MXPA99012104A - Method for manufacturing high carbon sintered powder metal steel parts of high density - Google Patents

Abstract

A manufacturing method is provided for the production of high density, high carbon, sintered powder metal steels. The composition consists of iron based powder, graphite, lubricant, and possibly at least one alloying element from the group of chromium, copper, manganese, molybdenum, nickel, niobium or vanadium. The composition is compacted in rigid tools, sintered and, during cooling, an isothermal or slow cooling treatment is introduced between 650°C and 750°C. The isothermal or slow cooling treatment may alternatively be applied during a heat treatment cycle that is carried out after a conventional sintering cycle. The material processed as described may then be formed to high density. Forming to high density is not practical with high carbon materials that have been processed by conventional methods. The high density article is then heat treated in a manner to suit specific product requirements. The mechanical properties achieved by the claimed process offer significant benefits when compared to conventionally processed sintered powder metal articles.

Description

METHOD FOR MANUFACTURING HIGH DENSITY STEEL PARTS METALE, IN CARBON CONCENTRATION SINTERED POWDER DESCRIPTION OF THE INVENTION The invention relates to manufacturing methods that allow the formation of steel compact powders of sintered steel with high concentration of carbon at high density at room temperature. The invention is related to specific thermal treatments that must be applied before the training operation. The invention is further related to specific compositions of iron-based powder mixtures that can be used in the manufacture of a high density article. In the previously named patent applications, US Patent Application 08 / 644,978 filed on 05/15/96 and PCT Application PCT / CA / 96/00879 filed on 12/24/96, the methods have been described for manufacturing of high density powder metal articles that can contain up to 0.5% carbon by weight. In some applications, a higher carbon content is desirable, along with a high density in order to achieve the specific mechanical property requirements. Because the addition of carbon to iron increases its hardness and reduces its ductility, the formation of high density materials with high carbon concentration is usually not practical. However, in this invention a method has been determined in which the combined selection of material composition and thermal processing methods can produce materials with high carbon concentration in a formable nature. The materials with high carbon concentration processed in the manner prescribed to be described herein are of significantly lower hardness than would ordinarily be expected, and offer advantageous forming characteristics that can be used to produce high density powder metal articles. . Formation as defined herein includes: (a) dimensioning - which can be defined as a final pressing of a sintered compact to ensure a desired size or dimension; (b) coining - which can be defined as the pressing of a sintered compact to obtain - a definite surface configuration; (c) repressed - which can be defined as the application of pressure to a sintered compact and previously pressed, usually for the purpose of improving the physical or mechanical properties and the dimensional characteristics; d) Revised - additional compaction of a sintered compact.

In carbon-containing powdered metal steels that are processed in the normal manner, Figure 1 illustrates that as the carbon content rises, the density achieved in cold forming is significantly reduced. For example, Figure 1 shows that at a forming pressure of 60 tons per square inch, a sintered part with 0.2% carbon, a density of approximately 7.5 g / cc could be achieved. With 0.6% carbon, at the same forming pressure, a density of only 7.3 g / cc could be achieved. It is "an object of this invention to provide an improved method for producing powdered metal parts having improved formability at higher carbon contents." This invention details the methods of processing materials with high carbon concentration in a manner that minimizes the previous reduction in the formability that is usually experienced at higher carbon contents. The invention discloses methods for manufacturing powdered metal compacts with high carbon concentration which are suitable for forming the high density in the range of 7.4 _ to 1. 1 g / cc. The compositions of the final articles are distinguished by having steel with medium to high carbon concentration where the carbon content is between 0.4% to 0.8% by weight, and preferably approximately 0.6% depending on the requirements of the finished article. The forming operation is carried out at room temperature (although high temperatures can be used) which provides acceptable forming tool life and excellent precision characteristics. The process preferably uses low cost iron powders which are mixed with calculated amounts of graphite and lubricant, calculated amounts of iron alloys can also be added in such a way that the final desired chemical composition can be achieved. The powder mixture is suitable for compaction in rigid compaction dies wherein the powder mixture will be pressed to form a compact having a theoretical density of about 90%. The process is generally described in U.S. Patent 5,476,632. The sintering of the compositions of the iron alloys is carried out at high temperature, generally higher than 1250 ° C in such a way that the oxides contained within the compact are reduced. The benefits of the invention can also be achieved by using elemental, pre-alloyed or partially pre-alloyed mixtures of metal powders containing elements either individually or in combination of the chromium, copper, molybdenum, manganese or nickel group, either individually or in combination. Such materials can be sintered at conventional sintering temperatures of 1100 ° C to 1150 ° C or alternatively at higher sintering temperatures above 1150 ° C. To achieve cooling after reaching sintering temperatures, in order to generate the desired formation characteristics of the material "containing high concentrations of carbon, it is necessary to introduce an -interruption at the cooling rate." Figure 2 shows a diagram of a typical conventional sintering furnace temperature cycle, which consists of a heating segment, a sintering temperature check, and a cooling segment Figure 3 shows a diagram of a modified temperature profile which is a characteristic of The invention described herein In the modified cycle shown in Figure 3, there is an interruption or an isothermal stop during the cooling segment Another embodiment of the invention may include the use of a conventional sintering cycle, but then subjecting the sintered articles to a subsequent heat treatment process which includes an ac segment heating, a seal segment that is usually at a temperature lower than the sintering temperature, and a cooling segment that includes an isothermal seal segment, all of which are illustrated in Figure 4.

'Such isothermal treatments as described above are well documented in the forging steel processing industries. However, the application of these processes to the powdered metal articles in a manner to allow subsequent formation at a high density, have not been previously described. After the aforementioned modified thermal processing, the sintered powder metal article with high carbon concentration is suitable for forming an analogous density as described in the North American patent application 08 / 644,978. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram illustrating the effect of carbon on the density formed with test rings formed at 60 tsi. Figure 2 is a diagram of a conventional sintering furnace temperature cycle. Figure 3 is a diagram of a modified sintering furnace temperature cycle including-an interruption during cooling. Figure 4 is a diagram of a heat treatment temperature cycle including an interruption during cooling.

Figure 5 is a diagram of an alternative temperature cycle including slow cooling over a critical temperature range, Figure 6 is an idealized isothermal transformation diagram, Figure 7 shows the microstructure of the sintered part after conventional cooling. Figure 8 shows the microstructure which is related to the modified chilling treatment described here Figure 9 is an example of a specific thermal cycle used with an iron, 0.6% by "C weight, 0.5% by weight of molybdenum alloy. . Figure 10 is a graph showing the effect of forming pressure on a formed density, Fe, 0.6% by weight, C, 0.5% by weight of Mo alloy. Figure 11 is a graph showing a mechanical property comparison. Figure 12 is a cross-sectional view of the forming process. Figure 13 is a cross-sectional view of the forming process for a sintered ring. Described here is a method for manufacturing a metal article of sintered powder with high concentration of carbon, suitable for forming at high density. The invention involves steel compositions with medium to high carbon concentration which after the described thermal processing can be formed at a high density at room temperature. More particularly, the steel compositions with medium to high carbon concentration, used herein are between 0.4% and 0.8% by weight of carbon, and preferably between 0.6 and 0.7% by weight of the final article. The actual carbon content used depends on the desired mechanical properties of the final sintered article. In one embodiment, the remaining composition of the article can be essentially iron and unavoidable impurities. The manufacturing method described herein can also be applied to a wide range of alloy compositions as required. The common state of the invention for various compositions resides in the thermal processing that can be applied to the wide range of compositions in order to provide a material containing high carbon concentration (ie, 0.4% to 0.8% by weight) which is suitable for forming at high density by the process described in US Patent Applications 08 / 644,978 and PCT / CA96 / 00879. In addition to carbon, the presence of other alloying elements may be required, such as chromium, copper, manganese, molybdenum and nickel.These alloying elements may be present either individually or in combination in a form to achieve mechanical and mechanical requirements. Desired metallurgists of the final article One mode of the preferred method of adding chromium, manganese and molybdenum would be to add this as ferroalloys (ie, ferrochrome, ferromanganese and ferromolybdenum) to the powder as iron base as described in US Pat.476,632, which is incorporated herein by reference. Ferromanganese, ferrochrome and ferromolybdenum can be used individually with the iron-based powder, or in any combination, as may be required to achieve the desired functional requirements of the manufactured article. In other words, one, two or three separate ferroalloys can be used or three ferroalloys can be mixed with the iron-based powder. Examples of such iron-based powders include Hoeganaes Ancorsteel 1000 / 1000B / 1000C, Quebec Powder Metal sold under the trademarks of QMP Atomet 29 and Atomet IO'OI. The iron-based powder compositions consist of commercially available substantially pure iron powder which preferably contains less than 1% by weight of unavoidable impurities. Additions of alloying elements are made to achieve the desired properties of the final article. "Examples of alloy element composition ranges that can be used typically include at least one of the following: 0.4 to 0.8% carbon, 0 to 1.5% manganese, 0 to 1.5% chromium and 0 to 1.5%" of molybdenum where% refers to the percentage by weight of the alloying element (apart from carbon) to the total weight of the sintered product. and the total weight of the alloying elements is between 0 to 2.5%. The reference to 0% refers to the situation where there is 0% of elements Mn, Cr, Mo of alloy, but between 0.4 to 0.8% of carbon-. The alloy elements Mn, Cr and Mo are added as ferroalloys, mainly FeMn, FeCr, FeMo. The particle size of iron powder will have a distribution generally in the range of 10 to 350 μm. The particle size of the alloy additions will generally be within the range of 2 to 20 μm. To facilitate the compaction of the powder, a lubricant is added to the powder mixture.These lubricants are regularly used in the powder metal industry.The typical lubricants employed are regular commercially available grades of the type including zinc stearate, stearic acid. or ethylenebystearamide The nickel and molybdenum content can be achieved using pre-alloyed grades of powder.The pre-alloyed powder metal with molybdenum having molybdenum compositions of 0.5% to 1.5% with the remainder being iron and unavoidable impurities. You can use: Powdered metal with pre-alloy molybdenum is available from Hoeganaes under the designation Ancorsteel 85HP (which has approximately 0.85% Mo per_weight) or Ancorsteel 150HP (which has approximately 1.50% Mo weight) or Quebec Powder Metal under the trademarks QMP at 4401 (which has approximately 0.85% by weight of Mo) The particle size of the molybdenum powder metal p re-alloyed is generally within the range of 45 μm to 250 μm typically. The same type of lubricant mentioned above can be used to facilitate compaction. An example of pre-alloyed molybdenum powder which is available on the market is sold under the name of QMP AT 4401 which may have the following physical and chemical properties. Apparent density 2. 92g / cm3 Flow 26 seconds / 50g Ana 1isis chemical C 0.003% 0 0.08% s 0.007% P 0.01% Mn 0.15% Mo 0.85% Ni 0.07% Si 0.003% Cr 0.05% Cu 0.02% Fe greater than 98% The copper and nickel content can be achieved by suitable additions of the elemental copper and nickel powders to the iron-based powder. Such elemental powders are commercially available and contain trace elements and unavoidable impurities. Alternatively, the content of copper, nickel and molybdenum can be achieved using partially pre-alloyed grades of powder, for example, grade of the type supplied by Hoeganaes, under the name of Distaloy. The formulated mixture of powders that contain either iron, pre-alloyed iron or partially pre-alloyed iron - together with carbon (which is usually added as graphite), ferroalloys if required and lubricant, will be compacted in the usual manner as described by pressing in rigid tools.The compaction pressures around 40 tons per square inch are normally used to produce a green compact with a density of approximately 90% of the theoretical density of forged steel The total theoretical density of forged steel is 7.86 g / cc.

The compacted article is then sintered either at conventional temperatures for pre-alloyed and partially pre-alloyed iron which are in the range of 1100 ° C to 1350 ° C. The sintering of the iron-based powder with ferroalloys is conducted at high sintering temperatures generally greater than 1250 ° C as described in US Pat. No. 5,476,632. During the sintering process, a reduction atmosphere will be maintained, or a vacuum to ensure the reduction of oxides within the compact during exposure to elevated temperature. During the cooling after reaching the sintering temperature, when the temperature reaches approximately 700 ° C, an isothermal retainer is introduced. The temperature, accurate of the isothermal seal depends on the carbon content and the alloy composition of the material being processed. Generally, the isothermal seal is in the range of 680 ° C to 700 ° C, although for some alloys, the isothermal seal may need within the temperature range of 650 ° C to 750 ° C. The isothermal seal duration will be within the range of 20 minutes to two hours, depending on the carbon content, the alloy composition and the component time that is being manufactured. In one embodiment, the isothermal seal technique is the preferred method for achieving the metallurgical condition required prior to the high density forming operation described in US Patent Applications 08 / 644,978 and PCT / CA96 / 00879. However, acceptable results can also be achieved by introducing a significantly slower cooling rate section during the generally faster cooling rate of either the maximum sintering temperature or the maximum heat temperature, such a thermal cycle being shown in Figure 5. The specific reason for the isothermal retainer is to produce a metallurgically desirable microstructure in the quex material that contains a high concentration of carbon such that the material is suitable for a subsequent high density forming operation. Figure 6 shows an ideal isothermal transformation diagram for steel. The exact shape of the diagram changes with each specific composition of steel. However, Figure 6 illustrates one of the characteristics of the diagram together with the effect of cooling speed and the isothermal retainer in the microstructure that will be produced in the finally cooled article. When cooling conventionally after reaching the sintering temperature or the heat treatment temperatures, the cooling rate is essentially linear as shown by the cooling path "1" in a Figure 6. With a material with high carbon concentration of say 0.6% by weight, the resulting microstructure will consist essentially of perlite, a small amount of other transformation phases may be present depending on the current carbon content, alloy content and precise cooling rate. Such a microstructure, as shown in Figure 7 is relatively hard. On the other hand, the microstructure shown in Figure 7 will not give a high density during a subsequent high density forming operation. In other words, a perlite structure as shown in Figure 7, although useful, is not sufficiently ductile or malleable. However, if the modified cooling method is used, as shown by path "2" in Figure 6, a surprisingly different microstructure is achieved from exactly the same material with high carbon concentration. The isothermal retainer temperature, and the duration of time are selected in such a way that during the cooling of the material, a residence time is achieved in the ferritic region of the isothermal transformation diagram. The result is that in the finally cooled article, a much larger proportion of ferrite, which is very soft, is present, which provides a microstructure in a material with high carbon concentration that is suitable with a subsequent high density forming operation. Therefore, by using the isothermal retainer technique described here one can control the transformation to maximize the ferrite content. Figure 8 shows the microstructure. resulting from the same material shown in Figure 7, but the modified cooling path was used during cooling after reaching the sintering temperature. Example - Molybdenum Carbon Material A 0.6% carbon, iron-based, 0.5% molybdenum alloy was prepared by mixing iron powder, ferromolybdenum lubricant and graphite. The mixture was compacted to form test rings with a compaction pressure of approximately 40 tons per square inch to give a green density of approximately 7.0 g / cc. The compacted rings were then heated to a sintering temperature at a heating rate of about 20 ° C per minute, the compact was maintained at the sintering temperature of 1280 ° C for 20 minutes. The compact was cooled after reaching the sintering temperature at 12 ° C per minute at 680 ° C where an isothermal retainer was introduced at 680 ° C for a period of 60 minutes. The cooling of 680 ° C continued until ambient at 12 ° C per minute. The thermal cycle is depicted in Figure 9. A nitrogen / hydrogen reduction atmosphere was maintained throughout the thermal cycle. "The rings were subjected to a high density forming operation as described in US Patent Application 08 / 644,978 and the PCT application PCT \ CA \ 96 \ 00879. The rings show a surprising increase in density that can not usually be achieved for such -material containing high carbon concentration (0.6% by weight). Figure 10 shows that after forming at pressures in the range of 50 to 80 tons per square inch, densities were achieved in the range of 7.4 g / cc to 7.6 g / cc. At 60 tons per square inch a density slightly higher than 7.5 g / cc was achieved. It should be noted "that, as shown in Figure 1, with the conventional thermal cycle, with an alloy of 0.6% carbon, a density of only 7.3 g / cc, it could be achieved after a formed at 60 tons per inch The mechanical properties of such material after high density forming are shown in Figure 11. In comparison, the mechanical properties of a conventionally processed powder metal material are shown.The improvements achieved by the claimed processes are clearly demonstrated The described process can be used with a wide range of alloying elements, which can be added to achieve specific product requirements, alloying elements of the chromium, copper, manganese, molybdenum, nickel, niobium and vanadium group can be "present either individually or in combination, together with the high carbon content (in the range of 0.4% C by weight to 0.8% C by weight). The process can be used to produce the number of products, including "backup clutch plates, sprockets," transmission gears and connecting rods. Heat Treatment Subsequent to the forming operation, in order to develop the full mechanical properties of the article, it may be necessary to submit the article to a heat treatment operation. The heat treatment operation is generally carried out within the temperature range of 800 ° C and 1300 ° C. The conditions can be varied within the aforementioned ranges to suit the desired functional requirements of the specific article. It is also "preferable to use a protective atmosphere during the heat treatment process.The atmosphere prevents oxidation of the article during exposure to the elevated temperature of the heat treatment process.The current atmosphere used may consist of mixtures of hydrogen / nitrogen mixtures. of nitrogen / exothermic gas, mixtures of nitrogen / endothermic gas, dissociated ammonium or a vacuum In the heat treatment stage it is generally preferable to maintain a neutral atmosphere in terms of carbon potential with respect to the carbon content of the article. For example, if the article requires high wear resistance, a carburizing atmosphere can be used during the heat treatment.The carburizing atmosphere can consist of methane or propane where the carbon atoms will migrate from the methane or propane to the surface layers of the In such an operation, carbon will be a introduced inside the superficial layers of the article. If the article is subsequently tempered, a product with a hardened cover can be introduced with wear-resistant beneficial properties. The heat treatment process specifically causes a metallurgical bond within the densified article. After forming, there is very little metallurgical bond between the compressed powder articles. Such a structure, while having high density, generally will not demonstrate good mechanical properties. At the elevated temperature of the heat treatment process, the cold worked structure will be recrystallized and the metallurgical bond will occur between the compressed particles. After completing the metallurgical bonding process, the article will demonstrate surprising mechanical properties which are unusual for articles sintered in PM. After heat treatment, the article is ready for use and will exhibit mechanical properties that are generally very similar to forged steel of the same chemical composition. Formed The forming process is described in its entirety in the US Patent Applications 08/644, 978 and PACT / CA96 / 00879, but this will be generally described here. Generally speaking, it will occur by sintering only small dimensional changes. The precise extent of the dimensional movement will depend on the sintering conditions used, such as temperature, time and atmosphere, and on the additions of specific alloys that are made.The sintered article will have approximately 90% of the theoretical density and will have a substantially The same as the final article, additional processes are allowed in terms of dimensions and should not be particularized in its entirety here.The sintered article is then subjected to the forming operation in which the dimensions are formed essentially in accordance with the requirements In other words, dimensional control is achieved in the movement of the sintered part during forming.

Furthermore, it is during the forming operation in which the high density is imparted to the article. The forming operation is very often called coined, dimensioned, repressed or reworked. In essence, all processes are carried out in a similar way. It is common to press a sintered article into a closed rigid die cavity. In the high density forming operation, the sintered article is pressed into a closed die cavity. The closed die cavity of the forming operation is shown in FIG. 12. The closed rigid cavity 10 is defined by the vertical die die separate walls 12 and 14, die or lower rod walls 16 and die or upper rod 18. The sintered part is represented by 20. During the forming operation the upper die or rod 18 imparts a compressive force on the sintered part 20. Alternatively, the compressive force can be imparted by a relative movement between the lower die wall or rod and the upper die wall. The closed die cavity is designed with a clearance 22 to allow movement of the ductile sintered material in a direction perpendicular to, or normal to, the compression force as shown by arrow A. During compression, the total compressed length or the height of the sintered article is reduced by the dimension S.

Conventional coining can allow the reduction or movement of the sintered material in an A direction by 1 to 3%. The invention described here allows the movement of the sintered material beyond 3% of the original height or length. It is possible as will be described here that the reduction S or percentage of closure of sintered material can reach as much as 30% reduction of dimension H. Particularly advantageous results are achieved by having a closure which represents a compressed length or height Ch, which is between 3% to 19%, less than the original uncompressed length. In other words, S represents the change in the total height h of the part, sintered compared to the height Ch compressed. On the other hand, the compression of the total length or the "height" collapses the microstructural pores in the sintered powder metal part and with this the sintered part is densified.Another example of the closed die cavity is shown in Figure 13, wherein the rigid die cavity 10 is once again defined by the rigid tools specifically the vertical walls 12 and 14 spaced apart from the die respectively, the die wall 16 or the lower rod and the wall 18 of the die or upper rod and the core 19. The core 19 moves in a coaxial sliding relationship within the "aligned holes formed in the upper die or rod" and the lower die or rod. In this case, the sintered part is represented by a ring 21 which has a hole 23 through it. Again, during the operation of forming the upper punch or rod 18 it imparts a compression force A on the sintered ring 21. Alternatively, the compression force may be imparted by the relative movement between the die wall or lower rod 16 and the upper die 18. The closed die cavity is once again designed with a clearance 22 to allow movement of the material sintered ductile in a direction perpendicular or normal to the compression force A. Once closed or compressed the sintered material will move inside the closed cavity from the position of the arrows Cv, Cn to Dv and Dn. In other words, the sintered material will move to fill the bypass 22. When compressed, the orifice 23 will have a smaller internal diameter after application of the compressive force. The compressed height of the sintered ring 21 can be reduced by approximately 3 to 19% of the uncompressed height. In the case shown in Figure 2, the height of the ring also represents the height that is in the axial direction of the ring. In other words, the sintered article is formed by axial compression allowing radial expansion to decrease the axial length of the sintered article by about 3 to 30% of the original axial length.

The tool clearance 22 depends on the geometry in Xa sintered part, and it is possible that one may have a different tool clearance 22 in the outer diameter of the part than in the tool clearance in the inner diameter. The invention described herein can be used to produce a variety of articles or part of sintered powder metal powder which have multiple levels. Examples of such are disclosed in US Patent Applications 08 / 644,978 and PACT / CA96 / 00879, and include transmission sleeves. A component with multiple levels is composed of the powder metal powders mentioned above. Although preferred embodiments of the process have been specifically described it should be understood that variations in the preferred embodiments can be achieved by the person skilled in the art without departing from the spirit of the invention as claimed herein.

Claims (30)

1. CLAIMS 1. A process for manufacturing a sintered powder metal article characterized in that it comprises mixing powders of a desired composition, with lubricant and iron-based powder, compacting the mixed powders to size, sintering the dimensioned article, then cooling the sintered article by an isothermal retainer or slow cooling, followed by the forming of the article at a density of between 7.4 to 7.7 g / cc.
2. 2. The process in accordance with the claim 1, characterized in that the article has a carbon content in the range of 0.4% to 0.8% by weight.
3. 3. The process in accordance with the claim 2, characterized in that the article comprises iron-based powder, with unavoidable impurities, which are mixed with one or more alloying elements selected from the group of chromium, copper, manganese, molybdenum and nickel.
4. 4. The process in accordance with the claim 3, characterized in that the article comprises iron-based powder, with unavoidable impurities, which are mixed with at least one elementary powder of the copper group, or nickel. The process according to claim 3, characterized in that the "mixed powders partially comprise partially pre-alloyed iron powders containing at least one alloy of the copper, molybdenum or nickel group 6. The process according to claim 24, 26, 4 or 5, characterized in that an isothermal treatment, or a slow cooling process, is applied during cooling after reaching the sintering temperature. The process according to claim 24, 26, 4 or 5, characterized in that the isothermal treatment, or a thermal cooling process, is applied during cooling in a heat treatment process which is carried out after sintering. 8. The process according to claim 6, characterized in that isothermal treatment or slow cooling occurs within the temperature range of 650 ° C to 750 ° C. 9. The process according to claim 6, characterized in that the isothermal treatment or the slow cooling occur during a period of time between 20 minutes and 120 minutes. The process according to claim 9, characterized in that the article formed is subjected to another heat treatment process to produce the desired mechanical properties of the manufactured article. 11. The process according to claim 9, characterized in that the article has a carbon content within the range of 0.6% to 0.7% by weight. 12. A process for manufacturing a sintered powder metal article characterized in that it comprises: heat treating a sintered powder metal article having a carbon content of 0.4% to 0.8% by weight of carbon, the heat treatment comprises (i) an isothermal retainer, or (ü) slow cooling of the article after sintering, within the temperature range of 650 ° C to 750 ° C for about 20 minutes to two hours, followed by the article forming at a density between 7.4 to 7.7 g / cc. 13. The process in accordance with the claim 12, characterized in that the formed is conducted at ambient temperatures. 14. The process in accordance with the claim 13, characterized in that the sintered powder metal article includes between 0 to 1.5% of Mn, 0 to 1.5% of Cr, 0 to 1. 5% of Mo where the total weight of the alloy element of Mn, Cr and Mo is between 0 to 2.5%, the remainder being iron and unavoidable impurities. 15. The process according to claim 13, characterized in that the sintered powder metal article includes Cu and Ni. The process according to claim 13, characterized in that the sintered powder metal article is produced by mixing powder with iron base, graphite, lubricant with one or more ferroalloy powders of the ferrochrome group, ferromanganese, ferromolybdenum, ferroniobium, or ferrovanadium and then compact and sinter the same at a temperature greater than 1250 ° C. 17. The process according to claim 13, characterized in that the sintered powder metal article is produced. mixing a metal of pre-alloy molybdenum powder having a molybdenum composition of between 0.5% to 1.5% by weight with the remainder being iron and inevitable impurities with graphite and lubricant and then compacting and sintering it at a temperature between 1100 ° C at 1350 ° C. 18. The process according to claim 13, characterized in that pre-alloyed grades of Ni, Cu and Mo powder are sintered having the following weight percentage: Ni - 0.0% to 4.0% Mo 0.5% at 1.5% Cu 0.0% to 3.0% 19. The process according to claim 13, characterized in that the sintered powder metal article is produced by mixing Cu and Ni elemental powder with iron-based powder and impurity. It is inevitable with graphite and lubricant and then compacting and sintering the same when the Cu and Ni have the same weight percentage: Cu 0.0% at 3.0% Ni 0.0% at 4.0% 20. The process according to claim 2, characterized in that The formed is conducted at room temperature. The process according to claim 3, characterized in that the mixed powders comprise an iron-based powder with unavoidable impurities, with one or more ferroalloyed powders selected from the group of ferrochrome, ferromanganese and ferromolybdenum. 22. The process according to claim 21, characterized in that the iron powder composition Xe comprises substantially pure iron powder with less than 1% by weight of unavoidable impurities. 23. The process according to claim 3, characterized in that the mixed powder comprises a pre-alloyed iron-based powder with one or more alloys selected from the nickel-and-molybdenum group. 24. The process in accordance with the claim 23, characterized in that the mixed powder comprises pre-alloyed molybdenum powder having a molybdenum composition of 0. 5% to 1.5% by weight with the remainder being iron and "unavoidable" impurities. A process for producing a sintered powder metal article characterized in that it comprises: (a) mixing powder of a selected composition; (b) compacting the mixed powder to size such article; "" (c) sintering the sized article; (d) treating the sintered article isothermally; (e) followed by the formation of the article at a density between 7.4 to 7.7 g / cc. 26. The process in accordance with the claim 25, characterized in that the article has a carbon content between 0.4 to 0.8% by weight. 27. The process according to claim 25, characterized in that the isothermal treatment comprises selecting the temperature and the duration of time during cooling to maximize the ferrite content of the article. 28. The process according to claim 27, characterized in that the isothermal treatment comprises: "" "(a)" an isothermal retainer, or (b) slow cooling treatment either as part of the sintered cooling step or a second thermal treatment step. 29. The process according to claim 20, characterized in that it includes an additional thermal treatment step after forming. 30. The process according to claim 29, characterized in that the forming step is conducted in a closed die cavity having a clearance for movement of the sintered powder metal to a final dimension wherein the sintered powder metal article. formed has a compressed length of 3 to 30% less than the original length.