US 3450511 A
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United States Patent D 5456 Int. Cl. 'C22c 29/00, 39/28; B22f 7/04 US. Cl. 29-1823 1 Claim ABSTRACT OF THE DISCLOSURE Sintered carbide hard alloys are known in which titanium carbide is embedded in a matrix consisting of an austenitic steel or a steel hardenable by phase transformation and/or by precipitation, the alloy being machinable when the steel matrix is an austenitic steel or is in a relatively soft state. Such carbide hard alloys however suffer from the defect that they often have insufficient abrasionresistance in service, and particularly that if they are sintered in a very high vacuum they generate a porous surface layer, and it is difiicult to sinter workpieces right through to the core.
It has now been discovered that these disadvantages are obviated if the said steel matrix is alloyed with from 1.2% to 15% of manganese.
This invention relates to a sintered carbide hard alloy containing 25 to 75% titanium carbide and 25 to 75 of a steel which is an austenitic steel, or a steel hardenable by phase transformation and/or by precipitation of inter-metallic phases.
Carbide hard alloys produced by powder metallurgy methods have previously been proposed which contain up to 75 carbide finely distributed in a steel matrix as a binder. Such carbide hard alloys differ from conventional hard metals in which the binder consisting of iron, cobalt or nickel, is hardenable. This composition allows the sintered semi-finished products to be machined to their final dimensions before they are hardened, and subsequent hardening being effected by a suitable heat treatment. The advantage of good machinability of the semifinished product can thus be combined with considerable hardness, which may be as high as 75 RC. Since an alloy containing between 25 and 75 carbide cannot be produced by fusion metallurgical methods, the carbide hard alloy is produced by well known powder metallurgy methods.
Carbide hard alloys usually contain titanium carbide as the carbide component, of which a certain proportion may be replaced by another carbide. The binders principally used are austenitic steels or steels which are transformation and/or precipitation hardenable. The austenitic and possibly also martensitic steels combine the advantage of hardenability with the useful properties of being corrosionand high temperature-resistant. Consequently carbide hard alloys containing this type of steel matrix can be used with advantage for components that are required to possess a satisfactory degree of corrosion resistance together with wear resistance and high temperature stability.
In the production of conventional carbide hard alloys difficulties have been found to arise when the alloys are sintered in a vacuum lower than 10* torr, due to the creation of porous surface layers due to vaporisation. The sinter bodies also tend to be carburised by hydrocarbons and carbon monoxide contained in the furnace atmosphere. Since the generation of a high vacuum exceeding 10- torr increases the cost of production, numerous at- 3,450,51 l Patented June 17, 1969 tempts have been made to achieve satisfactory results using a lower vacuum. Thus it has been proposed to avoid vaporisation in the surface zones and the consequental surface porosity, by binding the titanium carbide with chromium carbide to form a substantially saturated mixed carbide. Although this procedure allows carbide hard alloys to be sintered in a lower vacuum, for instance in an ordinary technical vacuum, and the formation of porous surface zones due to vaporisation to be suppressed, for unexplained reasons pressings exceeding about 60 mm. in diameter are found not to sinter through to their cores.
Conventional sintered steel-bound carbide hard alloys are used principally as materials for making hotand cold-working tools, which are exposed to a high degree of wear during service. Hardness however is not the only property required of a material that is to be used for making wear-resistant components. The decision property of a wear-resistant material is its resistance to abrasion.
Carbide hard alloys hitherto known possess insuflicient resistance to abrasion by foreign pulverulent or granular substances, such as metal powders, porcelain compositrons, cement, sand and the like, and the invention provides carbide hard alloys which possess a satisfactory reslstance to abrasive wear by pulverulent or granular substances.
It has now been found according to the invention that for a sintered carbide hard alloy of the type comprising 25 to titanium carbide and 25 to 75% of a steel that is an austenitic steel or a steel that is hardenable by phase transformation and/or precipitation of intermetallic phases, the aforesaid properties are provided if the said steel contains together with other alloying elements, from 1.2 to 15% of manganese.
Although carbide hard alloys of the said type are known which together with titanium carbide in the specified proportions also contain an austenitic steel matrix or a transformation and/ or precipitation hardenable steel, and which also contain in addition to the said steels, manganese in the stated proportions, it is surprising that when alloyed with manganese provides a steel matrix which inhibits the abrasive wear thereof by pulverulent or granular foreign substances experienced for instance by pressing dies for all types of powdered or granular metallic or ceramic products, mixer blades, dressing rollers for grinding wheels, sand blasting nozzles, grinding balls and like components. For example, a carbide hard alloy based on a steel matrix containing no manganese and possessing a hardness of about 70 \RC has a life when used for profiling grinding wheels, which despite the relative hardness of the alloy, does not exceed that of a steel containing 1.9% manganese and having a hardness of about 63 RC. A carbide hard alloy containing the manganese alloyed in its steel matrix has a comparative life which is five times longer.
Furthermore, carbide hard alloys according to the invention possess two other major advantages which are unexpected and could not have been perdicted. Firstly sintering of carbide hard alloys according to the invention can proceed in a vacuum as low as 5.10- torr without the formation of porous surface layers on the sinter bodies due to vaporisation. Secondly pressings having a diameter exceeding 60 mm. can be sintered through to the core.
The increase in wear resistance of components of a carbide hard alloy according to the invention in conjunction with the said two advantages result in the carbide hard alloys being greatly superior to that of conventional carbide hard alloys.
The following examples of the invention are provided.
Example 1 A carbide hard alloy was prepared containing 33% of titanium carbide and 67% of a steel consisting of:
The said steel provides a matrix for the carbide hard alloy which is hardenable by transformation and by the precipitation of inter-metallic phases (nickel martensite). The matrix has a hardness in the solution-treated state of between 45 and 49 RC and after hardening for 6 to 8 hours at 480 C., has a hardness between 64 and 66 RC.
Example 2 A carbide hard alloy was prepared containing 33 of titanium carbide and 67% of a steel containing:
Percent Carbon 0.90 Vanadium 0.12 Manganese 1.9 Iron Remainder The said steel provides a purely martensitic matrix which, having been hardened by quenching in oil from 810 C. and tempered at 150 to 350 C. according to the toughness required, possesses a hardness between 65 and 71 RC, according to temper.
Example 3 A carbide hard alloy was prepared containing 33% of titanium carbide and 67% of a steel containing:
Percent Carbon 1.2 Molybdenum 1.5 Manganese 6.0 Iron Remainder The said steel provides a martensitic, i.e. transformation-hardenable steel, matrix which still possesses a re sidual austenite content. This alloy achieves its optimum hardness after having been quenched in oil from 1040 C. Despite its residual content of austenite the alloy attains a hardness of between 70 and 72 RC.
Example 4 A carbide hard alloy was prepared, containing 30% of titanium carbide and 70% of a steel consisting of:
Percent Nickel 3 8 Chromium 1 3 4 Molybdenum 5.75 Titanium 2.75 Aluminium 1.60 Niobium 0.70 Boron 0.01 Manganese 1.95 Iron Remainder The said steel provides a steel matrix which is hardenable by the precipitation of inter-metallic phases. Its hardness when quenched from in the 'austenitic state was found to be 3 5 to 38 RC, and tempering for 16 hours at 790 C. and holding for 16 hours at 650 C., a hardness between 54 and 56 RC was obtained.
Example 5 A carbide hard steel was prepared containing 30% of titanium carbide and of a steel containing 1.25% carbon, 12.5% manganese, remainder iron.
The said steel provides a pure austenitic steel matrix due to its high manganese content, particularly after having been quenched. It is not therefore magnetic. Thi socalled maganese austenite has substantially better properties with respect to Wear resistance than the nickel austenite according to Example 4 and that possessed by stainless steels. The hardness of this alloy was measured and found to be 45 to 48 RC.
Carbide hard alloys according to the invention may be produced by conventional powder metallurgical methods. Thus the individual components may be ground to a grain size of about 2 to 5 microns, and the powder compacted to shapes and sintered. After having been sintered the components are machined to their final dimensions and then hardened by submitting them to a known suitable heat treatment to provide the desired properties.
What is claimed is:
1. In a sintered carbide hard alloy possessing a high wear-resistance to abrasion and erosion of the type comprising 25 to titanium carbide and 25 to 75% of a steel from the group consisting of austenitic, transformation hardenable, precipitation hardenable, and mixtures thereof, wherein the improvement consists in that the steel is alloyed with from 1.2 to 15% of manganese.
References Cited UNITED STATES PATENTS 2,828,202 3/1958 Goetzel 75123 3,053,706 9/1962 Gregory 14831 3,183,127 5/1965 Gregory 148-3l 3,369,891 2/1968 Tarkan 148-31 3,380,861 4/1968 Frehn 14831 CARL D. QUARFORTH, Primary Examiner. ARTHUR J. STEINER, Assistant Examiner.
US. or. X.R.