KR101769745B1 - Ferrite-martensitic oxide dispersion strengthened steel with excellent creep resistance and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a method of manufacturing a steel sheet comprising 0.02 to 0.2 wt% of carbon (C), 8 to 12 wt% of chromium (Cr), 0.1 to 0.5 wt% of yttria, 0.2 to 2 wt% of molybdenum (Mo) (Fe) in an amount of 0.01 to 1 wt%, vanadium (V) in an amount of 0.01 to 0.3 wt%, zirconium (Zr) in an amount of 0 to 0.3 wt%, and nickel (Ni) in an amount of 0 to 0.5 wt% To a ferrite-martensitic oxide-dispersed steel reinforced steel having improved high temperature creep resistance and a method for producing the same. The ferrite-martensitic oxide-dispersed steel reinforced steel is excellent in tensile strength and creep resistance at high temperature, especially at 700 ° C, and can be used as core structural parts (nuclear fuel cladding, duct, wire, It is expected that it can be usefully used as a material of an ultrashort pressure steam generator part (rotor, shaft, etc.) for thermal power generation, and further, it can be usefully used as a material of an engine part (disk, nozzle, etc.) for an aircraft.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a ferrite-martensite-based oxide dispersion strengthened steel having improved creep resistance and a method for producing the same.

The present invention is the creep resistance is improved ferrite-relates to a martensitic-based oxide dispersion strengthened steel and its manufacturing method, and more particularly to iron (Fe) - chromium (Cr) - yttria (Y ₂ O ₃₎ for the alloy system The present invention relates to a ferrite material having improved high temperature creep resistance by stabilizing a martensite phase by adding molybdenum (Mo), titanium (Ti) and vanadium (V) as an alloying element to improve high temperature strength by fine dispersion of precipitates, Martensitic oxide dispersion strengthened steel and a method of manufacturing the same.

Iron (Fe) -crome (Cr) alloys containing 8 to 12% by weight of chromium in iron are generally tempered and then tempered to form tempered martensite structure. These high chromium alloys have excellent neutron irradiation resistance and mechanical properties at high temperatures and are used as materials for structural parts of nuclear power systems and thermal power generators such as sodium cooling high speed furnace. However, at high temperatures above 600 ° C, the tensile strength and creep strength sharply decrease, limiting the temperature used as the structural material. Oxide Dispersion Strengthened steel has been developed as an alternative to dispersing oxides in an alloy base to improve high temperature mechanical properties. Oxide dispersion strengthened steel is an alloy in which iron oxide (Fe) - chromium (Cr) based alloy base is uniformly dispersed nano oxide with excellent thermal stability such as ytria (Y ₂ O ₃ ) High temperature mechanical properties such as creep strength were improved by dispersion strengthening compared with general alloys.

The conventional oxide-dispersed reinforced steel has an advantage of high-temperature strength compared to a general alloy, but still has a problem that design conditions are not sufficiently satisfied. To solve this problem, an alloy element such as tungsten (W), tantalum (Ta), or niobium (Nb) is added to an alloy of iron (Fe) - chromium (Cr) - yttria (Y ₂ O ₃ ) However, oxide-dispersed reinforced steels with tungsten (W) added as solid solution strengthening elements, when used for a long time in a high-temperature stress atmosphere, generate Laves phase such as brittle Fe (Cr) ₂ W, . Therefore, it is necessary to develop a ferrite / martensite oxide dispersion strengthened steel which is improved in high temperature creep resistance and neutron irradiation resistivity applicable to the core component of the core at high speed in sodium cooling.

Disclosure of Invention Technical Problem [8] The present invention has been made to solve the above-mentioned problems in the prior art, and it is an object of the present invention to provide a Fe-Cr-Y ₂ O ₃ -based alloy having a basic composition of 0.02 to 0.2% 12 wt%, yttria _{(Y 2 O 3) 0.1 ~} 0.5 wt%, molybdenum (Mo) 0.2 ~ 2 weight%, titanium (Ti) 0.01 ~ 0.5 wt.%, manganese (Mn) 0.01 ~ 1 wt%, vanadium ( V) 0.01 to 0.3% by weight of zirconium (Zr), 0 to less than 0.3% by weight of zirconium (Zr), 0 to less than 0.5% by weight of nickel (Ni) and the remainder is ferrite-martensitic oxide dispersion Reinforced steel and a method of manufacturing the same.

However, the technical problem to be solved by the present invention is not limited to the above-mentioned problems, and other matters not mentioned can be clearly understood by those skilled in the art from the following description.

The invention carbon (c) 0.02 ~ 0.2 wt.%, Chromium (Cr) 8 ~ 12% by weight of yttria _{(Y 2 O 3) 0.1 ~} 0.5 wt%, molybdenum (Mo) 0.2 ~ 2% by weight, titanium (Ti Manganese oxide dispersion strengthened steel having excellent creep resistance including 0.01 to 0.5% by weight, manganese (Mn) of 0.01 to 1% by weight, vanadium (V) of 0.01 to 0.3% by weight and the balance of iron (Fe) to provide.

The present invention also provides a method for producing a ferritic-martensitic oxide-dispersed steel reinforced steel excellent in creep resistance including the following steps:

(a) the carbon (c), chromium (Cr), molybdenum (Mo), titanium (Ti), manganese (Mn), vanadium (V), iron metal powder and yttria containing (Fe) (Y ₂ O ₃ ) Powders and then subjecting them to a mechanical alloying treatment to produce an alloy powder;

 (b) charging the canned alloy with the mechanically alloyed alloy powder to perform a degassing treatment;

(c) hot-working the degassed alloy powder to produce an oxide dispersion-strengthened steel; And

(d) cold-working the hot-worked oxide-dispersed steel.

The ferrite-martensitic oxide-dispersed steel reinforced steel according to the present invention contains 0.02 to 0.2 wt% of carbon (C), 8 to 12 wt% of chromium (Cr), 0.1 to 0.5 wt% of yttria (Y ₂ O ₃ ) (V) 0.01 to 0.3% by weight, zirconium (Zr) 0 to 0.3% by weight or less, nickel (Ni) (Ni) of more than 0 and less than 0.5% by weight and the balance of iron (Fe), and is excellent in creep resistance, and can be used as core structural parts (nuclear fuel cladding, duct, wire, It is expected that it can be used as a material of an edgy critical pressure steam generator part (rotor, shaft, etc.) for thermal power generation and furthermore it can be used as a material of an engine part (disk, nozzle, etc.) for an aircraft.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flowchart showing a method of manufacturing a ferrite-martensitic oxide-dispersed steel reinforced steel of the present invention. FIG.
2 is a graph showing the tensile test results of a conventional oxide dispersion strengthened steel and a ferrite-martensitic oxide dispersion strengthened steel according to the present invention at room temperature and 700 ° C.
3 is a graph showing the creep test results of a conventional oxide dispersion strengthened steel and a ferrite-martensitic oxide dispersion strengthened steel according to the present invention at 700 ° C.

The present inventors have found that the core structure parts of a sodium cooled fast, thermal power plant steam generator components or results, the conventional Fe-Cr-Y a study in order to improve the oxide dispersion strengthened Creep resistance is used as an aircraft material for engine parts for ₂ In the case of adding molybdenum (Mo) to the O ₃ -based oxide dispersion strengthening alloy and adding a trace amount of alloying elements of titanium (Ti), vanadium (V) and manganese (Mn) It was confirmed that the long-term creep resistance was improved by suppressing the generation of the film. Based on this, the present invention was completed.

Hereinafter, the present invention will be described in detail.

The present invention is a carbon (C) 0.02 ~ 0.2 wt.%, Chromium (Cr) 8 ~ 12% by weight of yttria _{(Y 2 O 3) 0.1 ~} 0.5 wt%, molybdenum (Mo) 0.2 ~ 2 weight%, titanium (Ti Martensitic oxide-dispersed steel reinforced steel comprising 0.01 to 0.5 wt% of manganese (Mn), 0.01 to 1 wt% of vanadium (V) and 0.01 to 0.3 wt% of vanadium (V) .

The oxide-dispersed reinforcing alloy may further include zirconium (Zr) and nickel (Ni), or a mixture thereof. The zirconium (Zr) may further include more than 0 and less than 0.3 wt% Ni) may be further contained in an amount of more than 0 to 0.5% by weight.

That is, the oxide dispersion strengthened steel of the present invention includes carbon, chromium, yttria, molybdenum, titanium, manganese, vanadium, and iron to obtain high creep resistance.

When the content of chromium (Cr) is less than 8% by weight, corrosion resistance is deteriorated. When it exceeds 12% by weight, a martensite phase is difficult to be formed. By weight, more preferably 9 to 11% by weight.

When the content of yttria (Y ₂ O ₃ ) is less than 0.1% by weight, the dispersion strengthening effect is insignificant. When the content is more than 0.5% by weight, the effect of strengthening dispersion due to the residual dispersion particles is increased, , Yttria (Y ₂ O ₃ ) is preferably from 0.1 to 0.5% by weight, more preferably from 0.3 to 0.4% by weight.

When the content of molybdenum (Mo) is less than 0.2% by weight, the effect of improving high-temperature strength is insignificant. When the content of molybdenum (Mo) exceeds 2% by weight, molybdenum (Mo) Mo) is preferably from 0.2 to 2% by weight, more preferably from 0.7 to 1.5% by weight. That is, compared with the conventional oxide dispersion strengthened steel, addition of molybdenum (Mo) instead of tungsten (W) improves the high temperature strength and also produces Laves phase under high temperature stress conditions exposed to a neutron irradiation atmosphere It is possible to improve the long-term creep characteristics as well.

The content of titanium (Ti) is 0.01 to 0.5 wt%. Such titanium (Ti) is combined with yttria (Y ₂ O ₃ ) during heating to form a Y-Ti-O composite oxide such as Y ₂ Ti ₂ O ₇ or Y ₂ TiO ₅ , The strength can be improved.

Manganese (Mn) is an austenite-forming element and enhances the strength of the matrix by strengthening martensite. The content of manganese (Mn) is preferably 0.01 to 1% by weight.

Vanadium (V) is a precipitation strengthening element that forms fine MX precipitates and is an element that improves high temperature tensile strength and creep resistance. When the content of vanadium (V) is less than 0.01% by weight, the effect is insignificant. When the content of vanadium (V) is more than 0.3% by weight, a brittle delta ferrite phase is formed. The present invention can achieve high creep resistance by using vanadium, preferably 0.05% to 0.15% by weight, and most preferably 0.1% by weight as in the new alloy 4 described in the examples of the present invention. When it has excellent strength.

The content of zirconium (Zr) is preferably in the range of more than 0 to 0.3% by weight, and the zirconium (Zr) also bonds with yttria (Y ₂ O ₃ ) to form a Y- By uniformly dispersing, strength characteristics can be further improved.

Nickel (Ni) also serves as an austenite forming element to enhance the strength of the matrix by strengthening martensite. The content of nickel (Ni) is preferably in the range of more than 0 to 0.5% by weight.

Therefore, the ferrite-martensitic oxide-dispersed steel reinforced steel of the present invention can be used for a high-speed fuel cladding, a duct, a wire, a sealing plug, a rotor of a super critical pressure steam generator for thermal power generation, And may be used as a structural component material.

As another aspect of the present invention,

There is provided a ferritic-martensitic oxide-dispersed steel reinforced steel manufacturing method excellent in creep resistance including the following steps:

(a) the carbon (c), chromium (Cr), molybdenum (Mo), titanium (Ti), manganese (Mn), vanadium (V), iron metal powder and yttria containing (Fe) (Y ₂ O ₃ ) Powders and then subjecting them to a mechanical alloying treatment to produce an alloy powder;

(b) charging the canned alloy with the mechanically alloyed alloy powder to perform a degassing treatment;

(c) hot-working the degassed alloy powder to produce an oxide dispersion-strengthened steel; And

(d) cold-working the hot-worked oxide-dispersed steel.

A method of producing the ferrite-martensitic oxide-dispersed steel reinforced steel is schematically shown in Fig.

In the step (a), the metal powder may further include zirconium (Zr) or nickel (Ni).

In the step (a), a metal powder containing carbon (c), chromium (Cr), molybdenum (Mo), titanium (Ti), manganese (Mn), vanadium (V) Y ₂ O ₃ ) powder are mixed to form an alloy powder. The alloy powder is carbon (C) 0.02 ~ 0.2 wt.%, Chromium (Cr) 8 ~ 12% by weight of yttria _{(Y 2 O 3) 0.1 ~} 0.5 wt%, molybdenum (Mo) 0.2 ~ 2 weight%, titanium ( (Ni) more than 0 and not more than 0.5% by weight, and at least one selected from the group consisting of Ti, The remainder contains iron (Fe). After mixing these metal powders, mechanical alloying powders are prepared using mechanical alloying equipment such as a horizontal ball mill.

In step (b), the mechanical alloying powder produced by step (a) is degassed in vacuum, and more specifically, the mechanical alloying powder produced by step (a) is introduced into a can of carbon steel or stainless steel And then degassed at 400 to 650 ° C and 10 ^{to 4} torr for 1 to 4 hours.

In step (c), the mechanical alloying powder degassed by step (b) is subjected to hot working, and more specifically, in the hot isostatic pressing, hot forging, hot rolling and hot extrusion processes, Steel is manufactured.

In step (d), the oxide-dispersed tempered steel produced by step (c) may be cold worked, and more specifically, it may be performed alone or in combination in the cold rolling, cold drawing and cold filing processes.

In one embodiment of the present invention, a carbon material is used in an amount of 0.02 to 0.2 wt%, chromium (Cr) 8 to 12 wt%, yttria (Y ₂ O ₃ ) 0.1 to 0.5 wt%, molybdenum (Mo) 0.01 to 0.5 wt% of titanium (Ti), 0.01 to 1 wt% of manganese (Mn), 0.01 to 0.3 wt% of vanadium (V), 0 to 0.3 wt% of zirconium (Zr) Martensitic oxide-dispersed steel containing ferrite-martensitic oxide-dispersed steel containing iron (Fe) in an amount of not more than 1 wt% and the balance of iron (Fe) , It was confirmed that the ferrite-martensitic oxide-dispersed steel-reinforced steel according to the present invention had excellent tensile properties (see Example 2) as well as creep resistance at 700 ° C as compared with the conventional oxide-dispersed steel-reinforced steel (see Example 3 ).

Hereinafter, preferred embodiments of the present invention will be described in order to facilitate understanding of the present invention. However, the following examples are provided only for the purpose of easier understanding of the present invention, and the present invention is not limited by the following examples.

[ Example ]

Example  1. Manufacture of oxide-dispersed steel

A ferrite-martensitic oxide-dispersed steel having the composition shown in the following Table 1 was produced.

Fe C Cr W Mo Ti Mn Zr Ni V Y ₂ O ₃ Reference alloy Honey. 0.12 9 2 - 0.25 - - - - 0.35 New alloys 1 Honey. 0.12 10 - 1.2 0.1 0.3 0.1 0.2 - 0.35 New alloys 2 Honey. 0.12 10 - 1.2 0.1 0.6 0.1 0.2 - 0.35 New alloy 3 Honey. 0.12 10 - 1.2 0.1 0.6 0.1 - - 0.35 New alloys 4 Honey. 0.12 10 - 1.2 0.1 0.6 0.1 0.2 0.1 0.35

In other words, a high purity raw material powder (Fe, C, Cr, W, Mo, Ti, Mn, Zr, Ni, V; particle size 200mesh or less and a purity greater than 99%) and Y ₂ O ₃ powder (50nm or less, a purity of 99.9%) Were mechanically alloyed in an ultra-high purity argon (Ar) atmosphere at a rotating speed of 240 rpm for 48 hours using a horizontal ball mill (ZOZ GmbH, SIMOLOYER CM20) Filled in a stainless steel can, sealed, and degassed at 400 DEG C for 3 hours at a degree of vacuum of 10 ^-5 torr or less. The prepared powder filled cans were pressurized by hot isostatic pressures at 1150 ℃ and 100MPa for 3 hours and then heated again at 1150 ℃ for 1 hour and hot rolled at a thickness reduction rate of 80% or more to prepare oxide dispersion strengthened steel.

Example  2. Determination of tensile properties of oxide-dispersed steels

The yield strength, the maximum tensile strength and the total elongation were measured at room temperature and 700 ° C of the five types of ferrite-martensitic oxide-dispersed reinforced steels prepared in Example 1, and the results are shown in FIG. Tensile specimens were prepared in accordance with ASTM E8 standards after gauge lengths were taken parallel to the hot rolling direction of the oxide dispersion strengthened steel. The tensile test was carried out at room temperature and at a strain rate of ¹ x 10 ^-4 s ^-1 at 700 ° C. The tensile test was performed at least three times for each specimen and temperature, and the average value was calculated and reflected in the results.

As shown in Fig. 2, the yield strength of the conventional oxide-dispersed strengthened reference alloy was 916 MPa at room temperature, and the yield strengths of the new alloys 1, 2, 3 and 4 were 913, 917, 921 and 927 MPa, respectively, Strength was similar. However, the yield strength of the reference alloy, which is a conventional oxide-dispersed strengthening alloy, was 150 MPa at 700 ° C., while the yield strengths of 197 and 192 in the case of the new alloys 1, 2 and 3 of the present invention containing molybdenum, titanium, manganese, zirconium, , The new alloy 4 of the present invention having a yield strength of 193 MPa and further added with vanadium had a yield strength of 210 MPa, and it was confirmed that the tensile strength at high temperature was higher than that of the reference alloy.

From the above results, it was confirmed that the ferrite-martensitic oxide-dispersed steel-reinforced steel according to the present invention showed no significant difference in the room-temperature yield strength as compared with the conventional oxide-dispersed steel-reinforced steel, but exhibited excellent yield strength at 700 ° C.

Example  3. Confirmation of creep resistance of oxide-dispersed steel

The creep tests were performed at 700 ° C on the five types of oxide-dispersed steels produced in Example 1, and the results are shown in FIG.

As shown in Fig. 3, creep rupture times of the new alloys 1, 2, 3 and 4 of the present invention were significantly higher than those of the reference alloys under the stresses of 150 and 120 MPa.

From the above results, it was found that the ferrite-martensitic oxide-dispersed steel-reinforced steel according to the present invention has excellent high-temperature creep resistance and excellent long-term stability as compared with the conventional oxide-dispersed steel.

It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (3)

(C), 0.0 to 0.2 wt% of chromium (Cr), 9 to 11 wt% of chromium (Cr ₂ O ₃ ), 0.3 to 0.4 wt% of yttria, 0.7 to 1.5 wt% of molybdenum (Mo) (Ni) more than 0 and not more than 0.5 wt%, and the remainder is iron (Ni) in an amount of not more than 0.5 wt%, manganese (Mn) of 0.01 to 1 wt%, vanadium (V) of 0.05 to 0.15 wt%, zirconium ≪ / RTI > Fe)
Wherein the generation of Laves phase is suppressed and the Y-Ti-O composite oxide and the Y-Zr-O composite oxide are contained,
As a result of the tensile test at a strain of 1 × 10 ^-4 s ^-1 at 700 ° C., the creep test was carried out at a yield stress of 210 MPa or more and a stress of 120 MPa and 150 MPa at 700 ° C., Each of which is at least 88.9 hours and at least 15.1 hours
High strength ferrite-martensitic oxide dispersion strengthened steel with improved high temperature strength and creep resistance.
The ferrite-martensite-based oxide dispersion strengthened steel according to claim 1, wherein the ferrite-martensite-based oxide dispersion reinforced steel is a high-speed fuel cladding, a duct, a wire, a sealing plug, a rotor of a super critical pressure steam generator for thermal power generation, Wherein the ferrite - martensite-based oxide dispersion strengthening steel is used as a structural component material containing a ferrite - martensite-based oxide dispersion strengthening steel.
(a) at least one metal selected from the group consisting of C, Cr, Mo, Ti, Mn, V, Fe, Zr, Mixing the metal powder and yttria (Y ₂ O ₃ ) powder, and then subjecting the alloy powder to mechanical alloying to produce an alloy powder;
(b) charging the canned alloy with the mechanically alloyed alloy powder to perform a degassing treatment;
(c) hot-working the degassed alloy powder to produce an oxide dispersion-strengthened steel; And
(d) the alloy powder, the method comprising cold working the hot working an oxide dispersion strengthened steel is carbon (C) 0.02 ~ 0.2% by weight, chromium (Cr) 9 ~ 11% by weight of yttria (Y ₂ O ₃ ) 0.3 to 0.4 wt%, molybdenum (Mo) 0.7 to 1.5 wt%, titanium (Ti) 0.01 to 0.5 wt%, manganese (Mn) 0.01 to 1 wt%, vanadium (V) Zr) of more than 0 and not more than 0.3% by weight, Ni (Ni) of more than 0 and not more than 0.5% by weight, and the balance comprising iron (Fe)
In the step (c), the hot working may be performed through any one or a combination thereof selected from the group consisting of hot isostatic pressing, hot forging, hot rolling and hot extrusion,
In the step (d), the cold working may be performed through any one or a combination thereof selected from the group consisting of cold rolling, cold drawing and cold peeling,
And a Y-Zr-O based composite oxide, wherein the Y-Ti-O based composite oxide and the Y-Zr-O based composite oxide are suppressed,
As a result of the tensile test at a strain of 1 × 10 ^-4 s ^-1 at 700 ° C., the creep test was carried out at a yield stress of 210 MPa or more and a stress of 120 MPa and 150 MPa at 700 ° C., Each of which is at least 88.9 hours and at least 15.1 hours
A method for producing a ferritic-martensitic oxide-dispersed reinforcing steel having improved high-temperature strength and creep resistance.

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