## 4 Application
### Dilution and Yield Strength of Stainless Steel-Based Weld Metal in 3.5-9% Ni Steels
While managing with a dilution of 40% or less may be feasible, given the relatively low fixed heat input of 10 kJ/cm, the expected yield strength with increasing heat input for 9% Ni steel is summarized in Table 7. Among the 3.5-9% Ni steels, the 9% Ni steel, predominantly utilized in LNG storage tanks and fuel tanks for LNG-powered ships [19,20,61], was selected. As the heat input increased, the critical dilution required to satisfy the minimum yield strength of 400 MPa decreased. Notably, when the heat input reaches 30 kJ/cm and the dilution is 5%, the predicted yield strength is 399 MPa, which falls short of the minimum requirement of 400 MPa. Hence, to accommodate higher maximum heat input levels while considering dilution, reassessing the composition adjustment of the fully austenitic stainless steel-based welding consumables employed in this study is imperative. Selection of Stainless Steel-Based Welding Consumable to Expand the Range of Heat Input and Dilution Applicable to 9% Ni Steel  
To prevent the decrease in yield strength caused by dilution when using an austenitic stainless steel-based welding consumable on 9% Ni steel, the C and Cu contents in the original fully austenitic welding consumable were increased, and the predicted yield strengths are shown in Table 8. The C and Cu contents were incrementally increased by 0.1 wt% and 0.05 wt%, respectively, until the C and Cu contents reached 0.45 wt% and 0.3 wt%, respectively, as listed as the maximum contents in Table 1. To check whether the original fully austenitic microstructure was maintained through chemical composition adjustment and dilution, the Cr and Ni equivalents of the welding consumables in Table 8 are summarized in a Schaeffler diagram, as shown in Figure 11. The original fully austenitic welding consumable resulted in a fully austenitic weld metal microstructure with a dilution of approximately 50%. The modified welding consumables have an increased Ni equivalent owing to the increase in the C content; therefore, the modified welding consumables are advantageous for maintaining a fully austenitic microstructure in the weld metal. In \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Dilution** & \multicolumn{3}{c}{**Predicted Yield Strength (MPa)**} & **Remark** \\ \cline{2-5}
**(\%)** & **3.5\% Ni** & **5\% Ni** & **9\% Ni** & **Base Metal** \\ \hline
0 & 477 & 477 & 477 & \\
5 & 468 & 467 & 467 & \\
10 & 459 & 457 & 457 & \\
15 & 450 & 447 & 447 & \\
20 & 441 & 437 & 438 & \\
25 & 433 & 428 & 428 & \\
30 & 424 & 419 & 418 & \\
35 & 417 & 410 & 409 & \\
40 & 410 & 402 & 400 & \\
45 & 403 & 395 & 392 & \\
50 & 397 & 388 & 384 & \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Results of predicting yield strength according to the increase in dilution for 3.5–9% Ni steels. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Dilution** & \multicolumn{3}{c}{**Predicted Yield Strength (MPa)**} & **Remark** \\ \cline{2-5}
**(\%)** & **10** & **15** & **20** & **25** & **30** & **Heat Input (k/cm)** \\ \hline
0 & 477 & 455 & 440 & 424 & 407 & \\
5 & 467 & 445 & 429 & 415 & 399 & \\
10 & 457 & 435 & 417 & 405 & 390 & \\
15 & 447 & 426 & 407 & 394 & 380 & \\
20 & 438 & 416 & 397 & 383 & 371 & \\
25 & 428 & 406 & 387 & 372 & 362 & \\
30 & 418 & 397 & 377 & 362 & 352 & \\
35 & 409 & 388 & 368 & 352 & 342 & \\
40 & 400 & 379 & 359 & 343 & 331 & \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Yield strength prediction according to increase in heat input and dilution for 9% Ni steel. particular, in modified Case 3, the fully austenitic microstructure was maintained up to a dilution of approximately 60%.