KR20120049992A - Method for manufacturing tensile strength 590mpa class hot rolled high burring steel with excellent variation of mechanical property - Google Patents

Abstract

PURPOSE: A method for manufacturing high-strength hot-rolled and burred steel with low variation of materials and tensile strength of 590MPa is provided to manufacture high-quality hot-rolled high-burring steel by reducing the variation of materials in the width and length directions of strip. CONSTITUTION: A method for manufacturing high-strength hot-rolled and burred steel with low variation of materials and tensile strength of 590MPa comprises the steps of: continuously casting steel to thin slab(a) with a thickness of 30-150mm, roughly rolling, heating, finally rolling, and winding the thin slab, a step of finish rolling the strip with a rolling speed difference of 15% or less, continuously cooling the finally rolled strip to 630-690°C on a runout table(60), and air-cooling the strip for 3-9 seconds and winding at 380-490°C. The steel comprises C(Carbon) of 0.03-0.1wt.%, Si(Silicon) of 0.01-0.3wt.%, Mn(Manganese) of 1.0-2.0wt.%, P(Phosphorus) of 0.001-0.025wt.%, S(Sulfur) of 0.001-0.004wt.%, Cr(Chromium) of 0.001-2.0wt.%, Al(Aluminum) of 0.01-1.0wt.%, N(Nitrogen) of 0.001-0.02wt.%, the total tramp element of 0.18wt.% or less, one or more among Ti(Titanium) of 0.001-0.1wt.%, Nb(Niobium) of 0.001-0.1wt.%, V(Vanadium) of 0.001-0.1wt.%, and B(Boron) of 0.0002-0.003wt.%, and Fe(Iron) and inevitable impurities of the remaining amount.

Description

METHOD FOR MANUFACTURING TENSILE STRENGTH 590MPa CLASS HOT ROLLED HIGH BURRING STEEL WITH EXCELLENT VARIATION OF MECHANICAL PROPERTY}

The present invention relates to a method of manufacturing high strength hot rolled high burring steel having excellent material deviation of tensile strength of 590 MPa, and more particularly, high strength hot rolled high burring steel having excellent stretch flange formability using thin slab playing method, etc. It relates to a method of manufacturing.

In the automotive industry, the application of high tensile strength steel to automobile bodies has recently been expanded to achieve both weight reduction for reducing CO ₂ emissions and reinforcement of bodies to improve crash safety. High-strength steel is a cost-effective material for realizing these conflicting demands, and its application is expected to increase over time to meet increasingly stringent regulations. In particular, as interest in collision safety increases, its role is increasing.

High-strength steel sheet is classified by tensile strength, but in the process of development, the strength has gradually increased by adding the required characteristics for each application site, and various kinds are developed according to not only strength but also required characteristics.

High burring strength has been developed as one of these specific high strength steel sheets. As the strength increases, local ductility dominates moldability rather than full extension. This local ductility is important in the stretched flange portion. For this reason, a high burring steel with an improved stretch flangeability, that is, local ductility, was developed. In hot-rolled steel sheets, single-phase structure types (such as bainite single phase, bainitic ferrite single phase, ferrite single phase, and types that reduce the hardness difference of each phase have been developed). Steel sheets with excellent ductility have been developed.

In order to improve the stretch flangeability (or hole expandability), it is effective to suppress the formation of fine cracks during processing, and the formation of such fine cracks is generally observed in the soft phase when the hard phase and the soft phase are mixed. That is, when the hardness difference between the hard phase and the soft phase is large, it is known that concentration of deformation occurs near the interface of the soft phase to generate fine cracks. Therefore, in order to manufacture the high burring steel, research has been mainly made on the method of controlling the tissue to prevent microcracks, that is, generating as much as possible bainite.

In addition, as shown in US Pat. Much effort has been devoted to producing this superior steel.

However, the prior art is all about the manufacturing method through the existing mill process to manufacture slabs of 200mm or more, since the main phase constituting the microstructure is ferrite and bainite to control the hot rolled shape in the actual commercial scale manufacturing line Not only is it difficult to prevent the occurrence of material deviation in the width direction or the longitudinal direction. In addition, in the conventional rolling mill, since the final finishing rolling speed is faster than 400mpm, there is a problem that it is difficult to secure a desired material stably due to the manufacturing characteristics of the high burring steel to be wound at a low temperature below the Bs temperature when manufacturing the high burring steel. .

On the other hand, a new steel manufacturing process that has recently attracted attention, a so-called thin slab manufacturing process (mini-mill process), because of the characteristics of the process because of the small temperature deviation in the width direction and the longitudinal direction of the strip is produced morphological tissue steel with good material deviation It is attracting attention as a process with the potential to do so. However, most of the patents are made of DP steel and TRIP steel, as shown in European Patent Nos.02019314, 02020294, US Patent Publication 2009-0214377, Japanese Patent Application Publication 2000-063955, PCT Publication WO00 / 055381 and the like. It is only about the technology, the development of high-strength hot-rolled high burring steel with superior material properties than conventional mills using the characteristics of the mini-mill process using thin slabs has not been made.

The present invention was developed in consideration of the state of the art, and by using the slab slab method to secure the inherent characteristics of the high burring steel, such as stretch flange workability, while significantly reducing the material deviation in the width direction and length direction of the strip. The main purpose is to provide a method for producing high strength hot rolled high burring steel with excellent material deviation of 590MPa grade.

In order to achieve the above object, the present invention provides a manufacturing method as follows.

The manufacturing method according to the present invention is C: 0.03 to 0.1%, Si: 0.01 to 0.3%, Mn: 1.0 to 2.0%, P: 0.001 to 0.025%, S: 0.001 to 0.004%, Cr: 0.001 to 2.0 %, Al: 0.01 to 1.0%, N: 0.001 to 0.02%, total tramp element (Cu + Ni + Sn + Pb): 0.18% or less, Ti: 0.001 to 0.1%, Nb: 0.001 to 0.1%, V : 0.001 ~ 0.1%, B: 0.0002 ~ 0.003% of one or more added, the steel consisting of the remaining Fe and other unavoidable impurities are continuously cast into thin slabs of 30 to 150mm thickness, and the thin slabs are roughly rolled, heated, In the method of manufacturing a hot rolled high burring steel through the finish rolling and winding step,

The finish rolling step is such that the rolling speed difference in one strip is 15% or less, and the winding step continuously cools the finish rolled strip to a temperature of 630 to 690 ° C. at a runout table, and for 3 to 9 seconds. After the air cooling process, 380 ~ 490 ℃ is composed of winding to a temperature.

Other manufacturing methods according to the present invention in weight% C: 0.03 ~ 0.1%, Si: 0.01 ~ 0.3%, Mn: 1.0 ~ 2.0%, P: 0.001 ~ 0.025%, S: 0.001 ~ 0.004%, Cr: 0.001 ~ 2.0%, Al: 0.01 to 1.0%, N: 0.001 to 0.02%, total tramp element (Cu + Ni + Sn + Pb): 0.18% or less, Ti: 0.001 to 0.1%, Nb: 0.001 to 0.1%, At least one of V: 0.001 to 0.1% and B: 0.0002 to 0.003% is added, and continuously cast steel composed of the remaining Fe and other unavoidable impurities into a thin slab with a thickness of 30 to 150 mm, and the thin slab is roughly rolled, In the method for producing hot rolled gober steel through the heating, finishing rolling and winding step,

The finish rolling step is finish rolling at a temperature directly above the Ar ₃ transformation point, and the winding step continuously cools the finish rolled strip to a temperature of 630 to 690 ° C. at a runout table, and then passes through an air cooling process for 3 to 9 seconds. It consists of winding up to temperature 380-490 degreeC.

Another manufacturing method of the present invention, by weight% C: 0.03 ~ 0.1%, Si: 0.01 ~ 0.3%, Mn: 1.0 ~ 2.0%, P: 0.001 ~ 0.025%, S: 0.001 ~ 0.004%, Cr: 0.001 ~ 2.0%, Al: 0.01 to 1.0%, N: 0.001 to 0.02%, total tramp element (Cu + Ni + Sn + Pb): 0.18% or less, Ti: 0.001 to 0.1%, Nb: 0.001 to 0.1% At least one of V: 0.001 to 0.1% and B: 0.0002 to 0.003% is added and continuously cast steel composed of the remaining Fe and other unavoidable impurities into a thin slab with a thickness of 30 to 150 mm, and the thin slab is roughly rolled. In the method for producing hot rolled gober steel through the heating, finishing rolling and winding step,

The finish rolling step is such that the rolling speed difference in one strip is 15% or less, the finish rolling step is finish rolling at a temperature directly above the Ar ₃ transformation point, and the winding step is performed on the runout table. It consists of continuous cooling to the temperature of 630-690 degreeC, and after 380-490 degreeC winding up to temperature through an air cooling process for 3 to 9 second.

On the other hand, the above manufacturing method is preferably a casting speed of 4.5 mpm or more in the continuous casting step. In addition, in the rough rolling step, it is preferable that the thin slab surface temperature at the entrance side of the rough rolling mill is 950 to 1100 ° C., and the cumulative rolling reduction rate at the rough rolling is 65 to 90%. In addition, in the heating step, it is preferable to heat or heat the roughly rolled strip at 1000 to 1150 ° C.

According to the manufacturing method of high strength hot rolled high burring steel having excellent material deviation of tensile strength of 590MPa grade according to the present invention configured as described above, the inherent characteristics of the high burring steel such as stretch flange formability (or hole expandability) using thin slab playing method At the same time, it is possible to produce a hot rolled high burring steel of excellent quality which significantly reduces material deviations in the width and length directions of the strip.

In addition, the thin slab playing method can omit the reheating process in the existing mill, thereby saving energy and improving productivity.

In addition, the thin slab playing method can be used to melt the scrap steel, such as scrap in the electric furnace can increase the recycling of resources.

1 is a schematic diagram illustrating a minimill process of the present invention.

Hereinafter, the technical configuration of the present invention will be described in more detail.

As described above, since the present invention relates to a method for manufacturing hot rolled govering steel through a mini mill process using a thin slab playing method, first, the mini mill process according to the present invention will be briefly described with reference to FIG.

First, in the continuous casting machine 10 to produce a thin slab (a) having a thickness of 30 ~ 150mm. This is called thin slab in comparison with slabs of 200 mm or more produced by continuous casting machines of conventional mills. Since a slab of 200 mm or more is completely cooled in a yard or the like, it has to be sufficiently reheated to a surface temperature of 1100 ° C. or more in a reheating furnace before hot rolling. On the contrary, since the thin slab is immediately transferred to the roughing mill 20 without passing through the reheating furnace, the heat slab can be used as it is, thereby reducing energy and greatly improving productivity.

After the rolling mill 20 is rolled into a hot rolled strip having a predetermined thickness or less, the temperature of the strip lowered in the process is compensated by the heating means 30, and then the heated hot rolled strip b is finished in the finishing mill 50. Rolled to the desired final thickness, cooled through ROT [Run Out Table 60] (hereinafter referred to as "runout table"), and then finally wound in a constant temperature in the winder 70 to produce a hot rolled steel sheet of the desired material do.

At this time, in order to compensate for the difference between the playing speed and the rolling speed, the coil box 40 may be installed in front of the finish rolling mill 50 so as to be configured to firstly wind the hot rolled strip b passed through the induction heater 30. have. As a high speed playing method of 6mpm or more has been realized recently, a true continuous rolling process without using the coil box 40 has been developed.

The composition of the hot-rolled burring steel of the present invention manufactured by the above-mentioned mini-mill process is weight% C: 0.03 to 0.1%, Si: 0.01 to 0.3%, Mn: 1.0 to 2.0%, P: 0.001 to 0.025%, S: 0.001 ~ 0.004%, Cr: 0.001-2.0%, Al: 0.01-1.0%, N: 0.001-0.02%, Total tramp element (Cu + Ni + Sn + Pb): 0.18% or less, Ti: 0.001-0.1% At least one of Nb: 0.001 to 0.1%, V: 0.001 to 0.1%, and B: 0.0002 to 0.003%, and is composed of the remaining Fe and other unavoidable impurities. The function of each element and its content range are briefly described.

First, C is an important element to increase the strength of the steel sheet and to secure a composite structure of ferrite and bainite. If the content is less than 0.03%, the target strength of the present invention cannot be secured, whereas if the content is more than 0.1%, the risk of martensite formation and weldability deteriorates as well as surface defects on the cast slab during thin slab playing. The probability of this occurring increases. Therefore, the content of C is preferably limited to 0.03 to 0.1%.

Si is a useful element capable of securing strength without lowering the ductility of the steel sheet. If the content is less than 0.01%, it is difficult to secure the above effects, while if it exceeds 0.3%, there is a risk of promoting C-concentration to austenite to promote martensite formation, as well as deteriorating surface properties and weldability. Is higher. Therefore, the content of Si is preferably limited to 0.01 to 0.3%.

The Mn is an element having a very high solid solution strengthening effect and at the same time promoting the formation of a complex structure composed of ferrite and bainite. If the content is less than 1.0%, while it is difficult to secure the strength targeted in the present invention, if the content exceeds 2.0%, there is a high possibility that problems such as weldability and hot rolling property are generated. Therefore, the content of Mn is preferably limited to 1.0 to 2.0%.

P corresponds to the impurity element in the present invention. It is difficult to produce the content less than 0.001%, and if it exceeds 0.025%, causing segregation problems and the like, it is preferable to limit the content of P to 0.001 to 0.025%.

S is an impurity element in steel, an element that inhibits the ductility and weldability of the steel sheet, and the element that most inhibits the high burring property, which is the main object of the present invention. It is difficult to manufacture the content to less than 0.001%, and exceeding 0.004% not only increases the possibility of inhibiting the ductility, weldability and high burring properties of the steel sheet, but also has the risk of generating slab edge cracks. Therefore, the content of S is preferably limited to 0.001 to 0.004%.

Cr is an element added to improve the hardenability of the steel and to secure high strength. When the content of Cr is less than 0.01%, it is difficult to secure the above effects, while when the content of Cr is more than 2.0%, the effect is not only saturated but also increases the possibility that the hole expandability is lowered. Therefore, the content of Cr is preferably limited to 0.01 to 2.0%.

The acid-soluble Al is an element effective in improving the hardenability of bainite by combining with oxygen in steel to deoxidize and distribute carbon in ferrite to austenite such as Si. When the Al content is less than 0.01%, the effect cannot be secured, whereas when the Al content exceeds 1.0%, the effect is saturated, but the manufacturing cost increases. Therefore, the content of acid soluble Al is preferably limited to 0.01 to 1.0%.

N is an element effective for stabilizing austenite. If the content of N is less than 0.001%, it is difficult to expect such an effect, and if it exceeds 0.02%, the effect does not increase significantly but weldability and manufacturing cost increase. Therefore, the content of N is preferably limited to 0.001 ~ 0.02%.

The tramp element (Cu + Ni + Sn + Pb) is a kind of impurity element derived from scrap used as a raw material in the steelmaking process, and when its content exceeds 0.18%, it causes a surface crack of the thin slab cast slab. Therefore, the content of the tramp element (Cu + Ni + Sn + Pb) in the steel is preferably limited to 0.18% or less.

In addition, one or more of Ti, Nb, V, and B may be added to the steel formed as described above. Although the elements are not an element decisively affecting the basic physical properties of the high strength hot rolled high burring steel, which is the object of the present invention, it is preferable to add one or more kinds for fine control of tensile strength, yield strength and surface quality of the product.

Ti, Nb and V are effective elements for improving the hole expandability, which is a measure of the strength increase, the grain size refinement and the high burring property of the steel sheet. When the content of the elements is less than 0.001%, it is difficult to secure such an effect, and when the content exceeds 0.1%, ferrite ductility may be lowered due to an increase in manufacturing cost and excessive precipitates. Therefore, the content of Ti, Nb and V is preferably 0.001 to 0.1%.

The B is a component that delays the transformation of austenite into pearlite during cooling during annealing, and at least 0.0002% or more should be added to obtain the effect, whereas when the content of B exceeds 0.003%, the hardenability is greatly increased. It may cause deterioration of workability. Therefore, the content of B is preferably limited to 0.0002 to 0.003%.

The present invention is composed of Fe and other unavoidable impurities in addition to the above components.

Using the molten steel consisting of the above components will be described in detail a method for producing a high strength hot rolled goring steel according to the present invention.

As described above with reference to Figure 1, the mini-mill process is composed of continuous casting, rough rolling, heating, finishing rolling, cooling and winding stages, the characteristic technical configuration of the present invention is to control the operating conditions of each of the above steps newly It is to produce high strength hot rolled high burring steel with excellent phosphorous material deviation.

First, in the continuous casting step, the casting speed is preferably at least 4.5 mpm. In general, steel with a tensile strength of 590 MPa or more has a higher content of elements added for the purpose of securing strength of C, Mn, Si, etc. in steel compared to soft products, so that the slower the casting speed, the higher the risk of segregation from the cast steel. When the stone is generated, it is difficult to secure the strength, and the speed is limited to 4.5mpm or more because of the high risk of material deviation in the width direction or the length direction.

In the rough rolling step, the continuous cast thin slab is roughly rolled in a rough rolling mill consisting of two to four stands. At this time, it is preferable that the thin slab surface temperature at the entrance side of the rough mill is set to 950 to 1100 ° C., and that the cumulative reduction rate at the time of rough rolling is 65 to 90%.

When the surface temperature of the thin slab at the entrance of the rough mill is less than 950 ℃, the rough rolling load increases not only significantly but also increases the risk of edge cracking, and if it exceeds 1100 ℃, the arithmetic scale may occur. Limit to 950 ~ 1100 ℃.

In addition, the cumulative reduction ratio during rough rolling plays an important role in obtaining a product having a uniform material targeted in the present invention. In other words, the higher the rolling reduction rate during rough rolling, the more uniform the microscopic distribution of Mn, Cr, Al, etc., which are important for the manufacture of high burring steel, and the smaller the temperature gradient in the width and thickness directions of the strip. Very valid. However, if the cumulative reduction ratio is less than 65%, the above effects are not sufficiently exhibited. If the cumulative reduction ratio is greater than 90%, the rolling deformation resistance is greatly increased to increase the manufacturing cost, so that the cumulative reduction ratio is rolled to 65 to 90%. It is desirable to.

In the heating step, it is preferable to heat and heat the roughly rolled strip to a temperature of 950 to 1100 ° C. When the surface temperature of the roughly rolled strip is less than 950 ° C., the rolling load is greatly generated during the finish rolling, and if it exceeds 1100 ° C., the energy cost for temperature rise is increased as well as the tendency of surface scale defects is increased. It is preferable to limit the heating temperature to 950-1100 ° C.

The finishing rolling step is preferably such that the rolling speed difference in one strip is 15% or less. The high-strength hot-rolled high burring steel of 590MPa grade used in the present invention has a high possibility of changing the material properties according to the rolling speed during finish rolling since the formation of the transformation structure is used as a reinforcing mechanism. In other words, if the difference in rolling speed exceeds 15% in the finishing mill consisting of a plurality of stands, it becomes difficult to obtain a uniform cooling rate and a target winding temperature in the runout table, which eventually increases the material deviation in the width direction or the length direction of the strip. It causes the occurrence.

In addition, it is preferable that the finish rolling step is finish rolling at a temperature directly above the Ar ₃ transformation point, because when the finish rolling temperature is less than the Ar ₃ transformation point, the possibility of mixing of the ferrite structure increases, which lowers the stretch flangeability. .

On the other hand, in the winding step, the finish-rolled strip is continuously cooled to a temperature of 630 to 690 ° C. at the runout table, and after passing through an air cooling process for 3 to 9 seconds, it is preferable to wind the temperature of 380 to 490 ° C. The reason for the first continuous cooling of the finished rolled strip to a temperature of 630 to 690 ° C. is to allow some tissue of the finished rolled strip to be transformed into ferrite in the austenite zone. Therefore, when the cooling temperature is lower than 630 ℃, the likelihood of precipitation of carbides such as cementite increases, and if it exceeds 690 ℃, it is difficult to obtain bainite effectively because the fraction of ferrite is small, so the cooling temperature is increased to 630 ~ 690 ℃. Restrict.

Next, the continuously cooled strip undergoes an air cooling process of 3 to 9 seconds on the runout table. If the time is less than 3 seconds, the C flange is insufficient due to the lack of C concentration to the residual austenite and the lack of time for ferrite transformation. This increases the risk of deterioration, and even if it exceeds 9 seconds, not only does the risk of deterioration of the stretching flange property due to carbide precipitation increases, but also the problem of lengthening of the equipment or a decrease in productivity. Limit to 9 seconds.

Finally, in winding the air-cooled intermediate strip, there is an increased risk of martensite increase when the coiling temperature is less than 380 ° C., and a pearlite is formed when the temperature exceeds 490 ° C., thus lowering the stretch flangeability. Limit the coiling temperature to 380 ~ 490 ℃ as it can cause.

The finish rolling step and the winding step described above are characteristic technical configurations of the present invention. By combining two or more of these, it is possible to produce a high strength hot rolled high burring steel having excellent material deviation of tensile strength 590MPa class required by the present invention.

In order to determine the technical effect of the present invention configured as described above was carried out the following experiment.

Using the steel composition shown in Table 1 below, hot-rolled strips were manufactured under the process conditions such as slab thickness, circumferential speed, rolling speed difference, etc., and then each material (tensile strength, stretch flangeability and material deviation) and surface scale. The occurrence or absence was measured and shown in Table 2.

In Table 1, the total tramp element (Cu + Ni + Sn + Pb) was controlled to less than 0.18% in all steel grades. In addition, steel grades 1 to 5 is a case of producing a hot rolled strip by a thin slab playing method (slab thickness: 84mm), steel grades 6 to 8 (slab thickness: 230mm) is a case of manufacturing a hot rolled strip under the conditions of the existing mill.

In Table 2, the slab surface temperature means the surface temperature measured immediately before rough rolling, and the rolling speed difference is the percentage of the difference between the maximum and minimum sheet speeds in one strip divided by the average sheet speed in the final finish rolling. The smaller the value, the smaller the variation in the rolling speed. The ROT intermediate temperature represents the surface temperature of the strip measured on the ROT immediately after finish rolling.

On the other hand, in the conditions of the steel grades 1 to 5 of Table 2, the heating temperature of the strip after rough rolling were all applied at 1080 ° C, and the finish rolling temperature was performed directly above the Ar ₃ transformation point determined for each steel type. In addition, in the conditions of the steel grades 6-8 of Table 2, all the reheating temperatures were applied at 1200 degreeC. The final thickness of the hot rolled strip in all steel grades was made equal to 3.2 mm.

Steel grade C Si Mn P S Cr Al N Ti Nb V B Remarks One 0.08 0.1 1.5 0.012 0.003 0.04 0.007 - 0.045 - -
foil
Slab
2 0.06 0.1 1.9 0.010 0.003 0.7 0.04 0.007 0.03 0.030 - - 3 0.06 0.1 1.6 0.012 0.003 0.9 0.03 0.008 0.03 0.015 - 0.002 4 0.06 0.1 1.8 0.010 0.003 0.7 0.04 0.007 - - 0.10 - 5 0.05 0.2 1.6 0.011 0.003 1.0 0.03 0.008 0.02 - 0.05 0.0025 6 0.08 0.1 0.5 0.012 0.003 0.04 0.007 - 0.045 - -
Original wheat
7 0.06 0.1 1.9 0.010 0.003 0.7 0.04 0.007 0.03 0.030 - - 8 0.06 0.1 0.6 0.012 0.003 0.9 0.03 0.008 0.03 0.015 - 0.0015

division Steel grade Slab thickness
(mm) Week
(mpm) Slab surface temperature (℃) Rolling speed difference
(%) ROT medium temperature (℃) ROT air cooling time (sec) Winding temperature (℃) Tensile Strength (MPa) Hole expandability (%) Material Deviation (△ TS, Mpa) Arithmetic scale generation Inventive Steel 1 One 84 5.8 1031 3 671 4.2 430 630 125 18 × Inventive Steel 2 2 84 5.8 1011 3 672 4.2 430 617 132 12 × Invention Steel 3 3 84 5.8 1030 3 665 4.2 430 641 108 13 × Inventive Steel 4 4 84 5.8 1022 3 681 4.2 430 625 120 15 × Inventive Steel 5 5 84 5.8 1023 3 670 4.3 430 615 135 16 × Inventive Steel 6 5 84 5.8 1011 3 678 4.1 430 628 127 10 × Comparative Steel 1 One 84 4.2 1025 3 666 4.2 430 625 90 37 × Comparative Steel 2 2 84 5.8 1120 3 670 4.2 430 635 105 20 ○ Comparative Steel 3 3 84 5.8 1026 23 678 3.9 430 630 95 45 × Comparative Steel 4 4 84 5.8 1021 3 601 4.2 430 657 78 20 × Comparative Steel 5 4 84 5.8 1000 3 712 4.2 430 572 85 15 × Comparative Steel 6 5 84 5.8 998 3 665 2.8 430 678 65 19 × Comparative Steel 7 5 84 5.8 1021 3 658 9.5 430 570 58 22 × Comparative Steel 8 5 84 5.8 1002 3 654 4.3 350 696 55 19 × Comparative Steel 9 5 84 5.8 995 3 681 3.9 510 565 71 15 × Comparative Steel 10 6 230 1.1 1084 35 685 4.0 440 632 95 65 × Comparative Steel 11 7 230 1.1 1080 35 662 4.0 440 625 90 60 × Comparative Steel 12 8 230 1.1 1069 35 658 4.0 440 611 103 58 ×

Tensile strength and hole expandability (stretch flange property) of Table 2 are measured by taking the JIS No. 5 specimen in the rolling perpendicular direction at the point of width w / 4, and measuring the material deviation in the longitudinal direction and the width direction of the coil. It shows the value of one material value minus the minimum value. On the other hand, the hole expandability test is a value calculated as a percentage of the initial hole (10.8mm) of the hole expanded until the crack is formed in the circumference by pushing the hole into the cone after punching the diameter of 10.8mm.

As shown in the experimental results shown in Table 2, according to the present invention, it is possible to manufacture high-strength hot rolled high burring steel with excellent hole expansion and a very small material deviation.

10: continuous casting machine 20: roughing mill
30: heating means 40: coil box
50: finish rolling mill 60: runout table
70: winder

Claims (6)

By weight% C: 0.03-0.1%, Si: 0.01-0.3%, Mn: 1.0-2.0%, P: 0.001-0.025%, S: 0.001-0.004%, Cr: 0.001-2.0%, Al: 0.01-1.0 %, N: 0.001 to 0.02%, total tramp element (Cu + Ni + Sn + Pb): 0.18% or less, Ti: 0.001 to 0.1%, Nb: 0.001 to 0.1%, V: 0.001 to 0.1%, B : One or more of 0.0002 to 0.003% is added, and continuously cast steel composed of the remaining Fe and other unavoidable impurities into thin slabs with a thickness of 30 to 150 mm, and the thin slabs are subjected to rough rolling, heating, finishing rolling and winding steps. In the method of manufacturing hot rolled gobering steel,
The finishing rolling step is such that the rolling speed difference in one strip is less than 15%,
In the winding step, the finish-rolled strip is continuously cooled to a temperature of 630 to 690 ° C. at the runout table, and then subjected to an air cooling process for 3 to 9 seconds, followed by winding at a temperature of 380 to 490 ° C. at a tensile strength of 590 MPa. Manufacturing method of high strength hot rolled high burring steel with excellent material deviation. By weight% C: 0.03-0.1%, Si: 0.01-0.3%, Mn: 1.0-2.0%, P: 0.001-0.025%, S: 0.001-0.004%, Cr: 0.001-2.0%, Al: 0.01-1.0 %, N: 0.001 to 0.02%, total tramp element (Cu + Ni + Sn + Pb): 0.18% or less, Ti: 0.001 to 0.1%, Nb: 0.001 to 0.1%, V: 0.001 to 0.1%, B : At least one of 0.0002 to 0.003% is added and continuously cast steel composed of remaining Fe and other unavoidable impurities into thin slabs with a thickness of 30 to 150 mm, and the thin slabs are subjected to rough rolling, heating, finishing rolling and winding In the method for producing a hot rolled high burring steel,
The finish rolling step is finish rolling at a temperature directly above the Ar ₃ transformation point,
In the winding step, the finish-rolled strip is continuously cooled to a temperature of 630 to 690 ° C. at the runout table, and then subjected to an air cooling process for 3 to 9 seconds, followed by winding at a temperature of 380 to 490 ° C. at a tensile strength of 590 MPa. Manufacturing method of high strength hot rolled high burring steel with excellent material deviation. By weight% C: 0.03-0.1%, Si: 0.01-0.3%, Mn: 1.0-2.0%, P: 0.001-0.025%, S: 0.001-0.004%, Cr: 0.001-2.0%, Al: 0.01-1.0 %, N: 0.001 to 0.02%, total tramp element (Cu + Ni + Sn + Pb): 0.18% or less, Ti: 0.001 to 0.1%, Nb: 0.001 to 0.1%, V: 0.001 to 0.1%, B : At least one of 0.0002 to 0.003% is added, and continuous casting of steel composed of the remaining Fe and other unavoidable impurities into a thin slab with a thickness of 30 to 150 mm is carried out, and the thin slab is subjected to rough rolling, heating, finishing rolling and winding steps. In the method for producing a hot rolled high burring steel,
The finishing rolling step is such that the rolling speed difference in one strip is less than 15%,
The finish rolling step is finish rolling at a temperature directly above the Ar ₃ transformation point,
In the winding step, the finish-rolled strip is continuously cooled to a temperature of 630 to 690 ° C. at the runout table, and then subjected to an air cooling process for 3 to 9 seconds, followed by winding at a temperature of 380 to 490 ° C. at a tensile strength of 590 MPa. Manufacturing method of high strength hot rolled high burring steel with excellent material deviation. The method according to any one of claims 1 to 3,
The continuous casting step is a manufacturing method of high strength hot rolled high burring steel excellent in material deviation of tensile strength 590MPa class, characterized in that the casting speed is 4.5 mpm or more. The method according to any one of claims 1 to 3,
In the rough rolling step, the thin slab surface temperature at the entrance of the rough rolling mill is 950 to 1100 ° C., and the cumulative rolling rate at rough rolling is 65 to 90%. Method for producing high strength hot rolled high burring steel. The method according to any one of claims 1 to 3,
The heating step is a method of manufacturing a high strength hot rolled high burring steel having excellent material deviation of the tensile strength 590MPa class, characterized in that to heat or heat the rough-rolled strip to 1000 ~ 1150 ℃.

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