Carburizing steel having excellent cold forgeability and method of manufacturing the same

Inactive Publication Date: 2013-07-25
JFE STEEL CORP
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Benefits of technology

[0068]According to the present invention, a carburizing steel that has not only excellent bending fatigue properties at tooth root, but also excellent contact f

Problems solved by technology

However, since such gears are not endurable in use under high stress conditions, attempts have been made to improve strength against bending fatigue of a gear toot

Method used

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  • Carburizing steel having excellent cold forgeability and method of manufacturing the same
  • Carburizing steel having excellent cold forgeability and method of manufacturing the same
  • Carburizing steel having excellent cold forgeability and method of manufacturing the same

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[0074]The present invention will be described in detail below.

[0075]First, the reasons why the chemical compositions of the steel materials are restricted to the aforementioned ranges in the present invention will be described below. As used herein, “%” used for elements of a steel sheet represents “mass %,” unless otherwise stated.

[0076]0.1%≦C≦0.35%

[0077]Carbon (C) content in steel needs to be 0.1 mass % or more in order to enhance hardness at the center portion thereof by quenching after carburizing treatment. However, C content in steel exceeding 0.35 mass % decreases toughness of the core portion of the steel. Therefore, the C content is limited in the range of 0.1% to 0.35%, preferably 0.1% to 0.3%.

[0078]0.01%≦Si≦0.22%

[0079]Silicon (Si) is an element that enhances resistance to softening within a temperature range of 200° C. to 300° C., which is expected to be reached by gears or the like while rotating. To obtain this effect, it is essential to add Si in an amount of at least ...

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Abstract

A carburizing steel has a composition containing, in mass %, C: 0.1-0.35%; Si: 0.01-0.22%; Mn: 0.3-1.5%; Cr: 1.35-3.0%; P: 0.018% or less; S: 0.02% or less; Al: 0.015-0.05%; N: 0.008-0.015%; and O: 0.0015% or less, each being contained in an amount within a range satisfying formulas (1), (2) and (3) below, and the balance of the composition being Fe and incidental impurities, and the carburizing steel having microstructures before spheroidizing annealing such that a total microstructure proportion of ferrite and pearlite is 85% or more and an average ferrite grain size is 25 μm or less.
3.1≧{([% Si]/2)+[% Mn]+[% Cr]}≧2.2   (1)
[% C]−([% Si]/2)+([% Mn]/5)+2[% Cr]≧3.0   (2)
2.5≧[% Al]/[% N]≧1.7   (3)
[% M] represents content (in mass %) of element M.

Description

TECHNICAL FIELD[0001]The present invention relates to a carburizing steel having excellent cold forgeability, which can be suitably used in, for example, automobiles and other various industrial equipment, and a method for manufacturing the same.BACKGROUND ART[0002]As vehicle weight is reduced more and more for better energy saving, there is an increasing demand for gears of smaller sizes for use in automobiles or the like, and the gears have to bear increasingly higher load exerted thereon. Furthermore, such gears have to bear increasingly higher load exerted thereon as the engine output is made higher and higher. Durability of a gear is primarily determined by degrees of gear tooth root fracture caused by bending fatigue and pitting fatigue fracture of gear tooth surface.[0003]Conventionally, gears have been manufactured by preparing gear materials with case hardening steel, which is specified in JIS G 4053 (2003) as SCM420H, SCM822H and so on, and subjecting the gear materials to...

Claims

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Application Information

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IPC IPC(8): C21D1/06C21D9/32
CPCC21D1/32C22C1/02C21D2211/009C23C8/22C22C38/001C22C38/002C22C38/02C22C38/04C22C38/06C22C38/18C22C38/20C22C38/24C22C38/40C21D1/06C21D9/32C23C8/02C23C8/80C21D2211/005
Inventor ICHIMIYA, KATSUYUKIMITAO, SHINJI
Owner JFE STEEL CORP
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