GB/T 3098.24-2020Mechanical properties of fasteners—Stainless steel and nickel alloys bolts, screws, studs and nuts for high temperature applications (English PDF)

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% and a carbon (C) content of no more than 1.2%.

3.2 Martensitic stainless steel

Stainless steel with a martensitic matrix, magnetic properties, whose mechanical properties can be adjusted by heat treatment.

3.3 Precipitation hardening stainless steel

Stainless steel with austenite or martensitic matrix that can be strengthened (hardened) by precipitation hardening (also known as aging hardening).

3.4 Nickel alloy

Alloy with a nickel content of not less than 50%.

3.5 Soaking time

The time the workpiece is kept at the temperature specified by the process.

3.6 Bolt and screw with full loadability

Bolts and screws or full-thread screws with head strength greater than the threaded part and the unthreaded shank (ds~d2 or ds > d2) and meeting the minimum ultimate tensile load.

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.

6.4 Design of bolt and nut connection pairs

Bolts, screws and studs and nuts matching combinations shall be as specified in Table 5.

6.5 High temperature environment

The high temperature materials for fasteners specified in this Part are mainly suitable for temperatures where creep strength is usually the size factor and high temperature oxidation occurs (it shall be noted that SD, SB and 718 materials also have good corrosion resistance in humid environments).

6.6 Fastener service temperature

Chapter 7 gives the mechanical properties of fasteners when tested in an ambient temperature range of 10 °C ~ 35 °C.

7.1 Mechanical properties of bolts, screws and studs

When tested in accordance with the methods specified in Chapter 9, all mechanical property requirements of bolts, screws and studs with specified fastener codes shall comply with the provisions of Tables 7 ~ 11 under ambient temperature conditions, regardless of whether the test is conducted during the manufacturing process or on the final product.

8.1 Applicability of test methods

The applicability of test methods is shown in Table 15.

8.2 Inspection by the manufacturer

Fasteners produced in accordance with this Part shall comply with all applicable requirements specified in Chapters 6 and 7, when tested according to the suitability tests specified in 8.1 and Chapter 9.

8.3 Inspection by the supplier

If the chemical composition and mechanical properties requirements specified in 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.).

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.

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.

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.

9.1.2 Test procedure for simultaneous determination of Rmf, Rpf and A The load F shall be measured continuously until fracture occurs, directly using an electronic device (such as a microprocessor) or a load-displacement curve (see GB/T 228.1), which can be drawn automatically or manually.

9.1.6 Test results and requirements for stress Rpf at specified plastic elongation of 0.2%

9.1.7 Test results and requirements for elongation at break A The elongation at break A shall comply with the provisions of Table 7.

In case of dispute, the test method specified in 9.1.3 shall be used for testing.

9.2 Hardness test of bolts, screws and studs

9.2.1 General

9.2.2 Test procedure

The hardness test shall be carried out on fasteners that have passed the dimensional inspection.

9.3 Proof load test of nuts

9.3.1 General

9.3.3 Test equipment

The tensile testing machine shall comply with GB/T 16825.1 Grade 1 or higher. Lateral thrust on fasteners shall be avoided, for example, an automatic centering device may be used.

9.3.4 Test equipment

The fixture and test mandrel shall comply with the following provisions.

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.

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.

9.4 Nut hardness test

9.4.1 General

This test is applicable to nuts that meet the following requirements. […]

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.

The hardness test shall be in accordance with the provisions of GB/T 4340.1, GB/T 230.1 or GB/T 231.1. The minimum load for Vickers hardness test is 98 N. The load for Brinell hardness test shall be equal to 30D2, in Newton (N). […]