The test materials are three grades of gray cast iron, namely ordinary HT250, low alloy HT250 and HT300, in which trace alloying elements with mass fraction less than 1% are added to low alloy HT250 and HT300.
Static tensile test refers to the method of measuring the basic mechanical properties of materials under axial load. According to the tensile test, five properties of materials can be obtained: elastic modulus, yield strength, tensile strength, elongation and section elongation. The tensile test results can not only understand the basic properties of materials, but also provide a basis for fatigue test design and test scheme. The tensile test sample comes from the test bar poured by the cooperative enterprise, and the size of the test bar Φ× L=30 × 300mm。 The tensile sample is processed according to the national standard GB / T228-2002, and the size of the tensile sample is shown in the figure. The tensile test at room temperature is carried out on the universal material testing machine wdw-300e. Because the cast test bar may have large casting defects (such as shrinkage, porosity, porosity, etc.), multiple samples of each brand of gray cast iron are selected for tensile test. The tensile properties of the material are taken as the average value of the effective tests of three samples, and the samples are dotted and marked before and after the test, Measure the length change before and after the sample, and calculate the elongation of three grades of cast iron samples. The calculation formula is shown in formula 2-1. After the test, mechanical cutting was carried out at 5mm below the tensile fracture of the sample, and the tensile fracture of three grades of gray cast iron samples was observed under scanning electron microscope.
Among them, δ Is the elongation, L 0 is the gauge distance of the sample before the test, and l is the sample after tensile fracture.