Low-alloy hot-rolled low-temperature steel plate and preparation method thereof

Abstract

The invention relates to the technical field of ferrous metallurgy, in particular to a low-alloy hot-rolled low-temperature steel plate and a preparation method thereof.The low-alloy hot-rolled low-temperature steel plate is characterized by comprising, by mass, 0.075%-0.095% of C, 0.15%-0.25% of Si, 1.52%-1.60% of Mn, smaller than or equal to 0.013% of P, smaller than or equal to 0.003% of S, 0.035%-0.075% of Al, 0.005%-0.02% of Ti and the balance Fe and inevitable impurities; the low-temperature steel comprises ferrite and pearlite, and the grain size of the ferrite and the grain size of the pearlite are both higher than the eighth grade.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, in particular to a low-alloy hot-rolled low-temperature steel plate and a preparation method thereof. Background Art

[0002] With the development of my country's industry and economy, energy consumption has increased significantly. As a high-quality, efficient and clean energy, natural gas has received increasing attention from the country and society. Various types of energy are often stored in cryogenic pressure vessels during storage and transportation. At present, cryogenic pressure vessels are constantly developing in the direction of high parameters and large-scale. For example, oil tanks have been reduced from 100,000 m 3 Developed to 150,000 m 3 The capacity of natural gas and liquefied gas spherical tanks ranges from hundreds, thousands to tens of thousands of m 3 The design operating temperature of propylene and ethylene storage tanks has dropped from -20℃--35℃ in the 1980s to -30℃--50℃ now, and some ethylene storage tanks even have a design temperature requirement of -104℃. From the perspective of energy storage safety, most pressure vessel steels are low-temperature steels with a temperature of -20℃ or below. With the increase in the use of low-temperature steel and the increase in safety requirements, the research and development of higher strength, higher toughness and relatively low-priced low-temperature steels has received more and more attention from the country and the industry.

[0003] In order to increase the low temperature resistance of steel, the prior art often adds more precious metals and even rare earth elements to the steel. The high content of precious metals and rare earth elements in the composition makes the existing low temperature steel have the problem of high cost. The present invention adopts the alloy design concept of replacing nickel with manganese and micro-titanium and optimizes the composition of other elements, and adopts a reasonable rolling process to make the material obtain excellent low temperature toughness. Summary of the invention

[0004] In view of the above situation, in order to overcome the defects of the prior art, the present invention provides a low-alloy hot-rolled low-temperature steel plate and a preparation method thereof. The technical solution to the problem is to include a low-alloy hot-rolled low-temperature steel plate, characterized in that the mass percentages of the components of the low-alloy hot-rolled low-temperature steel plate are: 0.075-0.095% C, 0.15-0.25% Si, 1.52-1.60% Mn, P ≤0.013%, S ≤0.003%, 0.035-0.075% Al, 0.005-0.02% Ti, and the balance is Fe and unavoidable impurities; the low-temperature steel includes ferrite and pearlite, and the grain sizes of the ferrite and the pearlite are both above level eight.

[0005] Preferably, the present application provides a low alloy hot rolled low temperature steel plate and a preparation method thereof, comprising the following steps: Providing molten iron, and desulfurizing the molten iron; Performing primary smelting on the molten iron to obtain molten steel; Refining molten steel, controlling the molten steel to include the following elements by weight at the end of refining: 0.075-0.095% C, 0.15-0.25% Si, 1.52-1.60% Mn, 0-0.013% P, 0-0.003% S, 0.035-0.075% Al, 0.005-0.02% Ti, and the balance Fe; Continuously casting the molten steel to obtain a steel billet; Rolling the steel billet to obtain steel; The steel material is cooled to obtain the low-temperature steel.

[0006] Preferably, after desulfurization of the molten iron, the sulfur content of the molten iron is ≤0.006wt%.

[0007] Preferably, the phosphorus content of the molten steel obtained after the primary smelting is ≤0.012wt%.

[0008] Preferably, the refining of molten steel comprises the following steps: smelting the molten steel in a LF refining furnace; The molten steel is vacuum degassed in a VD vacuum refining furnace.

[0009] Preferably, during the continuous casting of the molten steel, the superheat of the molten steel is 10-30°C.

[0010] Preferably, between the continuous casting of the molten steel and the rolling of the steel billet, the following step is also included: heating the steel billet at 1130-1200°C for a predetermined time.

[0011] Preferably, the predetermined time duration is calculated by the following formula: predetermined time duration = k × billet thickness, where 0.8≤k≤1.2.

[0012] Preferably, the rolling includes rough rolling, finish rolling and laminar cooling, and the thickness of the steel billet is 3.5 times the thickness of the low-temperature steel when the rough rolling is completed.

[0013] Preferably, the start rolling temperature of the steel billet finish rolling should be no greater than 940°C, and the final cooling temperature of the steel billet finish rolling should be 600±30°C.

[0014] The beneficial effects of the present invention are: The embodiments of the present application provide a low-temperature steel and a preparation method thereof, which solve the technical problem of high cost of existing low-temperature steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is the metallographic structure of 20mm steel plate. DETAILED DESCRIPTION

[0016] The following is combined with Figure 1 The specific implementation modes of the present invention are further described in detail.

[0017] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the present invention is now described in conjunction with embodiments.

[0018] The present invention rolls 150mm ingot into steel plate with thickness of 16mm-20mm on a single rolling reciprocating rolling mill, adopts rough rolling, finish rolling, laminar cooling and other procedures and process measures to produce low alloy steel plate with excellent low temperature toughness, and lists the implemented process and finished steel plate performance.

[0019] All technical and scientific terms used in this specification have the same meanings as those commonly understood by those skilled in the art to which this disclosure belongs. In this specification, "impact energy (KV2 / J)" is used as an indicator of the hardness value of steel. The impact energy (KV2 / J) is measured using GB / T 229.1-2007 "Metallic Material Charpy Pendulum Impact Test Method".

[0020] Example 1 The chemical composition and mass fraction of the low-temperature steel with a thickness of 20 mm are 0.075% C, 1.57% Mn, 0.21% Si, 0.014% Ti, 0.001% S, 0.011% P, and the balance of Fe and impurity elements. The billet is heated to 1180°C and kept for 150 minutes before being roughly rolled to 70 mm. The finishing rolling temperature is 920°C, the final rolling temperature is controlled at 800°C, and the temperature is lowered to 610°C after laminar cooling. Figure 1 It can be seen that the steel plate has a dual-phase composite structure of ferrite + pearlite, the grain size reaches level nine, the yield strength is 441MPa, the tensile strength is 524MPa, the elongation after fracture is 29%, and the -60℃ Charpy impact absorption energy is 171J.

[0021] Example 2 The chemical composition and mass fraction of the low-temperature steel with a thickness of 16 mm are 0.085% C, 1.60% Mn, 0.21% Si, 0.013% Ti, 0.002% S, 0.010% P, and the balance Fe and impurity elements. The billet is heated to 1200°C and kept warm for 150 minutes before being roughly rolled to 71 mm. The finishing rolling temperature is 940°C, the final rolling temperature is controlled at 780°C, and the temperature is lowered to 600°C after laminar cooling. The yield strength is 460MPa, the tensile strength is 563MPa, the elongation after fracture is 28%, and the -60°C Charpy impact absorption energy is 163J.

[0022] Example 3 The chemical composition and mass fraction of the low-temperature steel with a thickness of 18 mm are 0.078% C, 1.58% Mn, 0.20% Si, 0.010% Ti, 0.001% S, 0.010% P, and the balance Fe and impurity elements. The billet is heated to 1180 ° C and kept for 150 minutes, then roughly rolled to 70 mm, the finishing rolling temperature is 910 ° C, the final rolling temperature is controlled at 750 ° C, and the temperature is cooled to 590 ° C after laminar cooling. The yield strength is 463 MPa, the tensile strength is 555 MPa, the elongation after fracture is 29%, and the -60 ° C Charpy impact absorption energy is 153 J.

Claims

1. A low alloy hot rolled low temperature steel plate, characterized in that: The mass percentages of the components of the low alloy hot rolled low temperature steel plate are: 0.075-0.095% C, 0.15-0.25% Si, 1.52-1.60% Mn, P ≤0.013%, S ≤0.003%, 0.035-0.075% Al, 0.005-0.02% Ti, and the balance is Fe; The low alloy hot rolled low temperature steel plate comprises ferrite and pearlite, and the grain sizes of the ferrite and the pearlite are both above level eight.

2. The method for preparing a low alloy hot rolled low temperature steel sheet according to claim 1, characterized in that: The steps include: Step 1, providing molten iron, desulfurizing the molten iron so that the sulfur content of the molten iron is ≤0.006wt%, and performing primary refining on the molten iron to obtain molten steel, wherein the phosphorus content of the molten steel obtained after the primary refining is ≤0.012wt%; Step 2, refining the molten steel, and controlling the molten steel to include the following elements by weight at the end of refining: 0.075-0.095% C, 0.15-0.25% Si, 1.52-1.60% Mn, 0-0.013% P, 0-0.003% S, 0.035-0.075% Al, 0.005-0.02% Ti, and the balance is Fe; Step 3, continuously casting the molten steel to obtain a steel billet, rolling the steel billet to obtain a steel material, and cooling the steel material to obtain the low-temperature steel; The rolling includes rough rolling, finish rolling and laminar cooling; The thickness of the steel billet after the rough rolling is 3.5 times the thickness of the low-temperature steel.

3. The method for preparing low-temperature steel according to claim 2, characterized in that: The described steel refining comprises the following steps: smelting the molten steel in a LF refining furnace; The molten steel is vacuum degassed in a VD vacuum refining furnace.

4. The method for preparing low temperature steel according to claim 2, characterized in that: During the continuous casting of the molten steel, the superheat degree of the molten steel is 10-30°C.

5. The method for preparing low temperature steel according to claim 2, characterized in that: Between the continuous casting of molten steel and the rolling of the steel billet, the following step is also included: heating the steel billet at 1130-1200°C for a predetermined time.

6. The method for preparing low-temperature steel according to claim 5, characterized in that: The predetermined duration is 130 min to 240 min.

7. The method for preparing low temperature steel according to claim 3, characterized in that: The start temperature of the steel billet finish rolling should not be greater than 940°C, and the final cooling temperature of the steel billet finish rolling should be 600±30°C.

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