A fastener is a hardware device that mechanically joins or affixes two or more objects together. Fasteners can also be used to close a container such as a bag, a box, or an envelope; or they may involve keeping together the sides of an opening of flexible material, attaching a lid to a container, etc.
The ever-increasing global trade and the advancements of technology in energy sectors gives rise to a need for standards and standardizations. It’s worthwhile to consider that the standards are documented agreements containing technical specifications and other precise criteria to be considered as rules, guidelines or definitions of characteristics to make sure that the material, products, processes and services are appropriate.
Common austenitic stainless steel fasteners grades -
• SS 302: It is a well-known general purpose stainless retains untarnished surface finish under most atmospheric conditions and thus known as high-temperature steel. This speciality makes it suitable for wire products such as springs, screens, cables; common material for flat washers & screws.
• SS 302HQ: when the amount of Cu is Extra over 302, then it reduces work hardening during cold forming and known as SS302HQ. Its common applications include machine screws, metal screws and small lock nuts.
• SS 303: it contains small amounts of sulphur for improved machinability hence it is often used
for custom-made nuts and bolts.
• SS 304: Low in carbon and higher in chromium, this type of stainless steel is with higher corrosion resistance than 302 and 303. Mostly used for hex head cap screws, cold heading and for hot heading of large diameter Hex head bolts and long bolts.
• SS 304L: 304L is low in carbon as compared to 304, and therefore contains slightly lower
strength characteristics. The low carbon content is good for 304L corrosion resistance and welding capacity.Good material for Shoulder Bolts.
• SS 309 & SS 310: SS 309 & SS 310 are higher in both nickel and chromium content than the lower alloys, and hence are appropriate for use in elevated temperature applications.
Additionally, SS 310 contains extra corrosion resistance to salt and other hostile chemicals. better to use this material to make fasteners for Industrial purpose where acids and chemicals are used.
• SS 316 & SS 317: Have significantly improved corrosion resistance especially when exposed to salts present in seawater and many types of chemicals. Addition of molybdenum gives this a better resistance to surface pitting. SS 316 & SS 317L have higher tensile strength and creep strength at elevated temperatures compared to other austenitic alloys. This grade of stainless steel is better for Nuts, Bolts & Screws in high corrosive environment
Now, Let’s have a look at the martensitic stainless steel grades which are as follows-
• SS 410: In this type of chromium alloy there is absence of nickel. It is popularly known as general-purpose corrosion and heat resisting, hardenable chromium steel. This material has increased hardness, and therefore are commonly used for self-drilling and Self tapping screws. Corrosion resistance property of this type is not as good as SS 300 grades.
• SS 416: it is highly similar to 410 except that there is slightly more chromium in it, which makes it appropriate for machinability, whereas corrosion resistance is not upto the mark.
Let’s have a look at the following example to demonstrate the effectiveness of tempering:
Consider the 3 types with minimum tempering temperatures for each specification 1. ASTM A193 Grade B7: 1150°F, 2. SAE J429 Grade 8 : 800°F and 3. ASTM A574 Socket Head Cap Screws: 650°F.
Alloy steel standards are used to manufacture any of the three final products such as 4140 and 4142 alloy steel. The initial heat-treating process is relatively the same and the parts are heat treated until fully austenitized. The parts are then quenched (cold water or oil as a quenching medium ) and tempered in a liquid medium.
The final mechanical properties of ASTM A193 B7 are as follows
• Tensile Strength: 125,000 PSI minimum (2”-1/2” and below)
• Yield Strength: 105,000 PSI minimum (2”-1/2” and below)
• Hardness: HRC 35 Max SAE J429 Grade 8
• Tensile Strength: 150,000 PSI min 9,
• Proof Strength: 120,000 PSI
• Yield Strength: 130,000 PSI min.
• Hardness: HRC 33-39 ASTM A574 Socket Head Cap Screw
• Tensile Strength: 180,000 PSI minimum (through ½”), 170,000 PSI minimum (> ½”)
• Proof Strength: 140,000 PSI (through ½”), 135,000 PSI (> ½”)
• Yield Strength: 153,000 PSI min.
• Hardness: HRC 39-45 (through ½”) and HRC 37-45 (> ½”)
Lower temperature will produce a harder and higher tensile strength part for these alloy steels. However, the lower tempering temperatures indicate lower service conditions, ductility, impact strength and possible fatigue life. For example B7 has a high temperature limitation of approximately 750-800°F whereas ASTM A574 socket head cap screws and grade 8’s have a limitation of approximately 400-500°F.
The structural Bolts standards ASTM A325 & ASTM A490 are the 2 U.S. standard structural bolts. As per the Mechanical requirements ASTM A325 and SAE J429 Grade 5 appear similar. This also appears to be true for the ASTM A490 and the SAE J429 Grade 8.
You would also need to know that A325 and A490 bolts are produced with a heavy hex head configuration whereas Grade 5 and 8 bolts are produced to standard hex cap screw configuration.
Finally, a corollary of distinct international and regional standard organizations-
Here is a brief description of some the larger organizations for better understanding:
1. ANSI (American National Standard Institute):
It was founded in the year 1918. ANSI has served in its capacity as administrator and coordinator of the United States private sector voluntary standardization system. ANSI promotes the use of U.S. standards internationally, regional standards organizations and encourages the adoption of internal standards as national standards where these meet the needs of the user community. It doesn’t develop American National Standards on its own but it facilitates development by establishing consensus among the ANSI member associations such as ASTM, SAE, ASME, etc.
2. ASTM (The American Society for Testing and Materials):
It is a scientific and technical organization formed for the purpose of development of standards on characteristics and performance of materials, products, systems, and services; and the promotion of related knowledge. This committee publishes standard test methods, specifications, practices, guides, classifications and terminology. This standard typically covers metals, paints, plastics, textiles, petroleum, construction, medicinal, electronics, fasteners etc.
3. ASME (American Society of Mechanical Engineers):
Established in 1880, ASME is an organization working to develop codes and standards for the engineering profession, the public, industry and government. As of tnow, there are more than 600 standards published by ASME on topics such as screw threads, valves, flow measurement and much more.
4. SAE (Society of Automotive Engineers):
From the year 1905, SAE has been developing and implementing standards and safety specifically used in designing, building, maintaining and operating vehicles.
5. ISO (The International Organization for Standardization):
ISO is a specialized multinational and multicultural international organization with around 120- member countries governed by consensus and spanning the breadth of global technology. The vision of ISO is to promote the development of standardization and related activities throughout the world. This organization aggregates the interests of consumers, producers, governments and the scientific community in the formation of international standards covering everything like screw threads, surgical implants and many more.
6. DIN (Deutsches Institut fur Normung):
It is not a government agency. DIN plays a major role in which representatives for the manufacturing industries, consumer industries, consumer organizations, commerce, service industries, science will gather. These standards are technical rules that promote rationalization, quality assurance, safety and environmental protection as well as improving communication between industry, technology, science, government and also public. For continuing relevance after every five years, published standards are reviewed. conventionally, DIN has been the strongest standard for metric products throughout the world. Countries without their own metric standards base have usually referred to DIN in technical documentation.
7. JIS (Japanese Industrial Institute):
JIS is a leader in terms of metric hardware standards. Some of them are modified to meet the needs they have in Japan. additionally, they are typically used for electronic equipment in the US.
Description- In essence, the name stainless steel covers a variety of corrosion resistant steels. Ideally, they have a Chromium content between 12% and 18%. They can’t be hardened by heat treatment but have the useful property of being able to be work hardened. Before you buy stainless steel equipment, you should understand various grades of it and
the Organization of engineers that develops standards for professionals. You may also see this grading system called the JIS, DIN, ANSI, ISO, ASME, ASTM and so on.
|ASTM A193||• B6
• B8 class 1 & 2
• B8M class 1 & 2
• B8T class 1 & 2
|ASTM A194||• 2H
|ASTM A320||• L7
|ASTM A453||• 660A
|ASTM A453||• 660A
|ASTM A182, A276, A479||• 31803
|ASTM A182, A276, A479||• 31803
• 32760 SA, FG, FLT
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