FR2634221A1 - Cast articles made of alloys based on Fe-Mn-Al-Cr-Si-C - Google Patents

Abstract

New cast articles made of alloy based on Fe-Mn-Al-Cr-Si-C consisting essentially of 20 to 30 % by weight of manganese, 5 to 13 % by weight of aluminium, 0 to 5 % by weight of chromium, 0 to 2.5 % by weight of silicon and 0.5 to 1.4 % by weight of carbon, the remainder being iron; these cast articles, ready for use, can be employed at temperatures of up to 1100 DEG C without deterioration of their excellent mechanical properties and can furthermore be alloyed with small quantities of other elements such as boron, tungsten, molybdenum, niobium, titanium, vanadium, nitrogen, copper, nickel, yttrium, scandium, hafnium and tantalum in order to meet the particular requirements of various specific applications.

Description

ALLOY-CAST PIECES BASED ON Fe-Mn-Al-Cr-Si-C
The present invention relates to castings made of alloys based on Fe, Mn, Al, Cr, Si, C.

Castings that can withstand high temperatures are desirable for applications such as incinerators, furnaces, reactors and steel refiners. The temperatures in these applications can reach 1100 ° C. design of castings suitable for such applications is subject to the essential requirements of
(1) maintaining excellent mechanical performance; and
(2) maintaining resistance to hot corrosion at elevated temperatures.

 In addition, the cost, the regularity of the supply or even the possibility of supplying the addition components of the castings are also essential factors.

 Mechanical failures of castings at elevated temperatures are mainly due to softening and creep of the castings at these temperatures. In addition, the hot corrosion reaction initiated by the hostile atmosphere further accelerates the mechanical failure.

 The need for excellent mechanical performance of castings at elevated temperatures varies greatly depending on the rattle and location of the desired application. For example, it is essential that the impeller parts used as the blades of gas turbines satisfy extremely stringent standards of mechanical properties, such as stress, erosion and abrasion. On the other hand, the standards are not as severe in "static" applications as boiler bodies and jackets, however, whatever the variation in mechanical performance required from one application to another, the ability to withstand Hot corrosion of castings in a hostile atmosphere is always rigorously essential.

 As is well known in the art, aluminum, chromium and / or silicon are often used as adducts to improve the hot corrosion resistance of alloys for high temperature applications. The effectiveness of these elements derives from their ability to form protective films of oxides consisting respectively of aluminum oxide (Al 2 O 3), chromium oxide (Cr 2 O 3) and / or silicon oxide (SiO 2). For some applications at lower temperatures, nickel can also be used to provide relatively lower protection against hot corrosion by forming a film of nickel oxide (NiO) on the surface of the protected material. nickel oxide does not provide the same rate of resistance to hot corrosion as those of aluminum, chromium and silicon.

However, nickel may have the added advantage of promoting the mechanical performance of protected materials and is therefore often considered to be an important addition element in alloy design for high temperature applications.

 During the 1920s and 1930s, Fe-Cr-Al alloys were mainly preferred for high temperature applications.

However, because of their lower mechanical performance, specific to their ferrite structure or centered cubic structure, these alloys are rarely used to date.

 Recent commercialized alloys for high temperature applications are primarily characterized by a chromium content of 10 to 30% by weight. As previously mentioned, chromium forms a protective layer of Cr 2 O 3 by reaction with atmospheric oxygen.

However, at temperatures above 1000 ° C, Cr 2 O 3 undergoes additional CrO 3 oxidation which volatilizes upon reaction, so that the oxide layer becomes looser. For this reason, uses of this type of alloy are generally limited to temperatures below 1000-C. On the other hand, with such a high chromium content, a sigma phase precipitates in the alloy and renders the alloy brittle. To solve this problem, it is necessary to add some ingredients inhibiting the formation of the sigma phase. However, although the carbon, relatively inexpensive, is often used for this purpose in other types of alloys, the carbon can not be used in Fe-Cr alloys of this type because the alloy would be sensitized to a carbon content greater than about 0.04 wt. Alternatively, nickel can be used, which can inhibit the formation of the sigma phase while stabilizing an austenite phase to improve the toughness and other mechanical properties of the alloys. According to this strategy, many species of Fe-Cr-Ni-based alloys have been developed. For example, currently marketed alloys for high temperature applications include worked alloys, such as carbon-based superalloys. Inconel-718 nickel and stainless steel based on Fe-Ni AISI 310, a cast alloy such as nickel-based superalloy Inconel-738, Fe-Cr-based alloys such as SAE 60410 (JIS SCH-1 ) and SAE 60446 (JIS
SCH-2) and Fe-Ni-based alloys such as SAE 60442 (JIS SCH-11), SAE 60316 (JIS SCH-12), SAE 60312 (JIS SCH-13), SAE 60309 (JIS SCH-14) and SAE 60310 (JIS SCH-15). Table I summarizes the composition of the aforementioned alloys.

 As the table clearly shows, all these alloys contain a relatively high proportion of nickel and / or chromium.

Since nickel and chromium are rare and expensive, these alloys are all very expensive. Above all, as nickel and chromium are considered strategic materials by most countries, countries that do not have such resources can hardly afford them. Consequently, these alloys are extremely expensive, their price being several dozen or even hundreds of times higher than that of carbon steel. This is why these alloys are priced per kilogram and not per ton. This obviously prevents the mass use of these alloys. In addition, the high content of nickel or chromium also aggravates the welding difficulties, which further increases the construction costs.

TABLE I
Alloys marketed for applications to. temperatures
high
Name
Designation Ni Cr C Al no JIS
Inconel-718 53.0 18.6 0.04 0.4 3.1
Inconel-718 61.0 16.0 0.17 3.4 1.7
AISI 310 19-22 24-26 <0.08
SAE 60410 <1.0 12-15-0.2-0.4 SCH-1
SAE 60446 - 25-28 <0.5 SCH-2
SAE 60442 4-6 24-28 0.1-0.3 SCH-11
5AE 60316 8-12 18-23 0.2-0.4 SCH-12
SAE 60312 4 24-29 0.2-0.5 SCH-13
SAE 60309 18-22 24-28 0.3-0.6 SCE-14
SAE 60310 33-37 13-17 0.35-0.75 SCH-15
Faced with these economic and supply problems, the art attempted to find substitutes for chromium and nickel. Aluminum has thus been used to replace chromium to provide the required resistance to hot corrosion. Manganese and carbon have been used together to replace nickel to stabilize the austenitic phase so that high toughness can be achieved. obtained. In particular, the ability of the combination of manganese and carbon to stabilize the austenitic phase has been shown to be more effective than that of nickel.

However, these two strategies are contradictory. If alloys of this type contain too much carbon or manganese, the resistance to hot corrosion of aluminum oxide is greatly reduced. In many cases, the resistance to hot corrosion can be fifty times lower. No effective method has been mentioned to resolve this incompatibility between chemical performance and mechanical performance. Another problem with this type of alloy is that aluminum oxide is less effective than chromium oxide in providing protection against hot corrosion. To remedy this defect, silicon has been added to increase the formation of Al 2 O 3, which contributes most of the resistance to hot corrosion. However, silicon only acts at temperatures around 1100 C. At lower temperatures, the addition of silicon does not cause any significant effect. In conclusion, no alloy simultaneously having a satisfactory resistance to hot corrosion and satisfactory mechanical performance in the temperature range between room temperature and 1100-C while being relatively inexpensive has been described in the art prior.

In previous research on Fe-Mn-Al-based alloys, a portion of the Fe-nn-Al three-element phase diagram was constructed by Koster and Tonn in 1934 (W. Koster and W. Tonn, Bow
Eisenhuettenw, 7, 365 (1933)) and modified by Schmartz in 1959 (DJ

Schmatz, Trans. AINE, 215, 112-114 (1959)), Chakrabartic in 1977 CD.J.

 Chakrabarti'c, Metall. Trans., 8B, 121-123 (1977) and V.G. Rivlin in 1983 (V.G. Rivlin, International Metal Reviews, 28, No. 6, 309-337 (1983)).

However, this work was limited to temperatures close to 1000 C and many regions of the phase diagram remain uncertain. For example, the solidus line of the phase surface around Mn 20% by weight and Al 6% by weight remains undetermined. There is no four-element phase diagram of Fe-Mn-Al-C.

 U.S. Patent No. 3,201,230 issued to Mitchell et al. in 1965 discloses an alloy consisting essentially of 14 to 35 wt.% of manganese, 3.5 to 8.75 wt.% of aluminum, 4.5 to 8.75 wt.% of chromium, 0.25 to 1, 0% by weight of silicon, 0.25 to 1.0% by weight of carbon, the balance being iron. The alloy of this patent contains a relatively high amount of chromium and would therefore be relatively expensive to market. In fact, this patent has never received any practical application even after its expiry date. It is considered that the content of the patent is in contradiction with certain metallurgical theories and that the alloys described do not have the desired efficiency, in particular when they are designed for applications at temperatures between 400 and 1000 C.

The reasons are:
(1) The manganese content of 14 to 35% by weight of said patent is too
because, as Koster and Tonn indicated in 1934 (W. Koster and
W. Tonn, Arc Eisenhuettenw, 7, 365 (1933)), when the content of
manganese of the patented alloy is greater than 31 t by weight, from ss-Mn
precipitates around the grain boundaries of the alloy between 300 and
1,000 C. On the other hand, if the manganese content is less than
20% by weight, large carbides Fe3AlCx are formed, which weakens
alloys and consumes the aluminum they contain.
obvious that the corrosion resistance is reduced, which makes the
alloys unsuitable for applications at high temperatures when
aluminum is consumed by the formation of Fe3AlCx carbides.

(2) Chromium present at a high level reacts easily with the
carbon to form chromium carbide (Cr23C6 or Cr7C3) at
application temperatures. The alloy is thus sensitized and its
mechanical properties are reduced. Moreover, if the temperature is
above 800 C and that the chromium content falls between 5 and
8.75 t by weight, the chromium contained in the alloy reacts quickly and
massively with atmospheric nitrogen to form nitride
of aluminum in the form of needles (A1N). This makes the content
insufficient aluminum to form a protective layer of oxide.

However, Mitchell's patent does not indicate how this problem
could be solved. In the past, aluminum nitride was
erroneously considered as the product of the internal oxidation of
aluminum until the study of Wang et al. from Katerial
Science Research Institute of National Chin-hwa University, Taiwan,
performed with a scanning electron microscope for examination by
transmission, revealed this error in 1987. Wang's discoveries
et al. have been published in Journal of Material Science of Great
Britain in May 1988.

The invention is superior to all the aforementioned prior arts in that
(1) The manganese content is limited in a specific range which has
proved to suit the full range of application temperatures
desired. To prevent the formation of ss-manganese or Fe3AlCx
boundary of the manganese content, other elements
of addition are added to determine the morphology and
the location of the precipitates.

(2) Silicon is added to increase the resistance to corrosion at
hot.

(3) Auxiliary elements are added to further increase the
mechanical performance of castings according to the mechanism of
precipitation hardening at elevated temperatures.

(4) Through an appropriate adjustment of the relative ratios of the elements
addition, the addition of chromium is optional or even totally
unnecessary for some applications. This greatly reduces the cost of
cast parts of the invention.

(5) The castings of the invention have an oxidation weight gain
lower at high temperatures than any of the arts
aforementioned.

The invention aims to provide castings ready for use
which have excellent resistance to hot corrosion and
excellent mechanical performance in the temperature range
ranging from room temperature to 1100 ° C
that meet the above requirements without it being absolutely
necessary to incorporate expensive or rare elements, such as
chrome or nickel and
that can be modified to meet particular needs of
some specific applications by addition of elements
Auxiliary.

 The invention relates to novel ready-to-use castings made of Fe-Mn-Al-Cr-Si-C-based alloys and a process for their preparation. More particularly, the invention relates to new ready-to-use castings consisting essentially of 20 to 30% by weight of manganese, 5 to 13% by weight of aluminum, 0 to 5% by weight of chromium, 0 to 2% by weight of aluminum. 5% by weight of silicon and 0.5 to 1.4% by weight of carbon, the remainder being iron. These castings can be used at temperatures as high as 1000.degree. C. without diminishing their excellent mechanical performance. The castings of the invention may furthermore be in allied with a small amount of other elements, such as boron, tungsten, molybdenum, niobium, titanium, vanadium, nitrogen, copper, nickel, yttrium, scandium, hafnium and tantalum to meet specific needs for various specific applications.

 The invention will be better understood on reading the detailed description and the appended examples.

 The castings ready for use of the invention mainly comprise five addition elements in addition to the iron. The individual elements are described in detail below.

Manganese
In the invention, manganese is used as stabilizer of austenite to improve the toughness of the alloy by stabilizing the austenitic structure of the alloy. Manganese is readily oxidizable at temperatures above 750 ° C. This problem is solved by the addition of silicon, as described below.

 As previously mentioned, the corrosion resistance is reduced in the earlier alloys when the manganese content is too high. This problem has been solved in the invention by adjusting the relative ratios of manganese, carbon and aluminum.

 The ready-to-use castings of the invention comprise from 20 to 35% by weight, preferably from 20 to 32% by weight and most preferably from 24 to 30% by weight, of manganese.

Carbon
Carbon is also used in the alloys of the invention as a stabilizer for austenite to improve the mechanical performance of alloys. In the case where a carbide former such as niobium and molybdenum is added, the carbon content must be proportionately increased.

 As previously mentioned, the corrosion resistance is reduced in the earlier alloys when the carbon content is too high. This problem was solved by adjusting the relative ratios of manganese, carbon and aluminum. The ready-to-use castings of the invention comprise from 0.5 to 1.4 wt.%, Preferably from 0.5 to 1.2 wt.%, And most preferably from 0.5 to 1.1 t. by weight, carbon.

Aluminum
Aluminum can be oxidized at elevated temperatures to form an aluminum oxide layer that provides the majority of the corrosion resistance when hot. Aluminum is also used in the alloys of the invention as a ferrite former and therefore, the relative ratios of aluminum, manganese and other additive elements must be suitably balanced; Properly selected ratios of the other elements can provide a protective layer of maximum efficiency aluminum oxide and form ordered Fe3AlCx carbides in the matrix to further enhance the alloy.

 The ready-to-use castings of the invention comprise 5 to 13% by weight, preferably 8 to 12% by weight and most preferably 8 to 11% by weight of aluminum.

Chromium
Chromium can be oxidized at elevated temperatures to form a chromium oxide layer providing complementary resistance to hot corrosion. The corrosion resistance of chromium oxide is more effective at room temperature. Chromium is a ferrite trainer and it is also an effective carbide formator. To avoid the undesirable effect of chromium on the mechanical performance of alloys, care must be taken to adjust the relative ratio of chromium.

 The ready-to-use castings of the invention comprise from 0 to 5% by weight, preferably from 1 to 5% by weight and most preferably from 2 to 4% by weight of chromium.

Silicon
Silicon can spontaneously form a protective layer of silicon oxide. Since the oxidation rate and the oxidation dissociation pressure of the silicon are lower than those of the manganese oxide (no), the silicon is used in the alloy of the invention mainly as an inhibitor of the oxidation of the manganese and nucleation and growth of manganese oxide. As a result, the possibility of formation of aluminum oxide is greatly increased. However, silicon is a powerful ferrite former which greatly reduces the weldability of castings, so that its relative ratio must be carefully determined in this respect.

The ready-to-use castings of the invention comprise
0 to 2.5% by weight, preferably from 0.5 to 2% by weight and most preferably from 0.5 to 1.5% by weight of silicon.

Auxiliary elements
In addition to the above essential addition elements, the castings of the invention may further be combined with a small amount of other elements, such as boron, tungsten, molybdenum, niobium, titanium, vanadium, nitrogen, copper, nickel, yttrium, scandium, hafnium and tantalum, to meet specific needs for various specific applications. Addition of auxiliary elements is well known in the art and is discussed below to illustrate other aspects of the invention. The individual auxiliary elements are described below.

Boron
The addition of boron reduces the free surface energy of the grain boundaries, further reducing the precipitation of carbides on the grain boundaries. The addition of boron produces a homogeneous precipitation in the matrix which ensures better mechanical properties.

 The castings of the invention may optionally contain from 50 to 200 ppm boron.

Tungsten, molybdenum and niobium
These elements are used in the alloys of the invention to form a fine carbide-type reinforcing alloy in order to increase the resistance to erosion, to hinder the diffusion of carbon and to avoid deterioration by decarburization of the protective layer. oxide.

 Castings of the invention may optionally comprise 0.1 to 1.0 wt.% Tungsten.

 Castings of the invention may optionally comprise from 0.1 to 2.1% by weight of molybdenum.

 Castings of the invention may optionally comprise from 0.1 to 1.0% by weight of niobium.

Titanium and vanadium
The rattle of titanium and vanadium is the same as that of tungsten, molybdenum and niobium. In addition, titanium and vanadium can form a small amount of nitrides to prevent damage caused by nitriding and divert nitriding to contribute to surface hardening.

 Castings of the invention may optionally comprise from 0.1 to 2.0 weight percent titanium.

 Castings of the invention may optionally comprise from 0.1 to 1.0% by weight of vanadium.

Nitrogen
Nitrogen is also a powerful austenite formator. The addition of nitrogen stabilizes the austenitic phase with a lesser amount of carbon, resulting in improved resistance to hot corrosion.

 The castings of the invention may optionally comprise from 0.05 to 0.2 weight percent nitrogen.

Copper
Copper can be used to increase corrosion resistance at low temperatures. Copper can also be used to form a compound with residual phosphorus in castings to avoid hot brittleness caused by residual phosphorus.

 The castings of the invention may optionally comprise from 0.5 to 1.5% by weight of copper.

Nickel
The phosphorus and copper compound as described above still causes heat brittleness at temperatures. Nickel can be used to avoid this problem. In addition, nickel can be used to improve the gloss of the alloy. Excess nickel forms a gamma prime phase of metal compounds with aluminum that is harmful to the alloy. The amount of nickel and copper added must be carefully adjusted according to the grade. residual phosphorus.

 Castings of the invention may optionally comprise from 0.5 to 2.5 weight percent nickel.

Yttrium, scandium, hafnium and tantalum
Due to their high oxidation potential, these rare elements can be added to initiate internal oxidation in the alloy to absorb the vacuum produced during oxide film formation, to establish a key mechanism and to increase the adhesion of the oxide film by establishing a mechanism-interlayer, so that the oxide film is not easily peeled during repeated rinsing and a drop in temperature.

 The castings of the invention may optionally comprise from 0.01 to 1.0% by weight of yttrium.

 The castings of the invention may optionally comprise from 0.01 to 1.0% by weight of scandium.

 The castings of the invention may optionally comprise from 0.01 to 0.5 weight percent hafnium.

 The castings of the invention may optionally comprise from 0.01 to 0.8 weight percent tantalum.

 The following examples are presented to provide a better understanding of the invention and are not designed to limit its scope. Unless otherwise indicated, all parts and percentages are by weight.

EXAMPLE 1
This example illustrates the process for preparing castings of the invention
A mixture of iron, manganese, aluminum, silicon and carbon is melted with a high-frequency induction furnace to produce a bath of known composition. The bath is then cast with molds of different materials to produce castings having different surface conditions.

 The melting is carried out with a high frequency induction furnace having a capacity of 20 kg. The composition, shape and weight of the additive elements are shown in Table II.

TABLE II
Composition Weight
E% weight% kg Form
Manganese 30 4.5 Pure Manganese Trade
Aluminum 10 1.5 Pure Aluminum Commercial
Chrome 3 0.45 Pure Chromium Trade
Silicon 1 0.3 ferrosilicon containing
50 t of silicon
Carbon 1 0.15 Activated carbon powder
Iron Complement 8.1 Wire to wind 1008 with
0.08 t of carbon
Iron and ferrosilicon are introduced into the cold furnace. The furnace power is set at 20 kW and maintained for 10 minutes, after which the power is adjusted to 40 kW. Seven minutes later, the iron and ferrosilicon are completely melted at about 1 550 C. The power is then adjusted to 20 kW, 2.25 kg of manganese and all the chromium are added, and then the power is readjusted to 40 kW. After melting of the added manganese and chromium, 2.25 kg of manganese are added and 0.15 kg of carbon are added. Ten minutes later, the slag is removed. 1.5 kg of aluminum are added. The slag formation and the slag removal operation are carried out after the aluminum melting. The bath was decanted into a ladle having a capacity of 30 kg after the temperature reached 1580 ° C; then poured into four separate molds of different materials after the temperature has dropped to 1480 ° C. The four molds are respectively a shell mold, a sand mold, a ceramic mold and a steel mold with capacities of 4 kilograms.

 The surface conditions of the castings obtained are observed. Regarding the product shapes, the best results are observed with the caparace mold and the sand mold, the ceramic mold and the steel mold in the order indicated. Regarding the smooth state of the surface, the best results are observed with the steel mold and the shell mold, the ceramic mold and the sand mold in the order indicated. However, all castings are considered suitable for use.

 The cast piece is homogenized at 1200 ° C. for 4 hours with the ceramic mold and a sample is taken by drilling for chemical analysis. The results of the analysis are shown in Table III.

TABLE III
Composition of the analyzed table II castings
according to a chemical process
Mn Al Cr Si C Fe
28.67 9.33 3.14 1.12 0.94 Supplement
EXAMPLE 2
In the context of the invention, a series of castings is produced according to a process similar to that of Example 1 and the mechanical properties (tensile strength, elongation and hardness) of the alloys are determined and compared with those of conventional castings for application at high temperatures.

 17 cast parts made from Fe-Mn-Al-C alloys optionally containing other additive elements such as niobium, molybdenum and the like are prepared according to the same procedure as described in Example 1. nitrogen.

 The bath is then cast in a ceramic mold to obtain cylindrical ingots of 80 mm in diameter and 250 mm in length weighing about 15 kg. The ingots are cut into a 4 cm high cylinder and then forged at 1200.degree. C. until the height is reduced to 2 cm. The forged ingots are then cooled to room temperature and cut into test pieces having a reference length of 1 inch for tensile tests. The tensile strength, elongation and hardness of the samples are determined and the values are shown in Table IV. During the test, uniform deformations of all the samples are observed. Necking rates are relatively low.

Some typical mechanical properties of conventional high temperature castings shown in Table I are shown in Table V for comparison. As shown by the comparison between Tables IV and V, the mechanical performance of the castings of the present invention is greater than that of conventional commercial castings for high temperature applications. In particular, the castings of the invention have a higher elongation and toughness than those of the specification standard of IAIS 310 which is a forging steel for application at elevated temperatures.

TABLE IV Resistance to Allon
Composition (% by weight) traction
N Mn Al C Cr Nb Mo Other Fe MPa (ksi) (%) Hardness 1 33.04 7.45 0.72 - - - - Supplement 808.3 (117.2) 45.6 56.9Rb &num; 2 33.13 7.54 0.58 - - - - "776.9 (111.2) 46.6 64.7Rb &num; 3 28.78 7.83 0.6 - - - -" 812.4 ( 117.8) 48.2 59.5Rb &num; 4 25.6 11.24 1.24 - - - - "1175.2 (170.4) 6.35 44.5Rb &num; 5 25.3 6.72 0.46 5.52 - - - "724.2 (105.0) 33.85 &num; 6 27.2 7.22 0.79 5.92 - - 2.0 Ni" 875.9 (127.0) 43.33 98.6Rb &num; 7 27.8 7.24 0.41 5.89 - - - "893.8 (129.6) 40.34 96.0Rb &num; 8 32.7 7.36 0, 88 5.73 - - - "845.5 (122.6) 45.9 96.5Rb &num; 9 25.1 8.1 0.74 5.54 - - -" 838.6 (121.6) 42.2 &num; 10 30.51 10.99 0.78 - - - 1.40Si "749.6 (108.7) 41.4 98.0Rb &num; 11 30.3 7.6 1.08 - - 0.46 - "990.0 (144.85) 29.85 30.4Rc &num; 12 25.2 8.02 1.02 - - 0.66 -" 1084.8 (157.3) 26.5 32.8Rc &num;; 13 29.4 10.9 1.14 - 0.05 - - "1224.1 (177.5) 13.3 36.4 Rc &num; 14 30.2 11.1 1.13 - 0.1 - - "1110.3 (161.0) 15 36.2Rc &num; 15 33.9 11.0 1.19 - 0.3 0.76 -" 1139.3 (165.2) 19.3 39.3Rc &num; 16 30.7 10.9 1.09 - 0.1 - 0.004N "1089.6 (158.0) 12.9 36.5Rc &num; 17 28.87 10.22 0.72 - - - 0.002B" 849.6 (123.2) 23.7
2.0Ni "
Note: 1. ksi x 0.70325 = kg / mm
2. ksi x 6.8965 = MPa
TABLE V
Typical values of mechanical properties of commercial alloys
resistant to high temperatures
Resistance to
traction Elongation
Designation MPa (ksi) b Utility
AISI 310> 483 (> 70)) 45 transformation
JIS SCH-ll> 586 (> 85) not determined casting
JIS SCH-; 2> 483 (, 70)
JIS SCH-13> 483 (> 70,
JIS SCH-14> 448 (> 65)
JIS SCE-15> 393 (, 57)
EXAMPLE 3
A six-inch forged ingot of the No. 10 alloy of the preceding example prepared under the same procedure is cold rolled with a 90% reduction in size to obtain a thickness of 0.2 cm. The parts are then subjected to These were laminated to a solution treatment for 1 hour at 1050 ° C. and quenched in gear oil at room temperature. Five of the six rolled pieces were subjected to aging treatment at 550 ° C for different times. The tensile strength, elongation and hardness of the six rolled parts are determined, the results obtained shown in Table VI. As shown in Table VI, the tensile strength is remarkably increased, the elongation is reduced to a limited extent and the hardness is increased.

The laminated pieces are observed with an optical microscope. The analysis of the microstructure reveals that the improvement of the mechanical performances results from the formation of Fe-Al-C (Fe3AlCx) small carbides. It has therefore been proved that the mechanical performance of the castings of the invention is improved by adjusting the morphology of the precipitates at high temperatures.

TABLE VI
Mechanical properties of the alloy n 10 after treatment of
aging
Resistance to
traction Elongation
Processing Mode Time MPa (ksi)% Hardness
No aging - 880.7 (127.7) 51.4 54.8 Ra
Aging at 550 C 1 hr 955.2 (138.5) 39.6 64.5 Ra
Aging at 550 C 4 hr 1 060.0 (153.7) 39.6 63.0 Ra
Aging at 550C 8h 1 091.7 (158.3) 37.4 64.9 Ra
Aging at 550 ° C 16 hrs 1,046.2 (151.7) 44.0 65.0 Ra
EXAMPLE 4
This example illustrates the resistance to hot corrosion of the alloys of the invention.

 A series of castings having the composition indicated in Table VII is prepared by melting and forging at 1220 ° C. and homogenizing at 1050 ° C. for 8 hours, as described in Examples 1, 2 and 3. The pieces obtained are then cut away. in test samples of 2 x 4 x 8 mm. The surface of the samples is abraded with # 1200 SiC abrasive paper. The abraded samples are then placed in a thermogravimetric analyzer to determine their weight gain by oxidation. The dry air flow rate of the thermogravimetric analyzer was set at 100 cm3 / min, the temperatures at 760, 900 and 1100-C and the duration of the experiment at 24 hours. The oxidation weight gains of these samples are shown in Table VIII.

TABLE VII
Composition of the alloys of Example 4 (* by weight)
N 'Al C Fe
f18 5.5 0.55 Supplement
f19 8.5 0.65 Supplement
t20 10.0 0.52 Supplement
TABLE VIII
Weight gain by oxidation of the alloys of Example 4 after
24 hours of oxidation at 700, 900 and 1100 ° C (mg / cm 2)
N 700 C 900 C 1 100C
f18 1.71 5.68 10.76
t19 1.19 0.46 0.89
t20 <0.05 0.29 1.22
As shown in Tables VII and VIII, the addition of aluminum can inhibit the undesirable effect of carbon on the corrosion resistance of the castings of the invention. These examples confirm that, according to the invention, the resistance to the corrosion of carbon-containing alloys can be adjusted by the addition of aluminum.

EXAMPLE 5
A series of castings having the composition indicated in Table IX is prepared according to the procedure described in Examples 1 and 2. These castings are then treated as described in Example 4 and placed in a tubular furnace set to 400 to 750 ° C with a cast piece of AISI 304. Dry air is introduced into the tubular furnace at a rate of 200 cm 3 / min to oxidize the samples. After 24 hours of oxidation, these samples are cooled in air to room temperature and the surface condition of the samples is observed. It is observed that the color of the IAIS 304 becomes increasingly dark when the temperature rises and is totally black when the temperature is above 600 ° C. In contrast, the castings of the invention remain bright although somewhat yellow at high temperatures. When the temperature rises, the color of the castings of the invention changes from yellow to brown. The castings of the invention and AISI 304 are not peeled.

 The same procedure is repeated, except that the temperature is set at 1100 ° C. No peeling or apparent formation of oxide is observed on the surface of castings of the invention. The color of the castings of the invention is bright brown. On the other hand, a homogeneous black layer of oxide is observed on the surface of AISI 304 and, after cooling to room temperature, cracks are also observed. This example proves that the adjustment of the composition of the alloys, even when the carbon or manganese content is very high, makes it possible to obtain excellent resistance to corrosion.

TABLE IX
Mn Al C Fe
28.3 11.3 0.5 Supplement
EXAMPLE 6
As in Examples 1 and 2, a series of castings containing chromium having the composition shown in Table X were prepared, followed by cold rolling with a reduction of 90 t in thickness up to 2 minutes. The parts obtained are then homogenized at 1150 ° C. for 50 hours in order to completely eliminate the working stresses and ensure complete growth of the crystalline grains. The rolled pieces are cut, ground and polished with aluminum oxide powder to 0.05 μm to obtain samples for the oxidation test. The same procedure is used. the same apparatus for carrying out the oxidation test, except that the oxidation temperature is fixed at 1050 ° C and the rate of rise of the temperature from the ambient temperature is 100 ° C / min. The thermogravimetric analysis is carried out for 48 hours at 1050 ° C. It is found that the total weight gain by oxidation is only 0.42 mg / cm3. It should be noted that the increase in weight gain by oxidation is observed only in the first three hours and that one no longer observes an increase in the weight gain by oxidation; Analysis with an X-ray analyzer and an electron microprobe reveals that the growth of the aluminum oxide crystals was complete during the first three hours under the above test conditions. The samples are cooled in air to room temperature and the results show that there is no peeling of the oxides and that the color of the samples studied is changed to brownish silver.

 This example demonstrates that the proper addition of chromium to the castings of the invention with an appropriate adjustment of the rate of temperature rise provides an intact protective layer of aluminum oxide which is not peeled after cooling.

PAINTINGS
Composition of the Fe-Mn-Al-Cr-C alloy of Example 6
Mn Al Cr C Fe
f21 30.95 8.87 2.98 0.87 Supplement
EXAMPLE 7
A series of alloys based on Fe-Mn-Al having the compositions indicated in Table XI are prepared according to the same procedure as that described in Example 1. The castings obtained are then homogenized at 1200 ° C for 4 hours. hours and then hot rolled at 900-1000 C.

The rolled pieces were subjected to solution treatment at 1050 ° C. for 1 hour and then quenched with oil. The resultant pieces were cut to 8 x 8 x 10 min and abraded with SiC 1200 sandpaper to obtain samples for the hot-corrosion test.

To carry out the hot corrosion test, these cast samples are immersed in commercial Q-6 heat treatment salt solution containing mainly BaCl 2, KCl and LiCl for 268 hours.

The thickness of the corrosion product on # 24 is only 30> 2 and it is observed that corrosion occurred along the ferrite phase.

 This example shows that castings of the invention exhibit resistance to hot corrosion.

TABLE XI
Composition of alloys based on Fe-Mn-Al-C of Example 7
N Mn Al C Fe
22 32.3 9.7 0.03 Supplement
23 30.4 9.8 0.1 Supplement
24 30.8 9.8 1.0 Supplement
EXAMPLE 8
In areas where garbage sorting is not performed, all types of garbage containing acidic and basic wastes are taken to a garbage incinerator. Analysis of samples taken from a garbage incinerator in Taiwan reveals that garbage sent to an incinerator contains an average of 56 t of water, 15% of dust, 15% of carbon, 11 t of oxygen, 0.1 With their high water content, garbage in these areas can not burn spontaneously, so a fuel is often sprayed on garbage to facilitate incineration. It is considered that the internal environment of such an incinerator is particularly aggressive for alloys for applications at high temperatures.

A series of castings constituting incinerator grids made of Fe-Mn-Al-C-Cr-Si alloy having the compositions indicated in Table XII are prepared by melting electrolytically pure raw materials in an induction furnace. high frequency having a capacity of 500 kg and bath casting obtained in a sand mold to obtain the desired base plates. Two types of incinerator grates are being prepared, fixed grates to carry the incinerator residue and mobile grates to carry burning waste and to allow ventilation with hot air. Both types of grids support a heavy load in an atmosphere corrosive to the combustion temperature. In addition, these grids must withstand prolonged erosion caused by the transport of garbage. The movable grids, which weigh about 12.5 kg, have a length of 398 minutes and a width of 245 mm. Square holes of 60 mm x 12 nm are evenly distributed across all grids to allow the incinerator residue to fall during incineration and hot air ventilation. Fixed grids, which have a shape similar to that of movable grates, have a length of 398 mm and a width of 289 min. The working temperature of these grids is in the range of 700 to 950 ° C. These grids are tested in a garbage incinerator for 60 days and 1.5 years during which the incinerator is fed with a constant load of 200 tons of garbage per day. The thickness of the reaction layer after the test is shown in Table XIII. As Table XIII shows, grids
incinerators made from Fe-Mn-Al-C based alloys of the invention
meet the quality standard for steel incinerator grates
cast with high chromium content. If you add more chromium,
silicon or titanium, the performances of the grids are still acrues.

TABLE XII
Compositions of alloys based on Fe-Mn-Al-C of Example 8
Mn Al C Cr Si Ti Fe
t24 As in example 7
f25 29.53 9.5 1.31 3.0 0.8 - Complement
&num; 26 30.12 9.4, 24 5.96 0.7
&num; 27 29.45 10.2 ', 28 2.98 1.02 0.3
TABLE XIII
Thickness of the reaction layer of grids
in the incinerators
First Second
sampling sampling
N (2 months) (18 months)
JIS SCH-ll 150 tcm 240 m
24 70 m 125 m
* 25 25 trm 35 m
&num;; 26,320 m damaged
t27 18 m 26 Wm
EXAMPLE 9
A series of 15 kg ingots made of alloys based on
Fe-Mn-Al-C having the compositions shown in Table XIV by melting raw materials in a high frequency induction furnace and casting in ceramic molds. The bath raw materials are all in the form of electrolytically pure materials, with the exception of manganese which can be supplied by low carbon ferromanganese (as shown in Table XIV). These ingots are cut and the hardness of the cut faces is measured. In addition, a portion of the ingots are cut into tensile test pieces, as in Example 2. The values obtained for hardness and tensile strength are given in Table XV.

 As shown in Table XV, castings of the invention have higher tensile strength and toughness than commercial AISI series stainless steel, even in the form of an ingot. In working operations, the castings of the invention also have excellent toughness. For example, a suitable combination of a tungsten carbide drill head, a powerful drill and a drilling oil is required to drill the castings of the invention. In one test, a saw made of an alloy of. the JIS SK series for sawing the No. 31 alloy of this example and the saw is eroded after sawing only to a depth of 5 mm.

These phenomena reveal that the castings of the invention can hardly be worked on later.

TABLE XIV
Compositions of alloys based on Fe-Mn-Al-C of Example 9
N 'Mn Al C Cr Mo Nb. Neither BV Fe
t28 31.92 10.44 1.10 - - - - - - Supplement
f29 32.66 10.53 1.07 - 0.36 - - -
t30 32.81 10.53 0.98 - 0.72 - - - - I '
&num; 31 32.27 10.53 1.03 - 0.35 0.097 - -
&num; 32 32.99 10.67 1.03 - - 0.16 - - 0.298
t33 31,45fi11,45 1,10 - - - - -
t34 31.64 11.14 1.11 - - - 1.9 -
* 35 26.78 9.34 1.11 - - - - 0.026
f36 33.79 10.39 1.07 - - - - - 0.0284
&num; 37 28.43 10.45 1.17 - - - - -
&num; 38 26.52 10.52 1.12 2.76 - 0.26 1.8 -
&num;; 39 27.64 10.31 1.05 3.15 - 0.3 1.8 0.0167
&num; 40 * 28.18 9.89 0.96 3.06 - 0.29 1.9 - -
*: the manganese is brought by ferromanganese
TABLE XV
Hardness and tensile strength of the indicated alloys
in table XIV in the form of an ingot
Tensile strength
N 'Hardness (Rc) MPa (ksi)
&num; 28 32.9 + 0.9
29 31.2 + 0.8
&num; 30 30.5 t 0.7
&num; 31 30.4 + 1.0
&num; 32 31.4 t 0.4
&num; 33 30.4 + 1.0
&num; 34 30.1 + 2.3
35 37.5 + 0.8
&num; 36 35.7 t 0.9
&num; 37 36.2 + 2.1 793 t 21 (115 + 3)
&num; 38 38.0 t 1.4 552 t 34 (80 + 5)
&Num; 39 36.7 t 0.8 579 t 28 (84 + 4)
40 31.1 + 1.2 807 + 41 (117 t 6)
Although the invention has been described with respect to certain preferred examples and embodiments, the scope of the invention is limited only by the appended claims.

Claims (16)

 1. Fe-Mn-Al-Cr-Si-C casting part for application at high temperatures, characterized in that it consists essentially of 20 to 35% by weight of manganese, 5 to 13 in weight of aluminum, 0 to 5% by weight of chromium, 0 to 2.5% by weight of silicon and 0.5 to 1.4% by weight of carbon, the remainder being iron.  2. The Fe-Mn-Al-Cr-Si-C casting casting for the application at high temperatures according to claim 1, characterized in that it consists essentially of 20 to 32 wt.% Of manganese, 8 to 12% by weight of aluminum, 1 to 5% by weight of chromium, 0.5 to 2% by weight of silicon and 0.5 to 1.2% by weight of carbon, the balance being iron.  3. Fe-Mn-Al-Cr-Si-C casting casting for the application at high temperatures according to claim 1, characterized in that it consists essentially of 24 to 30% by weight of manganese, 8 to 11% by weight of aluminum, 2 to 4% by weight of chromium, 0.5 to 1.5% by weight of silicon and 0.5 to 1.1% by weight of carbon, the balance being iron .  4. Fe-Mn-Al-Cr-Si-C casting casting for the application at high temperatures according to claim 1, characterized in that it further comprises one or more auxiliary elements selected from the group consisting of boron, tungsten, molybdenum, niobium, tantalum, vanadium, nitrogen, copper, nickel, yttrium, scandium, hafnium and tantalum.  The Fe-Mn-Al-Cr-Si-C casting casting for high temperature application according to claim 1, further characterized by comprising from 50 to 200 ppm boron.  6. Fe-Mn-Al-Cr-Si-C casting casting for the application at high temperatures according to claim 1, characterized in that it further comprises 0.1 to 1.0 t by weight of tungsten.  7. Fe-Mn-Al-Cr-Si-C based casting for application at high temperatures according to claim 1, characterized in that it further comprises 0.1 to 2.1 t by weight of molybdenum.  8. Fe-Mn-Al-Cr-Si-C casting casting for the application at high temperatures according to claim 1, characterized in that it further comprises 0.1 to 1.0 t by weight of niobium.  9. Fe-Mn-Al-Cr-Si-C casting casting for the application at high temperatures according to claim 1, characterized in that it further comprises 0.1 to 2.0% by weight of titanium.  10. Fe-Mn-Al-Cr-Si-C casting casting for the application at high temperatures according to claim 1, characterized in that it further comprises 0.1 to 1.0. by weight of vanadium.  11. Fe-Mn-Al-Cr-Si-C casting casting for the application at high temperatures according to claim 1, characterized in that it further comprises 0.05 to 0.2 t by weight nitrogen.  12. Fe-Mn-Al-Cr-Si-C casting casting for the application at high temperatures according to claim 1, characterized in that it further comprises 0.5 to 1.5% by weight of copper.  13. Fe-Mn-Al-Cr-Si-C casting casting for the application at high temperatures according to claim 1, characterized in that it further comprises 0.5 to 2.5% by weight of nickel.  14. Fe-Mn-Al-Cr-Si-C casting casting for the application at high temperatures according to claim 1, characterized in that it further comprises 0.01 to 1.0% by weight yttrium.  15. Fe-Mn-Al-Cr-Si-C casting casting for the application at high temperatures according to claim 1, characterized in that it further comprises 0.01 to 1.0 wt. of scandium.  16. Casting composition based on Fe-Mn-Al-Cr-Si-C for application at high temperatures according to Claim 1, characterized in that it additionally comprises 0.01 to 0.5% by weight. hafnium.  '7. Fe-Mn-Al-Cr-Si-C casting for high temperature application according to claim 1, characterized in that it further comprises 0.01 to 0.8% by weight of tantalum .