WO2016136839A1 - Acier résistant à la chaleur à base de ferrite et procédé pour le fabriquer - Google Patents

Acier résistant à la chaleur à base de ferrite et procédé pour le fabriquer Download PDF

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WO2016136839A1
WO2016136839A1 PCT/JP2016/055523 JP2016055523W WO2016136839A1 WO 2016136839 A1 WO2016136839 A1 WO 2016136839A1 JP 2016055523 W JP2016055523 W JP 2016055523W WO 2016136839 A1 WO2016136839 A1 WO 2016136839A1
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resistant steel
heat resistant
ferritic heat
steel
nitrogen
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PCT/JP2016/055523
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English (en)
Japanese (ja)
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英治 中島
昌寿 光原
重人 山崎
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国立大学法人九州大学
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    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/30—Ferrous alloys, e.g. steel alloys containing chromium with cobalt
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D23/00—Casting processes not provided for in groups B22D1/00 - B22D21/00
    • B22D23/06—Melting-down metal, e.g. metal particles, in the mould
    • B22D23/10—Electroslag casting

Definitions

  • the present invention relates to a high-strength ferritic heat-resistant steel for structural members constituting high-temperature equipment such as power generation equipment or chemical plant equipment used in a high-temperature / high-pressure environment and a method for producing the same.
  • the upper limit of the usable temperature of the high chromium ferritic heat resistant steel having a conventional tempered lath martensite structure is 600 ° C., and austenitic heat resistant steel and nickel-based heat resistant alloy are used in a temperature range higher than that.
  • Conventional high chromium ferritic heat resistant steels are mainly strengthened by carbides.
  • heat-resistant steel that was developed about 30 years ago, put into practical use for about 20 years, and has been widely used up to now is carbon steel (Grade92 steel (fire) containing chromium (Cr) and tungsten (W). It is also called STPA29). Since this carbon steel contains carbon, carbides are precipitated, and this carbide contributes to strengthening of the steel. However, as a weak point of this carbon steel, the main strengthening phase carbide (also called M23C6 type carbide) contains chromium (Cr) that contributes to improving oxidation resistance and W that contributes to solid solution strengthening. Oxidation resistance and solid solution strengthening are impaired by the precipitation of M23C6 type carbide. Furthermore, since the thermally unstable carbides are coarsened early and lose their strengthening ability at 600 ° C. or higher, the upper limit of the use temperature of the conventional high chromium ferritic heat resistant steel is limited to 600 ° C.
  • a phase that is more thermally stable than carbide As the strengthening phase of high chromium ferritic heat resistant steel, it is possible to increase the applicable temperature range of the same material.
  • an intermetallic compound such as a Laves phase (Laves phase) which is a stable phase at a high temperature can be mentioned.
  • austenitic heat-resistant steels and nickel-based heat-resistant alloys have been developed with an intermetallic compound as a strengthening phase.
  • some high-chromium ferritic heat-resistant steels such as ferritic single-phase steels that do not have a solid phase transformation point even at high temperatures, have been strengthened by intermetallic compounds. It becomes.
  • the amount of these elements added to the conventional high chromium ferritic heat resistant steel is limited to about 2% at maximum for the purpose of solid solution strengthening.
  • elements that stabilize the austenite phase at high temperatures include carbon, nitrogen, nickel, manganese, copper, and cobalt.
  • carbon when carbon is increased, a large amount of carbides including chromium, tungsten, and molybdenum are precipitated, so that not only the oxidation resistance due to solid solution chromium is lowered but also the amount of precipitation of intermetallic compounds is reduced.
  • nickel or manganese is increased, creep strength is lowered, and when copper is increased, red brittleness becomes a problem in addition to creep strength.
  • Cobalt is an element that can stabilize the austenite phase without lowering the creep strength, but is an expensive element and is not suitable for adding a large amount.
  • Austenitic heat-resistant steels and nickel-based heat-resistant alloys have sufficient heat resistance, but they are more expensive than high-chromium ferritic heat-resistant steels because they contain a lot of rare elements, and are essentially thermally expanded due to the crystal structure of the material. The coefficient is large. Therefore, as a material for a thermal power plant that frequently starts and stops, damage due to thermal fatigue is inevitable. On the other hand, the crystal structure of ferritic heat-resistant steel has a small coefficient of thermal expansion, so if it can be given sufficient heat resistance and strength, it is optimal as a material for thermal power plants operating at 600 ° C or higher. Become. *
  • nitrides or carbonitrides that precipitate when high nitrogen is added instead of carbides (M 23 C 6 type carbides) used as the strengthening phase. It is planned to strengthen.
  • the nitrogen content is 0.10 to 0.50% by weight and the tungsten content is 0.50 to 3.00% by weight.
  • a ferritic heat resistant steel for example, Patent Document 1.
  • ferritic heat resistant steels having a nitrogen content of 0.10 to 0.50 wt% and a tungsten content of 0.20 to 1.50 wt% (for example, Patent Documents 2 and 3).
  • ferritic heat resistant steel in which the nitrogen content is 0.50 to 2.0% by weight and the tungsten content is 0.20 to 1.50% by weight for example, Patent Document 4).
  • the amount of tungsten added is at most about 3.00% by weight.
  • the amount of tungsten added is Fe 2 W. It is known that precipitation of the Laves phase impairs the solid solution strengthening of tungsten, that is, the Laves phase precipitation is known to cause weakening of the heat-resisting steel. Also has a statement to that effect.
  • tungsten itself is an element that stabilizes the ferrite phase, but on the other hand, if the added amount increases, The effect of eliminating the austenite phase region is strengthened, and as a result, the martensite structure formed by cooling of the austenite phase region is not generated, and a ferritic heat resistant steel itself composed of the martensite structure can be manufactured. Loss is a major factor.
  • the present invention has been made to solve the above-described problems, and an object of the present invention is to provide a ferritic heat resistant steel that achieves both a stable tempered lath martensite structure and high strength.
  • the present inventors added a large amount of tungsten and tempered lath martensite, which could not be achieved conventionally, by adding nitrogen, which is an element that is inexpensive and does not decrease the creep strength when added in a large amount under optimal conditions. It has been found that ferritic heat resistant steels that are compatible with structure formation can be produced.
  • the ferritic heat resistant steel disclosed in the present application is a ferritic heat resistant steel containing a martensite structure, and includes an intermetallic compound containing a nitride and a tungsten element, containing 0.1 to 2.0 wt% nitrogen element and 3.0 wt%. Contains up to 10.0% by weight of tungsten element.
  • the nitride is composed of nitride or carbonitride as required.
  • the intermetallic compound contains a tungsten element, a molybdenum element, and an iron element, and contains 0.5 to 3.0% by weight of a molybdenum element.
  • the ferritic heat-resisting steel disclosed in the present application includes, if necessary, 8.00 to 16.00 wt% chromium element, 0.2 to 2.0 wt% vanadium element, 0.01 to 1.0 wt% niobium element, and 0.5 to 3.0 wt% molybdenum element. 0.20 to 1.00% by weight of manganese element and 0.02 to 0.80% by weight of silicon element.
  • the ferritic heat resistant steel disclosed in the present application contains 2.0 to 6.0% by weight of cobalt element as required.
  • a method for producing a ferritic heat resistant steel disclosed in the present application is a ferritic heat resistant steel including a martensite structure, including a nitride and an intermetallic compound containing a tungsten element, and containing 0.1 to 2.0% by weight of nitrogen element and A method for producing a ferritic heat-resistant steel containing 3.0 to 10.0% by weight of tungsten element, in which a raw material steel containing a constituent element of the intermetallic compound is dissolved in a nitrogen-containing gas atmosphere under high pressure. To produce heat-resistant steel.
  • the ferritic heat resistant steel manufacturing method disclosed in the present application controls the amount of nitrogen contained in the ferritic heat resistant steel as necessary, and the existence ratio of the ferrite structure and martensite structure is controlled by the controlled amount of nitrogen.
  • the ferritic heat resistant steel manufactured is manufactured.
  • the manufacturing method of the ferritic heat resistant steel disclosed in the present application includes adding a cobalt element to the raw material steel as necessary, and reducing the nitrogen amount of the ferritic heat resistant steel according to the amount of the added cobalt element. And producing a ferritic heat resistant steel in which the abundance ratio of the ferrite structure and the martensite structure is controlled by the control.
  • the manufacturing method of the ferritic heat resistant steel disclosed in the present application controls the heating temperature until the austenite structure is formed in the heat treatment performed after the melting or after performing the processing as necessary after the melting.
  • a ferritic heat resistant steel in which the abundance ratio of the ferrite structure and martensite structure is controlled by the heating temperature is produced.
  • the present invention has a tempered lath martensite structure by adding nitrogen under the optimum conditions while ensuring that tungsten can be added in a larger amount than before. It provides excellent ferritic heat-resisting steels, and there are extremely large ones that contribute to industrial development.
  • FIG. 1 It is a schematic diagram of an ESR electrode, and shows the situation where a low carbon steel pipe filled with FCrN and a metal calcium wire are attached to a groove formed in a round bar made from a raw steel ingot. It is a schematic diagram of the ingot after ESR, and shows the cutting procedure and component analysis location of the ingot. It is the temperature dependence of the tensile test result of the heat-resistant steel which concerns on Example 1, and shows the result which confirmed 0.2% yield strength. As a comparative material, the values under the same test conditions of conventional steel (Tue STBA28) are also shown. The strength of the heat-resistant steel according to Example 1 in a high temperature range of 600 ° C. or higher is higher than that of the conventional steel.
  • the heat resistant steel according to Example 1 has a tendency that the creep rupture ductility increases as the creep rupture time becomes longer.
  • a left figure (a) is a low magnification image
  • a right figure (b) is a high magnification image.
  • the massive region indicated by the arrow in the left figure is a ferrite structure, and the other region is a lath martensite structure.
  • an intermetallic compound phase is observed with bright luminance
  • vanadium nitride is observed with dark luminance.
  • the result of having measured the creep rupture strength in 700 degreeC about the heat-resistant steel which concerns on Example 2, and a comparative example is shown.
  • the photograph which observed the fine structure of the heat resistant steel which concerns on Example 3, and the comparative example using the reflection electron detector of a scanning electron microscope is shown.
  • the result of having measured the creep rupture strength in 700 degreeC about the heat resistant steel which concerns on Example 3, and a comparative example is shown.
  • the result of having measured the creep rupture strength in 700 degreeC about the heat resistant steel which concerns on Example 4, and a comparative example is shown.
  • the ferritic heat resistant steel according to the present embodiment is a ferritic heat resistant steel including a martensite structure, and is a metal containing a nitride and a tungsten element. It contains an intermediate compound and contains 0.1 to 2.0% by weight of nitrogen element and 3.0 to 10.0% by weight of tungsten element.
  • a martensite structure is a very strong structure having a body-centered cubic structure, and is obtained by cooling the austenite phase formed at a high temperature state to a ferrite phase accompanied by a non-diffusion transformation. Refers to an organization.
  • the nitride is not particularly limited as long as it is a compound containing nitrogen, but is preferably composed of nitride or carbonitride from the viewpoint of increasing the strength of the heat-resistant steel.
  • the intermetallic compound is a compound containing at least a tungsten element (W), for example, a Laves phase (Fe 2 W) and the like, and as a strengthening phase for improving the strength of the ferritic heat resistant steel according to the present embodiment.
  • W tungsten element
  • Fe 2 W Laves phase
  • the ferritic heat resistant steel according to the present embodiment contains the above nitride and intermetallic compound, and the elemental composition ratio is 0.1 to 2.0 wt% nitrogen element and 3.0 to 10.0 wt% tungsten element (W ).
  • the above intermetallic compound more preferably contains tungsten element (W), molybdenum element (Mo), and iron element (Fe).
  • the ferritic heat resistant steel according to the present embodiment preferably contains 0.5 to 3.0% by weight of molybdenum element (Mo).
  • the ferritic heat resistant steel according to the present embodiment is not particularly limited with respect to other constituent elements, but for example, 8.00 to 16.00% by weight of chromium element (Cr), 0.2 to 2.0% by weight of vanadium element (V), 0.01 Contains ⁇ 1.0 wt% niobium element (Nb), 0.5 to 3.0 wt% molybdenum element (Mo), 0.20 to 1.00 wt% manganese element (Mn), and 0.02 to 0.80 wt% silicon element (Si) It is preferable.
  • the ferritic heat resistant steel according to the present embodiment preferably further contains 2.0 to 6.0% by weight of cobalt element (Co).
  • This cobalt element (Co) has a strong austenite stabilizing effect that exhibits an austenite stabilizing effect especially in a high temperature range of about 900 ° C. or higher, and a nitrogen element (N) that exhibits an austenite stabilizing effect similar to this. Since it can be substituted, the inclusion of cobalt element (Co) can suppress the content of nitrogen, which is a gas, and the ferritic heat-resistant steel can be produced under a lower pressure condition. Heat-resistant steel can be manufactured.
  • the ferritic heat resistant steel according to the present embodiment contains a certain amount of carbon element (C) including the carbonitride described above. This is because the carbon element (C) has an effect of stabilizing the austenite phase and can contribute to increasing the strength of the heat resistant steel.
  • the ferritic heat resistant steel according to the present embodiment does not require a large amount of carbon element (C) as compared with the prior art.
  • M 23 C 6 type carbide is not formed in the ferrite matrix of the heat-resistant steel. This is because when carbon is left, M 23 C 6 type carbides are formed, and the M 23 C 6 type carbides take away W (and Cr), so the tungsten element (W) introduced in large quantities is effectively used. It is because it becomes impossible.
  • the carbon element (C) content is preferably 1/8 or less of the niobium element (Nb).
  • the content of carbon element (C) is It is preferable to make it 0.125% by weight at the maximum, and when the amount of niobium is smaller, there is no need to actively reduce the content of carbon element (C), preventing excessive precipitation of M 23 C 6 type carbide
  • the carbon element (C) content is preferably 0.05% by weight at the maximum, and more preferably 0.001 to 0.05% by weight. More preferably, it can be 0.003 to 0.04% by weight, and more preferably 0.01 to 0.03% by weight.
  • cobalt element has a strong austenite stabilizing effect that exhibits an austenite stabilizing effect especially in a high temperature range of about 900 ° C. or higher, and a nitrogen element (N) that exhibits an austenite stabilizing effect similar to this. Since it can be substituted, the content of nitrogen (N), which is a gas, can be suppressed by containing cobalt element (Co), and ferritic heat-resisting steel is produced under low-pressure conditions with a lower nitrogen partial pressure. It is possible to manufacture ferritic heat-resistant steel with further reduced costs.
  • C 0.03% or less
  • Si 0.02 to 0.80%
  • Mn 0.20 to 1.00%
  • Cr 8.00 to 16.00%
  • V 0.2 to 2.0%
  • Nb 0.01 to 1.0%
  • W 3.0 to 10.0%
  • Mo 0.5 to 3.0%
  • Co 2.0 to 6.0%
  • the balance being Fe and P , S, O inevitable impurity element steel is dissolved in high-pressure mixed gas or nitrogen gas, and 0.1-2.0 wt% nitrogen, for example, 0.3-2.0% nitrogen is forcibly added.
  • a ferritic heat resistant steel having a tempered lath martensite structure while containing a larger amount of tungsten (W) and molybdenum (Mo) than the conventional one (high chromium ferritic heat resistant steel due to its high chromium ratio) And its manufacturing method.
  • each alloy element in the ferritic heat resistant steel is not particularly limited to the above, but the reasons for limiting the component ranges given as an example are as follows.
  • carbon (C) is required for maintaining the strength of steel, but in this embodiment, chromium (C) is precipitated while depositing a trace amount of niobium carbide (NbC) that can act as a nucleus of vanadium nitride (VN) precipitation.
  • NbC niobium carbide
  • VN vanadium nitride
  • the carbon element content is suitable for containing and maintaining a high proportion of tungsten element in the heat-resistant steel.
  • Silicon (Si) is an element suitable for ensuring oxidation resistance and steam oxidation resistance, and also acts as a deoxidizer, but as the amount added increases, the creep strength decreases.
  • the blending ratio of silicon (Si) is not particularly limited, but from the viewpoint of oxidation resistance and water vapor resistance, the effect is not sufficiently exhibited if it is less than 0.02%, while the creep strength is greater than 0.80%. Since this decreases, the range can be 0.02 to 0.80%.
  • Manganese (Mn) is effective for deoxidation, and is an element that is desirably added for securing the yield strength, but the creep strength is lowered when the addition amount is increased in the same manner as silicon (Si).
  • the blending ratio is not particularly limited, but 0.20% or more is necessary for securing the yield strength, and 1.00% is desirable from the viewpoint of preventing the creep strength from being lowered. Therefore, the range should be 0.20 to 1.00%. it can.
  • Chromium (Cr) is an element suitable for imparting oxidation resistance, and is not particularly limited. However, at least 8% is required for use at 600 ° C. or higher, and when added over 16%, Even if the amount of nitrogen is increased, a sufficient martensite structure cannot be obtained and the toughness is lowered, so the range can be made 8.00 to 16.00%.
  • the nitride chromium nitride (Cr 2 N) is finely precipitated by nitrogen (N) and chromium (Cr), which can contribute to strength improvement.
  • the purpose of vanadium (V) is to improve strength by precipitation of fine vanadium nitride (VN) by reaction with nitrogen (N) and to prevent coarsening of grains during solution treatment.
  • the range of the amount of addition is not particularly limited, at least 0.2% or more is necessary for stably depositing vanadium nitride (VN). When the amount exceeds 2%, coarse vanadium nitride (VN) is formed. In order to crystallize, it can be made 0.5 to 2.0%. Similar to vanadium (V), niobium (Nb) is intended for fine precipitation. However, niobium (Nb) is preferentially bonded to carbon (C), so it is precipitated as fine niobium carbide (NbC) and nitrided.
  • Tungsten (W) has a lower limit of 3.0%, which is not less than the solid solubility limit in the ferrite matrix, in order to precipitate a sufficient amount of intermetallic compounds that are the main strengthening phase of the ferritic heat resistant steel according to the present embodiment. Since it is difficult to obtain a martensite structure with addition of 10% or more, this can be made the upper limit.
  • Molybdenum (Mo) is also a constituent element of the intermetallic compound, and 0.5% or more is added to improve the thermal stability of the intermetallic compound by compound addition with tungsten (W). Similarly, if the amount added is increased, it becomes difficult to obtain a martensite structure, so the upper limit was made 3.0%.
  • Cobalt (Co) is not necessarily added, but even if a large amount of tungsten (W) or molybdenum (Mo) is added, the austenite phase is stabilized at a high temperature to stabilize the martensite structure more stably. In order to obtain the above, 2.0% or more, more preferably 2.0 to 6.0% by weight can be added.
  • ferritic heat resistant steel according to the present embodiment as described above, by forcibly adding 0.1 to 2.0% by weight of nitrogen element, this nitrogen addition plays a role in stabilizing the austenite phase and a large amount of tungsten.
  • a ferritic heat-resisting steel characterized by having a tempered lath martensite structure while containing V is easily obtained. This is the reason for limiting the chemical component range of the ferritic heat resistant steel according to the present embodiment.
  • 0.1 to 2.0% by weight of nitrogen is added, and more preferably 0.3% by weight to 1.0% by weight exceeding the solid solubility limit in the ferrite phase.
  • a manufacturing method thereof there is a method of melting and solidifying a steel material having the above composition excluding nitrogen in a mixed gas of high pressure nitrogen and an inert gas or nitrogen gas.
  • the atmospheric pressure is set to 10 atm or more, and the nitrogen partial pressure is set to 1.0 atm or more.
  • the target material can be obtained by subjecting the steel thus manufactured to a heat treatment according to the application. Further, by adding cobalt (Co) to 2.0% by weight or more, more preferably 2.0 to 6.0% by weight, cobalt (Co) exhibits an austenite phase stabilizing action in the same manner as elemental nitrogen (N). As a result, cobalt (Co ) Is reduced, the desired heat-resistant steel can be easily manufactured under a lower pressure condition, and the manufacturing cost can be suppressed.
  • the raw steel containing the constituent elements of the intermetallic compound is dissolved in a nitrogen-containing gas atmosphere under high pressure
  • the heating temperature until the austenite structure is formed is controlled, and the ferrite structure and the controlled heating temperature are controlled by the controlled heating temperature. It is possible to produce a ferritic heat resistant steel in which the abundance ratio of the martensite structure is controlled.
  • the heating temperature after the dissolution the abundance ratio of the ferrite structure and the martensite structure is easily controlled, and a ferritic heat resistant steel having the desired abundance ratio can be easily obtained. it can.
  • the ferritic heat resistant steel manufacturing method controls the amount of nitrogen contained in the ferritic heat resistant steel in the first embodiment, and the ferrite structure and martense are controlled by the controlled amount of nitrogen. Ferritic heat-resistant steel with controlled site structure content is manufactured.
  • the abundance ratio of each structure in the ferritic heat resistant steel is, for example, 5: Control from 95 to 20:80 can be implemented.
  • the desired characteristics in the ferritic heat resistant steel are obtained when the abundance ratio of the above-described structures in the ferritic heat resistant steel is, for example, 20:80, the amount of nitrogen that can provide the abundance ratio.
  • the amount of nitrogen contained in the ferritic heat resistant steel is controlled, and the ferritic heat resistant steel in which the abundance ratio of the ferrite structure and martensite structure is controlled by the controlled amount of nitrogen is manufactured.
  • the desired ferritic heat resistant steel having the characteristics specified by the abundance ratio of each structure can be easily obtained, and the ferritic heat resistant steel having the characteristics corresponding to the application can be easily obtained.
  • the manufacturing method of the ferritic heat resistant steel according to the third embodiment is the ferritic heat resistant steel according to the second embodiment, in which cobalt element is added to the raw steel, and the ferritic heat resistant steel is added according to the amount of the added cobalt element. Is controlled by reducing the amount of nitrogen, and a ferritic heat-resistant steel in which the abundance ratio of the ferrite structure and martensite structure is controlled by the control is manufactured.
  • cobalt element can stabilize the austenite phase without lowering the creep strength
  • the addition of cobalt element suppresses the addition amount of nitrogen element that acts to stabilize the same austenite phase. Can do. From this, by adding cobalt element to the raw material steel, the amount of nitrogen in the ferritic heat resistant steel can be reduced according to the amount of the added cobalt element. Furthermore, by adding this cobalt element, it is possible to control the abundance ratio of the ferrite structure and martensite structure using the increase or decrease of the nitrogen amount in the second embodiment by using both the nitrogen element and the cobalt element. By using cobalt element, the abundance ratio of the ferrite structure and the martensite structure can be controlled under a low pressure condition with a lower nitrogen partial pressure, that is, under a simpler reaction condition.
  • cobalt element was added about the manufacturing method of the ferritic heat-resistant steel which concerns on 3rd Embodiment about said 2nd Embodiment, it is not limited to this form, It is said about said 1st Embodiment. Cobalt element can also be added, and similarly, a ferritic heat resistant steel having characteristics according to the application can be obtained more easily.
  • Example 1 As shown in Table 1 below, a raw steel ingot having a composition not containing nitrogen was prepared in advance by vacuum induction melting and processed into a round bar having a diameter of 61 mm and a length of 1110 mm. As shown in Fig. 1, a groove is cut in a round bar, and a low carbon steel pipe filled with FCrN, a nitrogen addition source, and a metal calcium wire, which is a deoxidizing material, are TIG welded to form an electrode for electroslag remelting (ESR). . Electrodes were attached to an ESR furnace with a pressurization facility and redissolved at a dissolution rate of 0.32 kg / min. The slag was 99.99% pure CaF 2 and the slag was heated and melted by passing a current of about 24V and 2.8A to melt the electrode.
  • ESR electroslag remelting
  • the droplets that passed through the slag were cooled and solidified in a water cooling chamber.
  • the inside of the melting furnace was set to a pressure of 40 atm in a nitrogen gas atmosphere, and nitrogen dissolved in the molten metal was suppressed from being vaporized during solidification. After dissolution, it was cooled to room temperature in the furnace.
  • the ingot obtained by ESR was about ⁇ 100 mm ⁇ about 400 mm, and a good solidified structure without casting defects was obtained.
  • the approximately 150mm composition unstable part at the bottom of the ingot is cut off, and the remainder is divided into three equal parts in the longitudinal direction.
  • a dye penetration test and component analysis were performed. As shown in Table 2, almost no uneven distribution of nitrogen was observed in the longitudinal direction of the ingot as shown in Table 2, and the composition of the ingot after the ESR almost coincided with the target composition.
  • the ingot divided into three equal parts was held at 1200 ° C. for 30 minutes in the atmosphere and formed into a 40 mm square bar by hot forging. Then, after maintaining again at 1200 ° C. for 30 minutes, a 15.8 mm square bar was manufactured by hot groove roll rolling. After correcting the warp caused by the groove roll rolling, solution treatment was performed once at 1200 ° C. for 30 minutes. After solution treatment, the solution was air-cooled to room temperature and immediately tempered at 780 ° C. for 1 hour to prevent cracking.
  • a tensile test piece having a parallel part diameter of 6 mm was cut out from a 15.8 mm square bar parallel to the groove roll rolling direction, and a tensile test from room temperature to 750 ° C. was performed.
  • the strain rate was 0.3% / min up to 1.0% strain, 7.5% / min after 1.0%, and 0.2% proof stress, tensile strength, elongation and drawing were measured.
  • Creep characteristics were obtained by cutting a creep test piece having a parallel part diameter of 6 mm parallel to the groove roll rolling direction from a 15.8 mm square bar and measuring the creep rupture time by a uniaxial tensile creep test at a constant load at 650 ° C and 700 ° C.
  • FIGS. 3, 4, 5, and 6, The 0.2% yield strength, tensile strength, breaking elongation and drawing of the heat resistant steel according to this example obtained in the tensile test are shown in FIGS. 3, 4, 5, and 6, respectively.
  • Figures 3 to 6 show, for comparison, the conventional steel (steel equivalent to fire STBA28 in the JIS / thermal power technical standards) that is generally used in ultra-high pressure plants of 600 ° C class. Data obtained under the same tensile test conditions as those performed for the heat-resistant steel according to the example are also shown.
  • the chemical composition of the conventional steel is as shown in Table 3, and the tempering conditions are the same as in this example. It can be seen that the 0.2% proof stress of the heat-resistant steel according to this example at 600 ° C. or higher shown in FIG.
  • the value of the heat-resistant steel according to this example at 600 ° C. or higher is higher than that of the conventional steel by about 110 MPa to 170 MPa.
  • the breaking elongation of the heat resistant steel according to this example at 600 ° C. or higher is 20% or more, and the drawing at the breaking is 80% or more.
  • the heat resistant steel according to this example has high temperature strength and sufficient ductility that surpass conventional steel. is doing.
  • FIG. 7 shows the relationship between the stress and the rupture time in the creep test of the heat-resistant steel according to this example.
  • FIG. 7 also shows data of a conventional steel (Tue STBA28) for comparison of creep strength.
  • the rupture time at 650 ° C. of the heat resistant steel according to this example is 600 ° C. data group of the conventional steel, and the rupture time at 700 ° C. of the heat resistant steel according to this example is almost the same as that of the conventional steel 650 ° C.
  • the heat resistant steel according to the present example has a creep strength that can be used at a temperature about 50 ° C. higher than that of the conventional steel.
  • Fig. 8 shows the relationship between the creep rupture time and creep rupture ductility of the developed steel and conventional steel (Tue STBA28).
  • conventional steel the fracture ductility tends to decrease as the creep rupture time increases, and it is known that the same tendency appears in existing steels other than fire STBA28.
  • the newly developed steel has a unique property of the newly developed steel, with the fracture ductility increasing as the creep rupture time increases to about 800 hours. Having sufficient creep rupture ductility in the long-term range corresponding to the practical environment is important from the viewpoint of the reliability of the structural material, and this developed steel that has both high strength and high ductility against long-term creep deformation is It can be said that it has excellent properties as a high-temperature structural material.
  • FIG. 9 shows the microstructure of the heat-resistant steel according to this example, which was observed using a backscattered electron detector of a scanning electron microscope.
  • the phase containing the light element is darker, and the phase containing the heavy element is observed with brighter luminance. Therefore, the darker luminance particles in FIG. 9 are vanadium nitride and the brighter luminance particles are observed.
  • Example 2 In accordance with the same procedure as in Example 1 above, heat resistant steel was produced under the following conditions. That is, the heat-resisting steel is made from the raw steel so that the composition ratio Cr: V: Nb: N: C: W: Co: Mo becomes 9: 0.6: 0.02: 0.33: 0.01: 6: 4: 1. Manufactured.
  • This heat-resistant steel is represented as 9Cr-0.6V-0.02Nb-0.33N-0.01C-6W-4Co-1Mo (Example 2-1).
  • the composition ratio of heat resistant steel Cr: V: Nb: N: C: W: Co: Mo is 12: 0.6: 0.02: 0.33: 0.01: 6: 4
  • the heat-resisting steel was produced from the raw steel so that the ratio was 1.
  • This heat-resistant steel is expressed as 12Cr-0.6V-0.02Nb-0.33N-0.01C-6W-4Co-1Mo (Example 2-2).
  • a heat resistant steel serving as a comparative example was manufactured under the following conditions. That is, the heat resistant steel was produced from the raw steel so that the composition ratio Cr: V: Nb: N: C of the heat resistant steel was 9: 1.3: 0.02: 0.33: 0.01. This heat resistant steel is denoted as 9Cr-1.3V-0.02Nb-0.33N-0.01C (Comparative Example 1-1). Similarly, heat-resistant steel was manufactured from the raw steel so that the composition ratio Cr: V: Nb: N: C: W: Co of the heat-resistant steel was 9: 1.3: 0.02: 0.33: 0.01: 1: 2.
  • This heat-resistant steel is denoted as 9Cr-1.3V-0.02Nb-0.33N-0.01C-1W-2Co (Comparative Example 1-2).
  • heat-resistant steel was produced from the raw steel so that the composition ratio Cr: V: Nb: N: C: W: Co of the heat-resistant steel was 9: 0.6: 0.02: 0.33: 0.01: 1: 2.
  • This heat-resistant steel is expressed as 9Cr-0.6V-0.02Nb-0.33N-0.01C-1W-2Co (Comparative Example 1-3).
  • heat-resistant steel was produced from the raw steel so that the composition ratio Cr: V: Nb: N: C: W: Co of the heat-resistant steel was 9: 0.6: 0.60: 0.33: 0.01: 1: 2.
  • This heat-resistant steel is denoted as 9Cr-0.6V-0.60Nb-0.33N-0.01C-1W-2Co (Comparative Example 1-4).
  • the heat resistant steels shown in (Example 2-1) and (Example 2-2) according to the present example are (Comparative Example 1-1) to (Comparative), particularly at 700 ° C. to 80 MPa. Compared with Example 1-3), it was confirmed to have a very high creep rupture strength of 15 to 30 times.
  • the heat resistant steel shown in (Example 2-1) and (Example 2-2) according to this example has an extremely high creep rupture of 6 to 12 times compared to (Comparative Example 1-4). It was also confirmed to have strength.
  • Example 3 Next, the effect of adding nitrogen was verified. That is, 9Cr-0.6V-0.02Nb-0.33N-0.01C-6W-4Co-1Mo (Example 2-1) manufactured in Example 2 above was used as a comparative heat-resistant steel manufactured without adding nitrogen.
  • the composition ratio Cr: V: Nb: N: C: W: Co: Mo of the heat-resistant steel is 9: 0.6: 0.02: 0: 0.01: 6: 4 in which no nitrogen is contained from (Example 2-1).
  • the heat-resisting steel was produced from the raw steel so that the ratio was 1. This heat resistant steel is denoted as 9Cr-0.6V-0.02Nb-0.01C-6W-4Co-1Mo (Comparative Example 2).
  • FIG. 11 shows a photograph of these heat-resistant steels, the microstructure of which was observed using a backscattered electron detector of a scanning electron microscope. From the obtained results, the heat resistant steel shown in (Example 2-1) according to this example shows an average particle size of 80 ⁇ m, which is much finer than the average particle size of 1200 ⁇ m in (Comparative Example 2). It was confirmed to have a particle size.
  • chromium (Cr) is generally added to improve oxidation resistance at high temperatures, and it is added to improve high temperature strength.
  • Vanadium (V), Niobium (Nb), Tungsten (W), and Molybdenum (Mo) are elements that have a ferrite stabilizing effect. When these elements are added in the required amounts, the grains are coarse. Usually, a ferrite structure is obtained.
  • the heat-resistant steel according to this example has a material structure that is martensified by the effect of stabilizing the austenite of nitrogen by adding an optimal amount of nitrogen.
  • Example 4 it verified about the effect of nitrogen addition and cobalt addition. That is, 9Cr-0.6V-0.02Nb-0.33N-0.01C-6W-4Co-1Mo (Example 2-1) manufactured in Example 2 above was used as a comparative heat-resistant steel manufactured without adding cobalt. Was manufactured under the following conditions. That is, the composition ratio Cr: V: Nb: N: C: W: Co: Mo of the heat-resistant steel was 9: 0.6: 0.02: 0.33: 0.01: 6: 0 that no cobalt was contained from (Example 2-1). The heat-resisting steel was produced from the raw steel so that the ratio was 1.
  • This heat-resistant steel is denoted as 9Cr-0.6V-0.02Nb-0.33N-0.01C-6W-1Mo (Comparative Example 3). Moreover, about the heat resistant steel used as a comparative example manufactured without nitrogen addition, 9Cr-0.6V-0.02Nb-0.01C-6W-4Co-1Mo (Comparative Example 2) manufactured in Example 3 was used.

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Abstract

L'invention concerne un acier résistant à la chaleur à base de ferrite présentant une résistance élevée. L'acier résistant à la chaleur à base de ferrite a une structure de martensite, comprend un nitrure et un intermétallique contenant du tungstène élémentaire, et contient de 0,1 à 2,0 % en poids de tungstène élémentaire et de 3,0 à 10,0 % en poids de tungstène élémentaire.
PCT/JP2016/055523 2015-02-27 2016-02-24 Acier résistant à la chaleur à base de ferrite et procédé pour le fabriquer WO2016136839A1 (fr)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH06322487A (ja) * 1993-04-15 1994-11-22 Nippon Steel Corp 超高窒素フェライト系耐熱鋼およびその製造方法
JPH0885850A (ja) * 1994-09-20 1996-04-02 Sumitomo Metal Ind Ltd 高Ｃｒフェライト系耐熱鋼
JPH08218154A (ja) * 1995-02-14 1996-08-27 Nippon Steel Corp 耐金属間化合物析出脆化特性の優れた高強度フェライト系耐熱鋼
JPH0971846A (ja) * 1995-09-05 1997-03-18 Sumitomo Metal Ind Ltd 高Ｃｒフェライト系耐熱鋼

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH06322487A (ja) * 1993-04-15 1994-11-22 Nippon Steel Corp 超高窒素フェライト系耐熱鋼およびその製造方法
JPH0885850A (ja) * 1994-09-20 1996-04-02 Sumitomo Metal Ind Ltd 高Ｃｒフェライト系耐熱鋼
JPH08218154A (ja) * 1995-02-14 1996-08-27 Nippon Steel Corp 耐金属間化合物析出脆化特性の優れた高強度フェライト系耐熱鋼
JPH0971846A (ja) * 1995-09-05 1997-03-18 Sumitomo Metal Ind Ltd 高Ｃｒフェライト系耐熱鋼

Non-Patent Citations (2)

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Title
QIUZHI GAO ET AL.: "Martensite transformation in the modified high Cr ferritic heat-resistant steel during continuous cooling", JOURNAL OF MATERIAL RESEARCH, vol. 27, no. 21, 14 November 2012 (2012-11-14), pages 2779 - 2789 *
YUANTAO XU ET AL.: "Study on the nucleation and growth of Laves phase in a 10% Cr martensite ferritic steel after long-term aging", JOURNAL OF ALLOYS AND COMPOUNDS, vol. 621, 5 February 2015 (2015-02-05), pages 93 - 98 *

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