Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Patent
1995-10-31
1997-09-09
Yee, Deborah
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
148598, 148320, C22C 3800, C22C 3804, C21D 806
Patent
active
056651821
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 of 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 of 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: 0.10-0.30% as an alloying component.
(3) A method of producing high-carbon steel wire rod excellent in drawability characterized by, 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 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 completely finished.
(4) A method of producing high-carbon steel wire rod excellent in drawability according to paragraph 3 above wherein the starting slab further contains Cr: 0.10-0.30% 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, 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, than a period within the range in which bainite transformation does not begin of X sec determined by the following equation (1), and 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, 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, bainite transformation to prior to completion of bainite transformation, specifically for a period of not more than Y sec determined by the following equation (2), and 600-T.sub.1 (T.sub.1 : holding temperature after cooling) .degree.C. and holding it until bainite transformation is completely finished,
(7) A method of producing high-carbon steel wire excellent in drawability characterized by, composition which
Al: not more than 0.003%, C. at a cooling rate of 60.degree.-300.degree. C./sec, and 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
Kawana Akifumi
Nishida Seiki
Oba Hiroshi
Ochiai Ikuo
Nippon Steel Corporation
Yee Deborah
LandOfFree
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