JPH11286717A - Production of hot rolled steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve descaling easiness without the deterioration of the material quality and without a large-scale modification of apparatus by adding a compd. or alloy iron contg. P or S to the surface of a continuously cast slab, then subjecting this slab to heating and rolling. SOLUTION: The method of adding the P and the S preferably consists of incorporating an adhesive into the compd. or alloy iron contg. P or the S in the powder form and adhering the mixture to the slab surface. The addition of the P and the S by forming the compd. or alloy iron contg. P or the S to a roll form, then rolling this roll body on the surface of the slab kept at a temp. above its m.p. or heat-insulated from continuous casting is equally well. Further, the addition by pressing the compd. or alloy iron contg. P or the S which is a rectangular body, to the slab at the temp. above the m.p. of this rectangular body is equally well. For example, the thickness of the remaining scale decreases considerably if the compd. or the alloy steel is applied to a material contg. 1.2% Si and the material is subjected to descaling after heating. The P exists only near the base iron boundary in the scale layer and does not affect the material quality.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hot-rolled steel sheet, and more particularly to a method of heating and rolling after adding a compound containing P or S or ferromagnetic iron to a slab surface before heating. The present invention relates to a method for producing a hot-rolled steel sheet having good surface properties for performing descaling efficiently.

[0002]

2. Description of the Related Art When a slab manufactured by continuous casting or the like is heated and rolled, if rolling is performed with the scale remaining on the slab surface, surface defects due to the scale are generated in the rolled steel sheet. Conventionally, as a technique for efficiently removing scale generated in a slab, as described in JP-A-6-190433, a large amount of P is added to a slab component to improve the properties of the generated scale and to improve the peeling property. There are ways to improve. There is also a method of descaling with high collision pressure water (FIG. 1), as described in JP-A-7-222874. Note that reference numeral 1 shown in FIG.
Is a heating furnace, 2 is a finish rolling mill, 3 is a rough rolling mill, and 4 is a descaling device.

[0003]

However, in the above-mentioned conventional method, in the former technique, if a large amount of a component such as P or S is contained in steel, the brittleness during tempering deteriorates, so that not much can be added. On the other hand, in the latter technique, the pressure and flow rate of the descaling water must be made very high, and there is a problem that the equipment cost and the power cost are very high. The present invention improves the descaling properties of slabs, especially high-Si materials having poor descaling properties, without deteriorating the material and without extensive remodeling of the descaling device. A method for producing a steel sheet is provided.

[0004]

Means for Solving the Problems The present inventor uses P or S
By adding an element that forms a low-melting oxide in combination with Fe at the high-temperature base iron-scale interface, descaling in the molten state becomes possible, and difficult descaling like high Si material It has been found that the descaling property can be rationally improved with respect to the material.

The gist of the present invention is as follows. (1) In a method for producing a hot-rolled steel sheet by heating and rolling a continuous cast slab, a compound or alloy containing P or S is added to the surface of the continuous cast slab, and then heated and rolled. A method for producing a hot-rolled steel sheet having excellent descaling characteristics.

(2) The compound containing P or S or iron alloy is a powder, and the powder is sprayed on the surface of the slab, or an adhesive is mixed into the powder to form the slab. The method for producing a hot-rolled steel sheet having excellent descalability according to the above (1), wherein P or S is adhered to the surface. (FIG. 2) Reference numeral 5 shown in FIG. 2 is a slab.

(3) The compound containing P or S or iron alloy is a roll, and the roll is
The production of a hot-rolled steel sheet having excellent descalability according to the above (1), wherein P or S is added to the slab surface by rolling on the surface of the slab having a temperature equal to or higher than the melting point of the roll. Method. (Fig. 3)

(4) The compound or ferro-alloy containing P or S is a rectangular body, and the P or S is pressed by pressing the rectangular body against the surface of a slab having a temperature equal to or higher than the melting point of the rectangular body. The method for producing a hot-rolled steel sheet having excellent descalability according to the above (1), wherein the method is applied to a slab surface (FIG. 4).

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The present inventors performed a lab test to confirm the effect. In the test, FeP powder was sprayed on a sample containing 1.2% of Si, heated at 1200 ° C. for 2 hours in a heating furnace atmosphere, and then subjected to descaling equivalent to the actual operation. FIG. 5 shows the result. The evaluation was made based on the remaining scale thickness after deske. The FeP-sprayed material had good deskewability and reduced the remaining scale thickness to 1/10 or less.

[0010] The FeP sprayed material was heated in the same manner as in the deskew test, allowed to cool, and then subjected to skeletal analysis.
The result is shown in FIG. From this investigation, it was found that P was present only in the vicinity of the ground iron interface in the scale layer and had no effect on the material. In addition, as a method for adding P and S, a method of adding an adhesive to a powdery compound of a compound containing P and S or ferromagnetic iron and attaching it to the surface of the slab is more reliably added to the surface of the slab.

The above compound or ferroalloy may be added in the form of a roll, which is also heated to a temperature equal to or higher than the melting point of the roll, or rolled on a slab surface kept warm from continuous casting. Alternatively, the above compound or ferromagnetic iron, which is a rectangular body, may be added by pressing against a slab having a temperature equal to or higher than the melting point of the rectangular body.

[0012]

The embodiments will be described below in detail. 1.2
% Of carbon steel containing Si
The P powder was placed on the slab surface, heated to 1200 ° C., and subjected to hot rolling. For comparison, a portion to which FeP was not added was also prepared, and the descaling state and the surface properties of the hot coil were examined. As a result, it has been found that the descaling property is clearly improved in the portion coated with FeP. It was also found that the red scale was improved on the hot coil surface. FIG. 6 shows the result. L * value was measured by a color difference meter to evaluate redness. It became possible to reduce the red scale significantly from the result.

[0013]

According to the present invention, a method for producing a hot-rolled steel sheet having good surface properties without scale patterns and defects has been made possible.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a hot rolling line,

FIG. 2 is a diagram showing a method of attaching a powder body to a slab surface,

FIG. 3 is a diagram showing a method of adding a slab surface by a roll body.

FIG. 4 is a diagram showing a method of pressing a rectangular body against a slab surface;

FIG. 5 is a diagram showing the relationship between the presence or absence of FeP and the thickness of the remaining scale (lab test);

FIG. 6 is a diagram showing the relationship between the presence or absence of FeP and the actual coil surface L ^* value.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Finish rolling mill 3 Rough rolling mill 4 Deskering device 5 Slab

Claims (4)

[Claims] 1. A method for producing a hot-rolled steel sheet by heating and rolling a continuously cast slab, wherein a compound or alloy containing P or S is added to the surface of the continuous cast slab and then heated and rolled. A method for producing a hot-rolled steel sheet having excellent descaling properties. 2. A compound containing P or S or iron alloy is a powder, and the powder is sprayed on a slab surface.
Alternatively, an adhesive is mixed into the powder, and P or S is adhered to the surface of the slab.
A method for producing a hot-rolled steel sheet having excellent descaling properties. 3. The compound or ferro-alloy containing P or S is a roll, and the P or S is rolled on the surface of a slab at a temperature equal to or higher than the melting point of the roll. 2. The method for producing a hot-rolled steel sheet having excellent descaling properties according to claim 1, wherein slab is added to the slab surface. 4. A compound or ferro-alloy containing P or S is a rectangular body, and the P or S is pressed onto the surface of the slab having a temperature equal to or higher than the melting point of the rectangular body, thereby causing the P or S to have a slab surface. The method for producing a hot-rolled steel sheet having excellent descaling properties according to claim 1, wherein