Hot rolled steel coil for hollow stabilizer bar and production method thereof, hollow stabilizer bar

Abstract

The present invention relates to the field of iron and steel metallurgy technology, and in particular, to a hot-rolled steel coil for a hollow stabilizer rod and a production method thereof, and a hollow stabilizer rod; the method comprises: the production method of the hot-rolled steel coil for a hollow stabilizer rod comprises: subjecting the raw materials to molten iron pretreatment, converter smelting, LF refining, RH refining and continuous casting in sequence to obtain a slab; subjecting the slab to heating treatment and rolling treatment to obtain a strip steel; wherein the slab heating treatment is carried out in a weakly reducing atmosphere heating furnace, and the atmosphere in the furnace is strictly controlled; subjecting the strip steel to cooling treatment and coiling treatment to obtain a hot-rolled steel coil for a hollow stabilizer rod; wherein the cooling treatment adopts a relaxation-type rear-stage cooling method. The present invention overcomes the problems that the hot-rolled steel coils produced in conventional production processes are prone to surface decarburization and developed banded structures.

Description

Technical Field

[0001] The present invention relates to the technical field of iron and steel metallurgy, and in particular to a hot-rolled steel coil for a hollow stabilizer bar and a production method thereof, and a hollow stabilizer bar. Background Art

[0002] The stabilizer bar is an important part of the automobile suspension system. The automobile lateral stabilizer bar is widely used in independent suspension. Its function is to prevent the car from rolling over when turning or when the left / right wheels are subjected to different loads, improve the operational stability of the car, and also improve the ride comfort of the car. The traditional stabilizer bar is made of solid spring steel. In order to reduce the weight of the whole vehicle, the lateral stabilizer bar is gradually developing in the direction of being made of hollow round tubes. Compared with the stabilizer bar made of solid spring steel, the stabilizer bar made of hollow round tubes can generally achieve a weight reduction effect of 30-45%. There are two types of hollow lateral stabilizer bars. One is made of seamless steel pipes, generally using materials such as 35CrMo and 42CrMo. Its disadvantage is that the uniformity of the tube wall is poor and the cost is high; the other is made of welded pipes. The advantage is that the thickness of the tube wall is high, and the processing cost and raw material cost have a strong competitive advantage. Therefore, with the advancement of automobile lightweighting, welded tube type hollow stabilizer bars are a new trend in the development of automobile stabilizer bars. At present, the stabilizer bars of domestic automobiles are mainly solid stabilizer bars, and welded tube type hollow stabilizer bars are mainly imported. With the trend of reducing automobile costs and lightweighting, the domestic trial production and promotion of hollow stabilizer bars are being carried out in China.

[0003] The production of hollow stabilizer rods uses hot-rolled steel coils as raw materials. The following process steps are required to make hollow stabilizer rods from hot-rolled steel coils: hot-rolled steel coils (plates) → striping → ERW welding → heat treatment → pickling, lubrication → cold drawing / cold rolling (flaw detection) → heat treatment → correction → pipe cutting → cold bending → electric heating quenching → tempering → (internal corrosion protection) → end processing → shot peening → phosphating → painting → finished product. Due to the large number of processing steps, there are special requirements for hot-rolled steel coils. The hot-rolled steel coils prepared in the prior art have the following problems: the presence of a decarburized layer in the hot-rolled steel coil will aggravate the depth of the decarburized layer during subsequent heat treatment, resulting in a high rate of unqualified finished products; in order to obtain a lower yield strength, the conventional process uses a higher coiling temperature, so that the hot-rolled steel coil has a developed banded structure. The developed banded structure is prone to fatigue cracks under the action of alternating stress, affecting the fatigue life of the product. Summary of the invention

[0004] The technical problem solved by the present invention is at least one of the following problems: the presence of a decarburized layer in a hot-rolled steel coil will aggravate the depth of the decarburized layer during subsequent heat treatment, resulting in a high rate of finished product non-conformity; the conventional process uses a higher coiling temperature, resulting in a developed banded structure in the hot-rolled steel coil, which is prone to fatigue cracks under the action of alternating stress.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A method for producing a hot-rolled steel coil for a hollow stabilizer rod, wherein the components of the hot-rolled steel coil for a hollow stabilizer rod include, by mass percentage, C: 0.24-0.38%, Si: 0.15-0.35%, Mn: 1.0-1.50%, P≤0.020%, S≤0.005%, Alt: 0.015-0.060%, Cr: 0.10-0.50%, Ti: 0.010-0.050%, B: 0.0015-0.0050%, Ca: 0.0005-0.0035%, N≤0.0060%, and the rest are Fe and unavoidable impurities;

[0007] The production method of the hot-rolled steel coil for the hollow stabilizer bar comprises:

[0008] Step S1, subjecting the raw materials to molten iron pretreatment, converter smelting, LF refining, RH refining and continuous casting in sequence to obtain a slab;

[0009] Step S2, heating and rolling the slab to obtain a steel strip; wherein the heating treatment is performed in a weakly reducing atmosphere heating furnace;

[0010] Step S3, cooling and coiling the steel strip to obtain a hot-rolled steel coil for a hollow stabilizer rod; wherein the cooling treatment adopts a relaxation-type rear-stage cooling method, including: recovering the steel strip from a high temperature of 800-900°C for 5-20s, and then performing rear-stage water cooling, wherein the rear-stage water cooling rate is 25-50°C / s; and the coiling treatment temperature is 600-660°C.

[0011] Optionally, in step S2, the residual oxygen content in the tail gas of the weak reducing atmosphere heating furnace is not higher than 0.4%, and a slight positive pressure of 4-8 Pa is maintained in the furnace; the coal gas used for the heating treatment is converter gas, and the converter gas contains 40-50% CO by volume.

[0012] Optionally, in step S2, the heating treatment is performed at a temperature of 1190-1230° C. and for a time of 100-180 min.

[0013] Optionally, in step S2, the heating treatment is performed by hot loading and hot delivery, and the temperature of the hot delivery is 500-650°C.

[0014] Optionally, in step S2, the rolling process includes: rough rolling the heated slab to obtain an intermediate slab; and finish rolling the intermediate slab to obtain a strip steel; wherein the thickness of the intermediate slab is 40-52 mm, and the thickness of the strip steel is 3-8 mm.

[0015] Optionally, the start rolling temperature of the finishing rolling process is 950-1050°C, and the final rolling temperature of the finishing rolling process is 870-920°C.

[0016] Optionally, in step S3, the temperature in the final section 10 m of the strip during the coiling process is 10° C. higher than the temperature in the middle section.

[0017] Optionally, the method further comprises: step S4, subjecting the hollow stabilizer rod to a slow cooling treatment using a hot-rolled steel coil, wherein the cooling rate of the slow cooling treatment is 5-10° C. / h and the time is 36-45 hours.

[0018] The present invention also provides a hot-rolled steel coil for a hollow stabilizer rod, which is produced by the production method of the hot-rolled steel coil for a hollow stabilizer rod as described above.

[0019] The present invention also provides a hollow stabilizer bar, which is made from the hot-rolled steel coil of the hollow stabilizer bar as described above.

[0020] Compared with the prior art, the slab heating treatment in the present invention is carried out in a weak reducing atmosphere heating furnace. For example, heating is carried out using converter gas containing 40-50% by volume of CO, so as to strictly control the contents of O2, H2 and H2O in the reducing atmosphere heating furnace, reduce the possibility of decarburization on the slab surface during heating, and thus avoid the appearance of a decarburization layer in the hot-rolled steel coil; in the present invention, after the finish rolling, the strip is not immediately cooled by water spraying, but is subjected to high-temperature recovery at 800-900°C for 5-20s to exert a relaxation effect, thereby improving the temperature uniformity of the strip during water cooling, extending the high-temperature recovery time, eliminating part of the internal stress, and improving the uniformity of the structure after the phase change. The water cooling end point of the rear water cooling is close to the temperature detection point, and coupled with a lower coiling temperature, the strip cooling has a faster cooling rate, which can significantly improve the banded structure, so that the hot-rolled steel coil for the hollow stabilizer rod has a lower-rated banded structure. In addition, the hot-rolled steel coil for hollow stabilizer bars prepared by the present invention adopts the C-Mn-Cr-Ti-B composition system, and the elements are reasonably matched, which not only ensures that the hot-rolled steel coil has good cold processing deformation and welding performance, but also ensures the mechanical properties and heat treatment performance of the product. Compared with conventional designs, the use of B replaces alloys such as Mo, reduces the design cost of the product, and the comprehensive performance of the product is excellent. The hot-rolled steel coil for hollow stabilizer rods prepared by the present invention has a thickness specification of 3.0-8.0 mm, a tensile strength of not less than 600 MPa, a yield strength of not more than 500 MPa, and an elongation after fracture (A50) of not less than 25%; its microstructure is composed of ferrite + pearlite, etc., and the rest is ferrite and other components, and the banded structure is not greater than grade 2.0; the depth of the single-sided decarburization layer of the hot-rolled steel coil is not greater than 0.02 mm, the surface quality of the hot-rolled steel coil is excellent, and there are no defects such as red iron scale and easy peeling of oxide iron scale that affect subsequent processing. After the hot-rolled steel coil is heat treated, the tensile strength is not less than 1600 MPa, and the elongation after fracture (A50) is not less than 7%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the process of producing a hot-rolled steel coil for a hollow stabilizer rod according to an embodiment of the present invention;

[0022] Figure 2 This is one of the metallographic structure diagrams of the hot-rolled steel coil for the hollow stabilizer rod prepared in Example 2;

[0023] Figure 3 The second metallographic structure diagram of the hot-rolled steel coil for the hollow stabilizer rod prepared in Example 2;

[0024] Figure 4 The third metallographic structure diagram of the hot-rolled steel coil for the hollow stabilizer rod prepared in Example 2;

[0025] Figure 5This is one of the metallographic structure diagrams of the hot-rolled steel coil for the hollow stabilizer rod prepared in Comparative Example 1;

[0026] Figure 6 The second metallographic structure diagram of the hot-rolled steel coil for the hollow stabilizer rod prepared in Comparative Example 1;

[0027] Figure 7 This is the third metallographic structure diagram of the hot-rolled steel coil for the hollow stabilizer rod prepared in Comparative Example 1. DETAILED DESCRIPTION

[0028] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0029] It should be noted that, in the absence of conflict, the features in the embodiments of the present invention can be combined with each other. The meanings of the terms "comprising", "including", "containing", and "having" are non-restrictive, that is, other steps and other ingredients that do not affect the results can be added. The above terms cover the terms "consisting of" and "essentially consisting of". Unless otherwise specified, materials, equipment, and reagents are commercially available.

[0030] The production of hollow stabilizer rods uses hot-rolled steel coils as raw materials. The following process steps are required to make hollow stabilizer rods from hot-rolled steel coils: hot-rolled steel coils (plates) → striping → ERW welding → heat treatment → pickling, lubrication → cold drawing / cold rolling (flaw detection) → heat treatment → correction → pipe cutting → cold bending → electric heating quenching → tempering → (internal corrosion protection) → end processing → shot peening → phosphating → painting → finished product. Due to the large number of processing procedures, there are special requirements for hot-rolled steel coils. Since the subsequent hot-rolled steel coils need to be processed by pipe making and cold drawing / cold rolling, the mechanical strength of the hot-rolled steel coils, especially the yield strength, should not be too high; there are multiple heat treatment procedures in the manufacturing process, and the fatigue life requirements of the hot-rolled steel coils are relatively high, and the decarburization requirements of the hot-rolled steel coils are relatively stringent; the mechanical strength requirements of the finished product are relatively high, and the heat treatment performance requirements of the quenching + tempering of the hot-rolled steel coils are relatively high. If there is a decarburized layer in the hot-rolled steel coil, the depth of the decarburized layer will be aggravated during the subsequent heat treatment, resulting in the finished product not meeting the requirements; the developed banded structure is prone to fatigue cracks under the action of alternating stress.

[0031] Based on the above considerations, an embodiment of the present invention provides a production method of a hot-rolled steel coil for a hollow stabilizer rod. The components of the hot-rolled steel coil for a hollow stabilizer rod include, by mass percentage: C: 0.24-0.38%, Si: 0.15-0.35%, Mn: 1.0-1.50%, P≤0.020%, S≤0.005%, Alt: 0.015-0.060%, Cr: 0.10-0.50%, Ti: 0.010-0.050%, B: 0.0015-0.0050%, Ca: 0.0005-0.0035%, N≤0.0060%, and the rest are Fe and unavoidable impurities;

[0032] like Figure 1 As shown, the production method of the hot-rolled steel coil for the hollow stabilizer bar includes:

[0033] Step S1, subjecting the raw materials to molten iron pretreatment, converter smelting, LF refining, RH refining and continuous casting in sequence to obtain a slab;

[0034] Step S2, heating and rolling the slab to obtain a steel strip; wherein the heating treatment is performed in a weakly reducing atmosphere heating furnace;

[0035] Step S3, cooling and coiling the steel strip to obtain a hot-rolled steel coil for a hollow stabilizer rod; wherein the cooling treatment adopts a relaxation-type rear-stage cooling method, including: recovering the steel strip from a high temperature of 800-900°C for 5-20s, and then performing rear-stage water cooling, wherein the rear-stage water cooling rate is 25-50°C / s; and the coiling treatment temperature is 600-660°C.

[0036] It should be noted that the raw materials in step S1 refer to the raw materials required for preparing the hot-rolled steel coil for the hollow stabilizer rod of the present invention, and the composition of the hot-rolled steel coil prepared using these raw materials meets the above component requirements.

[0037] Compared with the prior art, the slab heating treatment in the present invention is carried out in a weakly reducing atmosphere heating furnace. For example, heating is carried out using converter gas containing 40-50% by volume of CO, so as to strictly control the contents of O2, H2 and H2O in the reducing atmosphere heating furnace, reduce the tendency of decarburization on the slab surface during heating, and thus avoid the appearance of a decarburization layer in the hot-rolled steel coil; in the present invention, after fine rolling, the strip is not immediately sprayed with water for cooling, but is subjected to high-temperature recovery at 800-900°C for 5-20s to exert a relaxation effect, thereby improving the temperature uniformity of the strip during water cooling, extending the high-temperature recovery time, eliminating part of the internal stress, and improving the uniformity of the structure after phase change; the water cooling end point of the rear-stage water cooling is close to the temperature detection point, and coupled with a lower coiling temperature, the strip cooling has a faster cooling rate, which can significantly improve the banded structure, so that the hot-rolled steel coil for the hollow stabilizer rod has a lower-rated banded structure. In addition, the hot-rolled steel coil for hollow stabilizer bars prepared by the present invention adopts the C-Mn-Cr-Ti-B composition system, and the elements are reasonably matched, which not only ensures that the hot-rolled steel coil has good cold processing deformation and welding performance, but also ensures the mechanical properties and heat treatment performance of the product. Compared with conventional designs, the use of B replaces alloys such as Mo, reduces the design cost of the product, and the comprehensive performance of the product is excellent. The hot-rolled steel coil for hollow stabilizer rods prepared by the present invention has a thickness specification of 3.0-8.0 mm, a tensile strength of not less than 600 MPa, a yield strength of not more than 500 MPa, and an elongation after fracture (A50) of not less than 25%; its microstructure is composed of ferrite + pearlite, etc., and the rest is ferrite and other components, and the banded structure is not greater than grade 2.0; the depth of the single-sided decarburization layer of the hot-rolled steel coil is not greater than 0.02 mm, the surface quality of the hot-rolled steel coil is excellent, and there are no defects such as red iron scale and easy peeling of oxide iron scale that affect subsequent processing. After the hot-rolled steel coil is heat treated, the tensile strength is not less than 1600 MPa, and the elongation after fracture (A50) is not less than 7%.

[0038] The functions and design basis of each element in the hot-rolled steel coil for the hollow stabilizer bar prepared by the present invention are as follows:

[0039] C: The strengthening effect of carbon is very obvious, which can significantly improve the strength of steel. However, high carbon content will also significantly reduce the toughness of steel, and the increase in carbon content will reduce the cold forming and welding properties of steel. In addition, the higher the carbon content, the more likely the product will decarburize, reducing fatigue life. In order to ensure the comprehensive performance of the product, the carbon content should be controlled to be no more than 0.40%. In the present invention, the carbon content is controlled to be 0.24-0.38%.

[0040] Si: a deoxidizing element, which also plays a role of solid solution strengthening in steel, and can strengthen ferrite to improve strength; however, if the Si content is too high, it is easy to cause "red rust" defects on the surface of the steel plate; in addition, if the Si content is too high, work hardening will be obvious, and the toughness of the steel pipe after subsequent cold deformation will be reduced, affecting the fatigue performance of the final product. In the present invention, the silicon content is controlled to be 0.15-0.35%.

[0041] Mn: improves hardenability and is an important solid solution strengthening element that can increase the strength of steel. If the Mn content is too high, the plasticity, toughness and weldability of the steel will be reduced, affecting the torsional fatigue performance. If the Mn content is too low, the austenite stability and steel strength will be insufficient. Therefore, in the present invention, the Mn content is controlled to be 1.0-1.50%.

[0042] Al: a deoxidizing element, which can reduce oxide inclusions in steel and purify steel, and is beneficial to improving the formability of steel plates; too high a content will lead to poor ductility; to ensure the cleanliness of molten steel, the content should not be too high, and the content of Alt in the present invention is controlled at 0.015-0.060%.

[0043] Cr: is an important element for improving the hardenability of steel and can improve the strength of steel; chromium increases the incubation period of pearlite and ferrite in the CCT curve and inhibits the formation of pearlite and ferrite. When the mass percentage of chromium is less than 0.15%, the effect on the CCT curve is not significant, but when the mass percentage of Cr is higher, the plasticity, toughness and cost of the steel are affected. Therefore, the Cr content in the present invention is controlled to be 0.15-0.30%.

[0044] B: is one of the key elements in the present invention, and mainly plays the role of improving the hardenability of steel, ensuring that the finished stabilizer rod has a higher strength during quenching + tempering. The content of B in the present invention is controlled to be 0.0015-0.0035%.

[0045] Ti: It is a nitride-forming element, which combines with N in steel to form TiN compounds, inhibits the precipitation of brittle BN, and improves the plasticity and toughness of steel. Too high Ti content is not conducive to reducing the yield strength of hot-rolled strip steel, so the Ti content in the present invention is controlled to be 0.020-0.040%.

[0046] Ca: Ca treatment after refining can modify the inclusions in the molten steel, which is conducive to the aggregation and growth of inclusions, so that they are easily removed from the molten steel and the number of oxide inclusions in the molten steel is reduced; in addition, the shape of the inclusions remaining in the steel is improved to reduce the impact on the steel properties. However, if the Ca content is too high, it will have an adverse effect on the continuous casting process, so the Ca content in the present invention is controlled to 0.0005-0.0035%.

[0047] P, S, N: impurity elements in steel have a great influence on formability and fatigue performance. The lower the content, the better. However, too low P content will increase steelmaking costs, so the P content is controlled below 0.020% to meet production costs and product requirements. Too high S content will cause "hot brittleness" of steel and deteriorate the quality of steel. The S content must be strictly limited and controlled to ≤0.005%. High N content will produce large particle inclusions and strengthen work hardening, so the N content is controlled to ≤0.0060%.

[0048] In some embodiments of the present invention, in step S2, the residual oxygen content in the exhaust gas of the weak reducing atmosphere heating furnace is not higher than 0.4%, and a slight positive pressure of 4-8 Pa is maintained in the furnace; the coal gas used for the heating treatment is converter gas, and the converter gas contains 40-50% CO by volume.

[0049] In some embodiments of the present invention, in step S2, the temperature of the heating treatment is 1190-1230°C and the time is 100-180 min, which can prevent the red iron scale defect on the surface of the hot-rolled steel coil from being generated due to the high-pressure descaling water being unable to eliminate the pinning effect of FeSiO4 on the surface of the steel billet due to the furnace temperature being too low.

[0050] In some embodiments of the present invention, in step S2, the heating treatment is performed by hot charging and hot delivery, and the hot delivery temperature is 500-650° C. The hot charging and hot delivery process shortens the time the slab is in the furnace.

[0051] In some embodiments of the present invention, in step S3, the temperature within the ending section 10m of the strip during the coiling process is 10°C higher than the temperature in the middle section, thereby eliminating the increase in mechanical strength of the tail of the hot-rolled steel coil caused by the slightly faster cooling rate of the tail of the strip.

[0052] In some embodiments of the present invention, in step S2, the rolling process includes: rough rolling the heated slab to obtain an intermediate slab, wherein the rough rolling process includes 6 rough rolling passes; finish rolling the intermediate slab to obtain a strip steel, wherein the finish rolling process includes 7 finish rolling passes; during the rolling process, 6 descaling passes are ensured, and the pressure of the high-pressure descaling water for each descaling pass is not less than 18MPa, the thickness of the intermediate slab is 40-52mm, and the thickness of the strip steel is 3-8mm. The starting rolling temperature of the finish rolling process is 950-1050℃, and the final rolling temperature of the finish rolling process is 870-920℃.

[0053] In some embodiments of the present invention, the production method of the hot-rolled steel coil for hollow stabilizer rods also includes: step S4, subjecting the hot-rolled steel coil for hollow stabilizer rods to a slow cooling treatment, wherein the cooling rate of the slow cooling treatment is 5-10°C / h and the time is 36-45h, thereby improving the performance uniformity of the hot-rolled steel coil for hollow stabilizer rods.

[0054] The embodiment of the present invention further provides a hot-rolled steel coil for a hollow stabilizer rod, which is produced by the production method of the hot-rolled steel coil for a hollow stabilizer rod as described above.

[0055] The embodiment of the present invention further provides a hollow stabilizer bar, which is made of the hot-rolled steel coil of the hollow stabilizer bar as described above.

[0056] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0057] Example 1

[0058] Measured in percentage by mass, the chemical composition of the hot-rolled steel coil for the hollow stabilizer rod prepared in this embodiment includes: C: 0.2653%, Si: 0.229%, Mn: 1.278%, P: 0.0154%, S: 0.0032%, Alt: 0.0304%, Cr: 0.1439%, Ti: 0.0289%, Ca: 0.002%, N: 0.0033%, B: 0.0029%, and the rest is Fe and unavoidable impurities.

[0059] 1.1. The raw materials are sequentially subjected to molten iron pretreatment, converter smelting, LF refining, RH refining and continuous casting to obtain slabs with a thickness of 230 mm;

[0060] 1.2. Heating treatment: the slab is hot charged and hot transported at a temperature of 634°C. The slab stays in the weak reducing atmosphere heating furnace for 142 minutes and the slab temperature out of the heating furnace is 1206°C. Converter gas containing 45% CO is used for heating, the furnace pressure is maintained at 6Pa, and the residual oxygen content in the tail gas of the weak reducing atmosphere heating furnace is ≤0.4%;

[0061] 1.3. Rolling treatment: After the slab has been heated and treated, it is descaled and subjected to 6 rough rolling passes to obtain an intermediate billet with a thickness of 48 mm; after the intermediate billet is descaled, it is rolled by a seven-stand hot continuous finishing rolling unit to obtain a strip steel with a thickness of 6 mm; wherein, the starting rolling temperature of the finishing rolling is 1035°C, and the final rolling temperature of the finishing rolling is 916°C;

[0062] 1.4. Cooling the steel strip, wherein the cooling treatment adopts a relaxation type rear cooling method, including: recovering the steel strip from high temperature at 800°C for 10s, and then performing rear water cooling, wherein the rear water cooling rate is 30.3°C / s;

[0063] 1.5. After the cooled strip is coiled, a slow cooling treatment is performed to obtain a hot-rolled steel coil for a hollow stabilizer rod; wherein the coiling temperature is 630°C, and the temperature within 10m of the end section of the strip during the coiling process is 10°C higher than the temperature of the middle section; the cooling rate of the slow cooling treatment is 5°C / h, and the time is 38h.

[0064] Example 2

[0065] Measured in percentage by mass, the chemical composition of the hot-rolled steel coil for the hollow stabilizer rod prepared in this embodiment includes: C: 0.351%, Si: 0.26%, Mn: 1.236%, P: 0.0138%, S: 0.003%, Alt: 0.0324%, Cr: 0.1332%, Ti: 0.0298%, Ca: 0.0009%, N: 0.0031%, B: 0.0022%, and the rest is Fe and unavoidable impurities.

[0066] 2.1. The raw materials are sequentially subjected to molten iron pretreatment, converter smelting, LF refining, RH refining and continuous casting to obtain slabs with a thickness of 230 mm;

[0067] 2.2. Heating treatment: the slab is hot charged and hot transported at a temperature of 534°C. The slab stays in the weak reducing atmosphere heating furnace for 155 minutes and the slab temperature out of the heating furnace is 1216°C. Converter gas containing 48% CO is used for heating, the furnace pressure is maintained at 6Pa, and the residual oxygen content in the tail gas of the weak reducing atmosphere heating furnace is ≤0.4%;

[0068] 2.3. Rolling treatment: After the slab has been heated and treated, it is descaled and subjected to six rough rolling passes to obtain an intermediate billet with a thickness of 45.5 mm; after the intermediate billet is descaled, it is rolled by a seven-stand hot continuous finishing rolling unit to obtain a strip steel with a thickness of 5.5 mm; wherein, the starting rolling temperature of the finishing rolling is 1038°C, and the final rolling temperature of the finishing rolling is 906°C;

[0069] 2.4. Cooling the steel strip, wherein the cooling treatment adopts a relaxation type rear cooling method, including: recovering the steel strip from high temperature at 850°C for 10s, and then performing rear water cooling, wherein the rear water cooling rate is 31.3°C / s;

[0070] 2.5. After the cooled strip is coiled, a slow cooling treatment is performed to obtain a hot-rolled steel coil for a hollow stabilizer rod; wherein the coiling temperature is 620°C, and the temperature within 10m of the end section of the strip during the coiling process is 10°C higher than the temperature of the middle section; the cooling rate of the slow cooling treatment is 10°C / h, and the time is 40h.

[0071] Example 3

[0072] Measured in percentage by mass, the chemical composition of the hot-rolled steel coil for the hollow stabilizer rod prepared in this embodiment includes: C: 0.3438%, Si: 0.219%, Mn: 1.263%, P: 0.0139%, S: 0.0035%, Alt: 0.034%, Cr: 0.1371%, Ti: 0.03%, Ca: 0.0023%, N: 0.0026%, B: 0.0021%, and the rest is Fe and unavoidable impurities.

[0073] 3.1. The raw materials are sequentially subjected to molten iron pretreatment, converter smelting, LF refining, RH refining and continuous casting to obtain slabs with a thickness of 230 mm;

[0074] 3.2. Heating treatment: the slab is hot charged and hot transported, the hot transport temperature is 656°C, the slab stays in the weak reducing atmosphere heating furnace for 126 minutes, and the slab temperature out of the heating furnace is 1203°C; the slab is heated using converter gas containing 45% CO, the furnace pressure is maintained at 6Pa, and the residual oxygen content in the tail gas of the weak reducing atmosphere heating furnace is ≤0.4%;

[0075] 3.3. Rolling treatment: After the slab has been heated and treated, it is descaled and subjected to six rough rolling passes to obtain an intermediate billet with a thickness of 48 mm; after the intermediate billet is descaled, it is rolled by a seven-stand hot continuous finishing rolling unit to obtain a strip steel with a thickness of 6.2 mm; wherein, the starting rolling temperature of the finishing rolling is 1040°C, and the final rolling temperature of the finishing rolling is 912°C;

[0076] 3.4. Cooling the steel strip, wherein the cooling treatment adopts a relaxation type rear-stage cooling method, including: recovering the steel strip at 900° C. for 10 seconds, and then performing rear-stage water cooling, wherein the rear-stage water cooling rate is 31.8° C. / s;

[0077] 3.5. After the cooled strip is coiled, a slow cooling treatment is performed to obtain a hot-rolled steel coil for a hollow stabilizer rod; wherein the coiling temperature is 625°C, and the temperature within 10m of the end section of the strip during the coiling process is 10°C higher than the temperature of the middle section; the cooling rate of the slow cooling treatment is 8°C / h, and the time is 36h.

[0078] Example 4

[0079] Measured in percentage by mass, the chemical composition of the hot-rolled steel coil for the hollow stabilizer rod prepared in this embodiment includes: C: 0.3491%, Si: 0.243%, Mn: 1.301%, P: 0.0168%, S: 0.0028%, Alt: 0.0302%, Cr: 0.1486%, Ti: 0.0235%, Ca: 0.0011%, N: 0.0029%, B: 0.0021%, and the rest is Fe and unavoidable impurities.

[0080] 4.1. The raw materials are sequentially subjected to molten iron pretreatment, converter smelting, LF refining, RH refining and continuous casting to obtain slabs with a thickness of 230 mm;

[0081] 4.2. Heating treatment: the slab is hot charged and hot transported, the hot transport temperature is 582°C, the slab stays in the weak reducing atmosphere heating furnace for 142 minutes, and the slab temperature out of the heating furnace is 1200°C; the slab is heated using converter gas containing 45% CO, the furnace pressure is maintained at 6Pa, and the residual oxygen content in the tail gas of the weak reducing atmosphere heating furnace is ≤0.4%;

[0082] 4.3. Rolling treatment: After the slab has been heated and treated, it is descaled and subjected to 6 rough rolling passes to obtain an intermediate billet with a thickness of 43 mm; after the intermediate billet is descaled, it is rolled by a seven-stand hot continuous finishing rolling unit to obtain a strip steel with a thickness of 4.0 mm; wherein, the starting rolling temperature of the finishing rolling is 1033°C, and the final rolling temperature of the finishing rolling is 885°C;

[0083] 4.4. Cooling the steel strip, wherein the cooling treatment adopts a relaxation type rear cooling method, including: recovering the steel strip from high temperature at 850°C for 7s, and then performing rear water cooling, wherein the rear water cooling rate is 34.5°C / s;

[0084] 4.5. After the cooled strip is coiled, a slow cooling treatment is performed to obtain a hot-rolled steel coil for a hollow stabilizer rod; wherein the coiling temperature is 640°C, and the temperature within 10m of the end section of the strip during the coiling process is 10°C higher than the temperature of the middle section; the cooling rate of the slow cooling treatment is 10°C / h, and the time is 42h.

[0085] Example 5

[0086] Measured in percentage by mass, the chemical composition of the hot-rolled steel coil for the hollow stabilizer rod prepared in this embodiment includes: C: 0.3375%, Si: 0.241%, Mn: 1.354%, P: 0.0144%, S: 0.0032%, Alt: 0.0264%, Cr: 0.1416%, Ti: 0.0247%, Ca: 0.0016%, N: 0.0026%, B: 0.0021%, and the rest is Fe and unavoidable impurities.

[0087] 5.1. The raw materials are sequentially subjected to molten iron pretreatment, converter smelting, LF refining, RH refining and continuous casting to obtain slabs with a thickness of 230 mm;

[0088] 5.2. Heating treatment: the slab is hot charged and hot transported, the hot transport temperature is 603°C, the slab stays in the weak reducing atmosphere heating furnace for 152 minutes, and the slab temperature out of the heating furnace is 1215°C; the slab is heated using converter gas containing 45% CO, the furnace pressure is maintained at 6Pa, and the residual oxygen content in the tail gas of the weak reducing atmosphere heating furnace is ≤0.4%;

[0089] 5.3. Rolling treatment: The slab after heating treatment is descaled and then subjected to 6 rough rolling to obtain an intermediate billet with a thickness of 41.5 mm; the intermediate billet is descaled and then subjected to a seven-stand hot continuous finishing rolling unit to obtain a strip steel with a thickness of 3.2 mm; wherein the starting rolling temperature of the finishing rolling is 1045°C and the final rolling temperature of the finishing rolling is 893°C;

[0090] 5.4. Cooling the steel strip, wherein the cooling treatment adopts a relaxation type rear cooling method, including: recovering the steel strip from high temperature at 850°C for 5s, and then performing rear water cooling, wherein the rear water cooling rate is 39.5°C / s;

[0091] 5.5. After the cooled strip is coiled, a slow cooling treatment is performed to obtain a hot-rolled steel coil for a hollow stabilizer rod; wherein the coiling temperature is 645°C, and the temperature within 10m of the end section of the strip during the coiling process is 10°C higher than the temperature of the middle section; the cooling rate of the slow cooling treatment is 10°C / h, and the time is 45h.

[0092] Comparative Example 1

[0093] Measured in percentage by mass, the chemical composition of the hot-rolled steel coil for the hollow stabilizer rod prepared in this comparative example includes: C: 0.2591%, Si: 0.22%, Mn: 1.223%, P: 0.0122%, S: 0.0029%, Alt: 0.0364%, Cr: 0.1251%, Ti: 0.0324%, Ca: 0.0022%, N: 0.0039%, B: 0.0021%, and the rest are Fe and unavoidable impurities.

[0094] 6.1. The raw materials are sequentially subjected to molten iron pretreatment, converter smelting, LF refining, RH refining and continuous casting to obtain slabs with a thickness of 230 mm;

[0095] 6.2. Heating treatment: the slab is hot charged and hot transported at a temperature of 587°C. The slab stays in the heating furnace for 155 minutes and the slab temperature out of the heating furnace is 1200°C. The slab is heated using a conventional high-coke mixed gas consisting of 30% coke oven gas and 70% blast furnace gas. The H2 content in the high-coke mixed gas is 20%, the furnace pressure is maintained at 6Pa, and the residual oxygen content in the tail gas of the heating furnace is ≤0.4%;

[0096] 6.3. Rolling treatment: After the slab has been heated and treated, it is descaled and subjected to six rough rolling passes to obtain an intermediate billet with a thickness of 48 mm; after the intermediate billet is descaled, it is rolled by a seven-stand hot continuous finishing rolling unit to obtain a strip steel with a thickness of 6 mm; wherein, the starting rolling temperature of the finishing rolling is 1033°C, and the final rolling temperature of the finishing rolling is 906°C;

[0097] 6.4. Cooling the steel strip, wherein the cooling process comprises: front-end water cooling the steel strip, wherein the front-end water cooling rate is 22.3°C / s;

[0098] 6.5. After the strip steel has been cooled, it is coiled and subjected to a slow cooling treatment to obtain a hot-rolled steel coil for a hollow stabilizer rod; wherein the coiling treatment temperature is 660°C.

[0099] Comparative Example 2

[0100] Measured in percentage by mass, the chemical composition of the hot-rolled steel coil for the hollow stabilizer rod prepared in this comparative example includes: C: 0.3611%, Si: 0.21%, Mn: 1.27%, P: 0.0139%, S: 0.0042%, Alt: 0.0339%, Cr: 0.1302%, Ti: 0.0284%, Ca: 0.0022%, N: 0.0018%, B: 0.0023%, and the rest are Fe and unavoidable impurities.

[0101] 7.1. The raw materials are sequentially subjected to molten iron pretreatment, converter smelting, LF refining, RH refining and continuous casting to obtain slabs with a thickness of 230 mm;

[0102] 7.2. Heating treatment: the slab is hot charged and hot transported at a temperature of 604°C. The slab stays in the heating furnace for 142 minutes and the slab exits the heating furnace at a temperature of 1223°C. The slab is heated using a conventional high-coke mixed gas consisting of 30% coke oven gas and 70% blast furnace gas. The H2 content in the high-coke mixed gas is 20%, the furnace pressure is maintained at 6Pa, and the residual oxygen content in the tail gas of the heating furnace is ≤0.4%;

[0103] 7.3. Rolling treatment: After the slab has been heated and treated, it is descaled and subjected to six rough rolling passes to obtain an intermediate billet with a thickness of 45 mm; after the intermediate billet is descaled, it is rolled by a seven-stand hot continuous finishing rolling unit to obtain a strip steel with a thickness of 5.5 mm; wherein, the starting rolling temperature of the finishing rolling is 1045°C, and the final rolling temperature of the finishing rolling is 886°C;

[0104] 7.4. Cooling the steel strip, wherein the cooling process comprises: front-end water cooling the steel strip, wherein the front-end water cooling rate is 24.5°C / s;

[0105] 7.5. After the cooled strip is coiled, a slow cooling treatment is performed to obtain a hot-rolled steel coil for a hollow stabilizer rod; wherein the coiling treatment temperature is 657°C.

[0106] Experimental example

[0107] The mechanical properties of the hot-rolled steel coils for hollow stabilizer bars prepared in Examples 1-5 and Comparative Examples 1-2 were tested, and the results are shown in Table 1. The microstructures of the hot-rolled steel coils for hollow stabilizer bars prepared in Examples 1-5 and Comparative Examples 1-2 were characterized, and the results are shown in Table 2. Figure 2-4 is a microstructure diagram of the hot-rolled steel coil for hollow stabilizer rods prepared in Example 2, Figure 5-7 is the microstructure diagram of the hot-rolled steel coil for the hollow stabilizer bar prepared in Comparative Example 2; from Table 1, Table 2 and Figure 2-7 It can be seen that the mechanical properties of the hot-rolled steel coils for hollow stabilizer bars prepared in Examples 1-5 are not much different, the decarburization layer depth is 0, the banded structure is not developed, and the banded structure level is below 1.5; the hot-rolled steel coils for hollow stabilizer bars prepared in Comparative Examples 1-2 have significantly developed banded structures, the banded structure levels are all above 2.5, the grain size is slightly increased, and there is a semi-decarburized layer phenomenon. It should be noted that Figure 6 The medium blue is the measurement display and does not affect the effect expressed in this figure.

[0108] Table 1

[0109]

[0110] Table 2

[0111]

[0112] The hot rolled steel coils for hollow stabilizer bars prepared in Example 1 and Example 2 were subjected to water quenching heat treatment tests, and the results are shown in Table 3. It can be seen from Table 3 that the hot rolled steel coils for hollow stabilizer bars prepared in Example 1 and Example 2 have excellent heat treatment performance. The heat treatment process of Example 1 is: heating the hot rolled steel coils for hollow stabilizer bars to 900°C, keeping the temperature for 7 minutes, and water quenching to room temperature; the heat treatment process of Example 2 is: heating the hot rolled steel coils for hollow stabilizer bars to 900°C, keeping the temperature for 6 minutes, and water quenching to room temperature.

[0113] Table 3

[0114]

[0115] In addition, it should be noted that, although the present invention is disclosed as above, the protection scope of the present invention is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A method for producing a hot-rolled steel coil for a hollow stabilizer bar, characterized in that: The components of the hot-rolled steel coil for the hollow stabilizer rod include, by mass percentage, C: 0.24-0.38%, Si: 0.15-0.35%, Mn: 1.0-1.50%, P≤0.020%, S≤0.005%, Alt: 0.015-0.060%, Cr: 0.10-0.50%, Ti: 0.010-0.050%, B: 0.0015-0.0050%, Ca: 0.0005-0.0035%, N≤0.0060%, and the rest are Fe and unavoidable impurities; The production method of the hot-rolled steel coil for the hollow stabilizer bar comprises: Step S1, subjecting the raw materials to molten iron pretreatment, converter smelting, LF refining, RH refining and continuous casting in sequence to obtain a slab; Step S2, heating and rolling the slab to obtain a steel strip; wherein the heating treatment is performed in a weak reducing atmosphere heating furnace; wherein the residual oxygen content in the tail gas of the weak reducing atmosphere heating furnace is not higher than 0.4%, and a slight positive pressure of 4-8 Pa is maintained in the furnace; the gas used in the heating treatment is converter gas, and the converter gas contains 40-50% CO by volume; Step S3, cooling and coiling the steel strip to obtain a hot-rolled steel coil for a hollow stabilizer rod; wherein the cooling treatment adopts a relaxation-type rear-stage cooling method, including: recovering the steel strip from a high temperature of 800-900°C for 5-20s, and then performing rear-stage water cooling, wherein the rear-stage water cooling rate is 25-50°C / s; and the coiling treatment temperature is 600-660°C.

2. The method for producing a hot-rolled steel coil for a hollow stabilizer rod according to claim 1, characterized in that: In the step S2, the temperature of the heating treatment is 1190-1230° C., and the time is 100-180 min.

3. The method for producing a hot-rolled steel coil for a hollow stabilizer rod according to claim 2, characterized in that: In step S2, the heating treatment is performed by hot loading and hot delivery, and the temperature of the hot delivery is 500-650°C.

4. The method for producing a hot-rolled steel coil for a hollow stabilizer rod according to claim 1, characterized in that: In step S2, the rolling process includes: rough rolling the heated slab to obtain an intermediate slab; and finish rolling the intermediate slab to obtain a strip steel; wherein the thickness of the intermediate slab is 40-52 mm, and the thickness of the strip steel is 3-8 mm.

5. The method for producing a hot-rolled steel coil for a hollow stabilizer rod according to claim 4, characterized in that: The start rolling temperature of the finishing rolling process is 950-1050°C, and the final rolling temperature of the finishing rolling process is 870-920°C.

6. The method for producing a hot-rolled steel coil for a hollow stabilizer rod according to claim 1, characterized in that: In the step S3, the temperature in the final section 10 m of the strip during the coiling process is 10° C. higher than the temperature in the middle section.

7. The method for producing a hot-rolled steel coil for a hollow stabilizer rod according to claim 1, characterized in that: The method further comprises: step S4, subjecting the hollow stabilizer rod to a slow cooling treatment using a hot-rolled steel coil, wherein the cooling rate of the slow cooling treatment is 5-10° C. / h and the time is 36-45 hours.

8. A hot-rolled steel coil for a hollow stabilizer bar, characterized in that: The hollow stabilizer rod is produced by the production method of the hot-rolled steel coil for hollow stabilizer rods as described in any one of claims 1 to 7.

9. A hollow stabilizer bar, characterized in that: The hollow stabilizer rod as claimed in claim 8 is made from hot-rolled steel coil.

Images