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
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
  • C21D8/0405—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium

Definitions

• An object of this invention is to provide a new and improved process for providing AISI Type 430 stainless steel sheet and strip :which is more effective than the prior art processes in minimizing the ridging problems associated therewith.
• Another object of this invention is to provide a process for producing Type 430 stainless steel sheet and strip having substantially reduced ridging characteristics when subjected to severe cold forming operations, and further having tensile properties equivalent or superior to those of prior art Type 430 stainless steel sheet and strip.
• a further object of this invention is to provide Type 430 stainless steel sheet and strip which can be drawn with minimum ridging in the strained portion thereof.
• the alloy may of course contain the usual steelmaking impurities in amounts insufiicient to affect the alloys properties.
• the process of this invention involves the careful control of all processing parameters in producing the sheet from slab form.
• processing parameters Of critical significance are the hot rolling temperatures, the box annealing times and temperatures following hot rolling, the cold reduction, and the continuous annealing temperatures following cold reduction.
• the preferred process of this invention comprises (1) hot rolling of a slab of Type 430 stainless steel between 1850 and 1950 F. to a thickness of from 0.1 to 0.25 inch; (2) box annealing the hot rolled product at a temperature between 1750 to 1900 F. for at least one hour, and then continuing the box anneal for at least two hours at a reduced temperature of from 14 50 to 1500 F and then furnace cooling the annealed product; 3) pickling and cold rolling the annealed product with a cold reduction of from 35 to and (4) finally continuous annealing the cold rolled product at a temperature of from 1400 to 1500 F. and pickling the cold rolled and annealed sheet or strip product. Steps (3) and (4) may be repeated if necessary in order to attain a product thinner than can be achieved with a. 7 5% cold reduction.
• this inventive process requires lower, critical box annealing temperatures as compared to prior art practices. Whereas box annealing temperatures are usually in the subcritical range, i.e., 1450-1500 F., prior art literature has taught that in order to minimize ridging in a Type 430 steel, higher box annealing temperatures of about 1950" F. are necessary. Contrary to both prior art practices, this process requires a critical annealing temperature not greater than 1900" F., and preferably within the range 1750 to 1900 F., for at least one hour, and then an even lower critical temperature of from 1450 to 1500 F. for at least two more hours.
• the box anneal be performed in a non-oxidizing, non-nitrogen containing atmosphere, such as hydrogen, in order to minimize annealing border, i.e., a heavily oxidized outer edge on the annealed coil.
• the dual temperature feature of the box anneal is primarily to prevent an undesirable open surface characteristic. That is to say, the pickling to remove surface scale following the box anneal has a tendency of producing an open or pitted surface. We believe this is caused by the pickling solution dissolving surface metal adjacent to precipitated carbides at the grain boundaries, which are formed during the box anneal. This detrimental open surface can be markedly reduced by lowering the temperature of the annealing furnace after at least one hour as described. This low temperature treatment reduces the susceptibility of the grain boundaries to attack by the pickling solution. If preferred, the metal can be completely cooled to ambient temperatures between the 1750-1900 F. anneal and the 1450-4500 F. anneal without adverse effect.
• the cold rolling procedure following the box anneal should reduce the annealed hot band from about 35 to about 75%.
• the extent of cold reduction seems to have little or no effect on ridging characteristics.
• total cold reductions of from 35 to 75% are critical to achieve a substantially greater degree of ridging resistance.
• the hot rolling temperatures and the box annealing times and temperatures do not individually have a significant eflect on the steels ridging behavior unless both of the other operations are practiced within the critical ranges.
• there is an unexplainable interaction between hot rolling temperatures, annealing times and temperatures and the degree of cold rolling which, when properly combined, will yield a Type 430 stainless steel sheet or strip having a substantially greater resistance to ridging than is possible with prior art practices.
• the final anneal, and any other intermediate anneal during cold rolling should be a continuous anneal at a temperature within the range 1400 to 1500 F.
• This anneal is a simple stress relief anneal below the transformation temperature, and is substantially the same as has been the practice in prior art processes and, therefore, needs no further discussion.
• specimens 1 /2 inch wide by 14 inches long were cut from the finished product in the longitudinal direction and then polished to a mirror finish. All specimens were then strained 15% in tension at room temperature. Specimens were visually examined and rated for severity of ridging according to the following arbitrary scale: 0none; 1very slight; 2slight; 3-moderate; 4severe; and 5-very severe.
• a process for producing a Type 430 stainless steel sheet product with substantially reduced ridging characteristics when drawn comprising forming a steel slab having the composition by weight percent:
• Percent carbon up to 0.15 manganese up to 1.0 silicon up to 1.0 chromium 16 to 18 iron, balance except for incidental impurities;
• hot rolling said slab at a temperature of from 1850 to 1950 F. to a thickness of from 0.1 to 0.25 inch; box annealing the hot rolled steel at a first annealing temperature of from 1750 to 1900 F. for at least one hour, and then at a second annealing temperature of from 1450 to 1500 F. for at least two hours; cold rolling the annealed steel to final thickness with a reduction of from 35 to continuous annealing the cold rolled steel at from 1400 to 1500 F.; and cooling the steel product.

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

Applications Claiming Priority (1)

Publications (1)

Family

ID=22139463

Family Applications (1)

Country Status (8)

Cited By (6)

Families Citing this family (3)

• 1970
  • 1970-10-02 US US77679A patent/US3684589A/en not_active Expired - Lifetime
• 1971
  • 1971-09-15 CA CA122,930A patent/CA956551A/en not_active Expired
  • 1971-09-20 GB GB4377471A patent/GB1322135A/en not_active Expired
  • 1971-09-23 DE DE19712147624 patent/DE2147624A1/de active Pending
  • 1971-09-23 BE BE772998A patent/BE772998A/xx unknown
  • 1971-09-24 FR FR7134382A patent/FR2109811A5/fr not_active Expired
  • 1971-10-01 NL NL7113539A patent/NL7113539A/xx unknown
  • 1971-10-01 IT IT70230/71A patent/IT942660B/it active

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