THERMAK 17. High Temperature Strength. Superior Oxidation Resistance. Excellent Thermal Fatigue Resistance. Equiaxed Microstructure

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1 THERMAK 17 Stainless STEEL Product Data Bulletin Applications Potential High Temperature Strength Superior Oxidation Resistance Excellent Thermal Fatigue Resistance Equiaxed Microstructure THERMAK 17 Stainless Steel has excellent high temperature strength, thermal fatigue and oxidation resistance. It s improved high strength will facilitate vehicle light weighting efforts. It is designed for demanding hot-end automotive exhaust applications where intermediate 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. Thermak 17 stainless steel

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 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 Manganese Phosphorus Sulfur.2 max. 1.2 max..5 max..1 max. Silicon Chromium Nickel Nitrogen.5 max..2 max. Copper Titanium Niobium.5 max..5 max. AVAILABLE FORMS AK Steel produces Thermak 17 Stainless Steel in coils 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 42 (58) 533 (77) 32 B86 Elevated temperature Properties SHORT TIME ELEVATED TEMPERATURE MECHANICAL PROPERITES 3.2% Offset Yield Strength, MPa Cr-Cb SS Type Temperature, C 4 35 Ultimate Tensile Strength, MPa Cr-Cb SS 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 Stainless Steel and Type 444 in the temperature range of 7 93 C. It was equivalent to 15 Cr-Cb Stainless Steel over the same temperature range. DEFLECTION AFTER 144 HOUR TEST DURATION Test Temperature C Condition* (mm) 15 Cr-Cb SS (mm) 18 Cr-Cb (mm) Type 444 (mm) As-annealed C/96hr As-annealed C/96hr As-annealed C/96hr * As-annealed tested in duplicate, 74 C aged single samples. thermal fatigue resistance Thermak 17 Stainless Steel has shown, in limited testing, to have 2-3% improved thermal fatigue resistance over intermediate 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 15 Cr SS 3

6 formability Thermak 17 Stainless Steel is readily drawn and formed. The ULTRA FORM Stainless Steel 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) 85 (52.4) ASTM Grain Size 5.5 Stretch r (plastic strain ratio) at 18% (ASTM E517) r-value r m 1.29 delta r.59 delta r (Max Min).84 Ridging No. 1 Olsen Cup Height (mm) 11.4 LDR 2.1 4

7 Corrosion Resistance Salt cycle test AK Steel 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 SS 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 SS 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.) Spalling Resistance Hot Salt Heat Treatment: 677 C (125 F) 6 Cycle Repeats 4 times per day Hot salt test Heat treat 9 min. at 677 C (125 F) One minute cold water quench Five minute soak in 5% sodium chloride Balance of day place in humidity chamber 6 C/(14 F)/85% RH Mass Loss (mg/cm 2 ) Total Mass loss Hot Salt Heat Treatment: 677 C (125 F) 15 Cr-Cb SS Measurements collected after ten cycles Mass Loss (mg/cm 2 ) Cr-Cb SS Type 439 Oxidation Resistance THERMAK 17 Stainless Steel provides an improved oxidation resistance compared to other ferritic alloys such as Type 439 stainless steel. 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 Stainless Steel 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 Stainless Steel 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, ( 7

10 AK Steel Corporation 9227 Centre Pointe Drive West Chester, OH Headquartered in West Chester, Ohio, AK Steel is a world leader in the production of flat rolled carbon, stainless and electrical steel products, primarily for automotive, appliance, construction and electrical power generation and distribution markets. The company operates seven steel plants and two tube manufacturing plants across four states Indiana, Kentucky, Ohio and Pennsylvania. All of the company s steel plants are ISO/TS 16949, ISO 91 and ISO 141 certified for their quality and environmental management systems. AK Steel is a publicly held company traded over the New York Stock Exchange under the symbol AKS aligning the company with many of the most prominent corporations in America. 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. Revision