ASTM G98-23 PDF

Overview

ASTM G98-23: Standard Test Method for Galling Resistance of Materials provides a laboratory procedure for ranking material couples based on their resistance to galling-a common and damaging wear phenomenon in sliding metal components. Developed by ASTM International, this standard aims to simulate conditions under which galling is likely to occur, especially in slow-moving, intermittently operated systems. The method is essential for industries seeking to identify materials or coatings that minimize galling risk and maintain component performance and reliability.

Key Topics

• Galling Definition: Galling is a form of severe surface damage and material transfer that occurs between sliding solids, resulting in roughening, protrusions, or even seizure of the components.
• Test Scope: The method is primarily intended for bare metals and alloys, but can also evaluate non-metallics, coatings, and surface-modified materials.
• Test Limitations:
  • Not suitable for lubricated sliding systems, as galling is unlikely under such conditions in this procedure.
  • Not recommended for final quantitative design calculations since in-service performance is influenced by lubrication, geometry, alignment, and other factors.
• Test Procedure:
  • Standardized flat-on-flat specimen geometry (button-on-block).
  • Incremental load application with specimen rotation to induce galling.
  • Threshold galling stress is determined by gradually increasing load until visible galling is observed.
  • At least three repeat determinations are averaged for accuracy.
• Reporting Requirements: Test reports should include specimen composition, hardness, thermal history, threshold galling stress, surface finish, test environment details, and any unusual occurrences.

Applications

ASTM G98-23 is widely used in quality control, materials selection, R&D, and failure analysis within industries where galling can compromise safety, functionality, or lifespan of components. Key applications include:

• Threaded Fasteners: Prevents seizure in nuts and bolts by selecting galling-resistant combinations.
• Valve Trim and Seals: Assures leak-free operation by minimizing surface damage in slow-moving, high-contact pressure systems.
• Pump Wear Rings: Maintains efficiency by reducing galling-related malfunctions.
• Prototypical Testing: Screens candidate materials before more complex, application-specific evaluations.
• Comparative Ranking: Provides a comparative, rather than absolute, ranking of material couples under defined laboratory conditions.

Related Standards

When evaluating galling and wear resistance, the following standards and resources are also relevant:

• ASTM G40: Terminology Relating to Wear and Erosion-Essential for understanding galling and other wear processes.
• ASTM G83: Test Method for Wear Testing with a Crossed-Cylinder Apparatus-Useful for scenarios dominated by gradual mechanical wear rather than discrete galling failure.
• ASTM E177 / E691: Standards for precision, bias, and interlaboratory study practices in test methods.

Practical Value

By following ASTM G98-23, manufacturers, engineers, and researchers can:

• Identify material combinations that will minimize galling in real-world applications.
• Streamline material selection processes for improved service life and reduced maintenance costs.
• Reduce the risk of unexpected component seizure, leaks, or failures in critical systems.
• Support quality assurance and compliance with international best practices in wear testing.

Keywords

Galling resistance, ASTM G98, galling test, wear testing, surface damage, sliding materials, threshold galling stress, material ranking, metals, alloys, failure prevention, laboratory test method.