Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D7/00—Casting ingots, e.g. from ferrous metals
  • B22D7/02—Casting compound ingots of two or more different metals in the molten state, i.e. integrally cast
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/49—Method of mechanical manufacture
  • Y10T29/4998—Combined manufacture including applying or shaping of fluent material
  • Y10T29/49988—Metal casting
  • Y10T29/49991—Combined with rolling

Definitions

• the composite is formed at the ingot stage by casting carbon steel or low alloy steel simultaneously about a stainless steel plate suspended in a 'mold, which plate has had its major surfaces covered by a protective layer so as to control the alloy depletion therefrom.
• the resulting product exhibits excellent resistance to pitting and penetration in those corrosive environments where such phenomena are known to be a problem.
• Corrosion which is the chemical breakdown of basic materials such as metal, is the result of environmental conditions. Where it is impossible to affect changes in the environment, the solutions to overcome the problems of corrosion necessarily shift to a consideration of the materials. And, while one obvious answer would be to select materials unaffected by the service to which the material is to be used, practical considerations often prohibit such a move. Therefore, the general approach by industrial concerns has been in the direction of selecting materials which offer the best resistance to corrosion at the lowest ultimate cost.
• the present invention was prompted by the need to find a material that would resist those corrosive conditions which promote localized attack commonly referred to as pitting.
• pitting For example, one problem area was in the field of culverts and underground storage containers, which encounter such conditions as salt water marsh, fresh water marsh, mine water, alkali and acid soil and water, farm field drainage, and domestic sanitary sewage.
• a corollary problem exists in automotive mufllers where condensate will collect and cause perforations and early failure.
• a stainless steel plate whose thickness is at least about 5%, but preferably about 28%, of the total ingot, is secured vertically, in sandwich relationship between chill plates made of carbon steel, through the center or other desired position of a mold. Only simple preparation is required for the surfaces of the stainless and chill plates, such as pickling or shot blasting.
• molten carbon or low alloy steel is poured into the two cavities formed by positioning the stainless-canbon steel composite in the mold.
• the composite ingot is stripped and processed by the conventional steps which may include: surface conditioning, heating, hot rolling, cold rolling, shearing, and coiling.
• the foregoing procedure results in a composite structure which exhibits an excellent bond between the stainless steel and the carbon or low alloy steel. While the starting ratios between the two materials and the percent reduction thereafter will generally dictate the final thickness of the layers, for practical purposes, the stainless layer should be no less than .001 inch in the finished product. Preferably, it should be at least .005 inch thick to insure that the core is continuous in the final product, as well as providing a product which resists mechanical damage.
• the composite of this invention comprises essentially three layers, the outside layers being carbon or low alloy steel, and the inner layer, stainless steel.
• the ratio of the total thickness to the stainless core thickness of a final hot rolled product is about 10:1 to about 50:1. Lower ratios, on the order of 3:1, may be developed from the same starting product by further cold reductions. This phenomenon occurs since the stainless core is reduced less than the outer carbon or alloy steel layers.
• this invention contemplates the provision of a metallic composite characterized by a thin, stainless steel core sandwiched between two relatively thhic-k carbon or low alloy steel layers. Such composite is particularly 'valuable in moist environments where pitting-type corrosion is a primary problem.
• the corrosion of metals is an electrochemical occurrence. That is, the flow of electric current is associated with the phenomenon. From this is would follow that excessive amounts of moisture, which is the vehicle for the current flow, tend to accelerate the action. From the above, it can be analogized that the phenomenon or corrosion is like that of a battery or electrolytic cell. In the respective systems, there is an anode and a cathode in a conducting solution, wherein said solution is called the electrolyte. Therefore, one of the major factors in the rate of corrosion is the magnitude of the current flow in the electrolyte. By directing said current flow, or in some way controlling it, the rate of corrosion can be minimized.
• Hot dipped zinc coated steel is a prime example of the latter method.
• a steel core is provided with a layer of zinc by the continuous hot dip or galvanizing process.
• the zinc acts like a barrier film to the steel core.
• galvanic protection takes over.
• This galvanic protection just described is essentially the same as found with the present invention.
• in the former situation once broad areas of the steel core become exposed general corrosion of the core takes place. In the latter, protection continues despite the exposure of the core.
• the composite contemplates a cathodic stainless steel core in a matrix of anodic carbon or low alloy steel. Since the stainless is cathodic to, or less anodic than the mild steel in corrosive environments, the corrosion of the mild steel protects the inner layer of stainless. However, when a corroded area or pit reaches the inner core of stainless steel, the pit enlarges rather than a penetration of the core. This was different than the combination of zinc on steel since the general corrosion rate of a plain carbon steel core is considerably higher than the rate of a stainless core.
• a further development recognized in the composite of the invention is the synergistic relationship between the stainless steel core and the outer layers of carbon or low alloy steel under conditions of localized corrosion. That is, it has been found that under severe pitting conditions the performance of the composite was superior to that of equal thickness stainless. While there is no desire to be bound by any theory, it is believed that as the corrosion proceeds, the phenomenon of polarization takes place. Under this theory, it is believed that hydrogen is deposited on the surface of the cathodic stainless, thereby retarding the current flow which tends to lower the rate of corrosion. It will be acknowledged that this result is apparent only in cases of localized corrosion or pitting such as occurs under chloride attack. Under conditions of generalized corrosion, a stainless plate alone would offer better protection.
• the preferred procedure forms the composite at the ingot stage, an early step in producing steel.
• a stainless steel plate whose thicknes when compared with the mold falls within the range described above, is disposed along the axial center of, and parallel to, two sides of the mold. However, it should be understood that said stainless plate may be positioned off-center of the mold. In either case, to each major surface of said plate there is provided a protective layer of film. This layer is provided to inhibit alloy depletion of the stainless plate.
• the protective layer will be in the form of mild steel or ingot iron chill plates placed adjacent the stainless core. This arrangement results in substantially two identical cavities in the preferred embodiment, on either side of the plate.
• a quantity of molten carbon or low alloy steel is poured to fill the respective cavities.
• the simultaneous casting may be accomplished by means of a tundish having dual nozzles. This procedure requires a minimum of surface preparation for the stainless insert plate. Generally, a minor pickling or shotblasting step may be used. With other known methods, considerable surface preparation is required.
• a skin of mild steel solidifies on the core plate. Since a stainless core (for example, AISI Type 304) has a melting point below that of the mild steel, there is sufficient heat to melt the stainless core. The solidified skin thickness and the alloy constituents of the stainless core begin to diffuse into the adjacent skin. It is believed that this lowers the melting point of a portion of the adjacent skin and that portion is remelted. Mixing ensues and a core of reduced alloy content forms. The new depleted core can be twice or more its initial volume When it finally stabilizes and solidifies. This procedure results in a composite structure, but one having a mild steel outer skin and a non-stainless core.
• Type 304 stainless other types of stainless steel are contemplated.
• the proposed application and the severity of the environmental conditions will dictate the type of stainless needed in the composite.
• a molybdenum bearing austenitic stainless steel may be desired.
• a Type 410 stainless steel will be adequate under less severe conditions. Therefore, stainless steel as contemplated herein includes all ferrous alloys containing about 11% or more chromium, and other alloying elements normally found therein.
• a further and final feature contemplated by this invention is the provision of an exterior coating on the finished clad product. It may be desirable to secure additional general corrosion protection or merely to enhance the appearance of the product. Accordingly, the coating may be metallic such as zinc, aluminum, terne, lead, chromium, nickel, cadimum, etc., or a non-metallic such as asphalt, paint, plastics, etc.
• this listing is merely illustrative and should not be read as excluding others. No attempt will be made here to suggest a coating or combination of coatings for a given environment as it is believed that a skilled worker in the art will know the most appropriate coating to be used, and the manner of applying same.
• the method of producing a metallic composite ingot having a thin core of stainless steel fused to two thick outer layers of carbon or low alloy steel comprising the steps of selecting a plate of stainless steel, applying to the major surfaces thereof a metallic protective layer suitable to control the depletion of chromium therefrom to a level no less than about 11%, and casting a carbon or low alloy steel to the outside of said protected stainless steel plate to form an ingot.
• said protective layer comprises a pair of mild steel or ingot iron plates disposed adjacent said stainless steel plate.
• the method according to claim 1 including a reduction step which comprises reducing said ingot to produce a strip whereby the thickness of the resulting stainless core is at least .001 inch.
• said reducing step comprises hot reduction to produce a strip whereby the ratio of the strip thickness to the core thickness is between about 10:1 to 50:1.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Laminated Bodies (AREA)
• Pressure Welding/Diffusion-Bonding (AREA)
• Metal Rolling (AREA)
• Continuous Casting (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=25168618

Family Applications (1)

Country Status (11)

Cited By (5)

Families Citing this family (2)

Family Cites Families (3)

• 1969
  • 1969-02-04 US US796616A patent/US3621561A/en not_active Expired - Lifetime
• 1970
  • 1970-01-22 CA CA072867A patent/CA929723A/en not_active Expired
  • 1970-01-22 NL NL7000900A patent/NL7000900A/xx unknown
  • 1970-01-29 BR BR216400/70A patent/BR7016400D0/pt unknown
  • 1970-01-29 BE BE745166D patent/BE745166A/fr unknown
  • 1970-01-29 FR FR7003146A patent/FR2030281B1/fr not_active Expired
  • 1970-02-02 LU LU60289D patent/LU60289A1/xx unknown
  • 1970-02-02 GB GB1289639D patent/GB1289639A/en not_active Expired
  • 1970-02-03 DE DE19702004681 patent/DE2004681A1/de active Pending
  • 1970-02-03 RO RO62336A patent/RO57888A/ro unknown
  • 1970-02-04 ES ES376200A patent/ES376200A1/es not_active Expired

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