JPH01242717A - Steel strip reduced in occurrence of plane strain at the time of heat treatment and its production - Google Patents

Abstract

PURPOSE:To manufacture a steel strip in which uniform hardenability is secured and the occurrence of plane strain due to hardening is reduced by previously providing a continuous geometric pattern to the surface to carry out surface roughening at the time of applying hardening to a high-carbon steel strip. CONSTITUTION:At the time of applying hardening treatment to a strip of a high-carbon steel containing >0.35wt.% C as a cutting tool material or a spring material, nicks consisting of a geometric pattern of circular, square, triangular, star, and other shapes are formed in the surface to 0.1-10mum depth at <=3mm spaces by using a grinding roll orthogonal to or forming an angle of inclination with the longitudinal direction of the continuously traveling steel strip, by which the surface is roughened. Since the steel-strip surface is formed into a frosted surface by the above roughening treatment and the whole surface is uniformly heated in a heating furnace, the occurrence of surface strain, such as sheet warpage, is reduced at the time of hardening, and as a result, a hardened material of high-carbon steel strip having flatness characteristic required of a cutting tool material and a spring material can be obtained in high yield.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a steel strip that has uniform hardenability and produces less plane strain during heat treatment, and a method for manufacturing the same. More specifically, the present invention roughens the surface of a high carbon steel strip by imparting a continuous geometric pattern to the surface to ensure more uniform hardenability and to minimize the occurrence of plane distortion during heat treatment. Regarding reduced steel strip and its manufacturing method.

BACKGROUND OF THE INVENTION Some types of high carbon steel strips are heat treated as hardened steel strips. They may be used as steel strips as they are, or after being slit, they may be subjected to heat treatment or other treatments.

After heat treatment, it is used as a cutting tool material or a spring material after undergoing a predetermined processing.

However, plane distortion such as temporary warpage occurs due to uneven quenching after heat treatment, resulting in a decrease in yield. In order to ensure the required dimensional accuracy as a blade material or as a spring material, it is a prerequisite that the material be properly flat. A high degree of flatness is required. Such plane distortion during heat treatment is caused by non-uniform heating, cooling, or volume variation due to transformation.

Conventionally, it has been thought that the occurrence of such quenching deformation itself cannot be prevented, and attempts have been made to suppress it as much as possible by using jig tempering, but this not only makes the process expensive and complicated, but also inevitably lowers the yield.

(Problems to be Solved by the Invention) Therefore, specifically, the object of the present invention is to provide a steel strip that is manufactured while being continuously conveyed to a heating furnace, and to provide a heat treatment FI!
To provide a steel strip that does not cause plane distortion such as plate warping even after being applied, and a method for manufacturing the same.

(Means for Solving the Problem) Therefore, the present inventors have made various studies to solve the problem, and although the reason is not necessarily clear, the inventors have created a continuous geometric pattern on the surface of the steel strip, and even a continuous geometric pattern on the surface of the steel strip. It was discovered that the above-mentioned temporary warping during quenching can be prevented by creating a cloudy surface by adding creases, leading to the discovery of the present invention.

It is true that there have been cases in the past where processing has been carried out to give unevenness as a dull finish, but such conventional processing is not used, for example, to remove surface flaws or to improve the sharpness of steel sheets. Usually, no further heat treatment is performed. Previously, there had been no attempt to provide a continuous geometric pattern in order to improve the uniformity of heat treatability and prevent the occurrence of plane distortion.

Therefore, the gist of the present invention is a steel strip that exhibits little plane distortion during heat treatment and is characterized by having a continuous Vt geometric pattern imparted to the surface through a surface roughening process.

According to one aspect of the present invention, the steel strip may further have overlapping striations that are inclined and/or parallel to the longitudinal direction of the steel strip.

Another aspect of the present invention is a method for producing a steel strip with little plane distortion during heat treatment, which includes a surface roughening step of providing a continuous geometric pattern on the surface of a continuously running steel strip by roll transfer.

In the surface roughening process for imparting the above-mentioned continuous geometric pattern, a polishing roll extending at a predetermined angle with respect to the longitudinal direction of the steel strip is further provided, and the polishing roll is brought into contact with the surface of the steel strip. inclined to the longitudinal direction of the steel strip and/or
Alternatively, there is provided a method for producing a steel strip with little plane distortion during heat treatment, further comprising the step of providing parallel streaks.

Here, the term "continuous geometric pattern" is intended to exclude non-continuous random patterns that do not have regular repeats. The continuous but random grooves and peaks can be thought of as lines.

In addition, the degree of surface roughness at this time is sufficient if the average depth of the surface irregularities and grooves of the grooves constituting the continuous Vt geometric pattern is, for example, 0.1 to 100 μm. The interval is 5
The amount may be 11 ml or less. If striations are provided in addition to the continuous geometric pattern, they may be substantially parallel to the longitudinal direction or may be inclined at an angle.

The angle of such inclined streaks with respect to the longitudinal direction of the steel strip is not particularly limited, but can be arbitrarily selected between 0 and 90 degrees. Preferably it is 30 to 60 degrees.

Furthermore, when such streaks are provided twice, that is, when they are provided in a meshed manner, the effect of improving hardenability is remarkable.

Many methods can be considered as means for imparting such a continuous geometric pattern, but transfer from a dull roll having a regular geometric pattern is a typical example from the viewpoint of ease of operation.

Such geometric patterns may have repeating unit shapes such as ◯, opening, △, ☆, ◎, etc., or may be used in combination. In short, it is sufficient if a cloudy surface can be obtained as a whole and the occurrence of plane distortion during heat treatment can be suppressed as much as possible.

Note that the continuous geometric pattern may be applied before or after the slitting process as long as it is before being conveyed to the heating furnace. Generally, it is preferable to apply it during cold working. Of course, the same applies to the case of streaks.

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

FIG. 1 is a typical process diagram of the method according to the present invention. In the illustrated example, a continuous geometric pattern is applied to a steel strip during cold rolling, and if necessary, skin pass rolling is performed before slitting. However, continuous geometric pattern imparting processing may be performed during temper rolling.

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 and heated and quenched. good.

As described above, according to the present invention, the steel strip is subjected to continuous geometric pattern imparting processing prior to being carried into the heating furnace, and as mentioned above, transfer using a double roll is a typical example. It will be done.

In addition, in order to form such a dull roll, laser treatment,
Transfer using another dull roll, etching, etc. are employed. These means are already well known and need not be explained in detail.

FIGS. 2(A) to 2(F) show several patterns of continuous geometric patterns on the surface of the steel strip described above with respective dimensions. The shapes of the illustrated examples are all concave portions, Corresponding protrusions are formed on the surface of the roll that transfers them. The formation of such a convex portion is performed in advance by laser processing or the like as described above.

When further scoring is desired, a polishing roll may be brought into contact with the surface of the steel strip.

When creating grooves that are inclined in the longitudinal direction of the steel strip, the circumferential 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 at 1 minute, the peripheral speed of the polishing roll is 30/min and by tilting the polishing roll with respect to the strip traveling direction, diagonal streaks can be imparted to the surface of the steel strip. When diagonal lines are provided to cross each other, it is sufficient to provide the above-mentioned line providing means twice, and there is no particular difficulty in manufacturing.

Although the degree of surface roughening is not particularly limited, the depth of the valleys of the continuous geometric pattern and the lines is generally 0.1 to 100 μm. If it is less than 0.1μ, no effective effect will be observed, while if it exceeds 100μ, the surface quality will deteriorate and the commercial value will be reduced, which is undesirable.For example, if it is about I~20μ, considered to be sufficient.

If the distribution of the constituent unit patterns of each continuous geometric pattern is too sparse, the original effect cannot be seen. Maximum pitch is 5m-
That's about it.

As mentioned above, the reason why hardenability is improved by the present invention,
In other words, the reason why the occurrence of plate warpage during hardening is prevented is not necessarily clear, but it can be inferred as follows.

That is, there is a subtle difference in gloss that cannot be visually determined on the bright surface as it is, and the emissivity is more non-uniform. On the other hand, roughening the surface rather makes them uniform, and this contributes to uniform heating during heat treatment. In addition, surface stress (e.g. thermal stress/contraction stress) is absorbed by the uneven portions and warping of the board is prevented.

In this way, the object of the present invention is steel strips, especially steel strips with a C content of 0.
It is a steel strip for hardening of 35% or more, more specifically a high carbon steel strip for hardening for cutlery or spring materials. Other materials include alloy steel (Cr-Mo steel) and heat treatable stainless steel such as martensitic stainless steel.

Next, the effects of the present invention will be explained in more detail with reference to Examples.

EXAMPLE A continuous geometric pattern shown in FIG. 2(C) was applied to both the front and back surfaces of a steel strip having the following composition during temper rolling according to the steps shown in FIG. 1. Growth rate of 1%! The roll transfer conditions for I-quality rolling were: roll diameter 600+*m;
The load was 500 tons and the plate speed was 000 a+/min.

After providing a continuous geometric pattern in this way, it was slitted, and each of the resulting slit strips was heat-treated. Continuing Vt
The dull rolls for imparting geometric patterns were produced by laser treatment and etching treatment under the conditions summarized in Table 2.

When inclined streaks were provided, the average streak interval was 0.8 μm, and the inclination angle with respect to the longitudinal direction of the steel strip was 0 degrees and 45 degrees.

For comparison, heat treatment was performed under similar conditions without surface roughening treatment of the steel strip, but in that case, temporary warping of 2 mm occurred for a width of 30 mm, resulting in approximately 7.8 mm. % defective rate was experienced.

However, in the examples in which the surface was roughened according to the present invention and then heat-treated, the results were summarized in Table 2, and the results were all 0.5% or less, and almost no plate warpage was observed.

The heat treatment conditions were as follows: heating at 650° C. for 60 seconds, cooling with oil, then heating at 380° C. for 15 seconds, and air cooling. Hardening was performed using a horizontal continuous annealing line with a line speed of 30 m/min.

Table 1 - Laser output crab 2 - Pulse frequency: 56 Ktlz Irradiation time per pulse: 13 μsec Tama Goten Z
Kugosara Note: Hydrochloric acid etching solution was used.

As explained above in Table 3, according to the present invention, the occurrence of sheet warpage after heat treatment, which has hitherto caused problems to those skilled in the art, can be avoided by simply roughening the surface. It can be almost completely prevented, and its practical effects are great.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the method according to the present invention; and FIGS. 2(A) to 2(F) are series Vf
, is a schematic explanatory diagram of a geometric pattern.

Claims (1)

[Scope of Claims] (1) A steel strip with little plane distortion during heat treatment, characterized in that a continuous geometric pattern is imparted to the surface by a surface roughening process. (2) The steel strip according to claim (1), characterized in that the steel strip is further provided with overlapping creases. (3) A method for manufacturing a steel strip that exhibits little plane distortion during heat treatment, including a surface roughening step in which a continuous geometric pattern is formed on the surface of a continuously running steel strip by roll transfer. (4) A polishing roll extending at a predetermined angle with respect to the longitudinal direction of the steel strip is provided, and by bringing the surface of the steel strip into contact with the polishing roll, the surface of the steel strip is polished at an angle inclined and/or parallel to the longitudinal direction of the steel strip. 4. The method for manufacturing a steel strip according to claim 3, further comprising the step of providing streaks.