Hydroelectric steel and preparation method thereof

Abstract

The present invention relates to a hydropower steel and a preparation method thereof, wherein the chemical composition of the hydropower steel is as follows by weight: C: 0.05-0.08%; Si≤0.20%; Mn: 0.6-1.2%; P≤0.015%; S≤0.004%; Cr: 0.5-0.9%; Ni: 4.0-4.8%; Mg: 0.005-0.008%; La: 0.012-0.018%; Zr: 0.02-0.03%; N: 0.008-0.015%; the remainder being Fe and unavoidable impurities. Based on the above chemical composition and proportion, the hydropower steel mentioned in the present application can meet the production of hydropower steel with a special thickness of more than 120 mm and a strength level of 1000 MPa.

Description

Technical Field

[0001] The present invention relates to the technical field of steel rolling, and in particular to hydropower steel and a preparation method thereof. Background Art

[0002] In recent years, with the rapid development of science and technology, the construction pace of my country's hydropower industry has also accelerated. Therefore, many large hydropower stations have put forward higher requirements on the strength, toughness and welding performance of hydropower steel plates. The performance strength of hydropower steel also increases with the increase of installed capacity and head values of hydropower stations.

[0003] In recent years, 800MPa grade hydropower steel plates have been widely used in power plants. Currently, the design process of new super-large hydropower stations has begun to require the use of 1000MPa grade hydropower steel.

[0004] Therefore, it is necessary to provide a hydroelectric steel and a preparation method thereof, which can at least partially meet the above-mentioned deficiencies. Summary of the Invention

[0005] (1) Technical issues to be resolved

[0006] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a hydropower steel and a preparation method thereof, which solves the technical problem of the difficulty in producing hydropower steel with a strength level of 1000MPa in the prior art.

[0007] (2) Technical solution

[0008] In order to achieve the above objectives, the main technical solutions adopted by the present invention include:

[0009] In a first aspect, an embodiment of the present invention provides a hydropower steel, comprising:

[0010] The chemical composition of hydropower steel by weight is: C: 0.05~0.08%; Si≤0.20%; Mn: 0.6~1.2%; P≤0.015%; S≤0.004%; Cr: 0.5~0.9%; Ni: 4.0~4.8%; Mg: 0.005~0.008%; La: 0.012~0.018%; Zr: 0.02~0.03%; N: 0.008~0.015%; the balance is Fe and unavoidable impurities.

[0011] Furthermore, Ceq≤0.59%; Pcm≤0.28%;

[0012] Where Ceq is carbon equivalent, Pcm is welding sensitivity;

[0013] Ceq=C+Mn / 6+Si / 24+Ni / 40+Cr / 5+Mo / 4+V / 14≤0.59%;

[0014] Pcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B≤0.28%.

[0015] In a second aspect, an embodiment of the present invention provides a method for preparing hydropower steel, which is used to prepare the hydropower steel according to the first aspect, comprising:

[0016] Step 1: Converter smelting

[0017] Use converter smelting to control the S content in the molten iron in the converter to ≤ 0.004%;

[0018] Step 2: RH Refining

[0019] Use RH refining method to refine molten iron and control the degassing time to be ≥15min;

[0020] Step 3: Continuous Casting

[0021] Rare earth La wire is fed in a double-wire feeding mode at the continuous casting mold position at a feeding speed of 7-9 m / min, and a slab is obtained after casting.

[0022] Step 4: Slab Heating

[0023] The target heating temperature of the slab is 1230-1260℃. After the slab comes out of the furnace, it is sent to the descaling machine to remove the iron oxide scale.

[0024] Step 5: Rolling

[0025] The slab rolling temperature is not less than 1150℃, high-pressure water is used for descaling during the rolling process, and the final rolling temperature is controlled at ≥900℃;

[0026] Step 6: Tempering

[0027] During the quenching and tempering process, the quenching temperature is controlled at 870-890°C, the heating rate is controlled at 1.4-1.8 min / mm, the net holding time is controlled at 1.2-1.5 min / mm, the tempering temperature is controlled at 600-620°C, the heating rate is controlled at 1.4-2.0 min / mm, and the net holding time is controlled at 2.0-2.5 min / mm.

[0028] Furthermore, during the smelting process, the final slag basicity R is controlled to be 2.6 to 3.4.

[0029] Furthermore, during the continuous casting process, the superheat of the molten steel in the tundish is controlled to be ≤35°C.

[0030] Furthermore, during the continuous casting process, a constant casting speed of 1.1 to 1.4 m / min is adopted.

[0031] Furthermore, during the continuous casting process, the secondary cooling water ratio is controlled at 0.35-0.38 L / kg.

[0032] Furthermore, the slabs after step 3 are stacked and slowly cooled offline, with a hot slab placed at the bottom and top of the stack, and hot slabs placed next to the stack for cooling. The stack is slowly cooled for more than 48 hours.

[0033] Furthermore, after rolling, the cooling bed is air-cooled to 300-400°C and stacked off the line for slow cooling for more than 24 hours.

[0034] (3) Beneficial effects

[0035] The beneficial effects of the present invention are as follows: the hydropower steel mentioned in the present invention has the following chemical components by weight: C: 0.05-0.08%; Si≤0.20%; Mn: 0.6-1.2%; P≤0.015%; S≤0.004%; Cr: 0.5-0.9%; Ni: 4.0-4.8%; Mg: 0.005-0.008%; La: 0.012-0.018%; Zr: 0.02-0.03%; N: 0.008-0.015%; the balance is Fe and unavoidable impurities, and by adding Mg element, magnesium-containing composite inclusion fine particles are introduced to form austenite nucleation The core, refines the structure, and improves the impact toughness of the steel. By adding the rare earth element La with a micro-alloying effect, the segregation of alloy carbides at the grain boundaries is effectively reduced, and the welding performance is improved. At the same time, the grains are significantly refined, the grain boundaries are purified, and the strength and toughness of the steel are improved. By designing the Ni element content, the hardenability and plasticity of the steel are improved. The elongation of the steel plate with a thickness of more than 120mm reaches more than 19%. At the same time, Zr and N elements are added, and the micron-level high-stability compound ZrN is generated by combining N and Zr to improve the low-temperature toughness of the steel. Based on the above description, the hydropower steel mentioned in this application can meet the production of hydropower steel with a special thick specification of more than 120mm and a strength level of 1000MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The present invention is a process flow chart of a method for preparing hydroelectric steel. DETAILED DESCRIPTION

[0037] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation methods in conjunction with the accompanying drawings.

[0038] When an amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed alone. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted as including the range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values and all integers and fractions within the range.

[0039] In these embodiments, unless otherwise indicated, the parts and percentages are all measured by mass. "Parts by mass" refers to the basic unit of measurement for expressing the mass ratio relationship of multiple components. 1 part can represent any unit mass, such as 1g, 3.527g, etc. If we say that the mass parts of component A are a parts and the mass parts of component B are b parts, then it means that the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it means that the mass of component A is aK and the mass of component B is bK (K is an arbitrary number, indicating a multiplication factor). It should not be misunderstood that, unlike the mass parts, the sum of the mass parts of all components is not limited to 100 parts. "And / or" is used to indicate that one or both of the situations described may occur, for example, A and / or B includes (A and B) and (A or B).

[0040] In the prior art, most of the hydropower steel produced is 800MPa strength grade hydropower steel. The hydropower steel provided in this application solves the technical problem of the difficulty in producing 1000MPa strength grade hydropower steel in the prior art.

[0041] The first aspect of the application of this article mentions a hydropower steel, wherein the chemical composition of the hydropower steel is as follows by weight: C: 0.05~0.08%; Si≤0.20%; Mn: 0.6~1.2%; P≤0.015%; S≤0.004%; Cr: 0.5~0.9%; Ni: 4.0~4.8%; Mg: 0.005~0.008%; La: 0.012~0.018%; Zr: 0.02~0.03%; N: 0.008~0.015%; the balance is Fe and unavoidable impurities.

[0042] It should be noted that by adding Mg element, magnesium-containing composite inclusion fine particles are introduced to form austenite nucleation core, refine the structure, and improve the impact toughness of steel;

[0043] It should be noted that the addition of rare earth element La, which has a microalloying effect, effectively reduces the segregation of alloy carbides at grain boundaries, improves welding performance, and significantly refines grains, purifies grain boundaries, and improves the strength and toughness of steel.

[0044] It should be noted that by designing the Ni element content, the hardenability and plasticity of the steel are improved, and the elongation of steel plates with a thickness of more than 120 mm reaches more than 19%. At the same time, Zr and N elements are added, and the micron-level high-stability compound ZrN is generated by combining N and Zr, thereby improving the low-temperature toughness of the steel.

[0045] In this technical solution, Ceq≤0.59%; Pcm≤0.28%;

[0046] Where Ceq is carbon equivalent, Pcm is welding sensitivity;

[0047] Ceq=C+Mn / 6+Si / 24+Ni / 40+Cr / 5+Mo / 4+V / 14≤0.59%;

[0048] Pcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B≤0.28%.

[0049] In a comparative example, the chemical composition is as follows: C: 0.06-0.17%, Si: ≤0.15%, Mn: 0.8-2.0%, P: ≤0.010%, S: ≤0.003%, Ni: 1.0-2.0%, Cu: 0.10-0.25%, Cr: 0.3-1.5%, Mo: 0.4-0.7%, V+Nb+Ti: ≤0.1%, Als: 0.015-0.045%, Ce ≤0.020%, CEV ≤0.64%, Pcm ≤0.28%, with the remainder being Fe and residual elements. This comparative example uses die-cast steel ingots as raw material, resulting in a low yield and high production costs. Furthermore, the maximum thickness of the produced steel plate is only 50 mm, and the elongation is only 15%, which cannot meet the requirements of large-scale hydropower projects for high-strength, ductile, and extra-thick steel plates.

[0050] The hydropower steel mentioned in this application can achieve the production of hydropower steel with a super-thick specification of more than 120mm and a strength level of 1000MPa.

[0051] refer to Figure 1 The second aspect of the present application mentions a method for preparing hydropower steel, which is used to prepare the hydropower steel as described in the first aspect, comprising:

[0052] Step 1: Converter smelting

[0053] Use converter smelting to control the S content in the molten iron in the converter to ≤ 0.004%;

[0054] For example, during the steel tapping process, slag blocking can be strictly controlled to achieve early slag reduction, good slag reduction during the process, and thorough slag reduction at the end. This application does not limit the method of slag blocking.

[0055] Step 2: RH Refining

[0056] Use RH refining method to refine molten iron and control the degassing time to be ≥15min;

[0057] It can be understood that the above-mentioned RH refining method is a vacuum cycle degassing method, which can also be called RH vacuum cycle degassing refining method. The RH refining method is an off-furnace refining method with a series of advantages such as short processing cycle, large production capacity, good refining effect, and easy operation.

[0058] Step 3: Continuous Casting

[0059] Rare earth La wire is fed in a double-wire feeding mode at the continuous casting mold position at a feeding speed of 7-9 m / min, and a slab is obtained after casting.

[0060] Step 4: Slab Heating

[0061] The target heating temperature of the slab is 1230-1260℃. After the slab comes out of the furnace, it is sent to the descaling machine to remove the iron oxide scale.

[0062] For example, after the slab comes out of the furnace, it is quickly sent to the descaling machine to remove the iron oxide scale, which can reduce impurities and further improve the quality of the steel;

[0063] Step 5: Rolling

[0064] The slab rolling temperature is not less than 1150℃, high-pressure water is used for descaling during the rolling process, and the final rolling temperature is controlled at ≥900℃;

[0065] Step 6: Tempering

[0066] During the quenching and tempering process, the quenching temperature is controlled at 870-890°C, the heating rate is controlled at 1.4-1.8 min / mm, the net holding time is controlled at 1.2-1.5 min / mm, the tempering temperature is controlled at 600-620°C, the heating rate is controlled at 1.4-2.0 min / mm, and the net holding time is controlled at 2.0-2.5 min / mm.

[0067] It should be noted that, as a preferred technical solution of the present invention, the quenching temperature is controlled to be 870-890°C, such as 890°C, 875°C or 877°C, etc., but it is not limited to the listed values. Other values not listed within the above numerical range are also applicable.

[0068] It should be noted that the preparation method of the hydropower steel mentioned in this application, including the steps of converter smelting, vacuum cycle degassing, continuous casting, slab heating, rolling, and tempering treatment, has achieved the production of hydropower steel with a tensile strength of 1000MPa and a super thick specification of 120mm or more. The above process flow is short, the cost is low, and it is easy to organize mass production.

[0069] In a feasible implementation manner, during the smelting process, the final slag basicity R is controlled to be 2.6 to 3.4.

[0070] It should be noted that, as a preferred technical solution of the present invention, the above-mentioned final slag basicity R=2.6~3.4, for example, 2.6, 2.8 or 3.1, etc., but is not limited to the listed values. Other values not listed within the above-mentioned numerical range are also applicable.

[0071] In a feasible implementation, during the continuous casting process, the superheat of the molten steel in the tundish is controlled to be ≤35°C.

[0072] It should be noted that, as a preferred technical solution of the present invention, the superheat of the molten steel in the tundish is controlled to be ≤35°C, such as 35°C, 33°C or 30°C, etc., but is not limited to the listed values. Other values not listed within the above numerical range are also applicable.

[0073] In a feasible implementation manner, during the continuous casting process, a constant casting speed of 1.1 to 1.4 m / min is adopted.

[0074] It should be noted that, as a preferred technical solution of the present invention, a constant casting speed of 1.1 to 1.4 m / min is adopted, such as 1.2 m / min, 1.3 m / min or 1.4 m / min, etc., but it is not limited to the listed values. Other values not listed within the above numerical range are also applicable.

[0075] In a feasible implementation manner, during the continuous casting process, the water volume ratio of the secondary cooling water is controlled at 0.35 to 0.38 L / kg.

[0076] It should be noted that, as a preferred technical solution of the present invention, the above-mentioned secondary cooling water volume ratio is controlled at 0.35-0.38 L / kg, for example, 0.38 L / kg, 0.37 L / kg or 0.36 L / kg, etc., but is not limited to the listed values. Other values not listed within the above numerical range are also applicable.

[0077] In a feasible implementation, the slabs after step 3 are stacked and slowly cooled offline, with a hot slab placed at the bottom and top of the stack, and hot slabs placed next to the stack for cooling. The stack is slowly cooled for more than 48 hours.

[0078] Illustratively, the hot billet may be a hot billet of other steels.

[0079] In a feasible implementation, after rolling, the cooling bed is air-cooled to 300-400° C., and the steel sheets are stacked off the production line and slowly cooled for more than 24 hours.

[0080] It should be noted that, as a preferred technical solution of the present invention, the above-mentioned cooling bed is air-cooled to 300-400°C, such as 300°C, 350°C or 370°C, etc., but is not limited to the listed values. Other values not listed within the above numerical range are also applicable.

[0081] In order to better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below. It should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a clearer and more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0082] Refer to Table 1, which shows the chemical compositions of various examples;

[0083]

[0084] Table 1

[0085] Refer to Table 2, which characterizes the steel process parameters of each embodiment;

[0086]

[0087] Table 2

[0088] Refer to Table 3, which shows the properties of the quenched and tempered steel plates in various embodiments (at 1 / 4 of the thickness, in the transverse direction);

[0089]

[0090] Table 3

[0091] With reference to Tables 1 to 3, it can be seen that the hydroelectric steel prepared according to the chemical composition ratio mentioned in this application and the above-mentioned hydroelectric steel preparation method can meet the production of hydroelectric steel with a special thickness of 120 mm or more and a strength level of 1000 MPa.

[0092] In the description of the present invention, each embodiment focuses on the differences from other embodiments, and reference can be made to the same or similar parts between the embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0093] In the description of the present invention, relational terms such as first and second are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined. Moreover, the term "comprises", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, article or equipment comprising a series of elements includes not only those elements, but also includes other elements not clearly listed, or also includes elements inherent to such process, method, article or equipment. In the absence of further restrictions, the elements defined by the statement "comprising a ..." do not exclude the presence of other identical elements in the process, method, article or equipment comprising the elements.

[0094] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0095] In the description of this specification, the terms "one embodiment", "some embodiments", "embodiments", "examples", "specific examples" or "some examples" refer to the specific features, structures, materials or characteristics described in conjunction with the embodiment or example and included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification and features of different embodiments or examples, unless they are mutually inconsistent.

[0096] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may alter, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for preparing hydropower steel, characterized in that: include: Step 1: Converter smelting Use converter smelting to control the S content in the molten iron in the converter to ≤ 0.004%; Step 2: RH Refining Use RH refining method to refine the molten iron and control the degassing time to be ≥15min; Step 3: Continuous Casting Rare earth La wire is fed in a double-wire feeding mode at the continuous casting mold position at a feeding speed of 7-9 m / min, and a slab is obtained after casting. Step 4: Slab Heating The target heating temperature of the slab is 1230-1260℃. After the slab comes out of the furnace, it is sent to the descaling machine to remove the iron oxide scale. Step 5: Rolling The slab rolling temperature is not less than 1150℃, high-pressure water is used for descaling during the rolling process, and the final rolling temperature is controlled at ≥900℃; Step 6: Tempering During the quenching and tempering process, the quenching temperature is controlled at 870-890°C, the heating rate is controlled at 1.4-1.8 min / mm, the net holding time is controlled at 1.2-1.5 min / mm, the tempering temperature is controlled at 600-620°C, the heating rate is controlled at 1.4-2.0 min / mm, and the net holding time is controlled at 2.0-2.5 min / mm; The chemical composition of the hydropower steel prepared by the preparation method is as follows by weight: C: 0.05-0.08%; Si≤0.20%; Mn: 0.6-1.2%; P≤0.015%; S≤0.004%; Cr: 0.5~0.9%; Ni: 4.0-4.8%; Mg: 0.005~0.008%; La: 0.012~0.018%; Zr：0.02～0.03％； N: 0.008-0.015%; the balance is Fe and unavoidable impurities; Ceq≤0.59%; Pcm≤0.28%; Where Ceq is carbon equivalent, Pcm is welding sensitivity; Ceq=C+Mn / 6+Si / 24+Ni / 40+Cr / 5+Mo / 4+V / 14≤0.59%; Pcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B≤0.28%.

2. The method for preparing hydroelectric steel according to claim 1, characterized in that: include: During the smelting process, the final slag basicity is controlled to R=2.6~3.

4.

3. The method for preparing hydroelectric steel according to claim 1, characterized in that: include: During the continuous casting process, the superheat of the molten steel in the tundish is controlled to ≤35℃.

4. The method for preparing hydroelectric steel according to claim 1, characterized in that: include: During the continuous casting process, a constant casting speed of 1.1 to 1.4 m / min is adopted.

5. The method for preparing hydroelectric steel according to claim 1, characterized in that: include: During the continuous casting process, the secondary cooling water ratio is controlled at 0.35-0.38 L / kg.

6. The method for preparing hydroelectric steel according to claim 1, characterized in that: include: After step 3, the slabs are stacked and slowly cooled off the line. A hot slab is placed at the bottom and top of the stack, and hot slabs are placed next to the stack to cool them. The stack is slowly cooled for more than 48 hours.

7. The method for preparing hydroelectric steel according to claim 1, characterized in that: include: After rolling, the cooling bed is air-cooled to 300-400℃ and stacked off the line for slow cooling for more than 24 hours.

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