This standard specifies a preloading test which is able to detect the occurrence of hydrogen embrittlement of fasteners at room temperature.
This standard is applicable to
a) Metric bolts, screws and studs;
b) thread rolling screws;
c) self-tapping screws;
d) self-drilling screws;
e) nuts;
f) washers
which are made of steel and are under tensile stress.
The test shall be carried out within a temperature range of 10 ℃ to 35 ℃.
The test is suitable only for in-process control and may be carried out after any step of the manufacturing process. It is not intended as an acceptance test. It is capable of assessing differences or changes in processing conditions or techniques and to determine the effectiveness of the various processing steps including pre- and post-coating treatments (baking) to reduce the mobile hydrogen in the fasteners.
This test does not relieve the manufacturer or processor from the responsibility of imposing and monitoring suitable process control.
Note: the chance of detecting hydrogen embrittlement decreases significantly if the test is started more than 24 h after the last step of manufacturing process. Therefore, in normal cases this test is not suitable for acceptance testing.
Special attention shall be given to the reference test in clause 7.3.
2 Normative References
The following standards contain provisions which, through reference in this standard, constitute provisions of this standard. At the time of publication, the editions indicated 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 editions of the standards indicated below.
GB/T 5277-1985 Fasteners - Clearance Holes for Bolts and Screws (eqv ISO 273:1979)
GB/T 3098.5-2000 Mechanical Properties of Fasteners - Tapping Screws (idt ISO 2702:1992)
GB/T 3098.7-2000 Mechanical Properties of Fasteners - Thread Rolling Screws (idt ISO 7085:1999)
GB/T 3098.11-1995 Mechanical Properties of Fasteners - Self-drilling Tapping Screws
3 Terms and Definitions
For the purposes of this standard the following terms and definitions apply.
3.1 susceptibility to hydrogen embrittlement
characteristic of a steel fastener to display brittle failure due to the presence of mobile hydrogen and when subjected to a significant degree of tensile stress and/or adverse service conditions
Notes:
1 With increasing susceptibility to hydrogen embrittlement, the critical amount of mobile hydrogen which may cause brittle failure increases markedly.
2 After the manufacturing process, susceptibility to hydrogen embrittlement cannot be reduced or changed into an unsusceptible condition, even by any post-coating heat treatment (baking).
3.2 risk of hydrogen embrittlement
risk of failure which arises if fasteners made from steel which are susceptible to hydrogen embrittlement absorb hydrogen and are subjected to tensile stress and/or residual tensile stress
Note: the risk of hydrogen embrittlement can be reduced when in the relevant process steps hydrogen supply is minimized and/or when suitable post-coating heat treatment (baking) is carried out to enable hydrogen to effuse and/or to trap hydrogen irreversibly in the steel.
3.3 manufacturing lot
quantity of fasteners of a single designation including product grade, property class and size, manufactured from bar, wire, rod or flat product from a single cast, processed through the same or similar steps at the same time or over a continuous time period through the same heat treatment and/or coating process, if any
Same heat treatment or coating process means: for a continuous process, the same treatment cycle without any setting modification; for a discontinuous process, the same treatment cycle for identical consecutive batches.
Note: the manufacturing lot may be split into a number of manufacturing batches for processing purposes and then reassembled into the same manufacturing lot.
3.4 manufacturing batch
quantity of identical fasteners from the same manufacturing lot processed together at one time
GB/T 3098.17-2000 The following standards are cited：
