Cemented carbide

This invention consists of two parts: "Cemented Carbide with Minimal Amount of Binder Metal", and "Nonmagnetic Cemented Carbide". The "Cemented Carbide with Minimal Amount of Binder Metal" is for cemented carbide bodies which are made from less than 2% binder metal powder and metal carbide powder. The raw powder is to be prepared following a conventional powder metallurgy method--especially the conventional method of making cemented carbide--milling, forming and sintering. The "Non-magnetic Cemented Carbide" is cemented carbides which have nickel-tungsten alloy as a binder metal. The process of manufacturing uses said conventional powder metallurgy. The purpose of this invention is to manufacture non-magnetic cemented carbide using more than two metal carbide powders and binder metal. More than one kind of metal carbides form solid solution carbide during the sintering process.

SUMMARY OF THE INVENTION 
This invention consists of two parts. The first part is for "Cemented 
Carbide with Minimal Amount of Binder Metal", and the second part is for 
"Nonmagnetic Cemented Carbide". 
The invention, "Cemented Carbide with Minimal Amount of Binder Metal", is 
for making a little or no binder cemented carbide material without using 
high pressure processes such as hot isostatic pressing (HIP), hot 
pressing, or rapid omnidirectional compaction (ROC). Cemented carbide is a 
relatively tough and hard composite material which contains metal which is 
tough, and carbide which is hard. This cemented carbide is an excellent 
material and is used for parts needing wear resistance and for tools. In 
cemented carbide compositions, the metal matrix phase is relatively more 
vulnerable to abrasive wear and corrosion. If the said cemented carbide 
part is exposed to abrasive particles or to a chemically corrosive 
environment, the relatively weak meatal phase is lost, leaving porosities. 
Later these porosities become the initial points for fracture. For the 
applications where parts are exposed to corrosive or abrasive environments 
and the said parts are exposed to moderate stress, non-or little binder 
cemented carbide would work better. Generally, cemented carbide without 
binder metal has lots of porosity. The purpose of this invention is to 
make a good quality cemented carbide with little or no binder, without 
high pressure treatment such as HIP, ROC or Hot Pressing. The cemented 
carbide composite of this invention is made from less than 2 percent by 
weight metal powder; the balance is cemented carbide powders. During the 
sintering process, especially a vacuum sintering process, a portion of 
metal binder is lost by evaporation. In the final sintered product, little 
binder metal is left. Depending on the carbon contents, this residual 
metal could form inter-metallic composites along with carbon and metal 
from the carbide. Because of the brittle nature of the inter-metallic 
composite, generally, it is better to avoid this structure by appropriate 
carbon amount and composition of the said cemented carbide. Here the metal 
powder includes cobalt, nickel, iron, molybdenum, chromium powder, and 
alloy powders containing the above metals, and mixtures of one or more 
said metals and alloy powders of the said metal. The metal carbide part of 
this cemented carbide consists of single metal carbides, and solid 
solution carbides of two or more metal carbides, the said metal carbides 
include carbides of transition metals. Although cobalt, nickel, iron, or 
their alloys are generally used as a binder meatal, other metals and 
alloys also can be used. This said cemented carbide could contain less 
than 1 percent by weight impurities or other elements could be contained 
in the said cemented carbide for enhancing mechanical, chemical or 
physical properties. 
The invention, "Non-magnetic Cemented Carbide" is for making non-magnetic 
cemented carbide body by adding carbide forming metals other than 
titanium. For certain applications of the cemented carbide, a titanium 
containing part may not be acceptable. The manufacturers would have more 
freedom to make non-magnetic cemented carbide if they could use a variety 
of carbide forming metals, not only titanium metal. The manufacturers 
would also have a greater freedom in not only the manufacturing process, 
but also in tailoring better micro-structures of the said cemented 
carbides for certain applications. 
BACKGROUND OF THE INVENTION 
The invention, "Cemented Carbide with Minimal Amount of Binder Metal" 
involves cemented carbide bodies containing little or no metal binder. For 
certain applications, it is desirable for cemented carbide wear resistant 
parts and tools to have little binder metal. The earlier U.S. Pat. No. 
4,945,073 is for binderless carbide made via a reaction sintering process 
using tungsten metal and carbon from a polymer, and U.S. Pat. No. 
4,923,512 is for a binderless carbide made via a ROC (Rapid 
Omnidirectional Compaction) Process. This invention is for a product and 
for a process to make high quality cemented carbide bodies with low or no 
binder metal, without using high pressure. 
Concerning non-magnetic cemented carbide, cemented carbide with nickel 
binder can be converted to non-magnetic cemented carbide by adjusting the 
carbon amount: U.S. Pat. No. 3,918,138 is for adjusting the carbon in 
nickel base cemented carbide by adding titanium metal during the powder 
milling process. This invention is for adding carbide forming metal other 
than titanium metal, as well as metal carbides to make high quality 
products as well as necessary micro-structures.

DETAILED DESCRIPTION OF INVENTION 
The microstructure of this said cemented carbide composite with minimal 
amount of binder metal shows very little binder metal between carbide 
particles. Although vacuum, hydrogen or pressurized furnace sintering can 
be used as a sintering process, vacuum sintering is the preferred method. 
Here, "hydrogen furnace" means a furnace used for sintering in either a 
hydrogen or an inert atmosphere of about one atmospheric pressure, and 
"vacuum furnace" means a furnace used for sintering at below one 
atmospheric pressure of hydrogen or inert gas. During the sintering 
process, some metal binder is lost by evaporation. The evaporation is 
heavier during a vacuum sintering process than during an atmospheric 
pressure sintering process. In this invention, "Cemented Carbide with 
Minimal Amount of Binder Metal", a small amount of metal is used to help 
the sintering, and in order to leave less metal in the sintered part, 
vacuum sintering is the preferred method. The manufacturing method of this 
invention is well known in the art of powder metallurgy. Raw materials, 
metal carbide powders and metal powders, are milled using an attrition 
mill, a ball mill or other conventional method; and then, typically, a 1 
to 3 percent by weight organic binder is mixed with the milled powder. 
Then the powder mixture is introduced into a mold cavity and pressurized 
to make a so called "green part". Wax is introduced in the powder, either 
before the milling process or after milling and drying. Wax acts as a 
lubricant in the molding process and helps maintain the molded shape 
before sintering. Generally the powder containing the organic binder is 
pelletized before the molding process to help the following molding 
process, in which powder is generally gravity fed to the mold. Spray 
drying or other methods are used as this pelletizing process. This milled 
and waxed powder is called "grade powder". There are various methods to 
make green parts such as cold dye pressing, extrusion or slip casting, 
etc. Sometimes, the parts are formed first, and then machined before 
sintering. Sometimes parts are pre-sintered at a lower temperature and 
machined to the appropriate shape, and then the part is fully sintered. 
Generally sintering is conducted between 1350 degree C. and 1600 degree C. 
for conventional higher binder cemented carbide which contains between 
about 4 weight percent and about 25 weight percent binder metal. This said 
cemented carbide composite with a minimal amount of binder metal needs 
higher temperature sintering compared with said conventional cemented 
carbide to enhance the sintering process. The sintering temperature of 
said cemented carbide composite with minimal amount of binder metal is at 
least about 1400 degree C. A temperature of from about 1650 degree C. to 
about 1750 degree C. is a preferred temperature. While the lower 
temperature limit is, generally, a limiting factor, the upper temperature 
limit is not so critical. Higher temperature helps reducing defects like 
voids or porosity. This said cemented carbide composite with minimal 
amount of binder metal also needs more intense milling compared with said 
conventional cemented carbide to enhance the sintering process, although 
it is difficult to define a definite milling time because milling time is 
dependent on mill, charge size, milling speed, etc. The metal carbide raw 
materials of this invention, can be mixtures of single metal carbide 
powders or solid solution carbides of more than one metal carbide. For 
this invention, cobalt, nickel, iron, or other metals, as well as their 
alloys and their mixture can be used as raw materials for metal binder. 
Detailed descriptions of nickel-tungsten binder carbide is as follows: 
Nickel metal powder, and metal carbide powders including tungsten carbide, 
and also more than 7 atomic percent of carbide forming metal powder are 
used as raw material for the said nickel-tungsten binder non-magnetic 
cemented carbide. The raw materials are milled and waxed and sintered. 
Non-magnetic cemented carbide can be made by forming a tungsten-nickel 
alloy binder while the sintering process. Here, added metal powder 
includes tungsten, tantalum, molybdenum, chromium, vanadium, niobium, 
zirconium, hafnium and alloys of said carbide forming metals including 
titanium. Also alloy powders of nickel with one or more said carbide 
forming metals can be included as raw material. Here, metal carbide 
includes tungsten carbide, titanium carbide, tantalum carbide, zirconium 
carbide, hafnium carbide, niobium carbide and vanadium carbide chromium 
carbide, and also solid solution carbides of said metal carbide. If exact 
the amount of carbon is measured for each element of raw material, the 
exact metal amount can be calculated to make non-magnetic cemented 
carbide. In reality, the necessary amount should be determined by 
experiment because the nickel base binder forms complicated alloys 
including small amounts of all the constituent materials. Also sintering 
conditions such as using a hydrogen atmosphere or vacuum, and sintering 
furnace will effect the final carbon amount. The added metals' carbon 
affinity--how it is a stronger carbide former--also affects the 
non-magnetic character of final product. Therefore the appropriate amount 
has to be determined by experiment. Chromium or molybdenum metals or their 
carbides also can be added to the non-magnetic cemented carbide. The 
manufacturing method of this said non-magnetic cemented carbide is also 
the said art of powder metallurgy. Preferably, the nickel-tungsten alloy 
binder non-magnetic cemented carbides contain tungsten carbide as majority 
constituent carbide and enough other metal carbides to form said solid 
solution carbide to help reduce porosity via said solid solution forming 
process. 
EXAMPLE 1 
By weight, 92.5% WC, 7% MoC and 0.5% Co powder were milled for 8 hours 
using an attritor mill and a 1.5% paraffin wax was added, then the powder 
was pressed in a die to form a piece and sintered at 1700 degree C. for 
one hour. The sintered piece showed good quality and high hardness; a 
porosity level of A02B00C00 on the ASTM (American Standard for Testing and 
Material) standard B276, and a hardness of 95.2 on the Rockwell A scale. 
EXAMPLE 2 
By weight, 90% WC, 6% MoC, 1% TaC, 0.5% TiC, 1.5% Cr.sub.3 C.sub.2, 1% Co 
powder was processed the same way as in EXAMPLE 1. The sintered piece 
showed high quality and high hardness as EXAMPLE 1: a porosity level of 
A02B02C00 on the ASTM standard B276, and a hardness of 94.9 on Rockwell A 
scale. 
EXAMPLE 3 
By weight, 91.1% WC, 7.5% MoC, 1% Cr.sub.3 C.sub.2, 0.4% Co powder was 
processed the same way as in EXAMPLE 1. The sintered piece showed good 
quality and result: a porosity level of A02B02C00 on the ASTM standard 
B276, and a hardness of 95.3 on the Rockwell A scale. 
EXAMPLE 4 
By weight, 96.4% WC, 1% TaC, 0.8% TiC, 1.2% Cr.sub.3 C.sub.2 and 0.6% Co 
powder were processed in the same way as in EXAMPLE 1, and same good 
results were obtained: a porosity level of A02B02C00 on the ASTM standard 
B276, and a hardness of 95.2 on the Rockwell A scale. 
EXAMPLE 5 
By weight, 91.8% WC, 8% MoC and 0.2% Co powder were processed the same as 
EXAMPLE 1, and the same good results were obtained: porosity A02B02C00 on 
the ASTM B276, and a hardness of 95.0 on the Rockwell A scale. 
EXAMPLE 6 
By weight, 96.4% WC, 1% TaC, 0.8% TiC, 1.2% Cr.sub.3 C.sub.2 0.6% Ni were 
processed the same as EXAMPLE 1, and the specimen had a porosity of 
A04B02C00 on the ASTM B276, and a hardness of 94.9 on the Rockwell A 
scale. 
EXAMPLE 7 
By weight, 92.5% WC, 7% MoC, 0.3% Co and 0.2% Fe powder were processed the 
same as in EXAMPLE 1, and the specimen had an A02B02C00 porosity on the 
ASTM B276, and a hardness of 95.0 on the Rockwell A scale. 
EXAMPLE 8 
By weight, 86.78% tungsten carbide, 2% tantalum carbide, 1% titanium 
carbide, 0.1% chromium carbide, 0.12% tantalum metal, 10% nickel metal 
powder were processed the same as EXAMPLE 1. The specimen was nonmagnetic 
and showed a porosity level of A02B02C00 on the ASTM B276 Standard. 
EXAMPLE 9 
By weight, 89.88% tungsten carbide, 10% nickel, 0.12% tungsten metal powder 
were processed the same as EXAMPLE 1. The specimen was non magnetic and 
had the same good quality as EXAMPLE 8.