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
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/02—Hardening by precipitation
• • 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
  • C23C30/00—Coating with metallic material characterised only by the composition of the metallic material, i.e. not characterised by the coating process
• • 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
  • C21D1/06—Surface hardening
• • 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
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16F—SPRINGS; SHOCK-ABSORBERS; MEANS FOR DAMPING VIBRATION
  • F16F2226/00—Manufacturing; Treatments
  • F16F2226/02—Surface treatments

Definitions

• the present invention relates to a surface hardened and coated precipitation hardened stainless steel said surface showing low static friction and improved wear resistance. Moreover, it relates to a coating of the surface of said stainless steel, in which a surface hardening is accomplished simultaneously with said coating. The resulting coated steel showing a very high hardness simultaneously as it shows improved adhesitivity.
• This steel can advantageously be used in applications with high requirements regarding a combination of high strength and/or toughness and wear resistance together with low friction, such as, e.g., shock absorbers and items for combustion engines and hydraulic systems, produced with a highly cost effective process.
• a hardening treatment which basically may be a bulk treatment or a surface treatment.
• the bulk treatment is intended to harden the steel material homogeneously, such as a plate or a wire, throughout the entire cross-section of the material, while the surface treatment is intended to harden only the surface of the component, leaving the substrate substantially unaffected.
• U.S. Pat. No. 5,632,826 (&WO-A-95/09930), which is hereby included in its entirety into the disclosure of the present application by this reference, discloses a precipitation hardened stainless steel in which the strengthening is based on the precipitation of particles throughout the material.
• the strengthening particles have a quasi-crystalline structure, said structure being essentially obtained at aging times up to about 1000 hours and tempering treatments up to about 650° C. This strengthening involves an increase in tensile strength of at least 200 MPa.
• casehardening is to transform a relatively thin layer of material at the surface of the part by enrichment of carbon or other ingredients, in order to make the surface harder than the substrate, the substrate being the bulk of the steel that remains unaffected by the surface modification.
• Stainless steels are often casehardened by carburization. This is a process where carbon atoms in solution diffuse into the surface of the substrate, i.e., the steel.
• Known casehardening processes are performed at high temperatures.
• Carburization processes are performed at temperatures of about 540° C. or higher (for stainless steel alloys). However, such high temperature processes can promote the formation of carbides in the surface of said stainless steel.
• a conventional way of lowering the static friction and to increase the hardness is to prepare a very smooth surface and then to apply hard chromium plating on this surface. Thereby a hardness level is achieved for low alloy wrought steel that amounts to about 1000 Hv.
• a surface hardening is often made before the hard chromium plating. The process is relatively complicated and involves several relocations of the work-piece due to the dimension alterations it undergoes during the hardening.
• a treated work-piece comprises, e.g., of a base body or substrate of steel and a hard material layer system next to the substrate, supplemented by a metal layer and finally a sliding layer system, whereby the latter is preferably made of carbide, especially tungsten carbide or chromium carbide, and dispersed carbon.
• a layer system which comprises of an adhesive layer, which is placed on a substrate, a transition layer, which is placed on the adhesive layer and an outer layer, which is made of diamond-like carbon.
• the adhesive layer comprises at least one element from the group consisting, e.g., of the 4 th , 5 th and 6 th subgroups and silicon.
• the transition layer consists of diamond-like carbon.
• the layer system has a hardness of at least 15 GPa, preferably at least 20 GPa, and an adhesive strength of at least 3 HF according to VDI 3824 (“Quality Assurance in the Case of PVD and CVD Hard Coatings”), sheet 4.
• Another object of the present invention is to obtain a low static friction on a very hard and wear resistant stainless steel surface in a simple and cost effective way, with as few procedural steps as possible.
• Still another object of the present invention to produce components of sophisticated geometry of said stainless steel with a low static friction on a very hard and wear resistant surface.
• a coated, surface hardened precipitation hardened stainless steel with following composition (in weight-%): Carbon max about 0.1 Nitrogen max about 0.1 Copper from about 0.5 to about 4 Chromium from about 10 to about 14 Molybdenum from about 0.5 to about 6 Nickel from about 7 to about 11 Cobalt 0 up to about 9 Tantalum max about 0.1 Niobium max about 0.1 Vanadium max about 0.1 Tungsten max about 0.1 Aluminum from about 0.05 to about 0.6 Titanium from about 0.4 to about 1.4 Silicon max about 0.7 Manganese max about 1.0 Iron balance
• a process for producing a stainless steel with a low static friction on a very hard and wear resistant surface comprising using a PVD to apply a low static friction coating in the same operation as surface hardening, said stainless steel having the following composition (in weight-%): Carbon max about 0.1 Nitrogen max about 0.1 Copper from about 0.5 to about 4 Chromium from about 10 to about 14 Molybdenum from about 0.5 to about 6 Nickel from about 7 to about 11 Cobalt 0 up to about 9 Tantalum max about 0.1 Niobium max about 0.1 Vanadium max about 0.1 Tungsten max about 0.1 Aluminum from about 0.05 to about 0.6 Titanium from about 0.4 to about 1.4 Silicon max about 0.7 Manganese max about 1.0 Iron balance
• the present invention relates to methods of application of a low static friction coating on a specific class of stainless steels. Moreover, this low static friction coating also results in a very hard and wear resistant surface.
• the coating is applied according to the well-known PVD (“Physical Vapor Deposition”) technique, in accordance with the state of the art referred to above.
• the steel has turned out to possess the surprising property of having a considerable inner hardness increase when the coating is applied whereby the necessary hard and carrying surface layer is created to carry the hard and low-friction top coating. Since the PVD operation is performed at a relatively low temperature, the dimensions of the work-piece are maintained without any distortions.
• the utilization of the PVD technique on some special stainless steel alloys brings about a number of advantages for the produciton of, e.g., cylinder tubes and piston rods for shock absorbers, pistons for hydraulic guide means, and cam followers for combustion engines.
• a suitable group of stainless steels for the purposes of the present invention was selected. It has the following composition ranges (in weight %): Carbon max about 0.1 Nitrogen max about 0.1 Copper from about 0.5 to about 4 Chromium from about 10 to about 14 Molybdenum from about 0.5 to about 6 Nickel from about 7 to about 11 Cobalt 0 up to about 9 Tantalum max about 0.1 Niobium max about 0.1 Vanadium max about 0.1 Tungsten max about 0.1 Aluminum from about 0.05 to about 0.6 Titanium from about 0.4 to about 1.4 Silicon max about 0.7 Manganese max about 0.1 Iron balance
• This stainless steel contains quasi-crystalline particles in a martensitic microstructure as a result of a precipitation hardening, as described in the above mentioned prior art references U.S. Pat. No. 5,632,826, WO-A-93/07303, WO-A-01/14601 and WO-A-01/36699.
• a specific precipitation hardened stainless steel was chosen having the following composition (in weight %): C + N max about 0.05 Cr 12.00 Mn 0.30 Ni 9.00 Mo 4.00 Ti 0.90 Al 0.30 Si 0.15 Cu 2.00 Fe Balance
• a low static friction coating is applied, said coating consisting essentially of titanium nitride or diamond-like carbon (DLC), which is applied by PVD technique.
• DLC diamond-like carbon
• the great advantage of the present invention is that the application of the low static friction and wear resistant coating and the necessary surface hardening are brought about in one and the same operation.
• Another significant advantage of the present invention is when the work-piece is of tubular shape for the manufacturing of tube-shaped items. Thanks to an excellent cold-workability of the stainless steel according to the invention, tubular products are readily produced. Costly long-hole drilling operations otherwise required for commonly available bar shaped products are thus eliminated.
• Plasma nitriding is an alternative casehardening process, which is carried out in a glow discharge in a nitrogen gas-containing mixture at a pressure of about 100 to about 1000 Pa (about 1 to about 10 mbar). It is one of the methods used to treat stainless steel surfaces thereby resulting in a nitrogen diffusion layer having high hardness and excellent wear resistance. Nitriding hardening is induced by the precipitation of nitrides in the surface layer.
• the plasma nitriding is the most recently developed surface hardening procedure. This process replaces traditional nitriding methods, such as gas nitriding and nitrocarburation (short-term gas nitriding, bath nitriding and tenifer (a salt-bath nitriding process sometimes called the “Tuffride process”) treatment), since identical thermo-chemical conditions can be established in this process. Plasma nitriding achieves higher hardness and wear resistance, while creating lower distortion. Furthermore, palsma nitriding is very cost effective. This is due to the fact that subsequent machining, finishing and residue removal processes are frequently not required. Similarly, supplementary protective measures, such as burnishing, phosphatizing, etc., are not necessary.
• the plasma nitriding is performed in a vacuum furnace.
• Treatment temperatures in the range of about 400 to about 580° C. are employed, subject to the requirements of the process in question. Typical treatment temperatures are in the range of about 420 to about 500° C.
• Treatment times vary between about 10 minutes and about 70 hours, depending upon the component to be treated as well as the desired structure and thickness of the layer(s) formed.
• the most commonly used process gases are ammonia, nitrogen, methane and hydrogen. Oxygen and carbon dioxide are used in the corrosion-protective step of post-oxidation.
• pressure, temperature and time are the main parameters of the treatment process. By varying these parameters in accordance with the knowledge of the skilled artisan, the plasma nitriding process can be fine-tuned to achieve the exact desired properties in any treated component.
• any iron-based material can be submitted to plasma nitriding.
• the process does not require the use of special types of nitriding steel.
• the results attained by plasma nitriding can be reproduced with pinpoint accuracy. This is especially important in the manufacture of serial products.
• plasma nitriding does not significantly reduce the static friction. It would cause no problem to submit the stainless steel to temperatures in the range of about 450 to about 500° C. twice, since it will easily resist this temperature without showing softening tendencies.
• Mechanical Properties of the stainless steel are: Tensile strength, R m 1700 MPa to 2000 MPa Yield strength, R p0.2 1500 MPa to 1800 MPa Elongation 8% to 6% Modulus of Elasticity 200 000 MPa General hardness 450 to 650 Hv10, about 45 to 58 HRC Surface hardness about 3000 Hv10 Toughness Impact strength (Charpy V) Min 27 J at ⁇ 20° C.
• the steel of the present invention maintains its mechanical properties even after long use at elevated temperatures up to about 400° C.
• the coefficient of thermal expansion of the steel of the present invention is about 10% lower than that of carbon steel and more than 30% lower than that of a conventional stainless steel, such as ASTM type 304L.
• the steel of the invention is cold formable and bendable to tight radii. It is also suitable for common machining operations such as cutting, turning and grinding.
• the steel has good welding properties, when using TIG and MIG welding methods.
• Another advantage of the steel of the present invention is the improved corrosion resistance compared to, e.g., standard steel ASTM type 304L.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Organic Chemistry (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Other Surface Treatments For Metallic Materials (AREA)
• Physical Vapour Deposition (AREA)
• Laminated Bodies (AREA)
• Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
• Chemical Vapour Deposition (AREA)

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• 2003
  • 2003-01-13 SE SE0300073A patent/SE526501C2/sv not_active IP Right Cessation
• 2004
  • 2004-01-12 WO PCT/SE2004/000018 patent/WO2004063400A1/en active Application Filing
  • 2004-01-12 EP EP04701444A patent/EP1599611A1/en not_active Withdrawn
  • 2004-01-12 JP JP2006500745A patent/JP4511514B2/ja not_active Expired - Fee Related
  • 2004-01-12 CN CNB2004800021021A patent/CN100549189C/zh not_active Expired - Fee Related
  • 2004-01-13 US US10/755,347 patent/US20040173288A1/en not_active Abandoned

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