HEX NUTS MATERIALS

ASTM A194

The ASTM A194 specification covers a variety of carbon, alloy, martensitic and austenitic stainless steel nuts. Hex-heavy nuts are components of boltings sets for flanges.

These nuts are intended for high-pressure or high-temperature service or both. Bars from which the nuts are made shall be hot-wrought.

According to the ASTM A194 norm, the material may be further processed by centerless grinding or by cold drawing.

Austenitic stainless steel may be solution annealed or annealed and strain-hardened. Each alloy shall conform to the chemical composition requirements prescribed.

Hardness tests, proof of load tests, and cone-proof load tests shall be made to all nuts to meet the requirements specified.

ASTM A194 Chemical Composition

ASTM A194 Mechanical Properties

Grade Identification Marking5	Specification	Material	Nominal Size, In.	Tempering Temp. °F	Proof Load Stress, ksi	Hardness Rockwell		See Note
						Min	Max
	ASTM A194 Grade 2	Medium Carbon Steel	1/4 – 4	0	150	159	352	1,2,3
	ASTM A194 Grade 2H	Medium Carbon Steel, Quenched and Tempered	1/4 – 4	850	175	C24	C38	1,2
	ASTM A194 Grade 2HM	Medium Carbon Steel, Quenched and Tempered	1/4 – 4	1150	150	159	237	1,2,3
	ASTM A194 Grade 4	Medium Carbon Alloy Steel, Quenched and Tempered	1/4 – 4	1100	175	C24	C38	1,2
	ASTM A194 Grade 7	Medium Carbon Alloy Steel, Quenched and Tempered	1/4 – 4	1100	175	C24	C38	1,2
	ASTM A194 Grade 7M	Medium Carbon Alloy Steel, Quenched and Tempered	1/4 – 4	1150	150	159	237	1,2,3
	ASTM A194 Grade 8	Stainless AISI 304	1/4 – 4	–	80	126	300	4
	ASTM A194 Grade 8M	Stainless AISI 316	1/4 – 4	–	80	126	300	4

OTHER ASTM GRADES FOR HEX NUTS

ASTM A563

• Scope: Provides specifications for carbon and alloy steel nuts.
• Grades: Offers a range of grades including Grade A (mild carbon steel), Grade C (medium carbon, quenched and tempered), Grade DH (carbon steel, quenched and tempered), and others, suitable for general use to high-strength applications.

ASTM F594

• Scope: Covers the requirements for stainless steel nuts used in general engineering applications.
• Grades: Classifies nuts based on alloy groups such as 304, 316, and 321, with conditions indicating the strength level (CW – cold worked, A – annealed).

ASTM F467

• Scope: This specification is for nonferrous nuts for general use, made from materials like aluminum, copper, and nickel alloys.
• Grades: Nuts are categorized by the material and its temper, e.g., Aluminum Alloy 6061-T6.

ASTM A563M (Metric)

• Scope: The metric companion to ASTM A563, covering carbon and alloy steel nuts in metric sizes.
• Grades: Similar to ASTM A563 but tailored for metric dimensions and strength classes.

ASTM F836M

• Scope: The metric version of ASTM F594, specifies stainless steel nuts in metric sizes for general engineering use.
• Grades: Classified by alloy group and condition, similar to ASTM F594 but in metric measurements.

EUROPEAN MATERIAL GRADES SPECS FOR NUTS

In Europe, the specifications for hexagonal nuts used with flanges are defined by several standards, ensuring compatibility and performance across various applications, particularly in the industrial, construction, and energy sectors. Here are some of the key European specifications:

1. EN ISO 4032

• Scope: This standard specifies the characteristics of hexagonal nuts, style 1, with threads from M1.6 up to and including M64, of product grade A for threads ≤ M16 and product grade B for threads > M16.
• Applications: These nuts are generally used for all types of flanged connections.

2. EN ISO 4033

• Scope: Similar to EN ISO 4032 but specifies the characteristics of hexagonal high nuts.
• Applications: Used where longer thread engagement is necessary or for aesthetic reasons in various assemblies, including flanged connections.

3. EN ISO 4034

• Scope: Specifies the characteristics of hexagonal nuts, style 1, with threads from M5 up to and including M39, of product grade C.
• Applications: Suitable for less critical applications where a coarse tolerance is acceptable.

4. EN ISO 4035

• Scope: This standard covers hexagon thin nuts (chamfered) with metric fine-pitch thread, product grades A and B.
• Applications: Used in applications where space constraints require a thinner nut, including some flange connections.

5. EN ISO 4036

• Scope: Specifies hexagon thin nuts (unchamfered) with metric fine-pitch thread, product grades A and B.
• Applications: Similar to EN ISO 4035, for applications needing a thin nut without a chamfer, such as certain flanged joints.

6. EN 1092-1:

While primarily focused on flanges and their joints, EN 1092-1 indirectly sets requirements for bolts and nuts used in flanged connections by specifying flange types, dimensions, and materials suitable for various pressure and temperature conditions.

Common ISO Grades for Nuts

In Europe, steel nuts and other fasteners are commonly classified according to ISO standards, which provide a uniform framework for specifications across international borders. The material grades for steel nuts under the ISO standards are designated to match specific mechanical properties, corrosion resistance, and intended use environments. Here are some common European material grades for steel nuts according to ISO:

ISO 898-2 for Carbon Steel and Alloy Steel Nuts

• Class 6: A low-strength grade used for light-duty applications where high tensile strength is not required.
• Class 8: A medium strength grade, widely used for general engineering applications.
• Class 10: A high-strength grade suitable for applications requiring good tensile strength and hardness.
• Class 12: Similar to Class 10 but with higher tensile strength and hardness for more demanding applications.

ISO 3506-2 for Stainless Steel Nuts

A1, A2, A4 Stainless Steel:

• A2 (AISI 304 equivalent): The most commonly used stainless steel grade for nuts, offering good corrosion resistance in standard environments. Suitable for both indoor and outdoor applications.
• A4 (AISI 316 equivalent): Offers enhanced corrosion resistance compared to A2, making it ideal for marine and chemical exposure environments due to the addition of molybdenum.

Tensile/Yield Strength Classification (8.8/10.9 Nuts)

The ISO 898 grading system for mechanical properties of hex nuts for flanges is a two-number system where:

• The first number multiplied by 100 gives the approximate minimum ultimate tensile strength in megapascals (MPa).
• The second number (when multiplied by the first number) gives the ratio of the yield strength to the tensile strength.

8.8 Grade Steel Nuts:

• Tensile Strength: The “8” in 8.8 indicates that the tensile strength is 800 MPa.
• Yield Strength: The “.8” indicates that the yield strength is 0.8 times the tensile strength, which calculates to approximately 640 MPa (0.8 x 800 MPa).
• Material and Coating: These are made from medium carbon steel or alloy steel and can be heat-treated. They may be coated with zinc or other protective coatings to enhance corrosion resistance.
• Applications: Grade 8.8 nuts are commonly used in automotive applications, construction, and manufacturing, where moderate levels of strength and toughness are required.

10.9 Grade Steel Nuts:

• Tensile Strength: The “10” in 10.9 indicates that the tensile strength is 1000 MPa.
• Yield Strength: The “.9” indicates that the yield strength is 0.9 times the tensile strength, which calculates to approximately 900 MPa (0.9 x 1000 MPa).
• Material and Coating: These are typically made from alloy steel and undergo a heat treatment process to achieve higher strength levels. Like the 8.8 grade, 10.9 nuts can also receive coatings for corrosion resistance.
• Applications: Grade 10.9 nuts are used in applications requiring high strength and durability, such as in heavy machinery, and structural applications, and where high loading is expected.

Key Considerations for Selection:

Application Requirements: Consider the mechanical loads, environmental conditions, and whether the application requires specific properties like corrosion resistance or prevailing torque.

Corrosion Resistance: Choose between A2 or A4 stainless steel grades based on the environmental exposure, with A4 being preferred for harsher conditions such as marine environments.

Mechanical Properties: Select the class (for carbon and alloy steel nuts) based on the required strength and application stress levels.