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

Definitions

• a sintered steel-bonded titanium carbide composition characterized by an improved combination of transverse rupture strength, resistance to impact, and resistance to thermal shock comprising by weight about 20% to 30% of primary grains of titanium carbide dispersed through a steel matrix making up the balance, the composition of said matrix consisting essentially by weight of about 3% to 7% chromium, about 2% to 6% molybdenum, about 0.1% to 1% nickel, about 0.3% to 0.7% carbon and the balance essentially iron.
• the matrix is characterized by the presence of martensite.
• This invention relates to a sintered steel-bonded titanium carbide composition and to a hardened wear resistant element produced from said composition, said sintered steel-bonded composition being characterized by an improved combination of physical properties, including improved transverse rupture strength, improved resistance to thermal shock, and improved resistance to impact and the like properties.
• Titanium carbide tool steel compositions are disclosed in US. Pat. No. 2,828,202 (assigned to the same assignee) comprising broadly primary grains of essentially titanium carbide distributed through a heat treatable steel matrix.
• a typical composition is one containing by weight 33% TiC in the form of primary carbide grains dispersed through a steel matrix, the steel matrix containing by weight 3% Cr, 3% M0, 0.6% C and the balance essentially iron.
• the steel is preferably produced using powder metallurgy methods which comprise broadly mixing powdered titanium carbide (primary carbide grains) with powdered steel-forming ingredients of, for example, the aforementioned composition, forming a compact by pressing the mixture in a mold and then subjecting the compact to liquid phase sintering under non-oxidizing conditions, such as in a vacuum.
• powder metallurgy methods comprise broadly mixing powdered titanium carbide (primary carbide grains) with powdered steel-forming ingredients of, for example, the aforementioned composition, forming a compact by pressing the mixture in a mold and then subjecting the compact to liquid phase sintering under non-oxidizing conditions, such as in a vacuum.
• primary carbide employed herein is meant to cover the titanium carbide grains per se added directly in making up the composition and which grains are substantially unaffected by heat treatment.
• TiC titanium carbide tool steel composition
• substantially the balance a steel matrix about 500 grams of TiC (of about 5 to 7 microns in size) are mixed with 1000 grams of steel-forming ingredients in a mill half filled with stainless steel balls. To the powder ingredients is added one gram of paraffin wax for each 100 grams of mix. The milling is conducted for about 40 hours, using hexane as a vehicle.
• the mix is removed and dried and compacts of a desired shape pressed at about 15 t.s.i. and the compacts then subjected to liquid phase sintering in vacuum at a temperature of about 2640 F.
• the compacts are cooled and then annealed 'by heating to about 1650 F. (900 C.) for 2 hours followed by cooling at a rate of about 27 F. (15 C.) per hour to about 212 F. (100 C.) and thereafter furnace cooled to room temperature to produce an annealed microstructure containing spheroidite.
• the annealed hardness is in the neighborhood of about 45 R and the high carbon tool steel is capable of being machined and/or ground into any desired tool shape or machine part prior to hardening.
• the hardening treatment comprises heating the machined piece to an austenitizing temperature of about 1750 F. for about one-quarter hour followed by quenching in oil or water to produce a hardness in the neighborhood of about 70 R
• an austenitizing temperature of about 1750 F. for about one-quarter hour
• over-tempering tended to occur, leading to softening of the die steel.
• a part made of the composition would be subject to thermal cracking.
• the transverse rupture strength while adequate for most uses, was not as high as desired, the transverse rupture strength usually ranging from about 250,000 p.s.i. to about 300,000 p.s.i.
• a steel-bonded carbide composition which exhibits resistance to softening at elevated temperatures is one covered by US. Pat. No. 3,053,706 (also assigned to the same assignee).
• a typical composition is one in which the refractory carbide is a solid solution carbide of the type WTiC containing about WC and 25% TiC. This carbide, preferably in an amount by weight of 45.6%, is dispersed through a steel matrix making up essentially the balance.
• the matrix which is capable of secondary hardening at 1000 'F. to 1200 F. (538 C. to 650 C.) typically may contain 12% W, 5% Cr, 2% V, 0.85% C and the balance essentially iron.
• the dissolved tungsten in the matrix is in equilibrium with the saturated solution of the primary carbide.
• Tooling and component part manufacturers have been constantly seeking newer and better materials capable of "withstanding stresses, thermal shock, impact, heat and wear encountered in certain hot work and impact-involving applications, such as warm heading dies, swedging dies, forging dies, die casting tools, and the like.
• This demand has created an urgent need for steel-bonded titanium carbide material having a unique combination of physical and mechanical properties at room and elevated temperatures, particularly improved resistance to impact and improved transverse rupture strength in combination with improved resistance to thermal shock.
• the invention resides in a sintered steel-bonded titanium carbide composition containing by weight about 20% to 30% of primary grains of titanium carbide dispersed through a steel-matrix making up essentially the balance of about 80% to 70%, said matrix consisting essentially by weight of about 3% to 7% chromium, about 2% to 6% molybdenum, about 0.1% to 1% nickel, about 0.3% to 0.7% carbon and the balance-essentially iron.
• a preferred composition is one containing 24% to 30% titanium carbide and the balance essentially the steel matrix of about 76% to 70%, the steel matrix preferably consisting essentially by weight of about 4% to 6% chromium, about 3% to molybdenum, about 0.25% to 0.75% nickel, about 0.3% to 0.5% carbon and the balance essentially iron.
• a preferred composition is one containing by weight approximately 25% TiC and approximately 75% the steel matrix, the matrix consisting essentially by weight of about 5% Cr, about 4% Mo, about 0.5% Ni, about 0.4% C and the balance essentially iron.
• transverse rupture strengths of over 325,000 p.s.i. and even over 350,000 p.s.i. are obtained, for example, transverse rupture strengths in the range of about 400,000 p.s.i. to as high as 550,000 p.s.i., agcolrglpanied by markedly improved resistance to thermal s cc As illustrative of the improved results obtained with the invention, the following example is given.
• the mix is removed and vacuum dried.
• a predeterminedamount of the. mixed powder is compressed in a die at about ,15 tonsper square inch (t.s.i.) to the desired shape.
• the shape is liquid phase sintered, that is, sintered above the melting .point of the matrix composition, at a temperature of about 1435 C. for one hour in vacuum, e. g.,. a vacuum corresponding to 20 microns of mercury or better.
• the shape is cooled and then annealed by heating to 900 C. for 2 hours followed by cooling at a rate of about 15 C.
• Both carbide compositions contained 25% by weight of TiC and 75 by weight of the steel matrix.
• compositions in the annealed state were oil quenched after 30 minutes at 1875 F. (1025", C.).
• the compositions were double tempered for one hour each at 975 F. (525 C.) and air cooled. i v
• the carbide steel alloy of the invention exhibits almost doublethe transverse rupture strength compared to the carbide .steel alloy outside the invention.
• v n n In the hardened state, the carbide alloys are. characterized by a microstructure of essentially marten site.
• compositions were produced by sintering similarly to the carbide steel alloy of the invention described herein. These compositions were compared to the preferred alloy of the invention comprising 25% TiC and 75% steel matrix (5% Cr, 4% M0, 0.5% Ni, 0.4% C and 'balance essentially Fe). All compositions were quench hardened and tempered and subjected to thermal TABLE 2 Number of cycles before thermal TRS 1 cracks X Materiel develop p.s.i.
• the invention exhibits markedly superior resistance to thermal shock and markedly superior transverse rupture strength.
• Material (B) in Table 2 was also compared with the composition of the invention as to impact resistance, the invention showing a value of 2.5 ft.-lbs. Charpy impact, while material (B) exhibited a Charpy impact value of 1.5 ft.-lbs., the invention being about 65 better than material (B).
• the rupture strength of the composition of the invention is over 325,000 p.s.i. and generally at least about 350,000 p.s.i., optimum values of 400,000 to 550,000 p.s.i. being attainable.
• composition containing by weight 25% TiC and 75 steel matrix with the matrix consisting essentially by weight of 5% Cr, 4% Mo, 1% Ni, 0.4% C and the balance essentially Fe, exhibited a transverse rupture strength of 375,000 p.s.i. and a resistance to thermal shock corresponding to 18 repeated cycles of heating and cooling. Too much nickel (that is, above 1%) should be avoided since it is an austenite former and, therefore, tends to adversely affect the properties of the alloy.
• titanium carbide it is also important that the amount of titanium carbide be controlled over the range of about to 30% by weight of the total composition. If the composition contains too much titanium carbide, the rupture strength falls off as does the resistance to thermal shock. Thus, a composition containing 35% TiC and 65% matrix (5% Cr, 4% Mo, 0.5% Ni, 0.4% C and the balance essentially iron) exhibited after quench hardening and tempering a transverse rupture strength of about 280,000 p.s.i. and a resistance to thermal shock corresponding to 5 repeated cycles of heating and cooling.
• the sintered composition of the invention provides a new and improved carbide steel composition which, when quench hardened and tempered, provides markedly improved properties compared to other broadly similar compositions described herein.
• the sintered composition when quenched from 1875 F. (1025 C.) exhibits a hardness of at least about 6 5 R and .when thereafter tempered at- 975 11 (525 C.) .for-l hour, a hardness of at least about 62 R .
• the composition I generally exhibits transverse rupture properties in the hardened ;s tate ;-of over 325,000 p.s.i., preferably over 350,000 p.s.i. and usually from about 400,000 to 550,000 p.s.i. combined with improved resistance to thermal shock and room temperatureimpact.
• the alloy in'the shape of 1 inch x 1 inch x inch can also berep'eatedly heated to l500- 'F; (815 C.) and quenched in oil for at least 10 times without cracking.
• the alloy tends to resist softening at elevated temperatures and is suited for use as wear resistant elements, such as dies, elements involving sliding motion, apex seal strips for use in rotary piston engines and a multitude of other wear resistant applications.
• the invention also provides as an article of manufacture, a hardened wear resistant element made of a steel-bonded carbide characterized by an improved combination of transverse rupture strength, resistance to impact and resistance to thermal shock, the composition comprising by weight about 20% to 30% of primary grains of TiC dispersed through a steel matrix constituting to 70% by weight, the composition of the matrix consisting essentially by weight of about 3%v to 7% chromium (preferably 4% to 6%), about 2% to 7% molybdenum (preferably 3% to 5%), about 0.1% to 1% nickel (preferably 0.25% to 0.75%), about 0.3% to 0.7% carbon (preferably 0.3% to 0.5%) and the balance of the matrix essentially iron, the steel matrix surrounding the primary carbide grains being characterized by a microstructure of essentially martensite.
• a sintered steel-bonded titanium carbide composition characterized by an improved combination of transverse rupture strength and resistance to thermal shock which comprises by weight about 20% to 30% of primary grains of titanium carbide dispersed through a steel matrix making up the balance, the composition of said matrix consisting essentially by weight of about 4% to 6% chromium, about 3% to 5% molybdenum, about 0.25 to 0.75% nickel, about 0.3% to 0.5 carbon and the balance essentially iron.
• a hardened wear resistant element made of a steel-bonded titanium carbide composition characterized by an improved combination of transverse rupture strength and resistance to thermal shock, said composition comprising by weight about 20% to 30% of primary grains of titanium carbide dispersed through a steel matrix making up the balance, the composition of said matrix consisting essentially by weight of about 4% to 6% chromium, about 3% to 5% molyb denum, about 0.25% to 0.75% nickel, about 0.3% to 0.5% carbon and the balance essentially iron, the steel matrix surrounding the primary carbide grains being characterized by a microstructure of essentially martensite.
• the sintered compositionv of claim 1 consisting essentially by weight of approximately 25% by weight of TiC and approximately 75% by weight of the steel matrix, said matrix consisting essentially of about 5% chromium, about 4% molybdenum, about 0.5% nickel, about 0.4% carbon and the balance essentially iron.
• V 7512 8 W composition consists essentially by weight of approxi- 3,109,917 11/1963 Schmidt et a1 219--76 mately 25% by weight of TiC and approximately 75% 2,828,202 3/1958 Goetlel et a1 148--126 by weight of the steel matrix, said matrix consisting essentially of about 5% chromium, about 4% molybdenum, CARL QUARFORTH, Primary Examiner about 0.5% nickel, about 0.4% carbon and the balance 6 SCHAFER Assistant Examiner essentially iron.

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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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Cited By (9)

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• 1972
  • 1972-12-29 US US00319151A patent/US3809540A/en not_active Expired - Lifetime
• 1973
  • 1973-09-03 DE DE2344321A patent/DE2344321B2/de not_active Ceased
  • 1973-12-31 JP JP49004784A patent/JPS4998307A/ja active Pending

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