1 Scope
1.1 This standard specifies limits for various types of surface discontinuities on bolts, screws and studs for special requirements.
It applies to bolts, screws and studs with:
— nominal thread diameters 5 mm and larger;
— product grades A and B;
— nominal lengths l ≤ 10d (or longer if specified);
— property class 12.9;
— property classes 8.8, 9.8 and 10.9 when specified in product standards or agreed between supplier and purchaser.
1.2 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 should still be met.
When fatigue strength requirements are specified, the fatigue strength should not be lower than that obtained on bolts without defects taken from the same lot.
Note 1: The figures in clause 3 are examples only. They apply correspondingly also to other types of bolts, screws and studs.
Note 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 text, constitute provisions of this standard. At the time of publication, all the editions listed were valid. All standards are subject to revision, and parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent edition of the standard indicated below.
GB/T 90-1985 Acceptance Inspection, Marking and Packaging of Fasteners (eqv ISO 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 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 II
ISO Foreword III
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
