Classifications

• • 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%
  • C22C33/0292—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% with more than 5% preformed carbides, nitrides or borides
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C29/00—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides
  • C22C29/02—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides
  • C22C29/06—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides based on carbides, but not containing other metal compounds
  • C22C29/067—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides based on carbides, but not containing other metal compounds comprising a particular metallic binder
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C29/00—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides
  • C22C29/02—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides
  • C22C29/06—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides based on carbides, but not containing other metal compounds
  • C22C29/08—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides based on carbides, but not containing other metal compounds based on tungsten carbide
• • 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
  • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium

Definitions

• ABSTRACT High-speed tool steels are prepared by a powder metallurgical process comprising pressing to shape a powdered mixture of 15-75 weight percent tungsten monocarbide and a matrix of cobalt and iron, the cobalt-to-iron ratio ranging from 0.65 to 2.0. The pressed mixture is then sintered to full density by partially iiquefying the ferrous phase of the alloy. The sintered compact is then hardened by heat treatment to transform the ferrous matrix to martensite.
• This invention relates to aprocess for the preparation of a shaped, high-speed tool steel alloy of tungsten monocarbide, cobalt and iron.
• high-speed tool steels depends to-a considerable extent upontheir microstructure, a microstructure normally obtained by hot-working.
• high-speed tool steels are processed to the final desired shapeby the relatively costly and laborioussteps of melting, casting, hot-working (e.g. forging, extruding or rolling) and machining. It would be much more economical to directly cast the desired shape but the ascast microstructure is very coarse and contains continuous carbide networks which cause severe embrittlement of the casting.
• The'hot-working procedure refines the caststructure to one which is fine and discontinuous and thus much harder and tougher.
• Tool steel compositions consisting of Fe-Co--W- and C are known.
• a typical composition of this type contains by weight 40 percent Co, 20 percent W, 1.3 percent C, balance Fe.
• These steels have been prepared by a modification of the normal process for preparing tool steels, consisting of atomizing a melt into powder, followed by the usual hot-working consolidation steps. The resulting steels exhibit metal-cutting characteristics superior to conventional tool steels.
• the processingmethod employed is at least as tedious and costly, however, as that used to make conventional high-speed tool steels.
• High-speed tool steels are normally characterized as alloy steelscapable of being hardened and tempered to a condition of high strength, wear resistance, and hot hardness. ln addition, they also exhibit certain metal-cutting performance characteristics which distinguish them from other tool steels and from cemented carbides.
• the process used in this invention differs fr'omthat used to make conventional cemented carbide alloys in several significant respects discussed below. However, the processes contain certain steps in common in that'they both ball-mill fine powders, press to shape, and sinter to full density. The compositions used by this process, however, more closely resemble high-speed tool steels in a number of respects.
• the present-alloys have a structure that, except in theupperportion of the WC range, primarily consists'of a ferrousalloy, with carbideparticlespresent asa secondary constituent, while: the-reverse .is true withcemented carbides in that thecarbide' particles are .the predominant phase and an ironvgroup metal is secondary.
• the present'alloys contain matrices which are hardenable by heat treatment and can be tempered to a condition of hot-hardness, both of which are not characteristic of the matrices of cemented carbides.
• the liquid-phase sintering of cemented carbides consists of raising to a temperature where essentially all of the iron-group metal becomes molten andthe compact is held together by the tightly packed carbide particles. If this same technique were employed with these new tool steel alloys, the compact would melt-and completely lose the desired shape. It is essential with these alloys that only a partial liquefaction of'the binder phase occur.
• the sintering temperature must be controlled within a range where-a sufficient amount of the'ferrous phase liquefies to permit full den sification but the amount of liquid is insufficient for the compact to lose shape by sagging or melting.
• the sintering temperature will vary with the specific composition and with the type of sintering-cycle used, but will-fall between about 1,200 C. and 1,400 C. This temperature may, however, easily be obtained by heating to a temperature within the range l,200-l ,400 C. to select, on-the one hand, the lowest temperature which produces a product of full density and, on the other hand, to select the'temperature above which the pressed mixture begins to sag. Any temperature between these extremes may be used.
• the range between minimum and maximum will be about 30 C.
• the critical sintering range is about l,325-l,355 C. when the composition is first presintered in hydrogen at500 C. and then sintered in vacuum.
• Heat treatment of'the alloys comprises heating to a temperature at which the matrix phase is transformed to an austenitic structure, normally from about l,000 C. to about 1,200 C. for a period of from several minutes to several hours or even more.
• the alloy is then rapidly cooled such as by oil quenchingtoconvertthe austenitic matrix to martensite.
• the alloy may then befurtherhardened by tempering by heating to about 425-650 C.
• the tempering'step forms a very fine precipitate which increases the hot hardness of the alloy. Both the hardening and tempering treatments are similar to these well-known heat treatment steps withhigh-speed steels.
• EXAMPLE I An Fe--CoW-C tool steel alloy of composition 20 "percent Fe, 30 percent Co, 47 percent W, 3 percent C was prepared by-ball-milling fine powders of Fe, Co and WC for 24 hours in a'4-inch diameter ball mill using acetone as a milling fluid. One percent paraffin was then added as a pressing lubricant and compacts were pressed at a pressure of 30,000 p.s.i. The compacts were then presintered at 500 C. in a hydrogen atmosphere to remove the paraffin and sintered l0 minutes'at .l ,340 C. in a vacuum furnace during which only partial liquefaction of the-binder occurred. The sintered compact was fully dense, as evidenced by the complete lack of porosity in the microstructure, and the microstructure consisted of fine, discrete particles of WC embedded in a ferrous matrix.
• the sintered compact was then given a heat treatment consisting of holding 20 minutes at l,200 C., oil quenching, then tempering 2 hours at 550 C., cooling to room temperature, and another 2 hours temper at 550 C. After heat treatment the hardness was R 70 and the transverse rupture strength averaged 475,000 p.s.i.
• T-lS is a premium high-speed tool steel, generally considered to have best metal-turning properties in the tool steel class.
• Singlepoint turning of 1045 steel showed the present alloy to be nearly comparable to T-lS in wear resistance and of essentially similar performance response, i.e., the tool lifeline slope,
• EXAMPLE II was R 74 and the transverse rupture strength was 255,000 psi.
• the hot hardness of this composition was superior to that of commercial T-l5 steel at all temperatures up to l,300 F.
• the tool lifeline of this composition was identical with that of T-l5 tool steel.
• a process for preparing a shaped, high-speed tool steel alloy comprising pressing to shape a mixture consisting essentially of l5-75 percent by weight of tungsten monocarbide, and a matrix material, said matrix material comprising cobalt and iron, the cobalt-to-iron weight ratio ranging from 0.65 to 2.0,

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Powder Metallurgy (AREA)

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Citations (5)

• 1969
  • 1969-12-29 US US888859A patent/US3658604A/en not_active Expired - Lifetime
• 1970
  • 1970-12-09 GB GB5847170A patent/GB1288133A/en not_active Expired
  • 1970-12-16 NL NLAANVRAGE7018362,A patent/NL175644C/xx not_active IP Right Cessation
  • 1970-12-24 FR FR7046610A patent/FR2074262A5/fr not_active Expired
  • 1970-12-24 DE DE2063846A patent/DE2063846C3/de not_active Expired
  • 1970-12-29 JP JP45121964A patent/JPS4923964B1/ja active Pending

Patent Citations (5)

Non-Patent Citations (1)

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