Alloy 317L (UNS S31703) is a molybdenum-bearing austenitic stainless steel with greatly increased resistance to chemical attack as compared to the conventional chromium-nickel austenitic stainless steels such as Alloy 304. In addition, Alloy 317L offers higher creep, stress-to-rupture, and tensile strength at elevated temperatures than conventional stainless steels. It is a low carbon or “L” grade which provides resistance to sensitization during welding and other thermal processes. 317L is a molybdenum bearing austenitic chromium nickel steel similar to type 316, except the alloy content in 317L is somewhat higher.
Stainless 317 L has a high tensile and creep strength at elevated temperatures. Due to its excellent corrosion resistance it has been used in handling many of the chemicals used by the chemical process industries.
It has a supperior corrosion resistance in special applications where it is desired to reduce contamination to a minimum. 317L was developed primarily to resist more effectively the attack of sulfurous acid compounds. Howerver, its proven ability to combat corrosion has widened its use considerably and is now being used for many other industrial applications.
The low carbon content of 317L provides immunity to intergranular corrosion in applications where heavy cross sections cannot be annealed after welding or where low temperature stress relieving treatments are desired.
Specifications – Stainless Steel 317L
317L (00Cr19Ni13Mo3, SUS317L) alloy is based on molybdenum and austenitic stainless steel. It is more resistant to chemical corrosion than normal chrome-nickel austenitic stainless steel, such as 304 alloys. In addition, compared with conventional stainless steel, 317L alloys have higher ductility, anti-stress corrosion, compressive strength and high temperature resistance. It is a low carbon grade or L rating, which has the ability to resist sensitization during welding and heat treatment.
- ASTM: A312, A403, A182
- ASME: SA312, SA403, SA182
Chemical Composition - Stainless Steel 317/317L
| Grade | 317 | 317L |
|---|---|---|
| UNS Designation | S31700 | S31703 |
| Carbon (C) Max. | 0.08 | 0.035* |
| Manganese (Mn) Max. | 2 | 2 |
| Phosphorous (P) Max. | 0.04 | 0.04 |
| Sulphur (S) Max. | 0.03 | 0.03 |
| Silicon (Si) Max. | 1 | 1 |
| Chromium (Cr) | 18.0–20.0 | 18.0–20.0 |
| Nickel (Ni) | 11.0–14.0 | 11.0–15.0 |
| Molybdenum (Mo) | 3.0–4.0 | 3.0–4.0 |
| Nitrogen (N) | — | — |
| Iron (Fe) | Bal. | Bal. |
| Other Elements | — | — |
Typical Mechanical Properties- Stainless Steel 317L
| Material | Ultimate Tensile Strength (Mpa) | 0.2 % Yield Strength (Mpa) | % Elongation in 2" | Rockwell B Hardness |
|---|---|---|---|---|
| Alloy 317 | 515 | 205 | 35 | 95 |
| Alloy 317L | 515 | 205 | 40 | 95 |
Design Features – Stainless Steel 317L
- A molybdenum bearing austenitic chromium nickel steel with an alloy content somewhat higher than the 316 grades.
- Superior corrosion resistance in difficult environments.
- Higher creep, stress-to-rupture and tensile strengths than other stainless steels.
- Reduced intergranular precipitation of chromium carbides during welding and stress relieving as well as minimized possibility of corrosion failure from intergranular attack due to low carbon content.
- Resistance to pitting and crevice corrosion making 317L a successful life-cost product in a variety of highly corrosive environments.
Typical Applications – Stainless Steel 317L
- Flue gas desulfurization scrubber systems
- Chemical and petro-chemical processing equipment
- Pulp and paper plants
- Food processing equipment
- Textile equipment
Tensile Requirements – Stainless Steel 317L
- Tensile Strength (KSI): 75
- Yield Strength (KSI): 30
317L(1.4438) General Property
Alloy 317LMN and 317L are molybdenum-bearing austenitic stainless steel tube with greatly increased resistance to chemical attack as compared to the conventional chromium-nickel austenitic stainless steel pipe such as Alloy 304. In addition, 317LMN and 317L alloys offer higher creep, stress-to-rupture, and tensile strengths at elevated temperatures than conventional stainless steels. All are low carbon or “L” grades to provide resistance to sensitization during welding and other thermal processes.
The “M” and “N” designations indicate that the compositions contain increased levels of molybdenum and nitrogen respectively. The combination of molybdenum and nitrogen is particularly effective in enhancing resistance to pitting and crevice corrosion, especially in process streams containing acids, chlorides, and sulfur compounds at elevated temperatures. Nitrogen also serves to increase the strength of these alloys. Both alloys are intended for severe service conditions such as flue gas desulfurization (FGD) systems.
In addition to excellent corrosion resistance and strength properties, the Alloys 316, 316L, and 317L Cr-Ni-Mo alloys also provide the excellent fabricability and formability which are typical of the austenitic stainless steel tubing .
317L (1.4438) Heat Treatment
Annealing
The austenitic stainless steel pipe are provided in the mill annealed condition ready for use. Heat treatment may be necessary during or after fabrication to remove the effects of cold forming or to dissolve precipitated chromium carbides resulting from thermal exposures. For the Alloys 316 and 317L the solution anneal is accomplished by heating in the 1900 to 2150°F (1040 to 1175°C) temperature range followed by air cooling or a water quench, depending on section thickness. Cooling should be sufficiently rapid through the 1500 to 800°F (816 to 427°C) range to avoid reprecipitation of chromium carbides and provide optimum corrosion resistance. In every case, the metal should be cooled from the annealing temperature to black heat in less than three minutes.
Forging
The recommended initial temperature range is 2100-2200°F (1150-1205°C) with a finishing range of 1700-1750°F (927-955°C).
Annealing
317LMN and Alloy 317L stainless steels can be annealed in the temperature range 1975-2150°F (1080-1175°C) followed by an air cool or water quench, depending on thickness. Plates should be annealed between 2100°F (1150°C) and 2150°F (1175°C). The metal should be cooled from the annealing temperature (from red/white to black) in less than three minutes.
Hardenability
- These grades are not hardenable by heat treatment.
- Alloys 316 and 317L stainless steel tube cannot be hardened by heat treatment.
Is Grade 317 Stainless Steel Worth the Cost Over 316 & 304?
With hundreds of different types of steel alloys on the market, it can be tough to find the perfect metal for your application. In many buying processes, the first consideration is the cost of the metal rather than the performance of the metal—which can be a serious mistake.
There are some cases where paying extra for a different, higher-performing alloy is necessary.
What Makes Grade 317 SS Different from 304 & 316 SS?
Grade 304, 316, and 317 stainless steel are all considered austenitic stainless steel alloys. These alloys all share some similar properties, such as high strength, corrosion resistance, and high concentrations of chromium and nickel.
What separates 316 and 317 SS from 304 SS is that these higher-numbered alloys have added molybdenum in their formulation—grade 316 has about 2-3% molybdenum, and grade 317 has more than 3% molybdenum.
This added molybdenum greatly improves the steel’s resistance to pitting from chlorides, which is why grade 316 SS is often used in the chemical processing and marine industries.
However, this added molybdenum content also influences the cost of these two alloys. Grade 317 SS is generally more expensive than grade 316 SS. 316 SS, in turn, is more expensive than grade 304 SS. The exact extra cost varies based on the market at the time.
When is 317 SS Worth the Extra Cost Over 316 SS?
For most strongly corrosive applications, grade 316 should be more than enough to resist frequent exposure.
However, 317 does achieve better resistance to some specific corrosives than 304 or 316. As noted by an ATI Metals publication, in a boiling test solution of 1% hydrochloric acid, the corrosion rate of 317 SS was 54.2 mils/year, while 316 SS corroded at a rate of 226 mils/year. 317 SS also significantly outperforms 316 SS in sulfuric acid and sodium hydroxide tests.
So, if your processes involve the use of very diluted (less than 3-4%) hydrochloric acid, mild concentration (10%) sulfuric acid, or sodium hydroxide (aka caustic soda), then grade 317 stainless steel might be worth the extra cost over 316 or 304 SS.
It’s important to note that hydrochloric acid in any concentration above 5% will quickly erode any austenitic stainless steel alloy with ease.
Also, in the previously-cited chemical corrosion tests, 317 performed worse against some corrosives than 316, such as phosphoric acid (0.72 mils/year vs 0.2 mils/year) and acetic acid (0.48 mils/year vs 0.12 mils/year).