**2. Materials and Methods**

The test materials used were two types of hot-rolled ferritic stainless steel. The chemical compositions of the test materials are shown in Table 1. The Trans-varestraint test method was used to evaluate the solidification crack sensitivities of these materials. The test equipment utilized the MTV2500 testing system produced by D. L. Wright Inc. Samples of dimensions 120 mm × 30 mm × 6 mm without the weld groove were machined for the Trans-varestraint tests. The weld was completed by arc remelting, and the remelting position and experimental principle are shown schematically in Figure 1 [19]. The principle of this method is to apply different strain values to study the crack generation. An autogenous gas tungsten arc welding method was used to melt the weld bead. The welding current and arc voltage were 150 A and 17 V, respectively. The welding speed was 100 mm/min. The welding shielding gas used was 99.999% argon gas, and the gas flow rate was 12 l/min. Nine series of strains (i.e. 0%, 0.25%, 0.50%, 1%, 2%, 3%, 4%, 5% and 6%) were used in the tests. The Trans-varestraint tests were performed in increasing order of strain from small to large values.

The surface cracks of the welds of the specimens that have completed the Trans-varestraint test are observed by scanning electron microscopy (SEM, ZEISS EVO MA 25, ZEISS Group, Cambridge, UK) to note the occurrence of cracks and to measure the lengths of these cracks. Metallographic specimens of the weld cross section were cut from the tested specimens under 0% strain. The specimens were machined, polished, corroded (corrosive solution, FeCl3:HCl:H2O = 5 g:50 mL:100 mL), cleaned with anhydrous ethanol, and dried. The microstructures of the specimens were observed by SEM (FEI QUANTA 600F, FEI Company, Eindhoven, Netherlands) and equipped with an energy dispersive spectrometer (EDS, OXFORD INCAx-act, Oxford Instruments, Oxfordshire, UK). The Scheil solidification simulation module of the thermodynamic calculation software Thermo-Calc was used along with the TCFE9 database to simulate the stainless steel welding solidification process.


**Table 1.** Chemical compositions of test materials (wt%).

**Figure 1.** Trans-varestraint test.
