Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F7/00—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/02—Making ferrous alloys by powder metallurgy
  • C22C33/0257—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements
  • C22C33/0278—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements with at least one alloying element having a minimum content above 5%
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B27/00—Rolls, roll alloys or roll fabrication; Lubricating, cooling or heating rolls while in use

Definitions

• This invention relates to powder metallurgy articles.
• tool steels In applications for tool steels, such as in the manufacture of hot working rolls and tooling used in rolling hot metal, the tooling is subjected to conditions of extreme wear as a result of contact with the workpiece, thermal shock, as a result of being subjected to high temperatures when in contact with the hot workpiece and then rapid cooling when out of contact with the workpiece, and high compressive stresses, as a result of the roll separating forces encountered during rolling.
• thermal shock As a result of being subjected to high temperatures when in contact with the hot workpiece and then rapid cooling when out of contact with the workpiece, and high compressive stresses, as a result of the roll separating forces encountered during rolling.
• tool steels from which work- rolls and other similar hot work tooling are made be characterised by good wear resistance, toughness, strength and resistance to thermal fatigue and shock.
• vanadium and sufficient carbon to combine therewith to produce vanadium carbides, which impart wear resistance to the alloy.
• An additional object of the invention is to provide for cold work tooling requirements by having a combination of high toughness and excellent wear resistance for critically demanding applications, such as slitter knives and shear blades..
• the present invention provides a powder metallurgy formed from compacted prealloyed powder, in which the powder is of an alloy having the composition, in weight percent:-
• a tool steel powder metallurgy article particularly adapted for the manufacture of hot work rolls and tooling, wherein the carbon content is controlled in relation to vanadium so that there is sufficient carbon to combine with vanadium to form vanadium carbides, which provide the required wear resistance.
• the alloy is heat treated by austenitising and air cooling or oil quenching during which cooling a fully martensitic structure is obtained.
• tool steels in accordance with the invention are characterised by excellent wear resistance because of the vanadium carbide content; good toughness because of the absence of excess carbon in the matrix over that required to ensure a fully martensitic structure; strength, because of the strengthening effect of the martensite; and resistance to thermal fatigue and shock,-resulting from the absence of carbon in the matrix other than that needed to form martensite.
• the alloy would be processed by powder metallurgy techniques in the conventional manner and would be characterised by a fully martensitic structure with essentially no carbon in the steel matrix in excess of carbon necessary to combine with vanadium to form vanadium carbide and to ensure a fully martensitic structure.
• the hardness After quenching from austenitising temperature the hardness may be at least 50 R for hot working applications; lower hardnesses may be provided for cold work tooling requirements.
• vanadium carbide content of the alloy powder metallurgy processing is required to ensure a fine, even carbide distribution necessary for toughness and grindability.
• powder metallurgy article as used herein is used to designate a compacted prealloyed particle charge which has been formedby a combination of heat and pressure to a-coherent mass having a density in final form, in excess of 99% of theoretical density; this includes intermediate products, such as billets, blooms, rod and bar and the like, as well as final products, such as tool steel articles including rolls, punches, dies, wear plates, slitter knives, shear blades and the like, which articles may be fabricated from intermediate product forms from the initial prealloy particle charge.
• the particle charge may be produced by conventional gas atomisation.
• MC-type vanadium carbides refers to the carbide characterised by the face-centred cubic crystal structure with M representing the carbide-forming element essentially vanadium this also includes P4 4 C 3 ttype vanadium carbides and includes the partial replacement of vanadium by other carbide forming elements such as iron, molybdenum, chromium and of carbon by nitrogen to encompass what are termed carbonitrides.
• the powder metallurgy article of this invention is defined herein as containing all MC-type and M 4 c 3 vanadium carbides, it is understood that other types of carbides, such as M 6 C, M 2 C and M 23 c 6 carbides, may also be present in minor amounts, but are not significant from the standpoint of achieving the objects of the invention specifically from the standpoint of wear resistance.
• compositions were prepared by powder metallurgical technology and microstructural studies were conducted on heat treated specimens to determine the compositional balance with respect to vanadium and carbon which is required to develop a fully martensitic structure.
• the 1.78 carbon - 8.80 vanadium alloy in accordance with the invention exhibited a C-notch impact strength value of 100 joules (74 ft.-lbs) at an HRC of 49.5 which demonstrates a drastic improvement in toughness at a hardness level comparable to the hardnesses of the conventional alloys set forth in Table II.
• Table IV shows the C-notch impact results, as well as hardness (Rockwell C scale); for a conventional powder metallurgy produced tool steel with a nominal composition, in weight percent, carbon 2.4, manganese .45, silicon ,89, chromium 5.25, vanadium 9.85, molybdenum 1.25 and balance iron.
• the distinguishing feature between this composition and the above-reported CPM 9V composition is that with this latter conventional composition there is excess carbon present in the matrix which is intended for strengthening.
• Table VI compares, after heat treatment, the wear resistance of the CPM 9V material of the invention with conventional high alloy hot work tool steels of conventional cast and wrought production. As may be seen from Table VI the CPM 9V material of the invention shows drastically improved wear resistance over the AISI H13, AISI H19 and AISI H21 steels even in instances wherein the hardness of the CPM 9V material is significantly lower than that of the conventional steels.
• the cross-cylinder wear test was used.
• a cylindrical specimen of 15.9mm( 5/8in)diameter of the respective cold work or warm-work tool material and a cylindrical specimen of 12.7mm (1/2 in.) diameter of tungsten carbide (with 6% cobalt binder) are positioned perpendicularly to one another.
• a 6.8kg(fifteen-pound) load is applied through weight on a lever arm.
• the tungsten carbide cylinder specimen is rotated at a speed of 667 revolutions -per minute. No lubrication is applied.
• a wear spot develops on the specimen of the tool material.
• the extent of wear is determined by measuring the depth of the wear spot on the specimen and converting it into wear volume by aid of a relationship specifically derived for this purpose.
• the wear resistance, or the reciprocal of the wear rate is then computed according to the following formula:
• thermal fatigue properties of the steel of the invention when compared with conventional powder metallurgy produced cold work tool steels and conventional cast and wrought steels of this type are shown in Table VII; in this Table, the steel of the invention, CPM 9V, is compared with a conventional powder metallurgy produced tool steel containing 2.46% carbon and 9.75% vanadium and a conventional cast and wrought steel of this type, which is identified asAISI H13..
• the thermal fatigue resistance of the CPM 9V material of the invention is drastically greater than that of both of the other conventional steels tested, including the 2.46 carbon - 9.75 vanadium material which is a powder metallurgy produced steel designed for cold or warm work tooling.
• the thermal fatigue test involves the use of an electrically heated lead pot, a hot water quenching bath and a solenoid valve operated, pneumatic-operated mechanical transfer for transferring the specimens between the lead pot and the bath. Specimens are transferred into the lead bath for a 4-second heating period. They are then transferred quickly to a position above the water bath wherein they are quenched for 2 seconds at a water bath temperature of 82 C(180 F). This cycle is repeated at a rate of 3 cycles per minute. Each specimen during each cycle is dried above the lead pot for a period of 5 seconds.
• each cycle takes approximately 20 seconds.
• differential heating occurs in the rim and hub of each specimen and hence from the thermal expansion, the rim periphery is mechanically strained to set up compressive stresses in this region.
• the hub opposes the thermal contraction of the rim causing residual (peripheral) tensile stresses to be set up.
• fatigue is demonstrated by the beginning of cracks in the rim periphery of the samples which propogate toward the hub with the rate of cracking- being determined by the thermal fatigue resistance of the steel being tested.

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• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Composite Materials (AREA)
• Manufacturing & Machinery (AREA)
• Powder Metallurgy (AREA)
• Reduction Rolling/Reduction Stand/Operation Of Reduction Machine (AREA)
• Manufacturing Of Micro-Capsules (AREA)
• Drilling And Exploitation, And Mining Machines And Methods (AREA)
• Metal Rolling (AREA)
• Breeding Of Plants And Reproduction By Means Of Culturing (AREA)
• Heat Treatment Of Articles (AREA)
• Moulds For Moulding Plastics Or The Like (AREA)
• Treatment Of Steel In Its Molten State (AREA)
• Turning (AREA)

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Citations (3)

• 1982
  • 1982-04-08 CA CA000400811A patent/CA1191039A/en not_active Expired
  • 1982-05-24 DK DK231882A patent/DK158795C/da not_active IP Right Cessation
  • 1982-06-25 ES ES513486A patent/ES8305424A1/es not_active Expired
  • 1982-07-20 JP JP57125235A patent/JPS5858255A/ja active Granted
  • 1982-07-26 IN IN567/DEL/82A patent/IN158518B/en unknown
  • 1982-08-02 EP EP82304064A patent/EP0076027B1/de not_active Expired
  • 1982-08-02 AT AT82304064T patent/ATE23567T1/de not_active IP Right Cessation
  • 1982-08-02 DE DE8282304064T patent/DE3274261D1/de not_active Expired
  • 1982-08-16 MX MX194025A patent/MX159525A/es unknown
  • 1982-09-28 KR KR1019820004373A patent/KR840001456A/ko unknown

Patent Citations (3)

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