JPH01242716A - Steel strip minimal 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 treatment is reduced by previously forming nicks in the surface to carry out surface roughening at the time of subjecting a high-carbon steel strip to hardening treatment. CONSTITUTION:At the time of applying hardening treatment to a strip of high- carbon steel containing >0.35wt.% C for use in cutting tool material and spring material, nicks running parallel to the longitudinal direction or diagonal or netlike nicks are formed in the surface of the steel strip to 0.1-100mum depth at spaces of <=5mm by using a grinding roll stretching in the direction perpendicular to the longitudinal direction of the continuously traveling steel strip or a grinding roll forming 30-90 deg. angle (theta) of gradient with the longitudinal direction of the steel strip or further using a grinding roll inclined at the same angle (Q1, Q2), by which the surface is roughened. Since the surface is not smooth, heat radiation rate at the surface is uniformized at the time of heating in a heating surface and the whole steel sheet is uniformly heated and, as a result, a heat-treated steel sheet free from plane strain, such as sheet warpage, at the time of hardening can be obtained in high yield.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a steel strip with little plane distortion during heat treatment and a method for manufacturing the same. More specifically, the present invention relates to a steel strip in which the surface of a high carbon steel strip is roughened to ensure more uniform hardenability and to prevent the occurrence of plane distortion during heat treatment, and a method for manufacturing the same. .

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 blade material or a spring material after undergoing a predetermined processing.

However, after heat treatment, plane distortion such as plate warpage due to uneven quenching occurs, resulting in a decrease in yield. In order to ensure the required dimensional accuracy as a cutter material or 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 using jig tempering, but the process is expensive. Not only did this lead to IM, but a decrease in yield was unavoidable.

(Problems to be Solved by the Invention) Therefore, 4. The purpose of the present invention is specifically to manufacture a steel strip while continuously conveying it to a heating furnace, and to solve the problem of plane distortion such as warpage even after heat treatment. It is an object of the present invention to provide a steel strip that does not generate carbon dioxide and a manufacturing method thereof.

(Means for solving the problem) Therefore, the present inventors have made various studies to solve the problem, and although the reason and other reasons are completely unknown, the steel strip surface is made with streaks to make it cloudy. It was discovered that the above-mentioned temporary warping during hardening can be prevented by forming a flat surface, and this led to the discovery of the present invention.There have been examples of crease processing being carried out in the past. , such conventional processing is only carried out, for example, to remove surface flaws or to improve the sharpness of the steel sheet, and usually no heat treatment is performed afterwards. The idea of adding creases to a steel strip in order to improve the uniformity of heat treatability and prevent the occurrence of plane distortion has never existed before.

Therefore, in the broadest sense, the gist of the present invention is to:
This steel strip is characterized by having a predetermined roughness imparted to the surface through a surface roughening process, and exhibits little plane distortion during heat treatment.

According to a specific embodiment of the present invention, the steel strip has streaks extending substantially parallel to the longitudinal direction of the steel strip and/or streaks that are inclined with respect to the longitudinal direction of the steel strip.

Furthermore, from another aspect, the present invention provides an abrasive roll and/or
Alternatively, by providing a polishing roll inclined at a predetermined angle with respect to the longitudinal direction of the steel strip, and bringing the surface of the steel strip into contact with the polishing roll, the polishing roll is substantially parallel to the longitudinal direction of the steel strip and/or
Alternatively, it is a method for producing a steel strip with little plane distortion during heat treatment, which is characterized by providing inclined creases.

In the above case, as a further alternative, at least two of the above-mentioned inclined abrasive rolls may be provided, each inclined in opposite directions with respect to the longitudinal direction of the steel strip.

Here, as a means for imparting surface roughness, as mentioned above, the provision of streaks is considered as a typical example, and the degree of surface roughness at that time is such that the average depth of the valleys of the streaks is, for example, 0.1 to 10
A level of 0μ is sufficient.

It is sufficient that the pitch is 5IllIl or less.

When diagonal streaks are provided around 1, the angle of the 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. When such inclined lines are provided twice, that is, when they are provided like a rope, the effect of preventing plane distortion during heat treatment is remarkable.

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

Furthermore, such score may be applied before being conveyed to the heating furnace, for example, before or after slitting. Note that, as described above, such slitting is not necessarily necessary and can be omitted depending on the purpose.

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

FIG. 1 is a schematic diagram of a method according to the present invention, comprising:
In the illustrated example, the steel strip is preliminarily scored and then slitted. That is, in the case of a wide steel strip, the steel strip is slit into several narrow slit strips, which are heated in a heating furnace and then quenched. Although the scoring may be performed at any stage before charging into the heating furnace, in the illustrated example, it is performed prior to slitting.

FIG. 2 schematically shows how the steel strip is scored. FIG. 2(a) shows means for imparting diagonal lines.

That is, before carrying the steel strip into the heating furnace, the circumferential speed of the polishing roll is made much higher than the advancing speed of the steel strip, in the illustrated example, the slit strip. By setting the circumferential speed of the roll to 300 m/min and tilting the polishing roll with respect to the traveling direction of the steel strip, diagonal streaks can be imparted to the surface of the steel strip. As already mentioned, the angle (θ) in the figure is between θ and 90 degrees, preferably between 30 and 60 degrees.

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. Figure 2 (B) is a schematic explanatory diagram showing such a double diagonal scoring means. In Figure 0, angles θ1 and θ2 are the same as the angles θ in Figure 2 (A) above. , both may be the same angle or different angles.

Although not shown, when creating parallel streaks on the steel strip, use a polishing pad (e.g. "Scotch Brite" Sumitomo 3-
Alternatively, a metal brush may be rotated or fixed while in contact with the surface of the steel strip to uniformly apply streaks to the entire surface of the steel strip.

The shape of the surface of the steel strip thus obtained is as schematically shown in FIG. Here, the degree of surface roughening is not particularly limited, but the depth of the grooves at this time is generally 0.1 to 100 μm.

If it is less than 0.1 .mu.m, no effective effect will be observed, and if it exceeds 100 .mu.m, the surface quality will deteriorate and the commercial value will be lowered, which is not preferable. It is considered that it is sufficient that the depth of the trough is preferably about 1 to 20 μm.

The upper limit of the interval (h) between each streak, that is, the pitch of the streaks, is about 5mm, and if there is too much, the action and effect will not be seen. When diagonal lines intersect, it may be a little rougher than this.

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.

In other words, there are subtle differences in gloss that cannot be determined visually on the bright surface, and! Therefore, the emissivity is non-uniform. On the other hand, roughening the surface rather makes them uniform, and this contributes to uniform heating during heat treatment. Additionally, surface stress (eg thermal stress/shrinkage stress) is absorbed by the uneven portions and temporary warping is prevented.

In this way, the object of the present invention is steel strips, especially steel strips with zero C content.
．． 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. In addition, in terms of materials, alloy m (eg Cr-Mom) and heat treatable stainless steel such as martensitic stainless steel may also be mentioned.

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

EXAMPLES According to the steps shown in FIG. 1, a high carbon steel strip having the following composition was subjected to score processing in the steel strip state, and then slitted, and each of the obtained slit strips was heat treated. Streaks were formed on the front and back surfaces using a polishing roll shown in FIGS. 2(a) and 2(b). The inclination angle of each streak was 45 degrees (
θ=θ, =02=45 degrees).

For comparison, heat treatment was performed under the same conditions without surface roughening treatment of the steel strip, but in that case, warping of 2 mm+ occurred for a width of 3 km, resulting in approximately 7.8 % yield loss was experienced.

However, in the examples in which the surface was roughened and then heat treated according to the present invention, as shown in Table 2, the defect rate was 0.8% or less in all cases, and almost no temporary warpage was observed. Ta.

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/hin.

Table 1 Table 2 (Effects of the Invention) As explained above, according to the present invention, by simply roughening the surface, it is possible to solve various problems that have hitherto caused problems to those skilled in the art. The occurrence of plate warpage after heat treatment can be almost completely prevented, which has a great practical effect.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the method according to the present invention; FIGS. FIG. 2 is a schematic enlarged explanatory view of the surface condition of a steel strip that has been subjected to such scoring. Outsourcer Sumitomo Metal Industries, Ltd.

Claims (6)

[Claims] (1) A steel strip with little plane distortion during heat treatment, characterized by having a predetermined roughness imparted to the surface through a surface roughening process. (2) The steel strip according to claim (1), characterized in that the steel strip is provided with streaks extending substantially parallel to the longitudinal direction of the steel strip. (3) The steel strip according to claim (1), characterized in that the steel strip is provided with streaks that are inclined with respect to the longitudinal direction of the steel strip. (4) A polishing roll extending perpendicular to the longitudinal direction of the continuously running steel strip is provided, and by bringing the surface of the steel strip into contact with the polishing roll, streaks are formed substantially parallel to the longitudinal direction of the steel strip. A method for manufacturing a steel strip with little plane distortion during heat treatment, characterized by providing a. (5) A polishing roll is provided that is inclined at a predetermined angle with respect to the longitudinal direction of the continuously running steel strip, and by bringing the surface of the steel strip into contact with the polishing roll, streaks are provided that are inclined with respect to the longitudinal direction of the steel strip. A manufacturing method for steel strips with minimal plane distortion during heat treatment. (6) The method for producing a steel strip according to claim (5), characterized in that at least two of the polishing rolls are provided and are arranged so as to be inclined in opposite directions with respect to the longitudinal direction of the steel strip.