May 2022 Volume 4

FORGING RESEARCH

Figure 1: The WAAM cell at Georgia Southern University Initial feeds and speed testing with the 410 stainless wire was performed using 75/25 CO2, trimix (He-Ar-CO2) and Ar-N2. The flow rate was adjusted to 20 lpmas higher flow rate was leading to the porosity as shown in Fig 2. We decided to use trimix combination for the high temperature testing, as our previous research [1] show better surface quality.

Figure 4: A typical lath martensitic microstructure of wire-arc additively manufactured 410 stainless steel Compression testing specification and results: The selection of test temperatures are based upon the fact that operating temperature for aluminum and magnesium forging dies are in 400 to 500 °C range. The compression testing were performed with Instron universal testing systemat three different temperatures: 400, 500 and 600 °C. The system were calibrated according to the standard prior to the testing. A standard size of 5x5x7.5 mm length rectangular specimen were extracted from the wire-arc additively manufactured samples. ASTM E209 was followed for the test. The nominal strain rate was 8.3 x 10-5. For the tests at 400 and 500 °C, the temperature tolerance is ± 5.5 °C. For the tests at 600 °C, the temperature tolerance is ± 6.2 °C. The ultimate compression strength and the yield strength values from the compression testing are presented in Fig 5. At 400 °C, the ultimate compression strength for the as-printed sample extracted in the horizontal direction is 1413 MPa, while in the vertical direction is 1310MPa respectively. Similarly, at 500 °C, the ultimate compression strength for the sample extracted in the horizontal direction is 1137 MPa, while in the vertical direction is 1275 MPa respectively. At 600 °C, the ultimate compression strength for the sample extracted in the horizontal direction is 284 MPa, while in the vertical direction is 254 MPa. The trend in data does appears to indicate that as the testing temperature increases the strength decreases (the initial increase from the room temperature to the 400 °C is due to age hardening), which is a typical of a metallic alloy. Being a newer process, there are not many literature data available to compare with the high temperature properties of 410 stainless steel. A wrought H13 alloy has a tensile strength of 1020 MPa at 600 °C [2]. The authors from [2] have shown that similar tensile strength in the range of 1000 -1200 MPa at 600 °C can be achieved when using selective laser melting additive manufacturing process for H-13 steel. Thus, the 254-284 MPa tensile strength at 600 °C for the 410 stainless steel may not be suitable for tooling application where the operating temperature is more than 500 °C. The data are compared with the baseline tensile strength data from Carpenter Technology

Figure 2: Observation of porosity (indicated by an arrow) right after depositing a bead and several layers of deposition on the right A test block was prepared to extract the specimen for the high temperature testing. The machining process for high temperature is shown in Fig 3.

Figure 3: Sample preparation for high temperature testing The wire-arc additively manufactured 410 stainless steel optical microstructure is presented in Fig 4. The metallography samples are prepared from the wall using standard metallographic procedures. The microstructure typically resembles a lath martensite based. The martensitic stainless steel with 11-14%Cr can solidify in either fully martensitic, martensitic and eutectic ferrite or martensite and delta ferrite [1].

FIA MAGAZINE | MAY 2022 75