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Ultrahigh-strength steel sheet superior in hydrogen-embrittlement resistance

An ultra-high-strength, thin-steel technology, applied in temperature control, etc., can solve problems such as poor mechanical production efficiency, and achieve the effect of improving hydrogen embrittlement resistance

Inactive Publication Date: 2007-07-04
KOBE STEEL LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, the delayed fracture characteristic of TBF steel disclosed in this document is only about 1000 seconds at best until a crack is generated in the cathode filling test, and it is difficult to say that it fully considers that parts such as automobiles are exposed to severe conditions for a long time. The result after using the environment
In addition, since the heat treatment conditions of the above-mentioned documents are set at a high heating temperature, there are cases where the production efficiency of the actual machine is not good, and there is an urgent need to develop a new TBF steel that is also excellent in production efficiency.

Method used

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  • Ultrahigh-strength steel sheet superior in hydrogen-embrittlement resistance
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Experimental program
Comparison scheme
Effect test

Embodiment approach 1

[0057] The ultrahigh-strength thin steel sheet according to Embodiment 1 of the present invention is characterized by containing C: 0.10 to 0.25%, Si: 1.0 to 3.0%, Mn: 1.0 to 3.5%, and P: 0.15% or less in mass percent , S: 0.02% or less, Al: 1.5% or less (excluding 0%), and also contains iron and unavoidable impurities as the rest, and contains more than 1% of residual austenite in terms of the area ratio of the entire structure. Bainitic ferrite and martensite totaling more than 80%, and ferrite and pearlite totaling less than 9% (including 0%). Wherein the average axial ratio (major axis / short axis) of the retained austenite grains is 5 or more, and the tensile strength is 1180 MPa or more. The reason for specifying these conditions, the measurement method, etc. are explained below.

[0058]

[0059] Retained austenite is not only useful for improving the total elongation, but also greatly contributes to the improvement of hydrogen embrittlement resistance, so it is made ...

Embodiment approach 2

[0130] The ultrahigh-strength steel sheet according to Embodiment 2 of the present invention is characterized by containing C: 0.10 to 0.25%, Si: 1.0 to 3.0%, Mn: 1.0 to 3.5%, and P: 0.15% or less in mass percent , S: 0.02% or less, Al: 1.5% or less (excluding 0%), and the rest are composed of iron and unavoidable impurities, which contain more than 1% of retained austenite in terms of the area ratio of the entire structure, totaling More than 80% of bainitic ferrite and martensite, and a total of less than 9% (including 0%) of ferrite and pearlite, and the average minor axis length of the retained austenite grains is 1 μm or less, and the closest adjacent distance between the retained austenite grains is 1 μm or less, the average axis ratio (major axis / short axis) of the retained austenite grains is 5 or more, and the tensile strength is 1180 MPa or more . Here, a total of 80% or more of bainitic ferrite and martensite, and / or a total of 9% or less (including 0%) of ferrite ...

Embodiment 1

[0139] The experimental steel No.A-1~Y-1 composed of the composition listed in Table 1 was vacuum smelted to make the slab for the experiment, followed by the following procedures (hot rolling→cold rolling→continuous annealing) to obtain a plate thickness of 3.2 After the hot-rolled steel sheet of mm, the surface scale was removed by pickling, and then cold-rolled until it became 1.2 mm thick. Start temperature (SRT) at : 1150~1250℃ for 30 minutes

[0140] Finish temperature (FDT): 850°C

[0141] Cooling rate: 40°C / s

[0142] Coiling temperature: 550°C

[0143] Cold rolling rate: 50%

[0144] For each experimental steel in the , after holding at point A3 + 30°C for 120 seconds, it was rapidly cooled (air-cooled) to To°C in Table 2 at an average cooling rate of 20°C / s, and held at this To°C at 240°C. seconds. Then air-water cooled to room temperature.

[0145] In addition, No. 116 in Table 2 is used as a comparative example. In order to produce a martensitic steel of con...

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Abstract

The purpose of the present invention is to provide a high strength thin steel sheet that has high hydrogen embrittlement resisting property. In order to achieve the above purpose, a high strength thin steel sheet having high hydrogen embrittlement resisting property comprises: C: 0.10 to 0.25%; Si: 1.0 to 3.0%; Mn: 1.0 to 3.5%; P: 0.15% or less; S: 0.02% or less; and Al: 1.5% or less (higher than 0%) in terms of percentage by weight, with balance of iron and inevitable impurities; and the metal structure comprises: residual austenite; 1% by area or more in proportion to the entire structure; bainitic ferrite and martensite: 80% or more in total; and ferrite and pearlite: 9% or less (may be 0%) in total, while the mean axis ratio (major axis / minor axis) of said residual austenite grains is 5 or higher, and the steel has tensile strength of 1180 MPa or higher.

Description

technical field [0001] The present invention relates to an ultra-high-strength thin steel plate with excellent hydrogen embrittlement resistance, and particularly relates to a steel plate with a tensile strength of 1180 MPa or more that can suppress hydrogen embrittlement caused by placement cracks and delayed failure. damage of ultra-high-strength thin steel plates. Background technique [0002] When high-strength parts constituting automobiles or industrial machinery are obtained by press forming or bending, steel sheets used for the processing are required to have both excellent strength and ductility. In recent years, the demand for ultra-high-strength steel sheets of 1180 MPa or more has been increasing due to the weight reduction of automobiles, and TRIP (TRansformation Induced Plasticity) steel sheets are attracting attention as steel sheets that meet this demand. . [0003] The TRIP steel plate has a residual austenite structure, and if it is processed and deformed...

Claims

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Application Information

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IPC IPC(8): C22C38/06C22C38/16C21D8/02B21B37/74
Inventor 汤濑文雄池田周之向井阳一赤水宏衣笠润一郎齐藤贤司杉本公一北條智彦
Owner KOBE STEEL LTD
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