US3905780A

US3905780A - Oxidation-resistant low alloy steel with Al coating

Info

Publication number: US3905780A
Application number: US373278A
Authority: US
Inventors: Joseph C Jasper; Marvin B Pierson
Original assignee: Armco Inc
Current assignee: Armco Inc
Priority date: 1973-06-25
Filing date: 1973-06-25
Publication date: 1975-09-16
Anticipated expiration: 1992-09-16
Also published as: DE2429023A1; FR2242480B1; BR7405155D0; JPS558579B2; IT1016158B; FR2242480A1; GB1471189A; NL7408256A; SE401690B; DE2429023B2; AR202484A1; AU6990974A; ES427610A1; ZA743709B; CA1041323A; JPS5037613A; IN142547B; BE816757A; SE7408277L

Abstract

A low alloy steel for use as a substrate for aluminum or aluminum alloy coatings, the steel containing from 0.01 percent to 0.13 percent carbon, from 0.5 percent to 3 percent chromium, from 0.8 percent to 3 percent aluminum, from 0.4 percent to 1.5 percent silicon, from 0.1 percent to 0.6 percent manganese, from 0.1 percent to 1 percent titanium and remainder substantially iron. The steel has good oxidation resistance at elevated temperature, good weldability and formability, thereby enhancing its utility for fabrication into a variety of wrought coated products.

Description

United States Patent [1 1 Jasper et al.

[4 1 Sept. 16, 1975 OXIDATION-RESISTANT LOW ALLOY STEEL WITH AL COATING Inventors: Joseph C. Jasper; Marvin B.

Pierson, both of Middletown, Ohio Assignee: Armco Steel Corporation,

Middletown, Ohio Filed: June 25, 1973 App]. No.: 373,278

U.S. Cl 29/1962; 75/124; 117/114 C Int. Cl. B321! 15/00 Field of Search 29/1962; 75/124;

References Cited UNITED STATES PATENTS 6/1955 Herzog 75/124 X 6/1958 Farrell 29/1962 5/1960 Brenner 29/1962 12/1960 BatZ 29/1962 3,059,326 10/1962 Jominy 29/1962 3,378,360 4/1968 McFarland.. 29/1962 3,698,964 10/1972 Caule 75/124 X Primary Examiner-L. Dewayne Rutledge Assistant Examiner-Arthur J. Steiner Attorney, Agent, or Firm-Melville, Strasser, Foster & Hoffman 5 7] ABSTRACT A low alloy steel for use as a substrate for aluminum or aluminum alloy coatings, the steel containing from 0.01 percent to 0.13 percent carbon, from 0.5 percent to 3 percent chromium, from 0.8 percent to 3 percent aluminum, from 0.4 percent to 1.5 percent silicon, from 0.1 percent to 0.6 percent manganese, from 0.1 percent to 1 percent titanium and remainder substantially iron. The steel has good oxidation resistance at elevated temperature, good weldability and formability, thereby'enhancing its utility for fabrication into a variety of wrought coated products.

5 Claims, No Drawings l OXIDATION-RESISTANT LOW ALLOY WITH AL COATING BACKGROUND THE INVENTION 1. Field of the Invention i This invention relates to a chromiumaluminum silicon-titanium steel of low alloy content for use as-fia substrate fo r aluminum or aluminum alloy coatings,

and wrought coated products thcreof having good resistance to oxidation at elevated temperatures up to about l,700 F, and resistance against attack by hydro-, carbon combustion products .at elevated tempcratpre, together with high strength. I

2. Description of the Prior Art 5,

Increasingly stringent requircmentsfor antipollution controls ,on motor vehicles has created a need for'rela v tively low cost alloys which will, be oxidation resistant at elevated temperatures, for use in automotive exhaust systems, such as catalytic converters, mufflers, and like articles,

Aluminum coated carbon steel has proved to be not completely satisfactoryfor some high temperature applications. The automotive industry has substituted stainless steels such as Armco 409(containing 0.05 percent carbon, l l percent chromium, traces of aluminum. residual nickel, 0.5 percent titanium and remainder iron) and other stainless steels containing 1 l percent or more chromium. The cost of such steel is high, thus making it undesirable for proposed use in automotive exhaust systems, such as catalytic converters, and

the like. Moreover. although this stainless steel has fair oxidation resistance at elevated temperature. and goodv lormability, it does not-adequately withstand-attack by molten salts and hydrocarbon combustion products at elevated temperature. The provision of an' aluminurn coating on such a steel has been found to result in a product having the desired properties, but this solution obviously adds even greater cost.

us. Pat. No. 3 ms %4, issued Oct. '17. 1972. 0 E.

J. Caule et al, discloses an iron base alloy with good ox idation resistance at temperatures of, about 700 110 800? C (about l,300 to l,475 F). The alloy of this patent contains up to 2 percent. carbon. l percent to 5. percent chromium, 1 percent to 4 percent aluminum, and/or l percent to 4 percent silicon. up to 1.5 percent manganese, up to 2 percent copper, up to 0.20'percent total of nickel, molybdenum, vanadium and other alloying elements. Preferably, a combination ofZ percent chromium and 3 percent aluminum, or3 percen't chromium and 2 percent siliconaare used, with manganese preferably up to.0.2 percent. coppernot more than 0.5 percent carbon not more than 1. percent and most preferably from 0.0l percent to 0.25 percent.

The high'carbon content of the steel of the Caule ct al patent results in a brittle structure having verylirn.

ited cold workability, poor welding characteristicsQand t1on products at elevated temperature, and relatively poor mechanical properties generally. The optional I presence of molybdenum-and,vanadium adverselyat fccts oxidation scale resistance, as well as adding to the- 1 cost. The harmful effect of molybdenum on-oxidationi nickel, and other austenite stabilizers in amounts greater than typical residual contents of about 02 percent each are undesirable since it can cause a phase.

change. with a consequent change, in volume.,on heat I 7 ing and cooling. Thisvolume change-results in spalling after cyclic heating and cooling: A

.U.S. Pat. No: 2,835,669, issued Mar. 4,.1958, toE. Herzog,. discloses a steel, andga heat treatment therefonwhereina microstructure, is produced having resistance to stress-corrosion cracking in wet hydrogen sulfideatmospheres. The steel of thispatent contains from 0.08 percent to 0.20 percent ,carbon, from 0.60 percent to 5.0 percent chromium, from 0.15 percentto 1.20 percent aluminum, from 0.30 percent to I20 percent manganese, from 0. l0 percent to 0.5 0 per cent silico n, to 0.50 p ercerit i nolybdentirn up to 1.0 percent vanadium, tol.0 percent titanium and remainder ironl heat treatment at 74 to 780;: C, a second heat treatment at. about 70 followed by a waterquench and a tempering treatment at about 625 to 670C. ar'stat ed it'oresult in ejdesi'red'hiicrostructure and an ultimate tensil e strength of at least 95 ksi. Oxidation resistance t e levated temperature is not contemplated in this paterit, and the composition would not inherently produce a steel having this prop-' e'rty. Moreover. the presence of'molybdh u'mand va' nadium'is deleteridus forreasons set forth above.

Other patents disclosing low alloy steels 'containing chromium, aluminum, and/orsiliconin varying amounts include U.S"Pat."-Nos. 3,431,101: 2,835,570; and 2,770,563. Y 1 wNone of the 'above'patents discloses a low alloy steel having a completely ferritic,struc-ture within' the contemplated operating temperature range and exhibiting" in combination-good oxidation resistance at elevated temperature, good resistance against attack by hydrocarbon combustion products, good weldability and formability and relatively high strength. Hence, there still exists a great need for a low-cost alloy having the The present invention provides a low alloy steel containing chromium, aluminum, silicon and titanium (preferably with a total alloy content of less than about 5 percent) which provides in sheet form a substrate for aluminum or aluminum alloy coatings, coated sheet being readily formable into w rt iugh t articles having good oxidation resistance at elevated temperature, 7

good resistance against attack by hydrocarbon combushighretained strength at elevated temperature. In its broad composition rangesfthej "steel of the invention consists essentially of fromabbtitttdl percent to about 0. l 3 percent carbonl from about'05percent to about L 3 percent chromium;'fronfabout- 0.8 percent to about 3 percent aluminum, from about 0.4 percent to about 1 .5pereent silicon; from about 0. l 'p'ercent to about 0.6 percent manganesejfrom about 0.1 percent to about I percent titanium. and remainderiron except for incidental impurities.,Molybde'numand vanadium are restricted to a maximum of about 0.05 percent each, and copper, nickel and other austenite stabilizers to less than about'0LZ percent each. l

The carbon, chromium, aluminum; silicon and titanium percentage pranges are critical and departure therefrom results in loss of one or more of the above properties. Control of the critically low molybdenum,

vanadium. copper. nickel and other austenitestabilizer contents is also essential.

Carbon is essential in an amount of at least about 0.0l percent in order to provide the necessary strength in the steel. More than about 0.13 percent carbon cannot be tolerated because of its adverse effect upon the weldability, formability and and general mechanical properties of the steel. and because it is a strong austenite former.

At least 0.5 percent chromium in combination with at least about 0.8 percent aluminum and about 0.4 percent silicon is necessary in order to provide good oxidation resistance. A maximum of 3 percent chromium should be observed in order to minimize cost and avoid processing difficulties.

At least about 0.8 percent aluminum is necessary not onlyfor oxidation resistance at elevated temperature but also to provide adequate tensile strength. More than 3 percent aluminum results in a loss of formability and workability.

At least about 0.4 percent silicon is essential since it co-operates with the chromium and aluminum to impart oxidation resistance. However. a maximum of about l.5 percent silicon should be observed since amounts in excess thereof also result in loss of formability and workability.

Titanium is essential in an amount of at least about 0.1 percent in order to impart good weldability to the steel. Moreover. excess titanium over that needed to stabilize carbon has been found to improve the oxidation resistance at elevated temperature. This excess can be slight in view of the high cost of titanium and ofthe relatively low residual sulfur. nitrogen and oxygen contents of the steel of the invention. Preferably the titanium content is 8 times the carbon content. and a maximum of about 1 percent titanium should thus be observed at the carbon levels contemplated herein. Since it is known that eolumbium and/or zirconium generally function in an equivalent manner in stainless steels. it is considered within the scope of the invention to substitute eolumbium and/or zirconium in whole or in part for titanium. Such substitution would be on a stoiehio metric basis. with a minimum weight ratio of columbium or zirconium to carbon of 8: l. preferably at least about 10:]. Columbium and/or zirconium would thus range from about 0. 10 percent to about 1.5 percent if substituted for titanium.

Impurities at residual levels normal for ferritic stainless steels ean be tolerated in the steel of the invention. More specifically, a maximum of about 0.03 percent sulfur and a maximum of about 0.04 percent phosphorus do not adversely affect the properties of the steel. Molybdenum and vanadium are undesirable in the steel of the invention as explained above, and are maintained at the minimum practicable levels. Copper and nickel are maintained at a maximum of less than 0.2

percent each for reasons set forth above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS While the desirable novel combination of properties is achieved in a steel having the broad composition ranges hereinabove set forth. optimum properties are obtained in a steel having the following preferred analysis by weight percent:

' Carbon about 0 04 to about 0.06%

('hromium I about 1.7 to about 2.] '71 Aluminum about l.7 to about 2.0 '71 Silicon about 0.6 to about 0.9 71 Manganese about 0.2 to about 0.4 '7! Titanium about 0.l to about 0.6 71

TABLE I Sample Code C (r Al Si Mn Ti l5 0.04X l.0 0.l 0.2 0.3 0.4 4l* 0.033 .5 L7 0.8 0.4 0.4 42* 0.033 l.0 L7 0.7 04 0.4 43* 0.034 l.5 l.7 0.7 0.4 0.4 (1|* 0.037 1.0 l.0 0.7 0.4 0.3 62* 0.038 L7 .9 0.8 0.4 0.3 XS 0.054 2.5 L) 0.47 0.2] 0 86* 0.073 2.0 1.92 0.8] 0.32 0.44%

*Steels ol' the invention also containing 0. I; Cu, 0.04; Mo, and 0.039; V.

The above materials were hot rolled from 2,100" F (l.l4'-) C) from 1 inch by 3 inch ingots to 0.1 inch thickness. Samples were annealed at l,700 F (927 C) for 10 minutes, descaled and cold rolled to 0.05 inch thickness. It should be recognized that annealing the hot rolled material is optional. Tensile strengths were determined on the cold rolled samples at this stage while the remainder of the cold rolled strip was annealed at l.600 F (87l C) for 6 minutes and pickled. This material was tested for the remaining mechanical properties reported below in Table I].

A consideration of the mechanical properties re-' ported in Table I] indicates that the steels of the invention have ultimate tensile strengths equivalent to those of'comparable prior art alloys but have improved elongation. This is believed to result from the relatively low carbon contents (ranging from about 0.03 percent to about 0.07 percent). The yield strength and tensile strengths of the alloys containing about 1 percent aluminum were about 5 ksi and 4ksi, respectively. less than those containing 2 percent aluminum. Of greater significance is the comparison with the 1 percent chromium alloy (Sample Code 15) also having low aluminum and silicon contents. It will be noted that the yield strength of the 1 percent chromium alloy was about 12 ksi lower and the tensile strength about 8 ksi lower than the steels of the invention containing from about 1.7 percent to about 2 percent aluminum with chromium ranging from 0.5 percent to 2 percent. At the same time the elongation values of these steels of the invention were about equivalent to that of Sample Code l5. For an optimum combination of mechanical properties. it is thus apparent that the carbon content should not exceed about 0.06 percent, that aluminum should range from about 1.7 to about 2 percent in combination with at least about 1.7 percent chromium and at least about 0.6 percent silicon.

TABLE ll ()lscn Sample 02% YS L'TS 'i llong. Hardness (up Test (ode lksi) (ksi) in I" (Rockwell B) Height-Inches 23.65 53.95 35.5 57.0 .300. .430 4| 30.40 61.85 36.0 73.0 .400. .410 42* 34.0 73.0 .40). v405 43" 0 1.5 731) 400. .400 ()l 37.0 (18.0 .380. .400 62 5H.b0 3-4.5 08.5 .395. .440 R5 6| .5 20.5 73.0 .390 36* (\l H) 20.0 73.0 .403

*Steels ol' the pre ent in\ cntion Samples of the steels ofTable l in the cold rolled. annealed and pickled condition were surface ground. and a full penetration autogenous GTA weld was run down the longitudinal axis of the strip of each sample. 180 bend and Olsen cup test specimens were cut from the s mens. For the coated specimens. a pure aluminum coating Was applied by hot-dipping using a Lundin flux. details of which are disclosed in U.S. Pat. Nos. 2.686.354 and 2.686.355. Coating weight was about ounce per square foot of sheet (total coating weight on samples and tested with both root and face Side in tenboth surfaces). For purposes of comparison. oxidation sion. These tests are reported in Table III. tests were also run on plain carbon steel coated with From the data in Table II] it is evident that optimum pure aluminum and with aluminum alloy containing up as-welded ductility is exhibited with about 1 percent to 10 percent silicon. uncoated Armco Type 409 stainaluminum and chromium in excess of 1 percent. At the less steel. and an uncoated commercial alloy containing 2 percent aluminum level better results apparently are 5 percent chromium. 0.5 percent molybdenum. 0.06 obtained with chromium at about 2 percent. percent carbon. 0.35 percent silicon. 0.4 percent man- The necessity for the presence of titanium for good ganese. residual aluminum and nickel. and balance subweld properties is demonstrated by Sample Code 85. stantially iron. The initial tests comprised 100 hours in wherein a poor Olsen cup value was obtained. In addistill air at [600 F. and l700 F. respectively. These tion. Sample Codes and 86 were subjected to a fur- 3 tests are reported in Table IV below.

ther bend test across the weld (not reported in Table III). and it was found that Sample Code 8. cracked at across the weld. whereas Sample Code 86 passed flat across the weld.

TABLE III Since still air tests are not necessarily definitive. further specimens of coated and. uncoated materials were subjected to cyclic testing. using a cycle of 25 minutes As-Wcldcd Properties |80 Bend 'I'est Parallel to Weld Sample (ode ()lscn (up Test Height-ditches .12 diam. Flat .lZ diam. Flat Root in Tension Face in 'l'cnsion 15 F P.F P.P P.P .3 I0, .290 340. .360 41 PP P.P F1" F.F .300. .300 .300. .305 42 P.P P.P PJ F1" .225. .400 .350. v3-10 43* P.P P.P P.P P.F .370. .370 .350. .390 \l P.P PP P.P P.P .405. .390 .330. .400 62* PP PP PP P.P 3N0. .3l5 .370. .3l0 x5 P P P P .065 1 86* PP PP Rho P Pass l" Fail Steels ol' the Invention Duplicate tests in each condition Oxidation resistance tests were conducted on the samples of Table I in the cold rolled. annealed and pickled condition. both on coated and uncoated speciin and 5 minutes out of the furnace for a total of l30l 35 cycles. These results are reported in Table V below.

TABLE IV Oxidation lcsts I00 Hours Still Air TAB LE 1V Continued Oxidation lcsls 100 Hours Still Air moo" F 1700" F Sample \Ncight Increase VVeiglil Increase (ode mg/in" nig/in -11 uneoated 7.6 14.1 42 uncozilcd (1.7 1 1.3 -13 uncoated 4.1 7.3 o1 uneoatcd 12.8 14.2 (\2 uncoatetl (v.3 19.3 35 uncoatctl 154.1 25.0 so uncozitcd 2.1 3.9 15 Al coated 15.8 30.2 41 Al coated 12.5 11.] -12 Al coated m2 10.0 43 Al coated 1.1.0 10.0 b] Al coated 14.8 13.6 (12 Al coated 10.6 0,8 1 so Al coated 6.1 6.2

TA V ature. good formability, and high strength, said article consisting of an outer layer applied by hot dip coating Oxidation Tests chosen from the class consisting of aluminum, and alu- (yl'llc /5 minum alloys. and a ferritic substrate consisting essensumplc Weighl mum. tially of, by weight percent, from about 0.01 percent to (nat- Conditions m /in" 25 about 0.13 percent carbon, from about 0.5 percent to about 3 percent chromium, from about 0.8 percent to Type 4W mink Us Cycles 500,: HS about 3 percent alum num, from about 0.4 percent to 15 KliiLUlllCkl I500F one about 1.5 percent silicon, from about 0.1 percent to 41 UI'ILOUICL: about 0.6 percent manganese, from about 0.1 percent 42 uncoatet 1 1 i I I 43 Hunted 135 Ll ISUUOF to about 1 percent titanium, and remainder iron except (11 uncoated 135 c \cli:s A- 1500F 382 for lncldental lmpuntlesunwllwd 135 Cycles 150ml 2. An article in sheet form having good oxidation re- 1 'Y D k 3 11 55 3 ,23, sistance at elevated temperature, good resistance 1 CR1 C t 15 Al coated 1J5 tit-act 1500F 371 against attack by hydrocarbon combustion products at 41 Al wills 135 QCICS ZE elevated temperature, good formability, good weldabil- :2 2: by: ity. and high strength, said article consisting of an outer ciiet (I M mined '35 titles 150m]; 143 layer applied by hot dip coating chosen from the class (2 Al CUZIlCLl I35 C \L'lt, 1500F 1&2 consisting of aluminum, and aluminum alloys, and a I v i v v v o '7 territic substrate consisting essentially of, by weight percent, from about 0.04 percent to about 0.06 percent Th d d th t n th t f h carbon, from about 1.7 percent to about 2.1 percent l that "l 5 e6 e chromium, from about 1.7 percent to about 2.0 percent Present cxhlbltcd gold Sculmg reslsmnce aluminum,from about 0.6 percent to about 0.9 percent both in still all and Cycllc tests Wlthout Coatmgs wlth silicon, from about 0.2 percent to about 0.4 percent aluminum coatings. the steels of the invention are supemanganese f uhuut 0 1 pfirccm to about rim to Arms yp 409 uncoilted Condltloll It 45 cent titanium, with the titanium content being about 8 should further be noted that the still air tests on alumi times h carbon content, and remainder iron, except num and aluminum alloy coated plain carbon steel base f i id t l i iti metal or substrate showed this material to be com- 3. Articles for high temperature applications such as pletcly unacceptable for oxidation resistance at elespace heaters, automotive exhaust systems. and the vated temperatures of the order of 1,500 l,700 F, like. said articles comprising an outer hot dip coating because f blistering d warpugc chosen from the class consisting of aluminum, and alu- Optimum oxidation resistance is achieved in a steel mlnum y the Wclght of 51nd Colltmg bemg 31mm 1/2 of the invention containing about 2 percent chromium. luncc b i l foot of Sheet and a f l redued und about 2 percent aluminum. about percent Silicon and anncaled territic sheet metal base consisting essentially about 0.5 percent titanium (with titanium about 8 55 2 1 Wught P B 15 2 P 2 times the carbon content). Sample Code 86. having this puccm out to out v 3 percent chromium, from about 0.8 percent to about approximate analysis, was superior to other samples in I 3 percent aluminum, from about 0.4 percent to about the coated condition despite the fact that it was sub- 00F d h 1.5 percent silicon, from about 0.1 percent to about 0.6 Jcued to i test mmpulmreb egmcs lg er percent manganese, from about 0.1 percent to about 1 than el l the other mammals In the uncoltcd percent titanium, and remainder iron except for incicondition it was at least equivalent to other uncoated dental impuriticg p v 4. The articles claimed in claim 3, wherein said sheet The embodiments f thc lnvcntlon Whlch cxclu' metal base consists essentially of, by weight percent, P y or Pnvllcgc 1S Clmmed defined from about 0.04 percent to about 0.06 percent carbon, lows: from about 1.7 percent to about 2.1 percent chromium,

1. An article having good oxidation resistance at elevated temperature, good resistance against attack by hydrocarbon combustion products at elevated temperlroni about 1.7 percent to about 2.0 percent aluminum, from about 0.6 percent to about 0.9 percent silicon, from about 0.2 percent to about 0.4 percent manga- 5. The articles claimed in claim 3, wherein 2m element chosen from the class consisting of columbium. zirconium, and mixtures thereof is substituted at least partially for titanium in a stoichiometrically equivalent amount.

Claims

1. AN ARTICLE HAVING GOOD OXIDATION RESISTANCE AT ELEVATED TEMPERATURE, GOOD RESISTANCE AGAINST ATTACK BY HYDROCARBON COMBUSTION PRODUCTS AT ELEVATED TEMPERATURE, GOOD FORMABILITY, AND HIGH STRENGTH, SAID ARTICLE CONSISTING OF AN OUTER LAYER APPLIED BY HOT DIP COATING CHOSEN FROM THE CLASS CONSISTING OF ALUMINUM, AND ALUMINUM ALLOYS, AND A FERRIC SUBSTRATE CONSISTING ESSENTIALLY OF, BY WEIGHT PERCENT, FROM ABOUT 0.01 PERCENT TO ABOUT 0.13 PERCENT CARBON, FROM ABOUT 0.5 PERCENT TO ABOUT 3 PERCENT CHROMIUM, FROM ABOUT 0.8 PERCENT TO ABOUT 3 PERCENT ALUMINUM, FROM ABOUT 0.4 PERCENT TO ABOUT 1.5 PERCENT SILICON, FROM ABOUT 0.1 PERCENT TO ABOUT 0.6 PERCENT MAGANESE, FROM ABOUT 0.1 PERCENT TO ABOUT 1 PERCENT TITANIUM, AND REMAINDER IRON EXCEPT FOR INCIDENTIAL IMPURITIES

2. An article in sheet form having good oxidatIon resistance at elevated temperature, good resistance against attack by hydrocarbon combustion products at elevated temperature, good formability, good weldability, and high strength, said article consisting of an outer layer applied by hot dip coating chosen from the class consisting of aluminum, and aluminum alloys, and a ferritic substrate consisting essentially of, by weight percent, from about 0.04 percent to about 0.06 percent carbon, from about 1.7 percent to about 2.1 percent chromium, from about 1.7 percent to about 2.0 percent aluminum, from about 0.6 percent to about 0.9 percent silicon, from about 0.2 percent to about 0.4 percent manganese, from about 0.1 percent to about 0.6 percent titanium, with the titanium content being about 8 times the carbon content, and remainder iron, except for incidental impurities.

3. Articles for high temperature applications such as space heaters, automotive exhaust systems, and the like, said articles comprising an outer hot dip coating chosen from the class consisting of aluminum, and aluminum alloys, the weight of said coating being about 1/2 ounce per square foot of sheet, and a cold reduced and annealed ferritic sheet metal base consisting essentially of, by weight percent, from about 0.01 percent to about 0.13 percent carbon, from about 0.5 percent to about 3 percent chromium, from about 0.8 percent to about 3 percent aluminum, from about 0.4 percent to about 1.5 percent silicon, from about 0.1 percent to about 0.6 percent manganese, from about 0.1 percent to about 1 percent titanium, and remainder iron except for incidental impurities.

4. The articles claimed in claim 3, wherein said sheet metal base consists essentially of, by weight percent, from about 0.04 percent to about 0.06 percent carbon, from about 1.7 percent to about 2.1 percent chromium, from about 1.7 percent to about 2.0 percent aluminum, from about 0.6 percent to about 0.9 percent silicon, from about 0.2 percent to about 0.4 percent manganese, from about 0.1 percent to about 0.6 percent titanium, with the titanium content being about 8 times the carbon content, and remainder iron except for incidental impurities, said articles having good oxidation resistance at elevated temperature, good formability, good weldability, good resistance against attack by hydrocarbon combustion products at elevated temperature, and high strength.

5. The articles claimed in claim 3, wherein an element chosen from the class consisting of columbium, zirconium, and mixtures thereof is substituted at least partially for titanium in a stoichiometrically equivalent amount.