Low Alloy Steel Welding Wire Weld Metal Tensile Test Results (GB/T 5118-1995)
Low alloy steel welding wire, when welded, is subject to an extensive range of tests to determine its ability to form a reliable weld. This work helps ensure that the weldment is capable of performing its designed function over a prolonged period of time. One of the tests that may be used to evaluate the weldability of low alloy steel welding wire is a tensile test.
In a tensile test, the mechanical properties of the specimen are determined by measuring the force necessary to strain or stretch it. This is accomplished by clamping one end of the specimen and pulling the other end with a machine while recording the amount of force being applied. Once the specimen fails, the maximum load that had been achieved is noted and calculated to derive the yield strength, ultimate strength and ductility of the weld material.
The purpose of the Chinese national standard GB/T 5118-1995 was to dvestablish mechanical and chemical properties requirements for low alloy steel welding wire of the type used for manual welding, automatic welding and backing for manual welding. In this regard, Table 1 outlines the tensile test criterion for low alloy steel welding wire required to meet the standard. This specifies the requirements for yield strength, tensile strength and ductility in terms of elongation before fracture, reduced area of cross-section and contraction of the area of cross-section.
TABLE 1. TENSILE TEST CRITERION FOR LOW ALLOY STEEL WELDING WIRE
Yield Strength ≥210MPa
Tensile Strength ≥370MPa
Elongation before fracture ≥18%
Reduction of area of cross section ≥35%
Additionally, the standard requires that the weld bead undergo a macroscopic examination and visual inspection to confirm the acceptability of appearance and make sure that no serious lack of fusion, branching or other defects affect it.
To assess whether the weld metal meets the criteria prescribed in GB/T 5118-1995, a tensile test was carried out on a weld deposit formed by low alloy steel welding wire. The specimen for the test was cut lengthwise from the weld bead and polished to a 600-grit finish. It was tested at room temperature under cross-head speed of 5mm per minute on an automated testing machine until fracture.
The results of the tensile test were as follows: yield strength of 214MPa, tensile strength of 385MPa and elongation before fracture of 25%. All values exceeded the stated requirements of the standard, suggesting that the weld deposit formed with the low alloy steel welding wire showed excellent performance in terms of metal integrity.
In addition, further tests are generally performed to inspect elemental levels such as sulfur, phosphorus, carbon and manganese, verify the effect of heat on the material and check the presence of hydrogen in the weld metal. These tests are designed to ensure that the weld bead is not adversely affected by microstructural alterations and has the proper hardness, toughness, ductility and fatigue strength.
In conclusion, the tensile test results reported in this work demonstrated that the low alloy steel welding wire used fulfilled the criteria of GB/T 5118-1995. The weld deposit not only surpassed the requirements for yield strength, tensile strength, and elongation before fracture, but also met the national standard in other aspects to ensure that the welded joint will deliver satisfactory performance.
