Now our commonly used material standard parts are:
ISO(international)
GB(China)
DIN(Germany)
AISI/SAE(USA)
JIS(Japan)
Materials for bolts and other external threads：
Some low carbon steel fasteners with no mechanical properties or ISO Class 4.8 SAE Grade 1-2 are sufficient with Q235A SAE 1015 DIN C15, without any heat treatment, directly cold working, and slightly higher grade fasteners such as: ISO Class 6.8 SAE Grade 3-4 is to use carbon content of more than 0.2% of steel, such as C1020 C1022 Ml20 ML35, such screws do not need any heat treatment, cold processing strength can fully meet the requirements. In fact, the higher the carbon content, the more difficult cold forming, there is no need for 6.8 grade screw oversize, special circumstances are another matter.
Our most commonly used screw is ISO Class 8.8 SAE Grade 5, generally use medium carbon steel, ML35 SAE 1035 DIN 35 JIS SWRCH35K after heat treatment (quenching + tempering), can also use SAE5140 40Cr, etc. The increase of alloying elements on the hardenability of heat treatment has a great help, so large specifications of screws can choose to use alloy steel, not to use carbon steel leads to the central part of what we often say is the existence of "quench through" phenomenon.
ISO Class 9.8 10.9 SAE Grade 8 is to use low to medium alloy steel materials, after heat treatment (quenching + tempering), with alloy materials in the mechanical properties of the material has a good combination, Commonly used materials for 40Cr 35CrMo SAE5140 SCM435 SAE4135 SAE4137 JIS SCr440(H) DIN 41Cr4 and so on, in fact, 45# can also achieve the required mechanical properties, but in the comprehensive mechanical properties than alloy steel slightly inferior.
ISO Class12.9 SATM A574 is a high strength bolt with high mechanical properties, which is heat-treated (quenched + tempered) with medium carbon alloy steel, such as SCM435 35CrMo SAE 4137 SAE4135 DIN 34CrMo4, If the surface treatment of this kind of high strength bolt is to go through the process of pickling, hydrogen embrittleness will occur, so it is necessary to have the process of hydrogen removal (especially for fasteners with sharp corners).
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