BRPI0400488B1 - Alloy for producing objects with high heat resistance and high thermal stability. - Google Patents

Description

Report of the Invention Patent for "ALLOY FOR PRODUCTION OF HIGH HEAT RESISTANCE OBJECTS AND HIGH THERMAL STABILITY". The invention relates to an alloy for producing objects with high heat resistance and thermal stability.

In particular, the invention relates to a hot working steel object with high hardness, high heat resistance and high thermal stability.

In general, hot-working steels may be designated as heat-resistant iron base alloys, the highest mechanical properties of which are retained after heat treatment, particularly high heat resistance and hardness, up to temperatures of 500 ° C. and above.

In accordance with the increasing demands of technical development, there is a general requirement that hot working materials be further improved in quality, particularly increasing their heat resistance, high thermal stability and increasing their toughness. . Usual hot work steels are carbon-based alloys containing carbon with 0.3 to 0.4 wt% carbon (C), the hardness of which is increased according to the requirement with a quenching quench, by martensite formation in the structure and a tempering. Addition of alloying elements, generally by weight%: silicon (Si) to 1,5 chromium (Cr) 2,5 to 5,5 molybdenum (Mo_) to 3,0 vanadium (V) to 1,0 Iron base material and the use of specially configured heat treatment processes make it possible to produce an object having high values for desired mechanical properties, at a use temperature of up to approximately 500 ° C. By adding tungsten alloy (W) up to 9 wt% and cobalt (Co) up to 3.0 wt%, the usage temperature can be increased slightly.

Substantially, the hot hardness of these steels is produced by a precipitation mechanism, which is referred to as secondary hardness increase by the technician, and very finely chromo-molybdenum-tungsten carbides are formed in the martensite grid.

Another increase in strength of a material, different in essence from quench quenching, can be obtained by precipitation quenching. The assumption for a precipitation quench is a decreasing solubility with the temperature of an alloy additive or alloying elements in the base metal.

In a precipitation quench, an alloying material is first subjected to a solution annealing treatment, with subsequent intensified cooling, whereby an alloying additive or phase is wholly or partially brought into solution and maintained. in supersaturated solution. Subsequent heating to a temperature below the solution annealing temperature causes precipitation of the supersaturated fraction of the element (s) or phase (s), which produces a change in material properties. generally an increase in the hardness of the material.

Precipitation-hardened iron-based materials generally have alloy content by weight% of: carbon (C) to 0,05 manganese (Mn) to 2,0 chromium (Cr) to 16,0 molybdenum (Mo) to 6.0 nickel (Ni) to 26.0 vanadium (V) to 0.4 cobalt (Co) to 10.0 titanium (Ti) to 3.0 aluminum (Al) to 0.3 Iron base alloys with a martenite formation in a quenching quench, as well as those that undergo a change in their mechanical properties by precipitation of elements and phases, have in common the disadvantage that in their respective composition of alloying and / or heat treatment technology, respectively only individual properties such as, for example, hardness and strength or temperature stability, are improved, but this is associated with a drop in other heat values. properties such as, for example, material toughness, thermal stability and the like. It is an object of the invention to indicate an alloy which makes it possible to improve the overall property profile of an object produced therefrom. In accordance with the task of the invention, a hot-working steel object with high hardness and high toughness, high heat resistance and high thermal stability must be created. The object of the invention cited above is obtained with an alloy containing by weight%: carbon (C) 0.15 to 0.44 silicon (Si) 0.04 to 0.3 manganese (Mn) 0.06 to 0 , 4 chromium (Cr) 1.2 to 5.0 molybdenum (Mo) 0.8 to 6.5 nickel (Ni) 3.4 to 9.8 vanadium (V) 0.2 to 0.8 cobalt (Co) 0.1 to 9.8 aluminum (Al) 1.4 to 3.0 copper (Cu) below 1.3 niobium (Nb) below 0.35 iron (Fe) remaining as well as ancillary elements and impurities caused by production .

The advantages presented with the invention can be seen substantially from the fact that by alloy technology measures a material has been created in which a precipitation temper can be superimposed on the hard quench or martensite quench. In this case, the activities of the alloying elements with respect to carbon and those relating to the formation of the joint or phases are chosen in such a way that also at comparatively low austenitization temperatures, a quenching temper can be simultaneously processed. precipitations of very fine secondary carbides, particularly chromium-molybdenum-vanadium carbides, and tempering by a precipitation of intermetallic phases, particularly AIFe2Ni, and a high hot hardness is obtained at a high toughness of the material.

According to the invention, a complete quenching of large parts is also possible, since a corresponding thermal transformation behavior of the material is adjusted by alloying technology. Likewise, tempering stability and thereby thermal stability of the beneficiated material at high hardness are substantially improved.

In an iron-based alloy according to the invention, a carbon content of at least 0.15 wt.% Is provided so that a sufficient amount of carbide can be separated for a desired secondary hardness increase. Carbon concentrations higher than 0.44% by weight may form with the intended carbide forming elements disturbing primary carbides, which decrease the tenacity, so that the carbon content must be between 0.15 and 0. 44% by weight. The silicon content, for an advantageous composition of a deoxidization product, must be at least 0.04 wt.%. On the other hand, it must not be higher than 0.3 wt.%. Higher silicon contents negatively influence the toughness of the material.

Manganese is provided in steel according to the invention at a concentration between 0.06 and 0.4% by weight. Lower contents could cause brittleness in the case of hot molding and higher contents, disadvantages for material tempering.

Chromium, molybdenum and vanadium contents are important for a desired secondary hardness formation of the material in beneficiation, and should be observed together. Chromium contents below 1.2 wt% have a negative effect on the overall tempering of the material; chromium contents below 5.0 wt% reduce the thermal stability of the material, as the molybdenum activity is suppressed.

At molybdenum concentrations below 0.8% by weight, during the heat treatment an insufficient amount of this element is brought into solution, which leads to low secondary hardness values. Over 6.5% by weight of molybdenum in steel can cause a too high carb fraction, which can lead to material toughness losses and economic disadvantages. The strong carbide former, vanadium, is provided according to the invention with a minimum content of 0.2% by weight to ensure a stable secondary tempering of the steel. Content higher than 0.8% by weight of vanadium can lead to precipitation of primary carbides, particularly in the case of carbon content at the upper limit of the concentration range, whereby the material toughness properties are deteriorated by leaps. .

Although the effect of niobium is similar to that of vanadium, it is nonetheless distinguished by very stable carbide formation, so that the niobium content should advantageously be below 0.35% by weight. Weight.

In order to guarantee a secondary hardness increase in a martensite structure revival of the alloy according to the invention, it therefore has a carbon concentration of 0.15 to 0.44 wt.%. by weight of chromium of 1,2 to 5,0, of molybdenum of 0,8 to 6,5 and of vanadium of 0,2 to 0,8. The nickel concentration of the steel and its aluminum content should be considered for the precipitation kinetics of the AIFe2NI phase to increase hardness in a predicted heat treatment technology. At nickel contents below 3.4 wt% and an aluminum concentration of less than 1.4 wt%, a precipitation temper is suppressed, so the increase in additive hardness as a material in tempering is small.

Contents higher than 9.8 wt.% Nickel shift the δ / α transformation to lower temperatures, which can lead to problems in the steel annealing treatment, high working hardness and kinetic disturbance. of precipitation.

Contents above 3.0% by weight of aluminum negatively stimulate a high range of DELTA- (6) ferrite in behavior, a nitride formation and lower alloy material toughness.

According to the invention, the nickel content and aluminum content of steel are therefore in weight% in the 3.4 to 9.8 nickel and 1.4 to 3.0 aluminum ranges.

Copper can form undesirable intermetallic phases and should be contained in the steel in a small concentration of below 1.3% by weight.

For further improvement of the alloy property profile according to the invention it may be provided that it has one or more of the elements having the following concentration by weight%: carbon (C) 0.25 to 0.4, preferably 0 0.31 to 0.36 silicon (Si) 0.1 to 0.25, preferably 0.15 to 0.19 manganese (Mn) 0.15 to 0.3, preferably 0.2 to 0.29 chromium ( Cr) 1.9 to 2.9, preferably 2.2 to 2.8 molybdenum (Mo) 1.2 to 4.5, preferably 2.1 to 2.9 nickel (Ni) 5.0 to 7, 6, preferably 5.6 to 7.1 vanadium (V) 0.24 to 0.6, preferably 0.25 to 0.4 cobalt (Co) 1.4 to 7.9, preferably 1.6 to 2.9 aluminum (Al) 1.6 to 2.9, preferably 2.1 to 2.8 By these narrower element content ranges in the chemical composition of steel, further refinement of the properties of the alloys can be obtained. objects produced with it.

For high overall mechanical steel values, but also particularly for high material toughness properties, a limited fraction of mixtures is of particular importance.

In an advantageous embodiment of the invention there is provided an alloy containing one or more accessory or impurity elements having the following MAXIMUM concentrations by weight: phosphorus (P) 0.02, preferably 0.005 sulfur (S) 0.008, preferably 0.003 copper (Cu) 0.15, preferably 0.06 titanium (Ti) 0.01, preferably 0.005 niobium (Nb) 0.001, preferably 0.0005 nitrogen (N) 0.025, preferably 0.015 oxygen (O ) 0.009, preferably 0.002 calcium (Ca) 0.003, preferably 0.001 magnesium (Mg) 0.003, preferably 0.001 tin (Sn) 0.01, preferably 0.005 tantalum (Ta) 0.001, preferably 0.0005 precipitation of the particularly pronounced alloy overlaid by secondary carbide quenching can be advantageous if the value of nickel content divided by aluminum content, respectively by weight%, is between 1.8 and 4.2, preferably between 2.1 and 3.9. Thus, a predominance of one of the elements that form precipitation is avoided. The proposed task of the invention is solved according to an improved property profile in a hot-worked steel object when a preliminary material, produced according to a melt metallurgical or powder metallurgical process, has been formed into a particular shape. - by transformation and hot work, a formed object which, after a tempering heat treatment, has secondary precipitated carbides as well as intermetallic precipitations. The total hardness of the material in this case is advantageously obtained by overlapping the secondary hardness increase due to carbide precipitations and the precipitation temper. In this way, high material hardness values can be obtained, although the beneficiation technology is geared towards obtaining a high material toughness and, compared to a hot working steel according to the state of the art, is used. low tempering temperatures. This lower austenitization temperature can also have considerable advantages with regard to small deformation in a beneficiation treatment of complicated formed parts.

If, however, tempering temperatures are set to a high level, then extremely high hardness values result in the otherwise usual good material toughness of the steel object.

If in the structure of the hot-working steel object there is an intermetallic precipitation ratio divided by secondary precipitated carbides, respectively in volume%, less than 3.0, preferably from 1.0 and below, but above 0.38, at high hardness values, toughness is especially high and thermal stability is shifted up to 50 ° C and above for higher temperatures.

A hot-working steel object according to the invention, which has secondary precipitated chromium molybdenum-vanadium mixed carbides and substantially AIFe2Ni type intermetallic phases in the structure, has a particularly preferred property profile and It can be produced economically in standard quenching facilities at comparatively low quench temperatures.

An accentuated thermal stability of the object can be obtained if the alloy has a ratio of chromium + molybdenum + vanadium divided by carbon, respectively, by weight% of greater than 13 but less than 19. The invention is explained. in more detail, for example, based on some test results and descriptions.

From an alloy A according to the invention, a usual hot-working steel B and a precipitation tempered steel C (Maraging steel), thermally benefited samples were produced and their material properties were examined. The alloys have the chemical compositions shown in Table 1.

Table 1 In the sample material, a measurement of the thermal expansion α [10'6 / K] at temperature dependence was initially performed at an initial material hardness of 50 to 52 HRC. The values extracted from Table 2 show that compared to a conventional hot-working steel B, the alloy according to the invention has a lower expansion, which also indicates better shape stability in a heat treatment.

After quenching for approximately 55 HRC respectively of alloy A samples according to the invention and of conventional hot-working steel B, the evolution of the hardness of the materials depending on temperature was determined. In this case, it is of fundamental importance that in order to obtain this hardness, alloy A according to the invention required an austenitization temperature of 990 ° C, but in the usual hot working steel B a temperature of 1050 ° C was required. Ç. Depending on the temperature, as shown in Table 3A and Table 3B, in the range between 500 ° C and 600 ° C the hardness of the sample A compound according to the invention has risen to around 60 HRC, while on the other hand On the other hand, conventional hot working steel B has a maximum hardness of 56 HRC at 500 ° C.

______________________________Table 3A

Table 3B

In graphical representation, the evolution of the respective hardness, depending on temperature, of material A according to the invention and hot-working steel alloy B according to the state of the art is shown comparatively.

Starting from equal hardness, which, however, is obtained with an optionally advantageous lower austenitization temperature in alloy A according to the invention, by an overlapping precipitation mechanism in which AIFe2Ni precipitations are formed finely in the structure. , there is a substantially greater increase in the hot hardness of the object, and it is also kept at higher temperatures.

Based on an indication of hardness according to Vickers, the softening behavior of the materials, over time, was examined at a temperature of 650 ° C.

A hardness determination in the specimen body at the test temperature was performed according to the Shore hardness method, for which there was, so far, only one conversion to Vickers hardness.

From a hardness approximately equal to the ambient temperature, more precisely, 50 - 52 HRC, which was obtained for alloys A, B and C, with a composition according to Table 1, by different thermal beneficiation processes, indicated in examination results annex - Sheet 1, a hardness test over time was given at 650 ° C.

Compared to a conventional hot-working steel B and a Maraging C steel, alloy A according to the invention had the same initial hardness at 650 ° C for up to 1000 minutes, the hardness of highest material. After that time, Maraging C steel had a higher hardness and high thermal stability, while hot-working steel A according to the invention lost approximately 10% of its hardness in up to approximately 2000 minutes. The thermal stability of conventional hot-working steel B was small; The hardness difference compared to alloy A according to the invention has constantly widened to 1000 minutes.

Result: See Figures 1 and 2 of the Drawings Result - Sheet 1 Initial Hardness: 50 - 52 HRC

Claims (4)

1. Alloy for the production of objects with high heat resistance and toughness, characterized in that it contains by weight%: carbon (C) 0.25 to 0.40, preferably 0.31 to 0.36 silicon (Si ) 0.1 to 0.25, preferably 0.15 to 0.19 manganese (Mn) 0.15 to 0.30, preferably 0.20 to 0.29 chromium (Cr) 1.9 to 2.9 preferably 2.2 to 2.8 molybdenum (Mo) 1.2 to 4.5, preferably 2.1 to 2.9 nickel (Ni) 5.0 to 7.6, preferably 5.6 to 7 Vanadium (V) 0.24 to 0.6, preferably 0.25 to 0.4 cobalt (Co) 1.4 to 7.9, preferably 1.6 to 2.9 aluminum (Al) 1, 6 to 2.9, preferably 2.1 to 2.8 copper (Cu) below 1.3 niobium (Nb) below 0.35 further comprising iron (Fe) remaining, as well as ancillary elements and impurities caused by production . Alloy according to claim 1, characterized in that it contains one or more of the accessory and impurity elements having the following MAXIMUM concentrations by weight: phosphorus (P) 0.02, preferably 0.005 sulfur (S ) 0.008, preferably 0.003 copper (Cu) 0.15, preferably 0.06 titanium (Ti) 0.01, preferably 0.005 niobium (Nb) 0.001, preferably 0.0005 nitrogen (N) 0.025, preferably 0.015 oxygen (O) 0.009, preferably 0.002 calcium (Ca) 0.003, preferably 0.001 magnesium (Mg) 0.003, preferably 0.001 tin (Sn) 0.01, preferably 0.005 tantalum (Ta) 0.001, preferably 0.0005. 3 An alloy according to claim 1 or 2, characterized in that the value of nickel content divided by aluminum content, respectively, amounts in weight% between 1.8 and 4.2, preferably from 2.1 to 3.9 M = 1.8 to 4.2, preferably 2.1 to 3.9. Al