GB/T 3098.15-2023 English PDF (GB/T3098.15-2023)

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GB/T 3098.15-2023: Mechanical properties of fasteners - Stainless steel nuts
GB/T 3098.15-2023
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 21.060.20
CCS J 13
Replacing GB/T 3098.15-2014
Mechanical properties of fasteners - Stainless steel nuts
(ISO 3506-2:2020, Fasteners - Mechanical properties of corrosion-resistant stainless
steel fasteners - Part 2: Nuts with specified grades and property classes, MOD)
ISSUED ON: MAY 23, 2023
IMPLEMENTED ON: DECEMBER 01, 2023
Issued by: State Administration for Market Regulation;
National Standardization Administration.
Table of Contents
Foreword ... 3
Introduction ... 8
1 Scope ... 11
2 Normative references ... 12
3 Terms and definitions ... 13
4 Symbols ... 14
5 Marking system ... 15
5.1 Nut type marking ... 15
5.2 Stainless steel group and performance grade marking system... 15
6 Design of bolt and nut connection pairs ... 17
7 Materials ... 18
7.1 Chemical composition ... 18
7.2 Heat treatment of martensitic stainless steel nuts ... 20
7.3 Surface finishing ... 20
7.4 Corrosion resistance ... 20
8 Mechanical and physical properties ... 21
9 Inspection ... 26
9.1 Manufacturer's inspection ... 26
9.2 Supplier's inspection ... 26
9.3 Buyer's inspection ... 27
9.4 Delivery of test results ... 27
10 Test method ... 27
10.1 Proof load test ... 27
10.2 Hardness test ... 31
11 Nut marking and labeling ... 33
11.1 Marking ... 33
11.2 Manufacturer's identification mark ... 34
11.3 Nut marking ... 35
11.4 Packaging marking (label) ... 37
Appendix A (Informative) Design principles for stainless steel nuts ... 38
Appendix B (Normative) Thread size of proof load test mandrel ... 41
References ... 43
Mechanical properties of fasteners - Stainless steel nuts
1 Scope
This document specifies the mechanical and physical properties of coarse and fine
thread nuts made of corrosion-resistant stainless steel, when tested at an ambient
temperature of 10 °C ~ 35 °C. The performance grades corresponding to the austenitic,
martensitic, ferritic and duplex (austenitic-ferritic) stainless steel nut groups are
specified.
GB/T 3098.25 provides general rules and additional technical information on applicable
stainless steels and their properties.
Nuts that meet the requirements of this document are tested at ambient temperatures of
10 °C ~ 35 °C. At high and/or low temperatures, the nuts may not maintain the specified
mechanical and physical properties.
Note 1: Fasteners that meet the requirements of this document are used at temperatures of -
20 °C ~ +150 °C, but can also be used at low temperatures of -196 °C and high temperatures of
+300 °C. For more detailed information, see GB/T 3098.25.
When used outside the temperature range of -20 °C ~ +150 °C, it is the user's
responsibility to consult an experienced fastener material expert and consider the
stainless steel composition, service time at high or low temperatures, the effect of
temperature on the mechanical properties of the fastener and the clamped parts, the
corrosive use environment of the bolted connection, to determine the appropriate choice
for the special application.
Note 2: When the use temperature is up to +800 °C, GB/T 3098.24 gives the selection of
appropriate stainless steel groups and performance grades.
This document applies to nuts with:
- Ordinary threads in accordance with GB/T 192;
- Combinations of diameter and pitch in accordance with GB/T 193 and GB/T 9144;
- Coarse thread M5 ~ M39, fine thread M8×1 ~ M39×3;
- Thread tolerances in accordance with GB/T 197 and GB/T 9145;
- Specified performance levels and proof loads;
- Three types of nuts: thin nuts, standard nuts and high nuts;
- Nut height mmin ≥ 0.45D;
- Outer diameter or width across flats smin ≥ 1.45D (see Appendix A);
- Any shape;
- Can be used with bolts, screws and studs in accordance with the performance
grades specified in GB/T 3098.6.
Stainless steel groups and performance grades can be used beyond the specification
range specified in this document (i.e., D < 5 mm or D > 39 mm), when all applicable
chemical composition, mechanical, physical performance technical requirements are
met.
This document does not specify the following performance requirements:
- Torque-clamping force performance;
- Effective torque performance;
- Weldability.
2 Normative references
The contents of the following documents constitute the essential terms of this document
through normative references in the text. Among them, for dated references, only the
version corresponding to that date applies to this document; for undated references, the
latest version (including all amendments) applies to this document.
GB/T 228.1 Metallic materials - Tensile testing - Part 1: Method of test at room
temperature (GB/T 228.1-2021, ISO 6892-1:2019, MOD)
GB/T 230.1 Metallic materials - Rockwell hardness test - Part 1: Test method (GB/T
230.1-2018, ISO 6508-1:2016, MOD)
GB/T 231.1 Metallic materials - Brinell hardness test - Part 1: Test method (GB/T
231.1-2018, ISO 6506-1:2014, MOD)
GB/T 3098.1 Mechanical properties of fasteners - Bolts, screws and studs (GB/T
3098.1-2010, ISO 898-1:2009, MOD)
GB/T 3098.25 Mechanical properties of fasteners - Guidance for the selection of
stainless steels and nickel alloys for fasteners
GB/T 3099.4 Terminology of fasteners - Control, inspection, delivery, acceptance
and quality (GB/T 3099.4-2021, ISO 1891-4:2018, MOD)
GB/T 4340.1 Metallic materials - Vickers hardness test - Part 1: Test method (GB/T
4340.1-2009, ISO 6507-1:2005, MOD)
GB/T 16825.1 Metallic materials - Calibration and verification of static uniaxial
testing machines - Part 1: Tension/compression testing machines - Calibration and
verification of the force-measuring system (GB/T 16825.1-2022, ISO 7500-1:2018,
IDT)
GB/T 39310 Fasteners - Types of inspection documents (GB/T 39310-2020, ISO
16228:2017, MOD)
3 Terms and definitions
The following terms and definitions apply to this document.
3.1
Stainless steel
Steel with stainless and corrosion resistance as its main characteristics, which has a
chromium (Cr) content of at least 10.5% (mass fraction) and a carbon (C) content of
no more than 1.2% (mass fraction).
[Source: GB/T 3098.24-2020, 3.1, modified]
3.2
Austenitic stainless steel
Stainless steel (3.1) with high chromium and nickel content, which cannot usually
be strengthened by heat treatment, has good corrosion resistance and ductility, is
usually weakly magnetic or non-magnetic.
[Source: GB/T 3098.6-2023, 3.6]
3.3
Martensitic stainless steel
Stainless steel (3.1) with a martensitic matrix, having magnetic properties, whose
mechanical properties can be adjusted by heat treatment. It has a high chromium
content, but a low content of nickel or other alloying elements.
[Source: GB/T 3098.24-2020, 3.2, modified]
3.4
Ferritic stainless steel
Stainless steel (3.1) with a carbon content of less than 0.1% and a chromium content
of usually 11% ~ 18%, which cannot usually be strengthened by heat treatment and
has strong magnetism.
[Source: GB/T 3098.6-2023, 3.8]
3.5
Duplex stainless steel
Stainless steel (3.1) with a microstructure containing two phases, austenite and
ferrite, has better corrosion resistance, higher chromium content, lower nickel
content, higher strength and magnetism than austenitic steel.
[Source: GB/T 3098.6-2023, 3.9]
4 Symbols
The following symbols apply to this document.
As, nominal: Thread nominal stress cross-sectional area, in square millimeters (mm2);
D: Nut thread nominal diameter, in millimeters (mm);
D2: Internal thread basic pitch diameter, in millimeters (mm);
dh: Fixture hole diameter, in millimeters (mm);
Fp: Proof load, in Newton (N);
h: Fixture thickness, in millimeters (mm);
m: Nut height, in millimeters (mm);
P: pitch, in millimeters (mm);
SP: Proof stress, in megapascals (MPa);
s: Width across flats, in millimeters (mm).
- A digit: Specifies the chemical composition range of the stainless steel in this
category.
The chemical composition of the stainless steel categories and groups in Figure 1 is
specified in Table 2.
5.2.3 Marking of standard nuts and high nut performance grades (Part 2)
The performance grade marking (Part 2) consists of 2 ~ 3 digits, which correspond to
1/10 of the nut's proof stress specified in Table 3 or Table 4; it also corresponds to the
performance grade of the stainless steel bolts, screws and studs that match it.
Example 1: A2-70 indicates austenitic stainless steel, work hardened, minimum proof stress of
700 MPa, full load capacity nut (m ≥ 0.8D).
Example 2: C1-110 indicates martensitic stainless steel, quenched and tempered, minimum
proof stress of 1100 MPa, full load capacity nut (m ≥ 0.8D).
5.2.4 Marking of thin nut performance grade (Part 2)
The performance grade marking (Part 2) consists of "0" and 2 ~ 3 digits, where:
- The first "0" indicates a thin nut, which has a reduced load capacity compared to
the standard nut or high nut specified in 5.2.3, so when overloaded, thread stripping
may occur;
- The number after that is equivalent to 1/10 of the proof stress of the nut tested with
a hardened test mandrel, in MPa. Equivalent to half the performance grade of
stainless steel bolts, screws and studs that match thin nuts.
Example: A4-040 indicates an austenitic stainless steel thin nut, which has the same material
and processing technology as the standard nut A4-80 (work hardened, high strength), but due
to the small nut height (m < 0.80D), the minimum proof stress is 400 MPa (reduced load-bearing
capacity).
6 Design of bolt and nut connection pairs
The combination of performance grades of nuts and bolts, screws and studs shall be as
specified in Table 1.
7.2 Heat treatment of martensitic stainless steel nuts
Standard nuts and tall nuts of groups and performance grades C1-70, C3-80, C4-70, as
well as the thin nuts of C1-035, C3-040, C4-035 shall be quenched and tempered.
Standard nuts and tall nuts of groups and performance grades C1-110, as well as thin
nuts of C1-055 shall be quenched and tempered, with a minimum tempering
temperature of 275 °C.
7.3 Surface finishing
Unless otherwise specified, nuts conforming to this document shall be cleaned and
polished.
In order to maximize the corrosion resistance of nuts, it is recommended that the surface
be passivated. Fasteners passivated in accordance with GB/T 5267.4 may have the letter
"P" added to the performance grade code (see 11.4).
Note 1: Passivated nuts generally do not have a bright surface.
Nuts in bolted joints are usually preloaded by applying torque. Therefore, it is
recommended that stainless steel nuts be lubricated to avoid thread seizure during
tightening.
Note 2: During tightening, some factors may increase the risk of thread seizure of stainless steel
nuts, such as thread damage, high preload, high tightening speed, etc.
Note 3: At present, the national standards for stainless steel nuts do not specify requirements
for surface defects, torque-clamping force performance, effective torque locking performance.
For stainless steel nuts, a controllable torque-clamping force relationship can be
obtained by appropriate surface treatment, whether using only lubricants or using
coatings, surface coatings and/or sealers including lubricants. In this case, the fastener
marking and/or labeling should be followed by the letters "Lu", e.g. A4-80Lu. At the
same time, appropriate tightening measures and methods should be selected to achieve
the required preload.
When special requirements need to be met, agreement shall be made at the time of
ordering.
7.4 Corrosion resistance
To prevent corrosion, nuts should be used with bolts, screws, studs, washers of the same
stainless steel group (e.g., A2 nuts with A2 bolts). Other combinations may be used
The nut test piece shall be mounted on the test mandrel according to Figure 2 or Figure
3.
The axial tension test or compression test shall be carried out according to GB/T 228.1.
The separation rate of the chuck of the testing machine shall not exceed 3 mm/min.
The proof load specified in Tables 5 ~ 8 shall be applied to the nut and maintained for
15 s; then unloaded. During the test, the situation where the proof load value is exceeded
shall be limited to the minimum.
The nut shall be able to be unscrewed from the test mandrel by hand, or the nut shall be
loosened with the help of a wrench, but not more than half a turn.
When the nut is loosened with the help of a wrench, and does not exceed half a turn of
the thread at most, it shall be recorded.
When the nut breaks or the thread is disengaged, it shall be recorded.
10.1.6 Additional test procedure for effective torque type nuts
In addition to 10.1.5, the following procedures apply to effective torque type nuts.
The nut test piece shall be screwed into a steel test bolt or a test mandrel specified in
10.1.4. When a test bolt is used for testing, the test bolt thread shall be rolled, with a
thread tolerance of 6 g and no coating; the test bolt shall comply with the provisions of
GB/T 3098.1; the minimum yield strength corresponding to the performance grade shall
be higher than the proof load of the tested nut. In case of dispute, the hardened mandrel
specified in 10.1.4 shall be used.
After the first thread of the test mandrel is completely threaded through the effective
torque part of the nut, the maximum effective torque value occurring during the 360°
rotation of the nut shall be measured and recorded.
After unloading, the maximum effective torque value occurring during the process from
half a turn of the nut to complete separation from the test mandrel shall be measured
and recorded.
10.1.7 Test results and requirements
The nut shall be able to withstand the proof load specified in Tables 5 ~ 8, without
thread disengagement or nut breakage.
For non-effective torque type nuts, after the proof load test, they shall be able to be
screwed out by hand (if n...