KR100363414B1 - Manufacturing method of hot rolled steel sheet with low material deviation of wire end of hot rolled steel sheet - Google Patents

Abstract

According to the present invention, in the method for manufacturing a hot rolled steel sheet, the material deviation in the longitudinal direction of the hot rolled coil steel sheet is reduced, so that the material deviation of the front and rear ends of the hot rolled steel sheet to produce a hot rolled steel sheet having a uniform material in the line, middle, and rear ends thereof. The purpose is to provide a method of manufacturing.

According to the present invention, in a method for manufacturing a hot rolled steel sheet, the method may include forming a component of a hot rolled steel sheet and adjusting a heat treatment temperature of a hot rolled bar, which is a raw material of the hot rolled steel sheet, wherein the component composition comprises 0.04 to 0.06 wt% of C, 0.2 % To 1.0 wt% Mn, 0.025 wt% or less Si, 0.008 wt% or less S, 0.1 wt% or less Cr, 0.2 wt% or less Ni, 0.4 wt% or less Cu, 0.001 to 0.04 wt% Sn Steel composition with 0.001 to 0.012 wt% Pb, 0.04 to 0.08 wt% acid value Al, 150 ppm or less N, 0.0002 to 0.008 wt% Ca, balance Fe, and other impurities to control the temperature In the step, the first rolled hot-rolled bar is heated 40 ~ 60 ℃ higher than the center part in the heating table, the atmosphere temperature of the coil box is maintained at 1020 ℃ or higher, and the rolling temperature is rolled at 850 ℃ or higher during post-rolling. After manufacturing the hot rolled steel sheet, the front and rear ends of the hot rolled steel sheet, characterized in that the coil is coiled in a state 20 ℃ or more higher than the center portion The negative material deviation is provided a method of making a small hot-rolled steel sheet.

Description

Manufacturing method of hot rolled steel sheet with low material deviation of wire end of hot rolled steel sheet

The present invention relates to a hot rolled steel sheet manufacturing method, and more particularly, to a hot rolled steel sheet manufacturing method that can reduce the material deviation in the front and rear ends of the hot rolled steel sheet.

In general, unlike the conventional blast furnace steelmaking method, the mini mill process melts scrap metal in an electric furnace and casts it into a thin slab (less than 100 mm thick) in a continuous casting machine, and then performs direct hot rolling by securing a rolling temperature in an intermediate facility. It is an energy-saving, environmentally friendly process.

Therefore, in the mini mill process, it is important for the mini mill process to secure the rolling temperature before directly hot rolling the thin slab.

Facilities for securing such a rolling temperature include a compact strip process (CSP) type and an in-line strip process (ISP) type mini mill.

In case of CSP type mini mill, the rolling temperature is secured in tunnel furnace about 150m and hot rolling bar is used in post-roller.In case of ISP type mini mill, surface temperature is about 900 ℃ after continuous casting. The first rolled hot rolled bar is heated in an inductive heater to secure an entrance temperature of 1000 ° C. of the after-roller. Then, after the installation of the coil box (8) to reach the post-rolling step.

Coil box (8) of the ISP-type mini mill is a hot-rolled bar extracted from the continuous casting machine is maintained for a predetermined time with the hot rolled coil bar coiled between the pre-rolling and the post-rolling.

It will be described in detail the operation relationship of the conventional ISP-type mini-mill facility.

In the linear rolling process, the hot rolled bar first rolled to a thickness of 20 to 30 mm has a surface temperature of about 850 to 950 ° C. In order to coil the hot rolled bar after rolling, the temperature of the hot rolled bar must be secured to a predetermined temperature or more. Coil box is installed to secure this constant temperature.

In the inductive heater, the hot rolled bar is further heated by about 200 to 300 ° C. by induction heating.

The heated hot rolled bar is coiled in the coil box 8 through the acceleration and then transferred to the uncoiler. And in the uncoiler, the hot rolled coil bar is unrolled and rolled in the post-roller.

When the hot rolled bar heated by the inductive heater is coiled in the coil box 8, it depends on the continuous casting speed but stays on average for about 15 minutes, and the hot rolled coil bar due to the low atmosphere temperature and the time to wait in the uncoiler during the transfer. There arises a problem that the outer winding is supercooled.

When the outer coil portion of the hot rolled coil bar is supercooled, the hot rolled coil bar becomes a hot rolled steel sheet and thus the temperature of the tip portion of the hot rolled steel sheet is not secured, resulting in a thickness deviation, and a rolling deformation structure exists because post rolling is performed at a low temperature.

At the rear end, fine grains are formed in comparison with the center part, the tensile strength is increased by 29.4 to 39.2 N / mm ² , and the elongation is decreased by 5 to 6%.

In addition, when coiling, by contacting the cold reel of the coiler, the temperature of the inner portion of the hot rolled coil bar, that is, the tip of the hot rolled bar is lowered, and the outer portion of the hot rolled coil bar, that is, the rear end of the hot rolled bar, is centered. Since the cooling rate is faster, tissue refinement is promoted, which increases the material deviation of the trailing end.

The present invention is provided to solve the problems of the prior art as described above, to provide a method for manufacturing a hot rolled steel sheet having a material guarantee and good workability throughout the hot rolled steel sheet by lowering the material deviation of the front and rear ends of the mini mill hot rolled steel sheet There is a purpose.

1 is a schematic diagram showing the induction heater of the general mini-mill to the inlet of the post-roller,

2 is a block diagram showing a calculation procedure of the temperature drop while the hot rolled bar is rolled into a hot rolled steel sheet according to an embodiment of the present invention.

♠ Explanation of symbols on the main parts of the drawing ♠

1: hot rolled bar 8: coil box

11: coiler 13: inductive heater

17: acceleration 24: uncoiler

30: after-rolling mill 41: hot rolled steel sheet

According to the present invention for achieving the object as described above, in the method for manufacturing a hot rolled steel sheet, comprising the steps of the composition of the hot rolled steel sheet, and the step of adjusting the heat treatment temperature of the hot rolled bar that is the raw material of the hot rolled steel sheet, the composition 0.04 to 0.06 wt% C, 0.2 to 1.0 wt% Mn, 0.025 wt% or less Si, 0.008 wt% or less S, 0.1 wt% or less Cr, 0.2 wt% or less Ni, 0.4 wt% or less Cu, 0.001 to 0.04 wt% Sn, 0.001 to 0.012 wt% Pb, 0.04 to 0.08 wt% acid value Al, 150 ppm or less N, 0.0002 to 0.008 wt% Ca, balance Fe and other impurities In the step of adjusting the temperature, the first and second hot rolled bars are heated 40 to 60 ° C. higher than the central part in the heating table, and the coil box maintains the ambient temperature at 1020 ° C. or higher at the time of post rolling. After rolling over 850 ℃ to produce hot rolled steel sheet, the coil at the rear end is 20 ℃ higher than the central part. Provided is a method for producing a hot rolled steel sheet having a small material deviation in the front and rear ends of the hot rolled steel sheet.

In the following, with reference to the accompanying drawings, a preferred embodiment of a method for producing a hot rolled steel sheet with less material deviation of the front and rear ends of the hot rolled steel sheet according to the present invention will be described in detail.

In the drawings, Figure 1 is a schematic diagram showing the induction heater of the general mini-mill to the post-roller entrance,

2 is a block diagram showing a calculation procedure of a temperature drop amount as a hot rolled bar is rolled into a hot rolled steel sheet according to an embodiment of the present invention.

The composition of steel sheet and heating temperature are important for the production of hot rolled steel sheet with low material deviation of wire end of hot rolled steel sheet.

First, the composition components of the steel sheet used in the production of hot rolled steel sheet with a small material deviation of the front and rear ends of the hot rolled steel sheet will be described in detail.

EXAMPLE

The hot rolled bars produced by continuous casting of the composition as shown in Table 1 were pre-rolled, the heating in the inductive heater and the temperature from the inductive heater to the post-roller were managed under the conditions of Table 2, and then the hot-rolled bar was Rolled to produce a hot rolled steel sheet.

The T part is the front end of the hot rolled bar, the M part is the center part, and the B part is the rear end part. In addition, TS is tensile strength, El is elongation, I / H represents an inductive heater, and data of part T and data of part B show deviation compared with data of M part.

The hot rolled bar 1 of the composition as shown in Table 1 measures the temperature in the entry thermometer (5) of the inductive heater 13, and heated in the inductive heater 13 to the target temperature, the exit thermometer (15) Measure the heated temperature. The hot rolled bar passed through the inductive heater 13 passes through an acceleration 17 having an acceleration function to secure a preparation time for going to the coiler 20.

The hot rolled bar 1 passing through the accelerator 17 proceeds to the coiler 20 in the state exposed to the air. The hot rolled bar 1 arriving at the coiler 20 is coiled. When coiling, the outer diameter of the hot rolled coil bar is heat transfer by radiation according to the air temperature, and in the case of the hot rolled coil bar 11 coiled more than one turn, except for the inner and outer parts of the hot rolled coil bar 11 Since it is in contact with the liver, heat transfer by tropical flow is achieved.

The coiled hot rolled coil bar 11 is seated in the holding furnace 22 through the transfer device. The holding furnace 22 is a place for storing a maximum of six coils for 60 minutes so that when an abnormality occurs in any one process between the continuous casting process and the post-rolling process.

The hot rolled coil bar 11 of the holding furnace 22 is transferred to the uncoiler 24 and is unwound by the uncoiler 24.

The rolling temperature of the post-roller 30 is set by measuring the temperature of the hot-rolled bar 1 by the entry thermometer 25 of the after-roller 30. The hot rolled bar 1 unrolled from the uncoiler 24 is formed of a hot rolled steel sheet 41 through a descaler 27 and a post-roller 30, and cooled by a water cooling table 28 to coiler of the hot rolled steel sheet ( Coiled to 29). As a result, the hot rolled bar 1 is made of a hot rolled steel sheet 41.

Next, the process of calculating the temperature change of the hot rolled bar 1 from the inductive heater 13 to the post-roller 30 will be described.

2 is a block diagram showing a calculation procedure of the temperature drop while the hot rolled bar is rolled into a hot rolled steel sheet according to an embodiment of the present invention.

The hot rolled bar which is finished rolling in the linear rolling mill is heated to the inductive target temperature in the inductive heater, and the surface temperature is measured at the inductive heater exit side (S1).

The inductive heater has a nonuniform temperature distribution in the thickness direction because of its rapid heating on its surface. Thus, in consideration of the surface heating degree of the hot rolled bar of the inductive heater, the thickness distribution in the thickness direction of the hot rolled bar is simulated using the finite difference method.

Heat applied in the accelerator is transferred to the surface of the hot rolled bar by radiation and convection, and heat is transferred by heat conduction inside the hot rolled bar.

In general, the atmospheric temperature in the accelerator is a high temperature of 1000 ℃ or more, at this time, considering the convection and radiation at the same time the heat flux on the surface is as follows.

q = Aat (T _S -T _O )

at = a + εδ (T _S ² + T _O ² ) ⋅ (T _S + T _O )

q: heat flux (Kcal / m ² · hr)

αt: Heat transfer coefficient considering radiation and convection

A: Area (m ² )

TS: Surface temperature of hot rolled bar

To: Atmosphere temperature in contact with the surface of hot rolled bar

ε: emissivity (0 ≤ ε ≤ 1)

ο: stefan-Boltzman constant (5.57 x 10-8 W / m ² K ⁴ )

Heat transfer over time is calculated with the equation

k: thermal conductivity (W / hrmK)

ρ: density (kg / m ³ )

Cp: Specific Heat (W / kgK)

The passage time in the accelerator is calculated by the progress speed of the hot rolled bar and the length of the accelerator, and the temperature distribution in the thickness direction of the hot rolled bar is calculated in consideration of the ambient temperature (S2).

The temperature drop to the accelerator and the coiler is calculated in the same manner as in the accelerator (S3). However, the atmospheric temperature at this time is different from the high temperature conditions of the accelerator because the hot rolled bar is exposed to the atmosphere.

On the other hand, the hot rolled bar is coiled in the coiler through the acceleration. Since the temperature drop calculation is coiled circularly in the coiling step, the thermal analysis model and analysis conditions change.

When the coiling starts, both surfaces of the hot rolled bar are heat-transferd by radiation and convection, but when two or more layers are wound, the inner and outer parts of the hot-rolled coil bar are heat-transferd by radiation and convection. The surface is heat transfer by convection and heat conduction.

Thus, equivalent heat transfer coefficients are introduced, taking into account convection and heat transfer.

The temperature drop in the coiling step is first calculated the length of the hot rolled bar coiled in the coiler (S4), the time when coiling (S5), considering the ambient temperature and the coiled shape factors Calculate the amount of temperature drop when coiling (S6).

The hot rolled coil bar coiled to the coiler is maintained in the holding furnace for up to 60 minutes, at which time, the temperature drop amount calculation is calculated in the same manner as the temperature drop amount calculation at the completion of the coiling (S7).

The temperature drop of the hot rolled coil bar in the uncoiler is calculated as opposed to when coiling (S8). However, due to the short uncoiling time, the effect on temperature is small, and the temperature drop from the uncoiler to the entrance thermometer of the post-mill is measured (S9).

And it determines the initial setpoint temperature of the after-roller by a thermometer installed before the after-roller (S10). According to the above calculation method, the temperature drop from the induction heater exit temperature to the entrance temperature of the after-roller is calculated to predict the temperature distribution from the front end to the rear end of the hot rolling bar.

As described in detail above, by uniformizing the temperature distribution of the front end, the rear end and the central portion of the hot rolled steel sheet of the present invention, there is an advantage that the material of the hot rolled steel sheet can be made uniform.

In order to confirm the above advantages, the hot rolled bar having the compositional components of Table 1 was managed under the temperature conditions as shown in Table 2, and then the hot rolled steel sheet manufactured through the post-rolling process was sampled at the 3m points and the center of the front and rear ends, respectively. Tensile strength and elongation were measured.

In the steel having the composition component of Table 1, the tensile strength was measured within 20N / mm ² , the elongation is within 3%. In the comparative steel, the tensile strength is 30 to 50 N / mm ² and the elongation is less than 5%. Therefore, it can be seen that the variation in tensile strength and the variation in elongation decrease.

Although the technical concept of the method for manufacturing a hot rolled steel sheet having a low material deviation at the front and rear ends of the hot rolled steel sheet according to the present invention has been described with the accompanying drawings, this is illustrative of the best embodiments of the present invention and the present invention is limited. It is not. In addition, it is obvious that any person skilled in the art can make various modifications and imitations without departing from the scope of the technical idea of the present invention.

Claims (1)

In the hot rolled steel sheet manufacturing method, Comprising the composition of the hot rolled steel sheet, and the step of adjusting the heat treatment temperature of the hot rolled bar which is the raw material of the hot rolled steel sheet, The ingredient composition step is 0.04 to 0.06wt% C, 0.2% to 1.0wt% Mn, 0.025wt% or less Si, 0.008wt% or less S, 0.1wt% or less Cr, 0.2wt% or less Ni, 0.4wt% or less Cu, 0.001-0.04wt% Sn, 0.001-0.012wt% Pb, 0.04-0.08wt% acid value Al, 150ppm or less N, 0.0002-0.008wt% Ca, balance Fe and The composition of the steel with other impurities, The step of adjusting the temperature is to heat the first rolled hot-rolled bar 40 ~ 60 ℃ higher than the center portion in the heating table in the heating zone, maintain the ambient temperature of the coil box at 1020 ℃ or more, the rolling temperature at the time of post-rolling 850 ℃ or more After manufacturing the hot-rolled steel sheet by rolling in the coil, the method of manufacturing a hot-rolled steel sheet having a small material deviation of the front and rear ends of the hot-rolled steel sheet, characterized in that the coil is coiled in a state where the front and rear ends 20 ° C or more higher than the center portion.