Mechanical Properties and Identification Markings for Threaded Fasteners By K. P. Shah Email: kpshah123[at]gmail.com (Please replace [at] with @) Committed to improve the Quality of Life For more articles on mechanical maintenance, visit www.practicalmaintenance.net The information contained in this booklet represents a significant collection of technical information about mechanical properties and identification markings for threaded fasteners. This information will help to achieve increased reliability at a decreased cost. Assemblage of this information will provide a single point of reference that might otherwise be time consuming to obtain. Most of information given in this booklet is mainly derived from literature on the subject from the sources as per the references given at the end of this booklet. For more information, please refer them. All information contained in this booklet has been assembled with great care. However, the information is given for guidance purposes only. The ultimate responsibility for its use and any subsequent liability rests with the end user. Please view the disclaimer uploaded on http://www.practicalmaintenance.net. (Edition: September 2020) 1 Mechanical Properties and Identification Markings for Threaded Fasteners www.practicalmaintenance.net Content Chapter Title Page No. 1 Introduction 3 2 Mechanical Properties 4 3 Mechanical Properties of Fasteners Made of Carbon Steel and 10 Alloy Steel as per ISO Standard (ISO 898) 4 Mechanical Properties of Steel Nuts as per DIN Standards 25 5 Mechanical Properties of Corrosion Resistant-Stainless Steel 28 Fasteners as per ISO Standard (ISO 3506) 6 ASTM Standards for Fasteners 38 7 ASTM Standards for Carbon and Alloy Steel Externally Threaded 41 Fasteners 8 ASTM Standards for Carbon and Alloy Steel Nuts 56 9 ASTM Standards for Alloy Steel, Stainless Steel and Nickel Alloy 61 Threaded Fasteners 10 Threaded Fasteners as per SAE International 76 11 ASTM Standards for Nonferrous Threaded Fasteners 80 12 Washers 82 13 IS 1367: Technical Supply Conditions for Threaded Steel Fasteners 85 14 Selection of Fastener Material 87 15 Mechanical Properties and Grade Marking as per ASTM and SAE 94 Specifications - References 96 For more information on threaded fasteners, please visit www.practicalmaintenance.net 2 Mechanical Properties and Identification Markings for Threaded Fasteners www.practicalmaintenance.net Introduction A standard or a norm is a document containing agreements, specifications or criteria about a material, product, process or service. They are used to ensure that materials, products, processes and services are fit for their purpose. Standards are established within a company, an organization, a consortium of organizations or recognized standardization bodies. When a standard exists, a product / material requires little or no further description. Most of the features of a product / material are described in the standard. Most industrial threaded fasteners are covered by two basic standards: one for materials and properties; the other, for dimensions and tolerances. In ordinary usage of steel bolts, the chemical composition of the material and the manufacturing process are of little interest to the user, provided that the service requirements are met. Fastener material specification systems have been developed according to this reasoning. Most specifications are basically performance specifications. They emphasize performance criteria such as strength, hardness, ductility, and impact resistance. The material composition is usually flexible. This allows the manufacturer to choose the best material for the fastener. There always seems to be some confusion regarding mechanical versus metallurgical properties. Mechanical properties are those associated with elastic or inelastic reaction when force is applied, or that involve the relationship between stress and strain. Metallurgical testing includes chemical composition, microstructure, grain size, carburization and decarburization, and heat treat response. The chemical composition is established when the material is melted. Nothing subsequent to that process will influence the basic composition. The microstructure and grain size can be influenced by heat treatment. Carburization is the addition of carbon to the surface which increases hardness. It can occur if heat treat furnace atmospheres are not adequately controlled. Decarburization is the loss of carbon from the surface, making it softer. Partial decarburization is preferable to carburization, and most industrial standards allow it within limits. There are two main systems for measuring weights and distances: the metric system and the imperial system. For material standards, the primary standardization organizations for the metric system fasteners are the International Organization for Standardization (ISO) and the German Institute for Standardization (DIN) whereas for the imperial fasteners they are the American Society for Testing and Materials (ASTM) and the Society of Automotive Engineers (SAE). In view of this, information about mechanical properties and identification markings as per them is given in this booklet. Note: In ISO standards, comma (,) is used as a decimal marker. However, to maintain uniformity with general practice, I have used full point (.) as the decimal marker for the information given about ISO standard in this booklet. 3 Mechanical Properties and Identification Markings for Threaded Fasteners www.practicalmaintenance.net Mechanical Properties Most fastener applications are designed to support or transmit some form of externally applied load. For joint designing, fasteners are covered by standards/specifications that define required mechanical properties such as tensile strength, yield strength, proof load and hardness. Other mechanical properties are shear strength, fatigue strength and torsional strength. In view of this, information about bolted joints and mechanical properties is given in this chapter. Bolted Joints Loads can be applied to bolted joints in a number of different ways, each of which produces unique effects on the joint. These effects result from the way the joint is loaded, as well as how the joint responds to the load. Some of the various load types include tensile, shear and bending. The type of bolted joint derives its name from the external load applied to the joint. The stress in the bolt when the bolt has been tightened to the design extent is known as the pre-stress. The tensile load corresponds to the force that clamps the joint members together. Torsion in the bolt results from friction between the threads in the bolt and the nut. Some bolts are also exposed to shear loads which occur when the external force slides the members of the joint in relation to each other perpendicular to the clamping force. In a properly designed joint the external shear force should be resisted by the friction between the components. A joint of this kind is called a friction joint. If the clamping force is not sufficient to create the friction needed, the bolt will also be exposed to the shear load. Joints are frequently designed for a combination of tensile and shear loads. Tensile Properties The tensile properties; tensile strength and yield strength are determined by a tensile test. To find out tensile properties of a fastener material, a machined test piece is fitted in the jaws of the tensile testing machine (Universal Testing Machine) and subjected to a tensile force. The applied force and the resulting elongation of the test piece are measured. The process is repeated with increased force until the test piece breaks. The gauge length of the test piece is the length of the parallel portion of the test piece between gauge length marks on which elongation is measured at any moment during the test. The percentage elongation of the test piece is the elongation expressed as a percentage of the original gauge length. The elongation of the test piece is measured as extension by an arrangement consisting of dial gauge and clamps called the extensometer. 4 Mechanical Properties and Identification Markings for Threaded Fasteners www.practicalmaintenance.net The stress (intensity of force) at any moment during the test is the force divided by the original cross-sectional area of the test piece. The strain is the elongation of the test piece, increase in the extensometer gauge length at any moment during the test. It is expressed as a percentage extension, extension (increase in extensometer gauge length) expressed as a percentage of the extensometer gauge length. Using the readings of the test, a stress - strain (percentage extension) diagram is plotted to find out tensile properties. Tensile Strength As shown in above stress - strain (percentage extension) diagram, tensile strength (Rm) is the stress corresponding to the maximum force, Fm. Fracture is phenomenon which is deemed to occur when total separation of the test piece occurs. Yield Strength Yield strength is the strength when the metallic material exhibits a yield phenomenon, stress corresponding to the point (called yield point) reached during the test at which plastic deformation occurs without any increase in the force. 5 Mechanical Properties and Identification Markings for Threaded Fasteners www.practicalmaintenance.net As shown in above figure, upper yield strength (ReH) is the maximum value of the stress prior to the first decrease in force and the lower yield strength (ReL) is the lowest value of the stress during plastic yielding, ignoring any initial