AL 18CrCb™Ferritic Stainless Steel

Data are typical and should not be construed as maximum or minimum valuesfor specification or for final design. Data on any particular piece of material mayvary from those shown herein.

GENERAL PROPERTIESATI Allegheny Ludlum's AL 18CrCb™ stainless steel isa heat-resisting ferritic grade providing good oxidation andcorrosion resistance for applications like automotiveexhaust system components. Ferritic alloys are not in-herently strong at elevated temperatures, but columbiumadditions coupled with appropriate solution annealingmarkedly improve long-time creep-rupture strength proper-ties. AL 18CrCb alloy is dual stabilized with columbiumand titanium to provide good weld ductility and resistanceto intergranular corrosion in the weld heat affected zone.

AL 18CrCb alloy has been developed for the severe tubebending and forming operations typical in automotive ex-haust manifold fabrication. Tight control on carbon andnitrogen levels plus improved mill processing result inenhanced formability in terms of higher tube bendingspeeds and lower breakage or scrap rate.

STRUCTUREAL 18CrCb stainless steel is a ferritic alloy, i.e., the matrixhas a body-centered cubic (BCC) crystal structure.Angular carbonitrides of titanium and columbium arerandomly dispersed throughout the structure.

Excess columbium is taken into solid solution during hightemperature annealing and precipitates as very fineparticles of Laves phase (Fe2Cb) upon either slow coolingor upon holding at intermediate temperatures (1500-1700°F, 816-927°C). Strengthening by this dispersion isresponsible for improved elevated temperature strength.

™Trademark of ATI Properties, Inc.

Typical Chemical Analysis-Weight Percent

Element AL18CrCb™

Carbon 0.015Manganese 0.40Phosphorus 0.025Sulfur 0.002Silicon 0.50Chromium 18.0Nickel 0.20Titanium 0.20Columbium 0.60Nitrogen 0.020Aluminum 0.05Iron Balance

Data are typical and should not be construed as maximum or minimum valuesfor specification or for final design. Data on any particular piece of material mayvary from those shown herein.

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TYPICAL PHYSICAL PROPERTIES

ELEVATED TEMPERATUREMECHANICAL PROPERTIESShort Time Tensile Properties.Elevated temperature tensile properties are shownin the following table on the next page andcompared with AL 409HP™ and AL 439HP™alloys. At 1300°F (704°C) and above, the yieldand tensile strengths of AL 18CrCb and AL 439HPalloys are about double those of AL 409HP alloy.It is assumed that the solid solution strengtheningeffects of chromium in AL 439HP alloy andchromium plus columbium in AL 18CrCb alloyprovide the improved short time tensile propertiesabove 1200°F (649°C).

Density - lb/in3 0.278

(g/cm3) (7.711)

Electrical Resistivity microhm-cm at 58.7 68°F (20°C)

ROOM TEMPERATUREMECHANICAL PROPERTIES

Coefficient of Linear Thermal Expansion for AL 18CrCb™ AlloyTemperature Range

10-6cm/cm•••••°C 10-6in/in•••••°F°C °F

20-100 68- 212 9.2 5.120-300 68- 572 10.3 5.720-500 68- 932 10.6 5.920-700 68-1292 10.8 6.020-800 68-1472 11.3 6.320-900 68-1652 11.9 6.6

Typical Annealed Tensile PropertiesAL 18CrCb™ Alloy

Yield Strengthksi 48.0MPa 331

Tensile Strengthksi 74.0MPa 510

Elongation% in 2" 29.0

Hardness Rb 84.0

AL 18CrCb™ Alloy

Technical Data BLUE SHEET

Data are typical and should not be construed as maximum or minimum valuesfor specification or for final design. Data on any particular piece of material mayvary from those shown herein.

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STRESS RUPTURE PROPERTIESThe long duration of stress rupture and creep testingenables the Fe2Cb Laves phase to precipitate, and 100and 1,000 hour stress rupture properties reveal thebeneficial strengthening effects due to columbiumadditions to AL 18CrCb alloy.

Stress Rupture Properties

Elevated Temperature Tensile PropertiesYield Strength and Tensile Strength (ksi)

AL 409HPTM AL 439HPTM AL 18CrCb™ Alloy

Temp. Y.S. T.S. Y.S. T.S. Y.S. T.S.

RT 35.5 62.0 40.3 65.6 43.7 68.5200 31.3 56.7 37.0 64.2 40.3 65.0400 27.0 51.7 33.4 60.3 36.4 60.0600 26.5 50.2 27.5 57.6 35.6 58.7800 24.1 43.1 26.7 51.7 32.5 56.5900 22.0 34.0 24.1 43.5 28.2 54.1

1000 21.0 29.6 22.8 36.7 24.0 53.11100 14.5 20.4 17.2 25.3 24.8 48.81200 8.5 11.7 12.0 15.0 19.0 25.41300 6.3 8.3 6.7 9.3 12.1 18.91400 5.0 6.3 5.0 6.1 9.8 11.01500 3.2 4.2 4.0 5.2 6.4 7.31600 - - - - 3.7 4.4

0.1

1.0

10.0

100.0

1 10 100 1000

Time (h)

Str

ess (

ksi)

AL18CrCb™ 1500°FAL439HP™ 1500°FAL409HP™ 1500°FAL18CrCb™ 1200°FAL439HP™ 1200°FAL409HP™ 1200°F

Data are typical and should not be construed as maximum or minimum valuesfor specification or for final design. Data on any particular piece of material mayvary from those shown herein.

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0.01

0.1

1

10

100

1400 1500 1600 1700 1800 1900 2000

Test Temperature (°F)

We

igh

t C

ha

ng

e (

mg

/cm

2)

AL409HP™304AL439HP™AL18CrCb™

OXIDATION RESISTANCELaboratory cyclic and continuous oxidation data are usefulfor preliminary screening or ranking of candidate alloysfor potential consideration in various applications. Testsare conducted in still air and the environment is oxidizing.

AL 18CrCb alloy has very good resistance to progressivescaling in both continuous and cyclic oxidizing laboratorytest environments. Continuous 100 hour tests are con-ducted in still air and total weight gain measurements areused to determine oxidation and progressive scalingresistance in the temperature range of 1500°F (816°C) to1900°F (1038°C). These results are plotted in the followinggraph and compared with Type 304 and the AL 409HPand AL 439HP alloys.

100 Hour Oxidation in Still Air

Very few service environments are continuous operationsand more often temperatures are cycling. Thermal cyclinginduces differential thermal expansion and contraction ofthe developing oxide and metal substrate causing thescale to flake or spall. Ferritic stainless steels have rel-atively low coefficients of thermal expansion comparedto the austenitic stainless alloys like Types 304, 309 and310. The ferritic stainless steels are, therefore, moreresistant to progressive scaling at higher temperaturesunder cyclic conditions than the austenitic grades.

Cyclic oxidation data has been developed over atemperature range of 1400°F (760°C) to 2200°F (1204°C).These results are shown in the following figure. Testingis conducted in still air where the procedure is torepetitively resistance heat 0.002” (.05 mm) thick x 0.250”(6.35 mm) wide strip samples to temperature for twominutes and subsequently cool to room temperature fortwo minutes. Failure occurs when the 0.002” (.05 mm)thick strip oxidizes through and breaks.

Cyclic Oxidation in Still Air

0

500

1000

1500

2000

2500

1400 1600 1800 2000 2200 2400

Temperature (°F)

Cycle

s-t

o-F

ail

ure

Type 304AL409HP™

AL439HP™AL18CrCb™

Technical Data BLUE SHEET

Data are typical and should not be construed as maximum or minimum valuesfor specification or for final design. Data on any particular piece of material mayvary from those shown herein.

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Projecting service temperature limits for a stainless alloyfrom either continuous or cyclic oxidation test modesrequires arbitrarily selected failure criteria. In thecontinuous test mode, 1.5 mg/cm2 weight gain or moreis considered the point above which spalling andprogressing scaling is occurring. Under the pure cyclictest conditions, 2,000 cycles has been selected to projectmaximum temperature limits. Results of these ratingsystems are shown in the following bar graph. The bargraph indicates a range of useful temperature limits foreach alloy where the actual limit would depend on thenumber of thermal cycles during the life cycle and howrapidly the metal parts are heated and cooled. Thisinterpretation projects a useful temperature range limitof approximately 1650°F (899°C) to 1850°F (1010°C) forAL 18CrCb alloy. This compares to a lower useful tem-perature range projection of 1475°F (801°C) to 1550°F(843°C) for Type 409.

Projected Maximum Use Temperature inStill Air Oxidizing AtmospheresCORROSION RESISTANCE

AL 18CrCb alloy has generally good overall corrosionresistance typical for 18% chromium stainless steels.Like all ferritic stainless alloys, it is highly resistant tostress corrosion cracking. The following tables and figuresshow the relative corrosion resistance compared to Types409, 439 and 304 in a variety of laboratory tests.

GENERAL CORROSIONPROPERTIESWELDING

304439

409

AL18CrCb™

ALFA-II™

ALFA-I™

1200

1300

1400

1500

1600

1700

1800

1900

2000

2100

2200

2300

2400

Tem

pera

ture

(°F)

Continuous Service

Cyclic Service

Alloy

Corrosion Rates in Inches Per Month(Millimeters Per Annum )

Medium T-304T-409T-439

20% Acetic Acid .00000 .0003 .0101 .00001Boiling (0.000) (.09) (3.08) (.003)

65% Nitric Acid .01303 .002 .0274 .0007Boiling (3.97) (.61) (8.35) (.22)

20% Phos- phoric Acid .00005 .00002 .0017 .00002Boiling (.015) (.006) (.52) (.006)

10%SodiumBisulfate .0010 .00001 .2058 .005Boiling (.304) (.003) (62.72) (1.53)

10%Sulfamic .0012 .00008 .2712 .013Acid Boiling (.037) (.025) (82.66) (4.0)

10% Oxalic .14002 .18 .1510 .004Acid Boiling (42.68) (55.0) (46.0) (1.22)

AL 18CrCb™

5% Neutral Salt Spray Test-ASTM B117

Type Time of ExposureHours

%Surface Attack

AL 18CrCb™ 100 0409 100 1%304 100 0

Data are typical and should not be construed as maximum or minimum valuesfor specification or for final design. Data on any particular piece of material mayvary from those shown herein.

6

Visit our Website atwww.alleghenyludlum.com AL 18CrCb™ Stainless Steel

AL 18CrCb alloy is weldable using traditional tungsteninert gas and metal arc inert gas procedures commonlyused with stainless steel. When a filler wire is required,a matching composition electrode can be used withboth alloys to maintain compatible corrosion andoxidation resistance in the weld area. It is suggestedthat hydrogen not be mixed with the inert gas (unlesspost weld annealing is planned) because ferritic stainlesssteels are subject to hydrogen embrittlement.

Each alloy is dual stabilized with columbium andtitanium to provide a ferritic microstructure up to themelting temperature. This stabilization with Cb and Tigetters both the carbon and nitrogen. Neither alloy issusceptible to continuous intergranular precipitationof carbides that may lead to sensitization and inter-granular corrosion. Postweld heat treatment is, therefore,not required to restore weld and heat affected zonecorrosion resistance.

AL 18CrCb tubing has been commercially welded usingthe high frequency induction process. With either highfrequency or arc welding, post weld annealing is sug-gested when the tube is going to be subsequently bent,formed or shaped. Annealing restores annealed propertiesto the cold worked tube and provides better ductility forfurther fabrication.

The successful application of any alloy is dependent uponmany variables. It is important to consider these carefullybefore selecting any material including AL 18CrCb alloy.

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© Copyright, ATI Allegheny Ludlum 2006® Starburst ATI logo and AL-in-Star are Registered

Trademarks of ATI Properties, Inc.

Typical Stress Corrosion Cracking Test ResultsIn Boiling Solutions

Type 42% MgCl2 33% LiCl 26% NaClAL18CrCb™ R (216 hrs.) R (501 hrs.) R (1,005 hrs)

439 R (200 hrs.) R (200 hrs.) R (200 hrs.)409 R (1,000 hrs) F (500 hrs.) R (1,000 hrs)304L F (20 hrs.) F (96 hrs.) F (744 hrs.)

Key: F=Fails; R=Resistant; ( ) test discontinued atindicated hours.