Bumax 88 Stainless Steel: Properties and Key Applications

Bumax 88 is a high-performance austenitic stainless steel known for its exceptional corrosion resistance and mechanical properties. Classified as a stainless steel grade, Bumax 88 primarily consists of iron, chromium, nickel, and molybdenum, which contribute to its robust characteristics. The alloying elements in Bumax 88 enhance its resistance to pitting and crevice corrosion, making it suitable for demanding environments, particularly in the chemical and marine industries.

Comprehensive Overview

Bumax 88 is classified as an austenitic stainless steel, which is characterized by its face-centered cubic (FCC) crystal structure. This structure provides excellent toughness and ductility, even at low temperatures. The primary alloying elements include:

• Chromium (Cr): Typically around 18-20%, chromium enhances corrosion resistance and contributes to the formation of a passive oxide layer on the steel surface.
• Nickel (Ni): Usually present in 8-10% concentrations, nickel improves the steel's toughness and ductility, as well as its resistance to corrosion.
• Molybdenum (Mo): Generally around 2-3%, molybdenum further enhances resistance to pitting and crevice corrosion, particularly in chloride environments.

The significant characteristics of Bumax 88 include high tensile strength, excellent weldability, and outstanding resistance to various corrosive agents. Its main advantages are its ability to withstand harsh environments, making it ideal for applications in the food processing, chemical, and marine industries. However, it may be more expensive than other stainless steel grades and can be challenging to machine due to its toughness.

Historically, Bumax 88 has gained recognition for its reliability in critical applications, positioning it as a preferred choice among engineers and designers seeking high-performance materials.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	S31600	USA	Closest equivalent to AISI 316
AISI/SAE	316	USA	Minor compositional differences
ASTM	A240	USA	Standard specification for stainless steel plates
EN	1.4401	Europe	Equivalent to AISI 316
JIS	SUS316	Japan	Similar properties, widely used in Japan

While Bumax 88 is often compared to AISI 316, it is essential to note that Bumax 88 may offer improved corrosion resistance in specific environments due to its unique composition. The presence of molybdenum in higher concentrations enhances its performance in chloride-rich conditions, making it a superior choice for marine applications.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
Fe (Iron)	Balance
Cr (Chromium)	18.0 - 20.0
Ni (Nickel)	8.0 - 10.0
Mo (Molybdenum)	2.0 - 3.0
C (Carbon)	≤ 0.03
Mn (Manganese)	≤ 2.0
Si (Silicon)	≤ 1.0
P (Phosphorus)	≤ 0.045
S (Sulfur)	≤ 0.03

The primary role of chromium is to provide corrosion resistance, while nickel enhances ductility and toughness. Molybdenum significantly improves resistance to pitting and crevice corrosion, particularly in chloride environments. The low carbon content minimizes the risk of carbide precipitation, which can lead to intergranular corrosion.

Mechanical Properties

Property	Condition/Temper	Typical Value/Range (Metric - SI Units)	Typical Value/Range (Imperial Units)	Reference Standard for Test Method
Tensile Strength	Annealed	620 - 720 MPa	90 - 104 ksi	ASTM E8
Yield Strength (0.2% offset)	Annealed	290 - 310 MPa	42 - 45 ksi	ASTM E8
Elongation	Annealed	40%	40%	ASTM E8
Reduction of Area	Annealed	60%	60%	ASTM E8
Hardness (Rockwell B)	Annealed	85 - 95 HRB	85 - 95 HRB	ASTM E18
Impact Strength	-40°C	50 J	37 ft-lbf	ASTM E23

The combination of high tensile and yield strength, along with excellent elongation properties, makes Bumax 88 suitable for applications requiring high mechanical loading and structural integrity. Its toughness at low temperatures is particularly advantageous in cryogenic applications.

Physical Properties

Property	Condition/Temperature	Value (Metric - SI Units)	Value (Imperial Units)
Density	-	7.98 g/cm³	0.288 lb/in³
Melting Point/Range	-	1400 - 1450 °C	2552 - 2642 °F
Thermal Conductivity	20 °C	16 W/m·K	92 BTU·in/(hr·ft²·°F)
Specific Heat Capacity	20 °C	500 J/kg·K	0.119 BTU/lb·°F
Electrical Resistivity	20 °C	0.72 µΩ·m	0.0000013 Ω·in
Coefficient of Thermal Expansion	20 - 100 °C	16.0 x 10⁻⁶ K⁻¹	8.9 x 10⁻⁶ °F⁻¹

The density of Bumax 88 indicates its substantial weight, which is a consideration in applications where weight savings are critical. The thermal conductivity and specific heat capacity suggest its suitability for applications involving thermal management, while the electrical resistivity is relevant in electrical applications.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C/°F)	Resistance Rating	Notes
Chlorides	3-10	20-60 / 68-140	Excellent	Risk of pitting
Sulfuric Acid	10-30	20-40 / 68-104	Good	Moderate resistance
Hydrochloric Acid	5-20	20-40 / 68-104	Fair	Susceptible to pitting
Acetic Acid	5-20	20-60 / 68-140	Good	Risk of localized corrosion
Seawater	-	20-60 / 68-140	Excellent	High resistance

Bumax 88 exhibits excellent resistance to corrosion in various environments, particularly in chloride-rich conditions, making it ideal for marine applications. However, it is susceptible to pitting in highly concentrated chloride solutions and should be used with caution in such environments.

When compared to other stainless steel grades like AISI 316 and Duplex stainless steels, Bumax 88 often outperforms in terms of pitting resistance due to its higher molybdenum content. This makes it a preferred choice for applications in aggressive environments, such as offshore oil rigs and chemical processing plants.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	800	1472	Suitable for high-temperature applications
Max Intermittent Service Temp	870	1598	Short-term exposure only
Scaling Temperature	900	1652	Risk of oxidation above this temperature
Creep Strength considerations	600	1112	Begins to decrease significantly

Bumax 88 maintains its mechanical properties at elevated temperatures, making it suitable for applications in high-temperature environments. However, care must be taken to avoid prolonged exposure to temperatures above 800 °C, as this can lead to oxidation and degradation of material properties.

Fabrication Properties

Weldability

Welding Process	Recommended Filler Metal (AWS Classification)	Typical Shielding Gas/Flux	Notes
TIG Welding	ER316L	Argon	Excellent weldability
MIG Welding	ER316L	Argon + CO₂	Good for thin sections
Stick Welding	E316L	-	Requires preheat

Bumax 88 is highly weldable, making it suitable for various welding processes. Preheating may be necessary for thicker sections to minimize the risk of cracking. Post-weld heat treatment can enhance the mechanical properties and relieve residual stresses.

Machinability

Machining Parameter	Bumax 88	AISI 1212	Notes/Tips
Relative Machinability Index	30%	100%	Requires slower cutting speeds
Typical Cutting Speed	20 m/min	60 m/min	Use carbide tools

Bumax 88 has lower machinability compared to carbon steels, necessitating the use of specialized tooling and slower cutting speeds. Proper cooling and lubrication are essential to prevent tool wear.

Formability

Bumax 88 exhibits good formability, allowing for cold and hot forming processes. However, due to its work-hardening characteristics, careful attention must be paid to bend radii and forming techniques to avoid cracking.

Heat Treatment

Treatment Process	Temperature Range (°C/°F)	Typical Soaking Time	Cooling Method	Primary Purpose / Expected Result
Solution Annealing	1000 - 1100 / 1832 - 2012	30 minutes	Air	Dissolution of carbides
Stress Relieving	300 - 400 / 572 - 752	1 hour	Air	Reduction of residual stresses

Heat treatment processes such as solution annealing enhance the corrosion resistance and mechanical properties of Bumax 88 by dissolving carbides and promoting a homogeneous microstructure.

Typical Applications and End Uses

Industry/Sector	Specific Application Example	Key Steel Properties Utilized in this Application	Reason for Selection (Brief)
Chemical Processing	Reactors and storage tanks	Corrosion resistance, strength	High resistance to aggressive chemicals
Marine Engineering	Ship components	Pitting resistance, toughness	Excellent performance in seawater
Food Processing	Equipment and piping	Cleanability, corrosion resistance	Meets hygiene standards
Oil and Gas	Offshore platforms	High strength, corrosion resistance	Reliability in harsh environments

Other applications include:

• Pharmaceutical equipment
• Heat exchangers
• Pressure vessels
• Architectural applications

Bumax 88 is chosen for its superior corrosion resistance and mechanical properties, making it ideal for critical applications where reliability is paramount.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	Bumax 88	AISI 316	Duplex Stainless Steel	Brief Pro/Con or Trade-off Note
Key Mechanical Property	High tensile strength	Moderate tensile strength	High tensile strength	Bumax 88 offers superior strength
Key Corrosion Aspect	Excellent in chlorides	Good in chlorides	Excellent in chlorides	Bumax 88 is more resistant to pitting
Weldability	Excellent	Good	Moderate	Bumax 88 is easier to weld
Machinability	Moderate	Good	Poor	Requires specialized tooling
Formability	Good	Good	Moderate	Similar performance
Approx. Relative Cost	Higher	Moderate	Higher	Cost may be justified by performance
Typical Availability	Moderate	High	Moderate	AISI 316 is more commonly available

When selecting Bumax 88, considerations include its cost-effectiveness in relation to performance, availability, and specific application requirements. Its unique properties make it suitable for niche applications where standard stainless steels may not suffice. Additionally, its magnetic properties are negligible, making it suitable for applications requiring non-magnetic materials.

In summary, Bumax 88 stainless steel is a high-performance material that excels in challenging environments, offering a unique combination of strength, corrosion resistance, and weldability. Its selection should be based on a thorough understanding of the specific application requirements and environmental conditions.