High-strength steel having superior brittle crack arrestability, and production method therefor

a high-strength steel and brittle crack technology, applied in the field of high-strength steel, can solve the problems of difficult to improve the brittle crack arrestability of an extremely thick high-strength steel, difficult to secure impact toughness in a central portion, coarse structure of a central portion, etc., and achieve excellent brittle crack arrestability and high yield strength

Inactive Publication Date: 2017-11-16
POHANG IRON & STEEL CO LTD
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  • Summary
  • Abstract
  • Description
  • Claims
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AI Technical Summary

Benefits of technology

[0025]According to an exemplary embodiment in the present disclosure, a high-strength...

Problems solved by technology

In general, for a high-strength steel, when an extremely thick steel sheet is manufactured, due to a reduction in a total reduction ratio, sufficient deformation does not occur in a central portion, so a structure of a central portion may become coarse.
In addition, due to the structure having been coarsened, it may be difficult to secure impact toughness in a central portion.
Therefore, it may be difficult to improve brittle crack arrestability of an extremely thick high-strength steel.
Howe...

Method used

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  • High-strength steel having superior brittle crack arrestability, and production method therefor

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Experimental program
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embodiment 1

[0127]After a steel slab with a thickness of 400 mm having a composition of Table 1 was reheated at a temperature of 1050° C., rough rolling was performed at a temperature of 1020° C., so a bar was manufactured. When a slab was rough rolled, an average temperature difference between a central portion and a surface is illustrated in Table 2, a cumulative reduction ratio of 50% is equally applied.

[0128]The average temperature difference between a central portion and a surface during rough rolling of Table 2 refers to a difference between a temperature of a surface of a slab or bar measured immediately before rough rolling, and a temperature of a central portion calculated in consideration of an amount of water sprayed to a bar and a slab thickness immediately before rough rolling, and is a result in which a temperature difference for each pass of rough rolling is measured and a total average value is calculated.

[0129]A thickness of the bar having been rough rolled was 180 mm, and a cr...

embodiment 2

[0142]Except for a change in a Cu / Ni weight ratio of a steel slab as illustrated in Table 3, a steel sheet was manufactured with the same composition and manufacturing conditions as Inventive steel 2 of Embodiment 1, surface properties of the steel sheet having been manufactured were investigated, and a result thereof is illustrated in Table 3.

[0143]In Table 3, surface properties of the steel sheet refer to a measure of whether a star crack in a surface occurred due to hot shortness.

TABLE 3Steel Composition (wt %)Cu / NiSteelPSweightSurfaceGradeCSiMnNiCuTiNb(ppm)(ppm)ratioPropertiesInventive0.0820.311.360.840.410.0160.01777250.48Non-occurrencesteel 7Inventive0.950.440.46Non-occurrencesteel 2Inventive0.370.120.32Non-occurrencesteel 8Inventive0.280.100.35Non-occurrencesteel 9Comparative0.230.180.78Occurrencesteel 7Comparative0.480.330.71Occurrencesteel 8

[0144]As illustrated in Table 3, when a Cu / Ni weight ratio is properly controlled, it is confirmed that surface properties of a steel s...

embodiment 3

[0145]Except for a change in a crystal grain size (μm) before finish rolling after rough rolling as illustrated in Table 4, a steel sheet was manufactured in the same composition and manufacturing condition as Inventive steel 1 of Embodiment 1. Properties of an average grain size of a central portion of a steel sheet having been manufactured were investigated, and a result thereof is illustrated in Table 4.

TABLE 4Crystal grain size (μm)before finish rolling afterAverage grain size (μm) ofSteel Graderough rollingcentral portionInventive steel 18021.2Inventive steel12529.710Inventive steel10725.611Inventive steel7519.812Inventive steel15521.513Inventive steel11024.514

[0146]As illustrated in Table 4, as a crystal grain size of a central portion of a bar after rough rolling decreases, it is confirmed that an average grain size of a central portion is refined. Thus, it is expected that brittle crack propagation resistance is to be improved.

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Abstract

Provided are high-strength steel having superior brittle crack arrestability and a production method therefor. The high-strength steel comprises 0.05-0.1 wt % of C, 0.9-1.5 wt % of Mn, 0.8-1.5 wt % of Ni, 0.005-0.1 wt % of Nb, 0.005-0.1 wt % of Ti, 0.1-0.6 wt % of Cu, 0.1-0.4 wt % of Si, at most 100 ppm of P, and at most 40 ppm of S with the remainder being Fe and other inevitable impurities, and has microstructures including one structure selected from the group consisting of a single-phase structure of ferrite, a single-phase structure of bainite, a complex-phase structure of ferrite and bainite, a complex-phase structure of ferrite and pearlite, and a complex-phase structure of ferrite, bainite, and pearlite. The high-strength steel has high yield strength and superior brittle crack arrestability.

Description

TECHNICAL FIELD[0001]The present disclosure relates to a high-strength steel having excellent brittle crack arrestability and a method of manufacturing the same.BACKGROUND ART[0002]Recently, in designing structures used in domestic and international shipbuilding, marine engineering, architecture and civil engineering fields, the development of an extremely thick steel having high strength properties is required.[0003]When high-strength steel is used in designing structures, since such structures may be lightened, an economical benefit may be obtained; and since a thickness of a steel sheet may be reduced, ease of machining and welding operations may be secured simultaneously.[0004]In general, for a high-strength steel, when an extremely thick steel sheet is manufactured, due to a reduction in a total reduction ratio, sufficient deformation does not occur in a central portion, so a structure of a central portion may become coarse. Therefore, as hardenability is increased, a low tempe...

Claims

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Application Information

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IPC IPC(8): C21D9/46C21D6/00C22C38/12C22C38/08C22C38/04C21D8/02C22C38/00C22C38/14C22C38/16C22C38/02
CPCC21D9/46C22C38/16C22C38/14C22C38/12C22C38/08C22C38/04C22C38/02C22C38/002C21D8/0226C21D8/0205C21D6/008C21D6/005C21D6/001C21D8/0247C21D2211/005C21D2211/002C21D2211/009B21C37/02C21D8/021C21D8/0263C21D2201/05
Inventor LEE, HAK-CHEOLJANG, SUNG-HO
Owner POHANG IRON & STEEL CO LTD
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