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Steel For Machine Structural Use With Excellent Strength, Ductility, And Toughness And Method For Producing The Same

a technology of ductility and toughness, which is applied in the direction of heat treatment equipment, manufacturing tools, furnaces, etc., can solve the problems of significant cost and threat to the production of steel, and achieve excellent strength, ductility and toughness

Inactive Publication Date: 2008-01-24
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0009] In light of the above problems of the related art, an object of the present invention is to provide a steel and steel sheet for machine structural use which have high strength, high ductility, and high toughness with a minimal increase in production costs, and also provide a metal belt suitable as an endless metal belt for CVT at low cost.
[0011] Further studies on detailed structures constituting the martensitic structure (hereinafter referred to as substructures) have found that an especially excellent strength-elongation balance can be achieved by controlling blocks constituting the martensitic structure to a predetermined size or less. These studies have also found that excellent toughness can be ensure if dissolved boron is contained in at least a predetermined amount and is present at boundaries of prior austenite grains in a concentration at least 1.5 times that in the prior austenite grains.
[0019] (7) A steel sheet for machine structural use with excellent strength, ductility, and toughness according to the present invention is formed of the steel for machine structural use according to one of Items (1) to (6) and has a thickness of 0.5 mm or less.
[0021] (9) A method for producing a steel for machine structural use with excellent strength, ductility, and toughness according to the present invention includes quenching a steel material by heating at a rate of temperature rise of 100° C. / s or more and tempering the steel material at 100° C. to 400° C. The steel material contains, in percent by mass, more than 0.30% to 0.5% of carbon, 1.0% or less of silicon, 1.5% or less of manganese, 0.025% or less of aluminum, 0.3% to 0.5% of molybdenum, and 0.0005% to 0.01% of boron, and the balance is iron and incidental impurities.
[0024] (12) A method for producing a steel sheet for machine structural use with excellent strength, ductility, and toughness according to the present invention includes quenching a steel sheet by heating at a rate of temperature rise of 100° C. / s or more and tempering the steel sheet at 100° C. to 400° C. The steel sheet contains, in percent by mass, more than 0.30% to 0.5% of carbon, 1.0% or less of silicon, 1.5% or less of manganese, 0.025% or less of aluminum, 0.3% to 0.5% of molybdenum, and 0.0005% to 0.01% of boron, and the balance is iron and incidental impurities. The steel sheet has a thickness of 0.5 mm or less.
[0030] The present invention can provide a steel for machine structural use which has excellent strength, ductility, and toughness without containing large quantities of expensive alloying elements, a metal sheet for machine structural use produced with the steel, and a metal belt produced with the metal sheet.

Problems solved by technology

Such steels are significantly costly, and the production thereof can be threatened by the recent shortage of materials.

Method used

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  • Steel For Machine Structural Use With Excellent Strength, Ductility, And Toughness And Method For Producing The Same

Examples

Experimental program
Comparison scheme
Effect test

example 1

[0082] Examples will now be described.

[0083] Steels shown in Table 1 were produced by vacuum melting. These steels were heated to 1,100° C. and were hot-rolled into sheets with a thickness of 3 mm. These sheets were pickled to remove surface scale and were cold-rolled. The rolling was repeated many times. After the sheets were rolled to a thickness of 0.8 mm, they were annealed to remove work strain and were further cold-rolled to a final thickness of 0.4 mm. These materials were subjected to heat treatment and evaluation described below.

[0084] The structures of the steels, which are to be subjected to high-frequency heating quenching, after the final heat treatment are expected to contain only a martensitic phase formed by transformation from the austenite temperature range, an untransformed ferrite phase that can result from insufficient heating, and undissolved inclusions and precipitates such as carbides. These phases can be discriminated by developing the structures by nital ...

example 2

[0094] The effect of structure was examined. All the test methods used were the same as those used in Example 1 except that the high-frequency heating was performed at varying temperatures to examine the effect of the volume percentage of martensite.

[0095] In comparative examples, for example, the amount of untransformed ferrite phase was increased by lowering the heating temperature. As a result, the volume percentage of martensite fell below 90%. The test results are shown in Table 2, which shows that the formation of less than 90% by volume of martensitic structure resulted in significantly decreased strength.

example 3

[0096] The effects of other components were examined. Steels shown in Table 3 were produced by vacuum melting. The test methods used were the same as those used in Example 1. The test results are shown in Table 3, which shows that excessive contents of chromium and titanium resulted in decreased strength and excessive contents of nickel, vanadium, and niobium resulted in a saturated effect.

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Abstract

A steel for machine structural use with a better strength-ductility-toughness balance than maraging steel and applications thereof are provided. The steel for machine structural use with excellent strength, ductility, and toughness contains, in percent by mass, more than 0.30% to 0.5% of carbon, 1.0% or less of silicon, 1.5% or less of manganese, 0.025% or less of aluminum, 0.3% to 0.5% of molybdenum, and 0.0005% to 0.01% of boron, and the balance is iron and incidental impurities. The steel has a structure including at least 90% by volume of martensitic structure. The martensitic structure includes blocks having a size of 1.5 μm or less. Dissolved boron is contained in an amount of at least 0.0005% and is present at boundaries of prior austenite grains in a concentration at least 1.5 times that in the prior austenite grains.

Description

TECHNICAL FIELD [0001] The present invention relates generally to steels for machine structural use, including components of automobiles and industrial machines. In particular, the present invention relates to steels for machine structural use which have excellent strength, ductility, and toughness and are particularly suitable for metal belts, for example, used in continuously variable transmission (hereinafter abbreviated as CVT), which are currently produced with expensive steels such as maraging steel. The present invention also relates to steel sheets for machine structural use and metal belts produced with such steels. BACKGROUND ART [0002] In the field of automobiles, higher fuel efficiency and emission control have recently been demanded with the growing awareness of environmental issues. Accordingly, developments have been directed toward miniaturized, high-powered driving systems. For example, the development of CVT is remarkable. Metals belts used for CVT require high str...

Claims

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Application Information

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IPC IPC(8): C21D9/46C22C38/00
CPCC22C38/00C21D9/46C21D1/18C21D2211/008C22C38/02C22C38/04C22C38/06C22C38/12
Inventor MARUTA, KEIICHIHAYASHI, TOHRUKUROSAWA, NOBUTAKAKIMURA, HIDETOTOYOOKA, TAKAAKIHASE, KAZUKUNIYAMADA, KATSUMI
Owner JFE STEEL CORP
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