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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/04—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for drawing, e.g. for deep-drawing
• • 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
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese

Definitions

• the steels used consists substantially of unalloyed ferritic steels, ferritic chromium steels and austenitic chromium nickel steels.
• the austenitic chromium nickel steels and the lowcarbon unalloyed steels have excellent deep drawing characteristics, it being a rule that a reduction of the strength characteristics, especially the yield point, results in an improvement in deep drawing ability.
• Rust-resistant steels of the quality X 8 Cr 17 according to DIN Preliminary Standard 17440 have substantially poorer deep drawing ability than unalloyed steel types (Blech No. l l, 1965, page 627).
• austenitic chromium nickel steels are superior to the ferritic chromium and chromiummolyêtum steels in regard to deep drawing qualities, but chromium nickel steels are substantially more expensive.
• chromium nickel steels are substantially more expensive.
• Austenitic types of steel have been develped to relieve the cost situation, which makes it possible to reduce the nickel content by partially replacing this element with manganese and/or nitrogen. These steels are not widely used, either, however, because they are still too expensive andthe problem of yellowishness is stillencountered in them. Examples of such steels are AlSl 201 and 202.
• the roundel diameter is an indication of the roundel area that is to be formed, if the roundel diameter is increased by about 10 percent, for example, about 20 percent more roundel area has to be formed, resulting in a corresponding increase in the cup depth. In practice, therefore, the object is to achieve the highest possible drawing ratios in one draw.
• the maximum drawing ratio thus permits comparison of the deep drawing characteristics of various materials.
• thegreatest possible roundel ratio that can be achieved in ferritic steels with their poor formingqualities is approximately 1.6 in a single draw, while the austenitic steels are much better, with values of 22 maximum.
• the present invention involves a new process whereby the deep drawing ability of ferritic chromium steels containing molybdenum is so substantially im proved that it is similar to the austenitic chromium nickel steels. That the fieldof application of this type of steel is thus substantially expanded.
• Annealing is performed between the individual cold rolling steps and after the final step at temperatures of 820 to 650C, with holding times of seconds to 10 minutes. followed by cooling.
• the steel composition used in this invention comes partially within the scope of the molybdenum alloy 17 percent chromium steels of the following composition:
• BaL iron and impurities.
• Known chromium steels contain, in their regular commercial form, a maximum of about 0.30% nickel, about 0.03% nitrogen, and a maximum of 0.20% coper. The aluminum content runs up to 0.05%. On the basis of these common alloying admistures, factors of F 2.5 are obtained when the above equation is applied.
• the F factor computed according to the above equation equals 3.4 to 5.3. It is furthermore advantageous to select the alloy composition such that F is between 3.5 and 4.5, and preferably between 3.7 and 4.3.
• the box annealing of hot rolled strips and sheets of chromium steels and chromium molybdenum steels which is designed to eliminate the linear arrangement of the ferrite grains and carbides produced as a result of the preceding hot rolling process, it customarily performed under inert gas in the 850 to 800C range (Bander Bleche Rohre," Duesseldorf, 2, 1963, p.61
• the box annealing of hot rolled strip is normally performed in one step. Multi-step annealing processes can be used if desired.
• a multi-step hot rolled strip annealing process for ferritic chromium steels prevents the occurrence of the so-called riffle structure and improves the mechanical-technological characteristics (German Auslegeschrift No. 1,222,520).
• the multi-step hot-rolled strip annealing prescribed according to theinvention in the form of three-step annea1ing, consists of the followingprocess steps: 1
• the mu1ti-step-hot-ro11ed strip annealing can consistof a continuous five-step treating process entailing the following steps:
• the annealed andpickled. hot-rolled strip can be cold-rolled by known methods.
• Cold-rolling hardens the chromium molybdenum steel and thereforeithas to be annealedprior to cold forming or deep drawing operations.
• the technical expert is familiar with the fact that higher temperatures result in *better ductility in the finished strips, butloss of surface quality places limits on the temperature that canbe used. Temperatures of 850C are rarely exceeded.” To protect the surface the steel strips are annealed in a continuous furnace and then pickled in chemical baths.
• temperatures of 850 820C are necessary in orderto achieve the state of optimum formability at short annealing times (e.g., max. 10 min for a strip 5 mm thick).
• this steel has to be annealed at temperatures of 780 to 700Cin order to have the maximum ductility and outstanding deep-drawingcharacteristics.
• An additional embodiment of the process calls for a preferred annealing range of 770 720C. Temperatures of 750 730C are also possible. It is sufficient that the strip beheld at these temperatures for 5 seconds to. 10 minutes. It is therefore advantageous to perform this annealingin continuous furnace, although stationary annealing process can also be used.
• the improvement in deep drawing properties is also produced when the final annealing is performed such that 1 to 10% transformation structrures are present in addition to ferrite in the finished strip.
• This effect with hfi slsshnkal ass isjf i arimis k P to 666" vfiien steels having a 'y to 60 transformation are heated so high and so long that the 7 region is present at least partially, and are then cooled in such a manner thatthe state of equilibrium the structure is forestalled.
• the application of the formula given above showed the F factor to be 1.136.
• the hot-rolled strips were annealed in a stack in the box annealing furnace for a period of 34 hours at 840C, then pickled, and then coldrolled to 1.5 mm thickness. Then the material was annealed at 840C for about 20 sec and pickled. Afterward, the strips were rolled again to a final thickness of 0.6 mm, treated for about 15 sec at 850C in the continuous annealing furnace and then pickled. After the continuous annealing process the strips were sensitive, in intermediate and final thickness, to the occurrence of the flaw known as flow figures. The material therefore had to be re-rolled twice in final thickness in a dressing machine.
• Run 2 The strips were annealed for 3 hours at 880C, then cooled in the furnace by 170C to 710C and held at this temperature for 20 hours. The total annealing time amounted to 41 hours.
• Run 2.2 These strips were annealed for 2.5 hours at 900C; after furnace cooling by C down to 740C they were held at the latter temperature for 6 hours, furnace-cooled again by 40C down to 700C and held at this temperature for 15 hours. The total annealing time was 43 hours.
• All of the hot-rolled strips were pickled.
• One strip 2.11 and strip 2.21 were cold rolled to 1.5 mm thickness and, in the roll-hard state, they were divided into two halves.
• the one half 2.1 1 1 and 2.21 l was annealed for about 20 sec at 760C, then rolled down to a final thickness of 0.6 mm and divided into two halves.
• the second hot-rolled strip -2. l2 and 2.22 was coldrolled directly to 0.6 mm and also divided into two strips while in the roll-hard state.
• the one half of the cold-rolled strip in each case, in the 0.6 mm thickness, was given a final annealing for about 15 sec at 760C.
• Examination of the material in the finished state showed a ferritic structure and flow-figure susceptibility in all strips of the 1.5 and 0.6 mm thicknesses. The finished strips therefore had to be dressed in two passes. Then the flow-figure susceptibility was eliminated.
• the strips 2.112 and 2.212 of the 1.5 mm thickness were annealed 25 sec at 810C and cold-rolled to 0.6 mm; all strips of the 0.6 mm thickness were treated at 810C in the continuous annealing furnace and force-cooled. After pickling, all of the strips in the finished state showed transformation structure along with 3 to 6% ferrite. All strips were free of flow figures and therefore they could be cut into plates and shipped to fabricators without any additional dressing procedure. In this state, maximum draw ratios B of 2.24 to 2.27 were found.
• Example 2 was made, as described in Example 1, into cold-rolled strip of the 0.6 mm thickness, some of it through the 1.5 mm intermediate thickness and some of it by direct rolling.
• the alloying quotient (F) of this melt was 4.169.
• the making of this melt into cold-rolled strip differed only in that, to eliminate the dressing procedure, the strips were annealed at a temperature of 800C with the same holding times as in Example 1, and after this separate annealing and forced cooling they were found to have 3 to 5% transformation structrue.
• step (a) is carried out at a temperature between 850 and 920C.
• step (c) is carried out at temperaturesbetween 740 and 650C.
• step (a) is carried out at a temperature between 850 and 920C.
• step (c) is carried out at temperaturesbetween 740 and 650C.
• step (a) is carried out at temperatures between 920 and 850C
• step (c) is carried out at temperatures between 800 and 720C
• step (e) is carried out at temperatures between 730 and 650C.

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• Chemical & Material Sciences (AREA)
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• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Heat Treatment Of Sheet Steel (AREA)

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Cited By (4)

Citations (4)

• 0
  • BE BE757711D patent/BE757711A/xx unknown
• 1969
  • 1969-11-03 DE DE1955026A patent/DE1955026C2/de not_active Expired
• 1970
  • 1970-10-14 LU LU61874D patent/LU61874A1/xx unknown
  • 1970-10-20 NL NL7015331A patent/NL7015331A/xx unknown
  • 1970-10-29 FR FR7039076A patent/FR2071873A5/fr not_active Expired
  • 1970-10-29 CH CH1614770A patent/CH546282A/xx not_active IP Right Cessation
  • 1970-11-02 AT AT984670A patent/AT317955B/de not_active IP Right Cessation
  • 1970-11-02 GB GB5200770A patent/GB1312309A/en not_active Expired
  • 1970-11-03 US US00086610A patent/US3784418A/en not_active Expired - Lifetime
  • 1970-11-03 CA CA097,240A patent/CA942643A/en not_active Expired
  • 1970-11-03 SE SE14863/70A patent/SE354295B/xx unknown

Patent Citations (4)

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