WO2011029164A1

WO2011029164A1 - Nickel-based superalloy for valves of internal combustion engines

Info

Publication number: WO2011029164A1
Application number: PCT/BR2009/000293
Authority: WO
Inventors: Celso Antonio Barbosa; David Delagostini Jarreta; Alexandre Sokolowsky
Original assignee: Villares Metals S/A
Priority date: 2009-09-09
Filing date: 2009-09-09
Publication date: 2011-03-17

Abstract

Low-cost alloys that withstand the mechanical stresses associated with high temperatures, that withstand corrosion and abrasion, exhibit high mouldability and satisfy the various requirements in conditions of use in an exhaust or intake valve for internal combustion engines. The main features of the alloys are the Ni₃Nb and niobium carbides precipitated in the microstructure thereof, which is composed, in percentage by weight, of: 0.15-0,50% C, maximum 3.0% Mn, maximum 1.0% Si, 12.0-25.0% Cr, 25.0-49.0% Ni, maximum 0.50% Mo, maximum 0.50% W, maximum 0.50% V, 0.50-5.0% Cu, 1.85-3.0% Al, 1.0-4.5% Ti, 3.1-8.0% Nb, 0.001-0.02% B, 0.001-0.10% Zr, maximum 2.0% Co, where (Ni + Co) is not higher than 50% by weight and not lower than 25% by weight, the remainder being iron and inevitable impurities due to the alloy production process.

Description

"Superalloy Nickel Base for Internal Combustion Engine Valve"

The present invention deals with a precipitation hardened Ni-Fe-Cr superalloy for application to internal combustion engine valves, having as main characteristics the precipitation of Ni ₃ (AI, Ti, Nb) and niobium and titanium carbides in their microstructure. The alloy design, based on its microstructural aspects, allows the alloy of the present invention to have equivalent or superior properties to alloys used in internal combustion engine valves, associated with significant reduction in alloy cost due to lower nickel content. .

The alloy of the present invention is intended for the manufacture of valves, which application requires of the alloy a need for various properties, namely: oxidation resistance, wear resistance and heat resistance, given the high temperatures involved in the application.

Conventionally, the materials used for diesel or gasoline exhaust valves were JIS SUH 35 or JIS SUH 38 with Stellite overlay on the valve face. With the historic rise in valve use temperatures in new engines, higher performance materials have begun to be employed in some applications, such as nickel-based superalloys.

Today, reducing production costs for high-performance materials is an industry trend, such as exhaust valves, which are parts exposed to the highest temperatures and high mechanical stresses in an internal combustion engine. These extreme demands on mechanical strength and corrosion resistance at elevated temperatures require the use of nickel based superalloys, which are costly. Another factor to be evaluated is the abrasion resistance. Many alloys are coated with Stellite (cobalt-based alloy) on the valve face, which also raises the final cost of the valve. This has increased the demand for high-performance abrasion materials that eliminate the need for valve face covering.

An example of an alloy with excellent performance in these applications is Inconel 751, which has a very high cost due to its high nickel content above 70%. In this sense, lower nickel alloys with properties of hot strength, corrosion resistance, long term microstructural stability and abrasion resistance have been developed. Examples are prior art alloys, NCF3015 (JIS3015D - US Patent 5,660,938) and HI 461 alloy.

With the use of lead-free gasoline since the 1970s, the corrosion resistance requirement of the exhaust valve material has been reduced so that corrosion by lead oxide is no longer a primary concern. Oxidation resistance at elevated temperatures is the property to be evaluated in terms of corrosion, based on the good performance of Inconel 751.

Therefore, the need for the development of new superalloy compositions resistant to high temperature, corrosion resistant, abrasion resistant, high conformability, and meeting the varied demands in the conditions of use of the exhaust or intake valve, is evident. able to meet the need for lower cost, which is related to the lower content of high cost alloying elements. Inconel 751 alloy is the most important material to be replaced.

The alloys of the present invention meet all these needs.

The properties of Ni-Fe-Cr alloys used in exhaust valves are closely related to the presence of intermetallic phases, alloying elements and carbides in their microstructures. Intermetallic phases are very important for high temperature resistance. For solid solution elements in the alloy, a composition that gives the material the corrosion resistance required in the medium of use is very important. The presence of carbides is important for the abrasion resistance of the material. The performance of alloying elements in the formation of these phases has been carefully analyzed and modified in relation to the traditional concept. In this regard, the present invention utilizes the use of relatively high amounts of niobium (higher than prior art alloys) as an alloying element, not only as a carbide former, but mainly as a fine intermetallic precipitate.

Another element that the present invention utilizes in higher amounts than prior art alloys is aluminum, which has the preponderant niobium-forming function of the niobium, Ni ₃ (AI, Nb), improving the heat resistance of the alloy. material. In addition, aluminum acts to improve the hot oxidation resistance of the alloy.

It is extremely important that there is a slight distortion between the network parameters of the phases γ and γ ^' , which leads to a low interfacial energy (γ / γ ^' ). The main driving force of the coalescence of these intermetallic precipitates is the minimization of total interfacial energy, so that a coherent or semi-coherent low energy interface leads to a more stable microstructure. Stability is a highly desirable property in high temperature applications.

The morphology of these precipitates is determined by the surface energy of the γ / γ ^' interface and the elastic energy generated by the misalignment of the γ and γ ^' lattices, being determined primarily by the lattice deformation. If this strain is small, the morphology that will minimize surface energy and volume strain energy will be the spherical. However, if the lattice deformation is considerably large, the morphology of the precipitates will not be spherical but cubic. When the lattice mismatch is up to 0.02% the γ ^' precipitates are spherical, in the case of mismatch between 0.5 and 1.0% these precipitates are cubic, and above 1.25% assume platelet shape.

Niobium presents a lower precipitation kinetics of the ordered Ni ₃ Nb phase than when compared to elements such as titanium and aluminum in the Ni ₃ phases (Ti, AI). In Ni-Cr-Fe superalloys, high levels of niobium lead to precipitation of the ordered phase γ ^" (Ni ₃ Nb), similar to phase γ ^' . When added to the alloy at lower levels, niobium only increases the volume of precipitates gamma line and the solubilization temperature of this phase, bringing its hardening effect to even higher temperatures.

In order to satisfy the aforementioned conditions, the alloys of the present invention have alloy element compositions which, by weight percentage, consist of:

• 12.0 to 25.0 chrome, preferably 14.0 to 24.0 chrome, typically 18.0 chrome.

• 4.0 to 15.0 for the ratio (Nb + 2 Ti), preferably (Nb + 2Ti) between 5.0 and 11 1.0, typically (Nb + 2ΤΊ) equal to 8.0; In this equation titanium and niobium can assume any value within the limits, but a minimum niobium content of 3.10%, preferably greater than 3.70%, should be maintained.

• 0.05 to 1.0 carbon, preferably 0.20 to 0.40 carbon, typically 0.27% carbon.

0.1 to 4.0 aluminum, preferably 1.0 to 3.0 aluminum, typically 2.0% aluminum.

Iron balance and metallic or non-metallic impurities inevitable to the steelmaking process, wherein said non-metallic impurities include, but are not limited to, the following elements, by weight:

• Maximum 5.0 for the manganese, copper, molybdenum and tungsten elements, preferably maximum 5.0, typically maximum

0.50.

• Maximum 0.20 for phosphorus and sulfur, preferably maximum 0.05, typically maximum 0.005.

The following are the reasons for specifying the composition of the new material, describing the effect of each of the alloying elements. The percentages given refer to the percentage by mass.

Chromium is used to give the alloy resistance to corrosion and oxidation at high temperatures, so its content should be greater than 10% for exhaust valve superalloys. Content above 25% threatens the stability of the microstructure due to the tendency of formation of phases such as the sigma phase and alpha line (σ and α '), which deteriorate the ductility. Thus, it was decided that the chromium content of the alloys would be between these limits, preferably between 14.0% and 22.0%, typically 18.0%.

Titanium and niobium are carbide formers. When added to the alloy, they first combine with carbon, given the high chemical affinity of these elements. Formed carbides contribute to abrasive wear resistance. The titanium and niobium content not combined with carbon is combined with nickel to form the intermetallic phases γ 'and γ ". For these two effects, titanium and niobium contents should be added to the alloy of the present invention according to the relationship , Nb + 2 Ti, which accounts for the atomic mass difference of the two elements, so for the desired effect on wear resistance and heat resistance properties, the Nb + 2Ti ratio should be greater than 4.0% and preferably higher. at 5.0%, typically equal to 8.0%.

A key point in the definition of this alloy was the variation of titanium and niobium contents to define an ideal composition within the relationship in question. It has been observed that the introduction of niobium in amounts above 3.0% generates beneficial effects, both in relation to the formed carbides and the residual niobium content (not combined in the form of carbides). Hot league. The idea of introducing Nb in higher quantities is to generate precipitation of the intermetallic phase γ "(NÍ3Nb) and modification of phase γ 'by introducing higher niobium content into its structure. In addition, the high amount of niobium causes precipitation NbC carbides. These MC-type niobium carbides are more effective in abrasion resistance than titanium because of their higher hot hardness.The niobium content must be carefully balanced against the carbon content. Since niobium has a greater tendency to bond to carbon, the niobium available for nickel intermetallic phase formation will be the amount of this element dissolved in the alloy matrix after reaction with carbon to form the primary carbides. : C must be greater than 7.4: 1 (by mass) so that there is still dissolved Nb in the austenitic matrix which will precipitate as Ni ₃ Nb. a for the element Nb is between 2.0 and 8.0% (by mass), with an intermediate range of 3.0 to 8.0% (by mass) of Nb and a narrow range of 3.1 to 8.0. % (by mass) Nb, or even narrower from 3.5 to 8.0.

In addition to improvements in heat and abrasion resistance, Nb also improves weldability of the γ "phase precipitation hardened superalloys, and furthermore improves corrosion resistance in sulfating environments such as diesel engines.

Nb can be partially replaced by tantalum (Ta) in equiatomic bases. Like Nb, Ta is also an intermetallic phase former with nickel and strongly stabilizes primary carbides, being equally beneficial for hot hardness and abrasion resistance.

The increase in the amount of niobium showed effect on the heat resistance properties. Although the mechanism is not fully defined, in the alloys of the present invention the niobium content not combined with carbon should form different intermetals than titanium intermetallics, probably of the two-line gamma (γ ") type, very stable to coalescence and thus , effective in improving the properties of high temperature strength In relation to carbides, a larger volumetric fraction of larger carbides was noted with the increase of niobium content and the reduction of titanium content, resulting in higher wear resistance.

The addition of niobium causes, for the same ratio content (Nb + 2 Ti), to decrease the total titanium percentage of the alloy. Studies of the present invention have shown that such a decrease is also beneficial for improving oxidation resistance at elevated temperatures - a property also essential in high temperature working valves.

Decreasing the total titanium percentage in the alloy by the addition of niobium in amounts above 3.5% improves its hot workability, as the alloy's hot ductility is threatened to values above 4.0 for the sum between titanium and aluminum contents. (Ti + Al) <4.0%.

For all these effects of heat resistance, oxidation resistance and wear resistance, the ratio (Nb + 2 Ti) must therefore have a minimum content of 2.0% niobium, preferably niobium above 3.5%. being the ideal niobium content equal to or greater than 3.7%.

Despite the beneficial aspects of titanium and niobium, the content of these elements cannot be excessively high as it would promote the formation of coarse intermetals, impairing the mechanical properties. of the alloy in terms of mechanical strength and ductility, and raise the cost of the alloy. Thus, the ratio value (Nb + 2 Ti) should be below 15.0%, preferably below 13.0%.

Carbon is added with the intention of combining with titanium and niobium to form hard carbide particles and impart abrasion resistance. For such a function, the carbon content must be at least 0.05%, preferably above 0.1%. However, the percentage of hard particles must be below 5% by volume so as not to deteriorate the toughness and hot workability properties, the latter essential for hot forged valves. The volume of these particles is determined by carbon since, in the formation of NbC or TiC, the alloy has excess Ti and Nb. Thus, the carbon content is used as a controller of the particle volume formed, being below 1.0%, preferably below 0.40%.

Aluminum is very important for gamma phase (γ ') precipitation, and therefore for high temperature resistance. Another extremely important function of aluminum in the alloy is to increase oxidation resistance at high temperatures by increasing the formation of Al 2 O 3 during heating. However, aluminum contents should be restricted as very high amounts of this element may lead to deterioration of resistance at high temperatures and hot workability due to the formation of nitrides and phases such as η and δ during long heating times. The aluminum content, therefore, should be between 0.5% and 4.0%, preferably between 1.0% and 3.0%, typically 2.0%.

Residuals: Other elements, such as manganese, tungsten, molybdenum, copper, sulfur, phosphorus and those normally obtained as normal residues from the steelmaking process or liquid nickel alloys, should be understood as impurities related to the steelmaking deoxidation processes. or inherent in manufacturing processes. Therefore, the content of manganese, copper, tungsten and molybdenum at 5.0%, preferably below 2.0%, due to the destabilization of the relationship between the austenite and ferrite phases, as well as possible effects on the intermetallic phases present in the alloy. Phosphorus and sulfur segregate into grain boundaries and other interfaces and should therefore be below 0.20%, preferably below 0.05%, preferably maximum 0.005%.

The alloy as described may be produced by conventional or special processes such as melting in electric or vacuum furnaces, whether or not followed by remelting processes. Casting can be done in ingots by conventional casting or continuous casting, or even by other manufacturing processes involving liquid metal disaggregation and further aggregation, such as powder metallurgy and the spray forming or continuous casting process. The end products can be obtained after hot or cold forming, end products being produced in the form of wire rod, blocks, bars, wires, plates, strips, or even can be products in the raw state of solidification.

In the following description of experiments performed, reference is made to the attached figures, so that:

Figure 1 shows the microstructure, observed under optical microscope, of alloys ET1 and PH to PI9, after polishing and attack with glyceregia reagent for 15 seconds. 120x magnification.

Figure 2 presents the result of computational image analysis to quantify the carbides observed in the alloys studied with different Ti, Nb and Al contents. The analysis was performed in a total area of (65990,417) μιη ² of the sample, in 50 random fields with 500x magnification.

Figure 3 shows the results of the alloy creep test of the present invention compared to the ET1 and ET2 alloys, evaluating the creep failure time at 800 ° C temperature and three stress levels. Figure 4 compares the heat resistance of the alloys of the present invention to ET1 and ET2 alloys from the yield stress for various temperatures.

Figures 5 and 6 show the result of the abrasive wear test performed on alloys ET1, ET2 and alloys PM to PI7. The test was performed with the sanding of pins (pin against sandpaper), the pins were made in the alloys after heat treatment of aging and the sanding with abrasives of alumina and grain # 120. The average contact speed between the sandpaper and the pins was 100 m / min

EXAMPLE: To define the alloy compositions of the present invention, various alloys were produced and compared to those of the prior art. Chemical compositions are shown in Table 1, hereinafter referred to as PI the alloys of the present invention and ET the alloys of the prior art; ET1 alloy corresponds to H1 461, ET2 to Inconel 751, and ET3 alloy to NCF 3015 (US 5,660,938). Relationships are also quantified: (Nb + 2 Ti); (Nb / C) and (Ti / Al) in Table 1.

Table 1 shows the significant reduction of the nickel content of the alloy in the compositions of the present invention in relation to the ET2 alloy, generating significantly lower cost. ET2 and ET3 alloys also do not have significant carbon content, which does not promote carbide formation and the high wear resistance observed in other alloys.

Table 1 also shows the addition of different niobium contents in the alloys of the present invention, unlike the state of the art alloy (ET1), which has only titanium. Relationship analysis (Nb + 2 Ti) is also interesting because it normalizes the atomic mass difference and thus relates to the atomic content. This is approximately constant between those of the present invention (PM to PI6) and the ET1 alloy; thus Ti atoms in the alloys of the present invention are gradually replaced by niobium until in the alloy PI4 titanium is completely replaced by niobium. Despite being similar in chemical nature, titanium and niobium show different effects on the studied alloys, so the substitution employed was very beneficial to the final properties, as described below. In this sense, it is very interesting to quantify and differentiate the alloys under study through the content of non-combined carbide niobium. This quantification can be assessed by the ratio (Nb / C).

The differences between titanium and aluminum contents between the different alloys can be assessed by the ratio (Ti / Al), which is very important for the properties of hot oxidation resistance and conformability of the alloys. This ratio (Ti / Al) is also shown in Table 1.

Ingot melting was performed in a close procedure for the ten alloys (ET1, ET2, ET3, PM, PI2, PI3, PI4, PI5, PI6, PI7) in a vacuum induction furnace, and casting was done in iron ingot molds. cast, producing a 55kg ingot. After solidification, the ingots were forged and rolled into 18 mm diameter round gauges. After solubilization, the bars were observed under an optical microscope, the result being shown in Figure 1. In the images it can be observed the increase of the carbides size with the substitution of the titanium for the niobium, fact confirmed by the quantitative analysis of the images presented in the Figure 2. Table 1: Chemical compositions of three state of the art alloys (ET1, ET2 and ET3 ) and the alloys of the present invention (PI1 to PI7). Percentage by mass and balance in 1 iron.

I2 0.27 0.10 0.15 18.0 46.0 1, 20 2.00 3.85 7.85 14.1, 7 I3 0.27 0.10 0.15 18.0 46.0 1, 20 1.00 5.80 7.85 21, 5 0.8 I4 0.27 0.10 0, 15 18.0 46.0 1, 20 - 7.70 7.70 28.5 - I5 0 , 0.10 0.15 18.0 46.0 1, 90 2.00 3.95 7.95 14.6 1, 1 I6 0.25 0.10 0.15 15.2 32.1 1, 92 2.10 3.90 7.92 15.6 1, 1 I7 0.25 0.10 0.15 18.8 36.0 1, 30 1.71 3.38 6.80 13.5 1, 3

Table 2 presents the hardness of ET1, ET2, ET3, PM,

PI2, PI3, PI4, PI5, PI6 and PI7 after solubilization at 1050 ° C and aging at 750 ° C for 1 hour and also after solubilization at 1050 ° C and aging for 4 hours. These data show equivalent hardness values of the aged alloys, except for the ET3 alloy which has lower hardness. In the soiubilized state, niobium alloys have lower hardness, which is interesting for the machinability of the material in this condition.

Table 2: Response to heat treatment of state of the art alloys (ET1, ET2 and ET3) and alloys of the present invention (PM, PI2, PI3, PI4, PI5, PI6 and PI7). Hardness results in HB after solubilization at 1050 ° C and aging at

750 ° C or 1 hour and 4 hours.

Another important parameter for these alloys is the mechanical properties at high temperature; such results are shown in Figures 3 and 4. The alloys of the present invention are significantly more creep-resistant than ET alloy, being in alloys PI2, PI3, PI5 and PI6 equivalent or better than ET2 alloy (Inconel 751), although have considerably lower nickel content than this alloy. In high resistance temperature, as measured by the yield stress (Figure 4), the same behavior is observed, being alloys PI2, PI3, PI5 and mainly PI6 more resistant than alloy ET1 and ET2. The PI4 alloy, due to the higher concentration of coarse phases, has a reduction in hot strength and creep.

In terms of oxidation resistance, the alloys of the present invention were also superior to ET1 and ET2 alloys, as shown in Table 3; It is observed that the lower the titanium content, the higher the oxidation resistance of the alloy, the better the resistance observed for PI4 alloy without titanium. This is due to the effect of titanium on destabilizing the oxide layer formed on the surface of nickel-iron alloys and thus decreasing oxidation resistance. Another interesting effect to note is that among the low titanium alloys (PI2, PI3, PI4, PI5, PI6 and PI7), those with higher aluminum content (PI5, PI6 and PI7) have resistance to hot oxidation. higher under the test conditions. The assay was performed so that all samples of all alloys involved had identical dimensions, so as to have identical contact surface. They were cylindrical specimens (diameter = 12mm and height = 14mm) in aged and solubilized condition, which were properly weighed and kept at 800 ° C for 100 hours. After de-molding, the specimen is air-cooled and re-weighed by measuring the change in mass. This process is repeated until the total assay time is completed. Alumina ceramic crucibles were used as sample holders during the test. The progress of the oxidation process at 800 ° C was evaluated for 400 hours when stabilization of the corrosion process could be observed.

Table 3: Mass gain (in mg / cm ² ) after 100, 200 and 400 hours at 800 ° C in atmosphere (air). The lower the mass gain, the greater the resistance to oxidation of the material.

100 hours 200 hours 400 hours ET1 (Ti = 4.0%; Al = 1.2%) 0.40 0.66 0.66

ET2 (Inconel 751) 0.41 0.54 0.54

PIP (Ti = 3.0%; Nb = 1.9%; Al = 1.2%) 0.40 0.54 0.54

P 2 (Ti = 2.0%; Nb = 3.85%; Al = 1.2%) 0.14 0.27 0.27

PI3 (Ti = 1.0%; Nb = 5.8%; Al = 1.2%) 0.14 0.27 0.27

PIP4 (Nb = 7.7%; Al = 1.2%) 0.140, 14 0.14

PI5 (Ti = 2.0% Nb = 3.9%; Al = 1.9%) 0 0.25 0.25

PI6 (Ti = 2.0% Nb = 3.9%; Al = 1.9%) 0 0.25 0.25

PI7 (Ti = 1.7% Nb = 3.4%; Al = 1.3%) 0 0.25 0.25

The abrasive wear resistance, compared in Figures 5 and 6, and quantified in Table 4, follows the same trend of oxidation resistance, but for different reasons. ET1 and PI1 to PI9 alloys have significantly higher wear resistance than ET2 alloy due to the presence of hard particles in their microstructures (as shown in Figure 1). However, it is also observed that the higher the niobium content the lower the wear rate and therefore the higher abrasive wear resistance; This is due to the larger size of the carbides present in the microstructure of the highest niobium alloys, as shown in Figure 1 and quantified in Figure 2.

Table 4: Wear rate of the studied alloys, calculated from the division of the slope of the curves of Figure 5 by the specimen area (Rate = (1 / area) ^* õ AV I õ AL). The lower the wear rate, the greater the wear resistance of the material as the less the loss of material due to wear. Thus, the material that exhibits the highest value for the inverse wear ratio has the highest wear resistance. That is: 1 / Rate = Wear Resistance.

Wear Resistance

turns on

Absolute value Regarding ET1

ET1 (Ti = 4.0%) 9.6 100%

ET2 (Inconel 751) 6.8 71%

MW (Ti = 3.0%; Nb = 1.9%) 10.1 105%

PIP (Ti = 2.0%; Nb = 3.85%) 10.3 107%

PI3 (Ti = 1.0%; Nb = 5.8%) 10.7 1 1% PI4 (Nb = 7.7%) 11 1.0 115%

PI5 (Ti = 2.0%; Nb = 3.9%) 10.4 108%

PI6 (Ti = 2.0%; Nb = 3.9%) 10.2 106%

PI7 (Ti = 1.7%; Nb = 3.4%) 10.2 106%

The industrial application of these alloys involves an aging heat treatment step after final part forming. The alloys of the present invention find it easier to obtain the minimum hardness required in the application (about 330 HB - Brinell hardness scale), ie hardness above 330 HB is observed after only 20 minutes of treatment at 750 ° C. ° C, the hardness being always higher for the alloys of the present invention (PI5, PI6) than prior art alloys for the same treatment time, as can be seen in Figure 7. Alloys PI5 and PI6 also exhibit better response to aging heat treatment at 690 ° C than the state of the art ET3 alloy, obtaining hardness above the minimum value required for application after one hour of treatment. This can be seen in Figure 8. The reduction in aging treatment temperature and time is of vital importance for cost savings and productivity gains in material processing.

The properties of temperature resistance and resistance to hot oxidation can be evaluated, respectively, as a function of (Nb / C) and (Ti / Al) ratios. Figures 9 and 10 show this analysis for the alloys of the present invention (PI1 to PI7) and the state of the art (ET1 and ET2). In Figure 9, we can clearly see that the alloys of the present invention are in the optimum range of Nb / C ratio for optimizing the heat resistance property, represented by the creep breakdown time at 800 ° C under 100 Mpa stress. Figure 10 shows that the alloys of the present invention are in the optimal Ti / Al ratio range for optimizing the hot oxidation resistance property represented by the inverse mass gain (in mg / cm ² ) after 400 hours at 800 ° C in atmosphere (air).

Therefore, comparison of the state of the art alloys with the alloys of the present invention showed that the introduction of higher niobium and aluminum contents, accompanied by the reduction of titanium contents, promotes improvement in the properties of hot strength, creep, oxidation resistance and to wear. A summary of such effects is shown in Table 5. Alloys PI2, PI3, PI5, PI6 and PI7 are always superior to prior art alloys in terms of all observed properties. However, for situations where wear and oxidation resistance should be privileged, PI4 shows better results.

In summary, it can be stated that the results discussed herein show that the alloys of the present invention, in addition to the economic advantage of working with lower nickel content, also have better properties. In relation to prior art alloys, the alloys of the present invention have superior levels of high temperature properties and wear resistance, thus being important improvements for industrial application in combustion engine valves or even other components employed at high temperature and corrosive environments. Table 5: Comparison of Properties for all studied alloys, in absolute and relative values (with reference to alloy ET1 = 100%). The "-" sign indicates unmeasured values and "~" indicates approximate values.

Results

ET1 ET2 ET3 PM PI2 PI3 PI4 PI5 PI6 PI7

Hardness After

330 335 300

Aging (HB) t? 3? 330 316? 50. 340

Flow Tension at

538 484 525 550 552 520 431. .: 554 560; 500 800 ° C (MPa)

Break Time Under

Voltage at 800 ° C and 100 MPa 302 900 - 312 906 1188 301 906 1060 578 (hours)

Claims

1. Ni-Fe-Cr alloys for internal combustion engine valves, characterized in that they have a chemical composition of elements consisting of a percentage by mass of 0,15 to 0,50% C up to 3,0% Mn; up to 1.0% Si, from 12.0 to 25.0% Cr, from 25.0 to 49.0% Ni, up to 0.50% Mo, up to 0.50% W, up to 0.50% V, 0.50 to 5.0% Cu, 1.85 to 3.0% Al, 1.0 to 4.5% Ti, 3.1 to 8.0% Nb, 0.001 to 0.02 % B, from 0,001 to 0,10% Zr, up to 2,0% Co, where (Ni + Co) is not greater than 50,0% by mass nor less than 25% by mass. The rest being iron and unavoidable impurities in the alloy manufacturing process. The ratio of mass percentages Nb: C must be in the range 14: 1 to 54: 1. The ratio of mass percentages (Ti / Al) must be less than 2;

The alloy of claim 1, wherein the element Nb is partially replaced by Ta on equiatomic bases.

Ni-Fe-Cr alloys for internal combustion engine valves according to claims 1 and 2, where the value of M calculated by the equation below respects the range: 2.0 <M <15.0;

M = (Nb) + 2 (Ti) * (mass percentage)

Ni-Fe-Cr alloys for internal combustion engine valves according to claims 1, 2 and 3, where the value of M calculated by the equation below respects the range: 5.0 <M <1 1.0;

M = (Nb) + 2 (Ti) ^* (mass percentage)

Ni-Fe-Cr alloys for internal combustion engine valves, characterized in that they have a chemical composition of elements consisting of a percentage by mass of 0.15 to 0.50% C, 0.05 to 1.0% Mn, 0.05 to 1.0% Si , 14.0 to 20.0% Cr, 25.0 to 39.0% Ni, up to 0.50% Mo, up to 0.50% W, up to 0.50% V, 0.50 to 5.0% Cu, 1.00 to 3.0% Al, 1.85 to 2.15% Ti, 3.1 a 8.0% Nb, 0.001 to 0.02% B, 0.001 to 0, 1% Zr, up to 2.0% Co, where (Ni + Co) is not greater than 50.0 mass% or less than 25% mass. The rest being iron and inevitable impurities to the alloy manufacturing process. The ratio of Nb: C mass percentages must be in the range of 14: 1 to 54: 1. The ratio of mass percentages (Ti / Al) must be less than 2;

6. Ni-Fe-Cr alloys for internal combustion engine valves, characterized in that they have a chemical composition of elements consisting of a percentage by mass of 0,15 to 0,50% C up to 3,0% Mn; up to 1.0% Si, from 14.0 to 22.0% Cr, from 27.0 to 49.0% Ni, up to 0.50% Mo, up to 0.50% W, up to 0.50% V, 0.50 to 5.0% Cu, 1.5 to 3.0% Al, 1.0 to 3.5% Ti, 2.5 to 8.0% Nb, 0.001 to 0.02 % B, from 0,001 to 0,10% Zr, up to 2,0% Co, where (Ni + Co) is not greater than 50,0% by mass nor less than 25% by mass. The rest being iron and unavoidable impurities in the alloy manufacturing process. The ratio of mass percentages Nb: C must be in the range of 14: 1 to 40: 1. The ratio of mass percentages (Ti / Al) must be less than 2;

The alloy of claim 6, wherein the element Nb is partially replaced by Ta on equiatomic bases.

Ni-Fe-Cr alloys for internal combustion engine valves according to claims 5 and 6, wherein the value of M calculated by the equation below respects the range: 2.0 <M <15.0;

M = (Nb) + 2 (Ti) ^* (mass percentage)

Ni-Fe-Cr alloys for internal combustion engine valves according to claims 5, 6 and 7, where the value of M calculated by the equation below respects the range: 5.0 <M <1 1 .0 ;

M = (Nb) + 2 (Ti) ^* (mass percentage)

Ni-Fe-Cr alloys for internal combustion engine valves according to claims 1, 2, 3, 4, 5, 6, 7, 8 and 9, where residual impurities from the manufacturing process such as Ca and Mg do not exceed a total of 0.03% by mass;

Ni-Fe-Cr alloys for internal combustion engine valves according to claims 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10, where impurities are controlled to obtain a maximum of 0,02 mass% of P and a maximum of 0,0050 of S;

Ni-Fe-Cr alloys according to claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and 11, produced by air induction furnace, vacuum induction furnace or electric arc furnace, by conventional casting processes, continuous casting processes or processes involving alloy fragmentation and aggregation, including powder metallurgy, powder injection and spray forming, resulting in end products obtained by hot forming, cold, or products used directly under the "gross solidification" condition;

Ni-Fe-Cr alloys according to claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12, applied as exhaust valves or inlet motors of internal combustion;

Ni-Fe-Cr alloys according to claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 and 13, applied as static components, tools or structural parts or dynamic, in applications requiring high temperature resistance, creep resistance and abrasion resistance: