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Distributor's Link Magazine Fall 2020 / Vol 43 No 4

10 THE DISTRIBUTOR’S

10 THE DISTRIBUTOR’S LINK Guy Avellon Guy Avellon has been in MRO and Fastener Distribution for over 30 years, in such positions Sales Engineer, Chief Engineer, Manager of Product Marketing, Product Engineering & Quality and Director of Quality & Engineering. He founded GT Technical Consultants where he performs failure analysis, lectures on fastener safety, works for law firms and designs/audits Quality systems. He is a member of SAE, is Vice Chairman of the ASTM F16 Fastener Committee, Chairman of the F16.01 Test Methods Committee and received the ASTM Award of Merit in 2005. Guy can be contacted at 847- 477-5057, Email: ExpertBoltGuy@gmail.com or visit www.BoltFailure.com. WHAT FASTENER DISTRIBUTORS NEED TO KNOW ABOUT IDENTIFYING STAINLESS STEEL The last article on stainless steels dealt with the different types of stainless steels. Generally, our common commercially available maintenance fasteners will consist of types 316 and 18-8. The 18-8 designation refers to a short-hand notation that these stainless steels contain 18% chromium and 8% nickel. However, 18-8 actually refers to five different types; 301, 302, 303, 304 and 305. Type 304 is the most common and exhibits the best properties of this group. The 300 austenitic series exhibits the best corrosion resistance properties of all other stainless steels, but they are not very hard or strong. The hardness is read on the Rockwell B scale and the tensile strengths hover slightly over 80 ksi at best. This barely bests the strength of an SAE Grade 2 fastener at 74 ksi. The 17-7 PH and 15-5 PH alloys are precipitation hardening, or age hardening alloys, that provide much higher tensile strengths and hardnesses, excellent fatigue properties and heat resistance to 900°F (482°C). They lack the chemical resistance of the 300 series but are still superior to other types of hardenable chromium alloys. Although adequate in many applications, the FDA (Food and Drug Administration) has allowed type 304 in various food handling equipment. Of course, type 316 and 316L is permitted for all uses, but is more costly. Stainless steel can be electropolished to produce a smooth surface resistant to abrasion and erosion. Contaminants do not easily adhere to ensure purity of food products and the alloys are suitable for high temperature sterilization. There are also no harmful chemicals in the steel CONTRIBUTOR ARTICLE that can migrate into the food to cause bacteria or contamination. Whenever in doubt, check with local FDA authorities. This is because under certain conditions, type 18-8 will become pitted from meat juices and blood. Even common mayonnaise will pit type 304. Strain hardening is another way of increasing the tensile strength of stainless steel. This is where the material is physically deformed into its plastic region from cold forming. The deformation leads into a reduced cross-sectional area that enhances its strength but will reduce the ductility of the part. Strain hardening a stainless steel fastener can produce tensile strengths equal to and greater than SAE Grade 5 (ISO 8.8). Being able to modify the properties of certain groups of stainless steels have created specifications to which the products are produced that will enhance their performance characteristics. The Unified Numbering System (UNS) employs an ‘S’ prefix, such as an ‘S30400’. Many ASME (American Society of Mechanical Engineers) specifications reference these UNS numbers for special industrial heat or chemical applications. The last two digits indicate other alloy additions, such as Boron, as in S30464, for nuclear applications. The UNS is managed jointly by the ASTM International and the SAE International. The ASTM has two committees for stainless products: The A193 and F593 Standards (there is a third which will be discussed later). The A193 is primarily for high temperature bolting and employs markings such as B8 or B8A for 304 and B8M for 316. In addition to the required manufacturer’s registered identification marking. CONTINUED ON PAGE 102

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