JPS61202703A - Manufacture of steel belt for power transmission - Google Patents

Abstract

PURPOSE:To manufacture the titled belt with high fatigue strength and less fatigue cracks by ring-roll rolling a ring stock obtained by cutting in round slices a pipe stock formed by butt welding both ends of a sheet stock rolled in one direction. CONSTITUTION:A pipe stock 13 is formed by mutually butt welding both ends of a sheet stock 12 obtained by cutting a strip 10, obtained by rolling a maraging steel, etc. in the arrow 11 direction. The direction of said butt welded part 14 is formed so that it is approximately parallel to the axial direction of pipe stock 13 and approximately perpendicular to the rolling direction of sheet stock 12. Next, the pipe stock 13 is cut in round slices at prescribed intervals in the pipe-axis direction into ring stocks 15. The ring stock 15 is homogenized by annealing and rolled successively by ring rolling as shown by an arrow mark 16, and then, subjected to solution heat treatment and aging treatment, etc. to obtain a steel belt for power transmission, less in the number of rolling cracks which causes fatigue cracks and excellent in fatigue strength.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method of manufacturing a power transmission steel belt used in continuously variable transmissions of automobiles, etc. The present invention relates to an improvement in a method of producing a tube material, cutting the tube material into ring shapes, and rolling the ring material with a ring roll.

(Prior Art) Steel belts for power transmission used in continuously variable transmissions of automobiles undergo repeated bending deformation during use.
Fatigue strength characteristics that can withstand such bending deformation stress are required, and high tensile strength steels such as maraging steel are generally used.

By the way, the production of this type of belt can be roughly divided into a method in which a ring material is made by cutting an extruded and drawn seamless steel pipe (seamless pipe) into rings, and this is produced by expanding and roll rolling (conventional example 1). ), as shown in FIG.
There is a method (Conventional Example 2) in which the ring material 4 is cut into rings at predetermined intervals in the tube axis direction, and the ring material 4 is rolled into ring rolls as shown by arrow B.

(Problems to be Solved by the Invention) Conventional Example 1 is proposed in, for example, Japanese Unexamined Patent Publication No. 56-119608. Because it requires a process to process, productivity is low and it is not suitable for mass production.

In addition, since there are no welds, it is expected that this method will be effective in ensuring stable fatigue strength, but in reality, the expected fatigue strength level and stability have not been achieved. be.

Conventional Example 2 has been proposed in, for example, JP-A-57-64489 and JP-A-58-119486, both of which are techniques for preventing a decrease in strength due to non-uniform structure of the weld, and therefore, The goal is to ensure the same strength as the base material, and in reality the fatigue strength is low and the variation in fatigue strength is large, and as with Conventional Example 1, cracks are likely to occur during ring rolling. Ta.

The present invention is basically an improvement on the technology of Conventional Example 2, and the starting point of a fatigue crank is a flaw on the belt surface.Although there are various forms of surface flaws, the starting point of the crank is a ring roll. We have learned from the results of fatigue tests and fracture surface observations that most of the cracks are caused by rolling cracks during rolling, and that rolling cracks occur around inclusions in a direction perpendicular to the circumferential direction of the belt. It was devised based on this.

(Means for Solving the Problems) The technical means taken by the present invention to solve the problems of the technology of Conventional Example 2 is to butt weld both ends of a thin plate material rolled in one direction to each other to form a pipe material. In this method, the pipe material is cut into rings at predetermined intervals in the pipe axis direction, and the ring material is rolled into a ring roll to manufacture a power transmission steel belt. The direction is approximately parallel to the axial direction and approximately perpendicular to the rolling direction of the thin plate material.

(Function) That is, during ring roll rolling, tensile bending stress is generated on the outer surface of the ring material, but the stress concentration around the inclusions at that time differs depending on the form of the inclusions.

When rod-shaped inclusions exist in a direction parallel to the rolling direction of ring roll rolling, the stress concentration factor is small and the occurrence of rolling cracks is small; however, when rod-shaped inclusions exist in a direction perpendicular to the rolling direction, the stress concentration factor becomes large. Cracks occur more frequently.

Therefore, rolling cracks, which are the starting point of fatigue cracks, can be prevented during rolling by making the extension direction of material inclusions before ring roll rolling substantially the same as the rolling direction of the ring roll.

(Example) An embodiment of the present invention will be described in detail with reference to FIG.

Reference numeral 10 denotes a strip plate, which is made of 18% Ni type maraging steel and is rolled in one direction as shown by arrow 11.

12 is II material, which is made by cutting the above-mentioned strip plate 10,
Both ends of this thin plate material 12 are butt welded to form a pipe material 13.
The reference numeral 14 indicates the direction of welding, that is, the welded portion.

Here, the welded portion 14 of the tube material 13 is substantially parallel to the tube axis direction and substantially perpendicular to the rolling direction 11 of the thin plate material 12.

15 is a ring material, which is made by cutting the tube material 13 at predetermined intervals in the tube axis direction, and this ring material I5 has a diameter of 80 mm.
Annealed for homogenization at temperatures above 0°C.

The ring material 15 is hung in a winding manner on a known ring roll rolling machine, and is subjected to ring roll rolling as shown by arrow 16, and then subjected to post-treatments such as solution treatment and aging treatment. It is.

Here, the chemical composition of maraging steel is as follows.

Next Next, conventional example 1 (using seamless pipe) and conventional example 2
(Using a welded pipe) and an embodiment of the present invention will be compared and explained.

In either case, the steel type is 18% Ni type maraging steel.

In conventional example 1, an extruded steel pipe with a diameter of 60w5 and a thickness of 3tm was spun and pressurized to a diameter of 61mm and a thickness of 0.6fi.
This was cut into rings and rolled into rings with a diameter of 183 mm.
An endless belt with a f-length of 0.0 and 0.2 n was used.

In Conventional Example 2 and the Example of the present invention, a tube material is made by butt welding both ends of a thin plate material having a thickness of 0.6 fl that is rolled in one direction, and this tube material is sliced into rings, annealed, and then subjected to a ring roll rolling machine. Diameter 183mm, thickness 0.2tm
I made it into an endless belt.

However, whereas in Conventional Example 2, the welding direction is parallel to the rolling direction, in the present invention, the welding direction is substantially parallel to the tube axis direction and substantially perpendicular to the rolling direction of the thin plate material.

The number of rolling cracks in Conventional Example 1.2 and the Example of the present invention is shown in FIG. 2, and the fatigue test results are shown in FIG. 3, respectively.

(Effects of the Invention) According to the present invention, when manufacturing a steel belt using a welded pipe by ring roll rolling, the direction of butt welding of the pipe material is substantially parallel to the pipe axis direction and substantially parallel to the rolling direction of the thin plate material. Since the directions are perpendicular to each other, even if tensile bending stress occurs on the outer surface of the ring material during ring roll rolling, the extension direction of the inclusions is almost the same as the ring roll rolling direction, so fatigue cranks can be prevented. The number of rolling cracks, which are the starting points, is significantly reduced, and the fatigue strength can also be improved, and its variation can be reduced.

[Brief explanation of drawings]

Figure 1 is a process explanatory diagram of an example of the present invention, Figure 2 is a comparison diagram showing the number of cracks generated during ring roll rolling between the present invention and two conventional examples, and Figure 3 is a comparison of fatigue test results. 4 are process explanatory diagrams of a conventional example. 12--Thin plate material, 13--Pipe material, 14--Welded part, 15
...-Ring material.

Claims (1)

[Claims] 1. Both ends of a thin plate material rolled in one direction are butt-welded to each other to make a pipe material, this pipe material is cut into rings at predetermined intervals in the pipe axis direction, and this ring material is rolled into ring rolls. A method of manufacturing a steel belt for power transmission, characterized in that the direction of butt welding of the tube material is substantially parallel to the tube axis direction and substantially orthogonal to the rolling direction of the thin plate material. manufacturing method.