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Thick steel plate

A technology of thick steel plate and plate thickness, applied in the field of thick steel plate with excellent base metal and HAZ toughness, can solve the problems of toughness deviation, adverse effect of toughness, base metal and HAZ toughness deviation, etc., to achieve the effect of toughness improvement

Inactive Publication Date: 2012-01-04
KOBE STEEL LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, the use of these inclusions such as oxides tends to generate coarse inclusions that adversely affect toughness. In addition, the number of inclusions such as oxides is generally smaller than that of TiN-based inclusions, so it is difficult to obtain stable HAZ toughness.
[0010] However, the amount of oxides is smaller than that of Ti-containing nitrides, and there is a problem that sufficient HAZ toughness cannot be obtained.
In addition, in the technology that utilizes oxides, the toughness of the base material and HAZ tends to vary due to the formation of coarse oxides, and there is a problem that the toughness of the base material and HAZ cannot be stably improved.
In addition, even if a fine structure is formed, if there are coarse Ti-containing nitrides and island-like martensite (MA), they will act as the starting point of brittle fracture and cause variations in toughness.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0110]While controlling the conditions shown in the following Tables 3 and 4 (the order of addition of Al and Ca, and the holding time T1 until casting), the steel with the composition shown in the following Tables 1 and 2 was smelted while controlling the casting time (1500~ 1400°C temperature range) for the cooling time T2, while cooling the molten steel to form a slab (cross-sectional shape: 150mm×250mm), the rolling conditions shown in the following Tables 3 and 4 (heating temperature Th before rolling, Pre-rolling heating time T3, rough rolling end temperature Tf) rolling to become a hot-rolled sheet with a plate thickness of 80 mm, and cooling to the cooling stop temperature Ts at the cooling rate Rc after rolling. In addition, tempering treatment is performed at 500° C. as necessary. In addition, in Table 1, REM is added in the form of misch metal containing about 50% of la and about 25% of Ce. In addition, "-" in Table 1 indicates that no element was added. In Tables...

Embodiment 2

[0144] Under the conditions shown in Tables 10 to 12, steels with the chemical composition shown in Tables 7 to 9 were smelted and cast to form slabs (cross-sectional shape: 150 mm × 250 mm), and then hot rolled to obtain hot rolled slabs with a thickness of 80 mm. plate. In addition, in Tables 7 to 9, REM is added in the form of mischmetal containing about 50% of la and about 25% of Ce. In addition, in Tables 10 to 12, the addition order of Al and Ca is "◯", which means that they are added in the order of Al→Ca.

[0145]

[0146]

[0147] Test pieces were cut from the hot-rolled sheets obtained above, and the number density of Ti-containing nitrides of various sizes was measured in the same manner as in Example 1, and the HAZ toughness was measured in the following manner.

[0148] Determination of HAZ toughness

[0149]A pendulum impact test piece (standard test piece specified in JISZ 2242) was taken from a position t / 4 deep from the surface of each hot-rolled she...

Embodiment 3

[0158] In No.1~3,5,14 of table 10 of described embodiment 2, No.31 of table 11 and Ni.c, d of table 12, extract test piece (12.5mm * 32mm) from the hot-rolled plate × 55mm), the same thermal cycle test as in Example 2 was carried out. In this test piece, EBSP (Electron Back-Scattering Pattern) measurement (field of view: 200 μm × 200 μm) was performed on a portion corresponding to a position at a depth of t / 4 from the surface of the hot-rolled sheet. The average grain size of the HAZ bainite structure surrounded by high-angle grain boundaries with a crystal orientation difference of 15° or more. The results are shown in Table 13, figure 1 middle.

[0159] 【Table 13】

[0160]

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Abstract

The invention provides a steel plate with excellent HAZ toughness even in high heat input welding. The thick steel plate of the invention comprises predetermined chemical compositions; and, has Ti nitride content above 5.0X106 / mm2 when the diameter of equivalent circle is smaller than 0.05 mum; has Ti nitride content above 1.0X105 / mm2 when the diameter of equivalent circle is between 0.05 and 1.0mum; and has the Ti nitride content below 5 / mm2 when the diameter of equivalent circle is larger than 1.0 mum.

Description

technical field [0001] The present invention relates to a thick steel plate suitable for welded structures such as bridges, high-rise buildings, and ships, and in particular to a thick steel plate with excellent toughness in the heat-affected zone (hereinafter simply referred to as "HAZ") after high-energy-input welding. It also relates to a base material (steel plate) after high heat input welding and a thick steel plate excellent in HAZ toughness. Background technique [0002] In recent years, with the increase in size of the various welded structures described above, welding of thick steel plates having a plate thickness of 50 mm or more is unavoidable. Therefore, in all fields, from the standpoint of improvement of welding work efficiency, there is a situation directed to welding with a large heat input of 50 kJ / mm or more. [0003] However, if high heat input welding is performed, the HAZ is heated to a high-temperature austenite region and then slowly cooled, so the s...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): C22C38/14C22C38/50C22C38/58
CPCC22C38/001C22C38/002C22C38/005C22C38/02C22C38/04C22C38/06C22C38/12C22C38/14C22C38/42
Inventor 名古秀德冈崎喜臣出浦哲史杉谷崇谷德孝金子雅人下山哲史
Owner KOBE STEEL LTD
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