JPH0660352B2 - Heat treatment method for steel strip - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention aims to prevent the occurrence of plane strain during heat treatment by ensuring a uniform quenching property on a steel strip quenching method, particularly on a high carbon steel strip surface. The present invention relates to a method of quenching a steel strip.

(Prior Art) Some types of high carbon steel strips are heat treated as hardened steel strips. They are processed as steel strips as they are or after slitting, followed by heat treatment.

After the heat treatment, it is used as a blade material or a spring material after being subjected to predetermined processing.

However, after the heat treatment, planar distortion such as plate warpage occurs due to uneven quenching, resulting in a decrease in yield. In order to secure the required dimensional accuracy as a blade material or a spring material, it is a premise to have a correct plane. A high degree of flatness is required. The plane strain during such heat treatment is caused by nonuniform heating, cooling, or volume change due to transformation.

Conventionally, it has been considered that such quenching deformation itself cannot be prevented, and the jig temper is used to suppress it as much as possible, but not only the process becomes expensive and complicated, but also the yield reduction is inevitable.

(Problems to be Solved by the Invention) Therefore, an object of the present invention is specifically a method of quenching while continuously transferring it to a heating furnace, in which planar strain such as a plate warp occurs even after quenching. It is an object of the present invention to provide a heat treatment method for a steel strip that does not occur.

(Means for Solving the Problem) Therefore, the inventors of the present invention have made various studies to solve such a problem, and although the reason and the like are completely unknown, the steel strip surface is streaked and clouded. Knowing that the surface will prevent the plate warp during quenching as described above,
The present invention has been found.

Certainly, there have been some examples in which streaking is performed on the surface of the steel sheet, but such conventional processing is performed only for removing surface flaws or improving the sharpness of the steel sheet. Usually, no heat treatment is performed thereafter. There has been no idea in the past to give the steel strip a streak in order to improve the uniformity of the heat treatment property and prevent the occurrence of plane strain.

Here, the gist of the present invention is a quenching method carried out by transporting a steel strip to a heat treatment furnace, wherein a scoring step is provided prior to the transportation to the heat treatment furnace, and the steel strip surface is provided in the scoring step. Is a surface roughness of a predetermined roughness to prevent the occurrence of plane strain during quenching.

As a means for imparting the above-mentioned surface roughness, as mentioned above, it is considered as a typical example to impart the lines, and the degree of the surface roughness at that time is, for example, the average depth of the troughs of 0.1 to 100 μm,
It is preferable to set the pitch to 1 to 20 μm and the pitch to 5 mm or less. Such roughening is preferably performed on both the front and back surfaces.

It should be noted that the lines may be provided before or after slitting, as long as they are conveyed to the heating furnace. The shape of the streaks may be distributed as uniformly as possible over the entire surface of the steel strip, and is not limited to a specific one. For example, the emissivity in the longitudinal direction and the width direction may be uniform as a specific reference. .

Further, slitting is not always necessary, and in some cases, it may be used as it is in the form of steel strip.

(Operation) Next, the present invention will be described in more detail with reference to the accompanying drawings.

FIG. 1 is a schematic process diagram of the method according to the present invention,
In the illustrated example, the steel strip is preliminarily scored and then slitted, but first, in the case of a wide steel strip, slitting the steel strip into several narrow slit strips Put in a heating furnace and heat.

As described above, according to the present invention, in the illustrated example, a polishing pad (eg, “Scotch bright”) is provided prior to loading into the heating furnace.
(Sumitomo 3M's product name) or a metal brush is rotated or fixed while contacting the steel strip to evenly give lines to the entire surface of the steel sheet. The state at this time is schematically shown in FIG. FIG. 2 (a) shows a fixed type striation imparting means, and FIG. 2 (b) shows a rotary striation imparting means.

The cross-sectional shape of the surface of the steel strip thus obtained is as schematically shown in FIG. In the case of the present invention, the degree of roughening of the surface of the steel strip is not particularly limited, but the depth of the troughs at this time is generally 0.1 to 100 μm. 0.1
If it is less than 100 μm, no effective effect of preventing surface strain is observed, while if it exceeds 100 μm, the surface properties are rather deteriorated and the commercial value is lowered, which is not preferable. For example, it is considered to be sufficient if the thickness is about 1 to 20 μm. The average spacing (pitch) of the lines is 5 mm or less. Even if it is roughened beyond this, the effect is not sufficient.

As described above, the present invention is targeted at steel strips, particularly, C content of 0.
It is a steel strip for quenching of 35% or more, and more specifically, it is a high carbon steel strip for quenching for blades or spring materials. In addition, heat treatment stainless steel such as alloy steel (Cr-Mo steel) and martensitic stainless steel can be mentioned from the viewpoint of material.

Next, the present invention will be described more specifically by way of examples.

Example In accordance with the process shown in FIG. 1, a high carbon steel strip having the following composition was subjected to slitting on the front and back sides in the state of the steel strip by the means shown in FIG. Hardened the slit strip. Average pitch of each line is 0.8
μm, and the valley depth was 1 μm.

As a result, when the surface roughening treatment of the steel strip is not performed,
Although a 2 mm plate warp occurred for a width of 30 mm and a yield decrease of about 7.8% was experienced, in the example of heat treatment after roughening according to the present invention, the defective rate was 0.8% and almost no plate warp occurred. I couldn't see it. A warp height of 0.5 mm or more in the width direction was determined to be defective.

In this example, the heat treatment conditions were heating at 650 ° C x 60 seconds, oil cooling, then heating at 380 ° C x 15 seconds, and air cooling. Such heat treatment was performed using a horizontal continuous quenching annealing line having a line speed of 30 m / min.

(Effect of the Invention) As described above, according to the present invention, quenching of a steel strip or a slit strip, which has been troubled by those skilled in the art in various ways by a simple means of simply roughening the surface. The subsequent generation of plate warp can be almost completely prevented, and its practical effect is great.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic process diagram showing a method according to the present invention; FIGS. 2 (a) and 2 (b) disclose fixed and rotary streak imparting means in the present invention, respectively. FIG. 3 and FIG. 3 are schematic enlarged explanatory views of the surface condition of the steel strip to which the score according to the present invention is applied.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shozo Muraoka 1850 Minato, Wakayama, Wakayama Sumitomo Metal Industries, Ltd. Wakayama Works (56) References JP 60-26816 (JP, B2)

Claims (1)

[Claims] 1. A quenching method carried out by carrying a steel strip to a heat treatment furnace, wherein a scoring step is provided prior to carrying it to the heat treatment furnace, and in the scoring step, the surface of the steel strip is roughened to a predetermined roughness. A steel strip quenching method characterized by preventing the occurrence of plane distortion during quenching.