JPS62240102A - Irregular section steel plate having excellent surface characteristic and its production - Google Patents

Abstract

PURPOSE:To obtain an irregular section steel plate having an excellent surface characteristic by specifying the respective contents of C, Si, Mn, P, S, and Al of the irregular section steel plate having the size ratio of the thickness difference to the pitch in the transverse direction within a prescribed range. CONSTITUTION:The irregular section steel plate is produced by using a billet consisting of, by weight, 0.05-0.60% C, 0.05-0.50% Si, 0.20-1.00% Mn, <=0.050% P, <=0.030% S, 0.01-0.10% Al, and the balance unavoidable impurities and Fe. Such irregular section steel sheet is produced by subjecting the above- mentioned billet heated to 1,100-1,250 deg.C to rough rolling, then to finish rolling until the size ratio (t1-t2)/p of the thickness difference (t1-t2) to the pitch p in the thickness direction is made within an about 1/1,000-1/50 range by using caliber rolls. The irregular section steel plate having the excellent surface characteristic is thereby produced. Such steel plate is applied to an automobile frame, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a steel plate with a modified cross section that does not cause surface flaws due to roll roughening, and a method for manufacturing the same.

(Prior Art) The present invention is directed to a steel plate with an irregular cross section, which is used for automobile frames and the like, and has irregularities in its thickness profile at large pitches in the width direction of the steel plate.

The present applicant previously filed Japanese Patent Application No. 128880/1988 (Japanese Patent Application Laid-Open No. 9911/1983) for a method of manufacturing using a caliber roll as the finishing roll of a Holatos IJ mill.

(Problems to be Solved by the Invention) During finish rolling, if the metal flow is large in the width direction of the steel sheet, seizure with the rolls occurs, resulting in rough skin of the rolls. occurs. In particular, the dimensional ratio of the plate thickness difference (tl-h) to the pitch in the plate width direction, which is determined by the degree to which the thickness of the thick part (1+) and the thickness of the thin part (tl) appear ( t
+ tz)/p is low, for example 1/1000 to 115
In the case of a steel plate with an irregular cross section of 0, surface flaws are generated on the steel plate due to the roughening of the roll surface.

This flaw poses a quality problem as a defect when the steel plate is exposed on the surface and is used, and a method for producing a modified cross-section steel plate that does not involve the occurrence of this flaw is desired. FIG. 1 is a cross-sectional view showing an example of a cross-sectional view in the width direction of a steel plate with a modified cross-section, which is the object of the present invention.

As a measure to prevent this flaw, we have repeatedly investigated combinations of steel plate profiles and rolling bus schedules that do not cause seizure, but we are constrained by the steel plate profile, and in order to meet the demands of various markets. I was hoping for a more fundamental solution.

(Means to Solve the Problem) The present invention provides a modified cross-section steel plate in which the size ratio of the plate thickness difference to the pitch in the plate width direction is 1/1 (JIJO ~ 1150), and the weight ratio O: 0.05 ~ 0.60~, si: o
, o 5~0.50X, Mn: 0.20~1.00
X.

P:≦O, (J50, S:60.030%, u:o
, t + i ~ 0.1 U%, remainder: unavoidable impurities and Fe, and a modified cross-section steel plate with a sharp surface texture, and a dimensional ratio of the thickness difference to the pitch in the width direction of 1/1000 ~ 1150, the weight ratio of O: 0.05 to 0.60 N,
Si: 0.05-0.50%, Mn: 0.2U-1
．． 00X, P:≦O, U30X, S:≦0.030.

Ai: 0.01~0.10 This is a method for producing a modified cross-section steel plate with a readily refined surface texture.

(Function) The present invention solves this problem by first specifying the components of the steel plate. That is, as a result of testing various changes in the composition system of the steel slab, it was found that by adding Si, which easily forms scales with a low melting point, roll roughness can be reduced, and the roughness can be transferred to the steel plate. There was nothing that could be done to prevent this. FIG. 2 shows the relationship between the amount of 8i added and the degree of surface flaws on the steel sheet.

The reasons behind the composition of the steel material according to the present invention will be explained.

In order to obtain mechanical strength in C, the lower limit is set to 0.05, and the upper limit is set to 0.6 depending on the stability of rolling using caliber rolls.
It was set to 0N.

81 C rough skin: Required at lower limit 0, oty to prevent A.

If it exceeds 0.050%, workability deteriorates, so the upper limit is set to 0.
．． It was set at 50%.

Mn requires a lower limit of 0.20% for hot workability, and 1.0%.
If it exceeds 0%, workability will deteriorate, so set the upper limit to 1.0 U.
I set it as X.

The upper limit of P was set to 0.050 to ensure weldability and toughness.

S is an element that worsens corrosion resistance, and the upper limit is 0.030
It was set as N.

A1 requires 0.01X to fully deoxidize, and 0.01X is necessary for sufficient deoxidation.
If it exceeds 10, oxide inclusions will increase and workability will deteriorate, so the upper limit was set at 0.1 U%.

Next, there is a manufacturing method of the present invention for stably manufacturing a container. Here, a steel slab having the above-mentioned components is manufactured by ingot-forming or continuous casting. This steel piece is 1100~1250
After heating to a temperature of 0.degree. C., the material is roughly rolled and then passed through a finishing mill equipped with caliber rolls to produce a modified cross-section steel sheet having a predetermined thickness distribution in the width direction.

The heating temperature of 1100°C is the lower limit of the temperature necessary for finish rolling without causing rough skin, and if it exceeds 1250°C, heating fuel and scale loss will increase, so it was set as the upper limit.

At this time, the occurrence of surface flaws on the steel plate due to roll surface roughness differs depending on the Sl content. This is thought to be due to the lubricating effect of a Fe0-8i02 compound having a low melting point of around 1200° C. that is generated on the surface of the steel sheet. With this method, the dimensional ratio of the plate thickness difference (tlt2) to the pitcher is 1/1 to 1
It becomes possible to roll steel plates with irregular cross sections up to 150 mm without damaging the surface properties.

(Example) Next, the present invention will be explained with reference to Examples.

The situation of surface flaws is shown when a modified cross-section steel plate was manufactured under the rolling conditions shown in Table 2 using test materials having the compositions of various components shown in Table 1.

Table 1 Composition of sample material (w t
) Table 2 Manufacturing conditions and surface flaw occurrence situation The surface flaw iQX of the present invention example has an area of occurrence of 0.3%, which is extremely small compared to the comparative material of 4.2 N and 10.6%, which is good.

(Effects of the Invention) As described above, the present invention provides an optimal lightweight mechanical structural material with few surface flaws.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram illustrating the dimensions of a steel plate with a modified cross section, and FIG. 2 is a diagram illustrating the relationship between the amount of Sl added and surface flaws. The relationship between the surface flaw rating and the surface flaw occurrence area is as follows. Surface flaw rating Surface flaw occurrence area

[0] → 0%/rI? [1] →
More than 0 and less than 1.0 [2] → More than 1.0 and less than 20 [3] → More than 2.0 and less than 5.0 [4] → More than 5.0 Agent Patent attorney Masaaki Akizawa and 1 other person

Claims (2)

[Claims] (1) The size ratio of the plate thickness difference to the pitch in the plate width direction is 1/
1000 to 1/50, the weight ratio of C: 0.05 to 0.60%, Si: 0.05 to 0.50%, Mn: 0.20 to 1.00%, P: ≦0. 050%, S: ≦0.030%, Al: 0.01 to 0.10%, and the remainder: unavoidable impurities and Fe. (2) The size ratio of the plate thickness difference to the pitch in the plate width direction is 1/
1000 to 1/50, the weight ratio of C: 0.05 to 0.60%, Si: 0.05 to 0.50%, Mn: 0.20 to 1.00%. , P: ≦0.050%, S: ≦0.030%, Al: 0.01 to 0.10%, balance: unavoidable impurities and Fe A steel billet was heated to a temperature of 1100 to 1250°C and then rough rolled. A method for producing a steel plate with an irregular cross section with excellent surface texture, characterized in that the plate thickness is differentiated by finish rolling using a caliber roll.