Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
  • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
  • C23C8/24—Nitriding
  • C23C8/26—Nitriding of ferrous surfaces
• • 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
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • 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
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/02—Pretreatment of the material to be coated
• • E—FIXED CONSTRUCTIONS
  • E06—DOORS, WINDOWS, SHUTTERS, OR ROLLER BLINDS IN GENERAL; LADDERS
  • E06B—FIXED OR MOVABLE CLOSURES FOR OPENINGS IN BUILDINGS, VEHICLES, FENCES OR LIKE ENCLOSURES IN GENERAL, e.g. DOORS, WINDOWS, BLINDS, GATES
  • E06B9/00—Screening or protective devices for wall or similar openings, with or without operating or securing mechanisms; Closures of similar construction
  • E06B9/01—Grilles fixed to walls, doors, or windows; Grilles moving with doors or windows; Walls formed as grilles, e.g. claustra
• • 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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/18—Hardening; Quenching with or without subsequent tempering

Definitions

• This invention relates to hardened steel security materials such as security plate and security bars for use, for example, as bars or grilles in windows, doors and other openings to prevent illegal egress or ingress in custodial institutions.
• security bars may have various cross-sections such as circular, rectangular, square or polygonal.
• COMSTEEL P8 is an austenitic steel grade with 1.1 to 1.25% carbon and 11 to 13% manganese. In castings, this material is frequently used in operational conditions where resistance to wear by impact is required such as in the mining and earth moving industries. In bar form, COMSTEEL P8 is inherently low in hardness but brittle in the remainder of its mechanical properties.
• the main reason for using COMSTEEL P8 in security applications is its propensity to work-harden, that is, during an attempt to saw, drill, mill or turn, the austenitic crystal structure (Face-Centred-Cubic) will twin along the miller (111) plane, forming a new crystal structure with each grain which resists the free movement of dislocations throughout the grains.
• work-harden that is, during an attempt to saw, drill, mill or turn, the austenitic crystal structure (Face-Centred-Cubic) will twin along the miller (111) plane, forming a new crystal structure with each grain which resists the free movement of dislocations throughout the grains.
• COMSTEEL P8 does not lend itself to workmanlike welding because of the strongly cored and large austenite grains. It has been observed that P8 bar assembly welds have cracked during the initial welding of the security screens. Egress from a welded COMSTEEL P8 assembly is readily achieved by a few blows with a heavy object causing the austenite grains in the heat affected zone adjacent to the weld to fail in a sudden and brittle mode. Furthermore, welded COMSTEEL P8 assemblies have a pronounced propensity for stress-corrosion cracking during manufacturing which is exacerbated after installation and the use of impactive forces.
• COMSTEEL P8 bars are no longer procurable in Australia and thus there is a need for a security bar which possess the positive benefits of the COMSTEEL P8 bar but in addition can provide a security grill which is tamper proof against attempts employing generic hand tools and which may be assembled by welding and which will respond to impactive forces like a spring and not deform or fail in a brittle mode.
• a hardened steel bar, grille, sheet, plate or other shaped material which is suitable for security purposes and which is formed from a nitridable steel which is subjected to austenitization followed by oil quenching and then tempered and nitrided to provide a hardened steel material having a surface hardness of at least 50 HR C .
• a method of preparing the hardened steel material comprising the steps of:- (i) selecting a nitridable steel; (ii) subjecting the nitridable steel to austenitization, quenching and tempering to provide a heat treated material, and (iii) nitriding the heat treated material to provide a hardened steel material having a surface hardness of at least about 50 HR C .
• the depth of nitriding may be from about 0.4 to about 0.6mm.
• the surface hardness of at least about 60 HR C may extend to a depth of about 0.2mm and the hardness at the 0.4 to 0.6mm extent of nitriding may be about 30 HR C .
• the nitridable steel preferably contains aluminium and may contain chromium and molybdenum.
• the aluminium content may be in the range of about 0.2 to about 2.0%, but preferably in the range of about 0.5 to about 2.0% or about 0.8 to about 1.2%.
• the chromium content may be in the range of about 1.00 to about 1.80%.
• the molybdenum content may be from about 0.15 to about 0.40%.
• the carbon content of the steel is preferably from about 0.28 to about 0.45%.
• the nitridable steel may be AISI 4140 or any other steel from the AISI 4000 and 8000 series or B S En 41 B.
• the family of nitridable steel grades is preferably limited to but a few and is generally restricted to the AISI 4000 and 8000-series mentioned above.
• Suitable alternatives to AISI 4140 are AISI 4130N, AISI 4340, AISI 8135/40 and AISI 8135/45.
• BISALLOY 500 and K10 are typical commercially available nitridable steel plates.
• Fig. 1 is a graph of hardness (HR C ) against depth of nitriding for a hardened steel bar according to an embodiment of the invention and for a galvanised hardened steel bar according to an embodiment of the invention.
• the second significant feature of the results is that the hardening process resulted in two distinct regions.
• the first region is the surface region which exhibited a hardness of 60-67 HR C to a depth of 0.2mm. In the second region, the hardness drops rapidly down to 33 HR C at a depth of 0.5 to 0.6mm.
• the En 41 B test material (which contains aluminium) is a preferred steel type which will achieve the greatest depth of hardening and the highest level of hardness at the surface. Other materials such as 4140 and 4340 will go close to achieving similar depth of hardening but the surface hardness will be less. The difference is the surface hardness for En 41 B versus 4140 would be of the order of 65 HR C at 0.2mm as against 54 HR C at 0.1mm.
• the heat treatment procedures prior to nitriding are similar for each nitridable steel as the parameters governing the balance of mechanical properties of the substrate are the Time-Temperature-Transformation, or I I I diagrams, which are essentially equivalent within the lower cost nitridable steel grades.
• austenitization is carried out by heating the material to about 880°C and holding it at that temperature for about 1 hour.
• the quenching step may be carried in medium fast oil (12 to 14 cubic inches/second) in a Seal- Quench furnace.
• the tempering step may be carried out at about 320°C for about 1.5 hours in an air-recirculation furnace.
• the nitriding step may be carried out by using any convenient process such as the BRISTUFF (Trade Mark) nitriding process.
• This process differs from the generally employed double dissolution of ammonia process by using single dissolution of ammonia which results in surface hardnesses in excess of 60 HR C (HARDNESS ROCKWELL “C” to AS 1815-1992).
• the nitrided layer may be to a depth of about 0.6mm.
• the security bar has a typical balance of mechanical properties of 1100 (MPa) U.T.S at a minimum elongation of 8%. Thus, the security bar is resistive to bending and there is no propensity for brittle failure.
• a grille or assembly of the security bars of the invention comprises a horizontal and vertical arrangement of the bars welded into a mesh of required aperture size.
• the mesh is contained within a frame to which the horizontal and vertical bar ends are welded with the ends protruding beyond the frame by about 60mm.
• the protruding ends are concreted into the surrounds of the opening to which the grille is applied.
• the welding is preferably a Metal-Inert-Gas (MIG) welding process using stainless steel filler wire to AISI 316L.
• MIG Metal-Inert-Gas
• test pieces were subjected to machine hacksaw testing at various downloads and speeds. It was found that the bar could not be excised without frequent machine blade changes since the blades were dulled by losing both set and tooth depth immediately after commencements of attempts to cut the bars.
• the weldments could not be cut. Owing to a 45% penetration of the weld puddle into the substrate, excisions through the remainder of the bar substrate were not successful - that is, the bars of a grill system could not be separate through the weldments since the parting tool contacted the fused substrate which does not permit separation by sawing.
• the resistance to corrosion of the security bars of the invention is basically governed by the type of protection such as Electroless Nickel Plating, Zinc-Aluming, Galvanizing or Primer/Paint applications.
• An anticipated service life of 15 to 20 years or more can be envisaged by employing any of the abovementioned permanent protection methods.
• a security bar of the hardened steel having a diameter of 20mm and a 0.6mm nitrided layer having a surface hardness of about 60 HR C , cannot be separated other than by 'angel wire', a diamond and CBN (Cubic Boron Nitride) laced wire used in the Engineering Industry.
• the hard particles are attached to the parent wire by means of a polymer and tend to dull when used to cut nitride layers. To cut through such a 20mm bar would consume approximately 5 wires.
• the harmonics created within the parent wire emit a loud, screeching sound, which can be heard by supervisory personnel.
• nitriding layer depth does not depend upon the mass heat treated, but on the nitriding parameters, which are, being a surface induced process, the same for varying diameters.
• An improved security grille could be constructed by creating a mechanical interlocking system of weft and weave pressed into the bars and connected by monel pins with the shaping of the substrate bars taking place prior to heat treatment.
• the nitridable steel material may be in the form of a plate or sheet which is treated in the same manner as the bar to provide a security sheet or plate.
• the security plate could be formed from a Bisalloy steel.
• the security material can be in any other convenient forms apart from bars and plate,

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Structural Engineering (AREA)
• Architecture (AREA)
• Civil Engineering (AREA)
• Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)

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• 2000
  • 2000-01-28 EP EP00904691A patent/EP1163063A4/de not_active Withdrawn
  • 2000-01-28 WO PCT/AU2000/000048 patent/WO2000044511A1/en not_active Application Discontinuation

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