Abstract
To obtain stronger metal foams, a heat treatment was done to strengthen the matrix of the foams. A powder of SUS440C stainless steel, the strongest of all stainless steels, was used as the starting material.
The green foams of the SUS440C steel powders with various porosities made by vacuum process using slurry were debound at 450°C and sintered at 1200°C in H2 into SUS440C steel foams. Some of the foams were heat-treated under a specified condition. The compressive test was done on both the heat-treated and non-heat-treated specimens.
Non-heat-treated SUS440C steel foams, even at a porosity as low as 53%, showed plateau regions with a stress of 168 MPa and a strain of 60%. These results suggest that these foams have potential for use as a good shock absorber. On the other hand, the plateau stress of the heat-treated SUS440C steel foams were twice as high as the non-heat-treated foams. The two heat-treated SUS440C steel foams, having densities of 2.7 and 4.5 g/cm3, showed almost the same yield stress as the wrought Al and Ti alloys, respectively. This demonstrates that the SUS440C steel foams could be inexpensive alternatives for those alloys. The maximum weight-lightening achieved with the SUS440C steel by making porosity inside was one-third of the guideline of the minimum weight design.
