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
  • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
• • 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
• • 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
  • 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
  • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
• • 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
  • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese

Definitions

• the invention relates to a high strength, air-hardening steel with excellent shaping properties, in particular for the construction of lightweight vehicles according to the preamble of claim 1 .
• Weight saving of all vehicle components plays hereby a role, on one hand, as is also, on the other hand, a substantially effective behavior of the individual structures, when exposed to static and dynamic stress during operation as well as in the event of a crash.
• Suppliers attempt to account for this requirement by reducing the wall thickness of available high strength and super high strength steel while at the same time improving the behavior of the structures during manufacture and operation.
• Such steels are thus required to satisfy the comparably high demands with respect to strength, ductility, toughness, energy absorption, and workability, for example through cold forming, welding, and/or surface treatment.
• R el and R p0.2 700-850[MPa]
• R m 800-1000[MPa]
• a 80 ⁇ 11 [%]
• a 5 ⁇ 13 [%]
• air-hardening steel materials have been developed as an alternative which overcome the shortcomings of conventional steels just by air-cooling the steel, following a heat treatment for example, in order to realize the demands on material properties.
• the cold workability can be realized by a subsequent soft annealing process, e.g. in a hood-type annealing furnace, or by homogenizing through annealing.
• cold workability may also be retained after hot rolling, when slowly cooling a coil that has been wound respectively tight in some circumstances in a special heat-insulated hood.
• air hardening with subsequent tempering may then be realized again by a following heat treatment, for example advantageously by high temperature galvanizing.
• DE 102 21487 B4 discloses the use of an air-hardening steel material for shaped parts in the construction of lightweight vehicles, containing the primary elements C (0.09-0.13%), Si (0.15-0.30%), Mn (1.10-1.60%), Cr(1.0-1.6%), Mo (0.30-0.60%), and V (0.12-0.25%), remainder iron including incidental accompanying elements.
• EP 0 576 107 B1 discloses an air-hardening steel with reduced Cr content for production of seamless, ungalvanized structural tubes, for example as door reinforcements in the manufacture of automobiles.
• the alloy concept on the basis of Mn—Si—Ti—B includes as primary elements C (0.15-0.30%), Mn (2.05-3.35%), Si (0.50-0.80%), Cr (0.5-1.0%), Mo (max. 0.6%), Ti (0.01-0.05%), B (0.0015-0.0035%), and N (0.002-0.015%), remainder iron and incidental accompanying elements.
• This steel known for the seamless tube production, has the drawback that as a result of the relatively high contents of C and Mn, this alloy concept places constraints on the basic welding capability of the steel, on one hand, and greatly limits the galvanizing capability through hot dipping or high temperature galvanizing as a result of the also high content of Si of up to 0.8%.
• a prerequisite for establishing a sufficient tempering resistance is the formation of a sufficient amount of Cr carbides, Mo carbides and/or V carbides, or carbon nitrides, which prevent slip dislocation at elevated temperatures as a result of precipitation on the grain boundaries. This process is called secondary hardening.
• a steel alloy is hereby used having the primary elements: C (0.17-0.28%), Mn (1.30-2.50%), Si (0.30-0.49%), Cr ( ⁇ 0.49%), Mo (0.20-0.40%), Ni (0.05-0.19%), Ti (0.02-0.07%), B (0.0015-0.0050%), Nb (0.01-0.10%), V(0.01-0.10%), and N ( ⁇ 0.015%), remainder iron and incidental accompanying elements.
• the total content of V+Nb+Ti may not exceed a value of 0.15%.
• This alloy concept with additives of Nb and Ni is expensive for an air-hardening steel to meet the demanded requirements, and welding is problematic because of the relatively high C content. Moreover, this steel has a content of 0.30 to 0.49% of silicon which is critical for galvanizing capability.
• invention is based on the object to provide a high strength air-hardening steel exhibiting excellent shaping properties, in particular for the construction of lightweight vehicles, by using a different cost-saving alloy concept, and realizing the desired mechanical properties while at the same time ensuring especially the HFI welding capability as well as exhibiting superior general welding, galvanizing, and tempering resistances.
• the high strength, air-hardening steel according to the invention for the construction of lightweight vehicles is characterized in that this alloy concept realizes an excellent welding capability during HFI welding, without the undesired chromium-carbide precipitations in the weld seam.
• this alloy concept realizes an excellent welding capability during HFI welding, without the undesired chromium-carbide precipitations in the weld seam.
• the decreased Si content ensures the galvanizing capability of the steel, and the addition of V ensures the tempering resistance.
• the alloy concept in accordance with the invention is based on the recognition that, in contrast to conventional steel for seamless tubes where nitrogen must completely react with titanium to avoid boron nitride precipitations and to thereby ensure the effectiveness of the added boron, nitrogen fixation may also be realized by other alloy elements such as Cr or Mo.
• variant 1 meets the demanded mechanic-technological properties, the high Cr content of 1.4% causes, as already described above, the undesired chromium-carbide precipitations and thus prevents the formation of a high-quality HFI weld seam and thus the production of longitudinally welded tubes.
• Variant 2 is used to date only for the seamless tube production in ungalvanized configuration.
• This steel exhibits in particular a small content of carbide-forming elements, primarily chromium.
• variant 3 Compared to variant 2, variant 3 has lower Si and Mn contents, whereas the C content is slightly increased.
• the variants 4 and 5 based on a V—Ti—B concept, exhibit in the “soft” state mechanical characteristic values which meet the requirements.
• tempering resistance of these variants can be improved in comparison to the variants 2 and 3 by addition of V as well as by a slightly elevated Mo fraction.
• Variant 4 having, compared to the variants 2 and 3, a Mo content which has been increased to 0.56%, still fails to provide sufficient tempering resistance.
• the Mo content of variant 5 has been slightly elevated to 0.63% and the Cr content significantly to 1.15%.
• the requirements have been met at tempering temperatures of up to about 550° C., whereas above this tempering temperature a significant strength rise has been determined which does not meet requirements.
• the chemical composition of the steel was as follows:
• the determined mechanical characteristic values, as determined in the soft state of the cold strip are listed in the following with respect to different tempering temperatures:
• Tempering should hereby simulate the heat treatment from the state “soft” during hot galvanizing. The results show that the requirements with respect to the steel properties in the soft state have been met even after galvanizing.
• the mechanical characteristic values, as determined in the tempered state of the cold strip, are listed hereinafter in the event of heat treatment comprised of austenitizing for 15 min at 920° C., subsequent air cooling to room temperature, and final tempering to different tempering temperatures:
• the results show the high tempering resistance of the steel up to temperatures of at least 700° C.
• the mechanical characteristic values as determined in the tempered state of the tubes in the event of a heat treatment, comprised of austenitizing at 930° C., the subsequent air cooling, and tempering to 575° C., are:
• this steel is not only advantageous for use in the automobile industry but furthermore in all applications in which enameling in combination with high steel strengths is required.
• the enameling temperature of the steel of above 900° C. may hereby be used to obtain high steel strengths using air hardening during subsequent cooling.
• the field of application for such enameled, air-hardened steels may, e.g., include the household appliance industry or the chemical apparatus construction industry.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Coating With Molten Metal (AREA)
• Heat Treatment Of Sheet Steel (AREA)

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• 2004
  • 2004-11-03 DE DE102004053620A patent/DE102004053620A1/de not_active Withdrawn
• 2005
  • 2005-11-03 DE DE502005002780T patent/DE502005002780D1/de active Active
  • 2005-11-03 EP EP05811386A patent/EP1807544B1/de active Active
  • 2005-11-03 US US11/718,573 patent/US20090173412A1/en not_active Abandoned
  • 2005-11-03 KR KR1020077010023A patent/KR20070073858A/ko not_active Application Discontinuation
  • 2005-11-03 WO PCT/DE2005/001991 patent/WO2006048009A1/de active Application Filing

Patent Citations (1)

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