Composition of particulate materials for forming self-lubricating products in sintered steel, product in self-lubricating sintered steel and process for obtaining self-lubricating products in sintered steel

Abstract

The composition includes the iron as the main particulate metallic material; at least one particulate alloy element, with the function of hardening the ferrous structural matrix; and a precursor non-metallic particulate compound, generally a carbide or a carbonate, which is capable of generating, upon its dissociation during the sintering, graphite nodules, whose formation is facilitated: by the precursor compound itself when it includes a chemical element which stabilizes the iron alpha phase of the ferrous structural matrix; or by an additional alloy element included in the composition and which is defined by a chemical element that stabilizes the iron alpha phase during the sintering. The composition can be conformed by compaction or by powder injection molding. The process of the invention leads to obtaining products in self-lubricating sintered steel from said composition.

1 . A composition of particulate materials for forming self-lubricating products in sintered steel, conformed by compaction or powder injection, characterized in that it comprises: the iron as a main particulate metallic material; at least one particulate alloy element, with the function of hardening the iron, forming therewith a ferrous structural matrix; and a non-metallic compound, precursor of a solid lubricant phase of graphite to be formed in the composite product during the sintering. 
     
     
         2 . The composition, as set forth in  claim 1 , characterized in that the non-metallic particulate compound, precursor of the solid lubricant phase of graphite, is a compound of the carbide or carbonate type and which includes, in its composition, a chemical element which stabilizes the iron alpha phase of the ferrous structural matrix. 
     
     
         3 . The composition, as set forth in  claim 2 , characterized in that the chemical element which stabilizes the iron alpha phase is selected between silicon carbide, molybdenum carbide and chromium carbide. 
     
     
         4 . The composition, as set forth in  claim 1 , characterized in that it further includes an additional particulate alloy element, which stabilizes the iron alpha phase when the non-metallic particulate compound is a carbide or carbonate deprived, in its composition, of any chemical element which stabilizes the iron alpha-phase of the ferrous matrix. 
     
     
         5 . The composition, as set forth in  claim 4 , characterized in that the additional particulate alloy element, which stabilizes the iron alpha phase of the ferrous structural matrix, is at least one the elements selected from silicon, phosphorus, molybdenum and chrome. 
     
     
         6 . The composition, as set forth in  claim 2 , characterized in that the non-metallic particulate compound, precursor of the solid lubricant phase of graphite, represents, preferably, a volumetric percentage lower than about 10% of the mass of the particulate material metallurgical composition to be conformed. 
     
     
         7 . The composition, as set forth in  claim 1 , characterized in that the particulate alloy element, with the function of hardening the iron of the ferrous structural matrix is defined by at least one of the elements selected from nickel, chrome, molybdenum, vanadium, manganese, copper, silicon, phosphorus and carbon. 
     
     
         8 . The composition, as set forth in  claim 1 , said composition being conformed by powder compaction (pressing, rolling, double pressing or compaction) and characterized in that the particles of the main particulate metallic material (iron powder) presents an average size lying between about 5 μm and about 90 μm, the particles of the particulate alloy element with the function of hardening the iron, and the particles of the non-metallic particulate compound which is the precursor of the solid lubricant phase present a size smaller than about 45 μm. 
     
     
         9 . The composition, as set forth in  claim 8 , characterized in that the average particle size of the main particulate metallic material, that is, of the iron, is larger than the average particle size of the particulate alloy element and of the non-metallic particulate compound, precursor of the solid lubricant phase. 
     
     
         10 . The composition, as set forth in  claim 1 , the composition being conformed by extrusion or by injection molding and characterized in that the main particulate metallic material in iron, as well as the particulate alloy element and the non-metallic particulate compound present a particle size lying between about 5 μm and about 25 μm. 
     
     
         11 . The composition, as set forth in  claim 10 , characterized in that it comprises a system of organic binders selected from the group consisting of paraffin and other waxes, EVA, and low melting point polymers, in a proportion ranging from about 40% to about 45% of the total volume of the metallurgical composition. 
     
     
         12 . A product in self-lubricating sintered steel, obtained from a composition of particulate materials, as defined in  claim 1  and submitted to a conformation previous to the sintering, characterized in that it presents a hardness between 230 HV and 700 HV, a coefficient of friction μ≦0.15 and a traction resistance between 350 and 900 MPa. 
     
     
         13 . The product, as set forth in  claim 12 , characterized in that it defines at least one surface layer of said metallurgical composition incorporated to a structural substrate. 
     
     
         14 . The product, as set forth in  claim 13 , characterized in that the structural substrate is defined in a particulate material to be sintered jointly with the surface layer of the metallurgical composition. 
     
     
         15 . The product, as set forth in  claim 14 , characterized in that the structural substrate takes the form of plate of strip with at least one of its opposite faces incorporating a surface layer of said metallurgical composition. 
     
     
         16 . The product, as set forth in  claim 14 , characterized in that the structural substrate takes the form of the structural core of a composite bar, circumferentially and externally incorporating a surface layer of said metallurgical composition. 
     
     
         17 . A process for obtaining self-lubricating products in sintered steel, from the composition of particulate materials as defined in  claim 8 , characterized in that it comprises the steps of:
 mixing, in predetermined quantities, the particulate materials which define the metallurgical composition;   homogenizing the particulate material mixture;   compacting the particulate material mixture, so as to provide the mixture with the shape of the product to be sintered; sintering the compacted and conformed mixture, at temperatures from about 1125° C. to about 1250° C., forming, during the sintering, graphite nodules by the dissociation of the precursor compound in the volume of the structural matrix.   
     
     
         18 . The process, as set forth in  claim 17 , characterized in that the step of compacting the particulate material mixture, which defines the composition, comprises rolling the latter in a plate or strip to be subsequently sintered. 
     
     
         19 . The process, as set forth in  claim 17 , characterized in that the step of compacting the particulate material mixture, which defines the composition, comprises rolling the latter on at least one of the opposite faces of a structural substrate in the form of a plate or strip of particulate material compatible with the main particulate metallic material which forms the structural matrix. 
     
     
         20 . The process, as set forth in  claim 18 , characterized in that it comprises, after the sintering of the particulate materials, the additional step of cold rolling the plate or strip for reducing the residual porosity, followed by an eventual annealing. 
     
     
         21 . The process, as set forth in  claim 18 , characterized in that the step of compacting the particulate material mixture, which defines the composition, comprises the extrusion in one of the shapes defined by a bar and a tube. 
     
     
         22 . The process, as set forth in  claim 17 , characterized in that the step of compacting the particulate material mixture, which defines the composition, comprises the extrusion of the latter in the form of a tubular sleeve around a structural core in the form of a bar of particulate material compatible with the main particulate metallic material which forms the structural matrix, so as to form a composite bar. 
     
     
         23 . The process, as set forth in  claim 21 , characterized in that the composition comprises an organic binder to be thermally removed from the product, before the sintering step. 
     
     
         24 . A process for obtaining self-lubricating products in sintered steel, from the composition of particulate materials, as defined in  claim 10 , and characterized in that it comprises the steps of:
 mixing, in predetermined quantities, the particulate materials which define the metallurgical composition;   homogenizing the particulate material mixture, at a temperature not inferior to that of melting the organic binder;   granulating the composition to facilitate its handling, storage and supply into an injection machine;   injection molding the particulate material mixture, so as to provide the mixture with the shape of the product to be sintered;   extracting the organic binder from the molded piece; and   sintering the pieces obtained by conformation of the powders, at temperatures from about 1125° C. and about 1250° C.