KR101275105B1 - High Cr Ferritic/Martensitic steels having an improved creep resistance for in-core component materials in nuclear reactor, and preparation method thereof - Google Patents

Abstract

The present invention relates to a high chromium ferritic / martensitic steel for the reactor core parts material with improved creep performance, and to a method of manufacturing the same, specifically, 0.04 to 0.13 wt% carbon, 0.03 to 0.07 wt% silicon, 0.40 to 0.50 wt% manganese, Nickel 0.40 to 0.50 wt%, Chromium 8.5 to 9.5 wt%, Molybdenum 0.45 to 0.55 wt%, Vanadium 0.10 to 0.25 wt%, Tantalum 0.02 to 0.10 wt%, Niobium 0.21 to 0.25 wt%, Tungsten 1.5 to 3.0 wt%, Nitrogen The present invention relates to a high chromium ferritic / martensitic steel made of 0.015 to 0.025% by weight, boron 0.01 to 0.02% by weight, and iron residue, and containing no cobalt. The high chromium ferrite / martensitic steel according to the present invention exhibits excellent tensile strength and creep performance by optimizing the nitrogen and boron content, in particular, and thus can be usefully used as the fourth generation SFR fuel material used in high temperature and high neutron irradiation conditions. have.

Description

High Cr Ferritic / Martensitic steels having an improved creep resistance for in-core component materials in nuclear reactor, and preparation method

The present invention relates to high chromium ferrite / martensitic steel for reactor core part materials with improved creep performance and a method of manufacturing the same.

Sodium-cooled Fast Reactor (SFR) has been developed in terms of efficient use of uranium resources since the early days of nuclear power generation because it has a characteristic of proliferating fuel using fast neutrons. In recent years, the sodium-cooled high-speed reactor is attracting attention again because of the use of spent fuel and the extinction treatment of ultra long-lived radionuclides, as shown in the Gen IV reactor system development program.

Nuclear fuel is a key element of sodium cooling fast reactors that produce energy from fission, multiply nuclear material, and destroy waste. Therefore, the safety of nuclear fuel containing radioactive fission products is directly related to the safety of the reactor.

Since the fuel cladding serves to seal the fuel core to prevent the outflow of radioactive material, it is the most important fuel component directly related to the safety of the fuel and the reactor. SFR fuel cladding is used in high temperature and high dose harsh conditions. Therefore, a cladding tube having excellent creep resistance at high temperatures, low swelling up to a high neutron dose, and maintaining ductility should be developed. In order to realize this, it is necessary to develop a new material having high temperature / radiation resistance that can withstand high temperature coolant and high neutron irradiation conditions and excellent compatibility with liquid sodium.

Recently, high chromium-containing ferrite-martensitic steel (FMS) has attracted attention as a material having excellent high temperature characteristics as a candidate material for major components of the fourth generation reactor and fusion reactor.

High chromium ferritic / martensitic steels containing 8 to 12% by weight of chromium are fast neutrons since the 1970s because of their superior thermal properties and irradiation swelling resistance compared to austenitic stainless steels (eg SS316 and SS304). Fast breeder reactors have been used as fuel cladding, an important part of the core, as a material for wrappers or ducts surrounding them.

The high chromium ferrite / martensite steels can be classified into 9Cr-1Mo (ASME T9) series and 12Cr (AISI 410) series, and the process of improving the high chromium ferrite / martensite steels is shown in the table of FIG. 1. As shown in FIG. 1, 9Cr-1Mo series includes 9Cr-2Mo (HCM 9), 9Cr-2MoVNb (EM12), and 9Cr-1MoVNb (Tempaloy F-9) having a creep rupture strength of 60 MPa for 105 hours at 600 ° C. Afterwards, 9Cr-1MoVNb (ASME T91) with a creep rupture strength of about 100 MPa was developed. In addition, Sumitomo of Japan has developed 9Cr-0.5Mo-1.8WVNb (ASME T92), which has a creep rupture strength of 130 MPa by reducing Mo content and adding W in ASME T91, and has a creep rupture strength of 150 MPa. A level NF12 (11Cr-WCo-NiVNb) alloy was also developed.

12Cr series has developed 12Cr-1Mo-VW (HT9), 12Cr-1Mo-1WVNb (HCM12), 11Cr-0.4Mo-2WVNbCu (ASME T122), and 11Cr-WCo-VNb (SAVE12) with creep breaking strength of 150 MPa Rivers have been developed.

Meanwhile, in the development process of high chromium ferrite / martensitic steel, as shown in FIG. 1, it can be seen that the creep rupture strength of the steel to which Co is added as an alloying element is excellent. In European Patent EP 0806490 B1, Co is added to provide heat resistance. And high chromium ferrite / martensitic steels with good creep rupture strength.

However, in the case of using a ferritic / martensitic steel with Co component added to the reactor as disclosed in EP 0806490 B1, workers who have to work in a closed nuclear power plant due to the use of Co, a highly radioactive material, As safety concerns arise, there are problems that are unsuitable for nuclear power, especially nuclear reactor-related materials.

Meanwhile, the concept of reduced-activation steel was introduced in the mid-1980s when the nuclear fusion reactor material development program began in earnest, and research on low-radiation ferrite / martensite steel (RAFMS) was carried out in earnest. The starting material is ferritic / martensitic steel of ASTM Gr. 91 alloy (major component: 9% Cr-1% Mo-0.20% V-0.08% Nb), known as modified 9Cr-1Mo steel. Low-spinning ferritic / martensitic steels have been followed by limitations of alloying elements to reduce the production of long-lived, high-level radioactive materials produced by high-speed neutron irradiation. In other words, the addition of molybdenum, niobium, nickel, copper and nitrogen was strictly restricted in low-emission ferritic / martensitic steels, and the addition of tungsten and tantalum was proposed instead of these elements. In addition, alloys with a reduced chromium content of 7-9% were preferred as a way to suppress the formation of δ-ferrite phases that adversely affect the impact properties without increasing the amount of carbon or manganese, which is an α-phase stabilizing element. In this series of studies, in Japan, the F82H alloy (major component: 8% Cr-2.0% W-0.25% V-0.04% Ta) and JLF-1 alloy (major component: 9% Cr-2.0% W-0.25% V-0.05% Ta-0.02% Ti) has been newly developed and EUROFER-97 alloy (main component: 9% Cr-1.1% W-0.20% V-0.12% Ta-0.01% Ti) in Europe and ORNL 9Cr- in the US 2WVTa (main component: 9% Cr-2.0% W-0.25% V-0.07% Ta) was developed.

However, SFR fuel cladding is used in harsh conditions where high temperature and high speed neutrons are irradiated, and there is still a need for the development of high chromium ferrite / martensitic steels having excellent creep performance at high temperatures.

Accordingly, the present inventors have been researching to develop high chromium ferrite / martensitic steels exhibiting excellent creep performance at high temperature, and have optimized creep performance by optimizing the content of alloying elements such as niobium, tantalum, tungsten, nitrogen, boron, and carbon. The high chromium ferrite / martensitic steels shown were developed and the present invention was completed.

It is an object of the present invention to provide a high chromium ferrite / martensitic steel for sodium cooled fast reactor (SFR) nuclear fuel materials having excellent creep performance and a method of manufacturing the same.

In order to achieve the above object, the present invention is 0.04 to 0.13% by weight of carbon, 0.03 to 0.07% by weight of silicon, 0.40 to 0.50% by weight of manganese, 0.40 to 0.50% by weight of nickel, 8.5 to 9.5% by weight of chromium and 0.45 to 0.55% by weight of molybdenum %, 0.10 to 0.25% by weight of vanadium, 0.02 to 0.10% by weight of tantalum, 0.21 to 0.25% by weight of niobium, 1.5 to 3.0% by weight of tungsten, 0.015 to 0.025% by weight of nitrogen, 0.01 to 0.02% by weight of boron and iron balance Provides chromium ferrite / martensitic steels.

The high chromium ferrite / martensitic steel is preferably characterized in that it does not contain cobalt.

The high chromium ferrite / martensitic steel according to the present invention exhibits excellent tensile strength and creep resistance by optimizing the content of alloying elements such as niobium, tantalum, tungsten, nitrogen, boron, and carbon. It can be usefully used as the fourth generation SFR fuel material used in the conditions.

1 is a schematic diagram showing the development of high chromium ferrite / martensitic steels;
2 is a graph showing the yield strength at 650 ℃ of high chromium ferrite / martensitic steel according to an embodiment of the present invention;
3 is a graph showing the tensile strength at 650 ℃ of high chromium ferrite / martensitic steel according to an embodiment of the present invention;
4 is a graph showing creep performance of high chromium ferrite / martensitic steel at 650 ° C. according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail.

The present invention comprises 0.04-0.13 wt% carbon, 0.03-0.07 wt% silicon, 0.40-0.50 wt% manganese, 0.40-0.50 wt% nickel, 8.5-9.5 wt% chromium, 0.45-0.55 wt% molybdenum, 0.10-0.25 wt% vanadium High chromium ferritic / martensitic steels containing%, tantalum 0.02-0.10 wt%, niobium 0.21-0.25 wt%, tungsten 1.5-3.0 wt%, nitrogen 0.015-0.025 wt%, boron 0.01-0.02 wt% and iron balance to provide.

In addition, the present invention is 0.04 to 0.13% by weight of carbon, 0.03 to 0.07% by weight of silicon, 0.40 to 0.50% by weight of manganese, 0.40 to 0.50% by weight of nickel, 8.5 to 9.5% by weight of chromium, 0.45 to 0.55% by weight of molybdenum and 0.10 to 0% of vanadium. 0.25 wt%, tantalum 0.02-0.10 wt%, niobium 0.21-0.25 wt%, tungsten 1.5-3.0 wt%, nitrogen 0.015-0.025 wt%, boron 0.01-0.02 wt% and the balance of iron, preferably cobalt It provides a high chromium ferrite / martensite steel, characterized in that it does not contain.

Further, the present invention is 0.04 to 0.13% by weight of carbon, 0.03 to 0.07% by weight of silicon, 0.40 to 0.50% by weight of manganese, 0.40 to 0.50% by weight of nickel, 8.5 to 9.5% by weight of chromium, 0.45 to 0.55% by weight of molybdenum and 0.10 to 0% of vanadium. 0.25% by weight, 0.02 to 0.10% by weight of tantalum, 0.21 to 0.25% by weight of niobium, 1.5 to 3.0% by weight of tungsten, 0.015 to 0.025% by weight of nitrogen, 0.01 to 0.02% by weight of boron and high chromium ferrite as the essential components Provides martensitic steel. The term “essential” means that in addition to the components, impurities may be included inevitably included in the manufacturing process.

Hereinafter, the role and effect of the element added to the high chromium ferrite / martensitic steel according to the present invention.

(1) carbon (C)

In the high chromium ferrite / martensitic steel according to the present invention, carbon forms carbide to exhibit precipitation hardening effect, and the preferred carbon content is 0.04 to 0.13% by weight. If the carbon content is less than 0.04% by weight, the room temperature mechanical strength is low and the toughness is also deteriorated. In particular, the Cr equivalent is increased, so that the delta ferrite is generated. When the carbon content is more than 0.13% by weight, many carbides are formed and such carbides are There is a problem that the coarsening during use loses the strengthening effect by the precipitate.

(2) silicon ( Si )

In the high chromium ferrite / martensitic steel according to the present invention, silicon serves to improve oxidation resistance and acts as a deoxidizer during steelmaking. Preferred silicon content is 0.03 to 0.07 wt%. If the content of the silicon is less than 0.03% by weight, there is a problem that the corrosion resistance is lowered, and when the content of the silicon exceeds 0.07% by weight, there is a problem of promoting the production of laves phase to reduce the toughness.

(3) manganese ( Mn )

In the high chromium ferrite / martensitic steel according to the present invention, manganese serves to improve the hardenability, and the preferred manganese content is 0.40 to 0.50% by weight. If the content of the manganese is less than 0.40% by weight, there is a problem in the hardenability, and if the content of the manganese exceeds 0.50% by weight, there is a problem of lowering creep resistance.

(4) nickel ( Ni )

In the high chromium ferrite / martensitic steel according to the invention, nickel serves to increase the chromium (Cr) equivalent to inhibit the production of delta ferrite, and the preferred nickel content is 0.40 to 0.50% by weight. If the content of nickel is less than 0.40% by weight, there is a problem of generating delta ferrite vulnerable to toughness, and if the content of nickel is more than 0.50% by weight, there is a problem of deteriorating creep resistance like manganese.

(5) chrome ( Cr )

In the high chromium ferritic / martensitic steels according to the invention, chromium is known to increase corrosion resistance and high temperature strength, and the preferred chromium content is 8.5 to 9.5% by weight. If the content of chromium is less than 8.5% by weight, there is a problem that the resistance to high temperature oxidation and corrosion is lowered, and if it is more than 9.5% by weight, creep resistance is deteriorated.

(6) molybdenum ( Mo )

In the high chromium ferrite / martensitic steel according to the present invention, molybdenum is an element exhibiting a solid solution strengthening effect, and a preferable molybdenum content is 0.45 to 0.55 wt%. The content of molybdenum is correlated with the content of tungsten, and in the steel with tungsten, when the content of molybdenum is less than 0.45% by weight, the chromium equivalent is lowered to produce delta ferrite. There is a problem of mass producing Laves images.

(7) vanadium (V)

In the high chromium ferrite / martensitic steel according to the present invention, vanadium is an alloying element exhibiting precipitation hardening, and a preferable content of vanadium is 0.1 to 0.25% by weight. If the content of the vanadium is less than 0.1% by weight, the formation position of the precipitate is reduced, and the carbides are not uniformly distributed, resulting in coarse carbides resulting in worse creep resistance. There is a problem of consuming both carbon and nitrogen, making it difficult to produce other forms of carbide during use.

(8) niobium ( Nb )

In the high chromium ferrite / martensitic steel according to the present invention, niobium is an alloying element exhibiting precipitation hardening, and a preferable niobium content is 0.21 to 0.25 wt%. If the content of niobium is less than 0.21% by weight, sufficient niobium precipitates may not be formed, resulting in austenite grain growth during normalizing and deteriorating mechanical performance. If the content of niobium exceeds 0.25% by weight, unused niobium during normalizing Increasing the content of the vanadium to reduce the effective amount of vanadium precipitates, and the consumption of carbon in the matrix to reduce the amount of carbide precipitation such as M23C6 has a problem of lowering the creep resistance for a long time.

(9) tantalum ( Ta )

In the high chromium ferrite / martensitic steel according to the present invention, tantalum is contained in the niobium precipitate as a low emissive element and serves to exhibit a precipitation strengthening effect. In the present invention, the tantalum is preferably added in an amount of 0.02 to 0.10% by weight in order to exhibit excellent mechanical properties, and when it exceeds 0.10% by weight, there is the same problem as an excessive addition of niobium.

(10) Tungsten (W)

In the high chromium ferrite / martensitic steel according to the present invention, tungsten is a representative solid solution hardened alloy element, and the preferred content of tungsten is 1.5 to 3.0% by weight. If the content of tungsten is less than 1.5% by weight, there is a problem in effective solid solution strengthening, and if it exceeds 3.0% by weight, there is a problem in that Laves phase is known to worsen creep resistance and toughness for a long time.

(11) nitrogen (N)

In the high chromium ferrite / martensitic steel according to the present invention, nitrogen forms a nitride or invades so as to increase the strength. However, in steels with more than a certain amount of boron, the added nitrogen forms boron nitride, which degrades creep performance. Therefore, the preferred nitrogen content in the boron-added steel is 0.015 to 0.025% by weight. If the content of nitrogen is less than 0.015% by weight, there is a problem that the corrosion resistance is lowered, and if the content of nitrogen exceeds 0.025% by weight, boron nitride is formed to cause a sharp decrease in creep performance.

(12) Boron (B)

In the high chromium ferrite / martensitic steel according to the present invention, boron segregates at grain boundaries to strengthen grain boundaries, thereby improving high temperature creep resistance, and the preferred boron content is 0.01 to 0.02% by weight. If the boron content is less than 0.01% by weight, effective grain boundary strengthening may not be obtained. If the boron content is more than 0.02% by weight, there is a problem in manufacturability.

The high chromium ferrite / martensitic steels according to the present invention are known to improve the heat resistance and creep rupture strength of ferrite / martensitic steels, but when used in nuclear reactors, cobalt (Co), which has a very large problem of radioactive energy, is used. It is not included and exhibits very good tensile strength and creep resistance compared to the high chromium ferrite / martensitic steels used as materials for conventional reactor components, and therefore, for nuclear power plant materials, in particular components of nuclear reactors (e.g., reactors) Core parts, etc.). Furthermore, the high chromium ferritic / martensitic steels according to the invention are ferritic / martensitic steels as parts of the fourth generation sodium cooling fasteners (SFR) used in harsh conditions of high temperature and high neutron weight, for example fourth generation It can be usefully used as SFR core parts.

In this case, the core refers to the portion of the nuclear fission reaction to represent the center of the nuclear reactor, the core component that can be used for the high chromium ferrite / martensite steel according to the present invention nuclear fuel cladding tube, duct, wire wrap, etc. By using the core parts made of high chromium ferrite / martensitic steel according to the present invention, it protects nuclear fuel safely from fission reaction even in harsh conditions of high temperature and high neutron weight, and radioactive material leaks to the outside. It can be prevented and exhibits compatibility and mechanical properties with excellent liquid sodium, so that it can be used for a long time in high temperature and high neutron irradiation environment.

The high chromium ferritic / martensitic steels according to the invention can be produced using conventional methods well known in the art, preferably

Mixing and dissolving the alloying composition elements to produce an ingot (step 1); Hot rolling the ingot prepared in step 1 (step 2); Cooling the ingot hot rolled in the step 2 after the normalizing (Normalizing) process (step 3); And by tempering (Tempering) the alloy subjected to the normalized in step 3 can be produced by a method comprising the step of producing a high chromium ferrite / martensite steel by air cooling (step 4).

Further intermediate heat treatment and cold treatment after the tempering treatment of step 3 above to produce the high chromium ferrite / martensitic steels according to the invention from the fuel components of the required type (e.g., fuel cladding or ducts in sodium cooling fast reactors). After repeating the process several times may further comprise the step of the final heat treatment.

Hereinafter, the manufacturing method of the present invention will be described in detail step by step.

First, step 1 is a step of preparing an ingot by mixing and melting the alloy composition elements.

As the alloy composition element, carbon, silicon, manganese, nickel, chromium, vanadium, tantalum, niobium, tungsten, nitrogen, boron, and balance iron may be used. Specifically, 0.04 to 0.13 wt% carbon and 0.03 to 0.07 wt% silicon. %, Manganese 0.40 to 0.50 weight%, nickel 0.40 to 0.50 weight%, chromium 8.5 to 9.5 weight%, molybdenum 0.45 to 0.55 weight%, vanadium 0.10 to 0.25 weight%, tantalum 0.02 to 0.10 weight%, niobium 0.21 to 0.25 weight% , Tungsten 1.5-3.0 wt%, nitrogen 0.015-0.025 wt%, boron 0.01-0.02 wt% and iron balance.

Vacuum induction (VIM) method can be used for the production of the ingot.

Specifically, an induction current is applied to the melting chamber in a high vacuum (1 × 10 ⁻⁵ to 0.5 torr) atmosphere to first dissolve the alloying element, and then a deoxidizer such as aluminum or silicon is added thereto. Trace elements, especially nitrogen, are charged to the molten metal at the point when dissolution is almost complete, and then a sample for component analysis is collected. After dissolution is completed, the molten metal is poured into a cuboid at 1500 ° C. to perform tapping, and an oxide layer on the surface is subjected to mechanical processing to prepare an ingot.

Next, step 2 is a step of hot rolling the ingot prepared in step 1.

Through the hot rolling to produce a hot workpiece suitable for hot working. At this time, the hot rolling is preferably carried out for 0.5 to 2 hours at a temperature of 1100 ~ 1200 ℃. If it is out of the above range, that is, below 1100 ° C., the purpose of solution annealing cannot be sufficiently achieved, and if it exceeds 1200 ° C., the size of the prior-γ phase grains will increase so that the mechanical properties of the final product may be increased. Can cause deterioration problems.

Next, step 3 is a step of air cooling after normalizing the product hot-processed in step 2.

The normalizing treatment is preferably performed for 0.5 to 2 hours in a γ-phase temperature range of 1000 to 1100 ° C., which re-dissolves an undesired precipitated phase in a hot processed product and adjusts the cooling temperature to control the size of the precipitate. This is to control the amount.

Next, step 4 is a step of manufacturing a high chromium ferrite / martensitic steel by tempering the alloy normalized in step 3 and then air cooled.

The tempering treatment is preferably performed at 600 to 800 ° C. for 1 to 3 hours, in order to produce a fine and uniformly desired stable precipitated phase.

By such a method it is possible to produce high chromium ferrite / martensitic steel according to the present invention.

In addition, in order to manufacture the high chromium ferrite / martensitic steel according to the present invention as SFR fuel parts, after the heat treatment in Step 3, the additional heat treatment and cold working may be further repeated, followed by a final heat treatment. have.

Specifically, the additional intermediate heat treatment is performed for 1 to 3 hours at 600 to 800 ° C., and the cold working is continuously performed for 2 to 4 times, and then the final heat treatment is performed for 1 to 3 hours at 600 to 800 ° C. Can be carried out to produce high chromium ferrite / martenside steels.

The high chromium ferrite / martensitic steels produced by the above method exhibited excellent tensile strength values and excellent creep performance at high temperatures of 650 ° C., thus exhibiting very good mechanical properties compared to conventional high chromium ferrite / martensitic steels. It can be very useful for materials such as fuel cladding, ducts and wire wraps, which are the main core components of the Sodium Cooling High-Speed Reactor, the fourth-generation reactor used in high-irradiation harsh conditions.

On the other hand, boron added to the high chromium ferrite / martensitic steel of the present invention is a high grain ferritic / martensitic steel by suppressing the movement of the grain boundary when used at a high temperature for a long time at high temperature when an appropriate amount is added as a grain boundary strengthening element. It can improve creep performance. However, when a certain amount of nitrogen is added together with boron, boron is easily combined with nitrogen to form boron nitride, and the formation of this precipitate greatly reduces the grain boundary strengthening effect of boron and also precipitates boron nitride. The creep performance of high chromium ferrite / martensitic steels is deteriorated. Therefore, in order to improve creep performance by addition of boron, it is necessary to not only add a certain amount of boron, but also limit the nitrogen content to a certain amount or less.

Hereinafter, the present invention will be described in more detail by way of examples.

However, the following examples are only examples of the present invention, and the scope of the present invention is not limited to the following examples.

Example 1 Fabrication of High Chromium Ferrite / Martensitic Steels

Test materials 0.065% carbon, 0.043% silicon, 0.45% manganese, 0.44% nickel, 0.44% chromium, 9.04% chromium, 0.5% molybdenum, 0.2% vanadium, 0.05% tantanium, 0.21% niobium, tungsten 1.99 Weight percent, 0.02 weight percent nitrogen, 0.015 weight percent boron and the balance iron were prepared in a 30 kg ingot in a vacuum induction furnace. The ingot was held at 1150 ° C. for 2 hours and then hot rolled to give a final thickness of 15 mm.

Since the following heat treatment was performed.

Specifically, the alloy was normalized at 1050 ° C. for 1 hour and then air cooled.

Thereafter, the normalized alloy was air cooled by performing a tempering treatment at 750 ° C. for 2 hours to prepare a high chromium ferrite / martensitic steel.

The high chromium ferritic / martensitic steel is additionally subjected to repeated repeated two to four times of intermediate heat treatment and cold working for 1 to 3 hours at 600 to 800 ° C., followed by final heat treatment at 600 to 800 ° C. for 1 to 3 hours. To produce a high chromium ferrite / martensitic steel in the final product.

<Example 2>

As test materials, carbon 0.069%, silicon 0.042%, manganese 0.452%, nickel 0.450%, chromium 9.1%, molybdenum 0.51%, vanadium 0.107%, tantalum 0.05%, niobium 0.21%, tungsten 2.0 A high chromium ferritic / martensitic steel was prepared in the same manner as in Example 1 except for using the wt%, 0.02 wt% nitrogen, 0.015 wt% boron and the balance iron.

&Lt; Comparative Example 1 &

A commercially available ASTM Gr.92 alloy was used.

Composition: 0.096 wt% carbon, 0.060 wt% silicon, 0.44 wt% manganese, 0.19 wt% nickel, 8.95 wt% nickel, molybdenum 0.48 wt%, vanadium 0.204 wt%, niobium 0.055 wt%, tungsten 1.9 wt%, nitrogen 0.045 Weight percent and balance iron)

Comparative Example 2

A commercially available HT9 alloy was used.

(Composition: Carbon 0.192%, Silicon 0.14%, Manganese 0.490%, Nickel 0.484%, Chromium 12.05%, Molybdenum 1.00%, Vanadium 0.304%, Niobium 0.022%, Tungsten 0.496%, Nitrogen 0.011 Weight percent and balance iron)

The compositions of the high chromium ferrite / martensitic steels prepared in Examples 1 and 2 and Comparative Examples 1 and 2 are summarized in Table 1 below.

division
Composition (% by weight) C Si Mn Ni Cr Mo V Ta Nb W N B Example 1 0.065 0.043 0.45 0.44 9.04 0.5 0.2 0.05 0.21 1.99 0.02 0.015 Example 2 0.069 0.042 0.452 0.450 9.1 0.51 0.107 0.05 0.21 2.0 0.02 0.015 Comparative Example 1 0.096 0.060 0.44 0.19 8.95 0.48 0.204 - 0.055 1.9 0.045 - Comparative Example 2 0.192 0.14 0.490 0.484 12.05 1.0 0.304 - 0.022 0.496 0.011 -

Experimental Example Measurement of High Chromium Ferrite / Martensitic Steels

(1) yield strength and The tensile strength  Measure

Yield strength and tensile strength were measured by a tensile test (ASTM E 8M-08) at 650 ° C. to measure the high-temperature characteristics of the high chromium ferritic / martensitic steels prepared in Examples 1 and 2 and Comparative Examples 1 and 2. The results are shown in Table 2 and FIGS. 1 and 2.

division Yield strength (MPa) Tensile Strength (MPa) Example 1 333 347 Example 2 329 342 Comparative Example 1 272 292 Comparative Example 2 323 356

As shown in Table 2 and FIGS. 1 and 2, the high chromium ferrite / martensite steel according to the present invention exhibits a yield strength of about 330 MPa and a tensile strength of about 340 to 350 MPa. It showed excellent yield strength and tensile strength when compared with steel (Gr. 92 alloy; Comparative Example 1, yield strength of 272 MPa and tensile strength of 292 MPa).

Therefore, the high chromium ferrite / martensitic steel according to the present invention exhibits high yield strength and tensile strength even at high temperatures of 650 ° C., so that it can be usefully used as the fourth generation SFR fuel material used in the harsh conditions of high temperature and high neutron irradiation. have.

(2) Elongation  Measure

In order to measure the high-temperature characteristics of the high chromium ferrite / martensitic steels prepared in Examples 1 and 2, the elongation was measured through a tensile test (ASTM E 8M-08) at 650 ° C. and the results are shown in Table 3.

division Elongation (%) Example 1 18.8 Example 2 18.5

As shown in Table 3, the high chromium ferrite / martensitic steels prepared according to Examples 1 and 2 of the present invention exhibited elongation of at least about 18%, thereby being used in the fourth generation SFRs used under the harsh conditions of high temperature and high neutron irradiation. It can be usefully used as a fuel material.

(3) creep performance measurement

In order to measure the creep performance at high temperatures of the high chromium ferritic / martensitic steels prepared according to Examples 1 and 2 and Comparative Examples 1 and 2, when a stress of 150 MPa was applied at a temperature of 650 ° C. and a stress of 140 MPa, 130 The break time at the time of applying the stress of MPa and the stress of 120 MPa was measured and the results are shown in Table 4 and FIG. 3.

division
Creep Resistance (Hour) 120 MPa 130 MPa 140 MPa 150 MPa Example 1 - 6889 5216 3071 Example 2 4896 4290 2928 1750 Comparative Example 1 2641 2012 814 451 Comparative Example 2 852 261 148 -

As shown in Table 4 and FIG. 3, the high chromium ferrite / martensitic steels produced by Examples 1 and 2 of the present invention exhibited much longer time than the breakdown than Comparative Examples 1 and 2. Compared with the conventional high chromium ferritic / martensitic steel of 2, it showed excellent creep performance.

Therefore, the high chromium ferrite / martensitic steel according to the present invention exhibits improved creep performance even at high temperatures of 650 ° C., and thus can be usefully used as the fourth generation SFR fuel material used in the harsh conditions of high temperature and high neutron irradiation.

Claims (12)

0.04 to 0.13 wt% carbon, 0.03 to 0.07 wt% silicon, 0.40 to 0.50 wt% manganese, 0.40 to 0.50 wt% nickel, 8.5 to 9.5 wt% chromium, 0.45 to 0.55 wt% molybdenum, 0.10 to 0.25 wt% vanadium, tantalum High chromium ferrite, comprising 0.02 to 0.10% by weight, niobium 0.21 to 0.25% by weight, tungsten 1.5 to 3.0% by weight, nitrogen 0.015 to 0.025% by weight, boron 0.01 to 0.02% by weight, remaining iron and other unavoidable impurities Martensite River.
The high chromium ferrite / martensitic steel of claim 1, wherein the high chromium ferrite / martensite steel does not comprise cobalt.
0.04 to 0.13 wt% carbon, 0.03 to 0.07 wt% silicon, 0.40 to 0.50 wt% manganese, 0.40 to 0.50 wt% nickel, 8.5 to 9.5 wt% chromium, 0.45 to 0.55 wt% molybdenum, 0.10 to 0.25 wt% vanadium, tantalum High chromium ferritic / martensitic steel consisting essentially of 0.02 to 0.10 wt%, niobium 0.21 to 0.25 wt%, tungsten 1.5 to 3.0 wt%, nitrogen, 0.015 to 0.025 wt%, boron 0.01 to 0.02 wt% and iron balance.
Mixing and dissolving the alloying composition elements to produce an ingot (step 1);
Hot rolling the ingot prepared in step 1 (step 2);
Cooling the ingot hot rolled in the step 2 after the normalizing (Normalizing) process (step 3); And
The high chromium of any one of claims 1 to 3 comprising the step of preparing a high chromium ferrite / martensitic steel by tempering the alloy subjected to the normalizing treatment in step 3 and then air-cooling (step 4). Method for producing ferritic / martensitic steels.
5. The method of claim 4, wherein the ingot of step 1 is manufactured using a vacuum induction melting (VIM) method. 6.
5. The method of claim 4, wherein the hot rolling of Step 2 is performed at a temperature of 1100 to 1200 ° C. for 0.5 to 2 hours. 6.
5. The method of claim 4, wherein the normalizing treatment of step 3 is performed at 1000 to 1100 ° C. for 0.5 to 2 hours. 6.
5. The method of claim 4, wherein the tempering treatment of step 4 is performed at 600 to 800 ° C. for 1 to 3 hours. 6.
According to claim 4, after performing step 4, the additional intermediate heat treatment is performed for 1 to 3 hours at 600 ~ 800 ℃ and successively cold working is performed two to four times, and then the final heat treatment Method for producing a high chromium ferrite / martensitic steel further comprises the step of performing for 1 to 3 hours at 600 ~ 800 ℃.
A core part of a nuclear reactor using the high chromium ferrite / martensitic steel of claim 1.
11. The core part of a nuclear reactor of claim 10, wherein said reactor is a sodium cooling fast reactor (SFR).
The core part of a nuclear reactor according to claim 10, wherein said core part is any one selected from the group consisting of a fuel cladding tube, a duct, and a wire wrap.

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