GB/T 3098.24-2020 English PDF (GB/T3098.24-2020)

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GB/T 3098.24-2020: Mechanical properties of fasteners - Stainless steel and nickel alloys bolts, screws, studs and nuts for high temperature applications
GB/T 3098.24-2020
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 21.060.10; 21.060.20
J 13
Mechanical properties of fasteners - Stainless steel and
nickel alloys bolts, screws, studs and nuts for high
temperature applications
ISSUED ON: NOVEMBER 19, 2020
IMPLEMENTED ON: JUNE 01, 2021
Issued by: State Administration for Market Regulation;
National Standardization Administration.
Table of Contents
Foreword ... 4
Introduction ... 6
1 Scope ... 7
2 Normative references ... 8
3 Terms and definitions ... 9
4 Codes ... 10
5 Marking system ... 12
6 Materials and processing ... 12
6.1 Chemical composition ... 12
6.2 Heat treatment of fasteners ... 16
6.3 Surface finishing ... 17
6.4 Design of bolt and nut connection pairs ... 18
6.5 High temperature environment ... 18
6.6 Fastener service temperature ... 19
7 Mechanical properties ... 19
7.1 Mechanical properties of bolts, screws and studs ... 19
7.2 Mechanical properties of nuts ... 23
8 Applicability of test methods and inspections ... 26
8.1 Applicability of test methods ... 26
8.2 Inspection by the manufacturer ... 26
8.3 Inspection by the supplier ... 26
8.4 Inspection by the purchaser ... 27
8.5 Delivery of test results ... 27
9 Test methods under ambient temperature conditions ... 27
9.1 Tensile test of bolts, screws and studs ... 27
9.2 Hardness test of bolts, screws and studs ... 36
9.3 Proof load test of nuts ... 37
9.4 Nut hardness test ... 40
10 Test methods under elevated temperature conditions ... 42
Mechanical properties of fasteners - Stainless steel and
nickel alloys bolts, screws, studs and nuts for high
temperature applications
1 Scope
This Part of GB/T 3098 specifies the mechanical property requirements of bolts, screws,
studs and nuts made of corrosion-resistant stainless steel and nickel alloys, for use at
high temperatures up to 800 °C when tested at an ambient temperature of 10 °C ~ 35 °C.
Note: The fasteners specified in this Part are also suitable for use at low temperatures, usually
to -50 °C. For more information, see GB/T 3098.25.
This Part specifies the properties of fasteners made of three types of materials:
martensitic stainless steel, austenitic precipitation hardening stainless steel, nickel
alloys. GB/T 3098.25 provides general rules and additional technical information on
applicable stainless steel and nickel alloys and their properties.
Fasteners applicable to this Part:
- Ordinary threads in accordance with GB/T 192;
- Combinations of diameter and pitch in accordance with GB/T 193;
- Tolerances in accordance with GB/T 197 and GB/T 9145;
- Coarse thread M3 ~ M39; fine thread M8 × 1 ~ M39 × 3;
- Full load-bearing capacity fasteners of any shape.
The provisions of this Part also apply to fasteners whose dimensions exceed the
applicable range but meet all use requirements.
This Part does not cover fasteners with reduced load-bearing capacity (such as thin nuts
and bolts, screws and studs whose head and shank strength is lower than that of the
threaded part).
This Part does not specify the following performance requirements:
- Torque-clamping force performance;
- Shear strength;
- Fatigue resistance;
- Weldability;
- Locking performance.
2 Normative references
The following documents are essential to the application of this document. For the dated
documents, only the versions with the dates indicated are applicable to this document;
for the undated documents, only the latest version (including all the amendments) is
applicable to this standard.
GB/T 90.3 Fasteners - Quality assurance system
GB/T 192 General purpose metric screw threads - Basic profile
GB/T 196 General purpose metric screw threads - Basic dimensions
GB/T 228.1 Metallic materials - Tensile testing - Part 1: Method of test at room
temperature
GB/T 230.1 Metallic materials - Rockwell hardness test - Part 1: Test method
GB/T 231.1 Metallic materials - Brinell hardness test - Part 1: Test method
GB/T 1800.2 Geometrical product specifications (GPS) - ISO code system for
tolerances on linear sizes - Part 2: Tables of standard tolerance classes and limit
deviations for holes and shafts
GB/T 3098.2-2015 Mechanical properties of fasteners - Nuts
GB/T 3098.6 Mechanical properties of fasteners - Stainless steel bolts, screws and
studs
GB/T 3098.25 Mechanical properties of fasteners Guide for selection of stainless
steel and nickel alloy fasteners
GB/T 4340.1 Metallic materials - Vickers hardness test - Part 1: Test method
GB/T 5277 Fasteners - Clearance holes for bolts and screws
GB/T 12160 Metallic materials - Calibration of extensometers systems used in
uniaxial testing
GB/T 16823.3 Fasteners - Torque/clamp force testing
GB/T 16825.1 Metallic materials - Calibration and verification of static uniaxial
b: The length of the thread, in millimeters (mm);
D: The nominal diameter of the internal thread, in millimeters (mm);
D2: The basic middle diameter of the internal thread, in millimeters (mm);
d: The nominal diameter of the external thread, in millimeters (mm);
dh: The aperture of the tensile test device or the nut load-keeping test device for
external threaded fasteners, in millimeters (mm);
ds: The diameter of the unthreaded rod, in millimeters (mm);
d1: The basic minor diameter of the external thread, in millimeters (mm);
d2: The basic middle diameter of the external thread, in millimeters (mm);
d3: The minor diameter of the external thread (for calculating the stress cross-
sectional area), in millimeters (mm);
Fmf: The ultimate tensile load, in Newtons (N);
Fmf,T: High temperature ultimate tensile load, in Newton (N);
Fn,T: High temperature ultimate release load of nuts, in Newton (N);
Fp: Proof load of nuts, in Newton (N);
Fpf: Load of the fastener when the actual plastic elongation is 0.2%, in Newton (N);
Fpf,T: Load of the fastener when the actual plastic elongation is 0.2% at high
temperature, in Newton (N);
H: Original triangle height of thread, in millimeter (mm);
h: Thickness of nut proof load test device, in millimeter (mm);
L0: Total length of fastener before load application, in millimeter (mm);
L1: Total length of fastener after breaking, in millimeter (mm);
L2: Clamping length before tensile test, in millimeter (mm);
l: Nominal length of external threaded fastener, in millimeter (mm);
lt: Total length of stud, in millimeter (mm);
lth: Length of unthreaded fastener in the test fixture, in millimeter (mm);
m: Nut height, in millimeters (mm);
P: Pitch, in millimeters (mm);
Rmf: Tensile strength of fastener, in megapascals (MPa);
Rmf,T: Tensile strength of fastener at high temperature, in megapascals (MPa);
Rn,T: Ultimate stripping strength of nut at high temperature, in megapascals (MPa);
Rpf: Stress of fastener at 0.2% of specified plastic elongation, in megapascals (MPa);
Rpf,T: Stress of fastener at 0.2% of specified plastic elongation at high temperature,
in megapascals (MPa);
Sp: Proof stress, in megapascals (MPa).
5 Marking system
All stainless steels and nickel alloys specified in this Part belong to three different
categories:
- Martensitic stainless steels: CH0, CH1, CH2, V, VH, VW;
- Austenitic precipitation hardening stainless steels: SD;
- Nickel alloys: SB and 718.
6 Materials and processing
6.1 Chemical composition
Tables 1 ~ 3 specify the chemical composition limits of stainless steel and nickel alloys
for fasteners. The chemical composition shall be evaluated according to the relevant
national standards. For information on domestic corresponding categories of materials,
see Appendix A.
Unless otherwise agreed by the purchaser and the manufacturer, the chemical
composition within the specified group range of fastener steel is ultimately selected by
the manufacturer.
GB/T 3098.25 specifies general guidelines and information for selecting stainless steel
or nickel alloys suitable for the application.
Chapters 6 and 7 are met, the supplier may choose its own method to control and/or
inspect the fasteners (regular evaluation of the manufacturer, verification of the test
results provided by the manufacturer, physical inspection of the fasteners, etc.).
In case of dispute, the test methods specified in 8.1 and Chapter 9 shall be followed.
8.4 Inspection by the purchaser
The purchaser may control and/or inspect the delivered fasteners according to the test
methods specified in Chapter 9.
In case of dispute, the test methods specified in 8.1 and Chapter 9 shall be used.
8.5 Delivery of test results
When the purchaser requires the test results of the supplier, it shall be agreed upon at
the time of ordering. The test report shall be prepared in accordance with the provisions
of GB/T 39310. The type of test report (F2.2, F3.1 or F3.2) and any additional or
specific tests shall also be specified by the purchaser and agreed upon at the time of
ordering.
9 Test methods under ambient temperature conditions
9.1 Tensile test of bolts, screws and studs
9.1.1 General
This test is used to determine the following parameters simultaneously or separately:
- Tensile strength Rmf of the actual fastener;
- Stress Rpf when the actual fastener specifies the plastic elongation of 0.2%;
- Elongation at break A.
This test is applicable to bolts, screws and studs that meet the following requirements:
- All stainless steel and nickel alloy categories;
- 3 mm ≤ d ≤ 39 mm;
- Bolts, screws and studs (with unthreaded shanks) with nominal length l ≥ 2.5d and
thread length b ≥ 2d;
9.3.5 Test procedure
A nut that has passed the size inspection shall be used for the proof load test.
The test mandrel thread shall be checked before each test. If the test mandrel thread is
damaged, it shall not be used within the damaged thread length, or replaced with a
qualified test mandrel.
Install the nut on the test mandrel according to Figure 7 or Figure 8.
Perform axial tension test or axial compression test according to GB/T 228.1. The
separation speed of the test machine chuck shall not exceed 3 mm/min.
Apply the proof load specified in Table 13 or Table 14; maintain for 15 s; then unload.
During the test, the load exceeding the proof load value shall be limited to the minimum.
The nut shall be able to be screwed out of the test mandrel by hand. It may be necessary
to use a wrench to turn the nut, but it can only be turned out within half a turn with the
help of a wrench. The occurrence of nut cracking or thread stripping shall also be noted.
9.3.6 Test results and requirements
The nut shall be able to withstand the proof load specified in Table 13 or Table 14,
without thread stripping or nut cracking.
After removing the proof load, the nut shall be able to be turned out by hand (if
necessary, with the help of a wrench, no more than half a turn).
In case of dispute, the axial tensile test specified in Figure 7 shall be used as the
arbitration method for acceptance.
9.4 Nut hardness test
9.4.1 General
This test is applicable to nuts that meet the following requirements:
- All stainless steel and nickel alloy types;
- All sizes;
- Any shape.
9.4.2 Test procedure
9.4.2.1 General
The hardness test shall be carried out on nuts that have passed the size inspection.
and the fixture).
In addition, the supplier and the purchaser shall also agree on the following:
- Minimum tensile strength Rmf,T at the test temperature;
- Stress Rpf,T at a specified plastic elongation of 0.2% at high temperature;
- Minimum elongation after rupture AT at high temperature;
- Nut high temperature limit tripping load Fn,T and/or corresponding limit tripping
strength Rn,T.
The test shall be carried out as follows:
a) Thermocouples shall be installed in accordance with ISO 7961. The number of
thermocouples shall be selected according to the screw-in length, to ensure
uniform temperature throughout the fastener (usually three thermocouples are
used, but for nuts and short bolts/screws this can be reduced to two).
b) Install the fastener to be tested into the test fixture as specified in 10.1.2; record
the actual screw-in length and clamping length.
c) The test fixture shall be heated to the specified test temperature; the time to reach
this temperature shall be at least 60 minutes per 25 mm fastener diameter.
d) Before applying the load, the test temperature shall be maintained for 30 minutes
to ensure that the test fixture is heated evenly and the temperature is balanced
before loading.
e) The load shall then be applied continuously; the loading rate shall comply with
the provisions of ISO 7961, but the speed of the running chuck shall not exceed
3 mm/min.
f) The test shall be carried out at least until the ultimate tensile load is exceeded; or
when the elongation is to be determined, the test shall be stopped before fracture
occurs (to avoid damage to the thermocouple).
10.1.4 Test report
The report shall contain at least the following information:
- Marking and/or part number of the fastener.
- Manufacturing batch number.
- Manufacturer identification mark.
- Material and heat treatment marking.
- Screw-on length and clamping length.
- Relevant standards or technical conditions for high temperature tensile tests.
- Test temperature.
- Test results:
● Externally threaded fasteners: Ultimate tensile load Fmf,T, ultimate tensile
strength Rmf,T, load Fpf,T and stress Rpf,T at a specified plastic elongation of 0.2%,
elongation AT after the fastener breaks;
● Nuts: Ultimate breakaway load Fn,T and corresponding ultimate breakaway
strength Rn,T;
● Bolt/nut connection pairs: The test results shall be expressed as bolt or nut
(depending on the failed component), but the load or stress at a specified plastic
elongation of 0.2% is irrelevant.
- Failure mode and location.
- Any specific conditions or instructions for the test.
- Conclusions of the test.
10.2 Stress failure tests on bolts, screws, ...