Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D17/00—Pressure die casting or injection die casting, i.e. casting in which the metal is forced into a mould under high pressure
  • B22D17/20—Accessories: Details
  • B22D17/22—Dies; Die plates; Die supports; Cooling equipment for dies; Accessories for loosening and ejecting castings from dies
  • B22D17/2209—Selection of die materials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C33/00—Moulds or cores; Details thereof or accessories therefor
  • B29C33/38—Moulds or cores; Details thereof or accessories therefor characterised by the material or the manufacturing process
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
  • B29C45/17—Component parts, details or accessories; Auxiliary operations
  • B29C45/26—Moulds
  • B29C45/37—Mould cavity walls, i.e. the inner surface forming the mould cavity, e.g. linings
• • 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
  • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
• • 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
  • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
• • 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
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur

Definitions

• the present invention relates to a steel block which may be used, in particular, for the manufacture of moulds for the injection moulding of plastics materials or for the moulding of metals such as light alloys or for the manufacture of metal-working tools.
• Moulds for the injection moulding of plastics materials are generally produced from steels of which the hardness is approximately 300 HB.
• these moulds are used for the moulding of plastics such as industrial plastics or thermosetting plastics, however, it is preferable to use harder steels which are more resistant to wear.
• a steel of the type 55 NCDV 7 containing about 0.55% of carbon, 1.75% of nickel, chromium, molybdenum and vanadium may therefore be used and allows the manufacture of moulds of which the hardness is approximately 400 HB.
• this steel has a plurality of drawbacks: it is difficult to machine and difficult to weld. In addition, this steel often has localised segregations which constitute hard points which are detrimental to polishing or to chemical graining.
• the object of the present invention is to overcome these drawbacks by proposing a steel for moulds or for the manufacture of parts for metal-working which is easier to weld and easier to machine, polish and grain and is a better conductor of heat than steels according to the prior art, and allowing the manufacture of parts or tools having a hardness of approximately 450 HB to more than 500 HB, even after surface-hardening by nitriding, and this means that the required characteristics, in particular hardness characteristics, have to be compatible with tempering at at least 530° C.
• the invention accordingly relates to a steel block having a thickness which is greater than 20 mm and may attain 1500 mm, of which the structure is martensitic or martensito-bainitic, of which the hardness is between about 430 HB and 520 HB at all points, for the manufacture of parts for moulds or for tools, the chemical composition of the steel comprising, in % by weight: 0.180% ⁇ C ⁇ 0.400% Si ⁇ 0.8% Mn ⁇ 2.5% Ni ⁇ 3% Cr ⁇ 3.5% Mo+W/2 ⁇ 2.8% V+Nb/2+Ta/4 ⁇ 0.5% Al ⁇ 0.4% Ti+Zr/2 ⁇ 0.1%
• the composition is such that: R/(2.7 ⁇ Tr) ⁇ 0.90, more preferably R/(2.7 ⁇ Tr) ⁇ 0.80.
• the composition is such that U/Dr ⁇ 9.0.
• the chemical composition of the steel is such that: 0.230% ⁇ C ⁇ 0.350% Si ⁇ 0.30% 0.1% ⁇ Mn ⁇ 1.8% Ni ⁇ 2.5% 0.2% ⁇ Cr ⁇ 3% Mo+W/2 ⁇ 2.5% V+Nb/2+Ta/4 ⁇ 0.3% Mo*+3 ⁇ V* ⁇ 0.8% and even more preferable, such that: 0.240% ⁇ C ⁇ 0.320% Si ⁇ 0.15% 0.1% ⁇ Mn ⁇ 1.6% Ni ⁇ 2% 0.2% ⁇ Cr ⁇ 2.5% 0.3% ⁇ Mo+W/2 ⁇ 2.5% V+Nb/2+Ta/4 ⁇ 0.3% Mo*+3 ⁇ V* ⁇ 1.2% It is therefore preferable that the composition is such that Tr ⁇ 4.5.
• the invention also relates to a mould part made of steel which is machined in a block according to the invention, of which at least a surface portion is hardened by nitriding and of which the hardness at all points is between 430 HB and 530 HB.
• the steel according to the invention has the advantage of being a better conductor of heat than the steels according to the prior art.
• This better thermal conductivity allows the cooling ducts to be further removed from the surface of the moulds than when using steels according to the prior art.
• the risk of fissures between the ducts and the surface of the mould impression is substantially reduced.
• the cooling of the moulds takes place more uniformly and this improves the quality of moulding.
• the steel according to the invention is also intended for the manufacture of metal working parts.
• the parts for moulds or for metal working are manufactured by machining solid blocks of steel which are quenched to obtain a homogeneous martensito-bainitic structure and tempered to obtain the desired properties of hardness and ductility. It is therefore necessary to use a steel having high temperability and significant hardenability. However, these hardened steels must have the best possible machinability and the highest possible thermal conductivity. This last property helps to improve the productivity of the moulding operations. The combination of these various properties is initially contradictory. In fact, it is known that, the harder the steel is, the easier it is to machine, and it is known that the machinability may be improved by adding alloying elements such as sulphur, calcium, selenium, tellurium or lead.
• the steel must contain:
• composition of the steel must be selected in order to obtain the desired characteristics for use.
• composition must be such that:
• the steel is produced, is cast and hot-rolled or hot-forged in a known manner and cut to obtain blocks of which the thickness is greater than 20 mm and may exceed 100 mm and attain 400 mm, possibly 600 mm and even 1500 mm. It should be noted that, with the smallest thicknesses, the blocks may be sheets or large plates and, with the greatest thicknesses, they are generally forged blocks.
• the blocks are austenitised, optionally in the forging or rolling heat, at a temperature higher than AC 3 and preferably lower than 950° C., in particular when the steel contains boron, and they are then quenched in air, oil or water, depending on the thickness and quenchability of the steel, so as to obtain a martensitic or martensito-bainitic structure in all the mass. Finally, they are tempered at a temperature higher than 500° C. and preferably of at least 550° C. but lower than AC 1 . A hardness between approximately 430 HB and 530 HB is thus obtained.
• parts of moulds comprising impressions which are polished and optionally grained are machined in a known manner.
• these parts are surface hardened, for example by gaseous nitriding. After gaseous nitriding, apart from the extreme nitrided surface of the parts, the hardness of the steel is between approximately 430 HB and 530 HB.
• Examples 1 to 6, 9 to 12 and 14 to 16 correspond to the invention and examples 17, 18, 20 and 21 are given by way of comparison. These steels do not contain additions of selenium, tellurium, lead, bismuth or calcium. However, they contain a little sulphur, between 0.010% and 0.020%.
• the hardness HB has also been determined in the tempered quenched state, in other words for a martensitic or martensito-bainitic structure tempered at 550° C., as well as the hardness HVHAZ in the heat-affected zone in the vicinity of a weld which has been compared with the hardness HVbasic of the basic metal not affected by the heat.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Metallurgy (AREA)
• Manufacturing & Machinery (AREA)
• Heat Treatment Of Articles (AREA)
• Heat Treatment Of Steel (AREA)
• Moulds For Moulding Plastics Or The Like (AREA)
• Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
• Lubricants (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Injection Moulding Of Plastics Or The Like (AREA)

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• 2002
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• 2003
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