ASTM GRADES

The Fundamental grades

CF8 (304) and CF8M (316) are the most common grades and are used in general corrosion and food processing industries.

CF3M (316L) offers better weldability and is used where welding is required without significant degradation.

CG8M (316L, Graphite-controlled) is a special version of 316L, which is optimized for applications requiring control over carbide formation during welding, thus ensuring better corrosion resistance.

HK (25Cr-20Ni) and HP (35Cr-25Ni) grades are high-performance alloys designed for extreme environments, with exceptional heat resistance and high oxidation resistance at elevated temperatures, commonly found in furnace components and reformer tubes.

ASTM casting grades are specific designations used to identify the composition and properties of materials used in the casting process to help maintain consistency.

Key Aspects of ASTM Casting Grades:

• Standard Specifications:

ASTM standards provide detailed specifications for each grade, covering chemical composition, mechanical properties, and other relevant characteristics. 

• Material Types:

ASTM grades encompass a wide range of materials, including steel, iron, and stainless steel castings, each with specific properties for various applications. 

• Grade Designations:

Grades are typically designated using a combination of letters and numbers, such as A27, A216 WCB, or A351 CF8. 

• Application-Specific:

The selection of a specific grade depends on the intended application, considering factors like strength, ductility, corrosion resistance, and high-temperature performance.

ASTM Stainless Steel Casting Grades have ASTM A series as follows :

• ASTM A351 - Austenitic stainless steel castings for pressure-containing parts.
• Grades: CF3, CF8, CF8M, CF3M, etc.
• ASTM A743 - Corrosion-resistant stainless steel castings.
• Similar grades to A351.
• ASTM A744 - Cast stainless steel for high-temperature and corrosion-resistant applications.

ASTM A351 - Austenitic Stainless Steel Castings

---

General Overview

ASTM A351 covers austenitic stainless steel castings intended for use in pressure-containing parts, especially in high-temperature or highly corrosive environments. These castings are commonly used in:

• Valves
• Pumps
• Flanges
• Pipe fittings
• Pressure vessels

They are known for:

• Good corrosion resistance
• High ductility
• Non-magnetic nature (unless cold-worked)
• Excellent weldability

---

---

Common Grades in ASTM A351

Grade	Cr-Ni-Mo Content	Description
CF8	18% Cr, 8% Ni	Equivalent to 304 stainless; good corrosion resistance.
CF8M	18% Cr, 8% Ni, 2-3% Mo	Equivalent to 316 stainless; better pitting and crevice corrosion resistance (e.g. seawater).
CF3	18% Cr, 8% Ni, low C	Similar to CF8 but low carbon (L grade); less susceptible to carbide precipitation.
CF3M	18% Cr, 8% Ni, 2-3% Mo, low C	Similar to CF8M but with low carbon; better for welding.
CN7M	High Ni, some Mo and Cu	Excellent resistance to sulfuric acid (e.g. Alloy 20).
CK20	25% Cr, 20% Ni	High-temperature and corrosion resistance.

---

Summary of Use-Case Recommendations:

• CF8: Standard, affordable, general-purpose stainless steel.
• CF3: Same as CF8 but with low carbon - ideal for welded components.
• CF8M: Has molybdenum - suitable for marine, chemical, or chloride-rich environments.
• CF3M: Best choice for corrosion + welding applications (e.g., pharma piping).
• CN7M: Specialized for acidic environments, especially sulfuric acid.
• CK20: Great at handling high temperatures, suitable for heat exchangers and furnace parts.

---

ASTM A743 - Standard Specification for Castings, Iron-Chromium, Iron-Chromium-Nickel, Corrosion Resistant

---

General Overview

ASTM A743 covers a broad range of corrosion-resistant cast stainless steels, including austenitic, martensitic, ferritic, and duplex grades. These are mainly intended for general corrosion-resistant applications, such as:

• Chemical processing equipment
• Marine hardware
• Food and dairy machinery
• Architectural components
• Industrial tools and structural parts

It does not necessarily require the stringent pressure containment requirements like ASTM A351, though many grades overlap.

---

Types of Stainless Steel Covered

ASTM A743 includes:

Category	Examples	Key Characteristics
Austenitic	CF8, CF8M, CF3, CF3M, CN7M	Good corrosion resistance, non-magnetic, weldable
Ferritic	CB30, CH20	Magnetic, good resistance to stress corrosion cracking
Martensitic	CA15, CA6NM	Hardenable, magnetic, moderate corrosion resistance
Duplex	CD4MCu, CD4MCuN	High strength, good resistance to chloride stress corrosion

---

Common Austenitic Grades in A743

These overlap with ASTM A351 but used in non-pressure parts:

Grade	Equivalent	Features
CF8	304	General purpose stainless steel
CF8M	316	Added Mo for better chloride resistance
CF3	304L	Lower carbon for better weldability
CF3M	316L	Mo + low carbon, ideal for welding
CN7M	Alloy 20	Sulfuric acid resistance, high Ni & Cu

---

Applications

• Structural supports and housings (non-pressure)
• Food and beverage processing equipment
• Heat exchangers
• Paper and pulp industry
• Water treatment and desalination

---

ASTM A744 - Standard Specification for Castings, Iron-Chromium-Nickel, Corrosion-Resistant, for Severe Service

---

Purpose

ASTM A744 is specifically developed for cast austenitic stainless steels used in high-temperature and mildly corrosive environments, such as:

• Heat treatment equipment
• Exhaust and flue gas systems
• High-temperature chemical processing
• Some pressure-retaining applications in mildly corrosive settings

It overlaps with ASTM A351 and ASTM A743 in chemical composition but is primarily selected for thermal resistance and light corrosion rather than mechanical pressure integrity or heavy-duty corrosion.

---

Common ASTM A744 Grades

Grade	Similar	Main Features
CF8	304	General purpose, good thermal resistance
CF8M	316	Improved corrosion & heat resistance
CF3M	316L	Better weldability + thermal & chloride resistance
CG8M	316 (controlled carbon)	Controlled graphite precipitation resistance
CH20	High-Cr Ferritic	Superior oxidation resistance at high temperature
HK	25Cr-20Ni	Excellent high-temperature strength & oxidation resistance
Ht	35Cr-25Ni	Even higher temp resistance than HK

---

Applications

• Heat exchanger components
• Furnace parts (baskets, trays, rolls)
• Flue ducts and stacks
• Exhaust manifolds
• Kiln components
• Reformer tubes

---

Key Differences: A744 vs. A351 vs. A743

Feature	ASTM A351	ASTM A743	ASTM A744
Primary Focus	Pressure-retaining parts	General corrosion resistance	Heat + mild corrosion
Material Type	Austenitic SS	Austenitic, Ferritic, Martensitic, Duplex	Austenitic SS only
Applications	Valves, pumps, pressure vessels	Tanks, piping, structures	Heat treat parts, flue systems
Heat Resistance	Moderate	Moderate	High
Pressure Rating	Yes	No	Sometimes
Surface Requirements	Stricter	Moderate	Usually less stringent

---

The ASTM A Super Duplex Stainless Steels are specified for various grades of super duplex stainless steel, which are typically used in highly corrosive environments./p>

Here are some of the common ASTM A Super Duplex grades, their compositions, and typical applications:

1. ASTM A890/A890M - Super Duplex Stainless Steel Castings

Grades:

• Grade 4A (UNS S32750)
• Grade 5A (UNS S32760)

Key Features:

• Grade 4A (S32750): Known for its excellent corrosion resistance to chlorides and seawater, it is suitable for offshore oil and gas production.
• Grade 5A (S32760): This grade is highly resistant to stress corrosion cracking and offers improved resistance to pitting and crevice corrosion compared to other duplex steels.

Applications:

• Offshore oil and gas platforms
• Chemical processing industries
• Desalination plants
• Marine environments
• Heat exchangers

---

2. ASTM A240/A240M - Super Duplex Stainless Steel Plate, Sheet, and Strip

Grades:

• UNS S32750
• UNS S32760

Key Features:

• These grades are used in plate, sheet, and strip form and offer high strength, excellent corrosion resistance, and pitting resistance in aggressive environments.

Applications:

• Pressure vessels
• Piping systems
• Marine structures
• Chemical reactors

---

3. ASTM A479/A479M - Stainless Steel Bars for General Industrial Use

Grades:

• UNS S32750
• UNS S32760

Key Features:

• These grades are available in bar form and are widely used in industries requiring high strength and resistance to aggressive environments.

Applications:

• Piping systems
• Valves
• Heat exchangers
• Marine applications

---

4. ASTM A995/A995M - Castings of Duplex Stainless Steel

Grades:

• UNS S32750
• UNS S32760

Key Features:

• These grades are available in bar form and are widely used in industries requiring high strength and resistance to aggressive environments.

Applications:

• Piping systems
• Valves
• Heat exchangers
• Marine applications

---

Properties of Super Duplex Stainless Steels (ASTM A890, A240, A479, A995)

Property	S32750 (F53)	S32760 (F55)	S31803 (F51)
Chromium (Cr)	24-26%	25-27%	21-23%
Nickel (Ni)	6-8%	6-8%	4.5-6.5%
Molybdenum (Mo)	3-5%	3-5%	2.5-3.5%
Nitrogen (N)	0.10-0.30%	0.10-0.30%	0.08-0.20%
Tensile Strength	700-900 MPa	800-1000 MPa	650-850 MPa
Yield Strength	500-700 MPa	600-800 MPa	450-600 MPa
Elongation	25-40%	25-40%	20-40%
Hardness (HB)	250-300	270-330	210-270
Impact Toughness	> 40 J at -50°C	> 40 J at -50°C	> 40 J at -50°C

---

These ASTM A super duplex grades provide excellent performance in terms of corrosion resistance, strength, and resilience in aggressive environments. They are used extensively in offshore and chemical industries, where both mechanical properties and corrosion resistance are critical.

Applications of ASTM A Super Duplex Stainless Steels:

1. Marine & Offshore:
• Super Duplex steels are commonly used in seawater environments due to their resistance to corrosion and chloride stress corrosion cracking.
• They are used for subsea equipment, offshore structures, pipelines, heat exchangers, valves, and pressure vessels exposed to aggressive marine conditions.
2. Chemical Processing:
• These materials are ideal for handling chemicals, especially in high-chloride and acidic environments where traditional stainless steels fail.
• Super duplex steels are used in reactors, tanks, and piping systems exposed to aggressive chemicals, including hydrochloric acid, sulfuric acid, and chlorides.
3. Desalination Plants:
• Super duplex steels are used in reverse osmosis systems and other desalination processes where they handle highly corrosive seawater.
4. Heat Exchangers & Pressure Vessels:
• The high strength and corrosion resistance of super duplex steels make them ideal for heat exchangers in industries that handle chemicals or high temperatures.

---

Benefits of Super Duplex Grades:

• Corrosion Resistance: Super duplex stainless steels offer exceptional resistance to pitting, crevice corrosion, and stress corrosion cracking, making them ideal for harsh environments, including chloride-rich and high-temperature applications.
• High Strength: These grades provide superior mechanical properties, including high tensile strength, yield strength, and impact toughness.
• Durability: The combination of austenitic and ferritic microstructures results in better resistance to fatigue and crevice corrosion compared to other stainless steels, leading to longer service life.

No, ASTM Super Duplex Stainless Steels are not martensitic. Instead, they are a blend of austenitic and ferritic structures, which is why they are called duplex steels.

---

Key Differences Between Duplex and Martensitic Steels:

Property	Duplex Stainless Steel (e.g., UNS S32750, UNS S32760)	Martensitic Stainless Steel (e.g., UNS S41000, UNS S42000)
Microstructure	A mix of austenite and ferrite (approximately 50/50)	Martensitic (single-phase microstructure)
Corrosion Resistance	Excellent (especially in chloride-rich environments)	Moderate (less resistance compared to duplex steels)
Strength	High strength and resistance to stress corrosion cracking	High hardness and strength (after heat treatment)
Toughness	High toughness and ductility	Lower toughness (more brittle)
Applications	Marine, chemical processing, offshore oil, heat exchangers	Cutlery, turbine blades, pumps, valves