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
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • 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
• • 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
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0226—Hot rolling

Definitions

• an object of this invention resides in the provision of inexpensive, weldable, tough and high strength steel for structure members that is perfectly usable in its as-hot-worked state, namely without any subsequent or independent heat treatment, having a set of mechanical properties which is characterized by strength, ductility and toughness all maintained at a high level.
• Another object is to determine the proper composition for the steel described above so that the steel may possess the set of mechanical properties as desired in the as-hotworked state when manufactured properly.
• the third is to give the proper method of hot-working for the particular steel described above, by which combination, namely proper hot-working on steel of proper composition, it is only possible to obtain the set of mechanical properties desired.
• Other objects of this invention will in part be mentioned in due course, and yet others will either be self-explanatory or be readily understood or appreciated by those who are skilled in the art.
• this invention relates to a weldable, tough and high strength steel for structure member that is capable of developing a tensile strength of at least 58 kg./mm. but not over 70 kg./mm. yield ratio, the ratio of yield strength to tensile strength, of at least 72%, a ductility of at least 25% in elongation on gauge length of four times the specimen diameter at room temperature, and a notch impact toughness of at least 80 ft.-1b. or 13.8 kg.-m./cm. at 0 C. by 2 mm. V notch Charpy test piece.
• a steel composition in the final product analysis which comprises by weight percent: carbon 0.08- 0.30%, silicon 0.02-0.60%, manganese 0.52.50% nitrogen less than 0.045%, the whole or at least 0.010% of which is to be bound to aluminum in the form of precipitated aluminum nitride of 0.03-0.12%, the rest to any one or combination selected from the group composed of: columbium less than 0.20%, titanium less than 0.12% and zirconium less than 0.20%: free uncombined nitrogen less than 0.004%, free metallic aluminum dissolved in matrix as solid solution (solid solution metallic aluminum) less than 0.15%, as well as at least one complementing alloying element selected from the group consisting of: nickel 0.101.0%, chromium 0.10l.0% molybdenum 0.051.0%, copper ODS-1.0%, vanadium ODDS-0.30%, boron 0.00050.01%; the balance substantially all iron with incidental or unavoidable impurities.
• This invention relates further to a method of manu tacture for weldable, tough and high strength steel or structure member characterized by the set of mechanical properties defined earlier in the as-hot-worked state, the method comprising hot-working the steel in any manner in the temperature range of 1200700 C., starting at. a temperature not above 1200 C. and finishing at not below 700 C., giving the steel a reduction in thickness, calculated on the final thickness of the product, of at least 20% in the temperature range below 1000 C. in one or more passes, thereafter cooling the steel.
• Silicon is added as deoxidizing agent for which at least 0.02% is needed, but tends to excessively harden the matrix by solid solution effect and to affect unfavorably the ductility when present by more than 0.60%, the preferable range being from about 0.3 to 0.5%.
• Manganese which is also an active deoxidizer, is an element that is capable of hardening the steel without impairing the weldability, for which purpose at least 0.5% is needed. However, when present in excess of 2.5%, it tends to stabilize the lower baim'te in the as-hot-worked steel to give rise to a higher strength at a considerable expense in the ductility and toughness. Thereupon, the manganese content is limited to from 0.5 to 2.5%, of which 0.5 to 2.0% is the preferred range.
• Aluminum nitride component of at least 0.03% on nitrogen of about 0.01% is necessary to ensure a high ductility and toughness.
• the nonmetalli-c inclusions particularly oxides of aluminum and silicon that are inevitably retained in the steel, increases rapidly and the cieanness, and with it the ductility and toughness, of the steel correspondingly declined.
• Some solid solution metallic aluminum content is unavoidable insofar as more aluminum must be provided over what is needed for the stoichiometric combination with available nitrogen to ensure the desired aluminu r n nitride content, but it is an unwelcome constituent for the steel because aluminum dissolved in solid solution with the matrix tends to coarsen the grain and thence to affect adversely the mechanical properties, particularly the low temperature toughness, of the steel. We have found that it is allowable only to 0.15% in the steels of this invention.
• columbium Of other metallic nitrides than that of aluminum, we found those of columbium, titanium and zirconium are effective for this invention when existing in conjunction with aluminum nitride without causing the oxide or grain coarsening trouble of the former.
• columbium less than 0.20%, titanium less than 0.12%, zirconium less than 0.20% may be provided.
• they when present in excess, they tend to form oxide and carbide which would act as the crack formation site, and the toughness of the steel is adversely aifected. Free uncombined nitrogen is again unavoidable and on the whole unwelcome, the less of it being the better, for its unfavorable etfect on the low temperature toughness completely overshadows its favorable effect on the yield point.
• Nickel is useful to increase the strength and particularly the toughness of the steel as well as to counter the hot shortness caused by the copper component, when present, and indeed the more of it, the better.
• a content between 0.10 to 1.0%, preferably about 0.2 to 0.8% was found to be proper.
• Chromium is advantageous to ensure a high strength in the as-hot-worked state, though it tends to adversely affect the toughness, hence a range of 0.10 to 1.0%, preferably 0.3 to 0.8%, is useful.
• Molybdenum like chromium, helps to strengthen the steel but also tends to impair the toughness, hence a range of 0.05 to 1.0%, preferably 0.1 to 0.6%, should be present.
• Copper is effective to improve the corrosion resistivity as well as to raise the strength level of the steel, but tends to develop hot shortness and to affect unfavorably on the weldability and low temperature toughness, hence we use a range of 0.05 to 1.0%, preferably 0.1 to 0.8%.
• Vanadium also strengthens the steel when dissolved. in the matrix as solid solution, but tends to enhance the weld-cracking trouble. Balancing those against its price, a range of 0.005 to 0.30%, preferably 0.02 to 0.1%, was found to be satisfactory.
• Boron imparts additional strength without impairing the toughness or weldability in a range of 0.0005 to 0.01%, preferably 0.0005 to 0.005%.
• the temperature range in which to hot-work must be 1200 to 700 C., that is to say, the starting temperature not above 1200 C. and finishing temperature not below 700 C., and the hotworking pass schedule such that a reduction in thickness, calculated on the final thickness of the product, of at least 20% be given in one or more passes which are to be conducted at a temperature below 1000 C.
• the steel thus prepared maybe cooled in any manner, for example, it may be left in air.
• the soaking temperature i.e. the starting temperature for hot-working must not be so high as to cause the dissolution of nitride precipitates; a temperature range of 1100 to 1200 C. has been found proper with regard to the preservation of once precipitated nitride particles and to the ease of hot-working as well.
• Tempew Tempem Reduction work ng a e equally sat1stactory nasmuch as the ture, 0. ture, 0. Per ent workrng is carried out in accordance w1th the method of this invention.
• 1,150 1,100 850 40 Having described heretofore the principles and applica- 22g t10ns of this invention, I do not wish to be confined to the 1:160 1:100 840 50 factual examples shown, but only by the claims as set 1,150 1,110 840 45 fo th 1,150 1, 090 800 25 1,150 1, 000 320 34 I 1.140 1,100 49 1.
• the steel consists of carbon 0.10-0.25%, silicon 0.3-0.5%, manganese 0.5-2.0%, precipitated aluminum nitride 0.03- 0.l2%, metallic aluminum dissolved in the matrix as solid solution less than 0.15%, at least one from: the group consisting of columbium less than 0.20%, titanium less than 0.12%, zirconium less than 0.20%, free uncombined nitrogen less than 0.004%, as well as at least one from: the group consisting of nickel 0.2-0.8%, chromium 03-08%, molybdenum 0.1-0.6%, copper 0.1-0.8%, vanadium 0.02O.1%, boron '0.0005-0.005%; the balance substantially all iron with incidental and unavoidable impurities.
• a weldable, tough and high strength steel for structure members usable in the as-hot-Worked state having a tensile strength of at least 58 kg./mm. but not over 7 kg./rnm. a yield ratio of at least 72%, a ductility at room temperature of at least 25% as measured on guage length of four times the specimen diameter, and a notch impact toughness of at least ft.-lb. or 13.8 kg.-m./cm. at 0 C. as measured by 2 mm.
• V notch Cha-rpy test piece said steel consisting of the ingredients and having been made by the steps defined in claim 1.

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• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Heat Treatment Of Steel (AREA)

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Citations (10)

• 1964
  • 1964-11-18 US US412231A patent/US3328211A/en not_active Expired - Lifetime
  • 1964-11-30 DE DE19641458420 patent/DE1458420A1/de active Pending
  • 1964-12-01 AT AT1015564A patent/AT266898B/de active
  • 1964-12-02 BE BE656553D patent/BE656553A/xx unknown
  • 1964-12-02 GB GB48949/64A patent/GB1083466A/en not_active Expired
  • 1964-12-04 SE SE14697/64A patent/SE321253B/xx unknown

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