Hot rolled wire material excellent in cold forging property after spheroidizing treatment, spheroidizing-annealed steel wire having excellent cold forging property, and method for production thereof

Abstract

A hot rolled wire material which comprises 0.005 to 0.6 mass % of C, and has a structure wherein pseudo-pearlite, bainite and ferrite account for 10 vol % or more, 75 vol % or less and 60 vol % or less, respectively, and the relationship that the sum of (pseudo-pearlite + bainite + ferrite) = 90 vol % is satisfied. A method for producing the above hot rolled wire material which comprises rolling a specific steel, followed by winding up at 750 to 1000 DEG C, cooling the steel from an upper limit temperature of 750 to 1000 DEG C to a lower limit temperature of 400 to 550 DEG C at a cooling rate of 20 DEG C / sec or higher, holding the steel for 20 sec or longer at 400 to 550 DEG C, and then cooling the steel. A steel wire comprises 0.005 to 0.6 mass % of C, and has a structure wherein the distances between cementite particles have a value of (standard deviation / average) of 0.50 or less. A method for producing the steel wire includes subjecting the above hot rolled wire material to spheroidizing annealing.

Description

technical field [0001] The present invention relates to shortening the spheroidizing annealing time for blanks before cold working and excellent cold workability after spheroidizing when manufacturing bolts, nuts, screws, gears, working coils, and other mechanical parts by cold working such as cold forging Hot-rolled wire rods, spheroidized annealed steel wires with excellent cold forgeability, and their manufacturing methods. [0002] This application claims priority to Japanese Patent Application No. 2005-039498 filed on February 16, 2005 and Japanese Patent Application No. 2005-137344 filed on May 10, 2005, the contents of which are incorporated herein by reference. Background technique [0003] Cold working (cold forging) can be used in a wide range of fields due to its high productivity, excellent dimensional accuracy of products, and good yield of steel products. Steel materials for such cold forging are required to have low tensile strength and high ductility (high c...

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Problems solved by technology

[0010] However, according to the technology described in Patent Document 1, although the spheroidizing annealing time can be shortened, the deformation resistance during the cold working after the spheroidizing treatment becomes high and the tool life is reduced for a single bainite structure. still can't solve the problem

[0011] In the technology described in Patent Document 2, since the structure is realized by slow cooling in the heat treatment after hot rolling, it leads to a decrease in productivity and an increase in cost

In addition, when the bainite fraction is excessive, there is also a problem that the deformation resistance during cold working after the spheroidizing treatment becomes high.

[0012] In the technique described in Patent Document 3, since ferrite and pearlite structures account for more than 80% by volume of the inner surface within 25% from the surface, it is caused by non-uniform dispersion of cementite (not an equidistant arrangement) The reduction in processing performance is worrying

In addition, since the low-temperature rolling is performed in the hot rolling process, and then slow cooling is performed, it leads to an increase in energy costs or a decrease in productivity.

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