JPH06104853B2 - Tight-scale steel sheet manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a method for producing a tight scale steel sheet suitable as a material for producing a steel frame building material, iron furniture, or automobile parts.

<Prior art> In the above-mentioned applications, with the goal of expanding the sales of products, aiming to reduce manufacturing costs, study to change the material from cold-rolled steel sheet to hot-rolled steel sheet and press working of hot-rolled steel sheet. Investigations such as prevention of contamination due to scale peeling in the process are continuing.

A proposal for responding to this is disclosed in JP-A-61-194112. This proposal is to cast and solidify steel containing C: 0.03 to 0.25% P ≤ 0.025% Si: 0.04 to 0.5% S ≤ 0.01% Mn: 0.3 to 2% Al ≤ 0.08% by weight, and then set the Ar ₃ point temperature. After hot rolling at a temperature of + 50 ° C or less, water cooling at a cooling rate of 40 ° C / sec or more is started within 5 seconds, and hot rolling having a scale with a winding thickness of 8 μm or less at a temperature of 500 ° C or less and 300 ° C or more It is a method of manufacturing a steel sheet.

<Problems to be Solved by the Invention> Since the above-mentioned proposal severely limits the hot rolling condition and the cold rolling condition as described above, the workability is poor, and the scale thickness is 8 μm or less and the 90 ° bending score ( Radius R = Plate thickness x 1.5
The punch was pressed and the steel plate piece bent at 90 ° was bent and the tape was attached to the outer surface and then peeled off to obtain the scale peeling area ratio (%), which was divided into 9 categories and ranked as scores) Is 5 or less, that is, Gr5 or less (indicating 5 or less of the 90 ° bending score), but in the length direction and width direction of the steel sheet, it is evaluated as a tight scale steel sheet that is currently preferred in this industrial field. The actual situation is that a 90 ° bending score of 3 or less has not been obtained.

It is an object of the present invention to provide a method for producing a steel sheet having a stable tight scale and a 90% bending score of 3 or less in the length direction and the width direction of the steel sheet, which is stable and with a high yield.

<Means for Solving the Problems> In order to solve the above problems, the present invention is (1) casting solidification of a steel for hot-rolled steel sheet containing Si: 0.02 to 0.2% Cr: 0.02 to 0.2% by weight. After that, the basic means is to start rolling at a temperature of 1150 ° C. or higher and rolling reduction of 90% or higher at 1000 ° C. or lower, finish at 860 ° C. or lower, and wind at 500 ° C. or lower. After casting and solidifying the steel for hot-rolled steel sheet containing Si: 0.02 to 0.2% Cr: 0.02 to 0.2%, after soaking at 1150 ° C or more, rolling with a reduction rate of 90% or more is started at 1000 ° C or less and at 860 ° C or less. The second means is to finish the process and wind it to 500 ° C or lower, and then cool it to room temperature in a low oxygen atmosphere. (3) Hot rolled steel sheet containing Si: 0.02 to 0.2% Cr: 0.02 to 0.2% by weight. After casting and solidifying the steel for casting, after soaking at 1150 ° C or higher, rolling with a reduction rate of 90% or higher starts at 1000 ° C or lower, ends at 860 ° C or lower, and winds at 500 ° C or lower, and a speed of 0.5 ° C / min or higher To cool to room temperature As a third means, (4) after casting and solidifying a steel for hot-rolled steel sheet containing Si: 0.02 to 0.2% Cr: 0.02 to 0.2% by weight, and after soaking at 1150 ° C or more, a rolling reduction of 90% or more The fourth means is to start rolling at 1000 ° C or lower, finish it at 860 ° C or lower, wind it at 500 ° C or lower, and cool it to room temperature in a low oxygen atmosphere at a rate of 0.5 ° C / min or higher. .

In general, as the steel for hot rolled steel sheet used in the industrial application field of the present invention, for example, the steel for hot rolled steel sheet disclosed in the above-mentioned JP-A-61-194112, that is, C has the strength of the hot rolled steel sheet. A lower bound for maintaining, and 2
Set an upper limit to maintain good peelability of the next scale,
Has a lower limit for maintaining weldability, and an upper limit for producing a good product scale, and Mn has a lower limit for maintaining the strength required for the use of hot-rolled steel sheet, similar to C, for a good economy. Property, an upper limit for maintaining the adhesiveness of the product scale is set for both P and S, an upper limit for maintaining the adhesiveness of the product scale is set for Al, and Cr is good. The upper limit is set to obtain a good product scale on the basis of good economic efficiency, and in% by weight, C: 0.03 to 0.25% Mn: 0.2 to 2.% Si: 0.04 to 0.5% P ≦ 0.025% S ≦ 0.015% Cr There is a steel for hot-rolled steel sheet containing: ≤0.1% Al ≤0.08%.

The steel can also be used in the present invention, and in the present invention, Si is 0.
Up to 02% and up to 0.2% Cr can be used for the same reason as above. Further, there is no restriction on the hot rolling for adjusting the shape dimension before hot rolling which is limited by the present invention.

<Operation> In order to solve the above-mentioned problems, the present inventors repeated various experiments and studies using the sample steels having the chemical components shown in Table 1, and obtained the following findings.

The inventors of the present invention used the 90 ° bending score, which is used to evaluate that the steel has good tight scale properties in the industry and the technical field, to obtain various hot rolled steel materials currently provided on the market as non-targets. Was evaluated.

As a result, it was confirmed that the steel material that achieved a 90 ° bending score of 3 or less fulfilled the requirements for all applications in this field.

As a result of further study based on this fact, the present inventors have found that a steel plate that achieves a 90 ° bending score of 3 or less as shown in FIG. 1 has a product scale thickness of 6 μm or less. As shown in FIG. 2, it was found that the final hot rolling (finish hot rolling) has a reduction rate of 90% or more.

In this regard, the inventors of the present invention have clarified the causal relationship. When the rolling reduction is 90% or more, the surface area of the billet produced by the secondary scale is reduced, and the biting of the primary scale by hot rolling is reduced. Improving the adhesion condition of the third scale. The present invention has been found that the reduction amount with respect to the same plate thickness increases, the secondary scale is sufficiently peeled off in hot rolling, and the conditions for forming the tertiary scale are improved in the length direction and width direction of the steel sheet. It was found that one of the conditions to achieve the purpose of is the reduction ratio of hot rolling.

In the classification of the above scale, the scale that appears to be generated by heating is defined as the primary scale, and the scale that is generated and peeled after the primary scale peels after heating until the completion of hot rolling is called the secondary scale. The scale that was observed to be generated from the completion of hot rolling after peeling of the secondary scale to the winding was taken as the tertiary scale.

In the present experiment, as shown in FIG. 3, the inventors of the present invention showed a 90 ° bending score showing peelability of the tertiary scale when heated at a temperature of less than 1150 ° C. at the stage where the above-described primary scale is generated in the steel piece at room temperature. Was deteriorated by more than 3, and it was found that the 90 ° bending score becomes 3 or less and the object can be achieved when heated at 1150 ° C. or higher, and another condition for achieving the object of the present invention is heating temperature. I found that.

The inventors of the present invention have found that the relationship of FIG. 3 described above, the holding temperature of the slab following the casting shown in FIG. 4 and the interface Cr between the primary scale and the base steel.
Focusing on the fact that the relationship of the Cr concentration indicated by the amount (% by weight) is in good agreement, the results of further studies showed that the heating temperature or holding temperature, that is, rolling, was found from the findings in FIGS. 1, 3, and 4. When the surface temperature of the previous slab becomes 1150 ° C and the soaking temperature becomes 1150 ° C or higher, the Cr content at the interface of the primary scale base iron becomes 1% or less, and the concentration is reduced and the primary scale peels. Property is improved, which leads to the formation of a secondary scale with good peelability, resulting in the formation of a good steel plate surface condition with a thickness of 6 μm.
It was found that the soaking temperature is still another condition of the present invention because it produces a stable third-order scale, which is as thin as the following, and gives a good 90 ° bending score of 3 or less. is there.

The relationship shown in FIG. 5 was obtained from the results of rolling under these conditions.

FIG. 5 shows the relationship between the starting temperature of hot rolling and the scale thickness. The steel sheet for which good tertiary scale formation was seen from FIG. 5 can be produced even if variations in process capability are taken into consideration. It was found that the steel sheet was manufactured in a range where the hot rolling start temperature did not exceed 1000 ° C and the end temperature did not exceed 860 ° C.

If the winding temperature exceeds 500 ° C. as in the above-mentioned Japanese Patent Laid-Open No. 61-194112, the thickness of the tertiary scale is easily 6
It has been found that the object of the present invention cannot be achieved, since it is more than μm and the 90 ° bending score exceeds 3.

In addition, after the winding, 0.
If forced cooling is performed at 5 ° C / min or more, the third scale does not grow after winding, and it is desirable to reduce atmospheric oxygen instead of this cooling, and the same effect can be obtained. Then, it was found that the effect of preventing the growth of the tertiary scale is further enhanced, which is preferable.

The present invention is based on the above findings.

<Examples> Examples of the present invention are shown below together with comparative examples.

(1) Test steel (shown in Table 2) (2) Manufacturing conditions and results obtained (shown in Table 2) As is apparent from Table 2, Steel Nos. 1 to 6 of the invention examples are primary and
A steel sheet covered with a good tertiary scale was obtained which had a good peelability of the secondary scale, was thin, but had a uniform thickness, and was in good contact with the steel plate metal.

On the other hand, the steel No. 7 of the comparative example had a low soaking temperature (heating temperature), so the peelability of the produced primary scale was poor, and the thickness of the tertiary scale exceeded 6 μm, and the rating did not become 3 or less. Further, Steel No. 8 had a low rolling reduction in hot rolling, and the peelability of the secondary scale was poor, and a tertiary scale with poor adhesion was produced. Steel No. 9 has a too high hot rolling start temperature, and steel No. 8
Similarly, a 3rd scale with poor adhesion is generated, and steel number 10
The end temperature of hot rolling was high, and the winding temperature of steel No. 11 was too high, the scale thickness exceeded 6 μm, and the 90 ° bending score exceeded 3.

<Effects of the Invention> In the present invention, first, the soaking temperature of the steel slab is limited to generate the primary scale having good peelability, so that the primary scale easily peels at the start of rolling.

Next, since the start temperature and end temperature of hot rolling and the rolling reduction of hot rolling are limited, smoothing of the secondary scale generation surface and good peelability of the secondary scale are achieved, and it is thin and stable. In addition, the steel plate surface conditions for producing a good tertiary scale that adheres to the base steel are adjusted.

Next, since the hot-rolled steel strip is wound in a temperature range that suppresses / prevents the formation of the tertiary scale, a thin and homogeneous tertiary scale with excellent adhesion is formed on the obtained steel sheet, which causes the above-mentioned problems. Resolve in a grudge.

The steel sheet thus obtained always has a 90 ° bending score of 3 or less in both the length direction and the width direction, satisfies the demands of the field of the art, and brings a great effect to the field of the field.

[Brief description of drawings]

Fig. 1 shows the relationship between the tertiary scale and the 90 ° bending score, Fig. 2 shows the relationship between the rolling reduction of the hot rolling and the thickness of the tertiary scale, and Fig. 3 shows the 90 ° bending score of the steel slab and heating. Fig. 4 shows the relationship of temperature. Fig. 4 shows the retention temperature of the steel slab and the base steel of the steel slab to be retained.
FIG. 5 shows the relationship between the Cr concentration at the interface of the next scale and FIG. 5 shows the relationship between the starting temperature and the ending temperature of the hot rolling and the thickness of the tertiary scale.

Claims (4)

[Claims] 1. A steel for hot-rolled steel sheet containing Si: 0.02 to 0.2% Cr: 0.02 to 0.2% by weight, after being cast and solidified, rolled at a temperature of 1150 ° C. or higher and a rolling reduction of 90% or more to 1000 ° C. A method for producing a tight-scale steel sheet, which is characterized by starting below and ending below 860 ° C and winding up below 500 ° C. 2. A steel for hot-rolled steel sheet containing Si: 0.02 to 0.2% Cr: 0.02 to 0.2% in weight% is cast and solidified, and then rolled at a temperature of 1150 ° C. or higher and a rolling reduction of 90% or more at 1000 ° C. A method for producing a tight-scale steel sheet, which comprises starting at 860 ° C or lower, winding at 500 ° C or lower, and cooling to normal temperature in a low oxygen atmosphere after winding at 500 ° C or lower. 3. A steel for hot-rolled steel sheet containing Si: 0.02 to 0.2% Cr: 0.02 to 0.2% in weight% is cast and solidified, and then rolled at a temperature of 1150 ° C. or more and a rolling reduction of 90% or more to 1000 ° C. A method for producing a tight-scale steel sheet, which is characterized by starting at the following, ending at 860 ° C or less, winding at 500 ° C or less, and cooling to room temperature at a cooling rate of 0.5 ° C / min or more. 4. A steel for hot-rolled steel sheet containing Si: 0.02 to 0.2% Cr: 0.02 to 0.2% in weight% is cast and solidified, and then rolled at a temperature of 1150 ° C. or more and then rolled at a rolling reduction of 90% or more to 1000 ° C. A method for producing a tight-scale steel sheet, which comprises starting at 860 ° C. or lower, winding at 500 ° C. or lower, and then cooling to a normal temperature in a low oxygen atmosphere at a cooling rate of 0.5 ° C./min or higher.