Why are 5.6 grade studs used with 6 grade nuts
Thread Content
Why are studs of grade 5.6 paired with nuts of grade 6? Could someone explain this: handshake
Did you say the opposite? Bolts of grade 5.6 are paired with nuts of grade 5. For more details, see this forum: https://bbs.hcbbs.com/forum.php?extra=page%3D100%26filter%3Ddigest%26orderby%3Dheats%26typeid%3D664%253Ffuvhvhocepojzfbj&mod=viewthread&tid=1321435
For general mechanical equipment, it is preferable for fractures to be visible when the bolts are installed, rather than the nuts slipping unnoticed; when matching nuts for mechanical use, the strength of the nuts should be higher than that of the bolts. On pressure vessels, the situation is exactly the opposite: nuts are not removed frequently. It is preferable for the nuts to become deformed due to lower hardness, rather than having the bolts break and cause an explosion; therefore, the strength of the bolts is higher than that of the nuts.
Clause 4.2.2 of NB/T 47020-2012 requires that the hardness of the stud (Brinell hardness) should be 20–30 higher than that of the matching nut.
Refer to HG/T20635-2009
According to HG/T20613, grade 5 bolts are not allowed; at least grade 6 bolts must be used.