By: Ingrid Hauer

North American Hoganas

New investments into laser cladding as well as wear and corrosion testing equipment have lead to the expanded use of stainless steels. Latest developments show these lower cost alloys are able to yield comparable physical properties to many of the traditional Ni-based and Co-based alloys commonly used today.

Three Fe-based materials are investigated and the compositions are presented in the table bellow.

The tests were done on laser clad samples using a 4kW Coherent Direct diode laser by means of an 808 nm wavelength and 1×12 mm raw beam size. Several properties were evaluated including pitting corrosion, hot hardness, wear, and resultant microstructures.

Cyclic polarization assessments were completed in order to determine tendency of the materials to undergo pitting corrosion. The three stainless powders were compared to a typical 316L, Inconel® 625, 2537-00 (type Stellite® 6), and 2541-00 (type Stellite® 12). The results are shown in Figures 1 and 2.

Figure 1. Cyclic polarization results for 3.33LC, 3533-00, 3533-10 and 316L

Figure 2. Cyclic polarization results for 3.33LC, Inc625, 2537-00 and 2541-00

Figure 1 shows that each of the three FeCrNi powders exceeded the pitting corrosion resistance compared to the standard 316L. The curves are steep in the passive region, indicating a stable passive layer. The pitting potential is highest for the 3.33 LC alloy.

Figure 2 indicate similar pitting corrosion behaviour for 3.33 LC as for the Ni and Co based materials. For further explanations on this test can be found through the ASTM G61 standard test method.

Hot hardness compares the ability of materials to maintain their respective hardness properties through a range of operating temperatures. These results are shown in Figure 3.

Figure 3. Hot hardness results

As shown by Figure 3, both the 3.33LC and 3533-00 maintain their hardness up to 700ºC. The chart also displays a trending similarity between the 3.33LC and Inc 625 alloy throughout the temperature range.

The microstructures and appropriate HRC values for each powder are shown in Figure 4.

Images above display that the eutectic from these Co-based alloys are made up mostly from Cr7C3 carbides along with M7C3 carbides and W rich M6C (shown by the dark brown regions). From this we are able to see that the 2541-00 contains more of this type of carbide compared to the 2537-00 effectively increasing the hardness of the material shown by the resultant tested values. The stainless powders’s microstructure consists of austenitic matrix and carbides.

The chart below illustrates that the three Fe-based alloys trialed here were able to effectively provide wear properties similar to that of the typical Co and Ni based alloys. Specifically, the Fe based 3533-00 and 3533-10 provided equivalent properties to the 2537-00 and 2541-00 respectively.

In conclusion, it can be proven that advancements in Fe-based alloys have lead to many effective and sometimes superior alternatives to many of the costly alloys commonly used in today’s market.