CN113862446B - Production method of X70 pipeline steel with high heating temperature - Google Patents
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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Abstract
The X70 pipeline steel with high heating temperature and the production method thereof are provided, the weight percentage of the steel is C =0.03 to 0.08, si =0.20 to 0.50, mn =1.00 to 1.80, P ≤ 0.015, S ≤ 0.003, al =0.02 to 0.05, ti =0.008 to 0.020, nb =0.090 to 0.100, ni =0.10 to 0.50, cr =0.10 to 0.50, and the balance of Fe and inevitable impurity elements; the invention can shorten the heating time of the X70 pipeline steel for 20 to 50min, can improve the hourly output of 20 percent of the X70 pipeline steel, can obtain the matrix structure of 50 to 55 percent of acicular ferrite and 45 to 55 percent of granular bainite from a steel plate, has the grain size of 11 to 12 grades, the yield strength of 500 to 600mpa, the tensile strength of 600 to 680mpa, the yield ratio of less than or equal to 0.88, the impact power of minus 40 ℃ of more than or equal to 250J, the drop weight DWTT of minus 30 ℃ of more than or equal to 90 percent and the cold straightening rate of the X70 pipeline steel plate within 5 percent.
Description
Technical Field
The invention belongs to the technical field of metallurgy, and relates to a production method of X70 pipeline steel with high heating temperature.
Background
Microalloying of steel is an important method for improving the comprehensive performance of steel, and reheating of a plate blank before rolling can promote solid solution strengthening and precipitation strengthening of microalloy, so that the mechanical properties of the material are remarkably improved, and great attention is paid to and a great deal of research is carried out. The heating system not only affects the sufficient solid solution of the microalloy, but also affects the prior austenite structure and the grain size. With the increase of the heating temperature, the prior austenite grains can grow up, thereby affecting the comprehensive performance of the final steel plate.
The pipeline steel is mainly used for oil and natural gas pipeline engineering, belongs to low-carbon microalloyed steel, and has higher production technical difficulty. High strength and high toughness are main technical indexes, and particularly, the low-temperature drop weight DWTT performance is a special requirement of pipeline steel. At present, the development trend of pipeline engineering is large pipe diameter, large wall thickness, high pressure transmission and the like, wherein X70 pipeline steel is a commonly used steel grade. When X70 pipeline steel is produced in a medium plate factory, in order to avoid abnormal growth of original austenite grains, the heating temperature is usually controlled to be 1150-1250 ℃, in order to ensure that a better microalloy solid solution effect can be obtained, the heating time and the tapping temperature of a pipeline billet are also required, and when the heating time or the tapping temperature does not meet the process requirements, the rolling line is usually adopted to stop rolling for waiting for temperature. Therefore, the heating system of the X70 pipeline steel is one of the main factors influencing the production efficiency and the ton steel cost of the medium plate plant.
Disclosure of Invention
The invention aims to provide a production method of X70 pipeline steel with high heating temperature, which adopts high Nb microalloy design, applies 'high heating temperature + TMCP technology' to produce X70 pipeline steel with the thickness of 8-25mm, can shorten the heating time in a furnace for 20-50min, can improve the production efficiency of the pipeline steel by more than 20 percent, has the yield strength of 500-600Mpa, the tensile strength of 600-680 Mpa, the yield ratio of less than or equal to 0.88, the impact power of minus 40 ℃ is more than or equal to 250J, the drop weight DWTT of minus 30 ℃ is more than or equal to 90 percent, and the cold correction rate of a steel plate is within 5 percent.
The technical scheme of the invention is as follows:
the production method of the X70 pipeline steel with high heating temperature comprises the following steps that the thickness of a steel plate is 8-25mm, the chemical composition weight percentage of the steel is C = 0.03-0.08, si = 0.20-0.50, mn = 1.00-1.80, P is less than or equal to 0.015, S is less than or equal to 0.003, al is 0.02-0.05, ti is 0.008-0.020, nb is 0.090-0.100, ni is 0.10-0.50, cr is 0.10-0.50, and the balance is Fe and inevitable impurity elements; the key process steps comprise:
(1) Plate blank off-line; smelting the components by a converter and casting the components into a steel billet, wherein the offline temperature of the steel billet is 750-900 ℃;
(2) Heating the plate blank at a high temperature: after the billet is taken off the line, a hot-delivery hot-charging mode is adopted, the surface of the casting blank is pumped with water and cooled to below 550 ℃ and then is fed into a furnace, and the mixed gas heat value of the heating furnace is 11000 to 12000 kJ/Nm 3 Controlling and heating the mixture according to the air-fuel ratio of 3.0 to 3.5, namely a preheating section, an I adding section, a II adding section and a soaking section, wherein the temperature of the preheating section is 800 to 1200 ℃, the temperature of the I adding section is 1200 to 1300 ℃, the temperature of the II adding section is 1300 to 1350 ℃, the temperature of the soaking section is 1300 to 1350 ℃, the total in-furnace time is 150 to 190min, the heating rate is 3 to 8min/cm, and the out-furnace temperature is 1220 to 1260 ℃;
(3) Rough rolling: after the plate blank is taken out of the furnace, primarily removing phosphorus by high-pressure water to the front of a roughing mill, wherein the initial rolling temperature is less than or equal to 1250 ℃, the final three-pass average reduction rate after widening is more than or equal to 15%, the roughing rolling finishing temperature is less than or equal to 1050 ℃, and the thickness of the intermediate blank is set according to the following steps: the rough rolling accumulated reduction rate is more than or equal to 50 percent, and the finish rolling accumulated reduction rate is more than or equal to 60 percent;
(4) Finish rolling: water-cooling the intermediate blank to the front of a finishing mill through an intermediate roller way, wherein the finish rolling start temperature is less than or equal to 980 ℃, the rolling is carried out for 7 to 9 times, the average reduction rate is more than or equal to 10 percent, and the final rolling temperature is 820 to 860 ℃;
(5) And (3) fast cooling control: directly cooling the steel plate in water after rolling, adopting a sectional mode for cooling, adopting a DQ mode in a first stage, wherein the cooling rate is 25 to 30 ℃/S, and ending the temperature is 600 to 650 ℃, adopting an ACC mode in a second stage, wherein the cooling rate is 5 to 10 ℃/S, and ending the temperature is 510 to 580 ℃.
The design principle of the steel grade components comprises the following steps:
carbon: carbon is an effective element for increasing the strength of steel, but the toughness, the plasticity and the weldability of the pipeline steel are all reduced along with the increase of the carbon content, the low-temperature DWTT drop hammer performance is obviously deteriorated when the carbon content is over 0.08 percent, but if the carbon content is too low, the strength of the pipeline steel is influenced, and the smelting is difficult for industrial production. Therefore, the invention adopts a low-carbon design, and the carbon content is determined to be 0.03-0.08%.
Silicon: silicon dissolves in ferrite in the steel for pipeline, and increases the strength and hardness of the steel, but decreases the plasticity and toughness. Silicon is also an element added to steel as a deoxidizer during steel making, and silicon and FeO in molten steel can be formed into a silicate slag having a low density and removed, so that silicon is an element useful for improving the purity of molten steel. However, an excessively high silicon content is disadvantageous in controlling the surface quality and inclusions of the steel, and also in ductility and weldability of the steel. The invention determines the range of the silicon content to be 0.20-0.50%.
Manganese: manganese is an important strong toughness element and can reduce the phase change Ar of gamma → alpha in steel 3 Temperature, thereby promoting bainite transformation. Mn causes solid solution strengthening by dissolving into ferrite, and improves the strength of the steel. The method has the advantage that the method has a promoting effect on grain refinement in the controlled rolling and controlled cooling process of the pipeline steel, so that the toughness of the steel can be improved while the strength is improved. However, manganese is also easily segregated, and the formation of a band-shaped structure such as MnS in combination with S affects the low-temperature DWTT performance. The invention determines the manganese content to be 1.00-1.80%.
Phosphorus: in general, phosphorus is a harmful element in steel, increases cold brittleness of steel, deteriorates weldability, and reduces plasticity. Therefore, the invention adopts a low-phosphorus design and limits the phosphorus content to be not more than 0.015 percent.
Sulfur: sulfur is a harmful impurity in steel, and reduces ductility, toughness and weldability of steel, and high-sulfur steel is susceptible to brittle fracture when subjected to high-temperature press working. In addition, S can form MnS segregation with Mn, and the comprehensive performance of the steel is seriously influenced. Therefore, the invention adopts a low-sulfur design and limits the sulfur content to be not more than 0.003 percent.
Aluminum: the aluminum is a deoxidizer in the steel, and the proper amount of Al and Ca are compounded, so that the quantity of the inclusions is reduced, the forms of the inclusions are changed, and the aluminum is favorable for the internal quality, the plasticity and the toughness of the pipeline steel. Al has a certain effect of refining grains, improves impact toughness and reduces the ductile-brittle transition temperature of steel. The invention determines the aluminum content to be 0.02% -0.05%.
Titanium: the titanium can refine the grain structure of the steel, thereby improving the strength and toughness of the steel, reducing aging sensitivity and cold brittleness and improving welding performance. TiN formed by micro-titanium treatment can effectively pin austenite grain boundaries and is beneficial to controlling the growth of austenite grains, but large-size liquated TiN is easily generated when the titanium content is higher, and the mechanical property of steel is influenced. The range of the determined titanium content is 0.008% -0.020%.
Niobium: niobium is a microalloying element and has two functions of solid solution strengthening and fine grain strengthening. The solid solution strengthening means that after the steel is dissolved in austenite, the hardenability of the steel can be obviously improved, and the strength and the impact toughness of the steel are improved. Nb can be combined with C and N to generate high-melting-point and highly-dispersed Nb (C and N), and the carbide has the function of strongly inhibiting austenite recrystallization, has the characteristics of precipitating and pinning austenite grain boundaries in gamma and refining original austenite grains, and enables the material to obtain a structure after phase transformation, and the grain size is smaller. The high Nb content, the austenite stability is stronger, the pipeline steel can be processed at a higher rolling temperature, and the volume fraction of bainite is improved by delaying the transformation from austenite to ferrite. In addition, the high Nb content can provide more ferrite phase transformation nucleation points, and ferrite grain size can be further refined in the controlled cooling process. The invention adopts high Nb design and determines the Nb content to be 0.090 to 0.100 percent.
Nickel: the nickel can form an infinite solid solution with iron, is an austenite stabilizing element, can obviously improve the strength and low-temperature toughness of steel, and particularly has a strong promoting effect on the low-temperature DWTT performance. However, nickel is a precious metal, and too high content of nickel easily causes the pressing of iron oxide scales, thereby affecting the surface quality of the finished steel plate. The pipeline steel is designed to be low-carbon, and the Ni content can be properly reduced. The range of nickel content determined by the invention is 0.10% -0.50%.
Chromium: chromium plays a multi-element and important role in pipeline steel, can form relatively stable and fine chromium carbide, is uniformly distributed in the steel volume, and plays a role in refining the structure and improving the strength and the wear resistance. Chromium and nickel form stable compounds, can play a role in resisting oxidation and corrosion, and has a good effect of protecting the surface quality of pipeline steel. The invention determines the chromium content to be 0.10-0.50%.
The production method of the invention is set according to the following steps:
the surface of the pipeline steel casting billet is far lower than A after strong cooling c1 The steel plate is fed into the furnace below a temperature line, and the proeutectoid ferrite film is inhibited from being distributed in a net shape at an austenite crystal boundary, so that the problem of the surface star crack of the steel plate in a hot charging and hot delivery mode is solved; the design of high Nb components is adopted, the pinning grain boundary effect of a large amount of dispersed solid-dissolved Nb (C, N) is utilized at a higher heating temperature, the abnormal growth of original austenite grains is inhibited, and the effect of casting blank heating homogenization can be achieved in a shorter time by utilizing a heat radiation mode of high-temperature heating; after the rough rolling stage is widened, the average reduction rate of the last three times is more than or equal to 15%, the accumulated reduction rate is more than or equal to 50%, the condition that the integral rough rolling process is finished at a recrystallization termination temperature Tnr above a critical deformation rate is ensured, the austenite structure of the billet is fully recrystallized, and crystal grains in the thickness direction are fully refined; the intermediate billet is cooled by water to reach the second stage rolling temperature in a short time, so that the temperature waiting time of the intermediate billet is fully reduced, and the production efficiency is improved. Finish rolling is carried out at (A) r3 Rolling in a +50 ℃) to Tnr temperature area, rolling in an unrecrystallized area with the cumulative reduction rate of more than or equal to 60 percent, and performing dispersion precipitation on a large amount of Nb (C, N), so that more sub-crystal boundaries and deformation zones can be generated, more nucleation particles are provided for subsequent medium-temperature transformation, and the ferrite and bainite tissues are fully refined. The high water inlet temperature provides a larger supercooling degree and a phase change driving force for subsequent medium-temperature transformation so as to increase the bainite content of a hard phase structure; the cooling control process adopts a mode of ' DQ + ACC ', a Mulpic front area is utilized to carry out DQ ultra-fast cooling on a steel plate at a speed of 25 to 30 ℃/S, a matrix structure avoids a gamma → QF (polygonal ferrite) area in a CCT curve, the matrix structure enters gamma → AF (acicular ferrite) + GB (granular bainite) as soon as possible at a temperature of 600 to 650 ℃, the steel plate is subjected to medium temperature transformation at a speed of 5 to 10 ℃/S at a Mulpic rear area, the temperature is stopped at 510 to 580 ℃, and the slow ACC cooling can reduce the Behcet ' S temperature of the steel plate at this stageThe bulk phase change stress has the effect of obviously improving the shape of the cold rear plate.
The invention has the beneficial effects that: (1) The method can shorten the heating time of the X70 pipeline steel for 20 to 50min, and can improve the hourly output of the X70 pipeline steel by 20 percent; (2) The steel plate can obtain matrix structures of 50-55% of acicular ferrite and 45-55% of granular bainite, the grain size reaches 11-12 grade, the yield strength is 500-600Mpa, the tensile strength is 600-680 Mpa, the yield ratio is less than or equal to 0.88, the impact power is more than or equal to 250J at minus 40 ℃, and the drop weight DWTT is more than or equal to 90% at minus 30 ℃; and (3) the cold straightening rate of the X70 pipeline steel plate is within 5 percent.
Drawings
FIG. 1 is a graph showing a temperature change in a heating process of a cast slab in example 2 of the present invention.
FIG. 2 is an optical micrograph of X70 pipeline steel at 1/4 of its thickness according to example 2 of the present invention.
Detailed Description
The invention is further illustrated by the following set of examples.
The chemical composition of the steel grades of the examples is shown in table 1.
Table 1 chemical composition of example steel grade (%)
Example 1: production of X70 steel with thickness of 8mm
The chemical composition of the steel is shown in Table 1, the thickness of the cast slab is 220mm, and the thickness of the steel plate is 8mm. The key production process parameters are as follows:
(1) Plate blank inserting: the compositions of example 1 of table 1 were smelted in a converter and cast into steel billets with a billet off-line temperature of 800 ℃;
(2) Heating the plate blank at a high temperature: after the billet is taken off the line, a hot-delivery hot-charging mode is adopted, the surface of the casting blank is cooled to 480 ℃ and then enters a furnace, and the mixed gas heat value of the heating furnace is 11500-12000 kJ/Nm 3 The air-fuel ratio is 3.1, the preheating section, the I adding section, the II adding section and the soaking section are controlled and heated, the temperature of the preheating section is 800 to 1200 ℃, the temperature of the I adding section is 1200 to 1300 ℃, the temperature of the II adding section is 1300 to 1350 ℃, the soaking section is 1300 to 1350 ℃, and the total temperature isThe furnace time is 151min, the heating rate is 4 to 6min/cm, and the furnace outlet temperature is 1230 to 1260 ℃;
(3) Rough rolling: the initial rolling temperature of rough rolling is 1230 ℃, the average reduction rate of the three times at the end of the widened pass is 24%, the final rolling temperature of the rough rolling is 1020-1040 ℃, the intermediate billet is 65mm, the cumulative reduction rate of the rough rolling is 71%, and the cumulative reduction rate of the finish rolling is 88%;
(4) Finish rolling: the intermediate blank is cooled to the front of a finishing mill by intermediate water, the finishing rolling start temperature is 980 ℃, the rolling time is 7 times, the average reduction rate is 13%, and the final rolling temperature is 840-860 ℃;
(5) And (3) fast cooling control: directly cooling the steel plate in water after rolling, adopting a sectional mode for cooling, adopting a DQ mode in the first stage, wherein the cooling rate is 30 ℃/S, and the finishing temperature is 620-650 ℃, and adopting an ACC mode in the second stage, wherein the cooling rate is 8 ℃/S, and the finishing temperature is 530-560 ℃.
Example 2: production of 17.5mm thick X70 steel
The chemical components of the steel are shown in Table 1, the thickness of the cast slab is 260mm, and the thickness of the steel plate is 17.5mm. The key production process parameters are as follows:
(1) Plate blank inserting: the compositions of example 2 of Table 1 were smelted in a converter and cast into steel billets at a billet end-of-line temperature of 850 ℃;
(2) Heating the plate blank at a high temperature: after a billet is taken off the line, a hot delivery and hot charging mode is adopted, the surface of a casting blank is forced to be cooled to 500 ℃, the casting blank is fed into a furnace, and the mixed gas heat value of the heating furnace is 11500 to 12000 kJ/Nm 3 The air-fuel ratio is 3.2, the preheating section, the I adding section, the II adding section and the soaking section are divided into a preheating section, a heating section I, a heating section II and a soaking section for controlled heating, the preheating section temperature is 800 to 1200 ℃, the heating section temperature is 1200 to 1300 ℃, the heating section temperature is 1300 to 1350 ℃, the soaking section is 1300 to 1350 ℃, the total in-furnace time is 163min, the heating rate is 4 to 6min/cm, and the out-furnace temperature is 1220 to 1250 ℃;
(3) Rough rolling: the initial rolling temperature of rough rolling is 1225 ℃, the final three-pass average reduction rate after broadening is 23%, the final rolling temperature of rough rolling is 1020-1040 ℃, the intermediate billet is 75mm, the cumulative reduction rate of rough rolling is 69%, and the cumulative reduction rate of finish rolling is 77%;
(4) Finish rolling: before the intermediate blank is cooled to the finishing mill by intermediate water, the finishing rolling start temperature is 890 ℃, the rolling is carried out for 7 times, the average reduction rate is 11 percent, and the final rolling temperature is 830-850 ℃;
(5) And (3) fast cooling control: directly cooling the rolled steel plate in water in a sectional mode, wherein the DQ mode is adopted in the first stage, the cooling rate is 28 ℃/S, and the ending temperature is 620-650 ℃, the ACC mode is adopted in the second stage, the cooling rate is 6 ℃/S, and the ending temperature is 520-550 ℃.
The microstructure of the steel sheet of example 2 was observed, and the microstructure of the steel sheet at 1/4 of the thickness was 50% of acicular ferrite and 50% of granular bainite, as shown in fig. 2.
Example 3: production of 25mm thick X70 steel
The chemical composition of the steel is shown in table 1. The thickness of the continuous casting billet is 300mm, and the thickness of the steel plate is 25mm. The key production process parameters are as follows:
(1) Plate blank inserting: the components of example 3 in Table 1 were smelted in a converter and cast into a steel billet with an off-line temperature of 890 ℃;
(2) Heating the plate blank at a high temperature: after the billet is taken off the line, a hot-delivery hot-charging mode is adopted, the surface of the casting blank is cooled to 530 ℃, and the casting blank enters a furnace, and the mixed gas heat value of the heating furnace is 11500-12000 kJ/Nm 3 The air-fuel ratio is 3.2, the preheating section, the I adding section, the II adding section and the soaking section are controlled and heated, the temperature of the preheating section is 800 to 1200 ℃, the temperature of the I adding section is 1200 to 1300 ℃, the temperature of the II adding section is 1300 to 1350 ℃, the soaking section is 1300 to 1350 ℃, the total in-furnace time is 172min, the heating rate is 4 to 6min/cm, and the out-furnace temperature is 1220 to 1240 ℃;
(3) Rough rolling: the initial rolling temperature of rough rolling is 1220 ℃, the average reduction rate of the last three times after broadening is 18%, the final rolling temperature of rough rolling is 1020-1040 ℃, the intermediate billet is 85mm, the cumulative reduction rate of rough rolling is 64%, and the cumulative reduction rate of finish rolling is 71%;
(4) Finish rolling: cooling the intermediate blank in the middle before the intermediate blank is cooled to a finishing mill, wherein the finishing rolling start temperature is 850 ℃, the rolling time is 7 times, the average reduction rate is 10 percent, and the final rolling temperature is 820-840 ℃;
(5) And (3) fast cooling control: directly cooling the steel plate in water after rolling, adopting a sectional mode for cooling, adopting a DQ mode in the first stage, wherein the cooling rate is 26 ℃/S, and ending the temperature at 620-650 ℃, and adopting an ACC mode in the second stage, wherein the cooling rate is 5 ℃/S, and the ending temperature at 510-540 ℃.
Tensile, impact and drop weight tests were carried out on the steel sheets of the above three examples, and the properties thereof are shown in Table 2.
TABLE 2 tensile Properties of the steel sheets of the examples
Claims (1)
1. A production method of X70 pipeline steel with high heating temperature is provided, the thickness of a steel plate is 8 to 25mm, and the method is characterized by comprising the following steps: the chemical composition weight percentage of the steel is C =0.03 to 0.08, si =0.20 to 0.50, mn =1.00 to 1.80, P ≤ 0.015, S ≤ 0.003, al =0.02 to 0.05, ti =0.008 to 0.020, nb =0.090 to 0.100, ni =0.10 to 0.50, cr =0.10 to 0.50, and the balance is Fe and inevitable impurity elements; the key process steps comprise:
(1) Plate blank off-line; smelting the components in a converter and casting the components into a steel billet, wherein the offline temperature of the steel billet is 750-900 ℃;
(2) Heating the plate blank at a high temperature: after the billet is taken off the line, a hot-delivery hot-charging mode is adopted, the surface of the casting blank is pumped with water and cooled to below 550 ℃ and then is fed into a furnace, and the mixed gas heat value of the heating furnace is 11000 to 12000 kJ/Nm 3 Controlling and heating the mixture according to the air-fuel ratio of 3.0 to 3.5, namely a preheating section, an I adding section, a II adding section and a soaking section, wherein the temperature of the preheating section is 800 to 1200 ℃, the temperature of the I adding section is 1200 to 1300 ℃, the temperature of the II adding section is 1300 to 1350 ℃, the temperature of the soaking section is 1300 to 1350 ℃, the total in-furnace time is 150 to 190min, the heating rate is 3 to 8min/cm, and the out-furnace temperature is 1220 to 1260 ℃;
(3) Rough rolling: after the plate blank is taken out of the furnace, primarily removing phosphorus by high-pressure water to the front of a roughing mill, wherein the initial rolling temperature is less than or equal to 1250 ℃, the final three-pass average reduction rate after widening is more than or equal to 15%, the roughing rolling finishing temperature is less than or equal to 1050 ℃, and the thickness of the intermediate blank is set according to the following steps: the accumulated reduction rate of rough rolling is more than or equal to 50 percent, and the accumulated reduction rate of finish rolling is more than or equal to 60 percent;
(4) Finish rolling: water-cooling the intermediate blank by an intermediate roller way to the front of a finishing mill, wherein the starting rolling temperature of the finish rolling is less than or equal to 980 ℃, the rolling time is 7 to 9 times, the average reduction rate is more than or equal to 10 percent, and the final rolling temperature is 820 to 860 ℃;
(5) And (3) fast cooling control: directly cooling the steel plate in water after rolling, adopting a sectional mode for cooling, adopting a DQ mode in the first stage, wherein the cooling rate is 25-30 ℃/S, and the finishing temperature is 600-650 ℃, adopting an ACC mode in the second stage, wherein the cooling rate is 5-10 ℃/S, and the finishing temperature is 510-580 ℃.
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| CN115351088A (en) * | 2022-08-05 | 2022-11-18 | 新疆八一钢铁股份有限公司 | Process for producing hot-rolled round pipe blank by using short-stress two-roll mill |
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| CN106480381B (en) * | 2015-08-31 | 2018-02-27 | 鞍钢股份有限公司 | Hot-rolled wide and thick plate with good plastic toughness for low-temperature pipeline and manufacturing method thereof |
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