Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/30—Ferrous alloys, e.g. steel alloys containing chromium with cobalt

Definitions

• the present invention relates a high-carbon steel suitable for super high tensile strength hard drawn steel wire having excellent ductility and heat treating ability, and particularly provides a steel suitable for hard steel wire having tensile strength of more than 180 kg/mm Convcntionally, as steel wire strands for bridge cables for a suspension bridge for example, hard drawn steel wires of about 5 mm diameter, zinc coated after cold drawing, have been used, and usually a piano steel wire grade .118 Grade No. 2 Z is used for this purpose.
• Rolled wire rod of about mm diameter is subjected to patenting and wire drawing to obtain wire products having tensile strength of about 170 kg/mm
• construction plans have been increasingly made for longer and larger bridges, and higher tensile strength of steel wire has been demanded for reducing the weight of bridges and also larger diameter of steel wire has been sought for in order to simplify the bridge construction work.
• the present inventors have made fundamental studies on functions of alloying elements for the refinement of pearlite, and have found that chromium is effective to shorten the interlamella spacing in the pearlite struc ture through the increase of transformation energy.
• the mechanism of the pearlite refinement by chromium is not based on the lowering of transformation temperature due to the increased hardenability as conventionally considered.
• an increased content of chromium is disadvantageous because it increases the lower limit of the transformation temperature of the pearlite.
• the chromium addition increases hardenability of the steel in a sense that it shifts the continuous cooling transformation curve toward the longer time side. This phenomenon causes a problem when importance is given on production efficiency because it also shifts the finishing time of the pearlite transformation toward the longer side so that longer time is required for immersion in the lead bath.
• Another problem is that a higher austenitizing temperature required for the dccomposition of chromium containing carbides results in the coarsening of the austenite grains so that the duetility of the transformed pearlite is reduced.
• Refinement of the austenite grains in the conventional steel is disadvantageous because it deteriorates the hardenability.
• Refinement of the austenite grains is also found to be effective in improving the ductility of the transformed pearlite. Improvement of the ductility is getting more important for higher tensile strength steels. Addition of Nb, V, Ti and/or Al is found to be effective for this purpose.
• the high-carbon steel according to the present invention comprises 0.75 to 1.0% of carbon, not more than 0.5% of silicon, 0.1 to 1.0% of manganese, 0.5% to 5.0% preferably 1.0 to 5.0% of chromium, and one or more of 1.0 to 4.0% of cobalt, 0.01 to 0.2% of niobium, 0.01 to 0.3% of vanadium, 0.001 to 0.05% of titanium, not more than 0.10% of aluminium, with the balance being iron and unavoidable impurities.
• Carbon is necessary to be present in an amount of 0.75% at least to increase strength, but excessive carbon causes proeutectoid cementite to precipitate in the grain boundary to lower drawability and toughness.
• the upper limit of carbon is defined at 1.0%.
• Silicon is necessary for deoxidization of the steel, but is undesirable for drawability and thus limited to not more than 0.5%.
• At least 0.1% manganese is necessary for deoxidization and adjustment, but with more than 1% of manganese, a longer time is required for the completion of transformation and the interlammella spacing in the pearlite is expanded.
• the upper limit of manganese is defined at 1.0%. Chromium is most important for refining the pearlite and for this effect more than 0.5% preferably more than 1.0% of chromium is necessary. But if chromium is contained in an excessive amount, a very long time is required for the completion of transformation, and thus chromium is limited to 5% as its upper limit. Cobalt is added in order to prevent the delay in the completion of transformation due to the addition of chromium and manganese. However, less than 1% of cobalt is not effective to promote the transformation while more than 5% of cobalt forms lump carbides harmful to drawability. Thus, the upper limit of cobalt is defined at 5%.
• Niobium, titanium, and vanadium are added in single or in combination in order to form fine carbonitrides to refine the austenite grains and lower the hardenability.
• niobium is defined from 0.01 to 0.2%
• titanium is defined from 0.001 to 0.05%
• vanadium is defined from 0.01 to 0.3%.
• Aluminum also acts for grain refinement by its nitride and is added in an amount enough for deoxidization, and thus limited to not more than 0.1%.
• Table 1 shows the chemical composition of the present inventive steel and Table 2 shows'the starting and finishing time of the transformation and mechanical properties under the patented condition of the present inventive steel.
• a super high strength steel wire having excellent heat treating ability consisting essentially of 0.75 -l .O% Conditions of patenting of carbon, not more than 0.5% of SlllCOn, 0.l to 1.0% 1. Wire Diameter 15 mm of manganese, 1.0 to 5.0% of chrom1um, and a metal 2. Austenization at 950C for 5 minutes 3- Lwd Bath Temperature 580C selected from the group consistlng of l to 4% of cobalt,

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Strip Materials And Filament Materials (AREA)
• Heat Treatment Of Steel (AREA)

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Cited By (5)

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Citations (6)

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• 1971
  • 1971-12-06 JP JP46097840A patent/JPS5120163B2/ja not_active Expired
• 1972
  • 1972-12-05 DE DE2259420A patent/DE2259420C3/de not_active Expired
  • 1972-12-06 US US312727A patent/US3907553A/en not_active Expired - Lifetime
  • 1972-12-06 GB GB5617872A patent/GB1404796A/en not_active Expired

Patent Citations (6)

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