Fatigue cracking resistant expansibility excellent steel plate

A scalable and fatigue-resistant technology, applied in the field of steel plates, which can solve the problem that the dispersion state of retained austenite is not disclosed in the slightest

Inactive Publication Date: 2009-08-05
KOBE STEEL LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, this document does not disclose at all about the dispersed state of retained austenite.

Method used

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  • Fatigue cracking resistant expansibility excellent steel plate
  • Fatigue cracking resistant expansibility excellent steel plate
  • Fatigue cracking resistant expansibility excellent steel plate

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0213] Example 1 (invention example and comparative example related to the first embodiment of the present invention)

[0214] According to the usual smelting method, after smelting the steel having the composition shown in Tables 1 and 2 into a slab, it is heated to the temperature shown in Tables 3 and 4 (expressed as "heating temperature" in Tables 3 and 4), This is followed by hot rolling and finish rolling. In Tables 3 and 4, the finish rolling temperature (expressed as "end temperature" in Tables 3 and 4) and the reduction rate to reach the finish rolling temperature + 50°C (expressed as "reduction rate" in Tables 3 and 4) are shown. "). Then after finish rolling, cooling to the temperature for ferrite transformation (in Tables 3 and 4 expressed as "holding temperature") for a specified time (expressed as "holding time" in Tables 3 and 4). After the ferrite phase transformation, cool at the cooling rate shown in Tables 3 and 4 (expressed as "second cooling rate" in Ta...

Embodiment 2

[0234] Example 2 (invention example and comparative example related to the second embodiment of the present invention)

[0235] According to the usual smelting method, the steel (No.1-30 of Example 2) with the composition shown in Tables 7 and 8 is smelted to become a steel slab, and after being heated to the low temperature γ region below Ar3+50°C, it is quenched to Below 300°C, after two pre-rolling treatments to generate martensite or bainite, the conditions shown in Table 9 (each heating temperature, finish rolling temperature, reduction in low temperature γ range (multiple finish rolling) temperature +50°C to the reduction of the final rolling temperature), the cooling rate after rolling (the first cooling), the cooling stop temperature, the holding time to this temperature and the cooling rate after the holding (the second cooling) By reheating, rolling, and cooling, high-tensile steel sheets having the thicknesses shown in Table 9 were produced.

[0236] [Table 7] (mas...

Embodiment 3

[0262] Example 3 (present invention example and comparative example concerning the third embodiment of the present invention)

[0263] Steels having the compositions shown in Tables 12 and 13 were melted into slabs and then hot-rolled according to a usual melting method. The reduction rates at temperatures up to 950° C. are shown in Tables 14 and 15 (expressed as “Reduction Rates” in Tables 14 and 15). After hot rolling, cool to a specified temperature (expressed as "first stop temperature" in Tables 14 and 15) at the cooling rate shown in Tables 14 and 15 (expressed as "first cooling rate" in Tables 14 and 15) ), hold for a specified time (expressed as "hold time" in Tables 14 and 15). Thereafter, the steel sheets were cooled to 200°C or lower at the cooling rates shown in Tables 14 and 15 (expressed as "second cooling rates" in Tables 14 and 15). Also, the cooling was stopped on the way of cooling to below 200°C, and the temperature was recorded in the column of "second st...

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Abstract

Provided is a steel plate having excellent resistance to fatigue crack growth. Steel sheets with excellent fatigue crack growth resistance contain C: 0.03 to 0.30%, Si: 0.5% or less (excluding 0%), Mn: 0.8 to 2%, Al: 0.01 to 0.1%, N: 0.010% or less 0%), P: 0.03% or less (excluding 0%), and S: 0.01% or less (excluding 0%), and the balance is Fe and unavoidable impurities, which are located in the Z direction (thickness direction) The structure at the position of depth t / 4 (t=sheet thickness) (hereinafter simply referred to as "the position") is substantially composed of a mixed structure of ferrite and hard phase.

Description

technical field [0001] The present invention relates to a steel plate excellent in fatigue crack growth resistance suitable for use in ships, marine structures, bridges, buildings, and the like. Background technique [0002] Ships, marine structures, bridges, buildings, etc. are usually welded to form thick steel plates with a plate thickness of 6mm or more. In the welded part of the steel plate, since stress concentration is likely to occur, the occurrence of fatigue cracks is unavoidable. However, even if fatigue cracks occur in the steel plate, if the rate of growth of the cracks can be suppressed, the cracks can be found and repaired before the structure is damaged through regular inspections or the like. [0003] Japanese Patent Application Laid-Open No. 2000-129392 discloses a steel material that is excellent in fatigue characteristics, especially fatigue crack growth resistance, and has a bainite structure or a martensite structure as a hard phase, or a combination o...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): C22C38/06C21D8/02
Inventor 高冈宏行冈崎喜臣杵渕雅男
Owner KOBE STEEL LTD
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