316H Stainless Steel: Properties and Key Applications

316H stainless steel is a high-temperature variant of the 316 grade, classified as an austenitic stainless steel. It is primarily alloyed with chromium (16-18%), nickel (10-14%), and molybdenum (2-3%), which enhance its corrosion resistance and mechanical properties. The "H" designation indicates a higher carbon content (0.04% to 0.10%) compared to standard 316, which improves its strength at elevated temperatures.

Comprehensive Overview

316H stainless steel is renowned for its excellent resistance to pitting and crevice corrosion in chloride environments, making it a preferred choice for marine applications and chemical processing. Its high nickel content contributes to its toughness and ductility, while molybdenum enhances its resistance to localized corrosion.

Advantages (Pros):
- Exceptional corrosion resistance, particularly in aggressive environments.
- High strength and toughness at elevated temperatures, making it suitable for high-stress applications.
- Good weldability and formability, allowing for versatile fabrication options.

Limitations (Cons):
- Higher cost compared to lower alloyed stainless steels.
- Susceptibility to sensitization if not properly heat-treated, which can lead to intergranular corrosion.
- Not magnetic, which may be a disadvantage in applications requiring magnetic properties.

Historically, 316H has been significant in industries such as petrochemical, power generation, and marine engineering due to its ability to withstand harsh conditions. Its market position is strong, particularly in sectors that demand high-performance materials.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	S31609	USA	Closest equivalent to AISI 316H
AISI/SAE	316H	USA	Higher carbon content than 316
ASTM	A240/A240M	USA	Standard specification for stainless steel plates
EN	1.4878	Europe	Equivalent grade in European standards
JIS	SUS316H	Japan	Similar properties with minor compositional differences

The differences between 316H and its equivalents, such as 316L (low carbon) and 316, primarily lie in their carbon content, which affects their high-temperature strength and susceptibility to sensitization.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
Cr (Chromium)	16.0 - 18.0
Ni (Nickel)	10.0 - 14.0
Mo (Molybdenum)	2.0 - 3.0
C (Carbon)	0.04 - 0.10
Mn (Manganese)	2.0 max
Si (Silicon)	1.0 max
P (Phosphorus)	0.045 max
S (Sulfur)	0.030 max

The primary role of chromium is to enhance corrosion resistance, while nickel contributes to toughness and ductility. Molybdenum increases resistance to pitting and crevice corrosion, particularly in chloride environments. The higher carbon content in 316H improves its strength at elevated temperatures, making it suitable for high-stress applications.

Mechanical Properties

Property	Condition/Temper	Typical Value/Range (Metric)	Typical Value/Range (Imperial)	Reference Standard for Test Method
Tensile Strength	Annealed	515 - 690 MPa	75 - 100 ksi	ASTM E8
Yield Strength (0.2% offset)	Annealed	205 - 310 MPa	30 - 45 ksi	ASTM E8
Elongation	Annealed	40% min	40% min	ASTM E8
Hardness (Rockwell B)	Annealed	70 - 90 HRB	70 - 90 HRB	ASTM E18
Impact Strength (Charpy)	-20°C	40 J	30 ft-lbf	ASTM E23

The combination of high tensile and yield strength, along with good elongation properties, makes 316H suitable for applications requiring structural integrity under mechanical loading. Its impact strength at low temperatures also enhances its performance in cryogenic applications.

Physical Properties

Property	Condition/Temperature	Value (Metric)	Value (Imperial)
Density	Room Temperature	8.0 g/cm³	0.289 lb/in³
Melting Point	-	1375 - 1400 °C	2500 - 2550 °F
Thermal Conductivity	Room Temperature	16.2 W/m·K	112 BTU·in/ft²·h·°F
Specific Heat Capacity	Room Temperature	500 J/kg·K	0.12 BTU/lb·°F
Electrical Resistivity	Room Temperature	0.72 µΩ·m	0.72 µΩ·in
Coefficient of Thermal Expansion	20 - 100 °C	16.0 x 10⁻⁶/K	8.9 x 10⁻⁶/°F

The density and melting point indicate that 316H can withstand high temperatures without significant deformation. Its thermal conductivity is moderate, making it suitable for applications where heat dissipation is necessary. The specific heat capacity is also favorable for thermal applications, while the electrical resistivity suggests it is not a good conductor of electricity.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C/°F)	Resistance Rating	Notes
Chlorides	3.5%	20°C / 68°F	Excellent	Risk of pitting
Sulfuric Acid	10%	25°C / 77°F	Good	Limited resistance
Hydrochloric Acid	5%	25°C / 77°F	Fair	Risk of localized corrosion
Sea Water	-	Ambient	Excellent	Highly resistant
Acetic Acid	10%	25°C / 77°F	Good	Susceptible to stress corrosion cracking

316H exhibits excellent resistance to a variety of corrosive agents, particularly in marine environments. Its performance in chloride-rich conditions is superior to that of 304 and 316L grades, which are more susceptible to pitting corrosion. However, it is important to note that while 316H performs well in many acidic environments, it can still be vulnerable to localized corrosion in specific conditions, particularly with strong acids like hydrochloric acid.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	800°C	1472°F	Suitable for high-temperature applications
Max Intermittent Service Temp	870°C	1598°F	Short-term exposure only
Scaling Temperature	925°C	1697°F	Above this temperature, oxidation occurs
Creep Strength considerations begin	600°C	1112°F	Creep resistance decreases above this temperature

316H maintains its mechanical properties at elevated temperatures, making it suitable for applications such as furnace components and heat exchangers. However, prolonged exposure to temperatures above 800°C can lead to oxidation and scaling, which may compromise its integrity.

Fabrication Properties

Weldability

Welding Process	Recommended Filler Metal (AWS Classification)	Typical Shielding Gas/Flux	Notes
TIG	ER316L	Argon	Good for thin sections
MIG	ER316L	Argon + CO2 mix	Suitable for thicker sections
SMAW	E316L	-	Requires preheat for thick sections

316H is highly weldable, but care must be taken to avoid sensitization during welding. Preheating and post-weld heat treatment are recommended to minimize the risk of intergranular corrosion. The use of filler metals like ER316L ensures compatibility and maintains corrosion resistance.

Machinability

Machining Parameter	316H	AISI 1212	Notes/Tips
Relative Machinability Index	30%	100%	316H is more challenging to machine
Typical Cutting Speed (Turning)	20 m/min	40 m/min	Use carbide tools for best results

316H has lower machinability compared to carbon steels, requiring slower cutting speeds and specialized tooling. Optimal conditions include using sharp tools and adequate lubrication to reduce work hardening.

Formability

316H exhibits good formability, allowing for cold and hot forming processes. However, due to its work hardening characteristics, careful control of bending radii is necessary to avoid cracking. It is suitable for applications requiring complex shapes and configurations.

Heat Treatment

Treatment Process	Temperature Range (°C/°F)	Typical Soaking Time	Cooling Method	Primary Purpose / Expected Result
Solution Annealing	1010 - 1120 °C / 1850 - 2050 °F	30 minutes	Air or water	Dissolve carbides, relieve stress
Stress Relieving	400 - 600 °C / 750 - 1112 °F	1 hour	Air	Reduce residual stresses

Heat treatment processes like solution annealing enhance the corrosion resistance of 316H by dissolving carbides and preventing sensitization. The metallurgical transformations during these treatments significantly impact the microstructure, leading to improved toughness and ductility.

Typical Applications and End Uses

Industry/Sector	Specific Application Example	Key Steel Properties Utilized in this Application	Reason for Selection
Marine Engineering	Shipbuilding	Corrosion resistance, strength	Exposure to seawater
Chemical Processing	Reactor vessels	High-temperature strength, corrosion resistance	Harsh chemical environments
Oil & Gas	Pipeline systems	Toughness, weldability	High-stress applications
Power Generation	Heat exchangers	High-temperature performance	Thermal efficiency

Other applications include:
* Pharmaceutical equipment
* Food processing machinery
* Architectural structures exposed to harsh environments

316H is chosen for these applications due to its superior corrosion resistance and ability to maintain strength at elevated temperatures, ensuring reliability and longevity in demanding environments.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	316H	304	321	Brief Pro/Con or Trade-off Note
Key Mechanical Property	High strength	Moderate strength	High strength	316H offers better high-temp performance
Key Corrosion Aspect	Excellent	Good	Excellent	321 is better for high-temperature applications
Weldability	Good	Excellent	Good	316H requires careful handling to avoid sensitization
Machinability	Moderate	Good	Moderate	316H is more challenging to machine
Approx. Relative Cost	Higher	Lower	Higher	Cost considerations may affect selection
Typical Availability	Moderate	High	Moderate	304 is more commonly available

When selecting 316H, considerations include cost-effectiveness, availability, and specific application requirements. Its high performance in corrosive environments and at elevated temperatures makes it a preferred choice in critical applications. However, its higher cost and lower machinability compared to alternatives like 304 may influence decisions, especially in less demanding environments.

In conclusion, 316H stainless steel is a versatile and high-performance material that excels in challenging conditions, making it indispensable in various industries. Its unique properties and capabilities warrant careful consideration during material selection to ensure optimal performance and longevity in applications.