ISO 2702 pdf download Heat-treated steel tapping screws — Mechanical properties
This International Standard specifies the characteristics of heat-treated steel tapping screws, with tapping screw thread from ST2,2 to ST9,5 inclusive according to ISO 1478, together with the corresponding test methods.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 898-7:1992, Mechanical properties of fasteners — Part 7: Torsional test and minimum torques for bolts and screws with nominal diameters 1 mm to 10 mm
ISO 6507-1, Metallic materials — Vickers hardness test — Part 1: Test method
Tapping screws shall be made from cold heading, case hardening quality steel.
4.1 Metallurgical requirements
4.1.1 Surface hardness
The minimum surface hardness after heat treatment shall be 450 HV 0,3 (see ISO 6507-1).
4.1.2 Case depth
The case depth shall conform to the values given in Table 1.
4.1.3 Core hardness
The core hardness after heat treatment shall be
270 HV 5 to 370 HV 5 for threads ST3,9, and
270 HV 10 to 370 HV 10 for threads ST4,2.
The microstructure shall show no band of free ferrite between the case and core.
4.2 Mechanical requirements
4.2.1 Thread-forming capability
Tapping screws shall form a mating thread without deforming their own thread when driven into a test plate, in accordance with 6.2.1.
4.2.2 Torsional strength
Tapping screws shall have a torsional strength such that the torque necessary to cause failure, when tested in accordance with 6.2.2, shall equal or exceed the minimum torque values given in Table 3 for the applicable screw threads.
For routine acceptance tests, the drive test, torsional test and core hardness test may be used, but for referee purposes all requirements specified in this International Standard shall be satisfied.
6 Test methods
6.1 Test methods for the metallurgical requirements
6.1.1 Surface hardness test
The Vickers hardness test shall be carried out in accordance with ISO 6507-1.
The impression of the pyramid shall be made on a flat face, preferably on the screw head.
6.1.2 Case depth — Microscopic test
Case depth shall be measured at the thread flank mid-point between crest and root or, in the case of smaller tapping screws up to ST3,9, in the root of the thread.
For referee purposes, a micro hardness plot shall be made using a Vickers indenter and a 300 g load on the thread profile of a properly prepared metallographic specimen. The case depth shall be the point at which the hardness recorded is 30 HV above the actual core hardness.
6.1.3 Core hardness test
The Vickers core hardness test shall be carried out in accordance with ISO 6507-1 at the mid-radius of a transverse section through the screw taken at a distance sufficiently behind the point of the screw to be through the full minor diameter.