CN110129539B

CN110129539B - Production process of 500MPa grade H-shaped steel for ocean engineering

Info

Publication number: CN110129539B
Application number: CN201910472158.1A
Authority: CN
Inventors: 赵宪明; 董春宇; 杨洋; 周晓光; 吴迪
Original assignee: Northeastern University China
Current assignee: Northeastern University China
Priority date: 2019-05-31
Filing date: 2019-05-31
Publication date: 2021-03-23
Anticipated expiration: 2039-05-31
Also published as: CN110129539A

Abstract

The invention belongs to the technical field of metallurgical materials, and particularly relates to a production process of 500MPa grade H-shaped steel for ocean engineering. A production process of 500MPa grade H-shaped steel for ocean engineering is characterized in that: heating the casting blank to 1100-1200 ℃, preserving heat for at least 2 hours, and forging a steel billet; heating the billet to 1200-1250 ℃, preserving heat for at least 2 hours, respectively carrying out two-stage rolling in an austenite recrystallization region and a non-recrystallization region for 5-7 times, cooling to Ms-650 ℃ in a bainite phase transformation region at a cooling rate of 30-150 ℃/s after rolling, and then air-cooling to room temperature to obtain the steel. The invention provides a production process of 500MPa grade H-shaped steel for ocean engineering, which develops 500MPa grade H-shaped steel for ocean engineering, improves the strength on the original basis, has stable performance and fills the domestic blank.

Description

Production process of 500MPa grade H-shaped steel for ocean engineering

Technical Field

The invention belongs to the technical field of metallurgical materials, and particularly relates to a production process of 500MPa grade H-shaped steel for ocean engineering.

Background

In the field of ocean engineering, a large amount of H-shaped steel is applied to an offshore oil platform and is used for bearing gravity load and transverse impact load, and smooth drilling and development of ocean oil and gas are guaranteed. The service time of the offshore oil platform is 50% higher than that of marine equipment such as ships, so the adopted steel is required to have higher toughness. The production process of the high-strength H-shaped steel mainly adopts the micro-alloying component design and recrystallization zone controlled rolling of V-N or V-Nb. The product structure mainly comprises ferrite and pearlite, the grain size is above grade 9, and the yield strength is lower than 450 MPa. The domestic H-shaped steel can meet the requirements of most ocean engineering, but the high-strength large-size H-shaped steel for ocean engineering still needs to be imported from abroad. Up to now, the industrial production of the 500MPa grade H-shaped steel for ocean engineering in China has not been realized, the main reasons are that the size of the continuous casting billet used in the production line is limited, the larger the specification is, the rolling compression ratio of the H-shaped steel is smaller, the flange thickness exceeds 24mmH700 multiplied by 300H-shaped steel, and the mechanical property is generally low. In addition, most of large-scale H-shaped steel production lines lack the ability of regulating and controlling the performance of rolled pieces. From the development trend of current steel production and the use condition of users, the products of the H steel for ocean engineering are developed to the limit specification. In order to meet future requirements, online heat treatment on rolled pieces is used for effectively controlling cooling and performance regulation, and the method is an important direction for H-shaped steel development.

Disclosure of Invention

Aiming at the H-shaped steel with the specification of more than H700 x 300, the production process method of the H-shaped steel for 500 MPa-level ocean engineering is provided for solving the technical problems, and mainly comprises three aspects of component design, rolling control in a non-recrystallization area and an ultra-fast cooling technology after rolling. The invention completes the development of 500MPa grade H-shaped steel for ocean engineering based on a component-process-structure performance regulation and control process, reduces the carbon content in component design, controls the carbon equivalent to be 0.42-0.52, increases alloy elements such as Nb, Ti, Cu, Cr, Ni and the like, adds micro alloy elements to improve the hardenability of steel, promotes the occurrence of bainite phase transformation, inhibits ferrite phase transformation, and ensures that the bainite structure can be obtained under the natural air cooling condition. The rolling process and the ultra-fast cooling technology are controlled in a non-recrystallization area, so that the microstructure of the experimental steel is changed from the conventional ferrite and pearlite into a bainite and acicular ferrite structure, the strength is improved, and the toughness is improved. The method of controlling rolling in the non-recrystallization zone can effectively refine the grain size and improve the mechanical property of the H-shaped steel; and after the rolling is finished, cooling to a bainite transformation interval by adopting an ultra-fast cooling technology to enable the bainite transformation to occur, and then naturally cooling to room temperature.

A production process of 500MPa grade H-shaped steel for ocean engineering comprises the steps of heating a casting blank to 1100-1200 ℃, preserving heat for at least 2 hours, and forging a steel billet; heating the billet to 1200-1250 ℃, preserving heat for at least 2 hours, respectively carrying out two-stage rolling in an austenite recrystallization region and a non-recrystallization region for 5-7 times in total, cooling to Ms-650 ℃ in a bainite phase transformation region at a cooling rate of 30-150 ℃/s after rolling, then air-cooling to room temperature to obtain the steel billet,

first-stage recrystallization zone: the initial rolling temperature is 1020-1100 ℃, the first stage of rolling is completed by 2 or 3 passes of rolling, and the total rolling reduction rate is 35-50%;

second-stage non-recrystallized region: the initial rolling temperature is 920-950 ℃, the final rolling temperature is 820-880 ℃, the rolling of the second stage is completed for 3 or 4 times, and the total reduction rate is 50-65%.

The production process of the 500MPa grade H-shaped steel for ocean engineering is preferable, a casting blank is heated to 1100 ℃, the temperature is kept for 2 hours, and a billet is forged; heating the steel billet to 1250 ℃, preserving heat for 2 hours, respectively carrying out two-stage rolling in an austenite recrystallization zone and a non-recrystallization zone for 7 times in total, cooling to Ms-650 ℃ in a bainite phase transformation zone at a cooling rate of 30-150 ℃/s after finishing rolling, then air-cooling to room temperature to obtain the steel billet,

first-stage recrystallization zone: the initial rolling temperature is 1050 ℃, the first stage of rolling finishes 3 times of rolling, and the total rolling reduction rate is 42%;

second-stage non-recrystallized region: the initial rolling temperature is 950 ℃, the final rolling temperature is 850 ℃, 4 passes of rolling in the second stage are completed, and the total reduction rate is 58.6%.

The process adopts a method of rolling without being controlled in a crystallization area, and increases 950-Ar of an austenite non-recrystallization area to the greatest extent₃The deformation and the finish rolling temperature are controlled to be 820-880 ℃, so that the structure of the experimental steel is kept to be refined to the maximum extent. The controlled rolling in the austenite non-recrystallization region is carried out at the temperature of 950-Ar₃In this temperature range, austenite recrystallization does not occur, and accumulatedPlastic deformation can cause the austenite grains to elongate, forming deformation zones within the grains. The increase of the grain boundary area increases the nucleation density of austenite, the growth of grains is also prevented by the elongated austenite and the second phase point of carbonitride preferentially precipitated at the deformed zone, and the austenite grains after transformation become thinner along with the increase of the reduction ratio of the unrecrystallized area, thereby improving the strength of the steel and the toughness of the steel. When the existing high-strength large-specification H-shaped steel for ocean engineering is rolled and produced, most of deformation is finished at about 950 ℃, only the last pass is rolled at 850 ℃, and the deformation of an unrecrystallized area is small. The invention adopts the non-recrystallization zone to control rolling, and the strengthening toughness of the steel can be obviously improved by increasing the deformation of the non-recrystallization zone below 950 ℃.

Meanwhile, the invention adopts the ultra-fast cooling technology after rolling, and the steel is cooled to Ms-650 ℃ in the bainite phase transformation region at the cooling rate of 30-150 ℃/s, so that the experimental steel obtains more refined bainite and acicular ferrite tissues.

The hardened austenite which finishes continuous large deformation and strain accumulation is subjected to ultra-fast cooling, so that a rolled piece rapidly passes through an austenite region, and cooling is stopped at a phase transformation point of transformation from austenite to ferrite, thereby effectively inhibiting the growth of austenite grains before phase transformation. The phase change under the ultra-fast cooling process can be controlled in a relatively low temperature range, so that a fine phase change structure is generated; meanwhile, the precipitation amount of the micro-alloy elements is reduced in the ultra-fast cooling process after rolling, so that the micro-alloy elements are precipitated and precipitated in a low-temperature area. With the continuous development of H-shaped steel and the continuous development of rolling technology, the temperature control is required to be realized quickly and accurately in the rolling process, and the conventional technologies such as laminar cooling, aerosol cooling and the like are difficult to meet the requirement due to low cooling speed. The ultra-fast cooling technology adopted by the invention has enough cooling speed and ultra-conventional cooling capacity, and high-pressure water sprayed by the cooling nozzles which are reasonably and densely arranged acts on the surface of the H-shaped steel to break through a steam film on the rolled surface of the H-shaped steel, so that the cooling water and the H-shaped steel are more fully subjected to heat exchange, the cooling water and the H-shaped steel are effectively contacted with steel, the final cooling temperature is reduced in a very short time, the comprehensive performance of the H-shaped steel is improved, and the problems of slow production rhythm, high cost, low product performance and the like of the existing H-.

In the production process of the 500MPa grade H-shaped steel for ocean engineering, the casting blank comprises the following components in percentage by weight: 0.04-0.1%, Si: 0.15 to 0.35%, Mn: 1.4-2.0%, Nb: 0.03-0.1%, Ti: 0.01-0.03%, Cr: 0.1 to 0.5%, Ni: 0.1 to 0.5%, Cu: 0.1 to 0.4%, Mo: 0.1-0.4%, and the balance Fe, the carbon equivalent is controlled to 0.42-0.52.

Further, the carbon equivalent is controlled to 0.48.

0.04-0.1% of C, 0.15-0.35% of Si, 1.4-2.0% of Mn, 0.03-0.1% of Nb0.01, 0.01-0.03% of Ti, 0.1-0.5% of Cr, 0.1-0.5% of Ni, 0.1-0.4% of Cu, 0.1-0.4% of Mo, and the balance of Fe and carbon equivalent being controlled to be 0.42-0.52. The component design adopts the design idea of replacing ferrite and pearlite with bainite and acicular ferrite, and the strength grade of the H-shaped steel for ocean engineering is improved.

C0.04-0.1%: strength is improved, austenite is stabilized, and excessive carbide is formed to damage toughness when the content is excessive;

0.15-0.35% of Si: the solid solution strengthening effect is strong, the strength and the hardness of the steel can be improved, a small amount of Si can refine pearlite and improve hardenability, and the hardenability and the tempering resistance of the steel can be further improved by adding Si and Mn simultaneously. Si contributes to the wear resistance due to the strengthening of ferrite, and simultaneously can improve the corrosion resistance of the steel, and the silicon-manganese steel has good seawater corrosion resistance after quenching and tempering. Si lowers the bainite transformation temperature and shifts the bainite transformation C curve to the right. Si can prevent carbide from being precipitated, increase the amount of residual austenite in the steel, form carbide-free bainite, and simultaneously improve the temperature range of low-temperature tempering brittleness of the steel, so that the steel can be subjected to tempering heat treatment at a higher temperature;

mn1.4-2.0%: austenite forming elements, so that the hardenability is improved, the bainite phase transformation is promoted, and the strength is improved;

nb0.03-0.1%: nb in the steel can refine grains, particularly austenite grains and a recrystallization structure, increase a phase interface and improve strength. Nb can be combined with C to form NbC, recrystallization in the high-temperature deformation process is inhibited through the pinning effect of NbC on the grain boundary and the dragging effect of solid-dissolved Nb atoms on the grain boundary, the range of a non-recrystallization region is expanded, and ferrite grains are refined finally. In addition, the Nb-containing phase precipitated in the low-temperature region can play a role in precipitation strengthening;

0.01-0.03% of Ti0.01: ti can form carbides with very stable, dispersed, high melting point and high hardness in steel, thereby improving the strength of the steel. The microalloy element Ti is combined with N in the steel to form fine and dispersed TiN particles which stably exist in -DEG crystal boundaries, the growth of austenite grains is prevented in the heating process, and the fine austenite grains are ensured to be obtained so as to ensure the toughness of the rolled steel plate;

0.1-0.5% of Cr0: the diffusion movement in iron is slow, the diffusion rate of carbon is reduced, Cr is increased, the isothermal curve is moved rightwards, the phase change incubation period is prolonged, the critical cooling rate is reduced, and the hardenability is improved. Meanwhile, as the amount of Cr increases, the pearlite transformation temperature increases and the bainite transformation temperature decreases. Cr enhances the hardenability of steel, is not as strong as Mn and Mo but is stronger than Si and Ni, and can exist in the form of carbide.

Ni0.1-0.5%: and austenite stabilizing elements can shift the C curve to the right, so that the hardenability of the steel is improved. Ni improves the phase transformation nucleation work of gamma/alpha, improves the free energy difference of gamma and alpha phases and reduces the critical transformation temperature. Ni can reduce the diffusion rate of each element in the steel and delay the decomposition and transformation of austenite, thereby improving the hardenability of the steel. The strength is improved, the defects caused by Cu in rolling are reduced, and the weather resistance under the action of salt is improved to a certain degree;

0.1-0.4% of Cu0: the simultaneous addition of Ni and Cu can improve the toughness of the steel while improving the strength of the bainite steel. In addition, the addition of Cu and Ni also improves the corrosion resistance of the steel. The corrosion rate of the steel with the same inches of added Cr, Ni and Cu elements is reduced.

Mo0.1-0.4%: solid-dissolved Mo can improve the hardenability of steel, and the carbide precipitation of Mo improves the strength;

the process is suitable for actual production and test of the H-shaped steel, and can be used for simulating flange deformation of the H-shaped steel by adopting the plate-shaped blank in order to reduce test cost, and specifically comprises the following steps:

heating the steel billet to austenitizing temperature, controlling the heating temperature at 1100 ℃, preserving heat for 2 hours, forging the steel billet into a steel billet with the section size of 80 multiplied by 100, and replacing the special-shaped billet by slab rolling to simulate the flange deformation of the H-shaped steel.

The casting blank is prepared according to the method disclosed by the prior art, namely the casting blank is prepared by smelting, refining and pouring according to set components.

A preferred technical scheme of the invention is as follows: a production process of 500MPa grade H-shaped steel for ocean engineering comprises the following process steps:

step 1: smelting, refining and pouring according to the set components to prepare a casting blank, wherein the components of the casting blank comprise 0.06 percent of C, 0.25 percent of Si, 1.65 percent of Mn, 0.08 percent of Nb, 0.015 percent of Ti, 0.25 percent of Cu, 0.3 percent of Cr, 0.3 percent of Ni, 0.25 percent of Mo and the balance of Fe by weight percentage, and the carbon equivalent is 0.48;

step 2: reheating the steel billet to austenitizing temperature, controlling the heating temperature at 1100 ℃, preserving heat for 2 hours, forging the steel billet into a steel billet with the section size of 80 multiplied by 100, and replacing special-shaped billet rolling by slab rolling to simulate flange deformation of H-shaped steel;

and step 3: heating the steel billet to 1250 ℃, preserving heat for 2 hours, respectively carrying out two-stage rolling in an austenite recrystallization zone and a non-recrystallization zone, carrying out 7-pass rolling, wherein the rolling temperature of the first-stage recrystallization zone is 1050 ℃, the rolling of the first stage is finished by three passes, the rolling temperature of the second-stage non-recrystallization zone is 950 ℃, the rolling temperature of the final stage is 850 ℃, and the rolling of the second stage is finished by four passes; the total pressure reduction rate of the first stage is 42%, and the total pressure reduction rate of the second stage is 58.6%;

and 4, step 4: and directly entering an ultra-fast cooling device for cooling after rolling, cooling to Ms-650 ℃ in a bainite phase change region at a cooling rate of 30-150 ℃/s after rolling, and then air-cooling to room temperature to obtain the experimental steel.

The yield strength of the steel obtained by the production process of the 500MPa grade H-shaped steel for ocean engineering is 500-700 MPa, the tensile strength is 650-900 MPa, the transverse impact energy at minus 40 ℃ is 50-300J, the longitudinal impact energy at minus 40 ℃ is more than 50-350J, and the elongation is 14-25%.

The invention has the beneficial effects that: the invention provides a production process of 500MPa grade H-shaped steel for ocean engineering, which develops 500MPa grade H-shaped steel for ocean engineering, improves the strength on the original basis, has stable performance and fills the domestic blank. The ultra-fast cooling technology after rolling of the process can fundamentally accelerate the cooling speed after rolling, improve the production rate, reduce the use of micro-alloy elements, save the production cost, have large adjustable range of the process and are suitable for industrial application.

Drawings

FIG. 1 is a microstructure 1/8 in the thickness direction of the experimental steel in example 1;

FIG. 2 is a microstructure 1/4 in the thickness direction of the experimental steel in example 1;

FIG. 3 is a microstructure 1/2 in the thickness direction of the experimental steel in example 1;

FIG. 4 is a microstructure 1/8 in the thickness direction of the experimental steel in example 2;

FIG. 5 is a microstructure 1/4 in the thickness direction of the experimental steel in example 2;

FIG. 6 is a microstructure 1/2 in the thickness direction of the experimental steel in example 2;

FIG. 7 is a microstructure 1/8 in the thickness direction of the experimental steel in example 3;

FIG. 8 is a microstructure 1/4 in the thickness direction of the experimental steel in example 3;

FIG. 9 is a microstructure 1/2 in the thickness direction of the experimental steel in example 3.

Detailed Description

The following non-limiting examples are presented to enable those of ordinary skill in the art to more fully understand the present invention and are not intended to limit the invention in any way.

The test methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials are commercially available, unless otherwise specified.

The "ultrafast cooling device" used in the following embodiments is an "ultrafast cooling device after rolling by ultrafast cooling technology" disclosed in the chinese utility model patent with the grant publication No. CN 202185466U.

Example 1

and 4, step 4: and (3) directly entering an ultra-fast cooling device for cooling after the rolling is finished, and after 6.7 seconds, performing air cooling to room temperature to obtain the experimental steel, wherein the final cooling temperature is 530 ℃, the reheating temperature is 575 ℃, and then performing air cooling.

The yield strength of the obtained experimental steel is 517MPa, the tensile strength is 764MPa, the transverse impact energy at-40 ℃ is 158J, the longitudinal impact energy at-40 ℃ is 231J, and the elongation is 21.3%. The structure of the obtained experimental steel in the thickness direction 1/8 is mainly composed of lath bainite and fine granular bainite, and the structure of the experimental steel in the thickness directions 1/4 and 1/2 is mainly composed of M/A islands dispersed on bainite ferrite.

Example 2

and 4, step 4: and (3) directly entering an ultra-fast cooling device for cooling after the rolling is finished, and after 8 seconds, performing air cooling to room temperature to obtain the experimental steel, wherein the final cooling temperature is 500 ℃, and the reheating temperature is 550 ℃.

The yield strength of the experimental steel is 521MPa, the tensile strength is 765MPa, the transverse impact energy at-40 ℃ is 244J, the longitudinal impact energy at-40 ℃ is 263J, and the elongation is 21.3%. The structure of the obtained experimental steel in the thickness direction 1/8 is mainly composed of lath bainite and fine granular bainite, and the structure of the experimental steel in the thickness directions 1/4 and 1/2 is mainly composed of M/A islands dispersed on bainite ferrite.

Example 3

and 4, step 4: and (3) directly entering an ultra-fast cooling device for cooling after rolling is finished, and after 10s, performing air cooling to room temperature to obtain the experimental steel, wherein the final cooling temperature is 480 ℃ and the reheating temperature is 520 ℃.

The yield strength of the experimental steel is 546MPa, the tensile strength is 762MPa, the transverse impact energy at minus 40 ℃ is 244J, the longitudinal impact energy at minus 40 ℃ is 254J, and the elongation is 21.3%. The structure of the obtained experimental steel in the thickness direction 1/8 is mainly composed of lath bainite and fine granular bainite, and the structure of the experimental steel in the thickness directions 1/4 and 1/2 is mainly composed of M/A islands dispersed on bainite ferrite.

Claims

1. A production process of 500MPa grade H-shaped steel for ocean engineering is characterized in that: heating the steel billet to austenitizing temperature, controlling the heating temperature at 1100 ℃, preserving heat for 2 hours, forging the steel billet into a steel billet with the section size of 80 multiplied by 100, and simulating flange deformation of H-shaped steel by replacing rolling of a special-shaped billet by slab rolling; heating the steel billet to 1200-1250 ℃, preserving heat for at least 2 hours, respectively carrying out two-stage rolling in an austenite recrystallization region and a non-recrystallization region for 7 times in total, cooling to Ms-650 ℃ in a bainite phase transformation region at a cooling rate of 30-150 ℃/s after rolling, then air-cooling to room temperature to obtain the steel billet,

first-stage recrystallization zone: the initial rolling temperature is 1020-1100 ℃, the first stage of rolling finishes 3 times of rolling, and the total rolling reduction rate is 35-50%;

second-stage non-recrystallized region: the initial rolling temperature is 920-950 ℃, the final rolling temperature is 820-880 ℃, 4 passes of rolling in the second stage are completed, and the total rolling reduction rate is 50-65%;

smelting, refining and pouring according to set components to prepare a casting blank, wherein the casting blank comprises the following components in percentage by weight: 0.04-0.1%, Si: 0.15 to 0.35%, Mn: 1.4-2.0%, Nb: 0.03-0.1%, Ti: 0.01-0.03%, Cr: 0.1 to 0.5%, Ni: 0.1 to 0.5%, Cu: 0.1 to 0.4%, Mo: 0.1-0.4%, and the balance Fe, the carbon equivalent is controlled to 0.42-0.52.

2. The process according to claim 1, characterized in that:

3. The process according to claim 1, characterized in that: the process comprises the following process steps:

and step 3: heating the steel billet to 1250 ℃, preserving heat for 2 hours, respectively carrying out two-stage rolling in an austenite recrystallization zone and a non-recrystallization zone, carrying out 7-pass rolling, wherein the rolling temperature of the recrystallization zone in the first stage is 1050 ℃, the rolling of the first stage is finished by 3 passes, the rolling temperature of the non-recrystallization zone in the second stage is 950 ℃, the rolling temperature of the final stage is 850 ℃, and the rolling of the second stage is finished by 4 passes; the total pressure reduction rate of the first stage is 42%, and the total pressure reduction rate of the second stage is 58.6%;

4. The process according to claim 1, characterized in that: the yield strength of the obtained steel is 500-700 MPa, the tensile strength is 650-900 MPa, the transverse impact energy at the temperature of-40 ℃ is 50-300J, the longitudinal impact energy at the temperature of-40 ℃ is more than 50-350J, and the elongation is 14-25%.