a thick steel plate
A technology of thick steel plate and quality, applied in the field of thick steel plate, to achieve the effect of excellent fatigue characteristics
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Embodiment approach 1
[0064] Hereinafter, Embodiment 1 of the present invention will be described. The inventors of the present invention first investigated the relationship between additive elements and fatigue strength for various thick steel plates. As a result, it was found that the addition of Si and Cu significantly improved the fatigue strength. In general, fatigue cracks are caused by the irreversible movement of mobile dislocations that repeatedly move under stress through cross sliding or the like. At this time, it is known that dislocations form a pore structure, and it has been clarified that the formation of the pore structure is suppressed by adding Si and Cu in a total amount of 0.3% by mass or more.
[0065] As a result of detailed observation, it is considered that these elements do not form precipitates, and are also clearly not dissolved in carbides and the like present in the steel sheet, and therefore exist in the form of solid solution in the matrix. That is, it is considere...
Embodiment approach 2
[0119] Next, Embodiment 2 of the present invention will be described. In steel sheets used for large-scale structures, reduction in crack growth rate, that is, improvement in crack growth characteristics is also sought. This is because even if fatigue cracks occur by chance, if the crack progresses slowly, the damaged part can be found before destruction and repair can be performed.
[0120] The inventors of the present invention conducted crack progress tests and tissue observations on various thick steel plates, and found that, in addition to the structure control of Embodiment 1, such as figure 1 As shown in (b), when the plate thickness is set as t, select the position from the surface along the plate thickness direction to be t / 4 of the plate thickness t, and control the microstructure on the longitudinal section parallel to the rolling direction in the following manner, so that A steel plate excellent in both fatigue properties and crack progression properties was obtai...
Embodiment 1
[0154] According to the usual smelting method, after melting and casting the steels with the chemical composition of the steel grades A to W shown in Table 1, hot rolling is carried out under various conditions of the rolling conditions No.a to l shown in Table 2, A steel plate with a thickness of 20 mm was obtained. In addition, in Table 1, the column shown by "-" shows no addition, and [Si]+[Cu] shows the total content of Si and Cu. In addition, the Ar shown in Table 1 3 The phase transition point is a value obtained by the above formula (5). In Table 2, the "cumulative rolling reduction in all hot-rolling steps" refers to the cumulative rolling reduction in all hot-rolling steps.
[0155] [Table 1]
[0156] [Table 1]
[0157]
[0158] [Table 2]
[0159]
[0160] For each steel sheet, the microstructure, effective grain size, size of the remaining microstructure serving as the second phase, tensile strength, fatigue properties, and dislocation density ρ of the ste...
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Abstract
Description
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