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Wire rod for manufacture of steel wire for pearlite structure bolt having tensile strength of 950-1600 mpa, steel wire for pearlite structure bolt having tensile strength of 950-1600 mpa, pearlite structure bolt, and methods for manufacturing same

A technology of tensile strength and manufacturing method, which is applied in the direction of bolts, manufacturing tools, nuts, etc., can solve the problems that have not been established and cannot fully improve the hydrogen embrittlement resistance, and achieve the effect of excellent hydrogen embrittlement resistance

Active Publication Date: 2016-02-03
NIPPON STEEL CORP +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, the hydrogen embrittlement resistance cannot be sufficiently improved only by this method, and the
Furthermore, techniques for improving both hydrogen embrittlement resistance and cold workability have not yet been established

Method used

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  • Wire rod for manufacture of steel wire for pearlite structure bolt having tensile strength of 950-1600 mpa, steel wire for pearlite structure bolt having tensile strength of 950-1600 mpa, pearlite structure bolt, and methods for manufacturing same
  • Wire rod for manufacture of steel wire for pearlite structure bolt having tensile strength of 950-1600 mpa, steel wire for pearlite structure bolt having tensile strength of 950-1600 mpa, pearlite structure bolt, and methods for manufacturing same
  • Wire rod for manufacture of steel wire for pearlite structure bolt having tensile strength of 950-1600 mpa, steel wire for pearlite structure bolt having tensile strength of 950-1600 mpa, pearlite structure bolt, and methods for manufacturing same

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0143] Steel slabs having the composition shown in Table 1 were heated and subjected to hot rolling to form wire rods, and the wire rods were subjected to constant temperature transformation treatment and subsequent cooling. At this time, the cooling start temperature of all the inventive wire rods and comparative wire rods was set to 450°C, and the cooling stop temperature was set to 280°C. The average block particle diameter, average lamellar interval, and pearlite area ratio of the surface layer portion (the region from the surface of the wire rod to a depth of 4.5 mm) of the obtained inventive wire rod and comparative wire rod were measured. The average block size of the pearlite block in the surface layer of the wire rod is measured by first measuring the average value of the circle-equivalent diameter of the pearlite block at a depth of 4.5 mm from the surface in the cross section of the wire rod at 45° intervals using an EBSD apparatus, Next, the measurement results at ...

Embodiment 2

[0149] Invention wires 1 to 7 and comparative wires 1 to 7 shown in Table 2 were subjected to wire drawing with a total reduction of area of ​​5 to 70% to produce steel wires, and the ultimate compressibility was measured. The results are shown in Table 3.

[0150]The ultimate compressibility is an index indicating cold workability. The measurement of ultimate compressibility is performed by the following procedure. A sample having a diameter D×height of 1.5D was produced by machining from the drawn steel wire. The end face of this sample was constrained and compressed using a die having concentric grooves. The maximum compressibility without cracks was taken as the ultimate compressibility of the sample.

[0151]

[0152] Comparative steel wires 1, 3, 4, 5, and 6 in which the average block diameter of the surface portion of the steel wire deviates from the range of the present invention, and comparative steel wires in which the average aspect ratio of pearlite block gra...

Embodiment 3

[0154] Inventive steel wires 1 to 7 and comparative steel wires 1 to 9 shown in Table 3 were processed into flanged bolts by cold forging. After processing, these bolts were maintained at 300 to 450° C. to manufacture bolts. The temperature holding time of all the bolts was set to 30 minutes. Table 4 shows the results of measuring the tensile strength, yield stress ratio, and hydrogen embrittlement resistance of the shaft portion of the bolt.

[0155] The evaluation of hydrogen embrittlement resistance was performed by the following procedure. First, 0.5 ppm of diffusible hydrogen was contained in the sample by electrolyzing the sample with hydrogen. Next, in order to prevent hydrogen from being released from the sample into the atmosphere during the test, the sample was plated with Cd. Thereafter, a load of 90% of the maximum tensile load of the sample was applied to the sample in the air. A sample that did not break after 100 hours was judged to be a sample with good hyd...

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Abstract

This wire rod for the manufacture of a steel wire for a pearlite structure bolt having a tensile strength of 950-1600 MPa has a predetermined chemical structure and is manufactured by performing an isothermal transformation process directly after hot rolling. If the C content is represented as [C] in unit mass%, then in a region 4.5 mm from the surface of the wire rod, the metal structure has a pearlite structure of 140 * [C] area% or more. In the region 4.5 mm from the surface of the wire rod, the mean block particle size of pearlite blocks as measured in a cross-section of the wire rod is 20 Mum or less. In the region 4.5 mm from the surface of the wire rod, the average lamellar spacing of the pearlite structure is more than 120 nm and not more than 200 nm.

Description

technical field [0001] The present invention relates to wire rods for manufacturing steel wires for pearlite structure bolts with a tensile strength of 950 to 1600 MPa, steel wires for pearlite structure bolts with a tensile strength of 950 to 1600 MPa, and excellent hydrogen embrittlement resistance and cold workability. Pearlitic bolts and their method of manufacture. [0002] this application claims priority based on Japanese Patent Application No. 2013-124740 for which it applied in Japan on June 13, 2013, The content is used here. Background technique [0003] In recent years, the demand for high-strength bolts has increased in order to reduce the weight and save space of automobiles. Conventionally, high-strength bolts with a tensile strength of 950 MPa or more are produced by forming alloy steel wires such as SCM435, SCM440, and SCr440 into a predetermined shape, followed by quenching and tempering. [0004] However, in high-strength bolts, when the tensile strength...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C22C38/00C21D8/06C21D9/00C22C38/60
CPCC21D8/06C21D9/00C22C38/00C22C38/60C21D8/065C21D9/0093C21D2211/009C22C38/001C22C38/002C22C38/02C22C38/04C22C38/06C22C38/08C22C38/12C22C38/14C22C38/16C22C38/18C21D1/60C21D1/607C21D6/004C21D6/005C21D6/008C21D9/525B21C1/02C22C38/22F16B33/00
Inventor 小此木真室贺也康菱田元树
Owner NIPPON STEEL CORP
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