Seamless steel pipe, hollow spring utilizing seamless steel pipe, and process for manufacturing the same

Inactive Publication Date: 2010-02-18
SHINKO METAL PROD +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0036]The seamless steel pipe of the present invention has smooth outer periphery surface and inner periphery surface, since it is produced by hot isostatic extrusion processing. Therefore, there can be eliminated most parts that would otherwise become origin for fracture when the seamless steel pipe as a spring is continuously extended and contracted, and as a result, the seamless steel pipe exhibits excellent endurance, such as a long fatigue life.
[0037]In addition, in the seamless steel pipe of the present invention, weight reduction by approximately 30 to 40% can be attained as compared with a solid-core steel material having the same diameter.
[0038]The hollow spring of the present invention is obtained first as a seamless steel pipe with enhanced material cleanliness and surface properties by extruding a heated spring steel material with fluid pressure; and then as a hollow body in a shape of a coil or a bar or a bar with curved part from the seamless spring steel pipe by applying a surface treatment to the seamless spring steel pipe so that the seamless spring steel pipe has compressive residual stress. In the resultant coiled spring, a material strength of the hollow spring becomes high, which in turn suppresses permanent transformation (permanent set) and fracture of the spring even under high stress, and design stress can be made higher, to thereby obtain both weight reduction effect and raise of fatigue strength.
[0039]Effects of the present invention when appli

Problems solved by technology

Demand for weight reduction is now increasing in the current situation where international awareness of global warming caused by emission from vehicle becomes stronger, and reduction of CO2 contained in exhaust gas became a big issue.
However, in the method for producing seamless steel pipe in which Mannesmann-piercing is performed, there is a limitation on a minimum diameter of the rolling.
Therefore, in the production method according to the above-mentioned patent document, there arises a problem that production efficiency becomes extremely poor.
Grinding may result in generation of flaws, especially in the inner periphery surface of the seamless steel pipe.
In addition, in the production method disclosed in the above-mentioned patent document, the seamless steel pipe is produced by Mannesmann-piercing, and when a material with high hardness is used, tools may frequently be damaged.
Therefore, there was

Method used

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  • Seamless steel pipe, hollow spring utilizing seamless steel pipe, and process for manufacturing the same
  • Seamless steel pipe, hollow spring utilizing seamless steel pipe, and process for manufacturing the same
  • Seamless steel pipe, hollow spring utilizing seamless steel pipe, and process for manufacturing the same

Examples

Experimental program
Comparison scheme
Effect test

example 1

Weight Reduction Effect

[0180]Table 2 shows a comparison between weight reduction effects of coiled spring. As shown in Table 2, coiled springs used were: a coiled spring (solid-core material) made of SiCr steel as solid-core material; a conventional hollow coiled springs (conventional hollow material) obtained using S45C or the like; and hollow coiled springs as example product made of SiCr steel or high-strength SiCrV steel, each having a coil inner diameter of φ 45 mm and an applied maximum load of 2750 N.

TABLE 2Coil inner diameter: φ 45 mmApplied maximum load: 2,750 NSolid-coreExample productmaterialConventionalhigh-strengthMaterial UsedSiCr steelhollow materialSiCr steelSiCrV steelHardness after quenchingHv545Hv440Hv545Hv580and temperingTS (MPa)1,8501,4801,8502,020Material diameter (mm)8.09.18.38.1Winding number5.467.15.755.39Thickness (mm)—2.2752.22.03Thickness ratio—25%26.5%25%Free height (mm)811028581Closed height (mm)41624541InnerOutside895716895972diameter-sideTS ratio of o...

example 2

[0186]Next, the seamless steel pipe and the method for producing the same according to the present invention will be explained with reference to Examples which meet requirements of the present invention and Comparative Examples which do not meet requirements of the present invention, with making a comparison therebetween.

[0187]For Test No. 1 to 9, first, cylindrical billets were made of KHV10N (manufactured by Kobe Steel Ltd.) as steel material. The billets were formed so as to have the outer diameter of 143 mm and the inner diameter of 52 mm. The billets were heated at 950 to 1400° C. as shown in Table 1. Each of the heated billets for Test No. 1 to 9 was subjected to hot isostatic extrusion processing using a hot isostatic extruder at a corresponding temperature (extrusion temperature), to thereby produce a seamless steel pipe. Subsequently, the seamless steel pipes of Test No. 1 to 9 were subjected to spheroidizing annealing processing at 680° C. for 16 hours, and Pilger mill rol...

example 3

[0200]Next, coiled springs were produced from: the seamless steel pipes which meet requirements of the present invention; the seamless steel pipe which do not meet requirements of the present invention; and a solid-core steel material. For each spring, a fatigue test was conducted. It should be noted that the steel materials are the same as in >.

[0201]First, seamless steel pipe was produced by hot isostatic extrusion at an extrusion temperature of 1,150° C., and then coiled springs (all hollowed product) of Test No. 10 and 11 each having an outer diameter of 76.0 mm, an inner diameter of 54.8 mm, a height of 153.5 mm, and a winding number of 6.76 were produced.

[0202]The coiled spring of Test No. 11 has surface flaw (artificial flaw corresponding to contiguous flaw), formed on the outer periphery surface and the inner periphery surface thereof.

[0203]The coiled spring of Test No. 11 was obtained by: forming a seamless steel pipe under the same conditions as those in Test No. 10; a sur...

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Abstract

There are provided: a seamless steel pipe formed from a cylindrical steel material billet through a hot isostatic extrusion step, wherein a depth of a contiguous flaw formed on an inner periphery surface and an outer periphery surface of the steel pipe is 50 μm or less; a hollow spring obtained by forming a hollow body in a shape of a coil or a bar or a bar with curved part from the seamless steel pipe made of spring steel and applying a surface treatment to the hollow body so that the hollow body has compressive residual stress; and a method for producing seamless steel pipe including: a billet molding step; a first heating step; a hot isostatic extrusion step; a second heating step; an extension step; a third heating step; and a pickling step.

Description

TECHNICAL FIELD[0001]The present invention relates to a cylindrical seamless steel pipe, to be used as a material for coiled spring and the like, and a method for producing the same.BACKGROUND ART[0002]Recently in automobile field, techniques of weight reduction have been developed: panels are more likely to be made of aluminum, and chassis and main bodies are improved to have high-tensile strength. Demand for weight reduction is now increasing in the current situation where international awareness of global warming caused by emission from vehicle becomes stronger, and reduction of CO2 contained in exhaust gas became a big issue.[0003]In the automobile field, techniques for reducing CO2 have been studied mainly towards the following two directions: a development of new power sources, such as hybrid engine, fuel cell motor system and battery motor system; and an improvement of existing engines.[0004]Major techniques for improving existing engines include “improvement of combustion me...

Claims

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Application Information

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IPC IPC(8): F16L9/00B21B47/00F16F1/06
CPCB21B1/42B21C23/007B21C23/08B21C23/085B21F3/02C21D9/08F16F1/18C22C38/34C22C38/46B21B19/04F16F1/04F16F1/042F16F1/06C22C38/04B21B21/00B21C1/22F16L9/02
Inventor TOYOTAKE, KOTAROIWAYA, KOJIMINAMI, TOMOYUKITAKAMURA, NORITOSHI
Owner SHINKO METAL PROD
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