CN112981234B

CN112981234B - Steel for square billet continuous casting and rolling microalloyed automobile safety air bag pipe and manufacturing method thereof

Info

Publication number: CN112981234B
Application number: CN202110080357.5A
Authority: CN
Inventors: 谭亮; 葛龙贵; 李国忠; 许晓红; 白云; 吴小林; 曹红福; 李正中; 李伟; 彭继承; 黄二新; 沈刚; 孙复程; 李亮亮; 王东; 狄梦龙; 孟羽; 廖书全; 芦莎; 张丽娜
Original assignee: Jiangyin Xingcheng Special Steel Works Co Ltd
Current assignee: Jiangyin Xingcheng Special Steel Works Co Ltd
Priority date: 2021-01-21
Filing date: 2021-01-21
Publication date: 2022-09-23
Anticipated expiration: 2041-01-21
Also published as: CN112981234A

Abstract

The invention relates to microalloyed steel for an automobile air bag safety pipe, which comprises the following chemical components: 0.08-0.15%, Si: 0.15 to 0.40%, Mn: 1.00-1.50%, Cr: 0.25-0.65%, Ni: 0.10 to 0.50%, Mo: 0.10-0.30%, V: 0.05-0.15%, Al: 0.10-0.50%, P is less than or equal to 0.015%, S: 0.008%, Cu is less than or equal to 0.15%, Ti: not more than 0.06%, Nb not more than 0.03%, Ca: 0.0005-0.005 percent of As, less than or equal to 0.04 percent of Sn, less than or equal to 0.03 percent of Sb, less than or equal to 0.005 percent of Pb, and more than or equal to 1 percent of Ca/S; the balance being Fe and unavoidable impurities. The product form of the invention is a hot-rolled round pipe billet, and the mechanical property, the looseness and segregation of rolled materials and the surface quality of the microalloyed steel for the automobile air bag safety pipe are ensured.

Description

Steel for square billet continuous casting and rolling microalloyed automobile airbag tube and manufacturing method thereof

Technical Field

The invention relates to square billet continuous casting and rolling microalloyed steel for an automobile safety air bag pipe and a manufacturing method thereof. Belongs to the technical field of metallurgical industry.

Background

Modern industrial civilization brings efficiency, wealth, comfort and convenience to human society, and meanwhile, the damage of rapidly-spreading mechanical technology to human life systems is not stopped all the time, so that the safety of automobiles is improved all the time along with the improvement of scientific technology and material technology. Although the technical means is used once by human beings to reduce the loss after danger occurs, at the present stage, when the human beings still serve as main bodies for operating the vehicle, the guarantee of personal safety is still crucial. While the automobile holding capacity is growing rapidly, more and more traffic accidents are accompanied. Statistically, in all potentially fatal car accidents, about 45% of the lives are saved if safety belts are used, and this proportion may rise to 60% if airbags are used simultaneously.

The automobile safety air bag (air curtain) is an important part of the automobile safety device, the number of the used positions is large, the automobile safety air bag comprises a front row of forward air bags, a rear row of forward air bags, a knee air bag, a waist air bag, a side air curtain and the like, and the requirement on materials is very high due to the requirement on long-term safety effectiveness and reliability. The steel for the automobile safety air bag pipe is an important steel raw material in a safety air bag assembly, and the steel is mainly used for bearing the pressure of explosion airflow generated by ignition of a preset explosive and guiding the air bag to timely expand and pop up along a specified direction when the safety air bag is triggered to work in a collision, so that a protection effect is generated. Because the requirements for safety and stability are too high, the air bag pipes and key components thereof used by domestic joint-venture brand automobiles and domestic medium-high grade automobile manufacturers are imported abroad basically, the technology and the market are monopolized by the Japanese automobile enterprises and the European and American automobile enterprises, the steel for producing the air bag pipes by the domestic steel mills is still in the blank stage basically, and even if samples are produced by experimental development, the samples are difficult to pass the product certification of the European and American manufacturers and the Japanese manufacturers, and the air bag pipes and the key components are difficult to apply to the European and American, daily-venture or joint-venture automobiles. Therefore, the localization of steel for an airbag tube for automobiles is in the process of being urgent.

Automobile safety air bags (air curtains) are generally permanent and cannot be replaced unless an accident occurs after loading, so that long-term safety and reliability are required, and the requirements on materials are very high. The automobile safety air bag tube has the main functions that when the safety air bag is triggered to work in case of collision, the pressure of explosion airflow generated by ignition of the preset explosive is born, and the air bag is guided along the specified direction to be expanded and popped up in time, so that the protection effect is generated. Meanwhile, due to the complex use environment of the vehicle, the steel pipe is required to adapt to normal temperature, also can adapt to extreme weather of dozens of degrees below zero, and cannot burst the air bag pipe in the explosion process of the air bag ejection, so that secondary damage to drivers and passengers is prevented. The materials used are therefore required to meet sufficient strength, toughness and impact resistance.

Depending on the conditions of use of the automotive airbag tube, the steel for the automotive airbag tube must have the following characteristics: high tensile strength, yield strength and toughness, and high impact resistance; and simultaneously, the pipe has good ductility and good surface quality so as to be beneficial to pipe penetrating processing.

Because the automobile air bag tube needs to be subjected to tube penetration and quenching and tempering processes, the automobile air bag tube is very sensitive to steel loosening and segregation, the steel tube structure is not uniform, the anisotropy of the tube is caused, the performance of the final product air bag tube is seriously influenced, and the service life of the air bag tube is shortened. Therefore, it is necessary to ensure the structural density and uniformity of the steel and reduce the porosity and segregation of the steel.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a steel for a billet continuous casting and rolling microalloyed automobile air bag tube and a manufacturing method thereof aiming at the prior art, so that the structure compactness and uniformity of the steel are ensured, the looseness and segregation of the steel are reduced, and the requirements of the strength, the toughness, the impact resistance and the surface quality of the automobile air bag tube are met.

The technical scheme adopted by the invention for solving the problems is as follows: a microalloyed steel for an automobile air bag restraint system pipe comprises the following chemical components in percentage by mass: 0.08-0.15%, Si: 0.15 to 0.40%, Mn: 1.00-1.50%, Cr: 0.25 to 0.65%, Ni: 0.10 to 0.50%, Mo: 0.10-0.30%, V: 0.05-0.15%, Al: 0.10-0.50%, P is less than or equal to 0.015%, S: not more than 0.008 percent, not more than 0.15 percent of Cu, Ti: not more than 0.06%, Nb not more than 0.03%, Ca: 0.0005-0.005 percent of As, less than or equal to 0.04 percent of As, less than or equal to 0.03 percent of Sn, less than or equal to 0.005 percent of Sb, less than or equal to 0.002 percent of Pb, more than or equal to 1 percent of Ca/S, and the balance of Fe and inevitable impurities; on the premise of meeting the component ranges, in order to enable the material to achieve designed mechanical properties and meet welding performance requirements, the carbon equivalent value is controlled to be 0.45-0.55%, and the carbon equivalent calculation formula is CEV (C + Mn/6+ (Cr + Mo + V)/5+ (Cu + Ni)/15).

The steel for an automobile airbag tube according to the present invention has the following chemical composition design basis:

1) determination of C content

C is the most basic element in steel and the most economic strengthening element, and improves the strength of the steel by solid solution strengthening and precipitation strengthening of carbide forming elements, but the higher the carbon content of C, the higher the hardness of the steel, which can bring adverse effect to the plasticity and toughness of the steel, and the higher the C content, which can reduce the welding performance of the steel, reduce the atmospheric corrosion resistance of the steel, and increase the cold brittleness and aging sensitivity of the steel. The content range of the C in the item is determined to be 0.08-0.15%, and the C belongs to the category of low-carbon steel.

2) Determination of the Si content

Si is a basic solid-solution strengthening element as a deoxidizing element and improves hardenability. However, too high Si content increases the brittleness of ferrite, and increases the heat sensitivity and crack sensitivity in steel. In general, the silicon content in killed steel is not more than 0.5%, and the influence on the steel performance is small. The Si content in this item is determined to be in the range of 0.10 to 0.40%.

3) Determination of Mn content

Mn is a solid solution strengthening element of steel, can obviously improve the hardenability of the steel, improves the heat treatment performance of the steel, strengthens the matrix of the steel and refines pearlite, thereby improving the strength and the hardness of the steel, and the manganese alloy is cheap and easy to obtain, and is a preferred element in the design of high-strength grade steel. However, the steel contains excessive Mn, so that the phenomenon of relatively obvious temper brittleness can be generated, and Mn promotes the growth of crystal grains, so that the overheating sensitivity and the crack tendency of the steel are enhanced. The Mn content range of the project is determined to be 1.00-1.50%.

4) Determination of the Cr content

Cr is a medium carbide forming element and can improve the hardenability and the wear resistance of steel, but the content of Cr is too high, so that the brittle transition temperature of the steel is improved, and the temper brittleness of the steel is promoted, and the content of Cr is determined to be 0.25-0.65%.

5) Determination of Ni content

Ni can improve the strength of steel, and maintain good plasticity and toughness, and the steel containing Ni is not easy to overheat, so that it can prevent the growth of crystal grains at high temperature, and can still maintain fine grain structure. Meanwhile, the welding performance and the low-temperature performance of the steel added with Cr and Ni are good. However, since Ni is a scarce resource, the Cr content of the steel is set to 0.10 to 0.50%.

6) Determination of Mo content

Mo is a carbide forming element, and can improve hardenability, refine crystal grains and improve toughness by combining with Cr. For the heat-treated alloy structural steel, the tempering brittleness can be greatly reduced, the toughness of the steel is improved, and the Mo content of the steel of the project is 0.10-0.30%.

7) Determination of the V content

Both V and O, N have great affinity and are also strong carbide elements. The common VC has high dispersivity and high stability, so that it can utilize deoxidation and deaeration to obtain compact fine crystal structure, raise plasticity, toughness and high strength, and its impact property and fatigue strength are higher than those of V-free steel, and its strength and toughness are high at high temp. and low temp. (less than 0 deg.C). Meanwhile, the high dispersion of vanadium carbide prevents coarse grains of a welding seam, so that the weldability of the steel can be improved. The range of the V content in the steel grade of the project is 0.05-0.15%.

8) S, P determination of content

S, P are inevitable impurity elements in steel, and are prone to form defects such as segregation and inclusion. P dissolves in ferrite to coarsen grains and increase cold brittleness. S causes hot shortness of the steel, reducing ductility and toughness of the steel. The project is to ensure the high strength and toughness performance of steel, and the P is controlled to be less than or equal to 0.015 percent and the S is controlled to be less than or equal to 0.008 percent.

9) Determination of Al content

Al is added as a deoxidizing element in steel, and in addition to the purpose of reducing dissolved oxygen in molten steel, Al and N form dispersed fine aluminum nitride particles to refine grains, but the content of Al is high, brittle inclusions such as Al2O3 are easily formed in the molten steel smelting process, and the purity of the molten steel is reduced, so that the range of the content of Al in the project is determined to be 0.010-0.050%.

10) Determination of the Nb content

Is an element which plays a significant role in grain refinement in the rolling process. In the recrystallization rolling stage, Nb is precipitated through strain induction to hinder the recovery and recrystallization of deformed austenite so as to refine grains, thus providing a foundation for the pipe blank to still have fine tissues after quenching and tempering treatment, and being beneficial to improving the toughness of the pipe blank. However, too high Nb cannot be dissolved by the limitation of the C content and the influence of the heating temperature, and does not work and increases the cost. In addition, too high a content of Nb has an adverse effect on the welding performance. The content of the invention is controlled to be less than or equal to 0.03 percent.

11) Determination of the Cu content

Cu can improve the hardenability and atmospheric corrosion resistance of steel and reduce the hydrogen induced crack sensitivity of steel. However, too high Cu content is disadvantageous in the weldability of the steel sheet, and also tends to cause copper embrittlement, which deteriorates the surface properties of the steel. The Cu content is controlled to be less than or equal to 0.15 percent.

12) Determination of the Ti content

The low-carbon Ti steel is usually mixed with non-metal due to high viscosity of molten steel, is not easy to separate and float out, and meanwhile, the titanium has high affinity with N, O, so that TiN and TiO2 are easy to form, and the defects of more non-metal impurities, subcutaneous porosity and the like are formed at a lower temperature of a steel billet. The invention controls the content of Ti to be less than or equal to 0.06 percent.

13) Determination of As, Sn, Sb, Pb content

As, Sn, Sb, Pb and other trace elements belong to low-melting-point nonferrous metals, and the existence of the trace elements in steel can cause soft spots and uneven hardness on the surface of parts, so the trace elements are regarded As harmful elements in the steel, and the content ranges of the elements are determined to be less than or equal to 0.04 percent of As, less than or equal to 0.03 percent of Sn, less than or equal to 0.005 percent of Sb and less than or equal to 0.002 percent of Pb.

14) Determination of Ca content and Ca-S ratio

Ca has a remarkable effect on the deterioration of inclusions in steel, so that the inclusions are spheroidized and uniformly distributed, the adverse effect on toughness is reduced, and meanwhile, the fluidity of molten steel is improved, and the problem of nozzle blockage is solved. In the invention, the Ca content is controlled to be 0.0005-0.005, and the Ca/S is more than or equal to 1.

15) Determination of carbon equivalent

Carbon equivalent is an important index for evaluating the welding performance of steel. The CEV is low, which is beneficial to the welding performance of the steel but not beneficial to the formation of a high-strength martensite structure during quenching, and the CEV is high, which is beneficial to the formation of the martensite structure but can deteriorate the welding performance of the steel, so the CEV is controlled to be 0.45-0.55%. The carbon equivalent calculation formula is CEV (═ C + Mn/6+ (Cr + Mo + V)/5+ (Cu + Ni)/15).

The manufacturing process of the steel for the microalloyed automobile air bag restraint system pipe comprises the following steps: molten iron + scrap steel → EAF electric furnace → LF refining furnace → VD vacuum degassing → CCM billet continuous casting (casting blank specification 300 x 340mm) → warm delivery/slow cooling → hot rolling → saw cutting → surface silver bright processing → surface + internal flaw detection → finished product inspection → packaging.

Further, the steel-making and continuous casting process comprises the following steps: smelting in an electric furnace, and then refining in an LF (ladle furnace), wherein deoxidation is enhanced in the LF refining process, and the time of furnace slag with good deoxidation is kept to be more than 15 minutes and the furnace slag has good fluidity. After the refining is finished, the ladle is transferred into a VD furnace for high vacuum degassing treatment, and the high vacuum degassing treatment is kept for more than 15 minutes under the high vacuum pressure (1.33 mbar). And after the VD is broken, an aluminum wire must be fed firstly for adjustment. After all the alloy is added, the steel ladle is subjected to soft argon blowing for more than 10 minutes to ensure the degassing effect and the impurities can fully float. And controlling the target superheat degree of molten steel at 20-30 ℃ during continuous casting, and shortening the residence time of the casting blank in a high-temperature area as far as possible. The whole process of continuous casting is protected against oxidation to reduce the quantity of inclusions in steel, and the proper drawing speed and the cooling strength of the secondary cooling section are provided, and meanwhile, the M-EMS and F-EMS dual measures are adopted in continuous casting, so that the component segregation of the continuous casting billet is effectively improved and reduced. The prepared continuous casting billet is a rectangular continuous casting billet with the diameter of 300mm multiplied by 340mm, the continuous casting drawing speed is controlled to be less than or equal to 0.8m/min and the matching secondary cooling strength is less than or equal to 0.50l/kg by considering the characteristics of large section of the casting billet and low-carbon peritectic steel crack sensitivity, so that the shrinkage cavity and central porosity of the casting billet are improved, and the good internal quality of the casting billet is ensured.

The specific process of the casting blank heating and rolling stage comprises the following steps: heating a continuous casting blank in a heating furnace in a neutral atmosphere to 1150-1250 ℃, preserving heat for 2 hours, keeping the total furnace time for 3-3.5 hours, directly entering a 17-frame tandem rolling unit for single-phase rolling after being discharged from the furnace and being subjected to high-pressure water descaling treatment, wherein the starting temperature is 1020-1050 ℃, the finishing temperature is 900-930 ℃, the final structure after hot rolling is ferrite and pearlite, steel rolling adopts a reasonably designed rolling deformation process in the rolling process, the rough rolling adopts a rhombus hole pattern series, and the flat and vertical rolling mills are alternately arranged, the two passes before the rough rolling adopt large rolling reduction to enable deformation to permeate to the core part of the rolled piece, and simultaneously, the distribution rolling reduction is scientifically calculated according to the specification and the rolling pass of the blank, so that the ratio of the rough rolling on the width surface and the narrow surface of the original blank is equal to the rolling reduction ratio, and finally the frame segregation length-width ratio of the rolled piece is controlled to be less than or equal to 1.05. And after rolling, blowing air on a cooling bed for cooling at a cooling speed of more than or equal to 5 ℃/s to refine crystal grains, controlling the hardness of a rolled material to be more than or equal to 180HBW, facilitating subsequent bright silver processing and reducing surface quality defects, and finally preparing a round pipe blank product with the diameter of 60 mm. Such as but not limited to: when a 300-340 mm casting blank is adopted, the reduction of each pass of rough rolling on a narrow surface (300mm surface) is A1 and A2 … … An respectively, and the reduction of each pass on a wide surface (340mm surface) is B1 and B2 … … Bn respectively; firstly, the rolling reduction of the first two rough rolling passes is ensured to be more than or equal to 50%, the rolling reduction of the second two rough rolling passes is ensured to be more than or equal to 30%, and secondly, the ratio of the total rolling reduction of the narrow face and the wide face meets A1A 2 An/B1B 2 Bn 340/300 through reasonable calculation distribution.

Compared with the prior art, the invention has the advantages that:

1. high-quality pig iron, waste steel and raw and auxiliary materials are adopted to reduce the content of harmful elements in molten steel.

2. The deoxidation in the refining process is enhanced, and the good dynamic conditions in the molten steel are utilized to carry out centralized advanced deoxidation and VD vacuum degassing treatment, so that the non-metallic inclusions are fully floated upwards, and the lower gas content is controlled.

3. The method is characterized in that the content, the size and the composition form of inclusions in steel are controlled, the quantity of the inclusions in the steel is reduced by adopting an electric furnace slag-off control technology, a refining slag composition and control technology, a deoxidizer selection and addition technology optimization, a vacuum treatment technology optimization, tundish metallurgy, ladle slag-off detection technology and other technologies in the whole continuous casting process through anti-oxidation protection, and in addition, the control technology of reducing the pollution of external inclusions to molten steel is selected to strengthen the control on the production process, so that the morphology and the composition of the inclusions are controlled.

4. In the continuous casting process, the casting superheat degree does not exceed 35 ℃, and the proper drawing speed and the cooling strength of the secondary cooling section are matched to ensure the tissue growth of the continuous casting billet.

5. The M-EMS and F-EMS duplex are adopted in the continuous casting process, so that the component segregation of the continuous casting blank is effectively improved and reduced, particularly, after the electromagnetic stirring is carried out at the solidification tail end, the density of the solidification structure of the casting blank is improved, the center porosity and shrinkage cavity of the casting blank are effectively controlled, the distance between secondary dendritic crystal arms is obviously improved, the center equiaxed crystal rate is obviously improved, and crystal grains are refined, so that the quality of the casting blank is obviously improved, and the component segregation is reduced.

6. The rolling process is reasonably designed, the length-width ratio of the frame-shaped segregation of the steel is reduced, the length-width ratio of the frame-shaped segregation is less than or equal to 1.05, the looseness and segregation of the steel are improved, and the anisotropy of the steel pipe after pipe penetration is reduced.

7. By the special controlled cooling method after rolling, the hardness of the low-carbon steel body is improved, and the damage to the surface in the subsequent bright turning and transportation and use processes is facilitated.

Drawings

FIG. 1 is a macrosegregation picture of hot-rolled round steel for a microalloyed automobile air bag restraint system in an embodiment of the invention;

FIG. 2 is a two-dimensional graph of in-situ analysis porosity of a longitudinal section of hot-rolled round steel for a microalloyed automobile air bag tube in an embodiment of the invention.

Detailed Description

The invention will be further explained and illustrated by the following description and specific examples in conjunction with the accompanying drawings, which are not intended to unduly limit the technical scheme of the invention.

The chemical compositions (wt%) of the steel for an automobile air bag tube according to the examples of the present invention and the steel for an automobile air bag tube currently used in the international market are shown in tables 1 and 2,

TABLE 1

Examples	C	Si	Mn	P	S	Cr	Mo	Ni	Al	V
											1	0.1	0.25	1.27	0.012	0.004	0.55	0.15	0.32	0.027	0.097
2	0.11	0.25	1.3	0.012	0.002	0.55	0.15	0.32	0.036	0.096
											3	0.12	0.26	1.3	0.011	0.002	0.55	0.15	0.32	0.033	0.096
Comparative example 1	0.11	0.33	1.39			0.12	0.08	0.39	0.033	0.008
											Comparative example 2	0.12	0.29	1.35			0.16	0.06	0.30	0.042	0.003

TABLE 2

Examples	Cu	As	Sn	Sb	Pb	Ca	Ti	O	CEV
										1	0.08	0.0095	0.0058	0.0007	0.001	0.0008	0.0013	0.00058	0.498
2	0.05	0.0084	0.0045	0.0012	0.001	0.0006	0.0019	0.00059	0.511
										3	0.06	0.0088	0.005	0.0008	0.001	0.0007	0.0017	0.00058	0.521
Comparative example 1	0.30					0.0052	0.0224
										Comparative example 2	0.15					0.0025	0.0035

A comparison of the mechanical properties of the steels of the examples is given in Table 3

TABLE 3

Mechanical property sampling in examples 1-3 mechanical property samples were taken on rolled round steel according to the requirements of the ISO 377 standard and used according to the requirements of the ISO 6892 standard

Heat treating the sample made of the blank, and measuring the longitudinal mechanical property of the steel; the heat treatment system is as follows: the quenching temperature is 930 ℃ plus or minus 30 ℃ and the tempering temperature is 500 ℃ plus or minus 50 ℃ and the water cooling is carried out.

Charpy impact performance test in examples 1-3 used 7.5mm x 10mm x 55mm V-notched impact test specimens, and the values of the impact energy reported in the table were converted to those of standard V-notched impact test specimens of 10mm x 55 mm.

As can be seen from table 3, the steel for an automotive air bag hose according to the above embodiments of the present invention is superior to the existing steels for international similar applications in terms of tensile strength, yield strength, elongation, low-temperature impact energy, and other indexes.

In addition, through detection, the length-width ratio of the frame segregation of the steel for the automobile air bag tube is less than or equal to 1.05, and the looseness and segregation of the steel are improved, so that the structural uniformity of the steel is ensured, and the anisotropy of the steel tube after the tube is penetrated is reduced.

In addition to the above embodiments, the present invention also includes other embodiments, and any technical solutions formed by equivalent transformation or equivalent replacement should fall within the scope of the claims of the present invention.

Claims

1. A method for manufacturing steel for a square billet continuous casting and rolling microalloyed automobile air bag restraint system pipe is characterized by comprising the following steps of: the steel comprises the following chemical components in percentage by mass: 0.08-0.15%, Si: 0.15 to 0.40%, Mn: 1.00-1.50%, Cr: 0.25-0.65%, Ni: 0.10 to 0.50%, Mo: 0.10-0.30%, V: 0.05-0.15%, Al: 0.010-0.050%, P is less than or equal to 0.015%, S: 0.008%, Cu is less than or equal to 0.15%, Ti: not more than 0.06%, Nb not more than 0.03%, Ca: 0.0005-0.005 percent of As, less than or equal to 0.04 percent of Sn, less than or equal to 0.03 percent of Sb, less than or equal to 0.005 percent of Pb, and more than or equal to 1 percent of Ca/S; the balance of Fe and inevitable impurities; the method comprises the following steps:

smelting in an electric furnace in the steel-making process, then refining in an LF (ladle furnace), strengthening deoxidation in the LF refining process, keeping the time of slag with good deoxidation longer than 15 minutes and good fluidity, transferring a steel ladle into a VD (vacuum distillation) furnace to perform high-vacuum degassing treatment after refining is finished, keeping the high-vacuum degassing treatment for more than 15 minutes under the high-vacuum pressure of 1.33mbar, feeding an aluminum wire for adjustment after VD is broken, and performing soft argon blowing on the steel ladle for more than 10 minutes after all alloys are added so as to ensure that the degassing effect and impurities can float up fully;

the target superheat degree of molten steel is controlled to be 20-30 ℃ during continuous casting, the residence time of a casting blank in a high-temperature area is shortened as far as possible, the whole continuous casting process is protected against oxidation, the number of inclusions in the steel is reduced, a proper drawing speed and secondary cooling section cooling strength are matched, and meanwhile, the continuous casting adopts an M-EMS and F-EMS dual measure, so that a rectangular continuous casting blank with qualified specification is prepared, the continuous casting drawing speed is controlled to be less than or equal to 0.8M/min, the matched secondary cooling strength is less than or equal to 0.50l/kg, the shrinkage cavity and center porosity of the casting blank are improved, and the good internal quality of the casting blank is ensured;

when a casting blank is heated, the continuous casting blank is heated in a heating furnace with neutral atmosphere to 1150-1250 ℃ and is kept warm for 2 hours, and the total in-furnace time is 3-3.5 hours;

the casting blank rolling process after heating is that the casting blank is discharged from a furnace, is subjected to high-pressure water descaling treatment and then directly enters a continuous rolling mill set for single-phase rolling, the initial rolling temperature is 1020-1050 ℃, the final rolling temperature is 900-930 ℃, and the final structure after hot rolling is ferrite and pearlite;

the steel rolling in the rolling process adopts a diamond square hole type series through a reasonably designed rolling deformation process, the rough rolling adopts a horizontal rolling mill and a vertical rolling mill which are alternately arranged, the two rolling passes before the rough rolling adopt large rolling reduction to ensure that the deformation permeates to the center of a rolled piece, meanwhile, the distributed rolling reduction is scientifically calculated according to the specification of a blank and the rolling pass, the rolling reduction proportion of the rough rolling on the wide surface and the narrow surface of an original blank is in inverse proportion, the frame segregation length-width ratio of the rolled piece is finally controlled to be less than or equal to 1.05, air blowing cooling is carried out on a cooling bed after the rolling is finished, the cooling speed is more than or equal to 5 ℃/s, crystal grains are refined, the hardness of the rolled material is controlled to be more than or equal to 180HBW, the subsequent silvering processing and the reduction of surface quality defects are facilitated, and a round tube blank product with the diameter of 60mm is finally prepared.

2. The method for manufacturing a steel for a billet continuous casting and rolling microalloyed automobile air bag tube as claimed in claim 1, wherein: in order to ensure the mechanical property and have good welding performance, the welding method is characterized in that: the carbon equivalent CEV of the steel is 0.45-0.55% of C + Mn/6+ (Cr + Mo + V)/5+ (Cu + Ni)/15.

3. The method for producing a steel for a billet continuous casting and rolling microalloyed automobile air bag tube according to claim 1, wherein: the yield strength of the steel is more than or equal to 640MPa, the tensile strength is more than or equal to 750MPa, the elongation is more than or equal to 20 percent, and the Charpy impact energy is more than 50J at the temperature of minus 40 ℃.

4. The method for producing a steel for a billet continuous casting and rolling microalloyed automobile air bag tube according to claim 1, wherein: the metallographic structure of the steel is ferrite and pearlite, and the refined grain size is more than 7 grades.