DE2429023A1 - STEEL ALLOYS AND THE MOLDED BODIES MADE FROM IT - Google Patents

Description

ARICO STEEL CORPORATION
703 Curtis Street
Middletown, "Ohio /VcSt.A ,

Our sign; A 1704

Steel alloy and those made from it - moldings

The invention relates to a new Stahllegierunt ^ and the molded bodies produced therefrom; it relates in particular to a low-alloy chromium-aluminum-silicon-titanium steel for use as a substrate for aluminum or aluminum alloy coatings and the forged coated products made therefrom with good resistance to oxidation at elevated temperatures of up to about 925 ° C (1700 ⁰ P) and good resistance to attack by hydrocarbon combustion products at elevated temperature together with high strength.

Due to increasingly stringent requirements regarding Anti-pollution controls on motor vehicles is a demand for relatively cheap alloys

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which are resistant to oxidation at elevated temperatures, for use in automobile exhaust systems, such as catalytic converters, mufflers and similar molded bodies.

Carbon steel coated with aluminum has not proven entirely satisfactory for some high temperature applications. The automotive industry has replaced this with stainless steels such as Armco 409 (containing 0.05% carbon, 11% chromium, traces of aluminum, remainder HL cover, 0.5% titanium and remainder iron) and other stainless steels with 11% or more chromium . However, the cost of such steel is high, making it suitable for proposed use in automobile exhaust systems such as e.g. B. catalytic converters and the like, is inconvenient. In addition, the stainless steel, if \ ^T ell it a pretty good OxyJ-at ions best ändigke it owns at elevated temperature and good formability, no sufficient resistance to attack by molten salts and hydrocarbon combustion products at elevated temperature. It has been found that the application of an aluminum coating to such a steel results in a product with the desired properties, but that it increases the costs even further.

In US Patent 3,698,964 an iron-base alloy having good oxidation resistance at temperatures of about 700 to about 800 ⁰ C is described (1300-1475 ° F). The alloy described in this patent document contains up to 2% carbon, 1 to 5% chromium, 1 to 4 ° / o aluminum and / or 1 to 4% silicon, up to 1.5% manganese, b.is to 2% copper , a total of up to 0.20% nickel, molybdenum, vanadium and other alloy elements.

409883/0932

A combination of 2% chromium and 3 % aluminum or 3 % chromium and 2% silicon with preferably up to 0.2% manganese, not more than 0.5% copper, not more than Λ, ° / ο and in particular 0 is preferred .01 to 0.25% carbon is used.

The high carbon content of the steel according to this US patent leads to a brittle structure with very limited cold formability, poor welding properties and poor general mechanical properties. The molybdenum and vanadium which may be present have a negative effect on the oxidation resistance and they increase the costs. The adverse effect of molybdenum on resistance to oxidation is described in "Stainless and Heat Resisting Steels", Colombier and Hochmann, p. 330, St. Martin's Press, New York, NY (1968). In addition, amounts of copper, nickel and other austenite stabilizers in excess of the typical residual amounts of 0.2% each are undesirable, since they can lead to a phase change with a subsequent change in volume during heating and cooling. This change in volume leads to the formation of splinters after the cyclical heating and cooling.

US Pat. No. 2,835,669 describes a steel and a heat treatment of the same in which a microstructure with a resistance to stress corrosion cracking is formed in humid hydrogen sulfide atmospheres. The steel described in this patent contains 0.08 to 0.20% carbon, 0.60 to 5.0% chromium, 0.15 to 1.20% aluminum, 0.30 to 1.20% manganese, 0.10 up to 0.50% silicon, up to 0.50% molybdenum, up to 1.0% vanadium, up to 1.0 % titanium and the remainder iron. It is stated therein that a heat treatment at 740 to 780 ⁰ C, a second heat treatment at about 970 to about 1080 ⁰ C and a

4098 83/0932

followed by quenching with water and a tempering treatment results in kg / cm (95 ksi) at about 625 to about 67o C ⁰ to the desired microstructure and a specific tensile strength of at least 6.68 · 1Cr. Nothing is said in this patent specification about the resistance to oxidation at elevated temperatures, and it cannot be assumed that the composition given therein will produce a steel which has this property. In addition, the presence of molybdenum and vanadium is disadvantageous for the reasons given above.

In other patents, low-alloy steels are described, containing chromium, aluminum and / or silicon in varying amounts, e.g. B. in U.S. patents 3 4-31 101, 2 835 570 and 2 770 563.

In none of these patents is there a low alloy steel with a fully ferritic structure inside of the considered operating temperature range, which provides good oxidation resistance with increased Temperature combined with good resistance to attack by hydrocarbon combustion products, has good weldability and ductility and a relatively high strength. It exists hence there is still a great need for an inexpensive alloy with the above combination of properties for processing into coated, welded and forged products, such as space heaters, automobile exhaust systems, z. B. catalytic converters and mufflers and the same.

The invention relates to a low-alloy steel which is characterized in that it essentially consists from 0.01 to 0.13% carbon, 0.5 to 3% chromium,

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0.8 to 3 % aluminum, 0.4 to 1.5% silicon, 0.1 to 0.6% manganese, 0.1 to 1% titanium and the remainder of bison with incidental impurities. Molybdenum and vanadium are on

etv / a
a maximum content of / 0.05% each and the copper, nickel and other austenite stabilizers are limited to a maximum content of less than about 0.2% each. The steel according to the invention preferably contains chromium, aluminum, silicon and titanium in a total amount of less than about 5 % and gives in the form of a sheet a substrate for aluminum or aluminum alloy coatings, the coated sheet easily becoming forged shaped bodies (objects) is deformable with good resistance to oxidation at elevated temperature, good resistance to attack by hydrocarbon combustion products at elevated temperature, and relatively high retained strength at elevated temperature. The carbon, chromium, aluminum, silicon and titanium percentage ranges are critical and any deviation therefrom will result in the loss of one or more of the above properties. Control of the critically low levels of molybdenum, vanadium, copper, nickel and another austenite stabilizer is also essential.

Carbon is essential in an amount of at least 0.01% in order to achieve the required strength in the steel. More than 0.13% carbon cannot be tolerated because of its detrimental effect on weldability, ductility and general mechanical properties of the steel and because it is a strong austenite former. At least 0.5% chromium in combination with at least 0.8 % aluminum and 0.4 % silicon are required to achieve good resistance to oxidation. To keep costs to a minimum and processing ^ -

40 9 8 83 / 0-9-3.2

To avoid difficulties, a maximum chrome content of 5% should be adhered to. At least 0.8 % aluminum is required, not only to achieve good resistance to oxidation at elevated temperatures, but also to achieve adequate tensile strength. More than 3 % aluminum leads to a loss of ductility and processability. At least 0.4% silicon is essential as it cooperates with the chromium and aluminum and gives the steel the desired resistance to oxidation. However, a maximum of 1.5% silicon should be adhered to, since larger amounts also lead to a loss of deformability and processability.

Titanium is essential in an amount of at least 0.1%, UU. to give the steel good weldability. aside from that Excess titanium was found to be in excess of that required to stabilize the carbon the resistance to oxidation at elevated temperatures is improved. This excess can in view of the high cost of titanium and the relatively low residual content of the steel according to the invention be low in sulfur, nitrogen and oxygen. The titanium content is preferably 8 times the carbon content and at the The carbon contents considered here should not contain more than about 1% titanium. As it is known that niobium and / or zirconium in stainless steels generally have an equivalent effect, it is also in Within the scope of the present invention to completely or partially replace titanium with niobium and / or zirconium. A such replacement would be on a stoichiometric basis with a minimum weight ratio of niobium or zirconium to carbon of 8: 1, preferably at least about 10: 1. Niobium and / or zirconium would thus

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are within the range of 0.10 to 1.5% if Replace titanium.

Impurities in the ferritic stainless steels normal Eest contents can in the steel according to the invention be tolerated. In particular, a maximum content of about 0.03% sulfur and a maximum content of about 0.04% phosphorus does not detrimentally affect the properties of the steel. As explained above, molybdenum and vanadium are undesirable in the steel according to the invention and they are used in kept the practicable minimum values. Copper and nickel are at a maximum level for the reasons given above held by less than 0.2% each.

Although the desired new combination of properties in a steel is within the broad compositional ranges given above is achieved, optimal properties in a steel of the analysis given below (in% by weight) achieved:

Carbon chromium aluminum silicon manganese titanium

with the titanium content being about 8 times the carbon content and the remainder being iron with the exception of incidental ones Impurities.

To investigate the influence of the relative proportions of chromium, 'aluminum, silicon and titanium on the properties of steel have been a series of experimental, Batches manufactured and tested. For comparison purposes

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0.04 until 0.06% 1.7 tis 2.1% 1.7 until 2.0% 0.6 until 0.9 % 0.2 until 0.4% 0.1 until 0.6 %

Tests were also carried out on a mild carbon steel coated with aluminum and on aluminum alloys containing up to 10 % silicon and on an Armco type 409 stainless steel. The compositions of the experimental batches are given in Table I below.

Table I.

sample C. Cr Al Si - Mn Ti No. 0.048 1.0 <0.1 0.2 0.3 0.4 15th 0.033 0.5 1.7 0.8 0.4 0.4 41 * 0.033 1.0 1.7 0.7 0.4 0.4 42 * 0.034- 1.5 1.7 0.7 0.4 0.4 43 * 0.037 1.0 1.0 0.7 ■ 0.4 0.3 61 * 0.038 1.7 0.9 0.8 0.4 0.3 62 * 0.054- 2.5 1.9 0.4-7 0.21 0 85 0.073 2.0 1.92 0.81 0.32 ' 0.48 86 *

* Steels according to the invention, also containing Ο, Ί% Cu, 0.04 % Mo and 0.03% V.

The above materials were hot rolled at 1149 ° C (2100 ° F) from 2.54 cm by 7.62 cm (1 "by 3") billets to a thickness of 0.254 cm (0.1 "). The samples were annealed for 10 minutes at 927 ° C (1700 ⁰ F), descaled and cold rolled to a thickness of 0.127 cm (0.05 inch). It should be noted that annealing the hot-rolled material is an optional measure. In the cold-rolled-out samples, the tensile strengths were determined at this stage, while the rest of the cold rolled strip for 6 minutes at 871 ⁰ C.

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(1600 ⁰ F) was annealed and pickled. This material was tested for the other mechanical properties given in Table II below.

A consideration of the mechanical properties given in Table II below shows that the steels according to the invention have specific tensile strengths which are equivalent to those of comparable known alloys, but that they have better elongation. It is believed that this is due to the relatively low carbon contents (within the range of about 0.03 to about 0.07%). The yield strength and the tensile strength of the about 1 % aluminum containing leather

■ 7 p

alloys were about 0.35 x 10 kg / cm (5 ksi) or

X P

0.28 10 kg / cm (4-ksi) and they were less than the steels containing 2% aluminum. The comparison with the alloy with 1 % chromium (sample Wr. 15), which also has a low content of aluminum and silicon, is of greater importance. It should be noted that the yield strength of the alloy with 1 % chromium is about

■ 2 p

0.84- χ 10 ^ kg / cm (12 ksi) and the tensile strength by about 0.56 χ 10 kg / cm (8 ksi) were lower than in the inventive steels containing about 1.7 to about 2% aluminum a chromium content within the range of -0.5 to 2% . At the same time, the elongation values of these steels according to the invention would be approximately equivalent to those of sample No. % _ are in combination with at least about 1 »7% chromium and at least about 0.6% silicon.

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Table II 65) Specific draft %
strength in 5,
) 103 kg / cm ^ (ksi) (2 (53 .95) ; 1,' , 390; Stretching over
08 cm
inches) 35.5 Sample no. 0.2% stretch
strength in
10 ^ kg / cm ^ (ksi 40) 3.78 (61 .85) ; 1, , 400; 36.0 15th 1.65 (23. 65) 4.33 (62 , 15) ; 1, , 410; 34.0 41 * 2.48 (36. 80) 4.35 (62 .55) ; 1, , 400; 35.5 42 * 2.50 (35. 95) 4.38 (58 .25) ; 1, , 380; 37.0 43 * 2.51 (35. 45) 4.08 (58 .60) ; 1, , 395; 34.5 61 * 2.08 (29. 70) 4.10 (61 .25) ; - , 390 20.5 62 * 2.14 (30, 15) 4.28 (61 , 10) ; _ , 408 26.0 85 2.78 (39. B) 4.27. 09 (ο 86 * 2.61 (37. 041 (0 430) Sample no. hardness
(Rockwell 029 (0 O, 410) 15th 57.0 010 (0 O, 405) 41 * 73.0 oioCo O, 400) 42 * 73.0 118 (0 ο, 400) zi 3 * 73.0 - (0 ο, 440) 61 * 68.0 - (0 ο, -) 62 * 68.5 Olsen Cup test
Height-cm (inches) -) 85 73.0 0.991 86 * 73.0 1.016 1.041 1.016 0.965 1.003 0.991 1.039

steels according to the invention

The surface of the steel samples in Table I was ground in the cold-rolled, annealed and pickled state and a fully penetrating autogenous GTA weld was made along the longitudinal axis of the tape (strip) every sample performed. 180 ° bending and Olsen Cup test specimens cut out and on both the root side (attachment side) and the surface side

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tested under tension. These tests are given in Table III below. The data in Table III below show that optimum ductility in the welded state was obtained with about 1% aluminum and more than 1 % chromium. Better results were obtained with an aluminum content of "2% than with a chromium content of around 2 %.

The need for titanium to be present for good welding properties is demonstrated by sample Hr. 85 demonstrates where a poor Olsen Cup value was obtained. In addition, samples No. 85 and No. 86 were another Bending test at the welding point (in the following table III not specified) and it was found that sample no. 85 at 90 ° at the weld broke while sample # 86 underwent a 180 ° bend protruded at the weld point.

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Table III

Properties when welded

180 bending test

parallel to the weld

Root under tension Surface under tension Rehearsal Fr. diameter
0.305 cm
(0.12 inches) flat diameter
0.305 cm
(0.12 inches) flat 15th P, F P, F Ρ, Ρ Ρ, Ρ 41 * Ρ, Ρ Ρ, Ρ F, F F, F 42 * Ρ, Ρ Ρ, Ρ Ρ, Ρ F ₁ F 43 * Ρ, Ρ Ρ, Ρ Ρ, Ρ P, F 61 * Ρ, Ρ Ρ, Ρ γ, ρ - Ρ, Ρ 62 * Ρ, Ρ Ρ, Ρ Ρ, Ρ Ρ, Ρ 85 - Ρ, Ρ - Ρ, Ρ 86 * - Ρ, Ρ - Ρ, Ρ

Olsen Cup test
Height-cm (inches)

Sample No. Root under tension Surface under tension

15 0.79; 0.74 (0.310, 0.290) 0.86; 0.91

41 * 0.76; 0.76 (0.300, 0.300) 0.76; 0.78

42 * 0.57; 1.02 (0.225, 0.400) 0.89; 0.86

43 * 0.94; 0.94 (0.370, 0.370) 0.89; 0.99

61 * 1.03; 0.99 (0.405, 0.390) o.97; 1.02

62 * C, 97; 0.80 (0.380, 0.315) C, 94; 0.79

85 p, 17; - (0.665 -)

86 * 0.91; _ (0.360 -)

(0.340, 0.360)

(0.300, 0.305)

(0.350, 0.340)

(0.350, 0.390)

(0.380, 0.400)

(0.370, 0.310)

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P = passed
F = fail

steels according to the invention
duplicate tests in each state

The oxidation resistance tests were performed on the samples of Table I in the cold rolled, annealed, and pickled condition on both coated and uncoated samples. A pure aluminum coating was applied to the coated samples by hot dipping using a flux made from zirconium and / or titanium fluorides (for more details see US Patents 2,686,355 and 2,686,355). The coating weight was approximately 0.0152 g per cm (1/2 ounce per square foot) of the sheet (total coating weight on both surfaces). For comparison purposes, oxidation tests were also carried out on an unalloyed carbon steel coated with pure aluminum and with an aluminum alloy containing up to 10% silicon, with an uncoated stainless steel of Armco type 409 and with an uncoated commercial steel, the 5% chromium, 0.5% molybdenum, 0.06% carbon, 0.35. % Silicon, 0.4% manganese, remaining amounts of aluminum and Mickel and the remainder essentially iron. The initial tests lasted for 100 hours in still air at 871 ⁰ C (1600 ⁰ F) and 927 ° C (17QO ⁰ F). These tests are given in Table IV below. Since still air tests are not necessarily definitive, additional samples of coated and uncoated materials were cycled using a 25 minute inside and 5 minute outside oven cycle for a total of 130 up to 135 cycles. The results obtained are given in Table V below.

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Table IV

Oxidation Tests

100 hours in calm air

Sample no.

Weight increase
in mg / 6.45 c /
(inc Ir ^) at
871 ⁰ C (160O ⁰ F)

Weight increase in mg / 6.45 cm (incli) at 927 ° C (1700 ° F)

Al-coated carbon steel

Carbon steel coated with Al and 10% Si

uncoated stainless steel of the type 5% Cr and 0.5 % Mo. uncoated

15 uncoated

41 uncoated *

42 uncoated *

43 uncoated *

61 uncoated *

62 uncoated

85 uncoated

86 uncoated *

15 coated with Al

41 coated with Al *

42 coated with Al *

43 coated with Al *

61 coated with Al *

62 coated with Al * 86 coated with Al * 22.0
26.5

-11.5
(Loss from detonators)

716.0

7.6

6.7

4.1

12.8

6.3

18.1

2.1

15.8

12.5
16.2
13.6
14.8
16.6
6.1

48.0 105.0 357.0 408.0

2070.0

14.1

11.3

7.8

14.2

19.3

25.0

3.9

30.2

11.1

10.0

10.0

13.6

9.8

6.2

steels according to the invention 40988 3/0932

Table V

Oxidation Tests Cycle 25/5

Sample ur. uncoated conditions 135 Cyclen - 816 ⁰ C (1500 ⁰ F) Weight
increase iüp
mg / 6.45 cm
(inch ^) stainless steel
Type 409 uncoated * 135 135 Cyclen - 816 ⁰ C (1500 ⁰ F) 118 15th uncoated * 135 135 Cycles - 816 ° C (1500 ⁰ F) 666 41 uncoated 135 135 Cycles - * 816 ° C (1500 ^o F) 315 42 uncoated * 135 135 Cyclen - 816 ⁰ C (1500 ⁰ F) 270 43 uncoated 135 130 Cyclen - 816 ⁰ C (1500 ⁰ F) 250 61 uncoated 135 Cycles - 816 ° C (1500 ⁰ F). 382 62 uncoated 135 Cycles - 816 ° C (1500 ⁰ F) 376 85 132 Cycles - 816 ° C (15OO ° F) 198 86 132 Cyclen - 816 ⁰ C (1500 ⁰ F) 117 15th coated with Al135 Cycles - 816 ° C (1500 ⁰ F) 37.2 41 EXt Al dam. * Cyclen - 816 ⁰ C (1500 ⁰ F) 17.4 42 coated with Al * Cycles - 816 ° C (150O ⁰ F) 15.0 43 coated with Al * Cycles - 816 ° C (1500 ⁰ F) 12.3 61 ir.it Al besch. * Cyclen - 816 ⁰ C . (1500 ⁰ F) 14.3 62 coated with Al * Cycles - 871 ° C (1600 ⁰ F) 18.2 86 coated with Al * 10.2

steels according to the invention

The oxidation tests show that all of the invention
Steels exhibited good scaling resistance both in still air and in cyclic tests with no coatings. With aluminum coatings, the steels of the invention were those of Armco Type 409 in the uncoated condition
think. It should also be noted that the tests

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in still air with an aluminum or an aluminum alloy coated plain carbon steel base metal or substrate showed that this material with respect to the Oxydationsbestandigkeit at elevated temperatures in the range 816-927 ° C (15OO to 1700 ⁰ F) due to the bubble formation and deformation (Distortion) was totally unacceptable.

Optimal oxidation resistance is achieved in a steel according to the invention which contains about 2% chromium, about 2 % aluminum, about 1 % silicon and about 0.5 % titanium (the titanium content being about 8 times the carbon content). The sample Kr. 86 was with about this composition, the other samples in the coated state superior in spite of the fact that AEIE cyclic test temperatures has been subjected to the times higher than those of the other materials tested to 55 ° C (100 ^ü P). In the uncoated state it was at least equivalent to the uncoated stainless steel of type 4-09 and superior to the other uncoated samples.

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Claims (9)

~ Λ? ~. 2423023 claims' 1. Stainless steel alloy with good resistance to oxidation at elevated temperature, good weldability and good deformability, characterized in that it essentially consists of 0.01 to 0.13 wt.% carbon, 0.5 to 3 wt.% chromium, 0.8 to 3 wt.% aluminum, 0.4 to 1.5% by weight silicon, 0.1 to 0.6% manganese, 0.1 to 1% titanium and the remainder essentially of iron except for incidental impurities. 2 »Steel alloy according to claim 1, characterized in that that it consists essentially of 0.04 to 0.06% by weight Carbon, 1.7 to 2.1% by weight chromium, 1.7 to 2.0% by weight aluminum, 0.6 to 0.9% by weight silicon, 0.2 to 0.4% by weight Manganese, 0.1 to 0.6 wt.% Titanium, the titanium content being about 8 times the carbon content, and for The remainder is essentially iron with the exception of incidental impurities. 3. Steel alloy according to claim 1, characterized in that that they are at most about 0.05% by weight molybdenum, at most about 0.05% by weight vanadium and less than about 0.2% by weight Copper ο nt lasts .. 4 ·. Steel alloy according to claim 1 or 2, characterized in that that it contains 0.1 to 1.5% by weight of an element from the group consisting of niobium, zirconium and mixtures thereof, which at least partially replaces titanium. 5. Coated with aluminum or an aluminum alloy Object with good resistance to oxidation at elevated temperature, good resistance to 409 883/0932 Attack by hydrocarbon combustion products elevated temperature and high strength, characterized in that it comprises a substrate which essentially consists of 0.01 to 0.13 wt.% carbon, 0.5 to 3 wt.% chromium, 0.8 to 3 wt.% aluminum, ^ 0.4 up to 1.5 wt.% silicon, 0.1 to 0.6 x wt.% manganese, 0.1 Up to 1% by weight of titanium and the remainder essentially of bison with the exception of incidental impurities. 6. Coated article according to claim 5, characterized in that that it has a substrate which consists essentially of 0.04 to 0.06% by weight of carbon, 1.7 to 2.1% by weight of chromium, 1.7 to 2.0% by weight of aluminum, 0.6 to 0.9% by weight silicon, 0.2 to 0.4% by weight manganese, 0.1 to 0.6% by weight of titanium, the titanium content being about 8 times the carbon content, and the remainder im essentially of iron with the exception of incidental impurities. 7. Items for use at high temperatures, such as B. space heaters, automobile exhaust systems and the like _t having a coating of aluminum or an aluminum alloy containing up to 10 wt.% Silicon, the weight of the coating being about 0.0152 g / cm (1/2 ounce / ft) sheet, characterized that they have a cold-rolled and annealed sheet metal base metal which consists essentially of 0.01 to 0.1-3% by weight of carbon, 0.5 to 3% by weight of chromium, 0.8 "to 3% by weight of aluminum , 0.4 to 1.5 wt.% Silicon, 0.1 to 0.6 wt.% Manganese, 0.1 to 1 wt.% Titanium and the remainder essentially of iron with the exception of incidental impurities. 8. Objects according to claim 7, characterized in that 40988 3/0932 the sheet metal base essentially consists of 0.04 up to 0.06% by weight carbon ,. 1.7 to 2.1 wt% chromium, 1.7 . to 2.0% by weight of aluminum, 0.6 to 0.9% by weight of silicon, 0.2 to 0.4% by weight of manganese, 0.1 to 0.6% by weight of titanium, the Titanium content is about 8 times the carbon content , and the remainder essentially of iron with the exception of incidental impurities, the objects good resistance to oxidation at increased Temperature, good resistance to attack by hydrocarbon combustion products at elevated temperature and have high strength. 9. Objects according to claim 7, characterized in that they an element from the group niobium, zirö.onium and mixtures contain thereof, which at least partially replaces titanium in a stoichiometrically equivalent amount. 40988 3/093 2