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Steel member, hot-rolled steel sheet for said steel member and production methods therefor

A technology of hot-rolled steel plate and manufacturing method, which is applied in the field of improvement of fatigue life, hot-rolled steel plate, and welded steel pipe for coiled tubing, and can solve the problems that the fatigue resistance characteristics of the plastic strain area cannot be obtained, etc.

Active Publication Date: 2019-11-22
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

On the other hand, the longitudinal strain applied to the coiled tubing corresponds to the constant strain condition determined by the inner diameter of the coil and the gooseneck, and the contribution of the fatigue ductility coefficient of the so-called Morrow formula increases. The problem that fatigue resistance in the expected plastic strain region cannot be obtained due to the improvement of life

Method used

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  • Steel member, hot-rolled steel sheet for said steel member and production methods therefor
  • Steel member, hot-rolled steel sheet for said steel member and production methods therefor
  • Steel member, hot-rolled steel sheet for said steel member and production methods therefor

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Experimental program
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Effect test

Embodiment 1

[0121] The slabs with the compositions (steel grades C to L) shown in Table 1 were extracted from the heating furnace when the surface temperature of the slab was about 1220°C and the center temperature of the slab was about 1210°C, and the final rolling reduction was 91%. The finishing temperature in the central part of the width of the coil is about 860°C, and the lowest finish rolling temperature in the width direction of the coil is about 850°C. Ti -400°C to T Ti Cool at an average cooling rate of about 20°C / s in the temperature range of -500°C, and hot-roll at a coiling temperature of about 560°C to make raw hot-rolled steel sheets (thickness: about 5mm, front and rear ends) The plate thickness is about 10% thicker than the central part of the length) (No. 3-12).

[0122] In addition, the steel slab with the composition (steel type A) shown in Table 1 was extracted from the heating furnace when the surface temperature of the slab was about 1250°C and the temperature of t...

Embodiment 2

[0142] Steel slabs having the composition of steel grades A, B, and C shown in Table 1 were subjected to hot rolling under the conditions shown in Table 3 to produce raw hot-rolled steel sheets (thickness: about 5 mm, the thickness of the front and rear ends relative to about 10% thicker in the center of the length). Next, after pickling these hot-rolled steel sheets as raw materials, they are slitting into predetermined width dimensions and continuously formed to form open tubes. The open tubes are resistance-welded by high-frequency resistance welding to obtain a width reduction ratio of 4% A welded steel pipe having an outer diameter φ of 50.8 mm and a wall thickness of about 5 mm. The entire welded steel pipe was continuously subjected to high-frequency heating, and heat treatment was performed under the conditions shown in Table 3. Test pieces were cut out from these welded steel pipes, and subjected to a microstructure observation test, a quantitative test of precipitat...

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Abstract

The purpose of the present invention is to provide a steel member with excellent fatigue resistance characteristics in the plastic strain range, a hot-rolled steel sheet as the material therefor and production methods therefor. A steel member, which contains 0.031-0.200 mass% Ti and in the structure of which at least 0.005 mass% of the Ti is precipitated as precipitates with a particle size of 20nm or less. A hot-rolled steel sheet for said steel member that contains 0.031-0.200 mass% Ti and in the structure of which at least 0.005 mass% of the Ti is present as Ti solid solution. A productionmethod for said steel member in which, after molding of the hot-rolled steel sheet, heat treatment is performed wherein the member is heated to a temperature greater than 550 DEG C and not exceeding1050 DEG C and then cooled at an average cooling rate of at least 10 DEG C / s for the temperature range of 550-400 DEG C. A production method for said hot-rolled steel sheet in which a steel slab containing 0.031-0200 mass% Ti is extracted under temperature conditions higher than the equilibrium solid solution temperature TTi determined from a specified formula, after which finish-rolling is completed at a temperature of at least TTi-400 DEG C, the sheet is cooled at an average cooling rate of at least 10 DEG C / s for the temperature range from TTi-400 DEG C to TTi-500 DEG C, and is coiled at atemperature of TTi-500 DEG C or less.

Description

technical field [0001] The present invention relates to steel members, hot-rolled steel sheets for said steel members, and methods for their manufacture. More specifically, the present invention relates to a steel member excellent in fatigue resistance in a plastic strain region, a hot-rolled steel sheet for the steel member, and a method for producing the same. In particular, the present invention relates to welded steel pipes for coiled tubing, welded steel pipes for line pipes, welded steel pipes for automotive structural members, which require high strength and fatigue resistance in the plastic strain region, and especially relate to welded steel pipes for coiled tubing. Improvement of fatigue life in the plastically strained region. Background technique [0002] Patent Document 1 discloses that high-strength structural members and driving force transmission members of automobiles, etc., or electric resistance welded pipes for cleaning oil well pipes, have strength and ...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C22C38/00B21B1/26B21C37/08C21D9/08C21D9/46C21D9/50C22C38/14C22C38/60
CPCB21B1/26B21C37/08C21D9/08C21D9/46C21D9/50C22C38/00C22C38/14C22C38/60C22C38/20C22C38/008C21D6/008C22C38/02C22C38/28C21D8/0205C21D8/0226C22C38/26C22C38/06C22C38/002C22C38/04C22C38/001C21D6/005C21D6/002C22C38/32C21D8/105C22C38/24C22C38/22
Inventor 丰田俊介杉本一郎川村修司
Owner JFE STEEL CORP
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