Fasteners - Surface discontinuities -
Bolts, screws and studs for general requirements
1 Scope
1.1 This standard establishes limits for various types of surface discontinuities on bolts, screws and studs for general requirements.
It applies to bolts, screws and studs with
- nominal thread diameters 5 mm and larger;
- product grades A and B;
- property classes up to and including 10.9, unless otherwise specified in product standards or agreed between supplier and purchaser.
1.2 Limits for surface discontinuities on bolts, screws and studs for special requirements (e.g. automatic assembly) are laid down in GB/T 5779.3. When the engineering requirements of the application necessitate that surface discontinuities on bolts, screws and studs be more closely controlled, it shall be specified in the respective product standard, or the purchaser shall specify the applicable limits in the inquiry and purchase order.
1.3 Where the permissible limits for surface discontinuities indicated in Clause 3 occur, the minimum values for the mechanical and functional properties specified in GB/T 3098.1 shall still be met.
Notes:
1 The figures in Clause 3 are examples only. They apply correspondingly also to other types of bolts, screws and studs.
2 The individual figures show the surface discontinuities exaggerated in some cases for clarity.
2 Normative references
The following standards contain provisions which, through reference in this standard, constitute provisions of this standard. At the time of publication, all the editions listed are valid. All standards are subject to revision, and all parties using this standard are encouraged to investigate the possibility of applying the latest editions of the following standards.
GB/T 90-1985 Acceptance inspection, marking and packaging of fasteners (eqv 3269: 1984)
GB/T 1031-1995 Surface roughness parameters and their values (neq ISO 468: 1982)
GB/T 2828-1987 Sampling procedures and tables for lot-by-lot inspection by attributes (Apply to inspection of successive lots or batches)
GB/T 3098.1-2000 Mechanical properties of fasteners - Bolts, screws and studs (idt ISO 898-1: 1999)
GB/T 5779.3-2000 Fasteners-Surface discontinuities - Bolts, screws and studs for special requirements (idt ISO 6157-3: 1988)
GB/T 15239-1994 Sampling procedures and tables for isolated lot inspection by attributes
3 Types, causes, appearance and limits of surface discontinuities
3.1 Cracks
A crack is a clean (crystalline) fracture passing through or across the grain boundaries and may possibly follow inclusions of foreign elements. Cracks are normally caused by overstressing the metal during forging or other forming operations, or during heat treatment. Where parts are subjected to significant reheating, cracks usually are discoloured by scale.
Foreword I
ISO Foreword II
1 Scope
2 Normative references
3 Types, causes, appearance and limits of surface discontinuities
4 Inspection and evaluation procedure
Annex A (Normative) Sampling plan for surface discontinuities
