JPH0660351B2 - Heat treatment method for steel strip - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heat treatment method for a steel strip ensuring uniform hardenability. More specifically, the present invention relates to a quenching method for a high carbon steel strip for roughening the surface to ensure more uniform hardenability and preventing the occurrence of plane strain during heat treatment.

(Prior Art) Some types of high carbon steel strips are heat treated as hardened steel strips. They are subjected to heat treatment or the like as they are as steel strips or after slitting.

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 premised that the plane is correct. 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 is considered that such quenching deformation itself cannot be prevented, and the jig temper is used to suppress it as much as possible. However, not only the process is expensive and complicated, but also the yield reduction is unavoidable.

(Problems to be Solved by the Invention) Therefore, specifically, an object of the present invention is a method for quenching a steel strip carried out while being continuously conveyed to a heating furnace, such as a plate warp even after quenching. It is an object of the present invention to provide a quenching method for steel strips in which no plane strain occurs.

(Means for Solving the Problem) Therefore, the inventors of the present invention have made various studies toward solving the problem, and although the reason is not always clear, the steel strip surface is roughened to form a cloudy surface. From that, know that the plate warp during quenching as described above is effectively prevented by cleaning the surface with an alkali or acid solution,
The present invention has been discovered.

Certainly, there have been examples of roughening the surface of the steel sheet, that is, processing to give streaks, and further processing to give unevenness as a dull finish, but such conventional processing is For example, it is only performed for removing surface flaws or for improving the sharpness of the steel sheet, and usually no heat treatment is performed thereafter. The idea of roughening the surface of the steel strip in order to improve the uniformity of the heat treatment property and prevent the occurrence of plane strain has never been considered. Furthermore, there was no idea to combine roughening and surface cleaning for such a purpose.

Therefore, the gist of the present invention is characterized in that the steel strip surface is subjected to a surface roughening treatment, and then a cleaning treatment with an alkali or an acid solution is performed in a cleaning line, and then the obtained steel strip is quenched. This is a quenching method for steel strips with little plane distortion during quenching.

Typical examples of the surface roughness imparting means include the above-described streak imparting process, discontinuous unevenness imparting process, further continuous geometric pattern imparting process, and a combination thereof. "Discontinuous unevenness" is a long groove.
The purpose is to eliminate mountain-shaped irregularities. Such grooves and mountains are considered to be lines. The "continuous geometric pattern" is intended to exclude a non-continuous random pattern that does not have regular repetition. Random grooves and mountains, which are continuous but random, are considered to be lines.

The degree of surface roughness at that time is, for example, the average depth of the surface irregularities and the troughs forming the continuous geometric pattern is 0.1
It is sufficient that the thickness is about 100 μm.

When streaks are provided, when streaks are provided in addition to discontinuous unevenness, and when streaks are provided in addition to continuous geometric patterns, the streaks may be substantially parallel to the longitudinal direction or inclined at an angle. May be. The angle of such a slanted line with respect to the longitudinal direction of the steel strip is not particularly limited, but 0
It can be arbitrarily selected between ~ 90 degrees. Preferably 30
~ 60 degrees. Further, when the double streaks are provided, that is, in the shaded manner, the effect of improving the hardenability is remarkable.

The streaking process may be performed by rotating or fixing a polishing pad (eg, “Scotch Bright”, a product name of Sumitomo 3M Co., Ltd.) or a metal brush while contacting the steel strip to give a streak.

There are many possible processes for imparting unevenness, but shot blasting, laser treatment, and
Typical examples are etching and electric discharge machining.

Although many means for providing a continuous geometric pattern are conceivable, a transfer from a dull roll having a regular geometric pattern is shown as a typical example because of the ease of operation. Such a geometric pattern may have a repeating unit shape such as ◯, □, Δ, ☆, and ⊚, or may be used in combination.

In short, in these surface roughening steps, a cloudy surface can be obtained as a whole, for example, the surface emissivity can be made as uniform as possible, and the occurrence of plane strain during quenching after cleaning can be prevented as much as possible. Of.

The roughening may be performed before or after the slit processing, as long as it is before the cleaning step performed before being conveyed to the heating furnace. Generally, it is preferably applied during cold working, temper rolling, or cleaning. Slitting is not always necessary, and in some cases, it may be used as it is in the form of strip steel.

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

FIG. 1 is a typical process chart of the method according to the present invention. In the illustrated example, the steel strip is cold-rolled and then surface-roughened during temper rolling. Although it is cleaned with an alkali or acid solution and slitted,
The surface may be roughened during cold rolling or may be used during cleaning.

In the case of a wide steel strip, the steel strip is slit into several narrow slit strips, which are then placed in a heating furnace for heating and quenching. You may go.

As described above, according to the present invention, the steel strip is subjected to the roughening process and the cleaning process before being carried into the heating furnace. As described above, as a typical example, a polishing pad process and a polishing roll process are performed. , Shot blasting, laser machining, electric discharge machining, transfer by dull roll and etching. These means are already well known,
Although it is not necessary to explain the details, the typical processing conditions used in the present invention are summarized as follows.

(1) Abrasive pad: For example, "Scotch Bright" (trade name of Sumitomo 3M Co., Ltd.) is fixed and pressed against the surface of the steel strip with a constant load, and the steel strip runs underneath to extend in the longitudinal direction of the steel strip. It gives a line. The trough depth can be adjusted by changing the load.

(2) Abrasive roll: This is a so-called grindstone or metal brush, which is pressed against the surface of the steel strip with a constant load as in the case of polishing and pad, but in this case, the polishing roll is held by a rotary type and the angle with respect to the longitudinal direction. By changing the length and extending it, it is possible to provide a line parallel to the longitudinal direction or inclined.

(3) Shot blast: Grit diameter: 60 mesh on impeller Rotation speed: 3000 rpm Rmax: 8 μm Mountain / number: 130 (4) Laser processing: Laser output: 2 KW Pulse frequency: 56 KHz Irradiation time per pulse: 13 μsec Laser processing May be applied directly to the surface of the steel strip or once applied to the surface of the roll to obtain a desired pattern and then transferred to the surface of the steel strip.

(5) Electric discharge machining: Peak current: 5A Pulse width: 125μsec Pause width: 65μsec (6) Transfer by dull roll: Regular geometrical or irregular pattern is formed on the roll surface in advance by laser machining or etching. By pressing this on the surface of the steel strip, the pattern is transferred to the surface of the steel strip.

(7) Etching treatment: Using hydrochloric acid etching liquid, immersing the material to be treated,
Corrodes only the required parts to produce the desired pattern.
This may be applied directly to the surface of the strip or may be applied to the surface of the roll to transfer the pattern to the surface of the strip.

2 (A) to (D) show some states of the above-mentioned surface roughening. Fig. 2 (A) shows an example in which lines are provided that are substantially parallel to the longitudinal direction. Fig. 2 (B) shows a mesh-like rough surface in which inclined lines are provided from two directions, and Fig. 2 (C) shows shot blasting. The obtained surface, and the same (D), show examples of continuous geometric patterns by the roll transfer method.

Such roughening is preferably performed on both the front and back surfaces of the steel strip.

When making diagonal lines, the steel strip is brought into contact with a polishing roll so that the peripheral speed of the polishing roll is much higher than the traveling speed of the steel strip. For example, when the traveling speed of the steel strip is 30 m / min. By setting the peripheral speed of the roll to 300 m / min and inclining the polishing roll with respect to the traveling direction of the steel strip, it is possible to impart diagonal lines to the surface of the steel strip. In the case where the diagonal lines are crossed with each other, the above-mentioned line providing means may be doubled, and no particular difficulty in manufacturing is observed.

Here, the degree of roughening of the surface is not particularly limited, but the depth of the continuous geometric pattern and the troughs at this time is generally 0.1 to 100 μm. If it is less than 0.1 μm, no effective action is observed, while if it exceeds 100 μm, the surface properties are deteriorated and the commercial value is reduced, which is not preferable. For example, it is considered to be sufficient if the thickness is about 1 to 20 μm.

If the distributions of the constituent units of the streaks, irregularities, and geometric patterns are too sparse, the original action and effect cannot be seen. The maximum pitch is 5 mm.

The steel strip thus roughened is then washed with an alkali or acid solution. Washing with an acid solution is preferred.

As described above, the reason why the present invention improves the hardenability,
In other words, the reason why the occurrence of plate warp during quenching is prevented is not always clear, but it can be presumed as follows.

That is, first, as the effect of roughening, there is a slight difference in gloss that cannot be visually judged with the bright surface as it is, and thereby the emissivity becomes non-uniform. On the other hand, the surface roughening rather makes them uniform, which contributes to uniform heating during the heat treatment. In addition, the surface stress (eg, thermal stress / contraction stress) is absorbed by the uneven portion, and the plate warp is prevented. Then, by adding a cleaning step with an alkali or an acid solution to the surface roughening step, deposits such as powder during the surface roughening process, the annealing color and various coloring defects are removed. By such a cleaning process, the uniformity during the heat treatment is further improved. In particular, when an acidic cleaning liquid is used, one kind of surface-dissolving action further enhances the above-mentioned action, and these effects synergistically show a remarkable improvement in hardenability. Be done.

The present invention is targeted at steel strips, particularly quenching steel strips having a C content of 0.35% or more, and more specifically, high-carbon steel strips for quenching for blades or springs. In addition, in terms of material, heat-treatable stainless steel such as alloy steel (Cr-Mo steel) and martensitic stainless steel can be mentioned.

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

Example According to the process shown in FIG. 1, a steel strip having the following composition was subjected to a surface roughening treatment shown in FIG. 3 during cold working, followed by annealing and temper rolling, and then roughening of the front and back surfaces. Surface treatment was performed, and then, cleaning with sodium metasilicate and then with hydrochloric acid was performed, and after slitting, the slit strip was quenched. The roughening treatment conditions were the conditions collectively shown in Table 2. When the slanted lines were provided, the average line spacing was 0.8 μm, and the inclination angle (θ) was 45 degrees.

For comparison, when the steel strip was not surface-roughened or washed, quenching was performed under the same conditions, but in that case, a 2 mm plate warp occurred for a width of 30 mm, and the like. Experienced a percent defective.

However, in the example of performing the surface roughening, the cleaning, and the heat treatment according to the present invention, as shown in the results in Table 2, in all cases, the defect rate was 0.5% or less and almost no plate warp was observed. There wasn't.

The quenching conditions are 650 ° C x 60 seconds and then oil cooling,
Then, it was heated at 380 ° C. for 15 seconds and air-cooled. Quenching was performed using a horizontal continuous quenching annealing line with a line speed of 30 m / min.

Table 2 Abrasive pad: "Scotch bright" manufactured by Sumitomo 3M was used to give parallel streaks.

Shot blasting: Grit diameter: 60 mesh on impeller Rotating speed: 3000 rpm Rmax: 8 μm Number of mountains / inch: 130 Transfer by dull roll: After applying a regular geometric pattern on the roll surface using hydrochloric acid etching solution, Transferred to the steel strip surface.

(Effects of the Invention) As described above, according to the present invention, the occurrence of plate warp after quenching, which has been troublesome to those skilled in the art, by a simple means of simply roughening the surface. Can be almost completely prevented, and its practical effect is great.

[Brief description of drawings]

FIG. 1 is a schematic process diagram showing the method according to the present invention; and FIGS. 2 (A) to (D) are schematic explanatory views of the surface state by the roughening treatment according to the present invention.

 ─────────────────────────────────────────────────── ─── 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 plane strain at the time of quenching, characterized in that the surface of a steel strip is roughened, then washed with an alkali or an acid solution in a washing line, and then the obtained steel strip is quenched. Quenching method for steel strips with less heat