KR100562660B1 - Continuous Annealing Heat Treatment of 22-Chromium Two-Phase Stainless Steel - Google Patents

Abstract

In the present invention, Cr: 20 to 27% by weight. Austenitic containing elements containing Ni: 4.0 to 8.0%, Mo: 2.0 to 5.0%, N: 0.08 to 0.3%, Ca: 0.0005 to 0.0025%, B: 0.0010 to 0.0035% and remaining iron and inevitably impurities And continuous annealing of the ferritic 22Cr two-phase stainless steel after cold rolling, wherein the amount of excess oxygen in the continuous annealing furnace is 6 to 8%, the annealing temperature is 1045 to 1060 ° C., and 0.3 to 0.55 kg _f / Summary of the Invention The continuous annealing heat treatment method of a 22 chromium two-phase stainless cold rolled material characterized in that heat treatment is performed at an annealing time of 30 to 60 seconds by applying a tensile stress of mm 2.

Stainless steel, 2-phase, continuous annealing, creep deformation

Description

A method of continuous annealing for cold-rolled 22Cr duplex stainless steel}

1 is a graph showing creep deformation behavior according to tensile stress at high temperature of 22 chrome-based two-phase stainless 2205 steel hot rolled and cold rolled materials.

Figure 2 is a graph showing the creep deformation behavior according to the annealing temperature and time and tensile stress of the 22 chromium two-phase stainless steel 2205 steel cold rolled material.

3 is a graph showing the effect of Ca and B on the tensile strength of 22 chromium two-phase stainless steel 2205 steel.

4 is a graph showing the effect of Ca and B on the creep deformation behavior according to the tensile stress of the 22 chromium two-phase stainless steel 2205 cold rolled material.

Figure 5 is a graph showing the corrosion resistance change with annealing temperature and time of 22 chromium two-phase stainless steel 2205 steel.

The present invention relates to a continuous annealing heat treatment method for a 22Cr two-phase stainless steel cold rolled material composed of austenite and ferrite phase, and more particularly, it is possible to secure excellent pickling and corrosion resistance while preventing creep deformation in the width direction of the material. A continuous annealing heat treatment method for a 22Cr two-phase stainless cold rolled material.

) 및 페라이트(

) 상을 각각 50% 함유하여 기계적 특성 및 내식성이 우수하기 때문에 탈황설비 및 화학약품 운반선의 소재로 사용되고 있다. Generally 20-27% chromium (Cr). 22Cr two-phase stainless steel containing 4.0-8.0% of nickel (Ni), 2.0-5.0% of molybdenum (Mo), and 0.08-0.3% of nitrogen (N) is austenitic.

) And ferrite (

) It is used as a material for desulfurization equipment and chemical carrier because it contains 50% of each phase and has excellent mechanical properties and corrosion resistance.

와

상의 고온강도 차이에 의하여 변형이

/

상 계면에 집중되어 표면결함 및 엣지균열(edge crack)이 다발하는 강종이다. 이러한 문제점을 해결하기 위하여 칼슘(Ca) 및 보론(B)을 첨가하여 열간 가공성을 개선시키고자 하였다.[J.I.Komi외 3명 : Proceedings of International Conference on Stainless Steels 1991, (1991) pp. 807-814, T.Kawasaki외 3명 : Kawasaki Technical Report, No.14, (1986) pp.50-60]2-phase stainless steel is hot rolled

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Deformation due to the difference in high temperature strength

Of

It is concentrated in the phase interface and has many surface defects and edge cracks. In order to solve this problem, calcium (Ca) and boron (B) were added to improve hot workability. [JIKomi et al. 3: Proceedings of International Conference on Stainless Steels 1991, (1991) pp. 807-814, T.Kawasaki and 3 others: Kawasaki Technical Report, No.14, (1986) pp.50-60]

The 2205 steel, a representative steel of 22Cr two-phase stainless steel, is pulled from the front and rear ends to maintain the flatness of the material while preventing the high-temperature sag caused by the material's own load during continuous annealing at high temperature after hot rolling and cold rolling. Force is applied to the line tension.

In the two-phase stainless steel 2205 steel, the content of ferrite phase increases at high temperature, and the high-temperature strength decreases, causing the width direction of the material to creep in the annealing furnace, which may not satisfy the width dimension of the material or cause breakage. Highly likely, continuous annealing is very difficult.

In particular, two-phase stainless steels exhibit superplastic behavior when they satisfy certain conditions at high temperatures. [K.Osada et al .: 2 Transactions ISIJ, 27 (1987) p713, Y. Maehara et al .: Metall. Trans. A, 18A (1987) p663] It is difficult to precisely control the width dimension of the material because the deformation in the width direction proceeds even if no plate break occurs. Since such superplasticity is remarkably generated in cold rolled materials having finer grains than hot rolled materials, continuous annealing of two-phase stainless cold rolled materials is very difficult.

In addition, since the chromium content is very high, about 22%, there is little generation of oxidative scale in the annealing furnace atmosphere, so the pickling property is lowered, so that residual scale remains on the surface, and in order to secure excellent corrosion resistance, additional coil polishing must be performed to remove the residual scale. There is a problem.

At present, annealing conditions of two-phase stainless steels are set to simply quench the temperature after heat treatment in a section of 950-1100 ° C. [JIS G 4304], and there are no accurate annealing methods and conditions for securing pickling and corrosion resistance.

The present invention has been made in order to solve the problems of the prior art as described above, the excess oxygen amount in the annealing furnace atmosphere, annealing temperature and time, tension when the cold rolled material of 22Cr two-phase stainless steel 2205 steel is subjected to continuous annealing at high temperature The purpose of the stress control is to prevent creep deformation in the width direction of the material and at the same time to ensure excellent pickling and corrosion resistance.

The present invention for achieving the above object is 20% to 27% Cr by weight. Austenitic containing elements containing Ni: 4.0 to 8.0%, Mo: 2.0 to 5.0%, N: 0.08 to 0.3%, Ca: 0.0005 to 0.0025%, B: 0.0010 to 0.0035% and remaining iron and inevitably impurities And continuous annealing of the ferritic 22Cr two-phase stainless steel after cold rolling, wherein the amount of excess oxygen in the continuous annealing furnace is 6 to 8%, the annealing temperature is 1045 to 1060 ° C., and 0.3 to 0.55 kg _f / It provides a continuous annealing heat treatment method of 22 chrome-based two-phase stainless cold rolled material characterized in that the heat treatment with an annealing time of 30 ~ 60 seconds by applying a tensile stress of 2 mm2.

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The present invention will be described in more detail with reference to the following Examples.

EXAMPLE

Table 1 shows the chemical composition of the 22Cr two-phase stainless steel 2205 steel used as an embodiment in the present invention, Table 2 is refined molten steel having the chemical composition in a conventional manner to make a slab, and then hot rolling After the cold rolled coil was made in the cold rolling process, the cold rolled sheet was annealed under continuous annealing conditions as shown in Table 2 to show the quality characteristics of the present invention, the comparative example and the conventional example.

ingredient Cr Ni Mo Mn Si P S Ca B weight% 20-27 4 to 8 2 to 5 1.5 or less 1.0 or less 0.025 or less Less than 0.003 0.0005 to 0.0025 0.0010 to 0.0035

division Annealing Temperature ( ^o C) Annealing time Tensile stress (kgf / mm ² ) Width creep deformation Excess oxygen in the annealing furnace Pickling Corrosion resistance Comparative Example 1 1025 and below Within 60 seconds 0.55 or less Not Occurred 6-8% △ X Comparative Example 2 1025-1050 Within 60 seconds 0.55 or less Not Occurred 6-8% O △ Comparative Example 3 1050-1075 Within 60 seconds 0.55 or less Some occurrence 6-8% ⊙ ⊙ Comparative Example 4 1045-1060 30 to 60 seconds 0.3-0.55 Not Occurred 4-6% △ O Inventive Example 1045-1060 30 to 60 seconds 0.3-0.55 Not Occurred 6-8% ⊙ ⊙ Conventional Example 1 Less than 1050 Within 60 seconds No control condition Possible 4-6% △ △ Conventional Example 2 1050-1075 Within 60 seconds No control condition Occurs frequently 4-6% O O

⊙: Excellent O: Good △: Normal X: Poor

As shown in Table 2, the prior art examples 1 and 2 did not have a condition capable of accurately controlling the tensile stress applied to the material during continuous annealing of the stainless 2205 steel, and thus the work was arbitrarily performed. Conventional Example 1 having an annealing temperature of 1050 ° C. or less and Conventional Example 2 of 1050-1075 ° C. have problems in which creep deformation occurs in the width direction during continuous annealing and some pickling scales remain, resulting in deterioration of pickling and corrosion resistance. .

FIG. 1 shows the creep deformation behavior of hot rolled and cold rolled materials of 22Cr two-phase stainless steel 2205 steel according to tensile stress at high temperature. It can be seen that the amount of deformation increases sharply as the tensile stress increases. Due to these characteristics, it can be seen that the cold rolled material is difficult while the continuous annealing conditions are limited than the hot rolled material.

Figure 2 shows the creep strain behavior according to the annealing temperature and time and tensile stress of the 22Cr two-phase stainless steel 2205 steel cold rolled material as the annealing temperature increases or as time passes, the creep strain increases as the tensile stress increases. The results are shown.

Therefore, the continuous annealing method of the 22Cr two-phase stainless steel 2205 steel cold rolled material of the present invention is to control the annealing temperature and the tensile stress (line tension) applied to the time and the material, the amount of excess oxygen in the annealing furnace atmosphere,

In Comparative Example 1, the annealing temperature is lowered to 1025 ° C., so that no creep deformation occurs in the width direction, but the rolling structure remains, or the pickling resistance decreases, as shown in FIG. 5. In other words, when the annealing temperature is lower than 1045 ° C, corrosion resistance is lowered because the redistribution of chromium, nickel and nitrogen in the ferrite phase and the austenite phase is not easily performed in the two-phase stainless steel 2205 steel during annealing. Therefore, in order to secure corrosion resistance, annealing is required for a long time of 90 seconds or more, but it is almost impossible in a continuous annealing pickling line.

In the case of Comparative Example 2, the annealing temperature is 1025 ~ 1050 ℃ higher than the case of 1 in comparison, but as mentioned above, redistribution of components such as chromium, nickel and nitrogen in the ferrite phase and austenite phase is not easy In order to ensure the annealing time requires more than 90 seconds has a disadvantage. However, it is almost impossible to maintain the annealing time in the continuous annealing line for more than 90 seconds, which has the disadvantage of lowering the corrosion resistance. If the annealing time is increased, there is a possibility that the widthwise creep deformation of the material occurs in the annealing furnace.

On the other hand, when the tensile stress applied to the cold rolled material is less than 0.3kgf / mm2, there is a disadvantage that the plate flatness can not be secured for the cold rolled material of the museum, it is preferable to specify the minimum tensile stress of 0.3kgf / mm2 or more. On the other hand, when the tensile stress exceeds 0.55kgf / mm2 plate flatness due to the deflection of the plate may be good, but the plate breakage is very likely to cause a high undesirable.

In Comparative Example 3, the annealing temperature was high at 1050 to 1075 ° C. and the excess oxygen in the annealing furnace was high at 6 to 8%, so the pickling resistance and the corrosion resistance were excellent, but the widthwise creep deformation appeared, which did not satisfy the width dimension after continuous annealing. There is a problem.

In the case of Comparative Example 4, the creep deformation did not occur in the width direction, but the excess oxygen in the annealing furnace atmosphere was low at 4 to 6%, so that the pickling resistance was lowered in sulfuric acid and mixed acid (fluoric acid + nitric acid) solutions, which are common stainless steel pickling solutions, and corrosion resistance. There is a disadvantage in that the coil polishing is lowered than this invention example.

Figure 3 shows the effect of Ca and B on the tensile strength of two-phase stainless steel 2205 steel, the addition of Ca and B to improve the hot workability, the higher tensile strength 15% or more than without Ca and B It can be seen that the improvement. When Ca and B are added, the grain boundary impurities are reduced and grain strength is increased. This result is influenced by high temperature creep deformation, and as shown in the creep characteristics of FIG. 4, Ca and B are added to the steel. When not added, it shows lower creep strain at the same tensile stress, which shows that the annealing temperature and tensile stress can be set more variously during continuous annealing. That is, in the present invention, in order to improve hot workability, it is preferable to contain calcium (Ca) in the range of 0.0005 to 0.0025% and boron (B) in the range of 0.0010 to 0.0035%.

5 is a result showing the corrosion resistance of the condition that satisfies the critical formula temperature of 40 ^° C according to the annealing temperature and time changes during continuous annealing of 2205 steel with Ca and B added. Critical formula temperature measurement was performed according to ASTM G48-97 method. As can be seen from the results of Figure 5 when the annealing temperature is less than 1045 ℃ annealing time must be maintained for more than 90 seconds to some extent to satisfy the corrosion resistance, but it is almost impossible to maintain more than 90 seconds in a continuous annealing line, increasing the annealing time 2 and 4, the creep deformation of the material also continuously increases in the annealing furnace, so that the widthwise creep deformation may occur.

Therefore, in order to satisfy the corrosion resistance above the critical formula temperature of 40 ℃ and to minimize the creep deformation in the width direction of the material within 2%, the annealing temperature should be limited to at least 1045 ℃ and the annealing time should be maintained at least 30 seconds and at most 60 seconds. . In addition, when the annealing temperature is 1070 ° C or more, the widthwise creep deformation is likely to occur, so the annealing temperature is preferably limited to a maximum of 1060 ° C or less. In addition, if the annealing time exceeds 90 seconds, since the amount of creep deformation greatly increases as shown in FIGS. 2 and 4, 60 seconds or less is preferable.

Therefore, the present invention controls the annealing temperature 1045-1060 ℃, annealing time 30 ~ 60 seconds, the tensile stress applied to the material in the range 0.3 ~ 0.55kgf / mm ² , wherein the excess oxygen in the annealing furnace atmosphere is continuous at 6-8% The annealing heat treatment does not cause the creep deformation in the widthwise direction, and the pickling property is excellent in sulfuric acid and mixed acid (hydrofluoric acid + nitric acid) solutions, which are common stainless steel pickling solutions. Two-phase stainless steel 2205 cold rolled material can be produced.

As described above, the present invention, by controlling the continuous annealing heat treatment conditions of the 22Cr two-phase stainless steel 2205 steel cold rolled material can prevent the creep deformation in the width direction and ensure excellent pickling and corrosion resistance, the coil polishing process can be omitted Can be.

Claims (2)

Cr: 20 to 27% by weight. Austenitic containing elements containing Ni: 4.0 to 8.0%, Mo: 2.0 to 5.0%, N: 0.08 to 0.3%, Ca: 0.0005 to 0.0025%, B: 0.0010 to 0.0035% and remaining iron and inevitably impurities And in the continuous annealing of the ferritic phase 22Cr two-phase stainless steel after cold rolling, In the continuous annealing furnace, the amount of excess oxygen is 6 to 8%, the annealing temperature is 1045 to 1060 ° C., and the heat treatment is performed at an annealing time of 30 to 60 seconds by applying a tensile stress of 0.3 to 0.55 kg _f / mm 2. Continuous annealing heat treatment of two-phase stainless cold rolled material. The method of claim 1, The continuous annealing heat treatment method of the 22 chromium two-phase stainless steel cold rolled material characterized in that the following coil polishing step can be omitted by performing the 22Cr two-phase stainless steel by the continuous annealing heat treatment method.

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