JP2003062604A - Manufacturing method for pipe with superior punchability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for a pipe that improves smoothness of a sheared surface of a punched hole on the pipe for punch-forming, which is required for the pipe for punch-forming use. SOLUTION: In a process shown in Fig. 1, a hot rolled pipe, whose chemical composition conforms to the alloy steel for machine structural use, is rolled to a pipe through a cold pilgar mill at 0.5<=R.B.<=1.0, wherein R.B.: reduction balance is (wall thickness reduction ratio/outer diameter reduction ratio), and then softening annealed at 550 deg.C or higher and 650 deg.C or lower. After the process the pipe acquires hardness in the center of the wall thickness of no 190 HV or more and 250 HV or less, as well as a 2-phase microstructure consisting of ferrite and pearlite.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a steel pipe having a good punching property and excellent dimensional stability after punching in a steel pipe subjected to a large number of drillings. About. 2. Description of the Related Art In many cases, steel sheets for processing generally used for automobiles and home electric appliances are often formed with a large number of holes, and most of the holes are formed by punching. It is. Therefore, good punching workability is required. When punching a steel sheet for punching, there are problems such as punching properties (that is, shearing area ratio) and generation of burrs due to punching. Hitherto, there are techniques disclosed in Japanese Patent Application Laid-Open Nos. Hei 3-226526 and Hei 10-168544 for improving the punching property of a steel sheet for punching. According to the findings so far, in order to improve the punchability of the steel sheet for punching, the ductility of the material (120 to 17) is required.
0 HV) is necessary, and in order to obtain it, it is effective to soften the material by spheroidizing the carbide by annealing, and it is known that the punching property is good in the case of a spheroidized structure. ing. [0004] As for the steel pipe for punching, improvement of the punching workability is required similarly to the steel plate for punching.
Furthermore, the smoothness of the shear cut surface of the punched hole may be particularly required. However, in the case of a steel pipe for punching, when the above-described conditions for improving the punching property of a steel sheet are applied, the punching property is improved, but the shape of the steel pipe is deformed, so that the punching property of the steel pipe is reduced. It is not an effective way to improve. SUMMARY OF THE INVENTION As described above, the present invention provides a method of manufacturing a steel pipe for improving the smoothness of a shear cut surface of a punched hole required for a steel pipe for punching. In addition, by smoothing the shear cut surface of the punched hole, it is possible to omit the grinding or cutting of the shear cut surface of the punched hole of the punched product steel pipe, which has been conventionally performed. An object of the present invention is to provide a steel pipe capable of omitting the processing of the steel pipe. [0007] Means for solving the above-mentioned problems of the present invention is to provide a hot-rolled steel pipe made of an alloy steel for a machine structure using a cold pilger with a reduction balance R.P. B. Is [thickness reduction rate / outer diameter reduction rate],
0.5 ≦ R. B. After rolling to a steel pipe with ≦ 1.0, soft annealing is performed at 550 ° C. or more and 650 ° C. or less, and the hardness at the center of the thickness of the steel pipe is 190 HV or more and 250 HV or less, and a two-phase structure of ferrite structure + pearlite structure is exhibited. This is a method for manufacturing a steel pipe. FIG. 1 schematically shows the steps of the present invention. That is, the present invention uses the following means for obtaining a steel pipe having excellent punching properties. In the method for manufacturing a steel pipe according to the present invention, the hardness at the center of the thickness of the steel pipe is set to 190.
HV or more and 250 HV or less, and ferrite structure +
It has a two-phase structure of a pearlite structure, and by using the steel pipe, it becomes possible to manufacture a steel pipe punched product excellent in the smoothness of a shear cut surface of a punched hole by a punching process. In the method for manufacturing a steel pipe according to the present invention, the hardness of the central part of the thickness of the steel pipe is set to 190 HV or more and 250 H or more.
V or less, an ideal shear area ratio can be obtained by setting it to 190 HV or more,
It is possible to suppress a change in the shape of the steel pipe due to the punching of the steel pipe punched product. The hardness at the center of the wall thickness of the steel pipe is 25
By setting it to 0 HV or less, the shear surface ratio of the shear cut surface of the punched hole of the steel pipe punched product is increased, and the cut surface can have smoothness. FIG. 2 shows the shape of the shear cut surface of a punched hole punched from the inside. 2 (a) is a schematic view of a punched hole in a steel pipe, (b) is a side view of a cross section, (c) is a schematic front view of a cross section of (b), and 1 denotes a wholly. 2, 2 is a shear surface, 3 is a fractured surface, 4 is a wall thickness, and 5 is a punching direction. Further, by forming a two-phase structure of a ferrite structure and a pearlite structure, the ratio of the shear surface 2 of the shear cut surface of the punched hole of the steel pipe punched product can be increased, and the cut surface can have smoothness. When the spheroidization of the structure progresses due to the annealing, the shear surface ratio of the shear cut surface of the punched hole of the steel pipe punched product decreases, and the smoothness deteriorates. In this case, the reduction balance R.D. B. Is defined as [thickness reduction rate / outer diameter reduction rate], 0.5 ≦ R. B. ≦ 1.0, but R.I. B. Is less than 0.5, the hardness is lower than a predetermined hardness when annealing is performed after processing because the processing rate is low. Also, R. B. Is 1.0 or more, the working ratio is high and exceeds a predetermined hardness. FIG. 1 is a process diagram of an embodiment of the present invention. For a rolled material having an alloy steel composition for machine structural use, a mother tube is formed by hot extrusion or assell rolling of Eugene Sejournet, annealed, and a cold-pilgered steel tube is obtained. At this time, the reduction balance of the steel pipe before and after cold pilger processing is reduced. B. Is defined as [thickness reduction rate / outer diameter reduction rate], 0.5 ≦ R. B. ≦ 1.0. Further, after cold pilger processing, annealing is performed at 550 ° C. or more and 650 ° C. or less, and the hardness is 190H.
A predetermined steel pipe having a microstructure of not less than V and not more than 250 HV and a two-phase structure of ferrite + pearlite is manufactured. EXAMPLES As typical compositions, C: 0.10 to 0.6
0%, Si: 0.5% or less, Mn: 1.0% or less, Cr and Mo if necessary, and the balance Fe A mother pipe having a size of φ60 mm × φ35 mm was manufactured by rolling, and subjected to softening annealing at 650 ° C. Thereafter, the mother pipe was subjected to cold pilger processing to have a diameter of 38.7 mm x 30 mm.
It was processed to a size of 4 mm. In this case, the reduction balance R. B. Is 0.51. 600 for the steel pipe
A predetermined steel pipe was obtained by performing annealing at ℃. The steel pipe obtained by the above manufacturing method is evaluated for punchability and dimensional stability by the following method. As a method for evaluating the punching property, a 10 mm × 5 mm hole punching process was continuously performed at equal intervals in the circumferential direction on the side surface of the steel pipe, and for each punched hole, the ratio of the shear surface to the shear cut surface was determined. The punching property was evaluated. Table 1 shows the results of the punching test of these steel pipes. In the evaluation of punching property, when the shear surface ratio was 50% or more,
Less than 50% was evaluated as x. As shown in Table 1, ferrite +
Has a pearlite structure and hardness of 190 HV or more and 250 HV
Only in the following cases, the shearing surface ratio of the punched cut was high and the punching property was good. [Table 1] As described above, the present invention provides excellent punching by selecting the reduction balance in cold pilger processing and the subsequent softening and annealing conditions for steel pipes having an alloy steel composition for machine structural use. This makes it possible to produce a steel pipe having an alloy steel composition for machine structural use, which has excellent industrial properties.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process diagram schematically showing a process for producing a steel pipe of the present invention. FIG. 2 is a view schematically showing a punched cut surface of a steel pipe;
(A) is a schematic perspective view, (b) is a side view of a punched section, and (c) is a front view of the punched section. [Description of Signs] 1 Whore 2 Shear surface 3 Fracture surface 4 Thickness 5 Punching direction

Claims (1)

Claims: 1. A hot-rolled steel pipe having an alloy steel composition for a machine structure is subjected to a reduction balance R.P. B. Is defined as [thickness reduction rate / outer diameter reduction rate], 0.5 ≦ R.
B. After rolling to steel pipe with ≦ 1.0,
A method for producing a steel pipe which is performed at a temperature of 50 ° C. or more and 650 ° C. or less, has a hardness of 190 HV or more and 250 HV or less, and has a two-phase structure of a ferrite structure and a pearlite structure and has excellent punchability.