Materials for flat washers Flat washers without mechanical performance requirements are generally made of corner materials, such as Q235A. If the hardness is required but not high, it can be rolled with a thicker sheet to achieve the required hardness. Spring washers and other anti-loosening washers are generally made of 65Mn 70# or S 50CM—S 70CM. They must be heat-treated (quenched + tempered). Rivets, pin rivets, pin rivets are generally made of the same material as bolts, but some rivets The hardness should not be too high, and some even require HRB60 or less. Generally, the hardness of the normalized material is HRB70-80, so some have to be annealed to meet the performance requirements. Self-tapping nail materials generally use C1018, C1020, C1022 and other materials, but some domestic manufacturers use 18# 15# 20# to save costs and cut corners, and some manufacturers use Q235A, and then the surface carburizing treatment is completed. The toughness of the nail's heart is not up to the requirement, and it is easy to break. The commonly used stainless steel fasteners are: 200 series: SUS201, SUS202300 series: SUS301, SUS302, SUS303, SUS304, SUS316400 series: SUS410, SUS440
Nuts and other internal thread materials that do not have mechanical performance requirements or ISO Class 5-6 SAE Grade 3-4 generally use C1010 Q235A or C15. No heat treatment is required, and cold processing is sufficient. ISO Class 8, SAE Grade 5, generally use Ml35 SAE1035 DIN C35, small size nuts do not need heat to achieve the required mechanical properties, large sizes must be heat treated (quenching + tempering), this is GB3098.2 That is very clear. ISO Class 10 and SAE Grade 8 generally use medium carbon steel after heat treatment to meet its strength requirements. Medium carbon steel such as SAE1035. One thing everyone must pay attention to is that nuts and bolts are different. Their stress is mainly compression rather than extension. Therefore, the strength of the nut is not only related to the material, but also related to many factors, including accuracy, thread pitch, and nut chamfering. , Nut thickness
For bolts and other external thread materials that do not have mechanical performance requirements or ISO Class 4.8 SAE Grade 1-2 and other low-carbon steel fasteners, Q235A SAE 1015 DIN C15 is sufficient. No heat treatment is required at all, and it is directly cold processed. For higher fasteners such as ISO Class 6.8 SAE Grade 3-4, steel with a carbon content of more than 0.2% should be used, such as C1020 C1022 Ml20 ML35, etc. This type of screw does not require any heat treatment, and the cold working strength is complete. Can meet the requirements. In fact, the higher the carbon content, the more difficult it is to cold-form, and there is no need to use a grade 6.8 screw for overkill. Special circumstances are another matter. The most commonly used screws are ISO Class 8.8 SAE Grade 5. Medium carbon steel is generally used. ML35 SAE 1035 DIN 35 JIS SWRCH35K is heat treated (quenched + tempered), and SAE5140 40Cr, etc. can also be used. The increase in alloying elements will affect heat treatment. Hardenability is of great help, so you can choose to use alloy steel for screws with large specifications, so that the use of medium carbon steel will not cause the phenomenon of "impermeability" in the central part that we often say. ISO Class 9.8 10.9 SAE Grade 8 uses low-to-medium alloy steel materials, after heat treatment (quenching + tempering), the alloy material has a good combination of mechanical properties of the material, the commonly used material is 40Cr 35CrMo SAE5140 SCM435 SAE4135 SAE4137 JIS SCr440(H) DIN 41Cr4, etc. In fact, 45# can also achieve the required mechanical properties, but it is slightly inferior to alloy steel in terms of comprehensive mechanical properties. ISO Class12.9 SATM A574 is a high-strength bolt that requires high mechanical properties. It needs to be heat-treated (quenched + tempered) with medium carbon alloy steel, such as SCM435 35CrMo SAE 4137 SAE4135 DIN 34CrMo4. When the surface treatment has to go through the pickling process, hydrogen embrittlement will occur, so hydrogen removal must be done (especially for fasteners with sharp corners), otherwise the result will be very serious.
Other special requirements for materials If the company is to make fasteners for welding, arc welding and gas welding generally have no requirements for materials. If the customer uses spot welding, it must be done with low-carbon steel. If the strength must be increased, some low-carbon materials with higher Mn elements can be used. This is just a very simple example, many of which can only be noticed in actual production. When the customer specifies to use a certain grade of material, and the company does not have this material for a while, or this material is not easy to purchase in the market, you can learn about the purpose of the customer’s fasteners and meet the requirements of mechanical properties. Submit a written application requesting replacement materials. Some purchasing customers are not very professional in fasteners, and the choice of materials is not always the best. As our professional manufacturer of fasteners, we can give customers better suggestions to achieve both benefits. Of course, the fastener materials should pay attention to more than these. For example, the material must pass the aging period before using it (I wrote an article about this before). The rusty surface material is used to make some full-threaded fasteners or Used for fasteners that need to be ground on the surface, and the center of the material has shrinkage holes. Do not use to make polished head screws