# High-Temperature Mechanical Properties of 4.5%Al \(\delta\)-TRIP Steel
## 2 Materials and Methods  
A \(\delta\)-TRIP steel ingot was prepared by vacuum induction melting using commercial-purity materials with a target composition of 0.4C-0.5 Si-2.0 Mn-4.5%Al-Fe (wt %). The dimensions and the shape of the \(\delta\)-TRIP steel ingot are shown in Figure 1. The concentrations of C and S were measured using the infrared absorptiometric method after combustion in current oxygen. Besides, the inert-gas carrier melting-thermoductometric method was employed for the measurement of N concentration. The contents of the other alloying elements (Si, Mn, and Al) were measured by the inductively coupled plasma optical emission spectrometric (ICP-OES) methodology. Figure 1 shows the dimensions and the shape of the \(\delta\)-TRIP steel ingot as well as the dimensions and the locations of the specimens. The shape of \(\delta\)-TRIP steel ingot, like an inverted cone, had an upper diameter (\(\Phi\)) of 120 mm and a total length of 240 mm. Gleeble tensile specimens were cut from the columnar grain region of the ingots. The Gleeble tensile specimens were standard cylindrical tensile specimens, of which the diameter was 10 mm and the length was 121.5 mm. The sampling position of the DSC specimen was near the sampling position of the Gleeble tensile specimens. The DSC specimen was required to have be a round flake with a diameter of 5 mm or a rectangular flake with a diagonal length no more than 5 mm, and its thickness was generally less than 1 mm. Due to the large contents of Al and Mn in the specimen, to minimize the contamination of the instrument support during the  
melting process, the DSC specimen size (diameter \(\times\) thickness) in this test was 3 mm \(\times\) 1 mm. Drill 6 equidistant holes were in the axis of the \(\delta\)-TRIP steel ingot and had a small amount of steel scrap. A cylindrical specimen with a diameter of 33 mm and a height of 10 mm at the bottom of the ingot was used, and this cylindrical specimen and the steel scrap were analyzed to determine the chemical composition of the ingot. The high-temperature mechanical properties of \(\delta\)-TRIP steel were studied by using the Gleeble 3500 thermomechanical simulator. With the electrical discharge machining (EDM) method to shape the ingot-carved cylindrical tensile steel and the area of the columnar crystal being placed at a temperature range of 700 to 1350 \({}^{\circ}\)C, the specimen was tensioned at a constant temperature and at a constant strain rate of 1 \(\times\) 10\({}^{-3}\) s\({}^{-1}\). All the tests were carried out in an atmosphere of argon to avoid steel oxidation. The temperature control diagram of the tensile test is shown in Figure 2. The steel samples were first heated to 1300 \({}^{\circ}\)C with a heating rate of 10 \({}^{\circ}\)C/s, and then they were subjected to insulation during the solid solution treatment for 180 s to homogenize the microstructure and eliminate the internal stresses. The steel was cooled at a rate of 3 \({}^{\circ}\)C/s for 3 min until its temperature reached the test temperature, which was maintained. At temperatures above 1300 \({}^{\circ}\)C, the steel was heated to the test temperature at a rate of 3 \({}^{\circ}\)C/s and incubated for another 3 min. Finally, the sample was tensioned until it fractured and cooled rapidly in argon. The measured area reduction was used as a function of the deformation temperature to evaluate the hot ductility behavior. The morphology of the fracture was observed under SEM. The fracture type was analyzed. The RA and the \(\sigma_{\mathrm{max}}\) of the steel were obtained in the high-temperature tensile test. The temperatures, at which both the RA and the \(\sigma_{\mathrm{max}}\) value of the sample were zero, were measured corresponding to the zero ductility temperature (ZDT) and the zero strength temperature (ZST), respectively [24; 25].