Hot-rolled ultra soft high-carbon steel plate and process for production thereof

A technology of hot-rolled steel plates and manufacturing methods, which is applied in the direction of manufacturing tools, metal rolling, heat treatment furnaces, etc., can solve problems such as difficult dissolution of carbides and reduced quenching strength, and achieve processing procedures, low costs, and uniformity Coarsening effect

Active Publication Date: 2009-04-15
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, in this case, the spheroidized carbides are coarsened and become the starting point of pores during machining, and at the same time, the carbides are difficult to dissolve in the heat treatment stage after machining, causing a decrease in quenching strength.

Method used

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  • Hot-rolled ultra soft high-carbon steel plate and process for production thereof
  • Hot-rolled ultra soft high-carbon steel plate and process for production thereof
  • Hot-rolled ultra soft high-carbon steel plate and process for production thereof

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0106] The steel having the chemical composition shown in Table 1 was continuously cast, and the obtained slab was heated to 1250°C, and hot rolled and annealed under the conditions shown in Table 2 to produce a hot rolled sheet with a thickness of 3.0mm. steel plate.

[0107] Next, a sample is taken from the hot-rolled steel sheet obtained above, and the average ferrite grain size, fine ferrite grain volume ratio, average carbide grain size, carbide aspect ratio, and contact between carbides are measured. Ratio, and determine the raw material hardness, total elongation and hole expansion rate for performance evaluation. The respective measurement methods and conditions are as follows.

[0108] [Average grain size of ferrite]

[0109] Using the cutting method described in JIS G 0552, it is measured from the optical microscope structure in the thickness section of the sample. In addition, the average grain size is set to an average value of 3000 or more ferrite crystal grain...

Embodiment 2

[0133] Steels having the chemical composition shown in Table 4 were continuously cast, and the resulting slabs were heated to 1250°C, hot-rolled and annealed under the conditions shown in Table 5, to produce hot-rolled steel sheets with a thickness of 3.0 mm .

[0134] Next, samples were taken from the hot-rolled steel sheet obtained above, and the average ferrite grain size, fine ferrite grain volume ratio, carbide average grain size, carbide aspect ratio, and contact ratio between carbides were measured. Ratio, and determine the raw material hardness, total elongation and hole expansion rate for performance evaluation. The respective measurement methods and conditions are the same as in Example 1.

[0135] Table 6 shows the results obtained by the above measurements.

[0136] In Table 6, steel plates No. 19 to 29 have chemical components within the scope of the present invention, and have an average ferrite particle size, a fine ferrite grain volume ratio (grain size below...

Embodiment 3

[0142] Steels having the chemical composition shown in Table 1 were continuously cast, and the resulting slabs were heated to 1250°C, hot-rolled and annealed under the conditions shown in Table 7, to produce hot-rolled steel sheets with a thickness of 3.0mm .

[0143] Next, samples were taken from the hot-rolled steel sheet obtained above, and the average ferrite grain size, fine ferrite grain volume ratio, carbide average grain size, carbide aspect ratio, and contact ratio between carbides were measured. Ratio, and determine the raw material hardness, total elongation and hole expansion rate for performance evaluation. The respective measurement methods and conditions are the same as in Example 1.

[0144] Table 8 shows the results obtained above.

[0145] In Table 8, the production conditions of steel plates No.31 to 47 are within the scope of the present invention, and have an average ferrite particle size, fine ferrite grain volume ratio (grain size of 20 μm or less), av...

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Abstract

An ultra soft high carbon hot-rolled steel sheet having excellent workability. The steel sheet is a high carbon hot-rolled steel sheet containing 0.2 to 0.7% C, and has a structure in which mean grain size of ferrite is 20 [mu]m or larger, the volume percentage of ferrite grains having 10 [mu]m or smaller size is 20% or less, mean diameter of carbide is in a range from 0.10 [mu]m to smaller than 2.0 [mu]m, the percentage, of carbide grains having 5 or more of aspect ratio is 15% or less, and the contact ratio of carbide is 20% or less. The steel sheet is manufactured by the steps of: rough-rolling the steel; finish-rolling the rough-rolled steel sheet at a temperature of 1100 DEG C or below at inlet of finish rolling, a reduction in thickness of 12% or more at the final pass, and a finishing temperature of (Ar3 - 10) DEG C or above; primary-cooling the finish-rolled steel sheet to a cooling-stop temperature of 600 DEG C or below within 1.8 seconds after the finish rolling at a cooling rate of higher than 120 DEG C/sec; secondary-cooling the primary-cooled steel sheet to hold the steel sheet at a temperature of 600 DEG C or below; coiling the secondary-cooled steel sheet at a temperature of 580 DEG C or below; pickling the coiled steel sheet; and spheroidizing-annealing the pickled steel sheet by the box annealing method at a temperature in a range from 680 DEG C to Ac1 transformation point.

Description

technical field [0001] The present invention relates to an ultra-soft high-carbon hot-rolled steel sheet, especially an ultra-soft high-carbon hot-rolled steel sheet excellent in workability and a manufacturing method thereof. Background technique [0002] High-carbon steel sheets used for tools or automotive parts (gears, transmissions), etc., undergo heat treatment such as quenching and tempering after stamping and forming. In recent years, manufacturers of tools and parts, that is, users of high-carbon steel sheets, are studying the simplification of parts processing from cutting and hot forging of cast materials to stamping of steel sheets (including cold forging) in order to reduce costs. ) processing steps. Accordingly, high-carbon steel sheets as raw materials are required to have excellent ductility for forming into complex shapes and excellent hole expandability (flangeability) in forming after punching. The hole expandability is usually evaluated by stretch flang...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C22C38/00C22C38/06C22C38/32B21B3/00C21D9/46
CPCC21D9/46B21B3/00C22C38/02C22C38/04C21D8/0226
Inventor 木村英之藤田毅中村展之青木直也佐佐木成人上冈悟史饭塚俊治
Owner JFE STEEL CORP
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