Stainless Steel SUS904L

A high-alloy stainless steel offering exceptional corrosion resistance, high strength, and toughness for use in extreme environments, including chemical and marine industries.

Introduction to Stainless Steel SUS904L: High Corrosion-Resistant Alloy for Demanding Environments

Stainless Steel SUS904L is a high-alloy, austenitic stainless steel known for its outstanding corrosion resistance, especially in acidic environments. With a low carbon content and a high proportion of chromium (19.0–23.0%), nickel (23.0–28.0%), and molybdenum (4.0–5.0%), SUS904L offers superior resistance to pitting, crevice corrosion, and stress corrosion cracking. This makes it an ideal choice for chemical processing, marine, and pharmaceutical industries, where components are exposed to harsh environments.

SUS904L has excellent weldability and can be used in various temperatures, providing strong structural integrity even under extreme conditions. It also demonstrates great formability, allowing for complex shapes to be produced using CNC machining. At Neway, CNC-machined SUS904L steel parts are precisely crafted to meet high tolerances, delivering durable and corrosion-resistant parts for critical applications.

SUS904L Stainless Steel: Key Properties and Composition

SUS904L Stainless Steel Chemical Composition

Element	Composition (wt%)	Role/Impact
Carbon (C)	≤0.020%	Low carbon content prevents carbide precipitation, ensuring excellent weldability.
Manganese (Mn)	1.00–2.00%	Enhances toughness and formability in high-stress applications.
Chromium (Cr)	19.0–23.0%	Provides outstanding corrosion resistance, particularly in acidic environments.
Nickel (Ni)	23.0–28.0%	Enhances strength and resistance to oxidation, improving the material’s ductility.
Molybdenum (Mo)	4.0–5.0%	Improves resistance to pitting, crevice corrosion, and stress corrosion cracking.
Phosphorus (P)	≤0.045%	Helps reduce corrosion susceptibility by limiting impurities.

SUS904L Stainless Steel Physical Properties

Property	Value	Notes
Density	8.00 g/cm³	Slightly denser than common stainless steels, providing robust strength.
Melting Point	1,400–1,450°C	Suitable for high-temperature applications, including pressure vessels.
Thermal Conductivity	14.4 W/m·K	Lower thermal conductivity than other stainless steels, suitable for heat-resistant applications.
Electrical Resistivity	7.5×10⁻⁶ Ω·m	Moderate electrical resistance, suitable for non-electrical applications.

SUS904L Stainless Steel Mechanical Properties

Property	Value	Testing Standard/Condition
Tensile Strength	520–720 MPa	ASTM A240/A240M standard
Yield Strength	200 MPa	Standard for components under moderate stress
Elongation (50mm gauge)	40%	High elongation indicating excellent formability and ductility.
Brinell Hardness	180–220 HB	Provides good hardness for wear resistance while maintaining formability.
Machinability Rating	60% (vs. 1212 steel at 100%)	Requires special tooling but is still machinable with proper techniques.

Key Characteristics of SUS904L Stainless Steel: Benefits and Comparisons

SUS904L stainless steel is renowned for its excellent corrosion resistance, high strength, and formability. Below is a comparison between SUS904L and other materials like SUS316L and SUS304, showing its unique advantages.

1. Corrosion Resistance

Unique Trait: The combination of high chromium, nickel, and molybdenum content makes SUS904L one of the most corrosion-resistant stainless steels, particularly in aggressive environments like sulfuric acid and chloride-containing solutions.
Comparison:
- vs. SUS316L: SUS316L is highly resistant to corrosion, but SUS904L offers superior resistance to pitting and crevice corrosion due to its higher molybdenum content.
- vs. SUS304: SUS304 has lower corrosion resistance compared to SUS904L, particularly in acidic environments where SUS904L excels.

2. High Strength and Toughness

Unique Trait: Despite being highly corrosion-resistant, SUS904L maintains good mechanical properties with a 520–720 MPa tensile strength and excellent formability, making it ideal for complex components.
Comparison:
- vs. SUS316L: SUS904L offers a higher tensile strength than SUS316L, making it more suitable for high-strength applications.
- vs. SUS304: While SUS304 is easier to machine, SUS904L provides much higher strength and toughness for industrial use.

3. Weldability

Unique Trait: The low carbon content in SUS904L minimizes the risk of carbide precipitation during welding, ensuring strong and crack-free welds without the need for post-weld heat treatment.
Comparison:
- vs. SUS316L: Both materials are highly weldable, but SUS904L's reduced risk of carbide precipitation makes it superior in preventing weld degradation.
- vs. SUS304: SUS304 is easier to weld, but SUS904L's resistance to stress corrosion cracking makes it the better choice for severe environments.

4. Machinability

Unique Trait: While SUS904L is harder than SUS304, it is still machinable with the right tools. However, machining this material requires carbide tooling and high-speed machining due to its hardness.
Comparison:
- vs. SUS316L: SUS316L is easier to machine but provides less corrosion resistance than SUS904L.
- vs. SUS304: SUS304 is easier to machine but lacks the superior mechanical properties of SUS904L.

5. Post-Processing Flexibility

Unique Trait: SUS904L can be easily polished to achieve a bright, shiny surface finish, making it ideal for functional and aesthetic applications in pharmaceutical and food processing industries.
Comparison:
- vs. SUS316L: While both are ideal for post-processing, SUS904L offers superior corrosion resistance when exposed to harsh environments.
- vs. SUS304: SUS304 is commonly polished, but SUS904L outperforms it in extreme corrosive environments.

CNC Machining Challenges and Solutions for SUS904L Stainless Steel

Machining Challenges and Solutions

Challenge	Root Cause	Solution
Work Hardening	High alloy content and hardness	Use carbide tools with TiN coatings to reduce friction and prevent work hardening.
Surface Roughness	Hard material properties causing rough finishes	Optimize feed rates and utilize climb milling for smoother finishes.
Burr Formation	Hardness leading to burr formation	Increase spindle speed and reduce feed rates during finishing passes.
Dimensional Inaccuracy	Residual stresses from alloy content	Perform stress-relief annealing to reduce dimensional variation.
Chip Control Issues	Hard material forming long chips	Use high-pressure coolant (7–10 bar) and implement chip breakers.

Optimized Machining Strategies

Strategy	Implementation	Benefit
High-Speed Machining	Spindle speed: 1,200–1,500 RPM	Reduces heat buildup and improves tool life by 25%.
Climb Milling	Directional cutting path for optimal surface finish	Achieves surface finishes of Ra 1.6–3.2 µm, improving part aesthetics.
Toolpath Optimization	Use trochoidal milling for deep pockets	Reduces cutting forces by 40%, minimizing part deflection.
Stress-Relief Annealing	Preheat to 650°C for 1 hour per inch	Minimizes dimensional variation to ±0.03 mm.

Cutting Parameters for SUS904L Stainless Steel

Operation	Tool Type	Spindle Speed (RPM)	Feed Rate (mm/rev)	Depth of Cut (mm)	Notes
Rough Milling	4-flute carbide end mill	800–1,200	0.15–0.25	2.0–4.0	Use flood coolant to prevent work hardening.
Finish Milling	2-flute carbide end mill	1,200–1,500	0.05–0.10	0.5–1.0	Climb milling for smoother finishes (Ra 1.6–3.2 µm).
Drilling	135° split-point HSS drill	600–800	0.10–0.15	Full hole depth	Peck drilling for precise hole formation.
Turning	CBN or coated carbide insert	300–500	0.20–0.30	1.5–3.0	Dry machining is acceptable with air blast cooling.

Surface Treatments for CNC Machined SUS904L Stainless Steel Parts

Electroplating: Adds a corrosion-resistant metallic layer, extending part life in humid environments and improving strength.
Polishing: Enhances the surface finish, providing a smooth, shiny appearance ideal for visible components.
Brushing: Creates a satin or matte finish, masking minor surface defects and improving aesthetic quality for architectural components.
PVD Coating: Boosts wear resistance, increasing tool life and part longevity in high-contact environments.
Passivation: Creates a protective oxide layer, enhancing corrosion resistance in mild environments without altering dimensions.
Powder Coating: Offers high durability, UV resistance, and a smooth finish, ideal for outdoor and automotive parts.
Teflon Coating: Provides non-stick and chemical-resistant properties, ideal for food processing and chemical handling components.
Chrome Plating: Adds a shiny, durable finish that enhances corrosion resistance, commonly used in automotive and tooling applications.
Black Oxide: Provides a corrosion-resistant black finish, ideal for parts in low-corrosion environments like gears and fasteners.

Industry Applications of CNC Machined SUS904L Stainless Steel Parts

Chemical Processing Industry

Pumps and Valves: SUS904L is ideal for components exposed to aggressive chemicals, ensuring long-lasting durability.

Marine Industry

Boat Fittings: SUS904L’s corrosion resistance in saltwater environments makes it the preferred choice for marine parts.

Pharmaceutical Industry

Sterilization Equipment: The material’s resistance to corrosion and high temperatures makes it suitable for medical device components.

Technical FAQs: CNC Machined SUS904L Stainless Steel Parts & Services

What are the advantages of using SUS904L in highly corrosive environments?
How does SUS904L compare to other stainless steels in terms of machinability?
What post-processing methods are recommended for SUS904L to enhance its corrosion resistance?
How does SUS904L perform in high-temperature applications such as pressure vessels?
What is the best way to ensure precise tolerances when machining SUS904L stainless steel?