Ferrite-based high-strength corrosion-resistant dual-phase alloy and preparation method thereof

文档序号：1885057 发布日期：2021-11-26 浏览：17次中文

阅读说明：本技术 一种铁素体基高强耐蚀双相合金及制备方法 (Ferrite-based high-strength corrosion-resistant dual-phase alloy and preparation method thereof ) 是由严靖博谷月峰袁勇于在松杨征张醒兴于 2021-08-26 设计创作，主要内容包括：本发明属于材料领域,具体涉及一种铁素体基高强耐蚀双相合金及制备方法,按质量百分比满足如下范围要求：C：0.07～0.1％,B：0.003～0.007％,Cr：17～19％,Ni：7～10％,Co：0.5～1.0％,Mn：7～12％,Si：0.2～0.5％,Nb：0.3～0.8％,Mo+W：1.0～2.0％,Ti+Al：2.0～3.0％,余量为Fe。本发明的合金采用真空熔炼及热轧加工的方式制备成型,热处理完成后合金基体由奥氏体及铁素体两相构成,其中,在奥氏体晶粒内部弥散分布颗粒状NiAl相,其平均直径不超过150nm。合金热膨胀系数介于铁素体钢与奥氏体钢之间,具有良好的室温及高温力学性能。(The invention belongs to the field of materials, and particularly relates to a ferrite-based high-strength corrosion-resistant dual-phase alloy and a preparation method thereof, wherein the ferrite-based high-strength corrosion-resistant dual-phase alloy meets the following range requirements in percentage by mass: c: 0.07-0.1%, B: 0.003-0.007%, Cr: 17-19%, Ni: 7-10%, Co: 0.5 to 1.0%, Mn: 7-12%, Si: 0.2 to 0.5%, Nb: 0.3-0.8%, Mo + W: 1.0-2.0%, Ti + Al: 2.0-3.0% and the balance Fe. The alloy is prepared and molded by adopting a vacuum melting and hot rolling mode, an alloy matrix after heat treatment is formed by two phases of austenite and ferrite, wherein a granular NiAl phase is dispersed and distributed in austenite grains, and the average diameter of the NiAl phase is not more than 150 nm. The alloy has thermal expansion coefficient between that of ferrite steel and that of austenite steel and excellent mechanical performance at room temperature and high temperature.)

1. The ferrite-based high-strength corrosion-resistant dual-phase alloy is characterized by comprising the following components in percentage by mass: c: 0.07-0.1%, B: 0.003-0.007%, Cr: 17-19%, Ni: 7-10%, Co: 0.5 to 1.0%, Mn: 7-12%, Si: 0.2 to 0.5%, Nb: 0.3-0.8%, Mo + W: 1.0-2.0%, Ti + Al: 2.0-3.0% and the balance Fe; wherein Al is 1.0-2.0%, Mo + W represents the total mass percent of Mo and W, Ti + Al represents the total mass percent of Ti and Al, the alloy consists of austenite and ferrite, and a granular NiAl phase is dispersed in the austenite grains.

2. The ferritic base high strength corrosion resistant dual phase alloy according to claim 1 wherein the particulate NiAl phase precipitates within the grains of the ferrite and has an average diameter of not more than 150nm and a volume fraction of not more than 15%.

3. The ferritic high-strength corrosion-resistant dual-phase alloy as claimed in claim 1, wherein the alloy has an average linear expansion coefficient of not more than 16 x 10 at 20 to 650 ℃^-6/K。

4. The ferritic-based, high strength corrosion resistant, dual phase alloy as claimed in claim 1 wherein the alloy has yield strength at room temperature not less than 450MPa, yield strength at 650 ℃ not less than 250MPa, elongation at room temperature not less than 12% and elongation at 650 ℃ not less than 70%.

5. A preparation method of ferrite-based high-strength corrosion-resistant dual-phase alloy is characterized by comprising the following steps of: 0.07-0.1%, B: 0.003-0.007%, Cr: 17-19%, Ni: 7-10%, Co: 0.5 to 1.0%, Mn: 7-12%, Si: 0.2 to 0.5%, Nb: 0.3-0.8%, Mo + W: 1.0-2.0%, Ti + Al: 2.0-3.0% and the balance Fe; smelting under vacuum, then discharging and pouring to obtain an ingot; wherein Al is 1.0-2.0%, Mo + W represents the total mass percent of Mo and W, Ti + Al represents the total mass percent of Ti and Al;

homogenizing the cast ingot, wherein the homogenizing temperature is not higher than 1100 ℃ and the homogenizing time is 8-24 h;

then, the solution treatment is carried out after the deformation is processed by adopting a hot rolling mode, and the water cooling is carried out after the treatment is finished.

And finally, carrying out aging treatment, and carrying out water cooling or air cooling after the treatment is finished.

6. The method for preparing the ferrite-based high-strength corrosion-resistant dual-phase alloy according to claim 5, wherein a vacuum degree during smelting is not higher than 0.5Pa, and a tapping and pouring temperature of the alloy is not lower than 1600 ℃.

7. The method of claim 5, wherein the transformation temperature is not lower than 700 ℃ and the single-pass transformation amount is not lower than 30%.

8. The method for preparing the ferrite-based high-strength corrosion-resistant dual-phase alloy according to claim 5, wherein the temperature of the solution treatment is 950-1050 ℃ and the time is 1-2 h.

9. The preparation method of the ferrite-based high-strength corrosion-resistant dual-phase alloy according to claim 5, wherein the temperature of the aging treatment is 650-750 ℃ and the time is 8-12 h.

10. The method for preparing the ferrite-based high-strength corrosion-resistant dual-phase alloy according to claim 5, wherein the alloy has a ferrite and austenite duplex structure after solution treatment, wherein the ferrite volume percentage is 35-75%.

Technical Field

The invention belongs to the field of alloy steel for high temperature, and particularly relates to a ferrite-based high-strength corrosion-resistant dual-phase alloy and a preparation method thereof.

Background

The high-efficiency clean high-parameter ultra-supercritical coal-fired power generation technology is one of the main development trends of the clean coal-fired power generation technology in the world. At present, the thermal efficiency of a 700 ℃ advanced ultra supercritical (A-USC) coal-fired power generation system which is researched can exceed 50%, and the power supply coal consumption is lower than 240G/KW. The commercial value of the A-USC technology will depend on a number of variables: coal prices, nickel-based alloy costs (about 20 times the cost of high-grade ferritic steels), and carbon taxes, among others. The thermal efficiency of 650 ℃ and the secondary reheating unit thereof can exceed 50%, the power supply coal consumption is lower than 260G/KW, and the method is one of effective ways for realizing high-level industrial upgrading of the electric power industry in China and realizing clean coal power generation in a standardized way at present in a short time.

Compared with the traditional austenitic heat-resistant steel, the ferritic heat-resistant steel has the characteristics of low thermal expansion coefficient, good thermal conductivity, excellent stress corrosion resistance, low alloy cost (containing a small amount of or even no precious metals such as nickel) and the like, and is a preferred material for hot end parts of a unit, particularly thick wall parts such as pipelines, headers and the like. However, with the further improvement of steam parameters, the existing commercial ferritic heat-resistant steel is difficult to meet the performance requirements of hot end parts of the unit on alloy high-temperature strength, steam oxidation resistance and corrosion resistance (small pipes), and the recommended use temperature of the widely-used 9-12Cr and improved ferritic heat-resistant steel is generally not higher than 620 ℃. The strength performance of the alloy is effectively improved by adding Cu element into the G115 alloy, but the corrosion resistance and oxidation resistance of the alloy under the higher-temperature service working condition can not be effectively guaranteed because the content of Cr element is not more than 9%. Austenitic heat-resistant steel with higher heat-resistant strength, such as Super304H, HR3C and the like, has higher thermal expansion coefficient and poorer heat transfer efficiency, so that the austenitic heat-resistant steel is sensitive to temperature fluctuation, and further easily causes the problems of thermal fatigue damage and the like, thereby causing the peak shaving operation capability of a boiler to be reduced. Therefore, the thick wall parts in the current USC unit still use ferrite heat-resistant steel such as P92 as the preferred material.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a ferrite-based high-strength corrosion-resistant dual-phase alloy and a preparation method thereof.

In order to achieve the purpose, the technical scheme of the invention is as follows:

a ferrite-based high-strength corrosion-resistant dual-phase alloy comprises the following components in percentage by mass: c: 0.07-0.1%, B: 0.003-0.007%, Cr: 17-19%, Ni: 7-10%, Co: 0.5 to 1.0%, Mn: 7-12%, Si: 0.2 to 0.5%, Nb: 0.3-0.8%, Mo + W: 1.0-2.0%, Ti + Al: 2.0-3.0% and the balance Fe; wherein Al is 1.0-2.0%, Mo + W represents the total mass percent of Mo and W, Ti + Al represents the total mass percent of Ti and Al, the alloy consists of austenite and ferrite, and a granular NiAl phase is dispersed in the austenite grains.

The further improvement of the invention is that the alloy has granular NiAl phase separated out in the ferrite and the average diameter of the granular NiAl phase is not more than 150nm and the volume fraction is not more than 15%.

The further improvement of the invention is that the average linear expansion coefficient of the alloy at 20-650 ℃ is not higher than 16 multiplied by 10^-6/K。

The further improvement of the invention is that the alloy has a yield strength at room temperature of not less than 450MPa, a yield strength at 650 ℃ of not less than 250MPa, an elongation at room temperature of not less than 12% and an elongation at 650 ℃ of not less than 70%.

A preparation method of ferrite-based high-strength corrosion-resistant dual-phase alloy comprises the following steps of: 0.07-0.1%, B: 0.003-0.007%, Cr: 17-19%, Ni: 7-10%, Co: 0.5 to 1.0%, Mn: 7-12%, Si: 0.2 to 0.5%, Nb: 0.3-0.8%, Mo + W: 1.0-2.0%, Ti + Al: 2.0-3.0% and the balance Fe; smelting under vacuum, then discharging and pouring to obtain an ingot; wherein Al is 1.0-2.0%, Mo + W represents the total mass percent of Mo and W, Ti + Al represents the total mass percent of Ti and Al;

homogenizing the cast ingot, wherein the homogenizing temperature is not higher than 1100 ℃ and the homogenizing time is 8-24 h;

then, the solution treatment is carried out after the deformation is processed by adopting a hot rolling mode, and the water cooling is carried out after the treatment is finished.

And finally, carrying out aging treatment, and carrying out water cooling or air cooling after the treatment is finished.

The further improvement of the invention is that the vacuum degree is not higher than 0.5Pa during smelting, and the tapping and casting temperature of the alloy is not lower than 1600 ℃.

The invention has the further improvement that the deformation temperature is not lower than 700 ℃, and the single-pass deformation is not lower than 30%.

The invention has the further improvement that the temperature of the solution treatment is 950-1050 ℃ and the time is 1-2 h.

The invention has the further improvement that the temperature of the aging treatment is 650-750 ℃, and the time is 8-12 h.

The invention is further improved in that the alloy after solution treatment has a ferrite and austenite bidirectional structure, wherein the ferrite volume percentage is 35-75%.

Compared with the prior art, the invention has the beneficial effects that: the performances of ferrite and austenite grains in the dual-phase alloy show larger difference at high temperature, and the austenite usually shows more excellent strength performance at high temperature. The alloy promotes the preferential precipitation of NiAl in ferrite grains, coordinates the performance matching relationship of two phases and further improves the comprehensive strength and toughness of the alloy; the mass percent of the Cr element is 17-19%, the higher Cr element content easily causes the instability of the structure, induces the precipitation of harmful phases and promotes the growth of carbides, thereby bringing harm to the strength performance of the alloy. The alloy improves the strength performance of the alloy by promoting the dispersion and precipitation of the NiAl phase in the crystal, and makes up the alloy strength reduction caused by carbide coarsening. Although the high Cr and Al element content can effectively improve the corrosion resistance and oxidation resistance of the alloy, the ductile-brittle transition temperature can be improved, and the alloy plasticity is deteriorated, so that the alloy disclosed by the invention can stabilize the austenite under the condition of not obviously improving the raw material cost by adding the Mn element with the mass percentage of 7-12%, finally obtains a ferrite and austenite dual-phase structure, and improves the room-temperature plasticity of the alloy. The alloy is suitable for high-temperature service working conditions of 650-700 ℃, such as a super-supercritical coal-fired unit reheater, a main steam pipeline, a steam turbine rotor and the like.

The invention adopts solid solution and aging treatment to avoid austenitizing of original ferrite grains in the aging process and influence on nucleation growth of a precipitation phase (NiAl precipitation phase mainly nucleates and grows in the ferrite grains in the short-term aging process), thereby ensuring good mechanical property of the alloy.

Further, the alloy of the present invention has a ferrite and austenite two-phase structure, and the aging temperature for promoting the precipitation of the strengthening phase is close to the lower limit of the austenite phase region of the alloy grains, so the relative proportion of the volume fractions of austenite and ferrite in the long-term service process of the alloy can be ensured within a reasonable range by adopting the solution and aging temperature and time of the present invention.

Drawings

FIG. 1 shows the XRD analysis results of the phase structure of the alloy of example 1.

FIG. 2 shows the granular NiAl phase inside the ferrite grains of the alloy of example 2.

FIG. 3 is an internal appearance of austenite grains of the alloy of example 2.

Detailed Description

The present invention will be described in further detail with reference to examples.

A ferrite-based high-strength corrosion-resistant dual-phase alloy comprises the following elements in percentage by mass: c: 0.07-0.1%, B: 0.003-0.007%, Cr: 17-19%, Ni: 7-10%, Co: 0.5 to 1.0%, Mn: 7-12%, Si: 0.2 to 0.5%, Nb: 0.3-0.8%, Mo + W: 1.0-2.0%, Ti + Al: 2.0 to 3.0%, 1.0 to 2.0% of Al, and the balance Fe. Wherein Mo + W represents the total mass percent of Mo and W, the mass percent of Mo may be 0, the mass percent of W is not less than 1%, and Ti + Al represents the total mass percent of Ti and Al. The matrix after the heat treatment of the alloy consists of austenite and ferrite phases, wherein a granular NiAl phase is dispersed and distributed in the austenite grains.

Smelting the elements according to mass percent in vacuum, controlling the vacuum degree to be not higher than 0.5Pa, and controlling the tapping and casting temperature of the alloy to be not lower than 1600 ℃ to obtain the ingot.

Homogenizing the cast ingot at 1000-1100 ℃ for 8-24 h.

Then, hot rolling is adopted for processing deformation, the deformation temperature is not lower than 700 ℃, and the single-pass deformation is not lower than 30%.

And then carrying out solid solution treatment, wherein the solid solution treatment is carried out at the temperature of 950-1050 ℃, the heat preservation time is 1-2 h, and water cooling is carried out after the treatment is finished.

And finally, carrying out aging treatment, wherein the temperature of the aging treatment is 650-750 ℃, the heat preservation time is 8-12 h, and water cooling or air cooling is carried out after the treatment is finished.

The alloy has a ferrite and austenite bidirectional organization structure after solution treatment, wherein the volume fraction of ferrite is 35-75%;

after the alloy is aged, the granular NiAl phase is only precipitated in the ferrite, the average diameter is not more than 150nm, the volume percentage is not more than 15%, and no NiAl phase is precipitated in the austenite crystal of the alloy in a heat treatment state.

The alloy and the austenitic steel have a coefficient of thermal expansion between those of the ferritic steel and the austenitic steel, and are flat at 20 to 650 DEG CCoefficient of uniform linear expansion not higher than 16 x 10^-6/K。

The alloy has good mechanical properties at room temperature and high temperature, the yield strength of the alloy at room temperature and 650 ℃ is not lower than 450MPa and 250MPa respectively, and the elongation is not lower than 12 percent and 70 percent respectively.

Example 1

The high-strength corrosion-resistant alloy material comprises the following components in percentage by mass: c: 0.08%, B: 0.005%, Cr: 18%, Ni: 8%, Co: 0.5%, Mn: 10%, Si: 0.4%, Nb: 0.5%, Mo: 0.5%, W: 1.0%, Ti: 1.4%, Al: 1.2 percent and the balance of Fe.