a chemical conversion treatment containing no hexavalent chromium. JP 2011-26669 A describes that, by adopting that method, the corrosion resistance property of the steel material in gasoline containing ethanol would be satisfactory.
• JP 2011-231358 A proposes a steel sheet for manufacturing pipes having excellent corrosion resistance, obtained by applying a “Zn—Co—Mo alloy where the composition ratio of Co to Zn in the alloy layer is 0.2 to 4.0 at %” on the steel sheet surface.
• the zinc-nickel alloy disclosed in JP 2011-26669 A would be effective for improving corrosion resistance.
• such zinc-nickel alloy requires electroplating treatment.
• the alloy can be applied for small tanks such as fuel tanks for automobiles without any problem, for thick steel material used for large structures such as storage tanks with a capacity of 1000 kL or more, or line pipes, treatment costs become very large, and therefore cannot be applied.
• coating failure or the like occurs, pitting corrosion progresses more easily and causes SCC to occur more easily, in that part. Therefore, it cannot be said that sufficient pitting corrosion resistance and SCC resistance would be obtained.
• the Zn—Co—Mo alloy disclosed in JP 2011-231358 A requires electroplating treatment as well, and due to the same reasons as JP 2011-26669 A, the alloy cannot be applied for thick steel material used for large structures. Further, again, due to the same reasons as JP 2011-26669 A, it cannot be said that sufficient pitting corrosion resistance and SCC resistance would be obtained.
• an anti-corrosion method using an alloy is not suitable for large structures, and the effect thereof regarding pitting corrosion resistance is not sufficient. Further, as for inhibitors, the effect of reducing corrosion is unstable. In view of the above, for large structures, it is advantageous to improve corrosion resistance of the steel material itself inside bio-ethanol, from the viewpoint of costs as well.
• a steel material excellent in alcohol-induced pitting corrosion resistance and alcohol-induced SCC resistance containing, by mass % C: 0.03% to 0.3%, Si: 0.01% to 1.0%, Mn: 0.1% to 2.0%, P: 0.03% or less, S: 0.01% or less and Al: 0.1% or less, and one or both of Mo: 0.03% to 1.0% and W: 0.03% to 1.0%, and at least two of Sb: 0.005% to 0.5%, Sn: 0.01% to 0.3% and Nb: 0.005% to 0.1%, and the balance including Fe and incidental impurities.
• C is a necessary element to provide strength of steel, and to provide our target strength (400 MPa or more), it is contained in an amount of at least 0.03%.
• the content thereof exceeds 0.3%, weldability decreases and restrictions are placed at the time of welding. Therefore, the upper limit of the content thereof is 0.3%.
• the content thereof is preferably 0.03% to 0.2%.
• Si is added for the purpose of deoxidation. However, if the content thereof is less than 0.01%, the deoxidation effect is limited. On the other hand, if the content thereof exceeds 1.0%, toughness and weldability deteriorate. Therefore, Si content is 0.01% to 1.0%. The content thereof is preferably 0.05% to 0.5%.
• Mn is added for the purpose of improving strength and toughness. However, if the content thereof is less than 0.1%, the effect thereof is not sufficient. On the other hand, if the content thereof exceeds 2.0%, weldability deteriorates. Therefore, Mn content is 0.1% to 2.0%. The content thereof is preferably 0.3% to 1.6%.
• P is contained as an incidental impurity. However, since it deteriorates toughness and weldability, P content is 0.03% or less. The content thereof is preferably 0.025% or less. Further, since excessive dephosphorization causes an increase in costs, the lower limit of P content is preferably 0.0003%. Therefore, the content thereof is preferably 0.0003% to 0.03%.
• S is also contained as an incidental impurity.
• the content thereof increases, not only does toughness and weldability decrease, but inclusions such as MnS increase and serve as the origin of SCC to decrease SCC resistance. Therefore, it is desirable to minimize S content, although a content thereof of 0.01% or less would be acceptable. Further, since excessive desulfurization causes an increase in costs, the lower limit of S content is preferably 0.0001%. Therefore, the content thereof is preferably 0.0001% to 0.01%.
• Al is added as a deoxidizer.
• Al content exceeding 0.100% decreases the toughness of the weld metal part when the steel is subjected to welding. Therefore, the content thereof is 0.100% or less.
• the lower limit of the content thereof is preferably 0.005%. More preferably, the content thereof is 0.005% to 0.070%.
• Mo is an important pitting corrosion resistance/SCC resistance improving element for the steel material. Mo forms an oxysalt as a corrosion product, and when a crack which serves as the origin of stress corrosion cracking occurs, the corrosion product functions to immediately protect the crack tip, and inhibit development of the crack. Further, with Mo being incorporated into the oxide film of the steel material surface, the solubility resistance of the oxide film under acid environment caused by an acetic acid contained in bio-ethanol as an impurity improves, and while reducing non-uniform corrosion, Mo also provides an effect of inhibiting pitting corrosion. However, if the content thereof is less than 0.03%, improving effects on pitting corrosion resistance and SCC resistance are limited. On the other hand, if the content thereof exceeds 1.0% , it is disadvantageous in terms of costs. Therefore, Mo content is 0.03% to 1.0%. Further, to prevent costs from increasing, the content thereof is preferably 0.03% to 0.5%.
• W is an important pitting corrosion resistance/SCC resistance improving element for the steel material.
• W, as well as Mo, forms an oxysalt as a corrosion product, and when a crack which serves as the origin of stress corrosion cracking occurs, the corrosion product functions to immediately protect the crack tip, and inhibit development of the crack.
• W being incorporated into the oxide film of the steel material surface, the solubility resistance of the oxide film under acid environment caused by an acetic acid contained in bio-ethanol as an impurity improves, and while reducing non-uniform corrosion, W also provides an effect of inhibiting pitting corrosion.
• the content thereof is less than 0.03%, improving effects on pitting corrosion resistance and SCC resistance are limited.
• W content is 0.03% to 1.0%. Further, to prevent costs from increasing, the content thereof is preferably 0.03% to 0.5%. At least two of Sb: 0.005% to 0.5%, Sn: 0.01% to 0.3% and Nb: 0.005% to 0.1% Sb: 0.005% to 0.5%
• Sb is an effective element in improving pitting corrosion resistance and SCC resistance under acid environment caused by an acetic acid contained in bio-ethanol as an impurity. However, if the content thereof is less than 0.005%, it is ineffective. On the other hand, if the content thereof exceeds 0.5%, limitations are caused in terms of steel material manufacturing. Therefore, Sb content is 0.005% to 0.5%. The content thereof is preferably 0.01% to 0.3%. Sn: 0.01% to 0.3%
• Sn as well as Sb, improves pitting corrosion resistance and SCC resistance under acid environment.
• the content thereof is less than 0.01%, the addition effect is limited.
• the content thereof exceeds 0.3%, the effect not only reaches a plateau but limitations are caused in terms of steel material manufacturing. Therefore, Sn content is 0.01% to 0.3%.
• the content thereof is preferably 0.02% to 0.2%.
• Nb is also an effective element in improving pitting corrosion resistance and SCC resistance under acid environment caused by an acetic acid. However, if the content thereof is less than 0.005%, the effect is not expressed. On the other hand, if the content thereof exceeds 1.0%, mechanical properties of the weld decrease. Therefore, Nb content is 0.005% to 0.1%. The content thereof is preferably 0.005% to 0.05%.
• Mo and W, and Sb, Sn and Nb are particularly important, and by containing these components in a total amount of 0.15% to 1.0%, and by containing Mo and W which are particularly important in a total amount of 0.08% or more, it is possible to further improve pitting corrosion resistance and SCC resistance.
• the basic components are as described above.
• the following components may also be contained according to necessity.
• Ca Ca/S ⁇ 0.5 and 0.01% or less
• Ca is added for the purpose of performing morphological control of precipitates of S (e.g. MnS) which are incidental impurities and preventing cracks such as SCC. Therefore, Ca is preferably added depending on S content, and with Ca/S (mass ratio) being 0.5 or more, Ca provides the effect of preventing cracks. Ca/S is more preferably 1.0 or more. However, if Ca is added excessively, coarse inclusions are formed to deteriorate toughness of the base material. Therefore, the upper limit of Ca content is preferably 0.01%.
• B is an element that enhances strength of the steel material and can be contained according to necessity. To obtain such an effect, B is preferably contained in an amount of 0.0002% or more. However, if B is added in an amount exceeding 0.03%, toughness deteriorates. Therefore, B is preferably contained in a range of 0.0002% to 0.03%. More preferably, the content thereof is 0.0003% to 0.003%.
• one or more of Zr, V and Ti may be contained. All of these elements have a limited addition effect if the contents thereof are less than 0.005%. On the other hand, if the contents thereof exceed 0.1%, mechanical properties of the weld decrease. Therefore, contents of these elements are 0.005% to 0.1%. The contents of these elements are preferably 0.005% to 0.05%.
• components other than those described above are Fe and incidental impurities.
• Molten steel with the above preferable chemical composition is obtained by steelmaking in known furnaces such as a converter, an electric furnace and the like, and made into steel raw material such as slabs and billets by known methods such as the continuous casting method or the ingot casting method.
• furnaces such as a converter, an electric furnace and the like
• steel raw material such as slabs and billets by known methods such as the continuous casting method or the ingot casting method.
• vacuum degassing refining or the like may be performed.
• the material when hot rolling the above steel raw material into a desirable dimension, the material is heated to a temperature of 1000° C. to 1350° C.
• a heating temperature below 1000° C. results in a large deformation resistance, which makes it difficult to perform hot rolling.
• a heating temperature exceeding 1350° C. may lead to generation of surface flaws, or an increase in scale loss and fuel consumption rate.
• the heating temperature is preferably 1050° C. to 1300° C. If the temperature of the steel raw material is already 1000° C. to 1350° C., the material may be subjected to hot rolling directly, without heating.
• finisher delivery temperature it is necessary to control finisher delivery temperature, and a temperature of 600° C. or higher and 850° C. or lower is preferable.
• finisher delivery temperature of lower than 600° C.
• the increase in deformation resistance causes an increase in rolling load and makes it difficult to perform rolling.
• the temperature exceeds 850° C., a desirable strength may not be obtained.
• air cooling or accelerated cooling with a cooling rate of 150° C./s or less is preferable.
• the cooling stop temperature is preferably 300° C. to 750° C. After cooling, re-heating treatment may be performed.
• Molten steel with the chemical composition shown in Table 1 was obtained by steelmaking using a vacuum melting furnace or a converter, and subjected to continuous casting to obtain slabs. Then, the slabs were heated to 1230° C., and then subjected to hot rolling under a condition of finisher delivery temperature of 820° C. to obtain steel sheets with thickness of 13 mm.
• a steel material was cut out into pieces of 10 mm ⁇ 25 mm ⁇ 3.5 mm t, subjected to wet polishing using emery polishing paper on both sides until reaching #2000, and then subjected to ultrasonic degreasing in acetone for 5 minutes, and then subjected to air drying to obtain corrosion test material.
• test material After immersing in the solution for 30 days, the test material was taken out and rust on the surface thereof rinsed using a sponge or the like. Then, corrosion products were removed in an acid with an inhibitor added thereto. The test material was washed using pure water, washed in ethanol, and then air dried. Then, the pitting corrosion depth of the surface of the test material was measured using a 3D laser microscope, and the maximum pitting corrosion depth was evaluated.
• Test materials with maximum pitting corrosion depth of less than 70% with respect to base steel were evaluated as having excellent pitting corrosion resistance.
• a steel material was processed into a round bar of 130 mm ⁇ 6.35 mm ⁇ . Then, both ends thereof were subjected to screw processing, and at the same time, the round bar was processed to have a diameter of 3.81 mm ⁇ over the length of 12.7 mm from the center part toward both ends.
• the test material was subjected to ultrasonic degreasing in acetone for 5 minutes, and then attached to an SSRT tester.
• a solution obtained by adding water: 10 ml, methanol: 5 ml, acetic acid: 56 mg, NaCl: 52.8 mg to ethanol: 985 ml was used as a simulated liquid of bio-ethanol.

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• 2013
  • 2013-12-02 WO PCT/JP2013/007057 patent/WO2014087628A1/ja active Application Filing
  • 2013-12-02 BR BR112015013191A patent/BR112015013191A2/pt not_active Application Discontinuation
  • 2013-12-02 CN CN201380063925.4A patent/CN104838029A/zh active Pending
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