WO2016105094A1 - 항복강도 및 충격인성이 우수한 슈퍼 듀플렉스 스테인리스강 및 그 제조방법 - Google Patents
항복강도 및 충격인성이 우수한 슈퍼 듀플렉스 스테인리스강 및 그 제조방법 Download PDFInfo
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- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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- 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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
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- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
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- 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
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- 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
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- C—CHEMISTRY; METALLURGY
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- 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
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- 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
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- 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
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- C—CHEMISTRY; METALLURGY
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- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
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- C—CHEMISTRY; METALLURGY
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- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/004—Dispersions; Precipitations
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- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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- 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
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
- C21D8/0426—Hot rolling
Definitions
- the present invention relates to a super duplex stainless steel and a method of manufacturing the same, and more particularly, to a super duplex stainless steel having excellent yield strength and impact toughness by adjusting a reduction ratio and heat treatment temperature.
- super duplex stainless steel (UNS S32750) containing 24 to 26% chromium (Cr), 6.0 to 8.0% nickel (Ni), 3.0 to 5.0% molybdenum (Mo) and 0.24 to 0.32% nitrogen (N)
- Cr chromium
- Ni nickel
- Mo molybdenum
- N nitrogen
- the matrix structure of the super duplex stainless steel has a structure characteristic in which the ferrite phase and the austenite phase are formed in equal proportions.
- the super duplex stainless steel has a great strength compared to the austenitic stainless steel, and has a great advantage of pitting corrosion and stress corrosion cracking resistance to chlorine ions.
- the super duplex stainless steel contains a large amount of chromium (Cr) and molybdenum (Mo) to secure the corrosion resistance, when maintained in the 750 °C to 850 °C section, sigma phase is easily generated, the brittleness is strong, corrosion resistance is significantly reduced This causes problems such as deterioration of quality.
- the method of avoiding a temperature section in which sigma phase generation is easy by increasing the temperature from 600 ° C. to an annealing temperature at a temperature increase rate of 10 ° C./s or more and maintaining it at 1,060 to 1,080 ° C. It is specifically known in the "continuous annealing method of super duplex stainless steel excellent in coil shape" (Patent Publication 10-2013-0034350).
- This heat treatment method is equally applicable to not only hot rolled coils of 8 mm or less but also thick plates of 10 mm or more.
- the above annealing method is mainly applicable to the hot rolled coil having a thickness of 8 mm or less, but the same heat treatment method is applicable to a thick plate having a thickness of 10 mm or more, but is 550 MPa or more over a plate of various thicknesses ranging from 5 mm to 50 mm.
- the problem of not satisfying the 0.2% Off-Set yield strength frequently occurred.
- the present invention has been made to solve the conventional problems as described above, super-duplex stainless steel excellent in yield strength and impact toughness improved mechanical properties by controlling the reduction rate and annealing conditions in the production of thick material super duplex stainless steel and It provides a manufacturing method.
- the super duplex stainless steel having excellent yield strength and impact toughness relates to a thick super duplex stainless steel having a thickness of 30 mm or more, in weight percent of Cr: 24 to 26% and Ni: 6.0. ⁇ 8.0%, Mo: 3.5 ⁇ 5.0%, N: 0.24 ⁇ 0.32%, containing the remaining Fe and inevitable impurities, the microstructure consists of a ferrite phase, austenite phase and secondary austenite phase, Its size is 25 ⁇ m or less.
- the super duplex stainless steel may be characterized by a yield strength of 550 MPa or more.
- the super duplex stainless steel may have a sum of yield strength and impact toughness of 750 or more.
- a method of manufacturing super duplex stainless steel having excellent yield strength and impact toughness is weight percent, Cr: 24 to 26%, Ni: 6.0 to 8.0%, Mo: 3.5 to 5.0%, and N:
- a casting step of producing a slab comprising 0.24 to 0.32% and comprising remaining Fe and inevitable impurities Hot rolling the slab to produce a thick plate having a thickness of 30 mm or more; Heating the thick plate to an annealing temperature to precipitate a CrN phase inside a ferrite phase, and to precipitate a sigma phase and a secondary austenite phase around the CrN phase; And an annealing step of remaining the secondary austenite phase inside the ferrite phase while solidifying the sigma phase to the ferrite phase.
- the temperature raising step may be characterized in that to increase the temperature at a rate of 0.11 ⁇ 0.17 °C / s from 700 °C to the annealing temperature.
- the annealing step may be characterized in that the annealing for 20 to 60 minutes at a temperature of 1020 ⁇ 1060 °C.
- the hot rolling step may be characterized by rolling at a rolling reduction rate of 80% or more so that the grain size of the microstructure is 25 ⁇ m or less.
- Figure 2 is a photograph showing the microstructure at 800 °C, 1000 °C, 1040 °C temperature according to the temperature increase rate
- 3 is a view showing the behavior of the precipitate according to the annealing temperature and the annealing time and its microstructure
- 5 is a graph showing the relationship between the thick plate thickness (rolling down ratio) and the grain size
- Figure 6 is a photograph comparing the microstructure of the super duplex stainless steel and the comparative material excellent in yield strength and impact toughness prepared according to an embodiment of the present invention.
- the super duplex stainless steel having excellent yield strength and impact toughness is, by weight, Cr: 24 to 26%, Ni: 6.0 to 8.0%, Mo: 3.5 to 5.0%, and N: 0.24 to 0.32% and the remaining Fe and inevitable impurities.
- Chromium (Cr) is a ferrite stabilizing element that not only plays a major role in securing the ferrite phase, but is also an essential element for securing corrosion resistance.
- Cr chromium
- the corrosion resistance is increased, but it is added in excess of 26%.
- austenite-forming elements such as expensive nickel (Ni) is increased to maintain the phase ratio, the manufacturing cost increases.
- the content of chromium (Cr) is preferably limited to the range of 24 ⁇ 26wt%.
- Molybdenum (Mo) is a very effective element to improve the corrosion resistance while stabilizing the ferrite together with chromium (Cr), but the disadvantage is very expensive. Therefore, the content of molybdenum (Mo) is preferably limited to 3.5 ⁇ 5.0wt%.
- Nitrogen (N) is one of the elements in which thickening occurs in the austenite phase during annealing. Increasing may result in increased corrosion resistance and higher strength. However, when the content of nitrogen is excessive, nitrogen may be caused to cause surface defects due to the generation of nitrogen pores during casting due to the excess of N (N) solubility.
- the content of (N) is preferably limited to the range 0.24 ⁇ 0.32wt%.
- the super duplex stainless steel having excellent yield strength and impact toughness according to an embodiment of the present invention preferably has a grain size of 25 ⁇ m or less in a microstructure composed of a ferrite phase, an austenite phase, and a secondary austenite phase. .
- the yield strength may be 550 MPa or more, and the sum of the yield strength and the impact toughness may be 750 or more.
- the super-duplex stainless steel manufacturing method excellent in yield strength and impact toughness is a casting step for producing a slab by playing the molten steel having the composition and rolling to produce a thick plate by hot rolling the slab It includes a step of heating and an annealing step of heating the thick plate material.
- the super duplex stainless steel annealing heat treatment having both an austenitic phase and a ferrite phase simultaneously controls the temperature increase rate, the annealing temperature and time, and the reduction rate.
- Figure 1 is a graph showing the sigma phase and CrN phase formation behavior in the temperature increase rate during annealing
- Figure 2 is a photograph showing the microstructure at 800 °C, 1000 °C, 1400 °C temperature according to the temperature increase rate.
- the temperature increase step according to an embodiment of the present invention is preferably heated to an annealing temperature having a temperature range of 700 °C to 1030 ⁇ 1050 °C at a rate of 0.11 ⁇ 0.17 °C / s Do.
- the CrN phases are finely formed inside the ferrite phase near 800 ° C.
- the formed CrN phase acts as a nucleation site, so that not only the austenite / ferrite phase interface but also the CrN phase is around.
- Low sigma phase and secondary austenite phases can be formed to refine the tissue.
- Figure 4 is a graph showing the yield strength and impact toughness according to the annealing conditions.
- the annealing step according to an embodiment of the present invention is carried out 20 to 40 minutes at a temperature of 1020 ⁇ 1060 °C, more preferably the annealing step of the present invention annealing according to the annealing temperature It is desirable to apply the time differently.
- the annealing time is carried out 20 ⁇ 40 minutes, when the annealing temperature is 1020 ⁇ 1030 °C, the annealing time is performed 40 ⁇ 60 minutes, when the annealing temperature is 1050 ⁇ 1060 °C The time is 5 to 20 minutes.
- the secondary austenite phase can remain in the ferrite phase while solidifying the sigma phase inside the ferrite phase, thereby miniaturizing the tissue, and as the annealing temperature increases, the sigma phase and the secondary Although the austenite phase tends to be dissolved, by shortening the annealing time, the secondary austenite phase remains inside the ferrite phase, thereby making it possible to refine the structure.
- Figure 5 is a graph showing the relationship between the thickness of the thick plate (rolling down rate) and grain size during thick plate production by rolling a slab of 150 mm
- Figure 6 is excellent in yield strength and impact toughness manufactured according to an embodiment of the present invention This is a picture comparing the microstructure of super duplex stainless steel and comparative material.
- the reduction ratio of the slab is 80% or more.
- the yield strength is lowered to 550 MPa or less, which does not satisfy the ASTM standard.
- This can be improved through the microstructure control method, but by applying a rolling reduction of 82.5%, the grain size of the microstructure can be formed to 25 ⁇ m or less and the yield strength can be improved.
- the thickness of the super duplex stainless steel excellent in yield strength and impact toughness according to an embodiment of the present invention may be 30 mm or more. That is, the present invention can be usefully applied to thick materials.
- the upper limit of the thickness is not particularly limited, and may be, for example, 100 mm, 70 mm or 50 mm.
- the inventors of the present invention while excellent in the properties of the super duplex steel, while forming a CrN phase during the heat treatment by controlling the temperature rise rate to 0.11 ⁇ 0.17 °C / s or less during annealing to secure yield strength and excellent impact toughness of 580 MPa or more at the same time , Sigma phase and secondary austenite phase were finely precipitated inside the ferrite phase.
- the annealing was performed for 20 to 60 minutes in the temperature range of 1020 to 1060 ° C., and the second austenite phase was left in the ferrite phase while all the sigma phase was dissolved, thereby simultaneously providing the yield strength and impact characteristics of the thick plate having a thickness of 30 mm or more. Improved.
- Table 1 shows the thickness (rolling down amount), the temperature increase rate, the annealing temperature and the annealing time of the slab for various examples and comparative examples.
- Examples and Comparative Examples A-Y steels were heated at a rate of 5 ° C./s to 700 ° C. and heated at a temperature increase rate of 1.3 / s, 0.66 ° C./s, 0.33 ° C./s, and 0.17 ° C./s from 700 ° C. to the annealing temperature.
- the annealing temperatures were 1000 ° C., 1020 ° C., 1040 ° C., 1060 ° C., and 1080 ° C., and the annealing time was 20 minutes, 40 minutes, and 60 minutes, respectively, followed by water cooling.
- Table 2 shows the change in the microstructure during the temperature increase process when hot rolling and heat treatment under the conditions described in Table 1.
- the CrN phase was finely formed inside the ferrite phase in the temperature range of 700 to 800 ° C during the temperature rising process, and the secondary phase was carried out at a temperature range of 1020 to 1060 ° C. It can be seen that the austenite phase remains inside the ferrite phase.
- P-U steels tend to be similar to K-O steels at a temperature increase rate of 0.17 ° C / s, but as the amount of precipitation of CrN phases increases, the remaining secondary austenite phases also tend to increase.
- the A-U steel has a reduction ratio of 77% and the grains of the final microstructure are coarsened, the size of which exceeds 25 ⁇ m, which is outside the scope of the present invention.
- the reduction ratio is 82.5%
- the temperature increase rate is 0.17 °C / s
- the annealing temperature is 1020 ⁇ 1060 °C V ⁇ X steel satisfying the embodiment of the present invention is a part of the V steel, X steel ( It can be seen that the CrN phase is properly precipitated in all the V3, X1) and W steels, and the second austenite phase is left inside the ferrite phase in the temperature range of 1020 to 1060 ° C to secure the finest structure.
- the annealing temperature is 1080 ° C as in the case of T steel secondary austenite phase is found to be out of the scope of the present invention.
- Table 3 shows the characteristics for the representative steel grades (T, R, W) of Table 2.
- yield strength was taken from the tensile test specimen of JIS No. 5 in the 90 ° direction of the rolling direction and subjected to a tensile test at a crosshead speed of 20 mm / min at room temperature.
- R steel has 77% reduction in grain size, and its size is larger than the reference value of 25 ⁇ m.
- R steel has a yield strength of 536MPa, which is less than the standard value of 550MPa, and the yield strength and impact toughness are also 708MPa. It was found that the yield strength and impact toughness were not improved because the reference value was not reached 750 MPa.
- the sum of yield strength, yield strength and impact toughness satisfies the reference value, but the rolling reduction is 77%, and the grain size exceeds 25 ⁇ m, which is the reference value.
- the rolling reduction is 82.5%
- the annealing temperature, the annealing time and the temperature increase rate satisfy the scope of the present invention, and the grain size is fine to 25 ⁇ m or less
- the yield strength is 585 MPa
- the yield strength and impact toughness The sum is 778 MPa, yield strength and impact toughness is improved, it can be confirmed that the mechanical properties compared to the comparative material.
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Abstract
Description
구분 | 공정변수 | 비고 | ||||
슬라브 두께(압하량) | 승온속도 (℃/s) | 소둔온도 (℃) | 소둔시간 (min) | |||
A | 77% | 1.3 | 1000 | 20분/40분/60분 | 비교예 | |
B | 77% | 1.3 | 1020 | 20분/40분/60분 | ||
C | 77% | 1.3 | 1040 | 20분/40분/60분 | ||
D | 77% | 1.3 | 1060 | 20분/40분/60분 | ||
E | 77% | 1.3 | 1080 | 20분/40분/60분 | ||
F | 77% | 0.66 | 1000 | 20분/40분/60분 | ||
G | 77% | 0.66 | 1020 | 20분/40분/60분 | ||
H | 77% | 0.66 | 1040 | 20분/40분/60분 | ||
I | 77% | 0.66 | 1060 | 20분/40분/60분 | ||
J | 77% | 0.66 | 1080 | 20분/40분/60분 | ||
K | 77% | 0.33 | 1000 | 20분/40분/60분 | ||
L | 77% | 0.33 | 1020 | 20분/40분/60분 | ||
M | 77% | 0.33 | 1040 | 20분/40분/60분 | ||
N | 77% | 0.33 | 1060 | 20분/40분/60분 | ||
O | 77% | 0.33 | 1080 | 20분/40분/60분 | ||
P | 77% | 0.17 | 1000 | 20분/40분/60분 | ||
Q | 77% | 0.17 | 1020 | 20분/40분/60분 | ||
R | 77% | 0.17 | 1040 | 20분/40분/60분 | ||
S | 77% | 0.17 | 1060 | 20분/40분/60분 | ||
T | 77% | 0.17 | 1080 | 20분/40분/60분 | ||
U | 82.50% | 0.17 | 1000 | 20분/40분/60분 | ||
V | V1 | 82.50% | 0.17 | 1020 | 20분 | |
V2 | 40분 | |||||
V3 | 60분 | 실시예 | ||||
W | 82.50% | 0.17 | 1040 | 20분/40분/60분 | ||
X | X1 | 82.50% | 0.17 | 1060 | 20분 | |
X2 | 40분 | 비교예 | ||||
X3 | 60분 | |||||
Y | 82.50% | 0.17 | 1080 | 20분/40분/60분 |
구분 | 압하량(%) | 승온속도(℃/s) | 소둔온도(℃) | 소둔시간(min) | CrN상 | 2차 오스테나이트상 | 결정립 평균 크기 | 비고 |
A~J | 77 | 1.3~0.66 | 1000~1080 | 20~60 | X | X | 41 | 비교예 |
K~N | 77 | 0.33 | 1000~1060 | 20~60 | O | O | 33 | |
O | 77 | 0.33 | 1080 | 20~60 | O | X | 38 | |
P~S | 77 | 0.17 | 1000~1060 | 20~60 | O | O | 30 | |
T~U | 77 | 0.17 | 1080 | 20~60 | O | X | 36 | |
V~X | 82.5 | 0.17 | 1000~1060 | 20~60 | O | O | 22 | 실시예 |
Y | 82.5 | 0.17 | 1080 | 20~60 | O | X | 26 | 비교예 |
구분 | 압하량(%) | 승온속도(℃/s) | 소둔온도(℃) | 소둔시간(min) | 결정립크기(㎛) | 항복강도 (A) | 충격인성 (B) | (A+B) | 비고 |
T | 77 | 0.38~0.17 | 1080 | 40 | 36~43 | 536 | 172 | 708 | 비교예 |
R | 77 | 0.33~0.17 | 1040 | 40 | 28~33 | 569 | 187 | 756 | |
W | 82.5 | 0.33~0.17 | 1040 | 40 | 21~24 | 585 | 193 | 778 | 실시예 |
Claims (7)
- 30㎜ 이상의 두께를 갖는 후물 슈퍼 듀플렉스 스테인리스강에 관한 것으로서,중량%로, Cr: 24 ~ 26%, Ni: 6.0 ~ 8.0%, Mo: 3.5 ~ 5.0%, N: 0.24 ~ 0.32% 를 포함하고, 나머지 Fe 및 불가피한 불순물을 포함하며,미세조직이 페라이트상, 오스테나이트상 및 2차 오스테나이트상으로 구성되되, 결정립 크기가 25㎛ 이하인 것을 특징으로 하는, 항복강도 및 충격인성이 우수한 슈퍼 듀플렉스 스테인리스강.
- 청구항 1에 있어서,상기 슈퍼 듀플렉스 스테인리스강은,항복강도가 550 MPa 이상인 것을 특징으로 하는, 항복강도 및 충격인성이 우수한 슈퍼 듀플렉스 스테인리스강.
- 청구항 2에 있어서,상기 슈퍼 듀플렉스 스테인리스강은,항복강도와 충격인성의 합이 750 이상인 것을 특징으로 하는, 항복강도 및 충격인성이 우수한 슈퍼 듀플렉스 스테인리스강.
- 중량%로, Cr: 24 ~ 26%, Ni: 6.0 ~ 8.0%, Mo: 3.5 ~ 5.0%, N: 0.24 ~ 0.32% 를 포함하고, 나머지 Fe 및 불가피한 불순물을 포함하는 슬라브를 제조하는 주조 단계;상기 슬라브를 열간에서 압연하여 30㎜ 이상의 두께를 갖는 후판재를 생산하는 열간압연 단계;상기 후판재를 소둔 온도까지 승온하여 페라이트상 내부에 CrN상을 석출시키고, 상기 CrN상 주위에 시그마상 및 2차 오스테나이트상을 석출시키는 승온 단계; 및상기 시그마상을 상기 페라이트상에 고용시키면서, 상기 2차 오스테나이트상을 상기 페라이트상 내부에 잔류시키는 소둔 단계;를 포함하는, 항복강도 및 충격인성이 우수한 슈퍼 듀플렉스 스테인리스강 제조방법.
- 청구항 4에 있어서,상기 승온 단계는,700℃ 부터 상기 소둔 온도까지 0.11 ~ 0.17 ℃/s의 속도로 승온시키는 것을 특징으로 하는, 항복강도 및 충격인성이 우수한 슈퍼 듀플렉스 스테인리스강 제조방법.
- 청구항 5에 있어서,상기 소둔 단계는,1020 ~ 1060℃의 온도로 20 ~ 60 분간 소둔하는 것을 특징으로 하는, 항복강도 및 충격인성이 우수한 슈퍼 듀플렉스 스테인리스강 제조방법.
- 청구항 4에 있어서,상기 열간압연 단계는,미세조직의 결정립 크기가 25㎛이하가 되도록, 80% 이상의 압하율로 압연하는 것을 특징으로 하는, 항복강도 및 충격인성이 우수한 슈퍼 듀플렉스 스테인리스강 제조방법.
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