Is your bolt tensile strength tested by a first party or a third party? Has there ever been a big difference in the test results between the two sides? How to judge the correct test method? This article will test the tensile strength test method of stainless steel bolts from the perspective of GB/T3098.6 “Mechanical Properties of Fasteners Stainless Steel Bolts, Screws and Studs” (equivalent to ISO3506.1).

1. Processing samples or physical inspection?

The original intention of testing the machined samples is to examine the thermal processing process of the material and whether the bolts are completely quenched, while the austenitic stainless steel products are improved in strength by cold working (there is no process of heat treatment to increase the strength). Clauses 2 and 7.23 clearly stipulate in the tensile test that “according to the provisions of GB/T228.1 and GB/T3098.1, the tensile strength (Rm) shall be measured on the fasteners with I≥2.5d, and the plasticity shall be specified. The stress Rp0.2 when the elongation is 0.2% is only tested on the actual bolt or screw, so the mechanical properties of austenitic stainless steel bolts can only be obtained by the actual tensile test. If the test specimen is machined, the tensile strength will be low.

2. How to choose the cross-sectional area of half tooth products?

The nominal length part of the half-thread bolt is composed of the polished rod part and the threaded part, and its theoretical cross-sectional area is different. Therefore, when the fracture position is in the polished rod part, which cross-sectional area should be selected for calculation? Many people take it for granted and directly select the cross-sectional area of the fracture site. However, in the standard “Table 2”, note a has a special instruction on the selection of tensile strength cross-sectional area “calculated according to the nominal stress area of the thread (see Appendix A)” (see the table below), therefore, without considering the fracture position, directly select the appendix The nominal stress cross-sectional area of the thread in A is sufficient. If the cross-sectional area of the rod is used, the tensile strength will be low.