US3552937A - Sintered alloys of a chromium carbide-tungsten carbide-nickel system - Google Patents

Sintered alloys of a chromium carbide-tungsten carbide-nickel system Download PDF

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US3552937A
US3552937A US797208A US3552937DA US3552937A US 3552937 A US3552937 A US 3552937A US 797208 A US797208 A US 797208A US 3552937D A US3552937D A US 3552937DA US 3552937 A US3552937 A US 3552937A
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alloy
percent
carbide
weight
nickel
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Satoru Mito
Kazuo Suzuki
Hiroshi Yoshida
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Toshiba Corp
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Tokyo Shibaura Electric Co Ltd
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    • 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

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  • the present invention relates to sintered alloys having prominent resistance to chemical corrosion and cavitation erosion.
  • Other known materials having great hardness include sintered alloys consisting of tungsten carbide and nickelchromium alloys.
  • Metallographical1y such alloy has a structure in which particles of tungsten carbide are dispersed in a matrix consisting of a nickel-chromium alloy.
  • This sintered alloy indeed has remarkable hardness and good mechanical strength due to the presence of dispersed particles of tungsten carbide having great hardness.
  • the tungsten carbide is not fully resistant to chemical corrosion, so that the sintered alloy as a whole is not durable to damage resulting from other causes than cavitation erosion.
  • the present invention provides sintered alloys mainly consisting of to 75 percent by weight of chromium carbide, 10 to 43 percent by weight of tungsten carbide and 15 to percent by weight of nickel and containing one percent max. by weight of impurities.
  • This sintered alloy has a structure in which particles of chromium carbide and those of tungsten carbide and bonded together by nickel and displays satisfactory resistance to chemical corrosion and cavitation erosion at elevated temperatures.
  • One of the other desirable properties of the sintered alloy is that since it is mainly produced by powder metallurgical technique, it is well adapted for machining. A material having such suitable properties is very valuable in application under severe conditions in which there often occurs cavitation erosion, for example, in the blades of a turbine for power generation or the nozzle of a temperature and pressure reducer.
  • FIG. 1 is the range of a composition of a alloy as specified by the present invention.
  • FIG. 2 is a 1200 fold magnified microscopic photograph of the composition of one alloy according to the invention.
  • FIG. 3 is a 1200 fold magnified microscopic photograph of the composition of another alloy according to the invention.
  • FIG. 4 is a chart derived from electron probe microanalysis, showing the distribution of chromium, tungsten and nickel in the alloy of FIG. 3;
  • FIG. 5 is a similar chart to that of FIG. 4, showing the distribution of chromium, tungsten and nickel in the alloy of FIG. 3;
  • FIG. 6 is a graph indicating the variation of hardness resulting from difierent contents of CI C +WC in a Cr C WCNi sintered alloy
  • FIG. 7 is a graph showing the variation of transverse rupture strength relative to different contents of FIG. 8 is a graph denoting the variation of erosion according to diiferent contents of Cr C +WC;
  • FIG. 9 is a graph comparing the erosion rate of the alloy of the invention and that of several known alloys.
  • FIG. 10 is a graph showing the increased amount of oxidation due to difierent compositions of the alloy of the invention.
  • FIG. 11 is a longitudinal section of the nozzle of a temperature and pressure reducer fabricated according to an embodiment of the alloy of the invention.
  • FIG. 12 is a longitudial section of part of the adjusting valve for a steam turbine prepared from the alloy of the invention.
  • FIG. 13 is a perspective view of a lining of a turbine blade formed of the alloy of the invention.
  • FIG. 14 is a perspective view of a turbine blade to which is fitted the lining of FIG. 13;
  • FIG. 15 is a longitudinal section of the reducer nozzle for supplying gas turbine fuel prepared from the alloy of the invention.
  • the alloy of the present invention has a composition confined within the range defined by point A (40% Cr C 50% Ni and 10% WC) shown in the composition diagram of FIG. 1, point B Cr C 15% Ni and 10% WC), point C (42% Cr C 15% Ni and 43% WC) and point D (25% Cr C 50% Ni and 25% WC) and less than 1% of impurities based on the weight of the alloy.
  • the resistance to chemical corrosion of the alloy of the present invention substantially depends on the content of chromium carbide. If said content falls below 25 percent, the alloy will not display sufiicient resistance to chemical corrosion. Conversely with a content exceeding 75 percent, the alloy will be reduced in mechanical strength due to the resultant decrease in the nickel content.
  • Tungsten carbide itself helps the alloy to increase its hardness and promotes the dispersion of fine particles of chromium carbide.
  • the minimum content of tungsten carbide to attain such effect is 10 percent.
  • the maximum content of tungsten carbide allowable in an alloy required to have satisfactory resistance to chemical corrosion will be 43 percent.
  • Nickel plays the roll of a binder to bond together the particles of chromium carbide and those of tungsten carbide. Small contents of nickel lead to the increased hardness and decreased toughness of the alloy, While large amounts thereof bring about the reverse results. The optimum content of nickel ranges between and 50 percent.
  • chromium carbide, nickel and tungsten carbide contain iron, cobalt and molybdenum respectively as impurities. Needless to say, the smaller their contents, the greater advantage will result. If the presence of these impurities only accounts for 1 percent max. on the basis of the entire alloy, its effect will be negligible.
  • the alloy of the present invention can be easily prepared by shaping and sintering a mixture of chromium carbide, tungsten carbide and nickel each in powders using the ordinary techniques of powder metallurgy.
  • the shaping of powdered raw materials may be made by press moulding, slip-casting, powder direct rolling or powder extrusion.
  • Ashaped body of powdered raw materials having a prescribed shape and size is preferably presintered under a non-oxidising atmosphere and finally sintered at the liquid sintering temperatures of this alloy, and preferably in a neutral or reducing atmosphere.
  • the finally sintered product has a density equal to 98 readiness to be sintered.
  • the shaped body of powders displays a volumetric contraction of about percent, so that as is known in this field, it is necessary to determine the initial dimensions of the shaped body allowing for such shrinkage.
  • FIG. 2 An example of the structure of a finally sintered alloy is illustrated by the microscopic photograph of FIG. 2.
  • the alloy of FIG. 2 was composed of percent of chromium carbide, 30 percent of tungsten carbide and 20 percent of nickel and sintered 1 hour at a temperature of 1300 C. The surface was etched by an etching reagent prepared from the Murakami solution.
  • this sintered alloy has a structure consisting of particles of chromium carbide, smaller particles of tungsten carbide distributed among the particles of the chromium carbide and a binder phase of nickel interposed between these particles and bonding them together.
  • FIG. 3 shows the surface of a sintered alloy formed of percent of chromium carbide, 30 percent of tungsten carbide and 15 percent of nickel, which was etched in the same way as described above. As apparent from FIG. 3, this alloy also has substantially the same structure as that of FIG. 2.
  • FIG. 4 shows the strength of the chromium contained in the chromium carbide, that of the tungsten contained in the tungsten carbide and that of the nickel forming a binding phase.
  • the chart shows that in the region where the intensity of the chromium is reduced, the tungsten and nickel increase in intensity indicating that the sintered alloy consists of particles of chromium carbide, a binder phase of nickel bonding together said particles and particles of tungsten carbide dispersed in said binder phase.
  • the chromium carbide has a larger content of carbon than the tungsten carbide, so that the strength of the carbon varies according to the strength of the chromium. This supports the fact that the chromium is present in the form of chromium carbide.
  • FIGS. 6 to 8 respectively show the Vickers hardness corresponding to changes in the total content of chromium carbide and tungsten carbide in a CR C WCNi sintered alloy transverse rupture strength and extent of erosion.
  • the zigzag lines 1 and 2 were obtained by plotting the results of analysing several alloys having a composition falling within the scope of the present invention corresponding to a line connecting points A and B and points on the dotted line a as shown in FIG. 1.
  • the zigzag line 3 was plotted from the results of analyzing several alloys having a composition outside of the scope of the present invention corresponding to points on the dotted line b of FIG. 1.
  • the date of erosion is expressed in the reduced weight of alloy samples to be determined which were placed in boiling water and subjected to vibrations having a frequency of 6100 c./s. and an amplitude of microns which were transferred through the water 150 minutes by a cavitation tester using magnetostriction vibrations.
  • FIG. 9 gives the results of determining under the same conditions as described above the rate of erosion displayed by the alloy of the present invention composed of 65 percent of chromium carbide, 20 percent of tungsten carbide and 15 percent of nickel, three known kinds of Stellite alloy and stainless steel. The figure clearly indicates that the alloy of the present invention has greater resistance to cavitation erosion than any of the known alloys.
  • FIG. 10 shows changes in the resistance to oxidation of the alloy of the present invention corresponding to the varied amounts of carbide contained therein. Resistance to oxidation was determined by heating the samples 5 hours at a certain temperature in the air and measuring an increased weight over that present before said heating. The results show that while the decrease in the content of chromium carbide, namely, the relative increase in the proportions of tungsten carbide and nickel indeed degraded the resistance to oxidation of the alloy as a whole, reduction in said resistance was practically negligible.
  • EXAMPLE 1 There were mixed hours in a wet ball mill 55 parts by weight of powders of chromium carbide having an average particle size of about 5 microns, 15 parts by weight of powders of nickel having a particle size of 325 mesh max. and 30 parts by weight of powders of tungsten carbide having an average particles size of about 2 microns. To the mixture were further added powders of paraflin. The mass was press moulded into a blind cylindrical body. The body was presintered 1 hour at a temperature of 600 C. in an atmosphere of dehydrated hydrogen 99.99 percent pure (dew point 50 C.) and finally sintered 1 hour at a temperature of 1280 C. in the same atmosphere.
  • the finally sintered cylindrical body was machined into a nozzle 12, 75 mm. in maximum diameter and mm. long shown in FIG. 11, which was perforated with eight nozzle holes 8 mm. in diameter defining an angle of 45 degrees to the axial centre of the cylindrical body and arranged at an equal space.
  • the nozzle 12 was fitted to a temperature and pressure reducer, and tested continuously for 50 days under the conditions where boiler steam at 500 C. and 200 atm., was reduced to 200 C. and 5 atm., respectively after passing through said nozzle.
  • the test confirmed that the nozzle showed no unfavourable change, but was fully durable under the aforesaid conditions.
  • there was prepared from Stellite alloy a nozzle having the same shape and size. This reference nozzle was put to test in the temperature and pressure reducer under the same conditions as described above. A test continuously running for 30 days caused the end portion of said Stellite alloy nozzle to be deformed by wear, ceasing to display the initial performance.
  • EXAMPLE 2 There were mixed in a wet ball mill 50 parts by weight of powders of chromium carbide having an average particle size of about 5 microns, 20 parts by weight of nickel having an average particle size of 325 mesh max., 30 parts by weight of tungsten carbide having an average particle size of about 2 microns and a suitable amount of parafiin powders. From the mass were prepared four rings having different sizes under the same conditions as in Example 1. The rings were subjected to preand final sintering.
  • the rings were fitted to the prescribed parts of a steam adjusting valve for a steam turbine made of an alloy having a composition of 1.25 percent of chromium, 1.0 percent of molybdenum, 0.2 percent of vanadium, 0.19 percent of carbon and iron as the remainder.
  • numeral 21 denotes a valve seat having a fluid passage 22, 23 an -O-ring made of the sintered alloy of the present invention fitted to the valve seat 21, 24 a movable main valve rod for opening or closing the fluid passage 22, 25 an O-riug mounted on the outer circumferential surface of the movable main valve rod 24, 26 a movable auxiliary valve rod for opening or closing a fluid passage 27 formed in the valve rod 24 and 28 and 29 O-rings fitted to the parts of the main and auxiliary valve rods at 'which they are brought into contact.
  • These O-rings 23, 25, 28 and 29 were silver brazed to the prescribed parts of the valve seat and rod applying high frequency induction heating.
  • the steam adjusting valve fitted with said O-n'ngs was used continuously for 500 hours in controlling the flow rate of steam at a temperature of about 500 C. running at the rate of 500 m./sec.
  • the O-rings and brazed parts did not present any substantial damage.
  • steam adjusting valves of the same composition as previously mentioned but having the O-rings replaced by Stellite alloy D-2 welded to the parts to which said O-rings were to be fitted presented during a continuous test of about 120 r hours under the aforementioned conditions an increased clearance between the valves due to the deformation and cavitation erosion of the welded parts..
  • EXAMPLE 3 There were mixed in a ball mill 130 parts by weight of powders of chromium carbide having an average particle size of about microns, 40 parts by weight of powders of nickel having a particle size of 270 mesh max. and 30 parts by weight of powders of tungsten carbide having an average particles size of about 1.5 microns. There were also added 1 part by weight of ammonium alginate and small amounts of water. The mass was further adjusted in viscosity by addition of a 3 percent solution of hydrochloric acid and 4 percent solution of caustic soda. The mass was introduced into a mould for fabricating a turbine blade lining.
  • the moulded body After being dried two days at normal temperatures, the moulded body was further dried at a temperature of about 120 C., and then heated 1 hour at 1280 C. in a graphite boat packed with graphite powders in a hydrogen stream with the temperature progressively raised to said level at the rate of 300 C. per hour.
  • FIG. 13 presents the external appearance of said lining 31.
  • the lining was fitted to the ordinary turbine blade 32 and tested at a temperature of 118 to 120 C. and rotating velocity of 400 m./sec. After the test was continued 500 hours, the lining made of the sintered alloy of the present invention did not present any undesirable change.
  • a Stellite alloy lining displayed cavitation erosion in a test continued 68 hours under the same conditions, the surface metal thereof losing its luster.
  • EXAMPLE 4 There were first mixed in a stainless steel pot 40 parts by weight of powders of chromium carbide having an average particle size of 4.5 microns, parts by weight of powders of nickel having a particle size of 325 mesh max., and 30 parts by weight of powders of tungsten carbide having an average particle size of 1.7 microns. There was also added a suitable amount of acetone. After thorough mixing, the acetone was removed. The mass to which there were further added 2 parts by weight of paraffin powders was pelletised into a form about microns thick using a pelletiser. The pellet was rolled into a ribbon 0.63 mm. thick in average and 30 mm. wide using ahorizontal type roller.
  • the ribbon was presintered minutes at a temperature of 600 C. in an atmosphere of hydrogen.
  • the ribbon was cut into a turbine blade lining shaped as shown in FIG. 13.
  • the lining was finally sintered 1 hour at a temperature of 1270 C.
  • the sintered alloy was contracted in size about 23 percent in the rolling direction and had a theoretical density of 98.7 percent.
  • the lining was fitted to a turbine blade and tested at a temperature of 120 C. and rotation velocity of 350 m./ see. as in Example 3. After the test was continuously run 500 hours, the lining was proved to be free from any unfavourable damage.
  • EXAMPLE 5 There were mixed hours in a wet ball mill 50 parts by weight of powders of chromium carbide having an average particle size of 5 microns, 25 parts by weight of powders of nickel having a particle size of 325 mesh max., and 25 parts by weight of powders of tungsten carbide having an average particle size of 1.7 microns. There were also added about 2 parts by weight of parafiin powders.
  • the mass was press moulded into a plate 30 mm. wide, 300 mm. long and 10 mm. thick using a pressure of 1 to 1.5 ton/cm.
  • the plate was presintered 1 hour at a temperature of 600 C. in an atmosphere of dehydrated hydrogen 99.998 percent pure.
  • This presintered material was cut into a turbine blade lining shaped .as shown in FIG. 13.
  • the lining was finally sintered 1 hour at a temperature of 1280 to 1300 C. in the same atmosphere.
  • the lining thus prepared was attached to a turbine blade, and tested continuously 500 hours under the same conditions as in Example 4 and as a result was proved to suffer substantially no damage.
  • EXAMPLE 6 There were fully mixed in a stainless steel pot 40 parts by weight of powders of chromium carbide having an average particle size of 4.5 microns, 40 parts by weight of powders of nickel having a particle size of 325 mesh max, 20 parts by weight of powders of tungsten carbide having an average particle size of 1.75 microns and a suitable amount of acetone. After the acetone was removed, there was introduced a small amount of a 5 percent aqueous solution of vinyl alcohol. The mass was extruded into a plane plate 10 mm. wide and 3 mm. thick at the rate of about 1 mm./ sec. through a tool steel nozzle. The late was formed in a wooden mould into a turbine blade lining as illustrated in FIG. 13.
  • the lining After being allowed to dry for two days, the lining was further dried 5 hours at a temperature of C. Then the lining was finally sintered 45 minutes at a temperature of 1280 C. in a graphite boat packed with graphite powders. The sintered lining had a theoretical density of 99.0 percent. After being fitted to a turbine blade, the lining was tested continuously 500 hours under the same conditions as in Example 4. The surface metal of the lining did not lose its luster, showing that the lining withstood the test.
  • EXAMPLE 7 There were mixed in a wet ball mill 45 parts by weight of powders of chromium carbide having an average particle size of microns, 20 parts by weight of powders of nickel having a particle size of 270 mesh max., and 35 parts by weight of powders of tungsten carbide having an average particle size of 1.75 microns. The mixture was press moulded into a blind cylindrical body using a pressure of 1.5 ton/cm. and then presintered 1 hour at a temperature of 600 C. and a pressure of to 10 torr units. After being cut into a reducer nozzle for supplying gas turbine fuel, the mass was finally sintered 1 hour at a temperature of 1300 C. and a pressure of 10" to 10 torr units.
  • the nozzle had a fluid passage 41 formed therein and seventeen nozzle holes 42 extending from the fluid path 41 to the outside in a direction intersecting the nozzle axis at right angles.
  • the sample nozzle was used continuously 5000 hours as a reducer nozzle for supplying gas turbine fuel, but presented no cavitation erosion or chemical corrosion. Thus the nozzle displayed a useful life 10 times or more longer than that prepared from the prior art nitride steel or Stellite alloy.
  • a sintered alloy consisting essentially of 25 to 75 percent by weight chromium carbide, 15 to percent by weight nickel and 10 to 43 percent by weight tungsten carbide, and also containing impurities of less than 1 percent based on the total weight of the alloy said chromium carbide and said tungsten carbide :being bonded together by said nickel.

Abstract

SINTERED ALLOYS MAINLY CONSISTING OF 25 TO 75 PERCENT BY WEIGHT OF CHROMIUM CARBIDE CR2C2, 10 TO 43 PERCENT BY WEIGHT OF TUNGSTEN CARBIDE WC AND 15 TO 50 PERCENT BY WEIGHT OF NICKEL NI AND CONTAINING ONE PERCENT MAX. BY WEIGHT OF IMPURITES. THESE ALLOYS ARE FULLY RESISTANT TO CHEMICAL CORROSION AND CAVITATION EROSION.

Description

Jan. 5, 1971 SATQRU M|TQ ETAL 3,552,937
' SINTERED ALLOYS OF A CHROMIUM CARBIDE-TUNGSTEN CARBIDE-NICKEL- SYSTEM I I Fi1ed Feb-. 6 1969- 6 Sheets-Sheet 1 Cr3C2 so wc VICKERS HARDNESS (Hv) Jan. 5, 1971 SATORU MlTO ErAL 3,552,937
SINTERED ALLOYS OF A CHROMIUM CARBIDE-TUNGSTEN CARBIDE-NICKEL SYSTEM 6 Sheets-Sheet 2 .Filed Feb. 6, 1969 FIG.2
FIG
Jan. 5, 1971- SATORU MITO ET AL 3,552,937
I v dlNl'EHEi) ALLOYS or A UHROMLUM CARUiDE-lUXUSl'lIN CARBIDE-NICKEL SYSTEM Filed Feb. 6, 1969 6 Sheets-Sheet FIG; 4
INTENSIT IES DISTANCE ACC VOLTAGE i5KV CRYSTAL= LiF, LiF, KAP SAMPLE CURR. OiZjJA DETECTOR Kr. ETA Kr. EXA, FPC
X-RAY=WLG CRKQ NiLCl CHART=20cm/min. SAMPLE 8,4.l/min.
| NTENSI TIES DiSTANCE ACC. VOLTAGE 15KV CRYSTAL= LiF, LiF, PbSC SAMPLE CURR. 0.12pA DETECTOR= Kr.EXA, Kr.EXA, FPC X-RAY=WL(I CRKQ CKQ CHART SPEED ZOmm/min.
, SAMPLE SPEED 8,u/min.
SATORU MITO ETAL SIXTEREU ALLOYS or A Jan. 5, 1971 CHROMIUM CARBIDE-TUXGSTEN (REL SYSTEM I 6 Sheets-Sheet 4 CARBIDE-N" Filed Feb. 6, 1969 FIG. 7
EEBx
O w V. I5
ooo 0 v 6 4 2 60 TO Cr3C2 WC (WP/o) Fuss 0 20605 mo E395 TEST PERIOD (min) SATORU MITO ET AL SINTERED ALLOYS OF A CHROMIUM CARBID 3,552,937 E-TUXGSTEN Jan, 5,1971
CARBIDE-NICKEL SYSTEM 6 Sheets-Sheet Q Filed Feb. 1969 US. Cl. 29182.7 1 Claim ABSTRACT OF THE DISCLOSURE Sintered alloys mainly consisting of 25 to 75 percent by weight of chromium carbide Cr C to 43 percent by weight of tungsten carbide WC and to 50 percent by weight of nickel Ni and containing one percent max. by Weight of impurities. These alloys are fully resistant to chemical corrosion and cavitation erosion.
The present invention relates to sintered alloys having prominent resistance to chemical corrosion and cavitation erosion.
Members exposed to a fast traveling fluid at elevated temperature are damaged by chemical corrosion caused by oxidation as well as by cavitation erosion. Accordingly, such members are demanded to consist of materials having great resistance to chemical corrosion and cavitation erosion. The best material now known is a cobalt-base alloy containing chromium, tungsten and nickel (commonly known as a Stellite alloy). The Stellite alloy had the drawback that since castings had to be machined to obtain members of the desired shape and size, it was practically impossible to prepare said alloy from a composition which would display a hardness exceeding Generally, strength to cavitation erosion depends on the hardness of material, so that the Stellite alloy cannot be. deemed most suitable in this respect.
Other known materials having great hardness include sintered alloys consisting of tungsten carbide and nickelchromium alloys. Metallographical1y, such alloy has a structure in which particles of tungsten carbide are dispersed in a matrix consisting of a nickel-chromium alloy. This sintered alloy indeed has remarkable hardness and good mechanical strength due to the presence of dispersed particles of tungsten carbide having great hardness. But the tungsten carbide is not fully resistant to chemical corrosion, so that the sintered alloy as a whole is not durable to damage resulting from other causes than cavitation erosion.
The present invention provides sintered alloys mainly consisting of to 75 percent by weight of chromium carbide, 10 to 43 percent by weight of tungsten carbide and 15 to percent by weight of nickel and containing one percent max. by weight of impurities. This sintered alloy has a structure in which particles of chromium carbide and those of tungsten carbide and bonded together by nickel and displays satisfactory resistance to chemical corrosion and cavitation erosion at elevated temperatures. One of the other desirable properties of the sintered alloy is that since it is mainly produced by powder metallurgical technique, it is well adapted for machining. A material having such suitable properties is very valuable in application under severe conditions in which there often occurs cavitation erosion, for example, in the blades of a turbine for power generation or the nozzle of a temperature and pressure reducer.
United States Paten 3,552,937 Patented Jan. 5, 1971 The present invention can be more fully understood from the following detailed description when taken in connection with the accompanying drawings, in which:
FIG. 1 is the range of a composition of a alloy as specified by the present invention;
FIG. 2 is a 1200 fold magnified microscopic photograph of the composition of one alloy according to the invention;
FIG. 3 is a 1200 fold magnified microscopic photograph of the composition of another alloy according to the invention;
FIG. 4 is a chart derived from electron probe microanalysis, showing the distribution of chromium, tungsten and nickel in the alloy of FIG. 3;
FIG. 5 is a similar chart to that of FIG. 4, showing the distribution of chromium, tungsten and nickel in the alloy of FIG. 3;
FIG. 6 is a graph indicating the variation of hardness resulting from difierent contents of CI C +WC in a Cr C WCNi sintered alloy;
FIG. 7 is a graph showing the variation of transverse rupture strength relative to different contents of FIG. 8 is a graph denoting the variation of erosion according to diiferent contents of Cr C +WC;
FIG. 9 is a graph comparing the erosion rate of the alloy of the invention and that of several known alloys;
FIG. 10 is a graph showing the increased amount of oxidation due to difierent compositions of the alloy of the invention;
FIG. 11 is a longitudinal section of the nozzle of a temperature and pressure reducer fabricated according to an embodiment of the alloy of the invention;
FIG. 12 is a longitudial section of part of the adjusting valve for a steam turbine prepared from the alloy of the invention;
FIG. 13 is a perspective view of a lining of a turbine blade formed of the alloy of the invention;
FIG. 14 is a perspective view of a turbine blade to which is fitted the lining of FIG. 13; and
FIG. 15 is a longitudinal section of the reducer nozzle for supplying gas turbine fuel prepared from the alloy of the invention.
The alloy of the present invention has a composition confined within the range defined by point A (40% Cr C 50% Ni and 10% WC) shown in the composition diagram of FIG. 1, point B Cr C 15% Ni and 10% WC), point C (42% Cr C 15% Ni and 43% WC) and point D (25% Cr C 50% Ni and 25% WC) and less than 1% of impurities based on the weight of the alloy.
The resistance to chemical corrosion of the alloy of the present invention substantially depends on the content of chromium carbide. If said content falls below 25 percent, the alloy will not display sufiicient resistance to chemical corrosion. Conversely with a content exceeding 75 percent, the alloy will be reduced in mechanical strength due to the resultant decrease in the nickel content.
Tungsten carbide itself helps the alloy to increase its hardness and promotes the dispersion of fine particles of chromium carbide. The minimum content of tungsten carbide to attain such effect is 10 percent. However, since tungsten carbide has lower resistance to chemical corrosion than chromium carbide, the maximum content of tungsten carbide allowable in an alloy required to have satisfactory resistance to chemical corrosion will be 43 percent.
Nickel plays the roll of a binder to bond together the particles of chromium carbide and those of tungsten carbide. Small contents of nickel lead to the increased hardness and decreased toughness of the alloy, While large amounts thereof bring about the reverse results. The optimum content of nickel ranges between and 50 percent.
The lower the purity of raw materials used, the lower will naturally be the purity of the sintered alloy produced. Generally, chromium carbide, nickel and tungsten carbide contain iron, cobalt and molybdenum respectively as impurities. Needless to say, the smaller their contents, the greater advantage will result. If the presence of these impurities only accounts for 1 percent max. on the basis of the entire alloy, its effect will be negligible.
The alloy of the present invention can be easily prepared by shaping and sintering a mixture of chromium carbide, tungsten carbide and nickel each in powders using the ordinary techniques of powder metallurgy. For instance, the shaping of powdered raw materials may be made by press moulding, slip-casting, powder direct rolling or powder extrusion. Ashaped body of powdered raw materials having a prescribed shape and size is preferably presintered under a non-oxidising atmosphere and finally sintered at the liquid sintering temperatures of this alloy, and preferably in a neutral or reducing atmosphere. These techniques of powder metallurgy are already known to those skilled in the art, and it will be understood that the processes and conditions involved will not restrict the present invention in any way.
The finally sintered product has a density equal to 98 readiness to be sintered. Throughout the first and second sintering operations, the shaped body of powders displays a volumetric contraction of about percent, so that as is known in this field, it is necessary to determine the initial dimensions of the shaped body allowing for such shrinkage.
An example of the structure of a finally sintered alloy is illustrated by the microscopic photograph of FIG. 2. The alloy of FIG. 2 was composed of percent of chromium carbide, 30 percent of tungsten carbide and 20 percent of nickel and sintered 1 hour at a temperature of 1300 C. The surface was etched by an etching reagent prepared from the Murakami solution. As clearly seen from FIG. 2, this sintered alloy has a structure consisting of particles of chromium carbide, smaller particles of tungsten carbide distributed among the particles of the chromium carbide and a binder phase of nickel interposed between these particles and bonding them together.
FIG. 3 shows the surface of a sintered alloy formed of percent of chromium carbide, 30 percent of tungsten carbide and 15 percent of nickel, which was etched in the same way as described above. As apparent from FIG. 3, this alloy also has substantially the same structure as that of FIG. 2.
There was carried out electron probe microanalysis to determine the distribution of the elements constituting this sintered alloy of the present invention which was formed of 55 percent of chromium carbide, 30 percent of tungsten carbide and 15 percent nickel. FIG. 4 shows the strength of the chromium contained in the chromium carbide, that of the tungsten contained in the tungsten carbide and that of the nickel forming a binding phase. The chart shows that in the region where the intensity of the chromium is reduced, the tungsten and nickel increase in intensity indicating that the sintered alloy consists of particles of chromium carbide, a binder phase of nickel bonding together said particles and particles of tungsten carbide dispersed in said binder phase. FIG. 5 gives the strength of the chromium contained in the chromium carbide, that of the tungsten contained in the tungsten carbide and that of the carbon included in all the carbides. The chart shows that there is present the tungsten carbide even in the region which lacks the chromium carbide. Now referring to the strength of the carbon, the chromium carbide has a larger content of carbon than the tungsten carbide, so that the strength of the carbon varies according to the strength of the chromium. This supports the fact that the chromium is present in the form of chromium carbide.
FIGS. 6 to 8 respectively show the Vickers hardness corresponding to changes in the total content of chromium carbide and tungsten carbide in a CR C WCNi sintered alloy transverse rupture strength and extent of erosion. Throughout these figures, the zigzag lines 1 and 2 were obtained by plotting the results of analysing several alloys having a composition falling within the scope of the present invention corresponding to a line connecting points A and B and points on the dotted line a as shown in FIG. 1. The zigzag line 3 was plotted from the results of analyzing several alloys having a composition outside of the scope of the present invention corresponding to points on the dotted line b of FIG. 1. The date of erosion is expressed in the reduced weight of alloy samples to be determined which were placed in boiling water and subjected to vibrations having a frequency of 6100 c./s. and an amplitude of microns which were transferred through the water 150 minutes by a cavitation tester using magnetostriction vibrations.
As seen from FIGS. 6 to 8, as the scope of the present invention is concerned, increasing contents of carbides elevate the hardness of the alloy without widely varying the deflective strength thereof. In contrast, alloys outside of the scope of the invention exhibit the greater rate of erosion with increasing contents of carbides.
FIG. 9 gives the results of determining under the same conditions as described above the rate of erosion displayed by the alloy of the present invention composed of 65 percent of chromium carbide, 20 percent of tungsten carbide and 15 percent of nickel, three known kinds of Stellite alloy and stainless steel. The figure clearly indicates that the alloy of the present invention has greater resistance to cavitation erosion than any of the known alloys.
FIG. 10 shows changes in the resistance to oxidation of the alloy of the present invention corresponding to the varied amounts of carbide contained therein. Resistance to oxidation was determined by heating the samples 5 hours at a certain temperature in the air and measuring an increased weight over that present before said heating. The results show that while the decrease in the content of chromium carbide, namely, the relative increase in the proportions of tungsten carbide and nickel indeed degraded the resistance to oxidation of the alloy as a whole, reduction in said resistance was practically negligible.
There will now be given some examples where there were tested samples of the alloy of the present invention under the conditions actually prevailing in manufacture as well as those in which the resultant alloy was subject to cavitation erosion.
EXAMPLE 1 There were mixed hours in a wet ball mill 55 parts by weight of powders of chromium carbide having an average particle size of about 5 microns, 15 parts by weight of powders of nickel having a particle size of 325 mesh max. and 30 parts by weight of powders of tungsten carbide having an average particles size of about 2 microns. To the mixture were further added powders of paraflin. The mass was press moulded into a blind cylindrical body. The body was presintered 1 hour at a temperature of 600 C. in an atmosphere of dehydrated hydrogen 99.99 percent pure (dew point 50 C.) and finally sintered 1 hour at a temperature of 1280 C. in the same atmosphere.
The finally sintered cylindrical body was machined into a nozzle 12, 75 mm. in maximum diameter and mm. long shown in FIG. 11, which was perforated with eight nozzle holes 8 mm. in diameter defining an angle of 45 degrees to the axial centre of the cylindrical body and arranged at an equal space.
The nozzle 12 was fitted to a temperature and pressure reducer, and tested continuously for 50 days under the conditions where boiler steam at 500 C. and 200 atm., was reduced to 200 C. and 5 atm., respectively after passing through said nozzle. The test confirmed that the nozzle showed no unfavourable change, but was fully durable under the aforesaid conditions. By way of comparison, there was prepared from Stellite alloy a nozzle having the same shape and size. This reference nozzle was put to test in the temperature and pressure reducer under the same conditions as described above. A test continuously running for 30 days caused the end portion of said Stellite alloy nozzle to be deformed by wear, ceasing to display the initial performance.
EXAMPLE 2 There were mixed in a wet ball mill 50 parts by weight of powders of chromium carbide having an average particle size of about 5 microns, 20 parts by weight of nickel having an average particle size of 325 mesh max., 30 parts by weight of tungsten carbide having an average particle size of about 2 microns and a suitable amount of parafiin powders. From the mass were prepared four rings having different sizes under the same conditions as in Example 1. The rings were subjected to preand final sintering. The rings were fitted to the prescribed parts of a steam adjusting valve for a steam turbine made of an alloy having a composition of 1.25 percent of chromium, 1.0 percent of molybdenum, 0.2 percent of vanadium, 0.19 percent of carbon and iron as the remainder. Referring to FIG. 12 illustrating the steam adjusting valve, numeral 21 denotes a valve seat having a fluid passage 22, 23 an -O-ring made of the sintered alloy of the present invention fitted to the valve seat 21, 24 a movable main valve rod for opening or closing the fluid passage 22, 25 an O-riug mounted on the outer circumferential surface of the movable main valve rod 24, 26 a movable auxiliary valve rod for opening or closing a fluid passage 27 formed in the valve rod 24 and 28 and 29 O-rings fitted to the parts of the main and auxiliary valve rods at 'which they are brought into contact. These O- rings 23, 25, 28 and 29 were silver brazed to the prescribed parts of the valve seat and rod applying high frequency induction heating.
The steam adjusting valve fitted with said O-n'ngs was used continuously for 500 hours in controlling the flow rate of steam at a temperature of about 500 C. running at the rate of 500 m./sec. The O-rings and brazed parts did not present any substantial damage. In contrast, steam adjusting valves of the same composition as previously mentioned but having the O-rings replaced by Stellite alloy D-2 welded to the parts to which said O-rings were to be fitted, presented during a continuous test of about 120 r hours under the aforementioned conditions an increased clearance between the valves due to the deformation and cavitation erosion of the welded parts..
EXAMPLE 3 There were mixed in a ball mill 130 parts by weight of powders of chromium carbide having an average particle size of about microns, 40 parts by weight of powders of nickel having a particle size of 270 mesh max. and 30 parts by weight of powders of tungsten carbide having an average particles size of about 1.5 microns. There were also added 1 part by weight of ammonium alginate and small amounts of water. The mass was further adjusted in viscosity by addition of a 3 percent solution of hydrochloric acid and 4 percent solution of caustic soda. The mass was introduced into a mould for fabricating a turbine blade lining. After being dried two days at normal temperatures, the moulded body was further dried at a temperature of about 120 C., and then heated 1 hour at 1280 C. in a graphite boat packed with graphite powders in a hydrogen stream with the temperature progressively raised to said level at the rate of 300 C. per hour. The sintered lining thus prepared had a theoretical density of 98.8 percent and and a hardness of Hv= 1350.
FIG. 13 presents the external appearance of said lining 31. As shown in FIG. 14, the lining was fitted to the ordinary turbine blade 32 and tested at a temperature of 118 to 120 C. and rotating velocity of 400 m./sec. After the test was continued 500 hours, the lining made of the sintered alloy of the present invention did not present any undesirable change. In contrast, a Stellite alloy lining displayed cavitation erosion in a test continued 68 hours under the same conditions, the surface metal thereof losing its luster.
EXAMPLE 4 There were first mixed in a stainless steel pot 40 parts by weight of powders of chromium carbide having an average particle size of 4.5 microns, parts by weight of powders of nickel having a particle size of 325 mesh max., and 30 parts by weight of powders of tungsten carbide having an average particle size of 1.7 microns. There was also added a suitable amount of acetone. After thorough mixing, the acetone was removed. The mass to which there were further added 2 parts by weight of paraffin powders was pelletised into a form about microns thick using a pelletiser. The pellet was rolled into a ribbon 0.63 mm. thick in average and 30 mm. wide using ahorizontal type roller. The ribbon was presintered minutes at a temperature of 600 C. in an atmosphere of hydrogen. The ribbon was cut into a turbine blade lining shaped as shown in FIG. 13. The lining was finally sintered 1 hour at a temperature of 1270 C. The sintered alloy was contracted in size about 23 percent in the rolling direction and had a theoretical density of 98.7 percent.
The lining was fitted to a turbine blade and tested at a temperature of 120 C. and rotation velocity of 350 m./ see. as in Example 3. After the test was continuously run 500 hours, the lining was proved to be free from any unfavourable damage.
EXAMPLE 5 There were mixed hours in a wet ball mill 50 parts by weight of powders of chromium carbide having an average particle size of 5 microns, 25 parts by weight of powders of nickel having a particle size of 325 mesh max., and 25 parts by weight of powders of tungsten carbide having an average particle size of 1.7 microns. There were also added about 2 parts by weight of parafiin powders. The mass was press moulded into a plate 30 mm. wide, 300 mm. long and 10 mm. thick using a pressure of 1 to 1.5 ton/cm. The plate was presintered 1 hour at a temperature of 600 C. in an atmosphere of dehydrated hydrogen 99.998 percent pure. This presintered material was cut into a turbine blade lining shaped .as shown in FIG. 13. The lining was finally sintered 1 hour at a temperature of 1280 to 1300 C. in the same atmosphere. The lining thus prepared was attached to a turbine blade, and tested continuously 500 hours under the same conditions as in Example 4 and as a result was proved to suffer substantially no damage.
EXAMPLE 6 There were fully mixed in a stainless steel pot 40 parts by weight of powders of chromium carbide having an average particle size of 4.5 microns, 40 parts by weight of powders of nickel having a particle size of 325 mesh max, 20 parts by weight of powders of tungsten carbide having an average particle size of 1.75 microns and a suitable amount of acetone. After the acetone was removed, there was introduced a small amount of a 5 percent aqueous solution of vinyl alcohol. The mass was extruded into a plane plate 10 mm. wide and 3 mm. thick at the rate of about 1 mm./ sec. through a tool steel nozzle. The late was formed in a wooden mould into a turbine blade lining as illustrated in FIG. 13. After being allowed to dry for two days, the lining was further dried 5 hours at a temperature of C. Then the lining was finally sintered 45 minutes at a temperature of 1280 C. in a graphite boat packed with graphite powders. The sintered lining had a theoretical density of 99.0 percent. After being fitted to a turbine blade, the lining was tested continuously 500 hours under the same conditions as in Example 4. The surface metal of the lining did not lose its luster, showing that the lining withstood the test.
EXAMPLE 7 There were mixed in a wet ball mill 45 parts by weight of powders of chromium carbide having an average particle size of microns, 20 parts by weight of powders of nickel having a particle size of 270 mesh max., and 35 parts by weight of powders of tungsten carbide having an average particle size of 1.75 microns. The mixture was press moulded into a blind cylindrical body using a pressure of 1.5 ton/cm. and then presintered 1 hour at a temperature of 600 C. and a pressure of to 10 torr units. After being cut into a reducer nozzle for supplying gas turbine fuel, the mass was finally sintered 1 hour at a temperature of 1300 C. and a pressure of 10" to 10 torr units.
As shown in FIG. 15, the nozzle had a fluid passage 41 formed therein and seventeen nozzle holes 42 extending from the fluid path 41 to the outside in a direction intersecting the nozzle axis at right angles. The sample nozzle was used continuously 5000 hours as a reducer nozzle for supplying gas turbine fuel, but presented no cavitation erosion or chemical corrosion. Thus the nozzle displayed a useful life 10 times or more longer than that prepared from the prior art nitride steel or Stellite alloy.
What is claimed is:
1. A sintered alloy consisting essentially of 25 to 75 percent by weight chromium carbide, 15 to percent by weight nickel and 10 to 43 percent by weight tungsten carbide, and also containing impurities of less than 1 percent based on the total weight of the alloy said chromium carbide and said tungsten carbide :being bonded together by said nickel.
Cemented Carbides, by Schwarzkopf V. Kietfer, 1960, pp. 197-198.
CARL D. QUARFORTH, Primary Examiner A. J. STEINER, Assistant Examiner US. Cl. X.R. 203
US797208A 1968-02-10 1969-02-06 Sintered alloys of a chromium carbide-tungsten carbide-nickel system Expired - Lifetime US3552937A (en)

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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3878592A (en) * 1971-12-22 1975-04-22 Ford Motor Co Molybdenum nickel chromium bonded titanium carbide
US3993446A (en) * 1973-11-09 1976-11-23 Dijet Industrial Co., Ltd. Cemented carbide material
US4606767A (en) * 1984-10-30 1986-08-19 Kyocera Corporation Decorative silver-colored sintered alloy
US5580833A (en) * 1994-10-11 1996-12-03 Industrial Technology Research Institute High performance ceramic composites containing tungsten carbide reinforced chromium carbide matrix
US5736658A (en) * 1994-09-30 1998-04-07 Valenite Inc. Low density, nonmagnetic and corrosion resistant cemented carbides
WO2003014406A2 (en) * 2001-08-03 2003-02-20 Kennametal Inc. Corrosion and wear resistant cemented carbide
US7438741B1 (en) * 2003-05-20 2008-10-21 Exxonmobil Research And Engineering Company Erosion-corrosion resistant carbide cermets for long term high temperature service
CN102839313A (en) * 2012-08-14 2012-12-26 四川理工学院 Nano Cr3C2-WC-Ni composite powder and preparation method thereof

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3878592A (en) * 1971-12-22 1975-04-22 Ford Motor Co Molybdenum nickel chromium bonded titanium carbide
US3993446A (en) * 1973-11-09 1976-11-23 Dijet Industrial Co., Ltd. Cemented carbide material
US4606767A (en) * 1984-10-30 1986-08-19 Kyocera Corporation Decorative silver-colored sintered alloy
US5736658A (en) * 1994-09-30 1998-04-07 Valenite Inc. Low density, nonmagnetic and corrosion resistant cemented carbides
US5580833A (en) * 1994-10-11 1996-12-03 Industrial Technology Research Institute High performance ceramic composites containing tungsten carbide reinforced chromium carbide matrix
WO2003014406A2 (en) * 2001-08-03 2003-02-20 Kennametal Inc. Corrosion and wear resistant cemented carbide
US6537343B2 (en) * 2001-08-03 2003-03-25 Kennametal Inc. Corrosion and wear resistant cemented carbide
WO2003014406A3 (en) * 2001-08-03 2003-05-08 Kennametal Inc Corrosion and wear resistant cemented carbide
US7438741B1 (en) * 2003-05-20 2008-10-21 Exxonmobil Research And Engineering Company Erosion-corrosion resistant carbide cermets for long term high temperature service
US20080276757A1 (en) * 2003-05-20 2008-11-13 Narasimha-Rao Venkata Bangaru Erosion-corrosion resistant carbide cermets for long term high temperature service
CN102839313A (en) * 2012-08-14 2012-12-26 四川理工学院 Nano Cr3C2-WC-Ni composite powder and preparation method thereof
CN102839313B (en) * 2012-08-14 2014-06-18 四川理工学院 Nano Cr3C2-WC-Ni composite powder and preparation method thereof

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