CN108546866B

CN108546866B - Production method of 690MPa grade high-toughness structural steel

Info

Publication number: CN108546866B
Application number: CN201810298745.9A
Authority: CN
Inventors: 杨永达; 王彦锋; 狄国标; 马长文; 黄乐庆; 周德光; 郑会平; 陆士平; 白学军; 马龙腾; 李战军; 韩承良; 孟东立
Original assignee: Shougang Corp
Current assignee: Shougang Corp
Priority date: 2018-04-04
Filing date: 2018-04-04
Publication date: 2020-03-27
Anticipated expiration: 2038-04-04
Also published as: CN108546866A

Abstract

A production method of 690MPa grade high-toughness structural steel, belonging to the technical field of controlled rolling of low-carbon structural steel. Converter smelting and combined blowing are adopted, so that the content of harmful gases and S is reduced; after continuous casting, the mixture is fed into a furnace, the heating temperature is between 1200 and 1300 ℃, and high-pressure water is used for removing phosphorus after the mixture is discharged from the furnace; and (3) controlling rolling in two stages by using double racks, wherein the initial rolling temperature of finish rolling is 720-760 ℃, and after rolling, water cooling is carried out on the ACC, and then stacking and slow cooling are carried out. Compared with the prior production process, the method has the advantages that the production process is shortened, the efficiency is greatly improved, and the steel plate has high strength and excellent low-temperature toughness and lamellar tearing resistance.

Description

Production method of 690MPa grade high-toughness structural steel

Technical Field

The invention belongs to the technical field of controlled rolling of low-carbon structural steel, and particularly relates to a production method of 690 MPa-grade high-toughness structural steel. In particular to a production method of a 690MPa grade high-toughness structural steel plate with the thickness of 12-60 mm, which is suitable for the fields of bridges, ocean engineering, high-rise buildings and the like. The steel plate strength is improved by adopting a low-carbon Nb and Ti-added component system, the low-temperature toughness and the welding performance of the steel plate are improved, and the hardenability is further improved and the steel plate strength is ensured by properly adding Cu, Ni, Cr, Mo and other elements.

Background

In recent years, the fields of steel bridges, steel structure buildings and the like in China develop rapidly, urgent needs are brought to upgrading and updating of steel for steel structures, China is currently a world wide country of steel bridges, more than half of large-span suspension bridges, cable-stayed bridges, arch bridges and the like which are built and built are in China, steel bridges with larger span and heavier load are continuously developed along with the development of high-speed railways and highways in China, and the steel plates for the structures with higher strength are required to be developed in the aspects of reducing the self weight of the bridges, improving the bearing capacity and the like. Currently, the bridge steel with the highest strength level in China is developed to 500MPa level and is applied to Shanghai Changjiang bridge, Wuhu Changjiang bridge and the like, and the bridge steel with the highest strength level of 690MPa is bound to be a key development target in the future.

The 690 MPa-grade bridge steel abroad is applied in batches in 2000, for example, 1000 tons of BHS700W steel plate is used for Japanese Ming Shi sea bridges, and the yield strength reaches 690MPa grade. The us was also developed and utilized HPS 100W. In order to meet the requirements of domestic bridge enterprises and large steel structure enterprises for constructing large-span steel bridges and ultrahigh buildings, the patent provides a production method of a bridge steel plate with the thickness of 12-60 mm, high strength, high toughness and good thickness directional performance.

The invention discloses a low-crack sensitivity steel plate with 690MPa grade yield strength and a manufacturing method thereof, which is applied to Baoshan steel product company Limited and is published under the publication number CN101418418A, and the component design of the steel plate is different from that of the steel plate, the hardenability of the steel plate is improved by adding B element, the B element has great influence on the low-temperature toughness of the steel, and the low-temperature toughness of the produced steel plate is obviously lower than that of the product in the patent.

The invention patent with the publication number of CN103695773A applied by Wuhan iron and Steel (group) company provides a production method of 690 MPa-grade fire-resistant weather-resistant earthquake-resistant steel for construction, which is mainly characterized in that 1.82-2.55% of Mn element is added, so that noble alloy elements such as Cu, Ni and Mo are reduced, the alloy cost is low, but the low-temperature toughness of the product only ensures the impact energy at the temperature of-20 ℃, and the difference of the low-temperature toughness of the product and the low-temperature toughness of the product is larger.

The invention patent with the publication number of CN105950849A applied by the dancing iron and steel Limited liability company provides a production method of a high-strength steel plate with a low yield ratio of 690MPa, which is mainly characterized in that 0.10 percent of carbon is added with Cu, Ni, Cr and Mo alloy elements as main components; the structure is mainly bainite and ferrite; the process is TMCP + tempering process, and the production of 690 MPa-grade steel plates is realized. The alloy is characterized in that 0.05 percent of carbon is added into Cu, Ni, Cr and Mo alloy, and La and Ce rare earth alloy elements are added; the structure control is mainly bainite without ferrite; TMCP technology is adopted in the technology, and the final cooling temperature is greatly lower than that of a comparison file; the low-temperature toughness of the steel plate developed by the method meets the condition that the temperature is higher than 120J at minus 80 ℃, and the toughness is higher.

Disclosure of Invention

The invention aims to provide a production method of 690MPa grade high-toughness structural steel, which solves the problem that a steel plate has high strength and cannot have both excellent low-temperature toughness and good lamellar tearing resistance. The composition is designed by adding Nb and Ti with low carbon, the strength of the steel plate is improved by means of fine grain strengthening, precipitation strengthening and the like, alloy elements such as Cu, Ni, Cr, Mo and the like are added, the hardenability of the steel plate is improved, the bainite structure type and content are controlled, the stable control of high strength and high toughness is realized, La and Ce rare earth alloy is added into the steel, the modification and refinement treatment on inclusions is realized, and the comprehensive performance is improved. In the process, the starting temperature of finish rolling is lower than 760 ℃, the accumulation of high-density dislocation is realized through low-temperature deformation, a strong cooling process is adopted after rolling, the final cooling temperature is controlled to be less than or equal to 350 ℃, the steel plate with the thickness of 1/4 and the core part are ensured to obtain a fine bainite structure, and the steel plate is ensured to have high strength and good low-temperature toughness.

A production method of 690MPa grade high-toughness structural steel is suitable for 690MPa grade high-toughness structural steel with the thickness of 12-60 mm. The specific steps and parameters are as follows:

1. the smelting process comprises the following steps: smelting in a converter, controlling the content of O at the top and bottom of the converter to be less than 15ppm, the content of H to be less than 1.5ppm, the content of S to be not more than 20ppm, controlling the content of elements influencing the cold crack sensitivity index to be less than or equal to 0.08 wt%, Si to be between 0.20 and 0.50 wt%, Mn to be between 1.00 and 3.00 wt%, Cu to be between 0.40 and 1.50 wt%, Cr to be between 0.40 and 1.30 wt%, Ni to be between 0.50 and 2.00 wt%, Mo to be between 0.2 and 0.80 wt%, ensuring that the Pcm of a steel plate is less than or equal to 0.30, and adding La to be less than or equal to 0.0080 wt% and rare earth alloy to be less than or equal to 0.0040Ce into the steel to ensure that Al is less than or₂O₃Refining the inclusions to be within 10 mu m;

2. the continuous casting process comprises the following steps: designing the blank size of a continuous casting blank, wherein the thickness specification is 180-400 mm, and the width is 1800-2400 mm;

3. a heating process: cold loading the steel billet into a furnace, heating at 1200-1300 ℃ for 240-400 min, and removing scale with high-pressure water after discharging;

4. the rolling process comprises the following steps: adopting a double-frame two-stage controlled rolling process, carrying out rough rolling reduction at 1050-1150 ℃, ensuring that the maximum rough rolling pass reduction rate is more than or equal to 20%, and continuously rolling until the temperature is controlled, and then discharging steel; and in the finish rolling stage, the finish rolling initial rolling temperature is 720-760 ℃, the ACC water cooling is carried out after rolling, the final cooling temperature is 270-350 ℃, and the stack slow cooling is carried out after water cooling.

The steel plate comprises the following chemical components in percentage by mass: less than or equal to 0.08 percent of C, 0.20 to 0.50 percent of Si, 1.00 to 3.00 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.002 percent of S, 0.020 to 0.05 percent of Al, less than or equal to 0.050 percent of Nb, less than or equal to 0.020 percent of Ti, 0.40 to 1.50 percent of Cu, 0.40 to 1.30 percent of Cr, 0.50 to 2.00 percent of Ni0.2 to 0.80 percent of Mo0.2, less than or equal to 0.0080 percent of La, less than or equal to 0.0040 percent of Ce, and the balance of Fe and. The B element cannot be added to the steel.

The produced steel plate has yield strength of more than 690MPa, tensile strength of more than 830MPa, elongation after fracture of more than or equal to 14 percent, longitudinal impact energy of more than 120J at minus 80 ℃, and Z-direction section shrinkage of more than or equal to 35 percent, and the developed structural steel has high strength, excellent low-temperature toughness and good thickness direction performance.

The method is based on the following steps: when 690MPa structural steel with high strength and high toughness is produced, because the strength index and the toughness index of a steel plate are required to be high, firstly, in order to ensure low-temperature toughness, the carbon content must be reduced, and the reduction of the carbon content inevitably leads to great reduction of the strength. The rare earth alloy La and Ce added into the steel is beneficial to refining inclusions, so that the toughness is improved, the addition of B element is strictly forbidden, and the adverse effect of the B element on the low-temperature toughness of the TMCP steel plate is avoided. The process adopts the processes of reducing the temperature of a finish rolling deformation area and reducing the final cooling temperature, improves the dislocation accumulated density in the crystal grains through the low-temperature deformation of the finish rolling area, promotes the phase transformation nucleation in the crystal grains through strong water cooling after rolling, refines the structure and improves the strength and the toughness of the steel plate.

The invention has the advantages that:

1. the steel plate with the thickness of 12-60 mm and the pressure of 690MPa is produced, converter steelmaking, continuous casting and steel rolling are adopted, and compared with the steel plate produced by adopting a quenching and tempering process, the production process is greatly shortened, and the production efficiency is greatly improved;

2. under the process conditions designed by the invention, a structural steel plate with the thickness of 12-60 mm has excellent mechanical properties, the yield strength is more than 690MPa, the tensile strength is more than 830MPa, the elongation after fracture is more than or equal to 14 percent, the impact energy at minus 80 ℃ is more than 120J, the Z-direction section shrinkage rate is more than or equal to 35 percent, and various mechanical property indexes are good.

Drawings

FIG. 1 is a schematic representation of metallographic structure at 1/4 mm thickness of a 16mm thick steel plate.

FIG. 2 is a schematic diagram of the metallographic structure of the center of a steel plate with a thickness of 1/2 and a thickness of 16 mm.

FIG. 3 is a schematic representation of the metallographic structure of a 56mm thick steel plate at 1/4.

FIG. 4 is a diagram of the metallographic structure of the center of a steel plate with a thickness of 1/2 and a thickness of 56 mm.

Detailed description of the invention

Example 1

A16 mm thick bridge steel plate is made of a continuous casting billet with the size of 250mm thick, 2000mm wide and 4000mm long, a finished product steel plate with the size of 16mm thick, 2650mm wide and 4000mm long is subjected to cold loading, the heating temperature is 1250 ℃, two-stage controlled rolling is carried out by a double-frame, in a rough rolling stage, the maximum pass reduction rate is 28.5%, steel is continuously rolled until the thickness to be heated is 60mm, steel is discharged, the finish rolling start temperature is 750 ℃, the finish rolling temperature is 720 ℃, water cooling is carried out after rolling, and the finish cooling temperature is 320 ℃. The chemical components of the steel plate are shown in a table 1, the mechanical properties are shown in a table 2, and the metallographic structure is shown in an attached figure 1.

Table 1: chemical composition of 16mm Steel plate (wt%)

C	Si	Mn	P	S	Alt	Nb	Ti	Ni	Cr	Cu	Mo
												0.05	0.26	1.4	0.012	0.0020	0.035	0.035	0.015	0.85	0.50	1.0	0.58

Table 2: mechanical property test result of 16mm steel plate

Example 2

The method is characterized in that a wide bridge steel plate with the thickness of 56mm and the width of 3500mm is adopted, the width of 400mm, the width of 1800mm and the length of 3900mm are adopted as continuous casting slabs, the size of a finished steel plate is 56mm, the width of 2200mm and the length of the finished steel plate, the cold charging is carried out, the heating temperature is 1280 ℃, the two-stage controlled rolling is carried out by a double-stand, the maximum pass reduction rate is 25%, the steel is continuously rolled to the thickness of 120mm to be warmed, the steel is released, the rolling start temperature is 720 ℃, the final rolling temperature is 696 ℃, the water cooling. The chemical components of the steel plate are shown in a table 3, the mechanical properties are shown in a table 4, and the metallographic structure is shown in an attached figure 2.

Table 3: chemical composition of 56mm Steel plate (wt%)

C	Si	Mn	P	S	Alt	Nb	Ti	Ni	Cr	Cu	Mo
												0.05	0.30	1.45	0.012	0.0015	0.035	0.030	0.018	1.35	0.60	1.0	0.60

Table 4: mechanical property test result of 56mm steel plate

Claims

1. A production method of 690MPa grade high toughness structural steel is characterized by comprising the following specific steps and parameters:

1) the smelting process comprises the following steps: smelting by adopting a converter, and carrying out top blowing or top-bottom combined blowing; the vacuum treatment is carried out by adopting an LF furnace and an RH furnace, the content of O is controlled to be below 15ppm, the content of H is controlled to be below 1.5ppm, the content of S is not more than 20ppm, the content of elements influencing the cold crack sensitivity index is controlled to be less than or equal to 0.08 wt%, the content of Si is controlled to be between 0.20 and 0.50 wt%, the content of Mn is controlled to be between 1.00 and 3.00 wt%, the content of Cu is controlled to be between 0.40 and 1.50 wt%, the content of Cr is controlled to be between 0.40 and 1.30 wt%, the content of Ni is controlled to be between 0.50 and 2.00 wt%, the content of Mo is controlled to be between 0.2 and 0.80 wt%, the Pcm is ensured to be less than or equal to 0.30, La and rare earth alloy less than or equal to 0₂O₃Refining the inclusions to be within 10 mu m;

2) the continuous casting process comprises the following steps: designing the blank size of a continuous casting blank, wherein the thickness specification is 180-400 mm, and the width is 1800-2400 mm;

3) a heating process: cold loading the steel billet into a furnace, heating at 1200-1300 ℃ for 240-400 min, and removing scale with high-pressure water after discharging;

4) the rolling process comprises the following steps: adopting a double-frame two-stage controlled rolling process, carrying out rough rolling reduction at 1050-1150 ℃, ensuring that the maximum rough rolling pass reduction rate is more than or equal to 20%, and continuously rolling until the temperature is controlled, and then discharging steel; in the finish rolling stage, the finish rolling initial rolling temperature is 720-760 ℃, the rolling is performed after ACC water cooling, the final cooling temperature is 270-350 ℃, and the stacking and slow cooling are performed after water cooling;

the method is suitable for 690MPa grade high-toughness structural steel with the thickness of 12-60 mm; the structural steel comprises the following chemical components in percentage by mass: less than or equal to 0.08 percent of C, 0.20 to 0.50 percent of Si, 1.00 to 3.00 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.002 percent of S, 0.020 to 0.05 percent of Al, less than or equal to 0.050 percent of Nb, less than or equal to 0.020 percent of Ti, 0.40 to 1.50 percent of Cu, 0.40 to 1.30 percent of Cr0.50 to 2.00 percent of Ni0.2 to 0.80 percent of Mo0.0080 percent of La, less than or equal to 0.0040 percent of Ce, and the balance of Fe and inevitable impurities, wherein B elements cannot be added into steel in chemical components;

the yield strength of the produced steel plate is more than 690MPa, the tensile strength is more than 830MPa, the elongation after fracture is more than or equal to 14 percent, the longitudinal impact energy at minus 80 ℃ is more than 120J, and the reduction of area in the Z direction is more than or equal to 35 percent.