Novel martensitic stainless steel plate for nuclear power unit key equipment

Abstract

The invention discloses a novel martensitic stainless steel plate for key equipment of a nuclear power unit, which relates to the technical field of materials and metallurgy and comprises the following components in percentage by mass: 0.07%-0.15% of C, 0.6%-1.50% of Mn, 0.5%-1.5% of Ni, 12%-19% of Cr, 1.00%-2.00% of Mo, 0.01%-0.2% of Cu, 0.0001%-0.0010% of TiO2, 0.03%-0.30% of V, 0.01%-0.20% of Ti, 0.0001%-0.0011% of Ca and the balance of Fe and inevitable impurities. The stainless steel plate produced by combining smelting, casting blank heating, rolling and heat treatment with reasonable component design has large thickness, high strength, low hardness, high temperature resistance and low temperature resistance, and meets high-end use requirements.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of materials and metallurgy, and more particularly to a new type of martensitic stainless steel plate for key equipment of nuclear power units. BACKGROUND

[0002] The nuclear power steam generator is one of the key equipment of nuclear power plants, which is a vertical inverted U-shaped tube natural circulation heat exchanger. It is connected with the reactor pressure vessel, and the heat of the primary side reactor coolant is transferred to the secondary side water through the U-shaped tube heat transfer pipe, to generate a two-phase steam-water mixture. The water in the steam-water mixture is separated by a steam-water separation device in the secondary side, and the dry saturated steam is output from the steam outlet for power generation in the steam turbine.

[0003] The main manufacturing difficulty of the martensitic stainless steel for the nuclear power steam generator support plate lies in the guarantee of high temperature performance. A significant feature of the martensitic stainless steel is that the high temperature tensile performance will be significantly reduced with the increase of the thickness of the steel plate. Therefore, it is a key technical problem to produce the martensitic stainless steel which can guarantee the high temperature performance. The conventional technology usually adopts short-time heat treatment to try to guarantee the comprehensive mechanical properties of the steel plate, but this method is easy to cause a large residual stress in the steel plate, and the excessive residual stress will cause the failure of the steel plate when it is punched. Therefore, it is the core problem of the development of the medium thick plate of the martensitic stainless steel to reduce the residual stress of the steel plate and guarantee its high temperature strength.

[0004] At present, there are many patents for the martensitic stainless steel at home and abroad. The Chinese patent with the application number 201010151833.X discloses a smelting process of 1Cr13 stainless steel, which is smelted by the method of induction furnace smelting + electroslag remelting, but the existing technology only introduces the smelting method of ferritic stainless steel, and does not involve the subsequent manufacturing process, so it cannot be judged whether the steel plate can meet the performance requirements. The Chinese patent application with the application number 201510999200.7 discloses a carbon steel and martensitic stainless steel composite steel plate and a production method thereof, which adopts single blank rolling and asymmetric blank rolling method, but this production method is low in efficiency and high in cost, and at the same time, when used in medium thick plate, the strength of the base material cannot meet the use conditions. Therefore, the cladding material and the base material of the composite plate are not reasonably matched. The Chinese patent application with the application number 201510344441.8 discloses a carbon steel and stainless steel composite steel plate with high toughness and a production method thereof, the steel plate produced by the invention has small width and thickness, which cannot completely meet the demand of pipe steel, and the composite plate does not consider the bonding strength of the steel plate, and if the bonding strength is low, the cracking of the bonding surface is easy to occur in the later pipe manufacturing process. SUMMARY

[0005] The present application aims at overcoming the above-mentioned defects existing in the prior art, and provides a new type of martensitic stainless steel plate for key equipment of nuclear power unit, which is produced by combining smelting, casting blank heating, rolling and heat treatment with reasonable component design, has large thickness, high strength, low hardness, high temperature resistance and low temperature performance, meets high-end use requirements, and is suitable for high strength and toughness supporting components of nuclear power plants.

[0006] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows: A new type of martensitic stainless steel plate for key equipment of nuclear power unit comprises the following components by mass percentage: C: 0.07%~0.15%, Mn: 0.6%~1.50%, Ni: 0.5%~1.5%, Cr: 12%~19%, Mo: 1.00%~2.00%, Cu: 0.01%~0.2%, TiO2: 0.0001%~0.0010%, V: 0.03%~0.30%, Ti: 0.01%~0.20%, Ca: 0.0001%~0.0011%, and 0.02≤(1.8Ti+0.6Ni) / (Cr+Mn)≤0.08, 4.00≤0.25Cr+1.6C+0.4e （Mo+Cu+0.1Ca） -3V≤7.50, the balance being Fe and unavoidable impurities; The preparation method of the new type of martensitic stainless steel plate for key equipment of nuclear power unit comprises the following steps: smelting, casting blank heating, rolling and heat treatment. In the smelting, electric furnace smelting, AOD smelting, LF refining and continuous casting process are used in sequence; wherein, the white slag retention time is 30min~50min, the superheat degree is 35℃~50℃, the weak cooling mode is used, the continuous casting speed is 1.5m / min~2.5m / min, and the electromagnetic stirring is poured at the end of the casting blank solidification; In the casting blank heating, three-stage heating is used, the preheating temperature is 600℃~800℃, the heating time is 1.0h~1.5h; the heating temperature is 1000℃~1200℃, the heating time is 2h~2.5h; the soaking temperature is 1150℃~1200℃, and the heating time is 0.5h~1.5h; In the rolling, two-stage controlled rolling method is adopted, and rolling is respectively carried out in a recrystallization zone and a non-recrystallization zone; the end rolling temperature of the recrystallization zone is 1100-1200 DEG C, large deformation rapid rolling is adopted, the rolling speed is 1-3 m / s, the reduction of each pass is 12-20%, and the total deformation is controlled to be 65%; the end rolling temperature of the non-recrystallization zone is 880-920 DEG C, small deformation rapid rolling is adopted, the rolling speed is 2-4 m / s, the reduction of each pass is 5-10%, and the total deformation is controlled to be 35%; after rolling, super-fast cooling process is adopted, the initial fast cooling temperature is 765-825 DEG C, the cooling speed is 35-50 DEG C / s, and the final cooling is to room temperature.

[0007] Optionally, the width of the martensitic stainless steel plate is 4300-5300 mm, and the thickness is 10-80 mm.

[0008] Optionally, the room temperature tensile yield strength of the martensitic stainless steel plate is greater than or equal to 580 MPa, the tensile strength is greater than or equal to 688 MPa, and the elongation is greater than or equal to 21%; the high temperature tensile yield strength at 360 DEG C is greater than or equal to 489 MPa, the tensile strength is greater than or equal to 587 MPa, the impact energy at -25 DEG C is greater than or equal to 48 J, the Brinell hardness is 160-169 HB; the sample is subjected to normal temperature bending test under the condition of D=a, b=a: no crack under the bending angle of 180 DEG.

[0009] Optionally, the metallographic structure of the martensitic stainless steel plate is ferrite and martensite, wherein the volume fraction of the ferrite is 3-10%.

[0010] Optionally, in the smelting, the time of the electromagnetic stirring is 10-60 s; and the proportion of columnar crystals in the continuous casting billet is 40-70%.

[0011] Optionally, in the heat treatment, the tempering temperature is 550-800 DEG C, and the holding time is 1-10 min / mm.

[0012] The embodiment of the present application has the following beneficial effects: (1) The present application achieves the basic mechanical properties of stainless steel through special chemical composition design, wherein special elements such as V, Ti and TiO2 are introduced to ensure the special performance requirements of the steel plate, thereby laying a foundation for producing a new type of martensitic stainless steel plate for nuclear power unit key equipment from the source; (2) The present application lays a foundation for producing high-quality martensitic stainless steel hot-rolled medium plate products from the source by specially designing the electromagnetic stirring process and casting speed in the continuous casting stage, so that the molten steel obtains a continuous casting billet, and the proportion of columnar crystals in the continuous casting billet is 40-70%; (3) The present application adopts three-stage heating to homogenize the austenite structure, control the temperature and heating time of the preheating section, avoid the heating in the thermal stress concentration interval, control the heating section temperature and heating time to completely remove the assembly stress, and control the soaking section temperature and heating time to maximize the austenite content.

[0013] (4) The present application adopts controlled rolling combined with tempering heat treatment, which can ensure the highest austenite content in the steel during rolling and the maximum refinement, and can obtain uniform and fine tempered martensite structure after heat treatment.

[0014] (5) The present application finally prepares a martensitic stainless steel wide medium plate with a width of 4300mm~5300mm and a thickness of 10mm~80mm, solves the difficult problem of producing ultra-wide martensitic stainless steel medium plate, and the room temperature tensile yield strength of the martensitic stainless steel plate is ≥580MPa, the tensile strength is ≥688MPa, the elongation is ≥21%, the high temperature tensile yield strength at 360℃ is ≥489MPa, the tensile strength is ≥587MPa, the impact energy at-25℃ is ≥48J, the Brinell hardness is 160~169HB, and the sample is bent under the condition of D=a, b=a: no crack under the bending angle of 180°. DETAILED DESCRIPTION

[0015] The present application will be further described below in combination with specific embodiments, but the present application is not limited in any way by the embodiments.

[0016] The present application discloses a novel martensitic stainless steel plate for key equipment of nuclear power unit, which comprises the following components by mass percentage: C: 0.07%~0.15%, Mn: 0.6%~1.50%, Ni: 0.5%~1.5%, Cr: 12%~19%, Mo: 1.00%~2.00%, Cu: 0.01%~0.2%, TiO2: 0.0001%~0.0010%, V: 0.03%~0.30%, Ti: 0.01%~0.20%, Ca: 0.0001%~0.0011%, and 0.02≤(1.8Ti+0.6Ni) / (Cr+Mn)≤0.08, 4.00≤0.25Cr+1.6C+0.4e （Mo+Cu+0.1Ca） -3V≤7.50, the balance being Fe and unavoidable impurities.

[0017] Specifically, the above component design reasons are as follows: (1) Carbon (C): one of the important elements in steel, which has an impact on the strength, toughness, hardenability, etc. of the steel plate. It interacts with other alloying elements to strengthen the steel plate and ensure the strength of the steel plate. However, higher C content can cause segregation in the steel, resulting in a significant decrease in the toughness and plasticity of the steel plate. Therefore, in the present application, the C content is controlled to be 0.07%~0.15% under the premise of ensuring the strength of the steel plate.

[0018] (2) Manganese (Mn): The purpose of adding manganese is to work together with Cr elements to increase the solubility of nitrogen elements in steel. In addition, excessive Mn can promote the segregation of Cr elements in the liquid phase. Limiting Mn to below 1.50% can avoid the segregation of Cr, therefore, Mn is controlled to be 0.6%~1.50%.

[0019] (3) Nickel (Ni): Ni is an austenitizing element that can expand the austenite region while inhibiting the formation of ferrite in the steel. At the same time, Ni interacts with Cr elements to ensure that the steel plate has good high-temperature performance and intergranular corrosion resistance, therefore, Ni is controlled to be 0.5%~1.5%.

[0020] (4) Chromium (Cr): Cr element is the main element for improving the high-temperature oxidation resistance and high-temperature corrosion resistance of the steel plate, and is also a key element for forming M 23 C6 carbide. However, excessive addition of Cr will lead to coarsening of carbides, which in turn will cause a decrease in the high-temperature strength and toughness of the steel plate. Therefore, the Cr content in the present application is controlled to be between 12% and 19%.

[0021] (5) Molybdenum (Mo): Mo is a strong carbide-forming element. Ferritic stainless steel generally has poor corrosion resistance and high-temperature resistance, but with the increase of Mo content, it can be beneficial to grain strengthening and avoid grain boundary corrosion by solid solution strengthening and mutual strengthening with other alloys. Therefore, the present application requires Mo: 1.00%~2.00%.

[0022] (6) Copper (Cu): Cu is an austenite-forming element, and the use of copper in the core of the steel plate can compensate for the loss of strength due to increased thickness, therefore, Cu is controlled to be 0.01%~0.2%.

[0023] (7) Titanium oxide (TiO2): TiO2 has the effect of refining grains, as nucleation points, promoting grain boundary nucleation during rolling, and inducing the formation of acicular ferrite, which is beneficial to the low-temperature toughness of the steel. Therefore, the TiO2 content added to the steel is controlled to be 0.0001%~0.0010%.

[0024] (8) Vanadium (V): V is a strong carbide-forming element that forms dispersed fine carbides, increasing the thermal strength and creep resistance of the steel. Therefore, the present application limits the V content range to V: 0.03%~0.30%.

[0025] (9) Titanium (Ti): Ti precipitates in the form of carbide at the grain boundary, thereby inhibiting the precipitation of Cr at the grain boundary, preventing the appearance of "chromium-poor zone" near the grain boundary, and increasing the intergranular corrosion resistance of the steel plate. However, too high Ti content will cause the welded joint to be brittle during welding, reducing the plasticity and toughness of the material. Therefore, the Ti content is controlled to be 0.01%~0.20%.

[0026] (10) Calcium (Ca): Ca is a common deoxidizer in steel, and a small amount of Ca can refine the grain and improve the strength and impact toughness of the steel. However, too high Ca content will affect the hot working performance, welding performance and cutting performance of the steel, so the Ca content is controlled to be 0.0001%~0.0011%.

[0027] (11) The present application further controls 0.02≤(1.8Ti+0.6Ni) / (Cr+Mn)≤0.08, 4.00≤0.25Cr+1.6C+0.4e （Mo+Cu+0.1Ca） -3V≤7.50, by precisely controlling the ratio of elements, high strength, low hardness, high temperature resistance and low temperature performance are considered.

[0028] In a specific embodiment, the width of the martensitic stainless steel plate is 4300mm~5300m, and the thickness is 10mm~80mm.

[0029] In a specific embodiment, the room temperature tensile yield strength of the martensitic stainless steel plate is ≥580MPa, the tensile strength is ≥688MPa, and the elongation is ≥21%; the high temperature tensile yield strength at 360℃ is ≥489MPa, the tensile strength is ≥587MPa, the impact energy at -25℃ is ≥48J, and the Brinell hardness is 160~169HB; the sample is subjected to normal temperature bending test under the condition of D=a, b=a: no crack under bending angle 180°.

[0030] In a specific embodiment, the metallographic structure of the martensitic stainless steel plate is ferrite and martensite, wherein the volume fraction of ferrite is 3%~10%.

[0031] The present application also discloses a preparation method of a novel martensitic stainless steel plate for nuclear power unit key equipment according to any embodiment of the present application, comprising the following steps: smelting, casting blank heating, rolling and heat treatment.

[0032] S1, in smelting, in turn, electric furnace smelting, AOD smelting, LF refining and continuous casting process; AOD smelting is completed blowing, decarburization and temperature adjustment; then desulfurization is carried out by LF refining, the white slag retention time is 30min~50min, the superheat is 35℃~50℃, the weak cold mode is used, and the continuous casting speed is 1.5m / min~2.5m / min, which can ensure that the columnar crystal in the continuous casting billet is developed, and the generation of equiaxed crystal in the core is reduced, and the electromagnetic stirring is poured at the solidification end of the casting billet to fully improve the internal quality of the casting billet, and the proportion of columnar crystal in the continuous casting billet is 40%~70%.

[0033] In a specific embodiment, in smelting, the time of electromagnetic stirring is 10s~60s.

[0034] S2, in the heating of the casting billet, three-stage heating is used to homogenize the austenite structure, the preheating temperature is 600℃~800℃, the heating time is 1.0h~1.5h, and the heating is avoided in the hot stress concentration zone; the heating temperature is 1000℃~1200℃, the heating time is 2h~2.5h, and the hot stress of the group billet is completely removed; the soaking temperature is 1150℃~1200℃, and the heating time is 0.5h~1.5h, and the austenite content is maximized.

[0035] S3, in rolling, a two-stage controlled rolling method is used, and rolling is carried out in the recrystallization zone and the unrecrystallization zone respectively; the recrystallization zone rolling end temperature is 1100℃~1200℃, the original austenite structure is fully refined, large deformation rapid rolling is used, the rolling speed is 1~3m / s, the reduction per pass is 12%~20%, and the total deformation amount is controlled to be 65%; the unrecrystallization zone finish rolling temperature is 880℃~920℃, small deformation multi-pass rapid rolling is used, the rolling speed is 2~4m / s, the reduction per pass is 5%~10%, the reduction per pass is less than 3mm, and the reduction per pass is calculated as 3mm, and the total deformation amount is controlled to be 35%, at this time, the austenite grains are further flattened and elongated, with the increase of the grain boundary area, the grains are fully refined; after rolling, the ultrafast cooling process is used, the fast cooling initial temperature is 765℃~825℃, the cooling speed is 35℃ / s~50℃ / s, and the final cooling is to room temperature, which further improves the strength of the steel plate.

[0036] S4, in heat treatment, the tempering temperature is 550℃~800℃, and the holding time is 1min / mm~10min / mm.

[0037] Specifically, the present application adopts controlled rolling combined with tempering heat treatment, and the combination of the two can ensure that the austenite content in the steel is the highest during rolling and can be refined to the maximum extent, and after heat treatment, uniform and fine tempered martensite structure can be obtained.

[0038] The following is a specific embodiment Examples 1-10 The preparation method of the new type of martensitic stainless steel plate for key equipment of nuclear power unit in examples 1-10 comprises the following steps: smelting, casting blank heating, rolling and heat treatment.

[0039] In the smelting, the processes of electric furnace smelting, AOD smelting, LF refining and continuous casting are sequentially adopted; after the blowing of AOD smelting is completed, decarburization and temperature adjustment are performed; then, desulfurization is performed through LF refining, and the weak cooling mode is adopted, and electromagnetic stirring is applied at the end of the solidification of the casting blank, and the proportion of columnar crystals in the casting blank is 40%-70%.

[0040] In the casting blank heating, three-stage heating is adopted, including preheating stage, heating stage and soaking stage.

[0041] In the rolling, two-stage controlled rolling is adopted, and rolling is performed in the recrystallization zone and the unrecrystallization zone respectively; the end temperature of the recrystallization zone is controlled, large deformation rapid rolling is adopted, and the total deformation amount is controlled to be 65%; the finish rolling temperature of the unrecrystallization zone is controlled, small deformation rapid rolling is adopted, and the total deformation amount is controlled to be 35%; after rolling, super-fast cooling process is adopted, and heat treatment is performed after the final cooling to room temperature.

[0042] Table 1 is the chemical composition of the example steel; Table 2 is the smelting process parameters of the example steel; Table 3 is the heating process parameters of the casting blank of the example steel; Table 4 is the rolling and heat treatment process parameters of the example steel; and Table 5 is the performance of the example stainless steel plate.

[0043] Table 1 Chemical composition of example steel (%)

[0044] Table 2 Smelting process of example steel

[0045] Table 3 Heating process of casting blank of example steel

[0046] Table 4 Rolling and heat treatment process of example steel

[0047] Table 5 Performance of example stainless steel plate

[0048] As can be seen from the examples, the room temperature tensile yield strength of the prepared steel plate is ≥580 MPa, the tensile strength is ≥688 MPa, the elongation is ≥21%, the high temperature tensile yield strength at 360℃ is ≥489 MPa, the tensile strength is ≥587 MPa, the impact energy at-25℃ is ≥48 J, the Brinell hardness is 160-169 HB, the bending angle of the sample under the condition of D=a, b=a is 180°, and no cracks are generated.

[0049] The above embodiments only express several implementation manners of the present application, which are described in a more specific and detailed manner, but cannot be understood as a limitation on the patent application scope. It should be noted that, for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, which all belong to the protection scope of the present application. Therefore, the protection scope of the present application patent should be subject to the appended claims.

Claims

1. A new type of martensitic stainless steel plate for key equipment of nuclear power units, characterized in that, Comprise the following components by mass percentage: C: 0.07%~0.15%, Mn: 0.6%~1.50%, Ni: 0.5%~1.5%, Cr: 12%~19%, Mo: 1.00%~2.00%, Cu: 0.01%~0.2%, TiO2: 0.0001%~0.0010%, V: 0.03%~0.30%, Ti: 0.01%~0.20%, Ca: 0.0001%~0.0011%, and 0.02≤(1.8Ti+0.6Ni) / (Cr+Mn)≤0.08, 4.00≤0.25Cr+1.6C+0.4e （Mo+Cu+0.1Ca） -3V≤7.50, the balance being Fe and unavoidable impurities; The preparation method of the new type of martensitic stainless steel plate for key equipment of nuclear power unit comprises the following steps: smelting, casting blank heating, rolling and heat treatment. In the smelting, the electric furnace smelting, AOD smelting, LF refining and continuous casting process are adopted in sequence; wherein, the white slag holding time is 30min~50min, the superheat degree is 35℃~50℃, the weak cooling mode is adopted, and the continuous casting speed is 1.5m / min~2.5m / min, and the electromagnetic stirring is poured at the end of the casting blank solidification; In the casting blank heating, three-stage heating is adopted, the preheating section temperature is 600℃~800℃, the heating time is 1.0h~1.5h; the heating section temperature is 1000℃~1200℃, the heating time is 2h~2.5h; the soaking section temperature is 1150℃~1200℃, and the heating time is 0.5h~1.5h; In the rolling, two-stage controlled rolling method is adopted, and rolling is carried out in the recrystallization zone and the unrecrystallization zone respectively; the recrystallization zone rolling end temperature is 1100℃~1200℃, large deformation rapid rolling is adopted, the rolling speed is 1~3m / s, the reduction of each pass is 12%~20%, and the total deformation amount is controlled to be 65%; the unrecrystallization zone finish rolling temperature is 880℃~920℃, small deformation rapid rolling is adopted, the rolling speed is 2~4m / s, the reduction of each pass is 5%~10%, and the total deformation amount is controlled to be 35%; after rolling, ultrafast cooling process is adopted, the fast cooling initial temperature is 765℃~825℃, the cooling speed is 35℃ / s~50℃ / s, and the final cooling is to room temperature.

2. The new type of martensitic stainless steel plate for key equipment of nuclear power units according to claim 1, characterized in that, The width of the martensitic stainless steel plate is 4300mm~5300mm, and the thickness is 10mm~80mm.

3. The new type of martensitic stainless steel plate for key equipment of nuclear power units according to claim 1, characterized in that, The room temperature tensile yield strength of the martensitic stainless steel plate is ≥580MPa, the tensile strength is ≥688MPa, and the elongation is ≥21%; the high temperature tensile yield strength at 360℃ is ≥489MPa, the tensile strength is ≥587MPa, the impact energy at-25℃ is ≥48J, the Brinell hardness is 160~169HB; the sample is bent under the condition of D=a, b=a: no crack under the bending angle of 180°.

4. The new type of nuclear power plant key equipment martensitic stainless steel plate according to claim 1, characterized in that, The metallographic structure of the martensitic stainless steel plate is ferrite and martensite, wherein the volume fraction of ferrite is 3%~10%.

5. The new type of nuclear power plant key equipment martensitic stainless steel plate according to claim 1, characterized in that, In the smelting, the time of the electromagnetic stirring is 10s~60s; the proportion of columnar crystal in the continuous casting blank is 40%~70%.

6. The new type of nuclear power plant key equipment martensitic stainless steel plate according to claim 1, characterized in that, In the heat treatment, the tempering temperature is 550℃~800℃, and the holding time is 1min / mm~10min / mm.

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