Steel plate for nuclear power plant crane module and method for manufacturing the same

Abstract

The present application belongs to the field of ferrous materials, and particularly relates to a steel plate for a nuclear power crane mechanical module and a manufacturing method thereof. The steel plate contains, in terms of percentage by weight, C, Mn, P≤0.010%, S≤0.015%, Ni, Cr, Mo, Nb, B, V, Ti, Cu, Y, Sb, Si3N4, and the balance of Fe and inevitable impurities. The product produced according to the chemical composition and the production process requirements of the steel plate has high strength and toughness, high modulus welding property, and high temperature resistance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of ferrous materials, and particularly relates to a steel plate for a nuclear power plant mechanical module and a manufacturing method thereof. BACKGROUND

[0002] Mechanical module refers to a combination of materials and components. The prefabricated module in the workshop is a whole unit, which facilitates and accelerates the construction on site. Prefabrication and assembly of the mechanical module before it is in place avoids excessive work in the narrow space at the final position, which allows installation and civil engineering to be carried out in parallel. With the increasing maturity of mechanical modularization technology and the accumulation of application experience, the range of nuclear power plants using modular design for construction is becoming wider and wider, and the mechanical modules designed are becoming larger and larger, and at the same time, the strength of the mechanical modules is required to be higher and higher, so the demand for high-strength steel for nuclear power plant mechanical modules is very urgent.

[0003] Chinese patent application No. 201110117614.4 discloses a nuclear container steel with a tensile strength greater than 690 MPa and a production method. The mass percentage of chemical elements is: C≤0.08%, Si: 0.15~0.50%, Mn: 1.30~1.60%, Alt: 0.01~0.05%, Ni: 0.42~0.70%, Mo: 0.32~0.60%, Cr: 0.10~0.30%, Ti: 0.01~0.04%, control elements: P≤0.008%, S≤0.005%, N≤0.005%, Cu≤0.03%, V≤0.007%, Sn≤0.005%, Sb≤0.005%, As≤0.010%, Pb≤0.005%, and the rest is Fe and unavoidable impurities. The yield strength of the steel plate of the invention is ≥570 MPa, the tensile strength is 690~860 MPa, and the impact at -20℃ is ≥100 J. The chemical composition of the invention has very strict requirements on elements such as P, S, N, and Cu, and the smelting difficulty is large and the requirements on raw materials are strict. Meanwhile, the mechanical properties of the steel plate after long-term simulated post-weld heat treatment are not considered in the invention.

[0004] Chinese invention patent application No. CN101343685 discloses a controlled rolling and controlled cooling and normalized controlled cooling production method for a 420 MPa grade building steel plate, but the Nb content needs to reach 0.03% or more to meet the corresponding mechanical properties. The purpose is to expand the unrecrystallization zone temperature and increase the finish rolling temperature by high Nb. This method is beneficial to the control of the shape of the steel plate, but after the increase of the finish rolling temperature, the super-fast cooling effect is weakened, which is not conducive to the rapid passing of the core of the steel plate through the austenite zone to the phase change zone, and thus the Nb in the core of the steel plate is not conducive to precipitation during the phase change, and the strength of the core of the steel plate is low. SUMMARY

[0005] In order to overcome the defects of the prior art, the present application provides a steel plate for nuclear power hoist mechanical module with a thickness of 30-150 mm and a manufacturing method thereof. The product produced according to the chemical composition and production process requirements of the steel of the present application has high strength and toughness, high modulus welding property and high temperature resistance.

[0006] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] A steel plate for nuclear power hoist mechanical module, the chemical composition of the steel is as follows in terms of percentage by weight: C: 0.15%-0.30%, Mn: 1.11%-2.10%, P≤0.010%, S≤0.015%, Ni: 0.01%-0.59%, Cr: 0.02%-1.5%, Mo: 0.01%-0.39%, Nb: 0.01%-0.20%, B: 0.0005%-0.007%, V: 0.09%-0.20%, Ti: 0.001%-0.07%, Cu: 0.30%-0.80%, Y: 0.0001%-0.0010%, Sb: 0.0001%-0.0010%, Si3N4: 0.001%-0.020%, and the balance is Fe and inevitable impurities.

[0008] The reasons for adopting the above-mentioned component design are as follows:

[0009] 1) Carbon: C can greatly strengthen through solid solution, and can also form fine carbide precipitates with alloying elements such as Nb, V, Ti, etc., which are precipitated before rolling deformation or austenite transformation, hinder grain growth, improve nucleation rate, and refine the structure; however, too high C content will form obvious banded structure during rolling, which seriously affects the consistency of the properties of the steel plate in all directions, therefore, the C content of the present application is 0.15%-0.30%.

[0010] 2) Manganese: it increases the strength of the steel in the form of solid solution strengthening, makes up for the deficiency caused by the decrease of C, is the main alloying element affecting strength, hardenability and weldability, and is low in cost, but too high content will easily cause segregation in the center and adversely affect the weldability of the steel, therefore, the content is controlled in the range of 1.11%-2.10%.

[0011] 3) P and S: they are both harmful elements in the steel of the present application, which will adversely affect the low-temperature impact toughness and lamellar tearing resistance of the steel plate, and increase the brittleness of the steel. Phosphorus reduces the weldability, reduces plasticity, and makes the cold bending performance worse; sulfur reduces the ductility and toughness of the steel, and causes cracks during forging and rolling. Therefore, the lower the content is, the better, but considering the steelmaking conditions and cost, the present application requires that P≤0.010% and S≤0.015% in the steel.

[0012] 4) Nickel: In the present invention, appropriate amount of nickel is added to form and stabilize austenite, improve the strength of the steel plate, reduce the carbon content, and improve the welding performance of the steel plate. However, too high nickel is not conducive to the precipitation of grain boundary carbide, thereby reducing the amount of intergranular carbide, which seriously affects the strength and toughness of the steel of the present invention. Meanwhile, high viscosity iron oxide skin is generated during the heating process of continuous casting billet, which affects the surface quality of the steel plate. The content of Ni in the present invention is controlled at 0.01% to 0.59%.

[0013] 5) Chromium: Cr is an important element of austenitic stainless steel. 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 cause carbide coarsening, thereby reducing the high-temperature strength and toughness of the steel plate. The content of Cr in the present invention is controlled at 0.02% to 1.5%.

[0014] 6) Molybdenum: Mo mainly relies on solid solution strengthening and grain boundary strengthening to improve the strength of the steel. Secondly, Mo increases the stability of supercooled austenite, which makes the austenite to ferrite transformation curve right shift, and the ferrite structure after phase transition is more fine. In addition, Ti and Mo combine to precipitate a large amount of nanometer-sized Ti-Mo (CN) carbide in the steel, which pinches dislocations, greatly improving the strength and toughness of the steel. Therefore, the present invention requires Mo: 0.01% to 0.39%.

[0015] 7) Niobium: As a strong carbide-forming element, Nb forms NbC phase with large dispersion and good high-temperature stability, which has a precipitation strengthening effect. Through multi-stage rolling, the grain can be effectively refined, and the toughness reduction caused by precipitation strengthening can be improved, so that the steel plate obtains high strength and high toughness. In addition, in the Nb-Mo composite added steel, Mo can also be segregated on the NbC matrix interface, preventing the coarsening of NbC particles, thereby greatly improving the high-temperature strength of the steel. Therefore, the content of Nb is controlled at 0.01% to 0.20%.

[0016] 8) Boron: can improve the hardenability of the steel plate. A small amount of B element can significantly improve the hardenability effect, ensuring the strength of the steel plate. However, when the B element is excessive, the brittleness of the steel plate increases, and the welding crack tendency increases. Therefore, the present invention controls B: 0.0005% to 0.007%.

[0017] 9) Vanadium: used for precipitation in finish rolling and tempering, which has a precipitation strengthening effect. After controlled rolling, V carbon and nitride precipitates, which strongly improves the strength of the steel plate and refines the grain size. However, too high content of V will have an adverse effect on the weldability. V: 0.09% to 0.20%.

[0018] 10) Titanium: can play a role in nitrogen fixation, the formation of TiN-based precipitates, can inhibit the grain growth of austenite under high temperature conditions, can also improve the toughness of the heat-affected zone after welding, and in the welding process, TiN particles prevent the grain growth of the heat-affected coarse grain zone, improve the low temperature toughness of the welded joint. In addition, Ti is easy to appear in the form of interphase precipitation during the transformation from austenite to ferrite due to its low solid solubility, thereby improving the strength. However, excessive Ti will reduce the toughness of the steel, so the content of Ti is controlled at 0.001% to 0.07%.

[0019] 11) Copper: Cu is an austenite forming element, and the use of copper in the support of the core of the steel plate can compensate for the loss of strength due to the increase in thickness, Cu: 0.30% to 0.80%.

[0020] 12) Yttrium: Y significantly improves the resistance to atmospheric corrosion and improves the toughness of the steel plate through precipitation strengthening, Y: 0.0001% to 0.0010%.

[0021] 13) Antimony: Sb reduces the corrosion rate while maintaining the strength of the steel plate, so the content is controlled at 0.0001% to 0.0010%.

[0022] 14) Silicon nitride: Si3N4 has excellent high-temperature strength and oxidation resistance, can act as a nucleation phase during smelting, as a recrystallization point during rolling, and can recrystallize and precipitate during heat treatment: 0.001% to 0.020%.

[0023] The steel plate has a room temperature yield strength of ≥838 MPa, a tensile strength of ≥916 MPa, an elongation of ≥10.5%, and a reduction of area of ≥53.5%; a 360°C high-temperature tensile yield strength of ≥722 MPa, a tensile strength of ≥808 MPa, an elongation of ≥11.5%, and a reduction of area of ≥64%; and a-20°C impact energy of the steel plate of 46J or more.

[0024] After the steel plate is subjected to simulated post-weld heat treatment, the room temperature yield strength is ≥838 MPa, the tensile strength is ≥916 MPa, the elongation is ≥10.5%, and the reduction of area is ≥53.5%; the 360°C high-temperature tensile yield strength is ≥722 MPa, the tensile strength is ≥808 MPa, the elongation is ≥11.5%, and the reduction of area is ≥64%; and the-20°C impact energy of the steel plate after simulated post-weld heat treatment is 46J or more.

[0025] The thickness of the steel plate is 30-150mm. The microstructure of the steel plate is 1%-2% polygonal ferrite, 1%-2% residual austenite, and the rest is sorbite.

[0026] A method for manufacturing a steel plate for a nuclear power plant crane mechanical module, the specific method comprising:

[0027] 1) Smelting: raw materials such as molten iron, scrap steel, etc. are added into a converter or an electric furnace for smelting.

[0028] 2) Continuous casting: the smelted molten steel is cast into a slab through continuous casting.

[0029] 3) Rolling: the heating temperature of the billet is 1100-1250 DEG C, the opening rolling temperature is 1100-1250 DEG C, and the final rolling temperature is 850-1000 DEG C; different rolling temperatures can ensure the control of precipitated phases and phase ratio during the rolling process.

[0030] 4) Quenching and tempering treatment: the quenching temperature is 850 DEG C-960 DEG C, and the holding time is 1-10 min / mm; the Cr-Mo-Mn alloy system improves the stability of austenite and delays the pearlite transformation. Si3N4 is introduced to inhibit the precipitation of carbides, stabilize a small amount of residual austenite, and improve the toughness.

[0031] The tempering temperature is 580 DEG C-680 DEG C, and the holding time is 1-10 min / mm.

[0032] The Mo-V-Cr alloy system delays the tempering softening to form stable carbides such as Mo2C, VC and Cr7C3, improves the tempering resistance, and moves the strength-toughness balance to a high range.

[0033] Nb and Ti secondary precipitation, nanoscale NbC and TiC are precipitated during the tempering process, which pins dislocations and refines the structure, contributing to the secondary hardening effect.

[0034] Y-Sb grain boundary purification ensures the homogenization of the tempering sorbite + residual austenite toughening.

[0035] After the steel plate is rolled, a quenching and tempering process is adopted to obtain fine and uniform tempering sorbite structure + polygonal ferrite structure and residual austenite structure, and the steel plate has good comprehensive mechanical properties.

[0036] Compared with the prior art, the beneficial effects of the present application are:

[0037] 1) The steel plate produced by the process technology of the present application has excellent low-temperature toughness indicators through the optimization of chemical composition and the reasonable design of process parameters. The impact energy at -20 DEG C of the steel plate after quenching and tempering treatment and simulated post-weld heat treatment is maintained at more than 46J.

[0038] 2) The steel of the present application has good strength and toughness in different states after quenching and tempering and simulated post-weld heat treatment (holding temperature 600℃, holding time up to 15 hours). The yield strength of the steel plate after quenching and tempering and simulated post-weld heat treatment is ≥838MPa at room temperature, the tensile strength is ≥916MPa, the elongation is ≥10.5%, and the reduction of area is ≥53.5%; the yield strength is ≥722MPa at 360℃, the tensile strength is ≥808MPa, the elongation is ≥11.5%, and the reduction of area is ≥64%; the impact energy at -20℃ is ≥46J. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 is the microstructure of the steel plate at room temperature. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical scheme and advantages of the present application more clear, the specific embodiments of the present application will be further described below in combination with examples. The following examples are used to specifically describe the present application, and these examples are only a general description of the present application, and do not limit the present application.

[0041] A steel plate with a thickness of 30-150mm for a nuclear power crane module and a manufacturing method thereof, the specific embodiments are as follows: the chemical composition of each example is shown in Table 1.

[0042] Table 1 Chemical composition of steel of each example (wt%)

[0043]

[0044] The simulated post-weld heat treatment process is temperature 600℃, holding time 15h, and the temperature rising and falling rate above 400℃ is ≤55℃ / h. The rolling and heat treatment process and the mechanical property results are shown in Table 2 and Table 3.

[0045] Table 2 Production process of example steel

[0046]

[0047] Table 3 Performance of example

[0048]

[0049] From the examples, the average mechanical properties of the steel plates are: the yield strength at room temperature is ≥838MPa, the tensile strength is ≥916MPa, the elongation is ≥10.5%, the reduction of area is ≥53.5%; the yield strength at 360℃ is ≥722MPa, the tensile strength is ≥808MPa, the elongation is ≥11.5%, the reduction of area is ≥64%; the impact energy at -20℃ is ≥46J. The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable the person skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit and essence of the present application shall be covered within the protection scope of the present application.

Claims

1. A steel plate for a nuclear power plant waste crane mechanical module, characterized in that, The chemical composition of the steel, by weight percentage, is as follows: C: 0.15%–0.30%, Mn: 1.11%–2.10%, P≤0.010%, S≤0.015%, Ni: 0.01%–0.59%, Cr: 0.02%–1.5%, Mo: 0.01%–0.39%, Nb: 0.01%–0.20%, B: 0.0005%–0.007%, V: 0.09%–0.20%, Ti: 0.001%–0.07%, Cu: 0.30%–0.80%, Y: 0.0001%–0.0010%, Sb: 0.0001%–0.0010%, Si3N4: 0.001%–0.020%, with the balance being Fe and unavoidable impurities; The microstructure of the steel plate, by volume percentage, is: 1%–2% polygonal ferrite, 1%–2% retained austenite, and the remainder is sorbite. The manufacturing method of the steel plate for the nuclear power plant waste crane mechanical module includes the following specific steps: Rolling: The billet heating temperature is 1100~1250℃, the initial rolling temperature is 1100~1250℃, and the final rolling temperature is 850~1000℃; Tempering treatment: Quenching temperature is 850~960℃, holding time is 1~10min / mm; The tempering temperature is 580–680℃, and the holding time is 1–10 min / mm.

2. The steel plate for a nuclear power plant waste crane mechanical module according to claim 1, characterized in that, The steel plate has a room temperature yield strength ≥838MPa, tensile strength ≥916MPa, elongation ≥10.5%, and reduction of area ≥53.5%; at 360℃, the yield strength is ≥722MPa, tensile strength ≥808MPa, elongation ≥11.5%, and reduction of area ≥64%; the steel plate absorbs more than 46J of impact energy at -20℃.

3. The steel plate for a nuclear power plant waste crane mechanical module according to claim 1, characterized in that, The simulated post-weld heat treatment process involves a temperature of 600℃ and a holding time of 15 hours. The heating and cooling rate above 400℃ is ≤55℃ / hour. After simulated post-weld heat treatment, the steel plate exhibits the following characteristics: room temperature yield strength ≥838MPa, tensile strength ≥916MPa, elongation ≥10.5%, and reduction of area ≥53.5%; at 360℃, the yield strength is ≥722MPa, tensile strength ≥808MPa, elongation ≥11.5%, and reduction of area ≥64%; and the steel plate after simulated post-weld heat treatment absorbs over 46J of impact energy at -20℃.

4. The steel plate for a nuclear power plant waste crane mechanical module according to claim 1, characterized in that, The thickness of the steel plate is 30-150mm.

5. A method for manufacturing steel plates for nuclear power plant waste crane mechanical modules as described in any one of claims 1-4, characterized in that, Specific methods include: Rolling: The billet heating temperature is 1100~1250℃, the initial rolling temperature is 1100~1250℃, and the final rolling temperature is 850~1000℃; Tempering treatment: Quenching temperature is 850~960℃, holding time is 1~10min / mm; The tempering temperature is 580–680℃, and the holding time is 1–10 min / mm.

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