In both types of tools, spray buildup of the tool steel is rapid, taking only a matter of minutes. McHugh added that the two processes also have differences in the thermal and physical properties of the droplets, resulting in more subtle differences in the microstructures of the deposited materials. Tailoring Properties RSP tooling can undergo either conventional heat treatment or low-temperature heat treatment known as artificial aging. Artificial aging allows the tailoring of steel properties, such as hardness, toughness, and thermal heat resistance, without the risk of tool distortion. Conventionally processed tool steel that is melted and cast at the steel mill contains segregates, resulting in nonuniform material properties that make high-temperature heat treatment necessary.
Segregation occurs when molten metal solidifies slowly.
With RSP, tool steel is melted and mixed up in the crucible, then solidifies rapidly during spraying, to prevent a chance for segregation to take place. RSP spray forming results in tool steel with a more uniform carbide distribution, allowing it to be artificially aged at a lower temperature. In tests, H13 tool steel that has been artificially aged compares well with commercial forged and heat-treated steel, said McHugh. RSP also may enable the use of unique tooling alloys that would be prohibitively expensive with standard tooling, according to James R. Knirsch, RSP tooling development manager at Global Metal Technologies' Solon, Ohio, plant, which is licensing the process. Premium grade tool steels such as H13 are made in huge lots with carefully controlled alloy additions.