A production method for a thick, low-yield-to-strength ratio, high-strength and toughness bridge steel plate

Abstract

A production method for a thick, low-yield-to-strength ratio, high-strength and toughness bridge steel plate, including die casting, rolling, quenching and tempering processes. In the rolling process, the maximum reduction in the first three passes is ≥30mm, the rolling pressure during the rolling process is 5000-6000t, and the roller cooling water pressure is >38.4*10 4 ‑58.8*10 4 Pa. The quenching process has a quenching temperature of 900-920°C; the tempering process has a tempering temperature of 530-580°C. The developed steel plate has a finished thickness of 140-200mm, a yield strength of ≥390MPa, a tensile strength of ≥540MPa, an elongation of ≥20%, a yield strength ratio of ≤0.80, and an impact energy of ≥250J at -40°C.

Description

Technical Field

[0001] The invention belongs to the technical field of large-thickness bridge steel plate production, and specifically relates to a production method of large-thickness, low-yield-to-strength ratio and high-strength and toughness bridge steel plates. Background Art

[0002] In the current application of construction engineering, the demand for bridge steel plates is mostly concentrated in thickness below 100mm, and the production process is relatively mature using thermomechanical rolling technology. However, as the overall bridge design and construction needs, bridge steel plates with a thickness greater than 100mm are often used in the main bridge brackets and key load-bearing parts. For such thick bridge steel plates, as the thickness of the steel plate increases, the difference in the structure in the thickness direction of the steel plate is large, the internal quality deteriorates, and the deformation during the rolling process is difficult to penetrate into the core, resulting in the difficulty of pressing the defects of the steel plate, the inability to fully refine the structure, and the difficulty of crushing and filling the inclusions. In addition, according to the GB / T714-2015 bridge steel standard, high strength and toughness must be taken into account, that is, while meeting high strength, it is also necessary to meet the extremely low yield strength ratio of ≤0.85 with a low-temperature impact toughness of more than 120J at -40℃. More specifically, in order to meet the weldability of bridge design and processing, the standard requires the use of a low-C component design. The lower C component system increases the technical difficulty index for the production of thicker steel plates, which requires upgrades and breakthroughs in composition and process. How to produce thick, high-strength and toughness bridge steel plates is currently a new research direction for major steel companies.

[0003] The patented invention adopts the production process of die casting + rolling + quenching + tempering and successfully develops large-thickness bridge steel plates. Summary of the invention

[0004] The technical problem solved by the present invention is to develop thicker bridge steel plates to meet the relevant requirements of GB / T714-2015 standard.

[0005] In order to solve the above technical problems, the technical solution of the present invention is: a method for producing a thick, low-yield-to-strength ratio, high-strength and toughness bridge steel plate, including die casting, rolling, quenching and tempering processes.

[0006] Particularly, in the mold casting process, the superheat of the molten steel is ensured to be 30-50° C., the casting Ar ventilation volume is 300-500 L / min, and the casting time is 30-50 min.

[0007] In particular, in the rolling process, the billet is heated in a soaking furnace at a temperature of 1240-1270°C for 10-15 hours, and the air volume of the combustion-supporting fan is ensured to be 6000-7000m3 / h and the total pressure is 12000-13000Pa.

[0008] In particular, in the rolling process, the maximum reduction in the first three passes is ≥30 mm, and the rolling pressure during the rolling process is 5000-6000t.

[0009] In particular, in the rolling process, the roller cooling water pressure is greater than 38.4*10 4 -58.8*10 4 Pa.

[0010] Particularly, in the rolling process, the horizontal plane of the guide plates before and after the rollers is 80-90 mm lower than the roller surface of the working rollers, and the gap between the rollers and the guide plates is ≤3 mm.

[0011] Particularly, in the rolling process, the rolling bite speed is ≥15r / min.

[0012] Particularly, in the quenching process, the quenching temperature is 900-910°C; in the tempering process, the tempering temperature is 530-580°C.

[0013] Particularly, the finished steel plate has a thickness of 140-200 mm.

[0014] In particular, the main chemical components of the steel plate and their weight percentages are: C 0.06-0.12%, Si0.20-0.30%, Mn1.40-1.55%, P≤0.015%, S≤0.005%, Nb0.02-0.04%, Ni0.20-0.30%, B≤0.0005%, CEV≤0.41%, and the rest are Fe and unavoidable impurity elements.

[0015] Using the above technology, the thick bridge steel plate successfully developed has a yield strength ≥390MPa, a tensile strength ≥540MPa, an elongation ≥20%, a yield strength ratio ≤0.80, and an impact energy at -40℃ ≥250J.

[0016] The design idea of ​​the present invention is: using low C components to add microalloying elements Nb and Ni to ensure that the steel plate has good low-temperature toughness and welding performance; Ar gas protection is performed during the die casting process, and a low superheat degree is combined to fully ensure the internal quality of the casting ingot and reduce steel liquid inclusions and segregation; the large reduction amount in the first few passes during the rolling process causes the austenite grains to be fragmented and recrystallized, thereby providing a good organizational foundation for the high strength and low-temperature impact toughness of the steel plate; the steel plate is subjected to quenching + medium-temperature tempering treatment after rolling to promote the diffusion of alloy elements, change the organizational type composition, and improve the performance.

[0017] The beneficial effects of adopting the above technical solution are:

[0018] 1) By adopting the process production method of the die casting, rolling, quenching and tempering steps of the present invention, a thick bridge steel plate is successfully developed, which broadens the production thickness of the bridge steel plate and is of great significance to promoting the upgrading of the entire bridge construction project;

[0019] 2) The successfully developed thick bridge steel plate has a yield strength of ≥390MPa, a tensile strength of ≥540MPa, an elongation of ≥20%, a yield strength ratio of ≤0.80, and an impact energy of ≥250J at -40℃, which can fully meet the design and use requirements of bridges;

[0020] 3) The steel plate adopts a low C + micro-alloying element composition system, CEV≤0.41%, which is very conducive to the welding of the steel plate, and the mechanical properties of the steel plate after welding are excellent, which greatly improves the processing and construction cycle;

[0021] 4) The production method of the present invention only innovates the production process without increasing equipment investment, and the production cost is relatively low. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments.

[0023] Examples 1-8

[0024] The production process of the steel plate includes die casting, rolling, quenching and tempering. The smelting chemical composition and its mass percentage are shown in Table 1. The superheat of the die casting molten steel after smelting, the casting Ar ventilation volume, and the casting time are shown in Table 2. In the rolling process, the billet is sent to the soaking furnace for heating. The heating temperature, furnace time, combustion fan air volume, and total pressure of the billet are also shown in Table 2. The first three passes of the rolling process, the rolling force, the roller cooling water pressure, the horizontal plane of the front and rear guide plates of the rollers below the roller surface of the working rollers, the gap between the rollers and the guide plates, and the mill bite speed are shown in Table 3. The quenching temperature and tempering temperature of the heat treatment process are shown in Table 4. The finished thickness and mechanical property test results of the steel plates of each embodiment are shown in Table 5.

[0025] Table 1 (Wt%)

[0026]

[0027] Table 2

[0028]

[0029] Table 3

[0030]

[0031] ①The horizontal plane of the front and rear guide plates of the roller is lower than the roller surface of the working roller

[0032] Table 4

[0033]

[0034] Table 5

[0035]

[0036] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for producing a thick, low-yield-to-strength ratio, high-strength and toughness bridge steel plate, comprising die casting, rolling, quenching and tempering steps; In the mold casting process, the superheat of the molten steel is ensured to be 30-50°C, the casting Ar ventilation volume is 300-500L / min, and the casting time is 30-50min; In the rolling process, the maximum reduction in the first three passes is ≥30mm, and the rolling pressure during the rolling process is 5000-6000t; The quenching process has a quenching temperature of 900-920°C; the tempering process has a tempering temperature of 530-580°C; The finished steel plate has a thickness of 140-200 mm; The steel plate has a yield strength of ≥390MPa, a tensile strength of ≥540MPa, an elongation of ≥20%, a yield strength ratio of ≤0.80, and an impact energy of ≥250J at -40°C; The chemical composition of the steel plate and its weight percentage are: C 0.06-0.12%, Si 0.20-0.30%, Mn 1.40-1.55%, P≤0.015%, S≤0.005%, Nb 0.02-0.04%, Ni 0.20-0.30%, B≤0.0005%, CEV≤0.41%, and the rest are Fe and unavoidable impurity elements.

2. The method for producing a thick, low-yield-to-strength ratio, high-toughness bridge steel plate according to claim 1, characterized in that: In the rolling process, the billet is heated in a soaking furnace at a temperature of 1240-1270°C, in the furnace for 10-15 hours, and the air volume of the combustion-supporting fan is 6000-7000m 3 / h, the total pressure is 12000-13000Pa.

3. The method for producing a thick, low-yield-to-strength ratio, high-toughness bridge steel plate according to claim 1, characterized in that: In the rolling process, the horizontal plane of the guide plates before and after the rollers is 80-90 mm lower than the roller surface of the working rollers, and the gap between the rollers and the guide plates is ≤3 mm.

4. The method for producing a thick, low-yield-to-strength ratio, high-toughness bridge steel plate according to claim 1, characterized in that: In the rolling process, the rolling bite speed is ≥15r / min.

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