Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
  • C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
• • 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
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/0093—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for screws; for bolts
• • 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
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • 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
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon

Definitions

• the present invention relates to a steel for cold working to be made into machine parts, such as bolts and nuts, particularly automotive parts, said steel being particularly in the form of wire or rod suitable for cold working.
• the present invention also covers cold-worked parts made out of said steel for cold working.
• Zr no more than 0.2% (excluding 0%)
• Ti no more than 0.1% (excluding 0%)
• Nb no more than 0.1% (excluding 0%)
• V no more than 0.5% (excluding 0%)
• Ta no more than 0.1% (excluding 0%)
• Hf no more than 0.1% (excluding 0%).
• Al no more than 0.001% (including 0%)
• Ti no more than 0.002% (including 0%)
• Nb no more than 0.001% (including 0%)
• V no more than 0.001% (including 0%)
• Zr no more than 0.001% (including 0%)
• B no more than 0.0001% (including 0%)
• Ta no more than 0.0001% (including 0%)
• Hf no more than 0.0001% (including 0%); and also satisfy the formula (2) below.
• the steel for high-speed cold working may additionally contain, when necessary:
• Mn is an element which is used for deoxidization and desulfurization in the steel-making process. Insufficient Mn leads to incomplete desulfurization which causes FeS film to separate out in the grain boundary, thereby greatly decreasing grain boundary strength and deteriorating deformability.
• the amount necessary for Mn to fully exhibit its effect is no less than 0.05%, with a preferable lower limit being 0.1%, and a more preferable lower limit being 1%. However, excess Mn adversely affects cold workability.
• the upper limit of Mn content should be 2%, preferably 1.5%, more preferably 1%.
• P is an element in inevitable impurities. When contained in ferrite, P segregates in the ferrite grain boundary, thereby deteriorating cold workability. In addition, P subjects ferrite to solid-solution hardening, thereby increasing deformation resistance. Therefore, the P content should be as low as possible from the standpoint of cold working. However, reducing the P content to an extreme leads to an increased steel making cost. With cold workability and process performance taken into account, the upper limit of P content is specified as being 0.05%, preferably 0.03%. It is industrially difficult to completely eliminate P, however.
• the lower limit of total N content is specified; however, the total N content should preferably be no less than 0.007%, more preferably no less than 0.008%, and most desirably no less than 0.009%, so that the amount of dissolved N is more than the lower limit mentioned later.
• the steel according to the basic embodiment of the present invention has the fundamental chemical composition as mentioned above, with the remainder being essentially iron. It may contain inevitable impurities resulting from raw materials, subsidiary materials, and manufacturing equipment, as a matter of course. Also, it may optionally contain any of the following elements.
• Mo increases hardness after working and enhances deformability.
• the Mo content should be no less than 0.04%, preferably no less than 0.08%, and more preferably no less than 0.1%. However, Mo in excess of 2% deteriorates cold workability. Thus, the Mo content should be limited to 2%, preferably 1.5%, and more preferably 1%.
• a steel not having the chemical composition that satisfies the formula (1) permits N compounds of Al etc. to be formed in large amounts, and this leads to an insufficient content of dissolved N.
• This trouble is circumvented by heating and keeping the steel at a temperature at which N compounds resulting from hot rolling dissolves to form solid solution and then quenching the steel.
• This solid-solution heat treatment to prevent N compounds from precipitation increases the amount of dissolved N.
• the object is achieved by heating the steel at a temperature above Ac 3 point plus 30° C. and then quenching it to 500° C. or below at a cooling rate no smaller than 0.5° C./s.
• the inevitable impurities mentioned above may include any of Al, T, Nb, V, Zr, B, Ta, and Hf. These elements readily combine with dissolved N to decrease the amount of dissolved N in the steel. Consequently, the third embodiment of the present invention specifies the content of these elements as follows.
• Al no more than 0.001% (including 0%)
• Ti no more than 0.002% (including 0%)
• Nb no more than 0.001% (including 0%)
• V no more than 0.001% (including 0%)
• Zr no more than 0.001% (including 0%)
• B no more than 0.0001% (including 0%)
• Ta no more than 0.0001% (including 0%)
• Hf no more than 0.0001% (including 0%).
• Part No. I-24 (Steel No. I-1X) suffers cracking due to excess Mn content.
• Part No. II-1 (formed from steel No. II-1A with a C content lower than specified in the second embodiment of the present invention) has a lower hardness than specified.
• Part No. II-50 (formed from steel II-2S containing a less amount of dissolved N than specified, with the formula (1) not satisfied, as shown in Table 9) is poor in balance between cold workability and hardness, with the formula (3) not satisfied.
• Those steels which do not satisfy the formula (1) may contain an adequate amount of dissolved N as specified in the second embodiment of the present invention if they undergo heat treatment adequately. This is true with material Nos. II-73, 74, 75, 78, 79, 81, 82, 83, 86, 87, 90, 91, 93, 94, 95, 98, 99, 101, 102, and 103, shown in Table 10.
• Parts No. III-31 to III-34 (formed from steel No. III-2E having the chemical composition as specified in the third embodiment of the present invention) suffer cracking due to dynamic strain ageing which results from a low strain rate at the time of high-speed cold working.
• Part No. III-57 (formed from steel No. III-2Z with a high content of Ti, V, and B, with the formula (2) not satisfied, is poor in balance between cold workability and hardness.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Heat Treatment Of Steel (AREA)

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• 2007
  • 2007-12-05 US US11/950,715 patent/US20080156403A1/en not_active Abandoned
  • 2007-12-10 EP EP07023882A patent/EP1939309A1/de not_active Withdrawn
  • 2007-12-27 KR KR1020070138127A patent/KR20080063137A/ko not_active Application Discontinuation

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