CN113913674B - Production method of hot rolled steel strip Q355B for economic welded pipe - Google Patents
Production method of hot rolled steel strip Q355B for economic welded pipe Download PDFInfo
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C33/00—Making ferrous alloys
- C22C33/04—Making ferrous alloys by melting
- C22C33/06—Making ferrous alloys by melting using master alloys
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
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- 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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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
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- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
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- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
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- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
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- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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Abstract
A production method of an economic hot rolled steel strip Q355B for welded pipes comprises the following steps: the method comprises the following steps of accurately designing alloy content, converter smelting, continuous casting, hot rolling and coiling, wherein the step of accurately designing the alloy content is carried out according to the following process: a. determining the content of carbon element; b. determining the content of manganese element: determining the minimum value of the manganese content according to the manganese-carbon ratio and the manganese-sulfur ratio; c. determining the content of titanium: the content of titanium element in the steel is calculated according to the yield strength requirement value of the product and the relation between the content of carbon, manganese and titanium element and the yield strength. According to the method, the contents of elements such as carbon, manganese and titanium are accurately determined, the chemical components are controlled in a narrow range, the oxygen content in steel is controlled, the process of an LF refining furnace is omitted, the temperature of a heating furnace is increased, the coiling temperature is reduced, the elongation after break of the steel strip is increased, and the Bacinger effect is reduced. By adopting the method, the production cost is reduced by about 5.21 yuan/t under the condition of the same carbon element content, and the mechanical property of the steel belt is superior to that of the prior art.
Description
Technical Field
The invention relates to a steel smelting method, in particular to a production method of a hot rolled steel strip Q355B for an economic welded pipe, belonging to the technical field of steel smelting.
Background
The iron and steel industry is developed into one of the most internationally competitive industries in China, the domestic iron and steel market competition is more serious, and for iron and steel enterprises, the iron and steel enterprises keep long-term stable operation, and the iron and steel enterprises not only have high-efficiency, low-cost and intelligent green manufacturing capacity, but also have high-efficiency, low-cost and intelligent green manufacturing capacity. The hot rolled steel strip Q355B for the welding pipe implements the GB/T3274 standard of carbon structural steel and low alloy structural steel hot rolled steel plate and steel strip, and the steel strip has the advantages of low temperature resistance, easy welding, cold stamping property, machinability and the like, and is applied to the fields of conveying pipelines, buildings, towers, bridges and the like. At present, the steel grade is produced mainly by two processes, namely a silicomanganese deoxidization alloying process, wherein manganese exists in the steel as an important deoxidizing element, plays a role in solid solution strengthening, and meets the requirement of mechanical properties; secondly, aluminum and titanium microalloying technology, wherein aluminum is used as a main deoxidizing element, and titanium is used as a main alloying element to be stored in steel, so that various technical requirements of the steel are met. The first method has simple process, but higher cost and no considerable market benefit; the second method has the advantages of high processing technology difficulty, good casting blank quality, low cost and considerable market benefit. The technical difficulty of the second process is mainly that the titanium element has extremely active chemical property, and is extremely easy to combine with oxygen and nitrogen to ensure that the yield of Ti is low, so that the steel contains more titanium inclusions, the Bacinger effect is serious, the toughness of the steel is reduced, and the comprehensive processing performance is influenced. Therefore, finding an economical and high-quality titanium microalloying hot rolled steel strip production process is a key to breaking through the bottleneck of the prior art.
Disclosure of Invention
The invention aims to provide a production method of an economic hot-rolled steel strip Q355B for welded pipes, which is used for precisely controlling the content of alloy elements in steel and dynamically regulating the content of carbon, manganese and titanium elements in the steel so as to produce the hot-rolled steel strip for welded pipes with low cost and high toughness.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
a production method of an economic hot rolled steel strip Q355B for welded pipes comprises the following steps: the method comprises the following steps of accurately designing alloy content, converter smelting, continuous casting, hot rolling and coiling, wherein the step of accurately designing the alloy content is carried out according to the following process:
a. determining the content of carbon element: determining the carbon element content according to the strength grade of the steel strip for the welded pipe, wherein the carbon content in the steel is controlled to be 0.15% -0.18%;
b. determining the content of manganese element: according to the manganese-carbon ratio and the manganese-sulfur ratio, the manganese element content in the steel simultaneously satisfies that the manganese-carbon ratio is more than or equal to 2.5, the manganese-sulfur ratio is more than or equal to 15, and the manganese element content in the steel simultaneously satisfies the minimum value of the manganese-carbon ratio and the manganese-sulfur ratio; wherein, the relation between the manganese-carbon ratio and the elongation after breaking of the steel belt is as follows:
delta= (1.1366x+27.18)/100 formula (1)
Wherein: delta represents elongation after break of steel strip,%
x represents a manganese-carbon ratio;
c. determining the content of titanium: the content of titanium element in steel is according to the requirement value of the yield strength of the product, and the relation between the content of carbon, manganese and titanium element in steel and the yield strength is as follows:
Y＝215+100*500X 1 +100*100X 2 +100*3000X 3 formula (2)
Wherein: y represents the yield strength of the steel strip and MPa
X 1 Representing the content of carbon element in steel%
X 2 Represents the content of manganese element in steel, percent
X 3 Indicates the titanium element content in the steel,%.
According to the production method of the hot rolled steel strip Q355B for the economic welded pipe, the Bactger effect and equipment errors in the pipe manufacturing process are considered, and the yield strength value of the Q355B steel strip is set to 465MPa.
According to the production method of the hot rolled steel strip Q355B for the economic welded pipe, the carbon content of the smelting end point of the converter is between 0.05 and 0.07 percent, and carbon powder is added for carburetion during tapping, so that the carbon content in the steel reaches 0.15 to 0.18 percent.
According to the production method of the hot rolled steel strip Q355B for the economic welded pipe, the smelting end temperature of the converter is controlled to 1630-1660 ℃, lime is added into a steel ladle before tapping to modify the top slag of the steel ladle, aluminum-containing materials are added for deoxidization in the tapping process, manganese and iron are added for alloying, oxygen is fixed after the furnace, the content of O in the steel is less than or equal to 30ppm, titanium-containing alloy is added in an argon blowing station, the soft blowing time of the steel ladle is more than or equal to 10 minutes, the content of N in the steel is less than or equal to 30ppm, and the process of an LF refining furnace is cancelled.
According to the production method of the hot rolled steel strip Q355B for the economic welded pipe, the soaking temperature of a heating furnace in the hot rolling process is more than or equal to 1270 ℃, the heating time of the heating furnace is more than or equal to 100 minutes, three times of descaling are adopted for rough rolling, and the descaling pressure is less than or equal to 20MPa; the finish rolling temperature is controlled between 820 and 860 ℃; the coiling temperature is controlled between 590 and 620 ℃.
The invention improves the problems of high production cost, serious Bactger effect and the like of a hot rolled steel strip Q355B for a conventional welded pipe. Through intensive research and repeated experiments, a method for realizing the lowest production cost while ensuring the product quality is designed. The method accurately determines the content of elements such as carbon, manganese, titanium and the like through public calculation, and controls the chemical components in a narrow range; the oxygen content in the steel is strictly controlled, so that the production of titanium oxide is reduced, and the recovery rate of titanium is improved; the LF refining furnace procedure is canceled, the nitrogen content in steel is reduced, the effective titanium content is improved, meanwhile, the heating furnace temperature is improved, the coiling temperature is reduced, and other means are adopted, so that the second phase particles of titanium are uniformly precipitated, the elongation after breaking of the steel belt is improved, the Bacinger effect is reduced, and the pipe making requirement of a customer is met. By adopting the method, the alloy production cost is reduced by 5.21 yuan/t under the condition of the same carbon element content, and the mechanical property of the steel belt is superior to that of the prior art.
Detailed Description
The method of the present invention is described in detail below.
The key technical condition of the hot rolled coil for the welded pipe is mechanical properties, wherein the mechanical properties mainly comprise yield strength, tensile strength, elongation after break and the like, and the fundamental factor for determining the mechanical properties is chemical composition. The elements which play a decisive role in the contribution of mechanical properties are carbon, manganese, niobium, titanium, vanadium and other trace refined grains. The Q355B steel band has the yield strength of more than or equal to 355MPa, and the yield strength is controlled to be higher than the standard value by considering the influence of the Bactger effect (Bactger effect: the phenomenon that plastic strain strengthening caused by forward loading in the plastic working process of metal causes plastic strain softening (yield limit reduction) of the metal material in the subsequent reverse loading process) on the yield strength caused by deformation of the steel band in the pipe working process. The chemical composition design of the Q355B steel aims at meeting the use requirements of clients in terms of mechanical properties, namely the steel needs to be provided with or added with reinforcing elements, and meanwhile, the Bactong effect of the steel strip after being processed into a pipe is reduced, the yield strength reduction value is reduced, and the economic production of the hot rolled steel strip for welded pipes is realized.
According to the invention, a set of economic chemical component system is selected, the types of elements of chemical components are needed to be determined in the first step, the basic five types of elements in steel are carbon, manganese, silicon, sulfur and phosphorus, the elements for refining grains adopt aluminum and titanium, and the effects of the three elements of carbon, manganese and titanium on the steel strip for welded pipes are as follows:
1. contribution of carbon element to mechanical properties: the carbon content in the steel is increased, the yield strength and the tensile strength are increased, but the elongation after breaking is reduced, when the carbon content exceeds 0.23%, the pearlite content in the microstructure of the steel is increased, the plasticity and the toughness of the steel are obviously reduced, and the welding performance is deteriorated in the process of welding a pipe, so that the carbon content of the steel for welding is generally not more than 0.20%. As the carbon content in the steel decreases, the yield strength and tensile strength decrease, but the elongation after breaking increases, and the plasticity and toughness of the steel increase, but as the carbon content in the steel decreases, other elements need to be added to satisfy the yield strength and tensile strength of the steel.
2. Contribution of manganese element to mechanical properties: manganese is a weak deoxidizer, and proper amount of manganese can effectively improve the strength of steel, eliminate the influence of sulfur and oxygen on the hot shortness of steel, improve the hot workability of steel, improve the cold shortness tendency of steel, and simultaneously not remarkably reduce the plasticity and impact toughness of steel. The content of manganese in the common carbon steel is about 0.3-0.8%. The content is too high (more than 1.0 to 1.5 percent) to embrittle and harden the steel, and reduce the rust resistance and weldability of the steel.
3. Contribution of titanium element to mechanical properties: titanium and carbon and nitrogen in the steel are combined and precipitated when the temperature and the cooling mode are changed, and the precipitation strengthening effect is achieved. The reason that the titanium is selected for the steel with different strength grades in the steel mill at present is mainly titanium precipitation strengthening effect, in addition, the alloy price advantage is obvious, when the titanium-nitrogen ratio in general steel is more than or equal to 3.4, the strength is increased by 30MPa about every time 0.01 percent of titanium is added, but when the titanium content in the steel is too high (the titanium content is more than or equal to 0.045 percent), a large amount of oxide of Ti is precipitated, the strength of the steel is rapidly improved, and the toughness and the plasticity of the steel are reduced. In addition, the titanium oxide exists in the steel as an inclusion, can induce ferrite precipitation, promotes acicular ferrite formation, improves the strength, toughness and weldability of the steel, and reduces the Bactyol effect.
The invention finds out two main factors affecting the low cost and high toughness of the hot rolled steel strip Q355B through long-term study and repeated experiments: 1. a chemical component system of the steel belt; 2. and the Bactger effect after tube making. The two main influencing factors are purposefully improved as follows:
1. the band steel of the invention has the following components:
in order to reduce the Bactger effect in the process of pipe welding, comprehensive consideration of mechanical property, technological property and cost is carried out in the process of designing chemical components, wherein the addition of carbon, manganese and titanium elements is mainly considered. The steps of designing the chemical composition are as follows:
(1) and determining the carbon element content according to the strength grade of the steel strip for the welded pipe, wherein the carbon element content in the steel is selected to be 0.15-0.18% when Q355B is produced, so that crack defects are prevented from being initiated in the peritectic region range of 0.08-0.15%. The carbon content of the smelting end point of the converter is between 0.05 and 0.07 percent, and carbon powder is added for carburetion when tapping, so that the carbon content in the steel reaches 0.15 to 0.18 percent.
(2) The determination of the manganese content is based on the manganese-carbon ratio and the manganese-sulfur ratio (the sulfur content in the steel is determined by the sulfur content at the smelting end point of the converter), and the manganese content in the steel simultaneously satisfies that the manganese-carbon ratio is more than or equal to 2.5 and the manganese-sulfur ratio is more than or equal to 15. Based on the low-cost control principle, the manganese element content in the steel meets the minimum value of the manganese-carbon ratio and the manganese-sulfur ratio simultaneously.
The higher the manganese-carbon ratio is, the stronger the toughness of the steel is, namely the higher the elongation after breaking is, and the relation between the manganese-carbon ratio and the elongation after breaking is obtained through a large amount of data statistics and analysis:
delta= (1.1366x+27.18)/100 formula (1)
Wherein: delta represents elongation after break of steel strip,%
x represents the manganese element content to the carbon element content, i.e., the manganese-carbon ratio, in the steel.
In the chemical composition design process, whether the design of a chemical composition system can meet the toughness requirement of the steel strip (the elongation standard requirement after the hot rolled steel strip Q355B for welded pipes is broken is more than or equal to 22%) can be evaluated by the formula.
(3) Determining carbon and manganese elements through deoxidization alloying in the converter tapping process, wherein the addition amount of ferromanganese (the manganese content in ferromanganese is 0.65%, the manganese content at the smelting end point of the converter is 0.10%, and the recovery rate in molten steel is 90%) = (X) 2 -0.1)/0.65/0.90*10(kg/t)
The content of titanium element in steel is mainly determined according to the product yield strength requirement value, and the invention obtains the relational expression of the content of carbon, manganese and titanium element in steel and the yield strength through long-term test and repeated verification as follows:
Y＝215+100*500X 1 +100*100X 2 +100*3000X 3 formula (2)
Wherein: y represents the yield strength of the steel strip and MPa
X 1 Representing the content of carbon element in steel%
X 2 Represents the content of manganese element in steel, percent
X 3 Representing the content of titanium element in steel, percent
According to the standard GB/T3274 of hot rolled steel plates and strips of carbon structural steel and low alloy structural steel, the yield strength of the Q355B steel strip is more than or equal to 355MPa, and the Bacinger effect in the pipe manufacturing process is considered,the yield strength of the steel strip needs to be increased by 30-80MPa on the basis of the standard minimum value, namely the minimum value of the yield strength of the Q355B steel strip is 405-435MPa. Considering that the error of experimental equipment is 30MPa, setting the yield strength of the steel belt to 465MPa, calculating the titanium content in the steel according to a formula (2), and converting to X as the adding amount of ferrotitanium 3 0.33/0.85 x 10 (kg/t) (titanium content in ferrotitanium alloy is 0.33%, recovery rate in molten steel is 85%).
2. The production process is as follows:
the production method of the hot rolled steel strip Q355B for the economic welded pipe comprises the working procedures of converter smelting, continuous casting, hot rolling and coiling, and the working procedure of an LF refining furnace is canceled. The primary function of the LF refining furnace is desulfurization, inclusion removal, uniform component removal and the like, and the reason for canceling the process is that argon blowing and top slag modification operations are carried out in an argon blowing station of the converter, so that the purposes of desulfurization, inclusion removal and uniform component removal can be achieved, and meanwhile, the production cost of ton steel is reduced by about 60 yuan. The smelting end temperature of the converter is controlled at 1630-1660 ℃, lime is added into a ladle before tapping to modify the top slag of the ladle, aluminum-containing materials are added for deoxidization in the tapping process, manganese and iron are added for alloying, oxygen is fixed after the converter, the content of [ O ] in the steel is less than or equal to 30ppm, titanium-containing alloy is added into an argon blowing station, the soft blowing time of the ladle is more than or equal to 10 minutes, and the content of [ N ] in the steel is less than or equal to 30ppm.
The temperature of a soaking section of a heating furnace in the hot rolling process is more than or equal to 1270 ℃, the heating time of the heating furnace is more than or equal to 100 minutes, and is 20 ℃ higher than the temperature of the conventional process, and the heating temperature of the heating furnace is increased so that titanium element can be fully dissolved in austenite, and the mechanical property of steel is improved; the rough rolling adopts three times of descaling, and the descaling pressure is less than or equal to 20MPa; the finish rolling temperature is controlled between 820 and 860 ℃; the coiling temperature is controlled between 590 and 620 ℃.
Examples of hot rolled steel strip Q355B produced according to the present invention are provided below:
example 1:
step (1): the carbon content of the smelting end point of the hot rolled steel strip Q355B converter for the welded pipe is 0.06%, the sulfur content is 0.020%, and the temperature of the smelting end point of the converter is controlled at 1650 ℃; adding carbon powder to make the content of carbon element in steel be 0.15% in the tapping process, adding aluminum-containing material to deoxidize in the tapping process, adding manganese and iron to alloy according to the manganese-carbon ratio being more than or equal to 2.5, and calculating to obtain the minimum content of manganese element in the tapping as follows: 0.15% x 2.5 = 0.375%; the content of sulfur element in the steel is 0.020%, the manganese-sulfur ratio is more than or equal to 15, and the minimum content of manganese element in the steel is calculated to be: 0.020% 15=0.3%, and the manganese element content in the steel is required to meet the manganese-carbon ratio and the manganese-sulfur ratio simultaneously, so that the manganese element content in the steel is 0.375%. The addition amount of ferromanganese is (0.375-0.10)/0.65/0.90 x 10 = 4.70kg/t, the tapping amount of the converter is 100t, namely 470kg.
Step (2): the content of carbon element and manganese element in the steel is brought into a relation between the manganese-carbon ratio and the elongation after break: delta= (1.1366x+27.18)/100, and when x is 2.5, delta= (1.1366 x 2.5+27.18)/100=30.02%, and the calculated elongation after break is 30.02% > 22%, namely the manganese-carbon ratio meets the toughness requirement of the steel belt.
Step (3): the yield strength of the steel strip was set at 465MPa, and according to the relationship between the carbon, manganese and titanium contents and the yield strength in the steel: y=215+100×500x 1 +100*100X 2 +100*3000X 3 Calculating the titanium content in the steel:
X 3 ＝(Y-215-100*500X 1 -100*100X 2 )/100*3000
＝(465-215-100*500*0.15％-100*100*0.375％)/100*3000＝0.046％
the addition amount of the converted ferrotitanium alloy is as follows: 0.046/0.33/0.85 x 10 = 1.64kg/t, the tapping amount of the converter is 100t, namely the adding ferrotitanium amount is 164kg. The hot rolled steel strip Q355B for the welded pipe is obtained by the following chemical components in percentage by weight: c:0.15%, mn:0.375%, si:0.068%, P:0.020%, S:0.020%, al s :0.025%, ti:0.046%, N:0.0028% iron and unavoidable impurities in balance. The alloy cost is 77.82 yuan/t.
Step (4): in the hot rolling process, three times of descaling are adopted for rough rolling, and the descaling pressure is less than or equal to 20MPa; the final rolling temperature is controlled at 840 ℃; the coiling temperature was controlled at 605 ℃. Yield strength of rolled steel strip: 465MPa, tensile strength: 526MPa, elongation after break: 30.02%. Sampling after the customer tubulation for mechanical property inspection: the yield strength is 435MPa, the tensile strength is 510MPa, and the elongation after breaking is 31.46%.
Comparative example 1: the hot rolled steel strip Q355B for welded pipes produced by the conventional method comprises the following chemical components in percentage by weight: c:0.15%, mn:0.45%, si:0.09%, P:0.025%, S:0.015%, al s :0.025%, ti:0.045%, N:0.0055%, the balance being iron and unavoidable impurities. Yield strength: 430MPa, tensile strength: 515MPa, elongation: 29.84%. The final rolling temperature in the hot rolling process of the conventional method is controlled at 850 ℃ and the coiling temperature is controlled at 640 ℃. Sampling after the customer tubulation for mechanical property inspection: the yield strength is 380MPa, the tensile strength is 495MPa, and the elongation after breaking is 30.07%. The alloy cost is 86.53 yuan/t.
Example 2:
step (1): the carbon content of the smelting end point of the hot rolled steel strip Q355B converter for the welded pipe is 0.06 percent, the sulfur content is 0.020 percent, and the temperature of the smelting end point of the converter is controlled to be 1645 ℃; adding carbon powder to make the content of carbon element in steel be 0.17% in the tapping process, adding aluminum-containing material to deoxidize in the tapping process, adding manganese and iron to alloy according to the manganese-carbon ratio being more than or equal to 2.5, and calculating to obtain the minimum content of manganese element in the tapping as follows: 0.17% 2.5=0.425%; the content of sulfur element in the steel is 0.020%, the manganese-sulfur ratio is more than or equal to 15, and the minimum content of manganese element in the steel is calculated to be: 0.020% 15=0.3%, and the manganese element content in the steel is 0.425% to meet both the manganese-carbon ratio and the manganese-sulfur ratio. The addition amount of ferromanganese is (0.425-0.10)/0.65/0.90 x 10 = 5.56kg/t, and the tapping amount of the converter is 100t, namely 556kg of ferromanganese is added.
Step (2): the content of carbon element and manganese element in the steel is brought into a relation between the manganese-carbon ratio and the elongation after break: delta= (1.1366x+27.18)/100, and when x is 2.5, delta= (1.1366 x 2.5+27.18)/100=30.02%, and the calculated elongation after break is 30.02% > 22%, namely the manganese-carbon ratio meets the toughness requirement of the steel belt.
Step (3): the yield strength of the steel strip was set at 465MPa, and according to the relationship between the carbon, manganese and titanium contents and the yield strength in the steel: y=215+100×500x 1 +100*100X 2 +100*3000X 3 Calculating the titanium content in the steel
X 3 ＝(Y-215-100*500X 1 -100*100X 2 )/100*3000
＝(465-215-100*500*0.17％-100*100*0.425％)/100*3000＝0.041％
The addition amount of the converted ferrotitanium alloy is as follows: 0.041/0.33/0.85 x 10 = 1.46kg/t, the tapping amount of the converter is 100t, namely the adding ferrotitanium amount is 146kg. The hot rolled steel strip Q355B for the welded pipe is obtained by the following chemical components in percentage by weight: c:0.17%, mn:0.425%, si:0.080%, P:0.020%, S:0.020%, al s :0.025%, ti:0.041%, N:0.0026% and the balance of iron and unavoidable impurities. The alloy cost is 82.26 yuan/t.
Step (4): in the hot rolling process, three times of descaling are adopted for rough rolling, and the descaling pressure is less than or equal to 20MPa; the final rolling temperature is controlled at 840 ℃; the coiling temperature was controlled at 605 ℃. Yield strength of rolled steel strip: 465MPa, tensile strength: 526MPa, elongation after break: 30.02%. Sampling after the customer tubulation for mechanical property inspection: the yield strength is 425MPa, the tensile strength is 505MPa, and the elongation after breaking is 31.52%.
Comparative example 2: the hot rolled steel strip Q355B for welded pipes produced by the conventional method comprises the following chemical components in percentage by weight: c:0.17%, mn:0.45%, si:0.09%, P:0.025%, S:0.015%, al s :0.025%, ti:0.045%, N:0.0060%, the balance being iron and unavoidable impurities. Yield strength: 450MPa, tensile strength: 525MPa, elongation: 29.16%. The final rolling temperature in the hot rolling process of the conventional method is controlled at 850 ℃ and the coiling temperature is controlled at 640 ℃. Sampling after the customer tubulation for mechanical property inspection: the yield strength is 390MPa, the tensile strength is 500MPa, and the elongation after breaking is 29.57%. The alloy cost is 86.62 yuan/t.
Example 3:
step (1): the carbon content of the smelting end point of the hot rolled steel strip Q355B converter for the welded pipe is 0.06%, the sulfur content is 0.020%, and the temperature of the smelting end point of the converter is controlled at 1650 ℃; adding carbon powder to make the content of carbon element in steel be 0.18% in the tapping process, adding aluminum-containing material to deoxidize in the tapping process, adding manganese and iron to alloy according to the manganese-carbon ratio being more than or equal to 2.5, and calculating to obtain the minimum content of manganese element in the tapping as follows: 0.18% 2.5=0.45%; the content of sulfur element in the steel is 0.020%, the manganese-sulfur ratio is more than or equal to 15, and the minimum content of manganese element in the steel is calculated to be: 0.020% 15=0.3%, and the manganese element content in the steel is 0.45% to meet the manganese-carbon ratio and the manganese-sulfur ratio simultaneously. The addition amount of the ferromanganese alloy is (0.45-0.1)/0.65/0.90 x 10 = 5.98kg/t, the tapping amount of the converter is 100t, namely 598kg.
Step (2): the content of carbon element and manganese element in the steel is brought into a relation between the manganese-carbon ratio and the elongation after break: delta= (1.1366x+27.18)/100, and when x is 2.5, delta= (1.1366 x 2.5+27.18)/100=30.02%, and the calculated elongation after break is 30.02% > 22%, namely the manganese-carbon ratio meets the toughness requirement of the steel belt.
Step (3): the yield strength of the steel strip was set at 465MPa, and according to the relationship between the carbon, manganese and titanium contents and the yield strength in the steel: y=215+100×500x 1 +100*100X 2 +100*3000X 3 Calculating the titanium content in the steel
X 3 ＝(Y-215-100*500X 1 -100*100X 2 )/100*3000
＝(465-215-100*500*0.18％-100*100*0.45％)/100*3000＝0.038％
The addition amount of the converted ferrotitanium alloy is as follows: 0.038/0.33/0.85 x 10 = 1.35kg/t, the tapping amount of the converter is 100t, namely the adding ferrotitanium amount is 135kg. The hot rolled steel strip Q355B for the welded pipe is obtained by the following chemical components in percentage by weight: c:0.18%, mn:0.45%, si:0.086%, P:0.020%, S:0.020%, al s :0.025%, ti:0.038%, N:0.0025% and the balance of iron and unavoidable impurities. The alloy cost is 81.40 yuan/t.
Step (4): in the hot rolling process, three times of descaling are adopted for rough rolling, and the descaling pressure is less than or equal to 20MPa; the final rolling temperature is controlled at 840 ℃; the coiling temperature was controlled at 605 ℃. Yield strength of rolled steel strip: 465MPa, tensile strength: 526MPa, elongation after break: 30.02%. Sampling after the customer tubulation for mechanical property inspection: the yield strength is 420MPa, the tensile strength is 505MPa, and the elongation after breaking is 31.58%.
Comparative example 3: for welded pipes produced by conventional methodsThe hot rolled steel strip Q355B comprises the following chemical components in percentage by weight: c:0.18%, mn:0.45%, si:0.09%, P:0.025%, S:0.015%, al s :0.025%, ti:0.045%, N:0.0065%, the balance being iron and unavoidable impurities. Yield strength: 460MPa, tensile strength: 530MPa, elongation: 28.69%. The final rolling temperature in the hot rolling process of the conventional method is controlled at 850 ℃ and the coiling temperature is controlled at 640 ℃. Sampling after the customer tubulation for mechanical property inspection: the yield strength is 380MPa, the tensile strength is 500MPa, and the elongation after breaking is 28.63%. The alloy cost is 83.95 yuan/t.
As can be seen from the examples and the comparative examples, the yield strength value of the hot rolled steel strip Q355B produced by the method is reduced by 30-45MPa due to the Bactogn effect after the hot rolled steel strip Q355B is produced by the method, which is lower by 50-80MPa than that of the hot rolled steel strip Q355B produced by the conventional method under the same carbon element content. Meanwhile, the cost of the alloy for producing the hot rolled steel strip Q355B is lower than that of the alloy for producing the hot rolled steel strip Q355B by a conventional method, and the average cost of the alloy for producing the hot rolled steel strip Q355B by the method is 5.21 yuan/t lower under the same carbon element content.
Claims (4)
1. A method for producing an economical hot rolled steel strip Q355B for welded pipes, comprising the steps of: the alloy content, converter smelting, continuous casting, hot rolling and coiling are accurately designed, the LF refining furnace procedure is canceled, argon blowing and top slag modification operations are carried out in an argon blowing station of the converter, the purposes of desulfurizing, removing inclusions and uniform components are achieved, and the alloy content is accurately designed according to the following steps:
a. determining the content of carbon element: determining the carbon element content according to the strength grade of the steel strip for the welded pipe, wherein the carbon content in the steel is controlled to be 0.15% -0.18%;
b. determining the content of manganese element: according to the manganese-carbon ratio and the manganese-sulfur ratio, the manganese element content in the steel simultaneously satisfies that the manganese-carbon ratio is more than or equal to 2.5, the manganese-sulfur ratio is more than or equal to 15, and the manganese element content in the steel simultaneously satisfies the minimum value of the manganese-carbon ratio and the manganese-sulfur ratio; wherein, the relation between the manganese-carbon ratio and the elongation after breaking of the steel belt is as follows:
δ=（1.1366x+27.18）/100 （1）
wherein: delta represents elongation after break of steel strip,%
x represents a manganese-carbon ratio;
c. determining the content of titanium: the content of titanium element in steel is according to the requirement value of the yield strength of the product, and the relation between the content of carbon, manganese and titanium element in steel and the yield strength is as follows:
Y=215+100*500X 1 +100*100X 2 +100*3000X 3 （2）
wherein: y represents the yield strength of the steel strip and MPa
X 1 Representing the content of carbon element in steel%
X 2 Represents the content of manganese element in steel, percent
X 3 Representing the titanium element content,%;
the smelting end temperature of the converter is controlled at 1630-1660 ℃, lime is added into a ladle before tapping to modify the top slag of the ladle, aluminum-containing materials are added for deoxidization in the tapping process, manganese and iron are added for alloying, oxygen is fixed after the converter, the content of [ O ] in the steel is less than or equal to 30ppm, titanium-containing alloy is added into an argon blowing station, the soft blowing time of the ladle is more than or equal to 10 minutes, and the content of [ N ] in the steel is less than or equal to 30ppm.
2. The method for producing an economical welded pipe hot rolled steel strip Q355B as claimed in claim 1, wherein: the yield strength value of the Q355B steel strip was set to 465MPa in consideration of the pocking effect and the equipment error during pipe machining.
3. The method for producing an economical welded pipe hot rolled steel strip Q355B as claimed in claim 2, wherein: the carbon content of the smelting end point of the converter is between 0.05 and 0.07 percent, and carbon powder is added for carburetion when tapping, so that the carbon content in the steel reaches 0.15 to 0.18 percent.
4. The method for producing an economical welded pipe hot rolled steel strip Q355B as claimed in claim 3, wherein: in the hot rolling process, the temperature of a soaking section of a heating furnace is more than or equal to 1270 ℃, the heating time of the heating furnace is more than or equal to 100 minutes, three times of descaling are adopted for rough rolling, and the descaling pressure is less than or equal to 20MPa; the finish rolling temperature is controlled between 820 and 860 ℃; the coiling temperature is controlled between 590 and 620 ℃.
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