This standard specifies the properties of heat treated screws with a tapping screw thread in accordance with GB/T 5280, and which are designed with a drilling point which automatically drills the core hole for the screw during assembly. Such screws then automatically form the mating screw thread, either in a non-cutting or in a cutting operation, with the aid of the threaded portion of the screw adjoining the drilling point.
The purpose of this standard is to ensure that the screws are able to drill their core hole and form their mating screw thread without becoming distorted or fracturing in the process, provided that no overstressing has occurred. Consequently the following characteristics are regarded as representing the most important aspects for the assessment of the mechanical and operational characteristics of a drilling screw:
——surface hardness;
——capability of core hole drilling and forming of the mating female screw thread;
——torsional strength.
2 Normative References
The following normative documents contain provisions which, through reference in this text, 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 3098.17-2000 Mechanical Properties of Fasteners - Preloading Test for the Detection of Hydrogen Embrittlement - Parallel Bearing Surface Method (idt ISO 15330: 1999)
GB/T 4340.1-1999 Metallic Materials - Vickers Hardness Test - Part 1: Test method (eqv ISO 6507-1: 1997)
GB/T 5267.1-2002 Fasteners - Electroplated Coatings (ISO 4042: 1999, IDT)
GB/T 5280-2002 Tapping Screws Thread (idt ISO 1478: 1999)
3 Technical Requirements
3.1 Material
Case hardening steel or heat treatable steel shall be used as the material for drilling screws.
3.2 Metallurgical properties
3.2 1 Surface hardness
The minimum surface hardness of drilling screws after heat treatment shall be 530HV0.3.
3.2.2 Core hardness
The core hardness after heat treatment shall be
——320HV5~400HV5 for threads ≤ST4.2;
——320HV10~400HV10 for threads >ST4.2.
including a recommended minimum tempering temperature of 330℃.
The tempering temperature range 275℃ to 315℃ shall be avoided in order to minimize the risk of tempered martensite embrittlement.
GB/T 3098.11-2002 The following standards are cited：
