ASTM A194 Heavy Hex Nuts

ASTM A194: Material and Performance Standard

ASTM A194 defines the mechanical and material requirements for carbon, alloy, and stainless steel nuts that are intended for high-pressure or high-temperature service. This specification covers the material composition, heat treatment, and mechanical properties (such as hardness and tensile strength) required for nuts used in demanding environments like pressure vessels, pipelines, and flanges.

At NINGBO DATIAN FASTENER, we produce nuts that conform to ASTM A194 grades such as 2H, 2HM, 7, and 7M. These nuts are commonly used with bolts made to ASTM A193 standards in high-stress, corrosive, or high-temperature environments, ensuring durability and safety in critical applications.

ASME B18.2.2: Dimensional Standard

ASME B18.2.2 provides the dimensional requirements for finished and heavy hex nuts, ensuring that they meet standardized tolerances for width across flats, height, and thread dimensions. This standard guarantees that the nuts we manufacture at NINGBO DATIAN FASTENER are precisely dimensioned for proper fit and interchangeability with bolts and other fasteners in a wide range of mechanical assemblies.

How They Work Together

While ASTM A194 governs the material properties and performance requirements of nuts, ASME B18.2.2 ensures the physical dimensions and fit. This dual compliance means that a Grade 2H heavy hex nut from NINGBO DATIAN FASTENER adheres to the stringent mechanical standards of ASTM A194 while also meeting the dimensional specifications set forth by ASME B18.2.2.

For example, a Grade 2H heavy hex nut produced by NINGBO DATIAN FASTENER is heat-treated to achieve the required mechanical properties like hardness and tensile strength according to ASTM A194. Simultaneously, it conforms to the dimensional tolerances for hex nuts defined in ASME B18.2.2, ensuring a perfect fit with corresponding bolts.

In Summary

ASTM A194 focuses on the performance, material composition, and mechanical strength of nuts used in specific high-stress environments.

ASME B18.2.2 ensures that the nuts have standardized dimensions to ensure they fit properly with bolts and other fasteners in mechanical assemblies.

At NINGBO DATIAN FASTENER, we ensure that our products meet both these essential standards, offering nuts that are reliable, durable, and dimensionally accurate for high-performance applications.

In ASTM A194, the different grades of nuts like 2H, 2HM, 7, 7M, and 4 refer to specific material properties and intended applications. Here’s how they differ:

1. Grade 2H:
   
   

   Material:	Made from medium carbon steel, either quenchedand tempered (heat-treated) for added strength.
   Applications:	Used in high-temperature and high-pressure environments, often paired with bolts made to ASTM A193 standards.
   Strength:	Provides high strength for critical applications, including structural, pressure vessel, and pipeline systems.
   Common Use:	Used in the oil and gas industry, for flange connections, and in other high-stress applications.

2.  Grade 2HM:

   
   

   Material:	Similar to 2H in composition (medium carbon steel), but the nuts are tempered to a lower hardness range.
   Difference from 2H:	Designed for use in applications where hydrogen embrittlement is a concern  (e.g., in environments that may cause stress corrosion cracking).
   Applications:	Primarily used in sour gas or H₂S environments where cracking from hydrogen absorption is an issue.
   Strength:	Slightly lower strength compared to 2H, but offers greater toughness and ductility to withstand specific environmental factors.

3. Grade 7:

   
   

   Material:	Made from low alloy steel, typically quenched and tempered.
   Applications:	Used in low-temperature service environments (e.g., cryogenic service).
   Strength:	Similar in strength to 2H but with improved  performance at low temperatures.
   Common Use:	Found in low-temperature applications, often paired with ASTM A320 Grade L7 bolts  for cryogenic systems.

4. Grade 7M:

   
   

   Material:	Same material as Grade 7 but with a the different tempering process to improve toughness.
   Difference from Grade 7:	The "M" designation indicates that it has been modified for greater toughness (lower hardness).
   Applications:	Specifically used in applications requiring better toughness at lower temperatures, where crack resistance is critical.
   Strength:	Slightly lower hardness than Grade 7 but with enhanced ductility, similar to the difference between 2H and 2HM.

5. Grade 4:

   
   

   Material:	Made from carbon molybdenum alloy steel, quenched, and tempered.
   Applications:	Generally used in high-pressure and high-temperature environments.
   Strength:	Grade 4 nuts are used in elevated temperature applications but are less common than Grades 2H and 7.
   Common Use:	Sometimes found in specific industrial applications requiring high strength under thermal stress, although it is not as widely used as other grades.

Summary of Key Differences:

2H and 7 grades are designed for general high-pressure/high-temperature applications.

2HM and 7M are modifications of their respective grades with a focus on hydrogen embrittlement resistance and improved toughness at low temperatures.

Grade 4 is less common but used for specific high-strength applications under high-temperature conditions.

Each grade is chosen based on the specific environmental conditions and mechanical requirements, ensuring that the nut's material and treatment are suited to the demands of the service environment.

In China, using 45# steel and B7 material to produce different grades of nuts according to the ASTM A194 standard is a reasonable substitution based on the availability and performance requirements of these materials within the local market.

1. Using 45# Steel to Produce Grade 2H and 2HM Nuts:

45# steel (equivalent to AISI 1045) is a commonly used medium carbon steel in China, known for its good mechanical properties. After quenching and tempering, it can achieve the required hardness and strength levels.

Grade 2H and 2HM nuts require medium carbon steel that has been quenched and tempered to meet the necessary strength and hardness requirements. 45# steel can reach these mechanical performance criteria through appropriate heat treatment processes. Therefore, 45# steel is widely used in China for producing Grade 2H and 2HM nuts, as it offers similar mechanical properties to the materials specified in the ASTM standard, such as AISI 1045.

2. Using B7 Steel to Produce Grade 7 and 7M Nuts:

B7 steel (equivalent to AISI 4140 or 4142) is a low alloy steel commonly used for high-strength bolts. After quenching and tempering, it achieves high strength and durability, making it especially suitable for applications in both high and low temperatures.

The materials for Grade 7 and 7M nuts need to have excellent low-temperature toughness and high strength. Typically, these nuts are made from low alloy steels like B7 steel. The quenching and tempering process gives B7 steel the necessary low-temperature toughness and high strength, meeting the performance requirements for Grade 7 and 7M. Therefore, using B7 steel to produce these nut grades is a common practice in China.

Summary:

45# Steel: This medium carbon steel, when properly heat-treated, can meet the mechanical performance requirements for Grade 2H and 2HM nuts.

B7 Steel: A low alloy steel that, when quenched and tempered, meets the requirements for Grade 7 and 7M nuts, particularly excelling in both high and low-temperature environments.

This choice of material substitution is based on the availability of materials in China and the feasibility of local manufacturing processes, while still ensuring that the mechanical properties of the nuts meet international standards.