KR101376564B1 - Method of manufacturing ferritic stainless steel - Google Patents

Abstract

A method of manufacturing ferritic stainless steel to prevent surface defects of high chromium ferritic stainless steel is introduced. The method of manufacturing ferritic stainless steel predicts the possibility of sticking defects of the material by considering the finishing rolling step of hot rolling the roughly rolled material by adjusting the initial rolling amount of the rough rolling, and considering the rough rolling exit temperature and the initial rolling amount of the rough rolling. A sticking defect predicting step, a sticking defect determining step of determining a sticking defect of the material by measuring the depth of the sticking defect when the sticking defect possibility of the material is predicted, and a sticking defect occurring in the material And a feedback step of feeding back a material to the finishing rolling step.
According to the method for manufacturing ferritic stainless steel according to the present invention, a sticking sensitivity index is derived in consideration of a constant correlation between the rough rolling side temperature of the material and the initial rolling amount of finishing rolling, and the sticking sensitivity index is derived from the derived sticking sensitivity index. Quick and accurate determination of king defects is possible.

Description

Manufacturing method of ferritic stainless steel {METHOD OF MANUFACTURING FERRITIC STAINLESS STEEL}

The present invention relates to a method for manufacturing ferritic stainless steel, and more specifically, to estimate the sticking defect of the material by calculating the sticking sensitivity index, and if it is determined that the sticking defect has occurred, feedback the process to the finishing rolling step. A method for producing ferritic stainless steel that prevents sticking defects.

In general, the hot rolling process is to roll a slab heated to 1,100 ~ 1,300 ℃ in a heating furnace to a thickness of 20 ~ 50mm in a rough rolling mill, rolled to 1.0 ~ 20.0mm in a finishing mill to produce a hot rolled sheet, then continuous It consists of a series of processes in which a cooler is cooled to a target temperature and the cooled hot rolled sheet is wound in a winder.

However, when hot-rolling ferritic stainless steel in a finishing mill shear stand (hereinafter referred to as "F1", "F2" and "F3"), a part of the pole surface layer of the ferritic stainless rolling material Sticks to the roll surface, causing sticking defects. Here, the sticking defect refers to a linear surface defect in which the base metal is repeatedly dropped and adhered upon contact between the base metal and the rolled roll on which the surface of the material is peeled off.

As a conventional technique for preventing such sticking defects, a "hot rolling method in which a sticking phenomenon is prevented (Patent Publication: 10-2000-0020552)" has been proposed.

In the case of this prior art, a mixed liquid comprising a particle size and water is sprayed between the F1 entrance and the F1-F2 stand, and fine scale particles are adsorbed on the surface of the rolling material by a roll of the finishing rolling stand to perform finishing rolling. .

However, in the case of the prior art, in order to prevent sticking defects, it is necessary to separately prepare a mixed liquid mixed with a scale and water, and add a process of spraying the prepared mixed liquid onto the surface of the rolled material to add adsorption. This increased and the addition of new processes resulted in lower product productivity.

Thus, there is a need for a method of reducing sticking defects of a material by adjusting only the rough rolling side temperature and the initial rolling rolling amount without additional material.

An object of the present invention to solve this problem, ferrite stainless steel to predict the possibility of sticking defects in consideration of the rough rolling temperature and the initial rolling initial rolling amount of the material and to maintain the depth of the sticking defect of the material below a certain depth It is to provide a method for manufacturing steel.

In order to achieve the above object, a method of manufacturing ferritic stainless steel according to the present invention is a method of manufacturing ferritic stainless steel for preventing surface defects of high chromium ferritic stainless steel, and hot-rolling the roughly rolled material by controlling the initial rolling amount. A sticking defect prediction step for estimating sticking defects of the material in consideration of the rough rolling step, the rough rolling exit temperature and the initial rolling amount of the rough rolling, and a sticking defect depth if the sticking defects are predicted. And a sticking defect determination step of measuring and determining a sticking defect of the material, and a feedback step of feeding back the material to the finishing rolling step when it is determined that a sticking defect is generated in the material.

Preferably, the sticking defect predicting step, by calculating the sticking sensitivity index of the following formula (1), if the sticking sensitivity index is less than 7.0, it is determined that there is a possible sticking defect of the material.

Sticking Sensitivity Index = 6.5 + 0.013 * RDT-0.79 * FRR ---------------------- (1)

(Here, RDT is rough rolling exit temperature and FRR is finishing rolling initial rolling amount.)

Preferably, in the sticking defect determining step, when the measured sticking defect depth exceeds 5 μm, it is determined that the sticking defect is generated in the material.

Preferably, the sticking defect predicting step, the sticking defect determining step, and the feedback step are implemented in a hot rolling correction step which is performed after the material which has passed the finishing rolling step is wound up in the winding machine by passing through the roller table.

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Preferably, the rough rolling exit temperature satisfies 1104 ~ 1138 ℃, the finishing rolling initial rolling amount satisfies 16.5 ~ 18.0mm.

In addition, the method of manufacturing ferritic stainless steel according to the present invention is a manufacturing method of ferritic stainless steel for preventing surface defects of high chromium ferritic stainless steel, and the finishing rolling step of hot-rolling the roughly rolled material by adjusting the initial rolling amount And a sticking defect predicting step of predicting a sticking defect possibility of the material in consideration of the rough rolling exit temperature and the initial rolling amount of finishing rolling, and feeding back the material to the finishing rolling step if a sticking defect possibility of the material is predicted. Including the feedback step, the sticking defect predicting step, by calculating the sticking sensitivity index of the following equation (1), if the sticking sensitivity index is 7.0 or less, there is a possibility of sticking defects of the material.

Sticking Sensitivity Index = 6.5 + 0.013 * RDT-0.79 * FRR ---------------------- (1)

(Here, RDT is rough rolling exit temperature and FRR is finishing rolling initial rolling amount.)

According to the present invention, the following remarkable effects can be realized.

First, the present invention has an advantage of preventing sticking defects by calculating a sticking sensitivity index, predicting a sticking defect potential of a material, measuring a sticking defect depth, and feeding back a process to the finishing rolling stage.

Second, the present invention derives the sticking sensitivity index from the constant correlation between the rough rolling temperature of the raw material and the initial rolling amount of filamentous rolling, and can determine quickly and accurately the possibility of sticking defects of the material through the derived sticking sensitivity index. There is an advantage that it can.

Third, the present invention can prevent the surface defect of the material by controlling the rough rolling exit temperature appropriately to suppress the generation of scale, maintain the initial rolling amount at the appropriate level to reduce the friction coefficient between the material and the roll surface There is an advantage.

1 is a block diagram showing a method of manufacturing a ferritic stainless steel according to the present invention.
Figure 2 is a graph showing the relationship between the rough rolling exit temperature and the sticking defect depth according to the manufacturing method of ferritic stainless steel according to the present invention.
3 is a graph showing the relationship between the initial rolling amount and the sticking defect depth in accordance with the manufacturing method of ferritic stainless steel according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a view showing a method for manufacturing a ferritic stainless steel according to the present invention.

As shown in Fig. 1, the method for manufacturing ferritic stainless steel according to the present invention predicts the possibility of sticking defects of the material, measures the sticking defect depth, and feeds back the process to the finishing rolling step, thereby preventing the sticking defects of the material. This should be kept within a certain depth.

In order to realize this, the ferrite stainless steel manufacturing method, after performing the finishing rolling step in the hot rolling process, calculates the sticking sensitivity index considering the rough rolling exit temperature and the initial rolling amount of finishing rolling to determine whether there is a possibility of sticking defects in the material. A predicting sticking defect prediction step is performed.

Here, a series of processes carried out before and after the finishing rolling step, for example, heating the slab in a heating furnace, rolling the slab in a rough rolling mill, cooling the rolled material in the finishing mill in a continuous cooler and winding it in a winder Since the processes are carried out, these processes are the same as the processes performed in the manufacturing process of the conventional ferritic stainless steel, and thus detailed description thereof will be omitted.

However, in this embodiment, after the raw material having the finishing rolling step is wound in the winding machine through the roller table, the hot rolling correction step is performed, in this hot rolling correction step, A king defect prediction step, a sticking defect determination step of determining whether a sticking defect of the material, and a feedback step of feeding back the material to the finishing rolling step are performed.

The sticking defect prediction step is a process of predicting the sticking defect possibility of the material using the sticking sensitivity index, and when the sticking sensitivity index is less than 7.0, the sticking defect is expected to occur.

Here, the sticking sensitivity index is a formula considering the correlation between the rough rolling exit temperature and the initial rolling amount of finishing rolling, the higher the rough rolling exit temperature, the better the sticking occurrence, and the lower the initial rolling amount, the sticking occurrence degree is higher. It is derived from the experimental result of being good.

Figure 2 is a graph showing the relationship between the rough rolling exit temperature and the sticking defect depth according to the manufacturing method of ferritic stainless steel according to the present invention, Figure 3 is the initial rolling amount and the stirrer rolling according to the manufacturing method of ferritic stainless steel according to the present invention It is a graph showing the king defect depth relationship.

For example, as shown in FIG. 2, when the crude rolling exit temperature drops below a predetermined temperature during the hot rolling process (1140 ° C. to 1080 ° C.), the surface brittle scale of the material becomes severe and the base structure and It has been confirmed that sticking occurs easily (0 → 60 μm) by direct contact with the roll surface, and the depth of occurrence also increases.

In addition, as shown in Figure 3, when the initial rolling amount of the finishing rolling increases at the same temperature (16mm → 21mm), the defect generation strength of the material is increased, eventually, the sticking defect generation depth of the material is confirmed to increase It became.

From the correlation between such a rolling exit temperature and the initial rolling initial rolling amount, the sticking sensitivity index of the following formula 1 is defined.

[Formula 1]

Sticking Sensitivity Index = 6.5 + 0.013 * RDT-0.79 * FRR

Here, RDT (Roughing Delivery Temperature) represents the rough rolling exit temperature, FRR (Finishing Rolling Reduction) represents the finishing rolling initial rolling amount which is the rolling amount of the finishing rolling F1 ~ F3 stand.

In particular, in order to secure the excellent surface quality of the stainless steel hot rolled product in terms of surface quality control, the steel grade is required to maintain the depth of the sticking defect is less than 5㎛, if the sticking sensitivity index is 7.0 or more, It can be expected to have excellent surface quality, and if the sticking sensitivity index is less than 7.0, the material can be expected to have poor surface quality due to sticking defects.

Hereinafter, the relationship between the sticking sensitivity index and the sticking defect depth will be confirmed through the following Example 1.

Example 1

In this embodiment, 445NF steel containing 21% of chromium was used, which was continuously cast into a slab of 220 mm thickness, maintained at a temperature of 1230 to 1280 ° C. in a heating furnace, and after 3 to 5 passes of rough rolling. The hot rolling was performed by adjusting the initial rolling amount according to the crude rolling temperature. Afterwards, annealing was performed on the hot-rolled material, and the depth of the defects was measured by collecting the sticking defect specimens from the annealing plant exit inspection panel.

As a result of the test, in this steel grade containing 20% or more of chromium, it was possible to make a condition that the sticking defect depth, which is a criterion of the steel sheet with excellent surface quality, satisfies 5 µm or less.

As shown in Table 1 below, when comparing the sticking sensitivity index and the sticking depth, it was confirmed that the sticking sensitivity index is less than 5㎛ when the sticking sensitivity index is 7.00 or more, and when the sticking sensitivity index is less than 7.00 It was confirmed that the king occurrence depth exceeded 5 µm. Particularly, when the ticking sensitivity index is 7.00 or more, the rough rolling exit temperature satisfies 1104 to 1138 ° C, and the initial rolling rolling amount satisfies 16.5 to 18.0 mm.

division Psalter Hot rolled
thickness RDT
(Cold rolling temperature) FRR
(Detail rolling initial rolling amount) Sticking
Sensitivity index Sticking
Depth of occurrence Invention river One 3.5 1110 17.6 7.03 4 탆 2 3.5 1138 16.9 7.94 2 탆 3 3.5 1104 16.5 7.82 2 탆 4 4.0 1136 18.0 7.05 5㎛ 5 3.5 1123 17.7 7.12 3 탆 6 4.0 1113 17.5 7.14 3 탆 Comparative steel One 4.0 1116 20.5 4.81 43㎛ 2 4.0 1135 19.3 6.01 30 μm 3 3.5 1101 17.7 6.83 11㎛ 4 3.5 1110 18.5 6.32 28 μm 5 3.5 1095 17.8 6.67 19 μm 6 3.5 1115 18.1 6.70 14 μm 7 4.0 1103 17.8 6.86 18 탆 8 3.5 1125 19.5 5.72 32 μm

On the other hand, in the sticking defect prediction step, if the sticking sensitivity index is calculated to be less than 7.00 and there is a possibility of sticking defects in the material, the sticking defect determination step is performed.

The sticking defect determination step determines the sticking defect of the material by measuring the sticking defect depth. In order to measure the sticking defect depth, a sticking defect measuring device can be used, and when the sticking defect depth is measured using this sticking defect measuring device, if the sticking occurrence depth is measured to exceed 5 m, It is determined that a sticking defect has occurred in the material, and a feedback step is performed.

In the feedback step, when it is determined that the sticking defect occurs in the material in the sticking defect determination step, the feedback is fed back to the above-described finishing rolling step. In the finishing rolling step, the rough rolling exit temperature RDT and the initial rolling rolling amount FRR are controlled so that the sticking sensitivity index is 7.00 or more.

In the above-described embodiment, after the finishing rolling step, the manufacturing method of the ferritic stainless steel including the sticking defect prediction step, the sticking defect determination step and the feedback step has been described. According to a modification, the present invention provides the finishing rolling step and the sticking method. It may be implemented including a defect prediction step and a feedback step.

In this modification, unlike the above-described embodiment, the feedback step is performed immediately after the sticking defect prediction step is performed.

In other words, after the hot-rolled material is hot-rolled by adjusting the initial rolling amount of finishing, the sticking sensitivity index is calculated, and if the sticking sensitivity index is 7.0 or less, it is predicted that there is a possibility of sticking defects in the material. Feedback to the rolling step.

In this way, if it is determined that there is a possibility of sticking defects in the material through the calculation of the sticking sensitivity index, it is possible to quickly process to prevent sticking defects in the material by directly feeding back to the finishing rolling step.

As described above, the present invention derives the sticking sensitivity index from a constant correlation between the rough rolling exit temperature of the material and the initial rolling amount of finishing rolling, and through the derived sticking sensitivity index, the possibility of sticking defects of the material can be quickly and By accurately controlling the rough rolling exit temperature, it is possible to suppress scale generation and to maintain the initial rolling amount at finishing level by reducing the friction coefficient between the material and the roll surface to prevent surface defects of the material. It can have an excellent advantage.

Although the present invention has been described in detail using the preferred embodiments, the scope of the present invention is not limited to the specific embodiments, and should be interpreted by the appended claims. It will also be appreciated that many modifications and variations will be apparent to those skilled in the art without departing from the scope of the present invention.

Claims (7)

As a method of manufacturing ferritic stainless steel for preventing surface defects of high chromium ferritic stainless steel,
A finishing rolling step of hot rolling the roughly rolled material by adjusting the initial rolling amount of the finishing roll;
A sticking defect predicting step of predicting a sticking defect possibility of the material in consideration of the rough rolling exit temperature and the initial rolling amount of finishing rolling;
A sticking defect determining step of determining a sticking defect of the material by measuring a sticking defect depth when a possibility of a sticking defect of the material is predicted; And
And a feedback step of feeding back the material to the finishing rolling step when it is determined that a sticking defect is generated in the material. The method according to claim 1,
The sticking defect predicting step, by calculating the sticking sensitivity index of the following formula (1), if the sticking sensitivity index is less than 7.0 it is determined that there is a possibility of sticking defects of the material, characterized in that the manufacturing method of ferritic stainless steel.
Sticking Sensitivity Index = 6.5 + 0.013 * RDT-0.79 * FRR ---------------------- (1)
(Here, RDT is rough rolling exit temperature and FRR is finishing rolling initial rolling amount.) The method according to claim 1,
The sticking defect determination step, the method of manufacturing a ferritic stainless steel, characterized in that it is determined that a sticking defect occurs in the material when the measured sticking defect depth exceeds 5㎛. delete The method according to claim 1,
The sticking defect prediction step, the sticking defect determination step and the feedback step, the ferrite stainless steel, characterized in that implemented in the hot rolling correction step is carried out after the material passed through the finishing rolling step is wound in the winding machine through the roller table Method of manufacturing steel. The method according to claim 2,
The rough rolling exit temperature satisfies 1104 ~ 1138 ℃, the finishing rolling initial rolling amount satisfies 16.5 ~ 18.0mm, characterized in that the manufacturing method of ferritic stainless steel. As a method of manufacturing ferritic stainless steel for preventing surface defects of high chromium ferritic stainless steel,
A finishing rolling step of hot rolling the roughly rolled material by adjusting the initial rolling amount of the finishing roll;
A sticking defect predicting step of predicting a sticking defect possibility of the material in consideration of the rough rolling exit temperature and the initial rolling amount of finishing rolling; And
And a feedback step of feeding back the material to the finishing rolling step when the possibility of sticking defect of the material is predicted.
The sticking defect predicting step, the method of manufacturing a ferritic stainless steel, characterized in that by calculating the sticking sensitivity index of the following formula (1) if the sticking sensitivity index is less than 7.0 there is a possibility of sticking defects of the material.
Sticking Sensitivity Index = 6.5 + 0.013 * RDT-0.79 * FRR ---------------------- (1)
(Here, RDT is rough rolling exit temperature and FRR is finishing rolling initial rolling amount.)

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