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Home17-4 Stainless Steel vs 316: Deciding Between the Two
May 06,2024 
17-4 Ph stainless steel vs 316 SS are differentiated on the bases of their composition and heat treatments that’s why have unique properties used in large range of applications. 17-4 Ph is used in applications where high strength is required while 316 SS is used in applications where corrosion resistance is required. Other designations used for 17-4 stainless steel are UNS S17400 and ASTM A693 while for 316 SS are UNS S31600 and ASTM A193 Grade B8M. In this article, you will get to know the basic difference between 17-4 Ph vs 316 SS and will be able to choose between them accurately for specific applications.
17-4 stainless Steel
17-4 stainless steel also known as martensitic stainless steel which is magnetic formed by heating at high temperature and then rapid cooling. 17-4 precipitation hardening stainless steel has high toughness and high strength. UNS S17400 composition contains 4 % Ni and 17 % Cr in it. ASTM A693 due to its high strength is used in the aerospace and automotive industry [2].
Image showing 17-4 stainless steel images.
YouTube video explaining 17-4 SS grades.
https://www.youtube.com/watch?v=InVtd3mWj58&pp=ygUVMTctNCBTdGFpbmxlc3MgU3RlZWwg
316 Stainless Steel
316 SS also known as austenitic stainless steel and is nonmagnetic. 316 SS contains 12% nickel, 18 % chromium, and 3% molybdenum. UNS S31600 is the best fighter against pitting corrosion due to the presence of nickel and chromium. Molybdenum prevent ASTM A193 Grade B8M corrosion in chloride environments too [3].
316 SS use in the food and beverage industry.
What is the Difference Between 17-4 Stainless Steel and 316?
Chemical Composition
|
Element |
17-4 Stainless Steel |
316 Stainless Steel |
|
Carbon |
0.07% |
0.08% max |
|
Chromium |
15.0-17.5% |
16.0-18.0% |
|
Nickel |
3.0-5.0% |
10.0-14.0% |
|
Manganese |
1.0% |
2.0% |
|
Silicon |
1.0% |
1.0% |
|
Phosphorus |
0.040% |
0.045% |
|
Sulfur |
0.030% |
0.030% |
|
Copper |
3.0-5.0% |
1.0-2.0% |
|
Niobium + Tantalum |
0.15-0.45% |
- |
|
Iron |
Balance |
Balance |
|
Molybdenum |
- |
2.0-3.0% |
|
Nitrogen |
- |
0.10% |
|
Selenium |
- |
0.030% |
Table showing the chemical composition of stainless steels 17-4 Ph and 316 SS [2].
Magnetic Properties of 17-4 PH and 316
UNS S17400 is a precipitation-hardening stainless steel. It is magnetic due to martensitic structure. Compared to 17-4 Ph steel 316 SS is nonmagnetic due to austenitic microstructure [3].
Mechanical Properties
|
Property |
17-4 Stainless Steel |
316 Stainless Steel |
|
Density (g/cm³) |
7.8 |
8.0 |
|
Hardness (HRC) |
34-40 |
25-39 (Typical) |
|
Tensile Strength (MPa) |
1100-1300 |
485-620 |
|
Yield Strength (MPa) |
1000-1200 |
170-310 |
|
Elongation (%) |
10-14% |
40-50% |
|
Toughness (J) |
- |
100-200 |
|
Fatigue Strength (MPa) |
380 (at 2x10^6 cycles) |
160 (at 10^7 cycles) |
17-4 Ph stainless steel vs 316 SS mechanical properties.
Machinability
17-4 Ph stainless steel vs 316 SS both provide excellent machinability.
- Welding: Although both 17-4 Ph stainless steel vs 316 SS can easily be welded 17-4 Ph stainless steel requires pre-heating and post-heat treatment to overcome distortion after welding. On the other hand, 316 SS is also annealed after welding to restore corrosion resistance properties. 316 SS is highly weldable which can be done through TIG, MIG, and spot welding [5].
- Machining: 17-4 Ph stainless steel vs 316 SS, the 316 SS can be machined very easily with typical machining tools. 316 SS gets a better finish and doesn't require any pre or post-heat treatments. 17-4 Ph stainless steel requires special tooling techniques and requires pre and post-heat treatments [6].
- Surface Finish: 17-4 Ph stainless steel vs 316 SS both surface finishes can be improved by grinding then polishing or buffing but specific surface finish treatments can be designed according to application requirements [7].
- Heat Treatment Process
- Strengthening through Heat Treatment
Strengthening through precipitate hardening of stainless steel can be done through heating UNS S17400 at 1010-1065°C and then the material is cooled rapidly allowing all alloying elements to dissolve completely. Aging of UNS S17400 can be done at low temperatures of 480-620°C to form precipitate [8].
Low-temperature performance of 316
ASTM A193 Grade B8M becomes brittle and loses its toughness at low temperatures especially below -50°C that why it cannot used in the application of low temperatures [9].
Flatness and Stability
UNS S31600 shows good flatness due to its martensitic high-strength structure. UNS S31600 shows good dimension stability at high temperature.
shows good flatness, especially for cold rollers and thinner gauges. 3016 Stainless Steel shows dimension stability at room temperature but at elevated temperature and low temperature, it loses its dimension stability [10].
316 thinner stainless steel gauges.
Corrosion Resistance
- Resistance to Pitting Corrosion
316 SS shows excellent resistance to pitting corrosion due to the presence of nickel and molybdenum.
Image showing pitting corrosion mechanism
- Suitability in Chloride Environments
316 SS shows excellent corrosion to stress corrosion cracking and chloride-induced corrosion that's why is the best choice to use in a chloride environment [12].
Summary Chart of 17-4 stainless Steel and 316
|
Characteristic |
17-4 Stainless Steel |
316 Stainless Steel |
|
Chemical Composition |
15-17.5% Cr 3-5% Ni 1% Cu, 0.07% C |
16-18% Cr 10-14% Ni 2% Mo 0.08% C |
|
Microstructure |
Martensitic |
Austenitic |
|
Strength |
High strength |
Moderate strength |
|
Corrosion Resistance |
Good |
Excellent |
|
Pitting Corrosion resistance |
Moderate |
Excellent |
|
Can withstand Chloride Environments |
Moderate |
Excellent |
|
Heat Treatment |
Precipitation hardening |
Annealing and then cooling |
|
Machinability |
Fair - good |
Fair - good |
|
Weldability |
Pre-heat treatment and post-weld heat treatment are required. |
Excellent |
|
Magnetic Properties |
Magnetic |
Non-magnetic |
|
Typical Applications |
Aerospace components industrial equipment |
Marine equipment chemical processing |
Advantages and disadvantages 17-4 Stainless Steel and 316
|
Aspect |
17-4 Stainless Steel |
316 Stainless Steel |
|
Advantages |
- High strength - Moderate corrosion resistance - Can be precipitation-hardened - Machinability good to fair. - Magnetic properties |
- sustainability against pitting corrosion and chloride environment. - Austenitic structure and have good toughness - Good weldability - Versatile use - excellent surface finish |
|
Disadvantages |
- weldability can be done with specific heat treatments - costly compared to other stainless-steel grades - Moderate pitting corrosion resistance - A complex heat treatment process is required. |
- Moderate strength - Loss of mechanical properties at higher temperatures and low temperatures. - Low toughness
|
he table shows the corns and pons of 17-4 stainless steel and 316 stainless steel [13].
YouTube video showing difference between stainless steel including 316 and 17-4 SS grades.
https://www.youtube.com/watch?v=HFqKNQGBHvs&pp=ygUNMzE2IHZzIDMyMSBTUw%3D%3D
Which Alloy is Better for Your Precision Machining Needs?
316 stainless steel is best known for precise machining needs compared to 17-4 stainless steel because it is austenitic and can be machined without pre- or post-heat treatments while 1704 stainless steel is martensitic making it hard to machined [16].
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