Analyze how to choose manufacturing materials for different types of standard parts
The choice of raw materials in the manufacturing process for different types of screws is very important. Most fastener materials are steel. The standard materials we use are: ISO (International) GB (China) DIN (Germany) AISI/SAE (USA) JIS (Japan).
Bolt and other materials for external threads
Some low-carbon steel fasteners such as ISOClass4.8SAEGrade1-2, which have no mechanical performance requirements, are sufficient for Q235ASAE1015DINC15. They are not heat-treated at all, and are directly cold-worked. The fasteners with a slightly higher grade are: ISOClass6.8SAEGrade3-4 It is necessary to use steel with a carbon content of 0.2% or more, such as C1020C1022Ml20ML35, etc., such screws do not need any heat treatment, and the cold working strength can fully meet the requirements. In fact, the higher the carbon content, the more difficult it is for cold forming, and there is no need to use 6.8 grade screws for small materials. The special case is another matter.
The most commonly used screws are ISOClass 8.8 SAEGrade5 screws. Generally, medium carbon steel, ML35SAE1035DIN35JISSWRCH35K is heat treated (quenched + tempered), and SAE514040Cr can also be used. The increase of alloying elements is very helpful for the hardenability of heat treatment, so Large-size screws can be used with alloy steel, so that the use of medium-carbon steel leads to the phenomenon that we often say that the central part is “hardenedâ€.
ISOClass9.810.9SAEGrade8 is to use low to medium alloy steel material, after heat treatment (quenching + tempering), alloy material has a good combination of mechanical properties. The commonly used material is 40Cr35CrMoSAE5140SCM435SAE4135SAE4137JISSCr440(H)DIN41Cr4, etc. Upper 45# can also achieve the required mechanical properties, but it is slightly inferior to alloy steel in terms of comprehensive mechanical properties.
ISOClass12.9SATMA574 is a high-strength bolt with high mechanical properties. It should be heat treated (quenched + tempered) with medium carbon alloy steel, such as SCM43535CrMoSAE4137SAE4135DIN34CrMo4. If the surface treatment is subjected to pickling, the high-strength bolts should be subjected to pickling. At the time, hydrogen embrittlement will occur, so there must be a process of dehydrogenation (especially fasteners with sharp corners), or it will die very badly.
Internal thread material such as nut
There is no mechanical performance requirement or ISOClass5-6SAEGrade3-4 generally uses C1010Q235A or C15. It does not require heat treatment and can be cold worked. ISOClass8, SAEGrade5, generally use Ml35SAE1035DINC35, the small size of the nut does not require heat to achieve the required mechanical properties, the large size of the heat treatment (quenching + tempering), this point GB3098.2 said very clear.
ISOClass10, SAEGrade8 generally uses medium carbon steel to achieve its strength requirements after heat treatment. Such as SAE1035 and other medium carbon steel. One thing that everyone must pay attention to is that the nut and the bolt are different. The force is mainly based on compression rather than stretching. Therefore, the strength of the nut is not only related to the material, but also related to many factors, including accuracy, pitch, and chamfer in the nut. , nut thickness, etc.
Flat washer material
Flat washers without mechanical properties are generally manufactured from angles, such as Q235A. If hardness is required but not high, it can be calendered with a thicker sheet to achieve the required hardness. Gaskets such as elastic pads are generally made of 65Mn70# or S50CM-S70CM and subjected to heat treatment (quenching + tempering).
Rivets, pins
Rivets and pins are generally the same material as bolts, but some rivets are not too high in hardness, and some require HRB60 or less. Generally, the hardness of normalized materials is HRB70-80, so some have to be annealed to meet performance requirements.
Self-tapping screws generally use C1018C1020C1022 and other materials, but some domestic manufacturers save money, cut corners, use 18#15#20# and use some manufacturers to use Q235A, then surface carburizing treatment, so that the self-tapping nails made by the heart The toughness is not up to the requirements and is easy to break.
Stainless steel fasteners I don't know much, it seems that SUS304 is very common.
Other special requirements for materials
If the company is to use fasteners for welding, arc welding and gas welding generally have no requirements for materials. If the customer uses spot welding, it is necessary to use low carbon steel. If it is necessary to increase the strength, some low carbon materials with higher Mn content can be used. This is just a very simple example, many of which can only be noticed in actual production.
When the customer specifies that a certain grade of material is to be used, and the company does not have such a material for a while, or the material is not easy to purchase on the market, you can understand the use of the fastener by the customer, and the mechanical properties can be met. Submit a written request for replacement of materials. Some purchasing customers are not very professional in fasteners, and the choice of materials is not always the best. As a manufacturer specializing in the production of fasteners, we can give better suggestions to customers and achieve double benefits.
Concerned about surprises
Label: Arc Welding Carburizing Treatment Material Selection Heat Treatment Low Carbon Steel
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