THERMAK 17 STAINLESS STEEL

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1 THERMAK 17 STAINLESS STEEL P R O D U C T D ATA B U L L E T I N High Temperature Strength Superior Oxidation Resistance Excellent Thermal Fatigue Resistance Equiaxed Microstructure Applications Potential THERMAK 17 Stainless Steel has excellent high temperature strength, thermal fatigue and oxidation resistance. It s improved high strength will facilitate vehicle lightweighting efforts. It is designed for demanding hot-end automotive exhaust applications where intermediate Chrome (Cr) and other high Cr ferritic grades may not be sufficient or where down gauging for light weighting is desired. It also may be appropriate for applications where Type 444 is currently supplied. Product uses in hot-end exhaust system components: manifolds, converters, maniverters and stamped flanges. T H E R M A K 1 7 S TA I N L E S S S T E E L

2 TABLE OF CONTENTS Product Description... 1 Physical Properties... 1 Mechanical Properties... 2 Elevated Temperature Properties... 2 Formability... 4 Corrosion Resistance... 5 Oxidation Resistance... 6 Weldability... 7

3 PRODUCT DESCRIPTION THERMAK 17 Stainless Steel is a ferritic stainless steel that is stabilized with both titanium and niobium (columbium). When given a high temperature final solution anneal, the alloy exhibits dramatic creep resistance. The dual stabilization prevents carbide sensitization exposure and makes the alloy thermally non-hardenable. COMPOSITION (wt %) Carbon (C).2 max. Manganese (Mn) 1.2 max. Phosphorus (P).5 max. Sulfur (S).1 max. Silicon (Si) Chromium (Cr) Nickel (Ni).5 max. Nitrogen (N).2 max. Copper (Cu) Titanium (Ti).5 max. Niobium (Nb).5 max. AVAILABLE FORMS AK Steel produces THERMAK 17 Stainless Steel coiled, in thicknesses from mm (.2.1 in.) and widths up to and including 1175 mm (48 in.). PHYSICAL PROPERTIES Density, g/cm 3 (lbs./in. 3 ) 7.69 (.278) Specific Heat, kj/kg K (BTU/lbs./ F) 1 C ( F).454 (.18) COEFFICIENT OF THERMAL EXPANSION 14. Average CET (1-6 / C) Temperature, C 1

4 MECHANICAL PROPERTIES TYPICAL ROOM TEMPERATURE MECHANICAL PROPERTIES.2%YS MPa (ksi.) UTS MPa (ksi.) Elongation % in 5.8 mm (2") Rockwell Hardness 469 (68) 586 (85) 3 B86 ELEVATED TEMPERATURE PROPERTIES SHORT TIME ELEVATED TEMPERATURE MECHANICAL PROPERITES 3.2% Offset Yield Strength, MPa Cr-Cb TM Type Temperature, C 4 35 Ultimate Tensile Strength, MPa Cr-Cb Type Temperature, C 2

5 ELEVATED TEMPERATURE PROPERTIES HIGH TEMPERATURE CREEP RESISTANCE Sag resistance testing is a simple, common measure of a materials resistance to creep. In testing, the sag resistance of THERMAK 17 Stainless Steel was found to be superior to 18 Cr-Cb and Type 444 in the temperature range of 7 93 C. It was equivalent to 15 Cr-Cb over the same temperature range. DEFLECTION AFTER 144 HOUR TEST DURATION Test Temperature C Condition* (mm) 15 Cr-Cb (mm) 18 Cr-Cb (mm) Type 444 (mm) As-annealed C/96 hr As-annealed C/96 hr As-annealed C/96 hr *As-annealed tested in duplicate, 74 C aged single samples. THERMAL FATIGUE RESISTANCE Preliminary testing shows THERMAK 17 Stainless Steel to have 2 3% improved fatigue resistance over intermediate Chrome (Cr) products currently used in automotive, hot end exhaust applications. Thermal fatigue life was determined by the cycle number when the tensile stress at 2 C reaches to 7% of the tensile stress at the first thermal fatigue cycle at 2 C. Relative Strain THERMAL MECHANICAL FATIGUE CYCLE TESTING x Stress Free Thermal Expansion Strain Cycle Thermal Cycles of 2 83 C -x Time, sec. v First Thermal Fatigue Cycle Controlled Strain with Restraint Ration of (x-y)/x=.4 -v Temperature, C Thermal Fatigue Life, Cycles THERMAL FATIGUE LIFE 3% Better Life 15 Cr-Cb Reduce gauge, save weight while maintaining the same durability 3

6 FORMABILITY THERMAK 17 Stainless Steel is readily drawn and formed. The ULTRA FORM technology enhances formability and improves the consistency from one coil to another. FORMING LIMIT CURVE THERMAK 17 STAINLESS STEEL COIL, 2 mm THICK Determined Using CamSys Localized Nodal Strain Measurement Method 2.54 mm Square Grid Pattern. 8 Mass Engineering Strain (%) Longitudinal to Sheet R.D. Transverse to Sheet R.D. Thinning Minor Engineering Strain (%) Orientation to Sheet R.D. Property L D T Tensile/Hardness Test (ASTM E8, E694, E18, A37).2%YS (MPa) UTS (MPa) % El. in 5.8 mm (man l) n-value (1%-Ult.) Strength Coeff. (MPa) HRB (HRA) 9 (55.5) ASTM Grain Size 5. Stretch r (plastic strain ratio) at 18% (ASTM E517) r-value r m 1.9 delta r.34 delta r (Max Min).62 Ridging No. 1. Olsen Cup Height (mm) 11.4 LDR 2.1 4

7 CORROSION RESISTANCE SALT CYCLE TEST THERMAK 17 Stainless Steel shows improved oxidation resistance and oxide adherence when compared to other 17% chromium ferritics. The high silicon and manganese, copper added alloy reduces spalling when exposed to cyclic high temperature salt conditions creating a barrier of oxide that provides protection to the steel substrate. The dual stabilized alloy resists intergranular corrosion when welded and provides comparable corrosion resistance to equivalent alloys in acidic, high sulfate and lower temperature, cyclic salt environments commonly found in automotive exhaust applications. Cycle Repeats every 7 days Heat treat 1 hr. at 343 C (65 F) (Day 1) 15 minute 5% sodium chloride immersion (Day 1 Day 5) Ambient Dry 1 hour 45 minutes (Day 1 Day 5) Place in humidity chamber 6 C (14 F)/85% RH Balance of the 24 hour period and Day 6 & Day 7 Pit Depths (um) SALT CYCLE Solution Concentration: 5% Sodium Chloride Heat Treatment: 343 C (65 F) 15 Cr-Cb Days Cycle Repeats every 5 days MUFFLER CONDENSATE TEST Heat treat 1 hr. at 5 C (932 F) Humidity exposure for 6 hrs. at 6 C (14 F)/85% RH 16 hrs. exposed to boiling test solution (boil solution to dryness) Balance of week: Continuous exposure to humidity at 6 C (14 F)/85% RH Samples are removed at 2, 4 and 6 week intervals Mass Loss (mg/cm 2 /yr.) Test Solution: 5 ppm SO ppm Cl 1 ppm NO 3 1 ppm Formic Acid MUFFLER CONDENSATE Heat Treatment: 5 C (932 F) 15 Cr-Cb Type 439 Solution ph is adjusted to using sulfuric acid by adding approximately 3 4 ppm SO 4 2- to the test solution 5

8 CORROSION RESISTANCE (cont.) Cycle Repeats 4 times in 8 hours HOT SALT TEST Heat treat 9 min. at 677 C (125 F) One minute cold water quench Five minute soak in 5% sodium chloride 16 hours in humidity chamber 6 C/(14 F)/85% RH Measurements collected after ten cycles OXIDATION RESISTANCE Mass Loss (mg/cm 2 ) Mass Loss (mg/cm 2 ) SPALLING RESISTANCE HOT SALT Heat Treatment: 677 C (125 F) Before Cleaning TOTAL MASS LOSS HOT SALT Heat Treatment: 677 C (125 F) 15 Cr-Cb 15 Cr-Cb Type 439 After Cleaning Less mass loss due to spalling THERMAK 17 Stainless Steel provides an improved oxidation resistance compared to other ferritic alloys such as Type 439. In addition to 17% Cr content, high Si and high Mn contents improve high temperature oxidation resistance in air and exhaust gas atmospheres. In continutous service, 2 hours at 93 C, THERMAK 17 Stainless Steel exhibited a uniform scale pattern and no spalling. 6

9 WELDABILITY THERMAK 17 is generally considered to be weldable by the common fusion and resistance welding processes. Grain growth in the weld heat affected zone, with reduced weld toughness, is a common occurrence in ferritic stainless steel weldments. Low weld heat input and elimination of weld discontinuities will provide maximum toughness in welded sections. Warming of welded parts prior to forming may also improve weld toughness. When a weld filler is required, 18 Cr-Cb is recommended for applications where high temperature thermal cycling is expected. Filler wires 38L or 39L will provide improved weld ductility for lower temperature applications. Additional information concerning the welding of ferritic stainless steels may be obtained from the following publications: 1. ANSI/AWS A5.9, A5.22 and A5.4 (stainless welding electrode specifications). 2. Welding of Stainless Steels and Other Joining Methods, SSINA, ( 87

10 AK Steel Corporation 9227 Centre Pointe Drive West Chester, OH STEEL AK Steel is a leading producer of flat-rolled carbon, stainless and electrical steel products, and carbon and stainless tubular products, primarily for automotive, infrastructure and manufacturing, construction and electrical power generation and distribution markets. Headquartered in West Chester, Ohio (Greater Cincinnati), the company employs approximately 8,5 men and women at eight steel plants, two coke plants and two tube manufacturing plants across six states (Indiana, Kentucky, Michigan, Ohio, Pennsylvania and West Virginia) and one tube plant in Mexico. Additional information about AK Steel is available at The information and data in this document are accurate to the best of our knowledge and belief, but are intended for general information only. Applications suggested for the materials are described only to help readers make their own evaluations and decisions, and are neither guarantees nor to be construed as express or implied warranties of suitability for these or other applications. Data referring to material properties are the result of tests performed on specimens obtained from specific locations of the products in accordance with prescribed sampling procedures; any warranty thereof is limited to the values obtained at such locations and by such procedures. There is no warranty with respect to values of the materials at other locations. AK and the AK Steel logo are registered trademarks of the AK Steel Corporation