WO2013058274A1 - 二相ステンレス鋼、二相ステンレス鋼鋳片、および、二相ステンレス鋼鋼材 - Google Patents
二相ステンレス鋼、二相ステンレス鋼鋳片、および、二相ステンレス鋼鋼材 Download PDFInfo
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Definitions
- the present invention relates to an inexpensive Sn-containing duplex stainless steel.
- the present invention also relates to a duplex stainless steel that contains Cu and Sn in combination, is excellent in corrosion resistance, and is inexpensive.
- the present invention relates to a duplex stainless steel, duplex stainless steel slab, and duplex stainless steel material that can be used as a seawater desalination device, tanks for transport ships, various containers, and the like.
- General-purpose duplex stainless steel contains a large amount of Cr, Mo, Ni, and N and has good corrosion resistance. However, since expensive Mo and Ni are contained, it is difficult to say that the alloy cost is high and the productivity is good. As a result, the price of the steel material is not so low, and it is difficult to say that it is often used instead of 316 series, 317 series stainless steel and the like.
- duplex stainless steel containing Sn For example, a duplex stainless steel containing 25% or more of Cr and 0.01 to 0.1% of Sn as a selective element is disclosed (see Patent Documents 1 and 2 below). Further, an alloy-saving duplex stainless steel containing 1% or less or 0.1% Sn is disclosed (see Patent Documents 3 and 4 below). Although these patent documents aim at improving the corrosion resistance by containing Sn, the relationship between the hot manufacturability of steel and the Sn content has not been studied.
- the steel whose N content is 0.2% or less is targeted.
- N is an element that reduces the hot workability of stainless steel.
- the hot workability of the duplex stainless steel containing less than 0.2% of N is desired. It is more difficult than securing it to a standard.
- the inventors focused on the possibility of improving acid resistance and pitting corrosion resistance by Sn in alloy-saving duplex stainless steel. Then, the relationship between the Sn content, corrosion resistance and hot manufacturability was investigated. As a result, the possibility of improving corrosion resistance was found by containing 0.01 to 0.2% Sn. However, it has been found that the hot productivity decreases in these duplex stainless steels containing a large amount of Sn. For this reason, the frequency with which the yield of steel materials decreases increases, and a significant cost increase is expected.
- the present inventors have focused on the possibility of improving acid resistance and pitting corrosion resistance by Sn and Cu in general-purpose duplex stainless steel. And in the duplex stainless steel in which the contents of Mo and Ni are reduced and N is 0.20% or more, the relationship between the contents of Sn and Cu, the corrosion resistance, and the hot manufacturability was investigated. As a result, the possibility of improving corrosion resistance was found by containing 0.01 to 0.2% Sn and 0.2 to 3.0% Cu. However, it has been found that the hot productivity is lowered in these duplex stainless steels containing a large amount of Sn and Cu. For this reason, the frequency with which the yield of steel materials decreases increases, and a significant cost increase is expected.
- the present inventors examined the conventional knowledge about the manufacturing technology of conventional Sn-containing duplex stainless steel hot rolled steel materials including Patent Documents 1 to 4. As a result, it has been found that there is little knowledge about the relationship between the temperature range of hot embrittlement due to Sn contained in the duplex stainless steel, the relationship with the Sn content, and the relationship with the content of other elements.
- an object of the present invention is to provide a Sn-containing duplex stainless steel, duplex stainless steel cast, and duplex stainless steel material that are favorable and inexpensive in hot productivity.
- Such a duplex stainless steel is expected to have an excellent balance between corrosion resistance and cost. For this reason, it is considered that the possibility of wide use in each field is increased.
- the contents of Ni and Mo, which are expensive elements are increased by increasing the contents of N and Mn and by adding Cu and Sn in combination. It is an object of the invention to develop an inexpensive general-purpose duplex stainless steel that saves energy.
- the inventors changed the Sn content and the contents of Ca, B, rare earth elements (REM), etc., for the alloy-saving duplex stainless steel targeted by the present invention.
- a melting material was prepared and the following experiment was performed.
- content of Ca, B, rare earth elements (REM), etc. improves hot productivity.
- a tensile test piece was collected from a slab cast from a melting material.
- the tensile test piece was subjected to high-temperature tension at 1200 to 700 ° C., and the drawing value (cross-sectional reduction rate of the fracture surface) was measured to evaluate high-temperature ductility.
- the hot rolled steel plate of 12 mm thickness was obtained by hot forging and hot rolling, and the ear cracking property was evaluated.
- the hot cracking heating temperature and the rolling temperature were changed to evaluate the ear cracking properties, and the correlation between the hot rolling heating temperature, the rolling temperature, and the high temperature ductility was obtained.
- the present inventors hot-rolled a slab of alloy-saving Sn-containing duplex stainless steel obtained by vacuum melting and casting, and observed the length of the ear cracks generated at that time. As a result, it has been found that there are rarely Sn-containing duplex stainless steel materials with few ear cracks.
- the hot rolling experiment was performed as follows. First, a slab of 90 to 44 mm thickness was heated to 1200 ° C. The thickness was then reduced to 12-6 mm through multiple rolling passes. The finish rolling temperature was controlled to about 900 ° C. Ear cracks occur on the left and right, and the maximum length of each was added to obtain the ear crack length.
- the present inventors conducted melting, casting, and rolling experiments with various element contents varied in order to find out the conditions for reliably obtaining a steel material with few ear cracks. And evaluation of the hot ductility of a slab and evaluation of the steel material ear crack after hot rolling were performed energetically. Through the above experiments, based on the obtained knowledge, the first aspect of the present invention in which the inexpensive Sn-containing alloy-saving duplex stainless steel was clearly specified was completed.
- PI Cr + 3.3Mo + 16N (1) (The element symbol in the formula (1) indicates the content of the element.) (2) Further, it contains at least one selected from Mo: 1.5% or less, Cu: 2.0% or less, W: 1.0% or less, and Co: 2.0% or less. The duplex stainless steel according to (1). (3) It further contains at least one selected from V: 0.05 to 0.5%, Nb: 0.01 to 0.20%, and Ti: 0.003 to 0.05%. The duplex stainless steel according to (1) or (2), which is characterized. (4) Further, it contains one or more selected from B: 0.0050% or less, Mg: 0.0030% or less, and REM: 0.10% or less (1) to (3 ) Duplex stainless steel according to any one of the above.
- the present inventors have made a general-purpose duplex stainless steel targeted by the present invention with a Sn content, a content of Ca, B, a rare earth element (REM), etc., and a Ni content.
- a melting material to which Co was further added was produced, and the following experiment was performed.
- Ca, B, rare earth elements (REM), etc. are contained, it is said that hot productivity improves.
- a tensile test piece was collected from a slab cast from a melting material.
- the tensile test piece was subjected to high-temperature tension at 1200 to 700 ° C., and the drawing value (cross-sectional reduction rate of the fracture surface) was measured to evaluate high-temperature ductility.
- the hot rolled steel plate of 12 mm thickness was obtained by hot forging and hot rolling, and the ear cracking property was evaluated.
- the hot cracking heating temperature and the rolling temperature were changed to evaluate the ear cracking properties, and the correlation between the hot rolling heating temperature, the rolling temperature, and the high temperature ductility was obtained.
- the inventors of the present invention hot rolled a slab of general-purpose duplex stainless steel obtained by vacuum melting and casting, and observed the length of the ear cracks generated at that time. As a result, it was discovered that there are rarely Sn-containing duplex stainless steel materials with few ear cracks.
- the hot rolling experiment was performed as follows. First, a slab of 90 to 44 mm thickness was heated to 1200 ° C. The thickness was then reduced to 12-6 mm through multiple rolling passes. The finish rolling temperature was controlled to about 900 ° C. Ear cracks occur on the left and right, and the maximum length of each was added to obtain the ear crack length.
- the present inventors conducted melting, casting, and rolling experiments in which various element contents were further changed in order to find out the conditions under which the above-mentioned steel material with few ear cracks could be obtained with certainty. And the hot ductility evaluation of the slab and the steel ear crack evaluation after hot rolling were performed energetically.
- the second aspect of the present invention which was clearly shown for inexpensive Sn-containing duplex stainless steel, was completed based on the obtained knowledge.
- duplex stainless steel slab and duplex stainless steel material of the present invention are shown below.
- duplex stainless steel having improved corrosion resistance and excellent balance with cost compared to steel conventionally used as a material for seawater desalination equipment, tanks for transport ships, various containers, etc.
- a duplex stainless steel slab and a duplex stainless steel material can be provided. For this reason, the aspect of the present invention greatly contributes to industrial development.
- the stainless steel slab means steel in a state after casting and before being subjected to processing such as hot working or forging, and the stainless steel material means that the slab is processed by various methods. It means a steel slab, a hot rolled steel plate, a cold rolled steel plate, a steel wire, a steel pipe, etc.
- Stainless steel means all forms of steel such as slabs and steel materials. The above processing includes hot and cold processing.
- the C content is limited to 0.03% or less.
- C is contained exceeding 0.03%, Cr carbide is generated during hot rolling, and corrosion resistance and toughness deteriorate.
- Si is added at 0.05% or more for deoxidation. However, when Si exceeds 1.0%, toughness deteriorates. Therefore, the upper limit of Si content is limited to 1.0%. A preferable range of the amount of Si is 0.2 to 0.7%.
- Mn has the effect of increasing the austenite phase and improving toughness. Further, since Mn has the effect of lowering the nitride precipitation temperature TN, it is preferable to add Mn positively in the steel material of this embodiment. 0.1% or more of Mn is added for the toughness of the base metal and the weld. However, when Mn is added exceeding 7.0%, corrosion resistance and toughness deteriorate. Therefore, the upper limit of the amount of Mn is limited to 7.0%.
- the Mn content is preferably 1.0 to 6.0%, more preferably 2.0 to 5.0%.
- P P is an element inevitably mixed from the raw material, and the P content is limited to 0.05% or less in order to deteriorate hot workability and toughness.
- the amount of P is preferably 0.03% or less.
- S is an element that is inevitably mixed from the raw material, and also degrades hot workability, toughness, and corrosion resistance, so the S amount is limited to 0.0010% or less. Moreover, reducing the amount of S to less than 0.0001% increases the cost for desulfurization refining. For this reason, the S content is determined to be 0.0001 to 0.0010%. The amount of S is preferably 0.0002 to 0.0006%.
- Ni stabilizes the austenite structure and contains 0.5% or more of Ni in order to improve corrosion resistance to various acids and toughness. By increasing the Ni content, the nitride precipitation temperature can be lowered. On the other hand, Ni is an expensive alloy, and the amount of Ni is limited to 5.0% or less from the viewpoint of cost in the steel of the present embodiment intended for alloy-saving duplex stainless steel.
- the Ni content is preferably 1.0 to 4.0%, more preferably 1.5 to 3%.
- the Cr content is set to 18.0% or more and 25.0% or less.
- a preferable Cr content is 19.0 to 23.0%.
- N is an effective element that improves the strength and corrosion resistance by dissolving in the austenite phase.
- 0.10% or more of N is contained.
- the solid solution limit increases depending on the Cr and Mn contents.
- the upper limit of N content was 0.30%.
- a preferable N content is 0.10 to 0.25%.
- Al is a deoxidizing element of steel and reduces oxygen in the steel as necessary. For this reason, Al is contained together with 0.05% or more of Si. In the Sn-containing steel, the reduction of the oxygen amount is essential to ensure hot productivity, and for this purpose, it is necessary to contain 0.003% or more of Al as necessary.
- Al is an element having a relatively large affinity with N, and if added excessively, AlN is generated and inhibits the toughness of stainless steel. The degree depends on the N content, but when Al exceeds 0.05%, the toughness is significantly lowered. For this reason, the upper limit of Al content was set to 0.05%.
- the amount of Al is preferably 0.04% or less.
- Ca is an important element for the hot manufacturability of steel, and it is necessary to contain Ca in order to fix O and S in the steel as inclusions and improve the hot manufacturability. .
- 0.0010% or more of Ca is contained for that purpose.
- excessive addition reduces pitting corrosion resistance. Therefore, the upper limit of the Ca content is set to 0.0040%.
- Sn is contained in order to improve the corrosion resistance of the steel of this embodiment. Therefore, it is necessary to contain at least 0.01% Sn. Furthermore, it is preferable to contain 0.02% or more of Sn.
- Sn is an element that hinders the hot manufacturability of steel.
- the heat at the interface between the ferrite phase and the austenite phase particularly at 900 ° C. or lower. Decrease the strength. The degree of the reduction depends on the contents of S, Ca, and O, but even if other limitations in the present embodiment are added, if Sn is contained exceeding 0.2%, the hot productivity is lowered. Therefore, the upper limit of the Sn content is set to 0.2%.
- the ratio Ca / O of the content of O and Ca is an important component index for improving the hot manufacturability and corrosion resistance of the steel of this embodiment.
- the lower limit of Ca / O is limited.
- the hot ductility of the Sn-containing steel decreases particularly at a temperature of 900 ° C. or less.
- the value of Ca / O is less than 0.3, the hot ductility at 1000 ° C. is also lowered, and hot productivity is greatly impaired.
- Ca / O is limited to 0.3 or more.
- Ca / O is preferably 0.4 to 0.8.
- O is an inevitable impurity, and its upper limit is not particularly defined, but is an important element constituting an oxide that is representative of non-metallic inclusions. Controlling the composition of the oxide is very important for improving hot manufacturability. In addition, when a coarse cluster-like oxide is generated, it causes surface defects. For this reason, it is necessary to restrict
- the O content is limited by setting the ratio of the Ca content and the O content to 0.3 or more.
- the upper limit of the O content is preferably 0.005% or less.
- 1 is selected from Mo: 1.5% or less, Cu: 2.0% or less, W: 1.0% or less, and Co: 2.0% or less as necessary. It may contain seeds or more. The reason for the limitation will be described.
- Mo is a very effective element that additionally enhances the corrosion resistance of stainless steel, and can be contained as required. In order to improve the corrosion resistance, it is preferable to contain 0.2% or more of Mo.
- Mo is an element that promotes precipitation of intermetallic compounds, and the upper limit of the Mo content is set to 1.5% from the viewpoint of suppressing precipitation during hot rolling in the steel of this embodiment.
- Cu is an element that additionally increases the corrosion resistance of stainless steel to acids, and has the effect of improving toughness. Therefore, it is recommended to contain 0.3% or more as necessary.
- ⁇ Cu precipitates exceeding the solid solubility during hot rolling to cause embrittlement. For this reason, the upper limit of the amount of Cu was made into 2.0%.
- a preferable content when Cu is contained is 0.3 to 1.5%.
- W is an element that additionally improves the corrosion resistance of stainless steel, and can be added as necessary.
- the upper limit of the W amount is set to 1.0%.
- a preferable W content is 0.05 to 0.5%.
- Co is an element effective for enhancing the toughness and corrosion resistance of steel and is selectively added.
- the Co content is preferably 0.03% or more.
- the preferable Co content when added is 0.03 to 1.0%.
- V 0.05 to 0.5%
- Nb 0.01 to 0.20%
- Ti 0.003 to 0.05%.
- V, Nb, and Ti can be added as necessary, and when contained in a very small amount, the corrosion resistance tends to be improved.
- Nitride and carbide formed by V are generated during the hot working and cooling of the steel material, and have the effect of enhancing the corrosion resistance. Although sufficient confirmation has not been made for this reason, there is a possibility of suppressing the generation rate of chromium nitride at 700 ° C. or lower.
- 0.05% or more of V is contained. When V is contained exceeding 0.5%, coarse V-based carbonitrides are produced and toughness is deteriorated. Therefore, the upper limit of the V amount is limited to 0.5%.
- the V content is preferably in the range of 0.1 to 0.3%.
- Nitrides and carbides formed by Nb are generated during the hot working and cooling of the steel material, and have the effect of increasing the corrosion resistance. Although sufficient confirmation has not been made for this reason, there is a possibility of suppressing the generation rate of chromium nitride at 700 ° C. or lower. In order to improve the corrosion resistance, 0.01% or more of Nb is contained. On the other hand, excessive addition causes precipitation as an undissolved precipitate during heating before hot rolling, thereby inhibiting toughness. For this reason, the upper limit of the Nb content is set to 0.20%. When Nb is added, the preferable range of Nb content is 0.03% to 0.10%.
- Ti is an element that forms oxides, nitrides, and sulfides in a very small amount, and solidifies the steel and refines the crystal grains of the high-temperature heating structure. Further, like V and Nb, Ti also has a property of substituting for a part of chromium in the chromium nitride. When Ti is contained in an amount of 0.003% or more, Ti precipitates are formed. On the other hand, when Ti is contained in the duplex stainless steel exceeding 0.05%, coarse TiN is generated and the toughness of the steel is inhibited. For this reason, the upper limit of the Ti content is set to 0.05%. A preferable content of Ti is 0.005 to 0.020%.
- B 0.0050% or less
- Mg 0.0030% or less
- REM 0.10% or less.
- B, Mg, and REM to be contained as necessary are limited as follows.
- B, Mg, and REM are all elements that improve the hot workability of steel, and one or more of them are added for that purpose.
- the upper limit of the content was defined as follows.
- the upper limit of the amount of B is 0.0050%.
- the upper limit of the amount of Mg is 0.0030%.
- the upper limit of the amount of REM is 0.10%.
- the preferred contents are B: 0.0005 to 0.0030%, Mg: 0.0001 to 0.0015%, and REM: 0.005 to 0.05%, respectively.
- REM is the total content of lanthanoid rare earth elements such as La and Ce.
- the hot productivity of the alloy-saving duplex stainless steel containing Sn can be remarkably improved.
- the fracture drawing value at 1000 ° C. is 70% or more.
- the stainless steel slab means steel in a state after casting and before being subjected to processing such as hot working or forging, and the stainless steel material means that the slab is processed by various methods. It means a steel slab, a hot rolled steel plate, a cold rolled steel plate, a steel wire, a steel pipe, etc.
- Stainless steel means all forms of steel such as slabs and steel materials. The above processing includes hot and cold processing.
- the C content is limited to 0.03% or less.
- C is contained exceeding 0.03%, Cr carbide is generated during hot rolling, and corrosion resistance and toughness deteriorate.
- Si is added at 0.05% or more for deoxidation. However, when Si exceeds 1.0%, toughness deteriorates. Therefore, the upper limit of Si content is limited to 1.0%. A preferable range of the amount of Si is 0.2 to 0.7%.
- Mn has the effect of increasing the austenite phase and improving toughness. Further, since Mn has an effect of suppressing the precipitation of nitride, it is preferable to positively add Mn to the steel material of this embodiment. 0.1% or more of Mn is added for the toughness of the base metal and the weld. However, when Mn is added exceeding 4.0%, corrosion resistance and toughness deteriorate. Therefore, the upper limit of the amount of Mn is limited to 4.0%.
- the Mn content is preferably 1.0 to 3.5%, more preferably 2.0 to 3.0%.
- P P is an element inevitably mixed from the raw material, and the P content is limited to 0.05% or less in order to deteriorate hot workability and toughness.
- the amount of P is preferably 0.03% or less.
- S is an element that is inevitably mixed from the raw material, and also degrades hot workability, toughness, and corrosion resistance, so the S amount is limited to 0.0010% or less. Moreover, reducing the amount of S to less than 0.0001% increases the cost for desulfurization refining. For this reason, the S content is determined to be 0.0001 to 0.0010%. The amount of S is preferably 0.0002 to 0.0006%.
- ⁇ Cr is contained 23.0% or more in order to ensure basic corrosion resistance.
- the Cr content is set to 23.0% or more and 28.0% or less.
- a preferable Cr content is 24.0 to 27.5%.
- Ni stabilizes the austenite structure and improves corrosion resistance and toughness against various acids. Furthermore, the deterioration of hot workability due to the addition of Sn and Cu is suppressed. For this reason, 2.0% or more of Ni is contained. By increasing the Ni content, the nitride precipitation temperature can be lowered. On the other hand, since Ni is an expensive alloy, the amount of Ni is limited to 6.0% or less. The Ni content is preferably 2.5 to 5.5%, more preferably 3.0 to 5.0%.
- Co is an element effective for enhancing the toughness and corrosion resistance of steel, and is an element that suppresses the decrease in hot workability due to the addition of Sn and Cu, and is desirably contained together with Ni. Moreover, when adding, it is preferable to contain Co 0.1% or more. When Co is contained exceeding 1.0%, Co is an expensive element, so that an effect corresponding to the cost cannot be exhibited. For this reason, the upper limit of the amount of Co is set to 1.0%. The preferred Co content when added is 0.1 to 0.5%.
- Non-Patent Document 1 Ni has the effect of increasing the solid solubility of Cu and suppressing the generation of a liquid phase having a low melting point due to the addition of Cu and Sn.
- Co is an element of the Ni family. For this reason, it is thought that the fall of the hot workability by Cu and Sn is suppressed by making the sum of content of Ni and Co high.
- the present inventors arranged the hot workability of the steel targeted in the present embodiment by the sum of the contents of Ni and Co, when the total amount of Ni and Co is less than 2.5%, the steel material It was understood that the ear cracking property of was increased. For this reason, the range of Ni + Co was set to 2.5% or more.
- Cu is an element that enhances the corrosion resistance of stainless steel to acids, and has the effect of improving toughness.
- 0.2% or more of Cu is contained together with 0.01% or more of Sn.
- ⁇ Cu precipitates exceeding the solid solubility during hot rolling, and embrittlement occurs.
- the upper limit of the amount of Cu was made into 3.0%.
- a preferable content when Cu is contained is 0.5 to 2.0%.
- Sn is contained in order to improve the corrosion resistance of the steel of this embodiment. Therefore, it is necessary to contain at least 0.01% Sn. Furthermore, it is preferable to contain 0.02% or more of Sn.
- Sn is an element that hinders the hot productivity of steel.
- the interface between the ferrite phase and the austenite phase particularly at 900 ° C. or less. Reduce hot strength. The degree of the reduction depends on the contents of S, Ca, and O. However, even if other restrictions in this embodiment are added, if Sn is contained in excess of 0.2%, the hot productivity decreases. Therefore, the upper limit of the Sn content is set to 0.2%.
- N is an effective element that improves the strength and corrosion resistance by dissolving in the austenite phase.
- 0.20% or more of N is contained. Increasing the amount of N makes it possible to reduce Ni. Therefore, N is an element to be actively added.
- the upper limit of the N content needs to be limited within the limit of the solid solution of N.
- the solid solubility limit of N increases depending on the Cr and Mn contents. In the steel of this embodiment, when N is contained in excess of 0.30%, Cr nitride is precipitated to inhibit toughness and corrosion resistance, and hot productivity is inhibited. For this reason, the upper limit of N content was 0.30%.
- a preferable N content is 0.20 to 0.28%.
- Al is a deoxidizing element of steel, and if necessary, Al is contained together with 0.05% or more of Si in order to reduce oxygen in the steel. In the Sn-containing steel, the reduction of the oxygen amount is essential to ensure hot productivity, and for this purpose, it is necessary to contain 0.003% or more of Al as necessary.
- Al is an element having a relatively large affinity with N, and if added excessively, AlN is generated and inhibits the toughness of stainless steel. The degree depends on the N content, but when Al exceeds 0.05%, the toughness is significantly lowered. For this reason, the upper limit of the Al content is set to 0.05%.
- the amount of Al is preferably 0.04% or less.
- Ca is an important element for the hot manufacturability of steel, and it is necessary to contain Ca in order to fix O and S in the steel as inclusions and improve the hot manufacturability. .
- 0.0010% or more of Ca is contained for that purpose.
- excessive addition reduces pitting corrosion resistance. Therefore, the upper limit of the Ca content is set to 0.0040%.
- the ratio Ca / O of the content of O and Ca is an important component index for improving the hot manufacturability and corrosion resistance of the steel of this embodiment.
- the lower limit of Ca / O is limited.
- the hot ductility of the Sn-containing steel decreases particularly at a temperature of 900 ° C. or less.
- the hot ductility at 1000 ° C. is also lowered, and the hot productivity is greatly impaired.
- Ca / O is limited to 0.3 or more.
- Ca / O is preferably 0.4 to 0.8.
- O is an inevitable impurity, and its upper limit is not particularly defined, but is an important element constituting an oxide that is representative of non-metallic inclusions. Controlling the composition of the oxide is very important for improving hot manufacturability. In addition, when a coarse cluster-like oxide is generated, it causes surface defects. For this reason, it is necessary to restrict
- the O content is limited by setting the ratio of the Ca content and the O content to 0.3 or more.
- the upper limit of the O content is preferably 0.005% or less.
- Mo is a very effective element that additionally increases the corrosion resistance of stainless steel, and can be contained as necessary. In order to improve the corrosion resistance, it is preferable to contain 0.2% or more of Mo.
- Mo is an expensive element.
- the upper limit of the Mo content is set to 2.0% from the viewpoint of suppressing the alloy cost.
- W is an element that additionally improves the corrosion resistance of stainless steel, and can be added as necessary. In the steel of this embodiment, the upper limit of the W content is set to 1.0% for the purpose of improving the corrosion resistance. A preferable W content is 0.1 to 0.8%.
- V 0.05 to 0.5%
- Nb 0.01 to 0.15%
- Ti 0.003 to 0.05%.
- V, Nb, and Ti can be added as necessary, and when contained in a very small amount, the corrosion resistance tends to be improved.
- V The nitrides and carbides formed by V are generated during hot working and cooling of the steel material, and have the effect of enhancing the corrosion resistance. Although sufficient confirmation has not been made for this reason, there is a possibility of suppressing the generation rate of chromium nitride at 700 ° C. or lower.
- V content is preferably in the range of 0.1 to 0.3%.
- Nitrides and carbides formed by Nb are generated during the hot working and cooling of the steel material, and have the effect of increasing the corrosion resistance. Although sufficient confirmation has not been made for this reason, there is a possibility of suppressing the generation rate of chromium nitride at 700 ° C. or lower. In order to improve the corrosion resistance, it is desirable to contain 0.01% or more of Nb. On the other hand, excessive addition causes precipitation as an undissolved precipitate during heating before hot rolling, thereby inhibiting toughness. For this reason, the upper limit of the Nb content is set to 0.15%. When Nb is added, the preferable range of Nb content is 0.03% to 0.10%.
- Ti is an element that forms oxides, nitrides, and sulfides in a very small amount, and solidifies the steel and refines the crystal grains of the high-temperature heating structure. Further, like V and Nb, Ti also has a property of substituting for a part of chromium in the chromium nitride. When Ti is contained in an amount of 0.003% or more, Ti precipitates are formed. On the other hand, when Ti is contained in the duplex stainless steel exceeding 0.05%, coarse TiN is generated and the toughness of the steel is inhibited. For this reason, the upper limit of the Ti content is set to 0.05%. A preferable content of Ti is 0.005 to 0.020%.
- B 0.0050% or less
- Mg 0.0030% or less
- REM 0.10% or less.
- B, Mg, and REM to be contained as necessary are limited as follows.
- B, Mg, and REM are all elements that improve the hot workability of steel, and it is desirable to add one or more of them for that purpose.
- the upper limit of the content was defined as follows.
- the upper limit of the amount of B is 0.0050%.
- the upper limit of the amount of Mg is 0.0030%.
- the upper limit of the amount of REM is 0.10%.
- the preferred contents are B: 0.0005 to 0.0030%, Mg: 0.0001 to 0.0015%, and REM: 0.005 to 0.05%, respectively.
- REM is the total content of lanthanoid rare earth elements such as La and Ce.
- the hot productivity of general-purpose duplex stainless steel containing Sn can be remarkably improved.
- the fracture drawing value at 1000 ° C. is 70% or more.
- Example 1 Examples of alloy-saving duplex stainless steel will be described below.
- Tables 1 to 4 show the chemical compositions of the test steels. The balance other than the components listed in Table 1 is Fe and inevitable impurity elements. In addition, regarding the components shown in Tables 1 to 4, the portion where the content is not described indicates an impurity level.
- REM means a lanthanoid rare earth element, and the content of REM indicates the total of these elements. A numerical value with an underline in the table indicates that it is outside the range defined in the first embodiment.
- a slab having a thickness of 100 mm was used, and the fracture drawing value was evaluated. Evaluation was performed as follows. First, the parallel part of an 8 mm ⁇ round bar was heated to 1200 ° C. using high frequency. Next, the temperature was lowered to a temperature at which a break test was performed (1000 ° C.). At that temperature, the film was pulled and broken at a speed of 20 mm / second to obtain the shrinkage ratio of the cross section. A steel with a fracture drawing value of 70% or more is evaluated as A (good), a steel with a drawing value of 60 to less than 70% is evaluated as B (fair), and a steel with a drawing value of less than 60% is C (bad). The results are shown in Tables 5 and 6.
- Hot rolling was performed as follows. It was heated to a predetermined temperature of 1150 to 1250 ° C., and then hot-rolled by the two-stage rolling mill in the laboratory under the following conditions. First, the reduction was repeated to adjust the plate thickness to 25 mm. Subsequently, finish rolling was performed from 1000 ° C., final finish rolling was performed at 900 ° C., and the steel sheet was rolled to a final plate thickness of 12 mm and a plate width of 120 mm to obtain a hot-rolled steel plate.
- the maximum value of the ear crack generated in the left and right ears of the obtained hot rolled steel sheet was measured, and the sum of the maximum values of the left and right ear cracks was obtained.
- Steel with an ear crack sum of less than 5 mm is evaluated as A (good)
- steel with an ear crack sum of 5 to 10 mm is evaluated as B (fair)
- steel with an ear crack sum of more than 10 mm is evaluated as C ( The results are shown in Tables 5 and 6.
- solution heat treatment was applied to this steel sheet as follows.
- the steel plate was inserted into a heat treatment furnace set at 1000 ° C., and a soaking time of 5 minutes was taken.
- the steel plate was then extracted and then water cooled to room temperature.
- the corrosion resistance of the steel sheet was evaluated by the corrosion rate in sulfuric acid.
- the corrosion rate in sulfuric acid was measured as follows. A 6-hour immersion test was performed on a test piece having a thickness of 3 mm, a width of 25 mm, and a length of 25 mm in boiling 5% sulfuric acid. The weight before and after immersion was measured, and the rate of weight reduction was determined.
- a steel having a corrosion rate in sulfuric acid of less than 0.3 g / m 2 ⁇ hr is evaluated as A (good), and a steel having a corrosion rate in sulfuric acid of 0.3 to 1 g / m 2 ⁇ hr as B (fair) Evaluation was made, and steels having a corrosion rate in sulfuric acid of 1 g / m 2 ⁇ hr or more were evaluated as C (bad), and the evaluation results are shown in Tables 5 and 6.
- Impact characteristics were measured using Charpy specimens taken long in the width direction. A full size 2 mm V notch was processed in the rolling direction to produce a test piece. The test was performed at ⁇ 20 ° C. using two test pieces each, and the impact characteristics were evaluated by the average value of the obtained impact values. Impact value and evaluate the 100 J / cm 2 than the steel and A (good), the impact value and evaluate the 50 ⁇ 100J / cm 2 steel and B (fair), impact value of 50 J / cm 2 less than the steel C (bad) was evaluated, and the evaluation results are shown in Tables 5 and 6.
- Tables 7 to 10 show the chemical compositions of the test steels. The balance of the components described in Tables 7 to 10 is Fe and inevitable impurity elements. In addition, regarding the components shown in Tables 7 to 10, the portion where the content is not described indicates an impurity level.
- REM means a lanthanoid rare earth element, and the content of REM indicates the total of these elements. A numerical value with an underline in the table indicates that it is outside the range defined in the second embodiment.
- solution heat treatment was applied to this steel sheet as follows.
- the steel plate was inserted into a heat treatment furnace set at 1050 ° C., and a soaking time of 5 minutes was taken.
- the steel plate was then extracted and then water cooled to room temperature.
- the corrosion resistance of the steel sheet was evaluated by the corrosion rate in sulfuric acid.
- the corrosion rate in sulfuric acid was measured as follows. A test piece having a thickness of 3 mm, a width of 25 mm, and a length of 25 mm was subjected to a 6-hour immersion test in sulfuric acid containing 2000 ppm of Cl ions, having a concentration of 15%, and a temperature of 40 ° C. The weight before and after immersion was measured, and the rate of weight reduction was determined. A steel having a corrosion rate in sulfuric acid of less than 0.1 g / m 2 ⁇ hr is evaluated as A (good), and a steel having a corrosion rate in sulfuric acid of 0.1 to 0.3 g / m 2 ⁇ hr is B (fair). The steel having a corrosion rate in sulfuric acid exceeding 0.3 g / m 2 ⁇ hr was evaluated as C (bad), and the evaluation results are shown in Tables 11 and 12.
- the general-purpose duplex stainless steel Nos. 2-1 to 2-23 satisfying the conditions of the second embodiment have good hot manufacturability, corrosion resistance and impact properties.
- steel Nos. 2-A to 2-K and 2-M to 2-T that do not satisfy the conditions of the second embodiment are inferior in any of hot manufacturability, corrosion resistance, and impact characteristics.
- Comparative Example 2-L satisfies the characteristics but is inferior in cost because it contains a large amount of Co.
- Comparative Example 2-U is S31803 steel, which has good hot manufacturability, corrosion resistance, and manufacturability. However, the contents of Ni and Mo are high, and the cost of the second embodiment is inferior.
- duplex stainless steel material can be used for seawater desalination equipment, tanks for transport ships, various containers, etc., and has a great industrial contribution.
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Abstract
Description
本願は、2011年10月21日に日本に出願された特願2011-231352号、及び2011年12月6日に日本に出願された特願2011-266351号に基づき優先権を主張し、その内容をここに援用する。
(1)質量%で、C:0.03%以下、Si:0.05~1.0%、Mn:0.1~7.0%、P:0.05%以下、S:0.0001~0.0010%、Ni:0.5~5.0%、Cr:18.0~25.0%、N:0.10~0.30%、Al:0.05%以下、Ca:0.0010~0.0040%、及びSn:0.01~0.2%を含有し、残部がFeおよび不可避的不純物からなり、CaとOの含有量の比率Ca/Oが0.3~1.0であり、(1)式で示す孔食指数PIが30未満であることを特徴とする二相ステンレス鋼。
PI=Cr+3.3Mo+16N (1)
(式(1)中の元素記号は、その元素の含有量を示す。)
(2)更に、Mo:1.5%以下、Cu:2.0%以下、W:1.0%以下、及びCo:2.0%以下、から選ばれる1種以上を含有することを特徴とする(1)に記載の二相ステンレス鋼。
(3)更に、V:0.05~0.5%、Nb:0.01~0.20%、及びTi:0.003~0.05%、から選ばれる1種以上を含有することを特徴とする(1)または(2)に記載の二相ステンレス鋼。
(4)更に、B:0.0050%以下、Mg:0.0030%以下、及びREM:0.10%以下、から選ばれる1種以上を含有することを特徴とする(1)乃至(3)のいずれか一項に記載の二相ステンレス鋼。
(5)質量%で、C:0.03%以下、Si:0.05~1.0%、Mn:0.1~4.0%、P:0.05%以下、S:0.0001~0.0010%、Cr:23.0~28.0%、Ni:2.0~6.0%、Co:0~1.0%、Cu:0.2~3.0%、Sn:0.01~0.2%、N:0.20~0.30%、Al:0.05%以下、及びCa:0.0010~0.0040%を含有し、残部がFeおよび不可避的不純物からなり、Ni+Coが2.5%以上であり、CaとOの含有量の比率Ca/Oが0.3~1.0であり、(1)式で示すPIが30以上、40未満であることを特徴とする二相ステンレス鋼。
PI=Cr+3.3Mo+16N (1)
(式(1)中の元素記号は、その元素の含有量を示す。)
(6)更に、Mo:2.0%以下、及びW:1.0%以下のうち、いずれか一方又は両方を含有することを特徴とする(5)に記載の二相ステンレス鋼。
(7)更に、V:0.05~0.5%、Nb:0.01~0.15%、及びTi:0.003~0.05%、から選ばれる1種以上を含有することを特徴とする(5)または(6)に記載の二相ステンレス鋼。
(8)更に、B:0.0050%以下、Mg:0.0030%以下、及びREM:0.10%以下、から選ばれる1種以上を含有することを特徴とする(5)乃至(7)のいずれか一項に記載の二相ステンレス鋼。
(9)(1)乃至(8)の何れか一項に記載の組成を有し、1000℃における破断絞り値が70%以上であることを特徴とする二相ステンレス鋼鋳片。
(10)(9)に記載の二相ステンレス鋼鋳片を熱間加工して製造されたことを特徴とする二相ステンレス鋼鋼材。
以下に、本発明の二相ステンレス鋼の第1の態様(省合金型二相ステンレス鋼)の限定理由について説明する。なお、各成分の含有量は質量%を示す。
鋳片の段階では、1000℃における破断絞り値が70%以上となる。また、この鋳片に熱間加工を含む加工を施すことによって、歩留まり良くかつ表面疵の少ない二相ステンレス鋼鋼材を得ることが可能となる。
以下に、本発明の二相ステンレス鋼の第2の態様(汎用型二相ステンレス鋼)の限定理由について説明する。なお、各成分の含有量は質量%を示す。
Moは、ステンレス鋼の耐食性を付加的に高める非常に有効な元素であり、必要に応じて含有させることができる。耐食性改善のためには0.2%以上のMoを含有させることが好ましい。一方でMoは、高価な元素であり、本実施形態の鋼では、合金コストを抑制する観点より、Moの含有量の上限を2.0%とする。
Wは、Moと同様にステンレス鋼の耐食性を付加的に向上させる元素であり、必要に応じて添加することが出来る。本実施形態の鋼において、耐食性を高める目的のためには、W含有量の上限を1.0%とする。好ましいW含有量は0.1~0.8%である。
鋳片の段階では、1000℃における破断絞り値が70%以上となる。また、この鋳片に熱間加工を含む加工を施すことによって、歩留まり良くかつ表面疵の少ない二相ステンレス鋼鋼材を得ることが可能となる。
以下に省合金型二相ステンレス鋼の実施例について記載する。表1~4に供試鋼の化学組成を示す。なお、表1に記載されている成分以外の残部は、Feおよび不可避的不純物元素である。また、表1~4に示した成分について、含有量が記載されていない部分は不純物レベルであることを示す。REMは、ランタノイド系希土類元素を意味し、REMの含有量はそれら元素の合計を示している。表中の下線を付した数値は、第1の実施形態で規定された範囲外であることを示す。
鋳片を熱間鍛造して60mm厚の鋼片とし、これを熱間圧延素材とした。熱間圧延を以下のように行った。1150~1250℃の所定の温度に加熱し、次いで実験室の2段圧延機により、以下の条件で熱間圧延を実施した。まず圧下を繰り返し、板厚を25mmに調整した。次いで、1000℃から仕上げ圧延を行い、900℃で最終仕上げ圧延を実施し、最終板厚が12mm、板幅が120mmになるように圧延して熱間圧延鋼板を得た。得られた熱間圧延鋼板の左右の耳部に発生した耳割れの最大値を測定し、左右の耳割れの最大値の和を求めた。この耳割れの和が5mm未満の鋼をA(good)と評価し、耳割れの和が5~10mmの鋼をB(fair)と評価し、耳割れの和が10mm超の鋼をC(bad)と評価して、結果を表5,6に示した。
硫酸中の腐食速度は、以下のように測定した。3mm厚×25mm幅×25mm長の試験片に対して、沸騰した5%の硫酸中で6hの浸漬試験を実施した。浸漬前後の重量を測定し、重量の減少速度を求めた。硫酸中の腐食速度が0.3g/m2・hr未満の鋼をA(good)と評価し、硫酸中の腐食速度が0.3~1g/m2・hrの鋼をB(fair)と評価し、硫酸中の腐食速度が1g/m2・hr以上の鋼をC(bad)と評価して、評価結果を表5,6に示した。
以下に汎用型二相ステンレス鋼の実施例について記載する。表7~10に供試鋼の化学組成を示す。なお表7~10に記載されている成分の残部は、Feおよび不可避的不純物元素である。また表7~10に示した成分について、含有量が記載されていない部分は不純物レベルであることを示す。REMは、ランタノイド系希土類元素を意味し、REMの含有量はそれら元素の合計を示している。表中の下線を付した数値は、第2の実施形態で規定された範囲外であることを示す。
硫酸中の腐食速度は、以下のように測定した。3mm厚×25mm幅×25mm長の試験片に対して、2000ppmのClイオンを含み、濃度が15%、温度が40℃の硫酸中で6hの浸漬試験を実施した。浸漬前後の重量を測定し、重量の減少速度を求めた。硫酸中の腐食速度が0.1g/m2・hr未満の鋼をA(good)と評価し、硫酸中の腐食速度が0.1~0.3g/m2・hrの鋼をB(fair)と評価し、硫酸中の腐食速度が0.3g/m2・hr超の鋼をC(bad)と評価して、評価結果を表11,12に示した。
Claims (10)
- 質量%で、
C:0.03%以下、
Si:0.05~1.0%、
Mn:0.1~7.0%、
P:0.05%以下、
S:0.0001~0.0010%、
Ni:0.5~5.0%、
Cr:18.0~25.0%、
N:0.10~0.30%、
Al:0.05%以下、
Ca:0.0010~0.0040%、及び
Sn:0.01~0.2%を含有し、
残部がFeおよび不可避的不純物からなり、
CaとOの含有量の比率Ca/Oが0.3~1.0であり、
(1)式で示す孔食指数PIが30未満であることを特徴とする二相ステンレス鋼。
PI=Cr+3.3Mo+16N (1)
(式(1)中の元素記号は、その元素の含有量を示す。) - 更に、
Mo:1.5%以下、
Cu:2.0%以下、
W:1.0%以下、及び
Co:2.0%以下から選ばれる1種以上を含有することを特徴とする請求項1に記載の二相ステンレス鋼。 - 更に、
V:0.05~0.5%、
Nb:0.01~0.20%、及び
Ti:0.003~0.05%から選ばれる1種以上を含有することを特徴とする請求項1又は請求項2に記載の二相ステンレス鋼。 - 更に、
B:0.0050%以下、
Mg:0.0030%以下、及び
REM:0.10%以下から選ばれる1種以上を含有することを特徴とする請求項1乃至請求項3のいずれか一項に記載の二相ステンレス鋼。 - 質量%で、
C:0.03%以下、
Si:0.05~1.0%、
Mn:0.1~4.0%、
P:0.05%以下、
S:0.0001~0.0010%、
Cr:23.0~28.0%、
Ni:2.0~6.0%、
Co:0~1.0%、
Cu:0.2~3.0%、
Sn:0.01~0.2%、
N:0.20~0.30%、
Al:0.05%以下、及び
Ca:0.0010~0.0040%を含有し、
残部がFeおよび不可避的不純物からなり、
Ni+Coが2.5%以上であり、CaとOの含有量の比率Ca/Oが0.3~1.0であり、
(1)式で示すPIが30以上、40未満であることを特徴とする二相ステンレス鋼。
PI=Cr+3.3Mo+16N (1)
(式(1)中の元素記号は、その元素の含有量を示す。) - 更に、
Mo:2.0%以下、及び
W:1.0%以下のうち、いずれか一方又は両方を含有することを特徴とする請求項5に記載の二相ステンレス鋼。 - 更に、
V:0.05~0.5%、
Nb:0.01~0.15%、及び
Ti:0.003~0.05%、から選ばれる1種以上を含有することを特徴とする請求項5または請求項6に記載の二相ステンレス鋼。 - 更に、
B:0.0050%以下、
Mg:0.0030%以下、及び
REM:0.10%以下、から選ばれる1種以上を含有することを特徴とする請求項5乃至請求項7のいずれか一項に記載の二相ステンレス鋼。 - 請求項1乃至請求項8の何れか一項に記載の組成を有し、1000℃における破断絞り値が70%以上であることを特徴とする二相ステンレス鋼鋳片。
- 請求項9に記載の二相ステンレス鋼鋳片を熱間加工して製造されたことを特徴とする二相ステンレス鋼鋼材。
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US14/347,437 US20140255244A1 (en) | 2011-10-21 | 2012-10-17 | Duplex stainless steel, duplex stainless steel slab, and duplex stainless steel material |
ES12842430T ES2768088T3 (es) | 2011-10-21 | 2012-10-17 | Acero inoxidable dúplex, plancha de acero inoxidable dúplex y material de acero inoxidable dúplex |
KR1020147009392A KR101632516B1 (ko) | 2011-10-21 | 2012-10-17 | 2상 스테인리스강, 2상 스테인리스강 주조편 및 2상 스테인리스강 강재 |
CN201280050356.5A CN103857816B (zh) | 2011-10-21 | 2012-10-17 | 双相不锈钢、双相不锈钢铸坯以及双相不锈钢钢材 |
KR1020167005157A KR101648694B1 (ko) | 2011-10-21 | 2012-10-17 | 2상 스테인리스강, 2상 스테인리스강 주조편 및 2상 스테인리스강 강재 |
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ZA2014/02169A ZA201402169B (en) | 2011-10-21 | 2014-03-24 | Duplex stainless steel, duplex stainless steel slab, and duplex stainless steel material |
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JP2011-231352 | 2011-10-21 | ||
JP2011-266351 | 2011-12-06 | ||
JP2011266351A JP5329634B2 (ja) | 2011-12-06 | 2011-12-06 | 二相ステンレス鋼、二相ステンレス鋼鋳片、および、二相ステンレス鋼鋼材 |
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CN103498355B (zh) * | 2013-10-14 | 2015-12-09 | 无锡通用钢绳有限公司 | 一种耐腐蚀钢丝绳 |
WO2015091366A1 (en) * | 2013-12-20 | 2015-06-25 | Höganäs Ab (Publ) | A method for producing a sintered component and a sintered component |
CN104152818A (zh) * | 2014-08-12 | 2014-11-19 | 昆明理工大学 | 一种双相不锈钢及其制备方法 |
CN105018850A (zh) * | 2014-08-21 | 2015-11-04 | 太仓钧浩自行车科技有限公司 | 一种低钨钼耐热耐腐蚀不锈钢及其制备方法 |
WO2016074057A1 (pt) * | 2014-11-12 | 2016-05-19 | Companhia Siderúrgica Nacional | Produto laminado a quente em aços longos e uso do mesmo |
KR101647210B1 (ko) | 2014-12-11 | 2016-08-10 | 주식회사 포스코 | 개재물이 저감된 듀플렉스 스테인리스 강판의 제조 방법 |
FI128294B (en) * | 2015-01-27 | 2020-02-28 | Outokumpu Oy | A process for preparing a sheet material for an electrochemical process |
WO2016152622A1 (ja) * | 2015-03-26 | 2016-09-29 | 新日鐵住金ステンレス株式会社 | せん断端面の耐食性に優れるフェライト・オーステナイト系ステンレス鋼板 |
CN105349906B (zh) * | 2015-11-02 | 2018-08-10 | 四川维珍高新材料有限公司 | 超级双相不锈钢卧螺离心分离机转鼓离心浇铸方法 |
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KR102160735B1 (ko) * | 2018-08-13 | 2020-09-28 | 주식회사 포스코 | 강도가 향상된 오스테나이트계 스테인리스강 |
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EP2770076B1 (en) | 2019-12-04 |
EP2770076A1 (en) | 2014-08-27 |
KR20160028514A (ko) | 2016-03-11 |
TWI460293B (zh) | 2014-11-11 |
EP2770076A4 (en) | 2016-03-09 |
CN103857816A (zh) | 2014-06-11 |
KR101648694B1 (ko) | 2016-08-16 |
CN103857816B (zh) | 2017-02-15 |
KR101632516B1 (ko) | 2016-06-21 |
ES2768088T3 (es) | 2020-06-19 |
ZA201402169B (en) | 2015-04-29 |
KR20140064941A (ko) | 2014-05-28 |
US20160340764A1 (en) | 2016-11-24 |
US20140255244A1 (en) | 2014-09-11 |
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