Although duplex stainless steels (DSSs) are generally resistant to solidification cracking, such cracks have been observed across various welding methods and in wire-based additive manufacturing. High restraint and elevated impurity levels in base materials and filler wires are key contributing factors. This study investigates the influence of sulfur (S) and phosphorus (P) contents in DSS E2209T0 and E2209T1 flux-cored wires on hot cracking susceptibility. Single V-joints in fully restrained UNS S32205 plates were manually welded using the flux-cored arc welding (FCAW) process. Weld cross-sections were examined via light optical microscopy (LOM), and fracture surfaces from impact toughness and side bend test samples were analyzed using scanning electron microscopy (SEM). Ferrite content was quantified by image analysis and Feritscope measurements. Three different self-restraint weldability tests were used to evaluate the susceptibility of these filler metals to solidification cracking. A T-joint test per EN ISO 17641-2 was not severe enough to promote cracking in these filler metal deposits. A simplified test method, inspired by the FISCO test, was developed to rank cracking susceptibility under high restraint, with root passes welded against a ceramic backing. It produced cracking in 0–14% of the weld length, closely reflecting real weld performance. The FISCO test was found to be excessively severe (68–100% cracked length). Higher levels of S and P increased cracking susceptibility, with 0.030 wt.-% P having a somewhat more detrimental effect than 0.007 wt.-% S. These findings indicate that the impurity limits permitted by AWS A5.22 (0.040 wt.-% P, 0.030 wt.-% S) are excessively high, and that even the stricter EN ISO 17633 limits (0.030 wt.-% P, 0.025 wt.-% S) may warrant further reductions to prevent solidification cracking.