High-strength steel with low-temperature toughness as well as preparation method and application of high-strength steel

Abstract

The invention provides high-strength steel with low-temperature toughness and a preparation method and application thereof, and relates to the technical field of metal material preparation. According to the high-strength steel, a low-C-Mn system is adopted, trace V and Zr elements are supplemented for component design, then a reasonable controlled rolling and controlled cooling technology and a heat treatment technology are adopted, the high-strength steel plate with the thickness being 60-80 mm is produced, the yield strength ReL of the high-strength steel plate is larger than or equal to 560 MPa, the tensile strength Rm of the high-strength steel plate is larger than or equal to 700 MPa, the elongation A of the high-strength steel plate is larger than or equal to 22%, the yield ratio of the high-strength steel plate is smaller than or equal to 0.85, and the transverse impact energy-60 DEG C KV2 at the position 1 / 2 of the plate thickness is larger than or equal to 100 J; the alloy has the characteristics of high strength, excellent low-temperature toughness, excellent weldability, simplicity and convenience in production operation and low cost.

Description

Technical Field

[0001] The present invention relates to the technical field of metal material preparation, and in particular to a high-strength steel with low-temperature toughness and a preparation method and application thereof. Background Art

[0002] With the rapid development of economy and society, large-scale steel structures have been widely used due to their high construction efficiency and excellent performance. With the increasing social demand, the thickness of steel plates used in steel structures has become thicker and the strength has become higher. In actual application, thick steel plates have many defects, resulting in poor toughness in the core. In the welding process, problems such as insufficient impact toughness of the core and welding cracking often occur, which greatly affects the safety of steel structures and poses certain risks to social security.

[0003] In the prior art, the patent document with application number 202211018305.6 and publication date June 27, 2023, entitled "A super-thick, high-strength, high-toughness, high-homogeneity, super-thick steel plate for hydropower and its manufacturing method" discloses a super-thick, high-strength, high-toughness, high-homogeneity, super-thick steel plate for hydropower. It is made by quenching + tempering process. The tensile strength of the steel plate is above 800MPa, and the impact toughness of the core at -60℃ is above 100J. However, the Mn content of the thick steel plate exceeds 4.0%, and it contains relatively high precious alloy elements such as Cr, Mo, Ni, Cu, etc., and the weldability is poor. In addition, the quenching and tempering processes of this technical solution require preheating, and the production operation is difficult and the cost is high.

[0004] In view of this, it is necessary to design an improved high-strength steel with low-temperature toughness and a preparation method and application thereof to solve the above problems. Summary of the invention

[0005] The object of the present invention is to provide a high-strength steel with low-temperature toughness and a preparation method and application thereof.

[0006] To achieve the above-mentioned object of the invention, on the one hand, the present invention provides a high-strength steel with low-temperature toughness, which is composed of the following chemical components by mass percentage: C: 0.04-0.08%, Si: ≤0.40%, Mn: 1.65-1.85%, Mo: 0.08-0.20%, Ni: 0.20-0.40%, V: 0.07-0.15%, Zr: 0.05-0.15%, B: 0.0005-0.0020%, P≤0.008%, S≤0.002%, As≤0.005%, H≤1.5ppm, and the balance is Fe and unavoidable impurity elements;

[0007] The high-strength steel meets the following conditions at the same time:

[0008] Carbon equivalent CE (%) = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 ≤ 0.42,

[0009] Welding crack sensitivity index Pcm (%) = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15 + V / 10 + 5B ≤ 0.21.

[0010] Preferably, the thickness of the high-strength steel is 60-80 mm, and its yield strength R eL ≥560MPa, tensile strength R m ≥700MPa, elongation A≥22%, yield strength ratio≤0.85, transverse impact energy at 1 / 2 of the plate thickness -60℃ KV2≥100J.

[0011] On the other hand, the present invention also provides a method for preparing the high-strength steel, comprising the following steps:

[0012] S1. The pre-treated blast furnace molten iron is smelted by top converter smelting, and low-carbon ferromanganese, ferromolybdenum and ferronickel alloy are added when 1 / 3 of the steel is tapped; then the steel is further desulfurized by ladle furnace refining, and ferroboron and ferrozirconium alloy are added according to the target value to adjust the chemical composition; then the steel is vacuum treated in RH vacuum treatment furnace with vacuum degree ≤90Pa, and smelted into molten steel after soft blowing for more than 15 minutes; the steel is cast into 370mm thick continuous casting slabs on the continuous casting machine by full-process protection casting and light pressure reduction technology, and the slabs are stacked and slowly cooled;

[0013] S2. The billet is hot-charged, the surface temperature of the hot-charged billet is ≤500℃, the temperature of the soaking section is 1170-1220℃, and the billet is descaled by high-pressure water after being taken out of the furnace to remove the iron oxide scale on the surface of the billet; two-stage controlled rolling is adopted, the first stage rolling temperature is 1020-1100℃, the final rolling temperature is 1000-1060℃, and the single-pass reduction of the last two passes is ≥45mm; the second stage rolling temperature is 850-880℃, and ACC cooling is carried out after rolling, the cooling rate is controlled at 10-20℃ / s, the red-return temperature is 580-620℃, and the steel plate is rolled and stacked for slow cooling for more than 48h;

[0014] S3. Quench and temper the steel plate stack.

[0015] Preferably, the molten steel is composed of the following chemical components in percentage by mass: C: 0.04-0.08%, Si: ≤0.40%, Mn: 1.65-1.85%, Mo: 0.08-0.20%, Ni: 0.20-0.40%, V: 0.07-0.15%, Zr: 0.05-0.15%, B: 0.0005-0.0020%, P≤0.008%, S≤0.002%, As≤0.005%, H≤1.5ppm, and the remainder is Fe and unavoidable impurity elements.

[0016] Preferably, in step S3, the temperature of the quenching treatment is 880-920°C.

[0017] Preferably, in step S3, the temperature of the tempering treatment is 600-660°C.

[0018] Preferably, the thickness of the steel plate is 60-80 mm.

[0019] Preferably, the molten steel is composed of the following chemical components in percentage by mass: 0.07% C, 0.23% Si, 1.72% Mn, 0.11% Mo, 0.31% Ni, 0.11% V, 0.10% Zr, 0.0013% B, 0.006% P, 0.001% S, 0.003% As, H=1ppm, and the rest is Fe and unavoidable impurity elements.

[0020] Preferably, in step S1, Zr is controlled to be 0.08-0.15% during smelting.

[0021] In particular, the high-strength steel produced by the preparation method proposed in the present invention can be manufactured into steel structures, containers, ships, and bridges.

[0022] The beneficial effects of the present invention are:

[0023] 1. The high-strength steel with low-temperature toughness provided by the present invention mainly adopts a low C-Mn system and is supplemented with trace V and Zr elements. Then, through a reasonable controlled rolling and controlled cooling process and a heat treatment process, a high-strength steel plate with a thickness of 60-80 mm is produced. Its yield strength R eL ≥560MPa, tensile strength R m ≥700MPa, elongation A≥22%, yield strength ratio≤0.85, transverse impact energy at 1 / 2 of the plate thickness -60℃ KV2≥100J.

[0024] 2. The high-strength steel with low-temperature toughness provided by the present invention has the characteristics of high strength, excellent low-temperature toughness, excellent weldability, etc., and has a simple production process and low cost. It is suitable for manufacturing various large steel structures, containers, ships, bridges, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The metallographic structure diagram of the steel plate prepared in Example 1 of the present invention at 1 / 2 thickness;

[0026] Figure 2 This is a metallographic structure diagram of the steel plate prepared in Example 1 of the present invention at 1 / 4 of the thickness. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the scheme of the present invention are shown in the drawings, while other details that are not closely related to the present invention are omitted.

[0029] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0030] On the one hand, the present invention provides a high-strength steel with low-temperature toughness, which is composed of the following chemical components by mass percentage: C: 0.04-0.08%, Si: ≤0.40%, Mn: 1.65-1.85%, Mo: 0.08-0.20%, Ni: 0.20-0.40%, V: 0.07-0.15%, Zr: 0.05-0.15%, B: 0.0005-0.0020%, P≤0.008%, S≤0.002%, As≤0.005%, H≤1.5ppm, the remainder is Fe and unavoidable impurity elements, and the following conditions are met at the same time:

[0031] Carbon equivalent CE (%) = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 ≤ 0.42;

[0032] Welding crack sensitivity index Pcm (%) = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15 + V / 10 + 5B ≤ 0.21. When the thickness of high-strength steel is 60-80mm, the yield strength R eL ≥560MPa, tensile strength R m≥700MPa, elongation A≥22%, yield strength ratio≤0.85, transverse impact energy at 1 / 2 of plate thickness -60℃ KV2≥100J, transverse impact energy at 1 / 4 of plate thickness -60℃ KV2≥200J.

[0033] In the above technical scheme, the steel composition design is based on the low C-Mn system, and appropriate amounts of Mo and Ni are added to ensure tempering stability and low-temperature toughness, and then supplemented with trace amounts of V and Zr elements to form fine dispersed second phases in the steel to refine the grains and change the morphology of inclusions in the core of the thick steel plate, thereby improving its low-temperature toughness. The reasons for controlling the proportion of each chemical composition within a specific range are as follows: C is an important element to improve the strength of steel plates, but too high C will affect the weldability and plastic toughness of steel. In order to ensure the high strength, high toughness and weldability of steel, the C content is controlled to 0.04-0.08%; Mn can replace C elements to improve the strength of steel without reducing the toughness of steel, and improve the hardenability of steel, and can also improve the stability of tempering structure, but too high content will make the steel grain coarsening at high temperature, reduce the toughness and weldability of steel plates and welded joints; Mo can improve the toughness of welded joints, improve tempering stability and refine grains, but Mo is a precious metal, and excessive addition will significantly increase the cost of steel, and will also affect the production of granular bainite in the core of the steel plate; Ni is beneficial to the low-temperature impact toughness of steel plates, but Ni is expensive, and excessive addition will significantly increase the production cost of steel, so the Ni content is controlled to 0.20-0.40%; V forms carbonitrides in the ferrite at the austenite grain boundary. Precipitation can inhibit the recrystallization of austenite and prevent grain growth during rolling, thereby refining ferrite grains, improving the strength, toughness and weldability of steel, and precipitating carbonitride during tempering to play a precipitation strengthening role; Zr can form fine and dispersed Zr composite oxides in steel, especially for modifying inclusions such as MnS, improving the shape, size and distribution of inclusions in the center of steel and improving the toughness of the core of thick steel plates, but Zr is expensive, and excessive addition will increase production costs, so the Zr content is controlled to 0.05-0.15%; B can significantly improve the hardenability of steel and increase the strength of steel, but excessive B will affect the weldability and low-temperature toughness of steel; As, P, S are inevitable impurity elements in steel, which are harmful to the low-temperature toughness and weldability of steel, and the lower their content, the better; H hydrogen atoms are easy to diffuse in the ingot, especially easy to gather in the gap between the inclusions and iron in the core of the thick steel plate, affecting the low-temperature toughness of the core of the thick steel plate.

[0034] On the other hand, the present invention also provides a method for preparing the high-strength steel with low-temperature toughness, comprising the following steps:

[0035] S1. Smelting and continuous casting process: The blast furnace molten iron with low As and low S after desulfurization pretreatment is smelted by top converter smelting, and low carbon ferromanganese, ferromolybdenum and ferronickel alloy are added when 1 / 3 of the steel is tapped; then the ladle furnace refining treatment is further desulfurized, and ferroboron and ferozirconium alloy are added according to the target value to adjust the chemical composition; then vacuum treatment is carried out in the RH vacuum treatment furnace with a vacuum degree of ≤90Pa, and high-purity molten steel is smelted after soft blowing for more than 15 minutes; the whole process protection casting and light pressure reduction technology are used to cast 370mm thick continuous casting slabs on the continuous casting machine, and the slabs are stacked and slowly cooled; the composition of the molten steel is as follows: C: 0.04-0.08%, Si: ≤0.40%, Mn: 1.65-1.85%, Mo: 0. 08-0.20%, Ni: 0.20-0.40%, V: 0.07-0.15%, Zr: 0.05-0.15%, B: 0.0005-0.0020%, P≤0.008%, S≤0.002%, As≤0.005%, H≤1.5ppm, the balance is Fe and unavoidable impurity elements, and the following conditions are met at the same time: carbon equivalent CE(%)=C+Mn / 6+Si / 24+Ni / 40+Cr / 5+Mo / 4+V / 14≤0.42, welding crack sensitivity index Pcm(%)=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B≤0.21;

[0036] S2. Rolling process: The billet is hot-charged, the hot-charged surface temperature is ≤500℃, the soaking section temperature is 1170-1220℃, and the billet is descaled by high-pressure water after being taken out of the furnace to remove the iron oxide scale on the surface of the ingot; two-stage controlled rolling is adopted, the first stage rolling temperature is 1020-1100℃, the final rolling temperature is 1000-1060℃, and the single pass reduction of the last two passes is ≥45mm; the second stage rolling temperature is 850-880℃, and ACC cooling (accelerated cooling control) is carried out after rolling, the cooling rate is controlled at 10-20℃ / s, and the red-return temperature is 580-620℃, and the finished steel plate with a thickness of 60-80mm is rolled, and the steel plate is quickly stacked and slowly cooled for more than 48h after rolling;

[0037] S3, heat treatment process: after quenching at 880-920℃, tempering at 600-660℃.

[0038] In particular, the high-strength steel produced by the preparation method proposed in the present invention can be further made into various large-scale steel structures, containers, ships, bridges, etc.

[0039] The high-strength steel with low-temperature toughness and its preparation method and application proposed by the present invention are further described below in conjunction with specific embodiments:

[0040] Example 1

[0041] In this embodiment, a high-strength steel with low-temperature toughness is prepared. The process flow is molten iron pretreatment → converter smelting → ladle furnace refining → vacuum treatment → continuous casting → hot delivery of ingot → heating of ingot → controlled rolling and controlled cooling → stacking and slow cooling → quenching → tempering → flaw detection → performance inspection, which specifically includes the following steps:

[0042] The blast furnace molten iron with low As and low S that has been pre-treated with desulfurization is smelted by top converter smelting. Low-carbon ferromanganese, ferromolybdenum and ferronickel alloy are added when 1 / 3 of the steel is tapped, and then further desulfurization is carried out by ladle furnace refining treatment, and ferroboron and ferrozirconium alloy are added according to the target value to adjust the chemical composition; then vacuum treatment is carried out in an RH vacuum treatment furnace with a vacuum degree of ≤90Pa, and high-purity molten steel is smelted after soft blowing for more than 15 minutes; the whole process protection casting and light pressure reduction technology are used to cast 370mm thick continuous casting slabs on the continuous casting machine, and the slabs are stacked and slowly cooled for 16 hours before hot delivery, and the surface temperature of the slabs is 460℃;

[0043] The continuous casting billet is heated to 1210℃, and after being taken out of the furnace, it is descaled by high-pressure water to remove the iron oxide scale on the surface of the billet; then it is rolled in two stages, with the initial rolling temperature at 1078℃, the final rolling temperature controlled at 1042℃, and the reduction of the last two passes is 46mm; the finishing rolling temperature is 858℃, and ACC cooling is performed after rolling, the cooling rate is 15℃ / s, the red-returning temperature is 605℃, and it is rolled into a 80mm thick finished steel plate, the steel plate is stacked and slowly cooled for 56 hours, and then quenched at 890℃, and then quenched at 6 After tempering at 20°C, the steel was air-cooled to room temperature after being taken out of the furnace to obtain high-strength steel, wherein the composition of the high-strength steel is as follows: 0.07% C, 0.23% Si, 1.72% Mn, 0.11% Mo, 0.31% Ni, 0.11% V, 0.10% Zr, 0.0013% B, 0.006% P, 0.001% S, 0.003% As, H=1ppm, CE=0.409, Pcm=0.193, and the rest is Fe and unavoidable impurity elements. The metallographic structure of the steel plate obtained in this embodiment at 1 / 2 thickness is shown in FIG. Figure 1 As shown, the structure is ferrite + bainite. The metallographic structure of the steel plate at 1 / 4 thickness is shown in Figure 2 As shown, the structure is tempered troostite, which not only ensures that the steel has good strength and toughness, but also makes it have a lower yield strength ratio.

[0044] Examples 2 to 3

[0045] The difference between Examples 2 to 3 and Example 1 is that the process parameters of the preparation process are different from those of Example 1, and the process parameter settings of Examples 1 to 3 are shown in Table 1. The composition of the high-strength steel prepared in Example 2 is as follows: 0.05% C, 0.22% Si, 1.83% Mn, 0.12% Mo, 0.30% Ni, 0.14% V, 0.09% Zr, 0.0012% B, 0.006% P, 0.001% S, 0.003% As, H=1ppm, CE=0.412, Pcm=0.182, and the rest is Fe and unavoidable impurity elements.

[0046] Transverse samples of the steel plates obtained in Examples 1 to 3 were processed into tensile specimens and impact specimens, and mechanical properties were tested. The results are shown in Table 2. It can be seen from the data in the table that the steel plates prepared by the method proposed in the present invention have higher strength, greater elongation and impact toughness.

[0047] Table 1 Process parameters of Examples 1 to 3

[0048]

[0049]

[0050] Table 2 Performance test results of steel plates obtained in Examples 1 to 3

[0051]

[0052] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A high-strength steel with low-temperature toughness, characterized in that: It is composed of the following chemical components in percentage by mass: C: 0.04-0.08%, Si: ≤0.40%, Mn: 1.65-1.85%, Mo: 0.08-0.20%, Ni: 0.20-0.40%, V: 0.07-0.15%, Zr: 0.05-0.15%, B: 0.0005-0.0020%, P≤0.008%, S≤0.002%, As≤0.005%, H≤1.5ppm, and the balance is Fe and unavoidable impurity elements; The high-strength steel meets the following conditions at the same time: Carbon equivalent CE (%) = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 ≤ 0.42, Welding crack sensitivity index Pcm (%) = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15 + V / 10 + 5B ≤ 0.

21.

2. The high-strength steel according to claim 1, characterized in that: The thickness of the high-strength steel is 60-80 mm, and its yield strength R eL ≥560MPa, tensile strength R m ≥700MPa, elongation A≥22%, yield strength ratio≤0.85, transverse impact energy at 1 / 2 of the plate thickness -60℃ KV2≥100J.

3. A method for preparing the high-strength steel according to claim 1 or 2, characterized in that: The steps include: S1. The pre-treated blast furnace molten iron is smelted by top converter smelting, and low-carbon ferromanganese, ferromolybdenum and ferronickel alloy are added when 1 / 3 of the steel is tapped; then the ladle furnace refining treatment is further desulfurized, and ferroboron and ferrozirconium alloy are added according to the target value to adjust the chemical composition; then vacuum treatment is carried out in an RH vacuum treatment furnace with a vacuum degree of ≤90Pa, and soft blowing is carried out for more than 15 minutes to smelt into molten steel; The whole process protection pouring and light pressure reduction technology are used to cast 370mm thick continuous casting slabs on the continuous casting machine, and the slabs are stacked and slowly cooled; S2. The billet is hot-charged, the surface temperature of the hot-charged billet is ≤500℃, the temperature of the soaking section is 1170-1220℃, and the billet is descaled by high-pressure water after being taken out of the furnace to remove the iron oxide scale on the surface of the billet; two-stage controlled rolling is adopted, the first stage rolling temperature is 1020-1100℃, the final rolling temperature is 1000-1060℃, and the single-pass reduction of the last two passes is ≥45mm; the second stage rolling temperature is 850-880℃, and ACC cooling is carried out after rolling, the cooling rate is controlled at 10-20℃ / s, the red-return temperature is 580-620℃, and the steel plate is rolled and stacked for slow cooling for more than 48h; S3. Quench and temper the steel plate stack.

4. The preparation method according to claim 3, characterized in that: The molten steel is composed of the following chemical components in percentage by mass: C: 0.04-0.08%, Si: ≤0.40%, Mn: 1.65-1.85%, Mo: 0.08-0.20%, Ni: 0.20-0.40%, V: 0.07-0.15%, Zr: 0.05-0.15%, B: 0.0005-0.0020%, P≤0.008%, S≤0.002%, As≤0.005%, H≤1.5ppm, and the remainder is Fe and unavoidable impurity elements.

5. The preparation method according to claim 3, characterized in that: In step 3, the temperature of the quenching treatment is 880-920°C.

6. The preparation method according to claim 3, characterized in that: In step 3, the temperature of the tempering treatment is 600-660°C.

7. The preparation method according to claim 3, characterized in that: The thickness of the steel plate is 60-80 mm.

8. The preparation method according to claim 4, characterized in that: The molten steel is composed of the following chemical components in percentage by mass: 0.07% C, 0.23% Si, 1.72% Mn, 0.11% Mo, 0.31% Ni, 0.11% V, 0.10% Zr, 0.0013% B, 0.006% P, 0.001% S, 0.003% As, H=1ppm, and the rest is Fe and unavoidable impurity elements.

9. The preparation method according to claim 3, characterized in that: In step 1, Zr is controlled to be 0.08-0.15% during smelting.

10. Application of high-strength steel with low-temperature toughness in manufacturing steel structures, containers, ships, and bridges, characterized in that: The high-strength steel is prepared by the preparation method described in any one of claims 3-9.

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