Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Patent
1995-10-31
1997-08-19
Yee, Deborah
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
148598, 148320, C21D 806, C22C 3802
Patent
active
056584024
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to high-carbon steel wire rod and wire excellent in drawability and methods of producing the same.
BACKGROUND ART
Wire rod and wire are ordinarily drawn into a final product matched to the purpose of use. Before conducting the drawing process, however, it is necessary to put the wire rod or wire in a condition for drawing.
As a conventional measure for this, Japanese Patent Publication No. Sho 60-56215 discloses a method for heat treatment of steel wire rod of high strength and small strength variance characterized in that wire rod of steel containing C: 0.2-1.0%, Si<0.30% and Mn: 0.30-0.90% and at austenite formation temperature is cooled between 800.degree. and 600.degree. C. at a cooling rate of 15.degree.-60.degree. C./sec by immersion in fused salt of one or both of potassium nitrate and sodium nitrate fused by heating to a temperature or 350.degree.-600.degree. C. and stirred by a gas.
However, the wire rod of pearlite texture obtained by the heat treatment method described in the aforesaid patent publication involves the problems or ductility degradation during drawing at a high reduction of area and of cracking in twist testing (hereinafter referred to as "delamination").
The object of this invention is to provide high-carbon steel wire rod and wire excellent in drawability and methods of producing the same which advantageously overcome the aforesaid problems of the prior art.
DISCLOSURE OF THE INVENTION
The gist of the invention is as set out below.
(1) High-carbon steel wire rod or wire excellent in drawability characterized in that of, in terms of area ratio, not less than 80% upper bainite texture obtained by two-stepped transformation and an Hv of not more than 450.
(2) High-carbon steel wire rod or wire excellent in drawability according to paragraph 1 above further containing Cr: 0.10-0.50% as an alloying component.
(3) A method of producing high-carbon steel wire rod excellent in drawability characterized by,
rolling into wire rod a steel slab of a composition which
cooling the rolled wire rod from the temperature range of 1100.degree.-755.degree. C. to the temperature range of 350.degree.-500.degree. C. at a cooling rate of 60.degree.-300.degree. C./sec, and
holding it in this temperature range for a specified time period within the range in which bainite transformation does not begin or within a range from after the start of bainite transformation to prior to completion of bainite transformation, and
increasing the temperature and holding it until bainite transformation is completely finished.
(4) A method of producing high-carbon steel wire rod excellent in drawability according to paragraph B above wherein the starting slab further contains Cr: 0.10-0.50% as an alloying component.
(5) A method of producing high-carbon steel wire rod excellent in drawability according to paragraph 3 or 4 above characterized by,
after the starting slab has been rolled into wire rod, cooling the rolled wire rod from the temperature range of 1100.degree.-755.degree. C. to the temperature range of 350.degree.-500.degree. C. at a cooling rate of 60.degree.-300.degree. C./sec,
holding it in this temperature range for not less than 1 sec and not more than a period within the range in which bainite transformation does not begin of X sec determined by the following equation (1), and
increasing the temperature not less than 10.degree. C. and not more than 600-T.sub.1 (T.sub.1 : holding temperature after cooling) .degree.C. and holding it until bainite transformation is completely finished,
(6) A method of producing high-carbon steel wire rod excellent in drawability according to paragraph 3 or 4 above characterized by,
after the starting slab has been rolled into wire rod, cooling the rolled wire rod from the temperature range of 1100.degree.-755.degree. C. to the temperature range of 350.degree.-500.degree. C. at a cooling rate of 60.degree.-300.degree. C./sec,
holding it in this temperature range for a period from after the start of bainite transformation to prior
Kawana Akifumi
Nishida Seiki
Oba Hiroshi
Ochiai Ikuo
Nippon Steel Corporation
Yee Deborah
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