Hardness of studs and nuts in pressure vessels
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For studs with M>36, is it necessary to require that the nut’s hardness be 20–30 HBW lower than that of the stud? Is this requirement applicable to all materials such as 35CrMoA and stainless steel studs?
Based on the information you provided, the hardness grade of the stud is M>36. If it is required that the hardness of the nut be 20-30 HBW lower than that of the stud, then for studs of this grade, the hardness of the nut should be M36, and it must also meet the requirement that its hardness is 20-30 HBW lower than that of the stud. However, the specific design requirements need to be determined based on actual conditions to ensure the safety and reliability of the bolt connections. Therefore, in the actual design, detailed consideration must be given to the practical circumstances and usage requirements. .
The technical specifications for high-temperature fasteners in thermal power plants explicitly require a specified hardness difference. More remains to be discovered. But this is generally the requirement: a difference in hardness is needed.
The hardness of the nut is 20~30 HBW lower than that of the stud