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
  • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
• • 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
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • 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
  • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
• • 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
  • C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
• • 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
• • 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
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/004—Dispersions; Precipitations

Definitions

• the invention relates to a steel more particularly intended for the production of mechanical parts which can be used under severe conditions of use, in nuclear installations but also in industries such as the food industry, energy or mechanical engineering. .
• cobalt-based alloys pose both economic and technical problems.
• cobalt is an expensive raw material with few sources of supply.
• this element is highly undesirable in the nuclear environment because it forms isotopes with long lifespan which are released by the wear of the parts and are one of the main sources of exposure to radiations of the people working in these installations.
• the cobalt content must therefore be limited as much as possible in the steels or alloys which are used in particular in this industry for the production of valve seats.
• US Patent 3,912,503 describes compositions of stainless steels resistant to wear and corrosion. They include 0.12% by weight of carbon at most, 7 to 13% by weight of manganese, 3 to 5% by weight of silicon, 12 to 19% by weight of chromium, 4 to 12% by weight of nickel, 0 , 03 to 0.3% by weight of nitrogen, the balance consisting of iron. These compositions have a coefficient of friction close to that of cobalt-based alloys but have a hardness at room temperature of only 200 Vickers, hardness which drops to 150 Vickers from 200 ° C. In addition, their ductility is much too great to allow use for the production of mechanical parts subjected to high stresses.
• US Patent 4,814,140 describes the same type of steel as US Patent 3,912,503 and makes it possible to improve the resistance to seizing.
• the claimed compositions comprise 0.25% by weight of carbon at most, 2 to 7% by weight of manganese, 1 to 5% by weight of silicon, 12 to 20% by weight of chromium, 2 to 7.75% by weight of nickel, 0.35% by weight of nitrogen at most, the remainder consisting of iron.
• the mechanical properties which include ductility, hardness at room temperature and when hot, are similar to that of the compositions of US Pat. No. 3,912,503 and are therefore also insufficient for the applications envisaged.
• the main object of the present invention is therefore to provide such a material.
• a first object of the invention consists of a steel composition comprising, expressed in percentages by weight:
• the steel composition comprises, expressed in percentages by weight:
• unavoidable impurities mention will be made in particular of sulfur and phosphorus which should be kept at the lowest level compatible with the manufacturing process or the raw materials used.
• the hardnesses obtained with the steels according to the invention are between 350 and 550 Vickers.
• the carbon content of the steels according to the invention is between 0.40 and 0.50% by weight, when the parts to be produced do not require hardness and resistance to l 'very high wear. In another preferred embodiment of the invention, the carbon content of the steels according to the invention is between 0.50 and 0.60% by weight, when the parts to be produced require hardness and resistance to slightly higher wear. In another mode preferred embodiment of the invention, the carbon content is between 0.70 and 0.80% by weight for applications in which the hardness and the resistance to wear must be high. It can therefore be seen that these two characteristics of steel can be adjusted by varying this carbon content, within certain predefined limits.
• the silicon is present at a content of 3.00 to 4.50% by weight, preferably 3.50 to 4.00% by weight. It plays a role in improving friction and seizure resistance due to the formation of adherent oxide film on the surface of the parts. It also has a favorable role in corrosion resistance.
• Nickel is a gamma element which participates in balancing the composition. It is present in a content of 3.50 to 4.50% by weight and provides the steel compositions with good corrosion resistance.
• Manganese is present at a content of 7.00 to 10.00% by weight. Its role is similar to that of nickel.
• the chromium is present in an amount of 20.00 to 27.00% by weight, preferably 24 to 26% by weight. It also plays an important role in the good resistance against corrosion of the steels according to the invention. It may be possible to replace part of the chromium present in the composition with molybdenum on the basis of 1% molybdenum for 3% chromium.
• the tungsten is present in an amount of 0.50 to 4.50% by weight, preferably 0.50 to 1.50% by weight. It makes it possible in particular to obtain good heat resistance of the compositions according to the invention.
• the niobium is present in an amount of 0 to 2.5% by weight. It is a carburetor element which contributes to the hardness of the shade while having a favorable action on the heat resistance of steel compositions.
• the nitrogen is present in an amount of 0.20 to 0.50% by weight in the compositions according to the invention. It contributes to the balance of the composition by its gamma influence, and to the hardness by its participation in the formation of niobium carbonitrides in particular.
• Cobalt is an undesirable element the content of which is limited to a maximum of 1% by weight, preferably 0.5% by weight. Its content will be limited technically as much as possible and will be more particularly reduced to a trace state.
• a second object of the invention consists of a process for the preparation of mechanical parts, characterized in that it comprises the following steps: a - constitution of a charge intended to obtain a chemical composition according to any of the variants previously exposed , b - preparation of said load, c - shaping of a blank of said mechanical part by molding, d- machining of said mechanical part from the blank, e - optional, heat treatment for use of said mechanical piece.
• a process for the preparation of mechanical parts comprises the following stages: a - constitution of a charge intended to obtain a chemical composition according to any of the variants previously exposed, b - melting of said charge in a crucible, c - "molding" by centrifugation of a blank of said mechanical part, and machining of said mechanical part from the blank, e - as an option, heat treatment using said mechanical part.
• This centrifugal molding process is traditionally used to form cobalt-based alloys, since it has great advantages, it consists in gradually introducing the mass of molten metal into a jacket heated in rotation, so that that a very thin layer of metal, on the order of a tenth of a millimeter, is deposited on the inside of the liner each turn. ie therefore independently of the previously deposited layers, which makes it possible to obtain a blank with a fine and isotropic structure, without micro-porosities.
• the finished parts obtained after machining the blank are free from shrinkage, very resistant and have a very good surface condition.
• the present inventors have therefore found, quite surprisingly, that it is perfectly possible to centrifuge mold the mechanical parts to be produced in the compositions according to the invention.
• the melting of the steel compositions it can be carried out by any known process, in particular in an arc furnace.
• the steel compositions according to the invention can in particular be in three different forms depending on their thermal state. These are the so-called “raw pouring” state, the state dissolved in temperatures from 1050 to 1150 ° C. and the stabilized state obtained by practicing one or more stabilization treatments of 700 at 900 ° C on a part in the raw casting state or in the dissolved state.
• the thermal state essentially depends on the conditions under which the part will be used.
• a stabilization treatment by aging comprising dissolving followed by slow cooling in a fluid such as air. This treatment allows the formation of precipitates in the steel matrix which will then no longer vary in hardness or dimensions.
• a third object of the invention consists of the mechanical parts produced in the compositions and / or using the methods described above. Examples include valve seats, valve seats, friction rings and discs, gas turbine components, punches and cutting tools for hot work, knives and shear blades working at high temperature.
• R p o, 2 conventional elastic limit at 0.2% deformation
• A elongation
• Z necking
• HV Vickers hardness
• HRC Rockwell hardness
• grade ES the composition of which is as follows:
• the tests were carried out on steel samples in the three previously defined thermal states, namely the raw casting state, the dissolved state and the stabilized state.
• the reference material of the prior art chosen for comparison is a cobalt base alloy CoCr29W5, the composition of which is as follows: C 1, 10%
• - 8 corresponds to a material having a few spots around the bites.

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

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• 2000
  • 2000-07-04 FR FR0008698A patent/FR2811336B1/fr not_active Expired - Fee Related
• 2001
  • 2001-07-03 DE DE60142968T patent/DE60142968D1/de not_active Expired - Lifetime
  • 2001-07-03 ES ES01949617T patent/ES2349399T3/es not_active Expired - Lifetime
  • 2001-07-03 AU AU2001270741A patent/AU2001270741A1/en not_active Abandoned
  • 2001-07-03 WO PCT/FR2001/002121 patent/WO2002002830A1/fr active Application Filing
  • 2001-07-03 EP EP01949617A patent/EP1297192B1/de not_active Expired - Lifetime

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