Metal strip via roll compaction and related powder metallurgy routes

Abstract

The basic unit processes for making thin strip by the powder metallurgy (PM) route based on roll compaction are reviewed. The various powder and plant parameters that affect the quality of the green strip, together with the basic limitations of the process are described. Bonded metal powder rolling overcomes some of the limitations of the former method, but the cost of the binder is a major drawback. The technology and difficulties associated with the sintering of the green strip are emphasised. The methods adopted for densification are discussed, together with their relative advantages and disadvantages. The mathematical modelling of hot rolling of sintered strip is also reviewed. The mechanical properties of PM strip compare favourably with those of conventional stock. The advantages and applications of the PM route for making strip together with its technoeconomics are also described. The combination of powder production by atomisation and powder rolling offers applications in making strip from systems prone to segregation, rapidly solidified powder, etc. The application of the PM route for making speciality strips, such as strip from alloying components that are immiscible, metal/alloy strip containing a dispersed second phase, etc., are also discussed. There are some routes that do not use powder but liquid metal droplets, small metal particles, high purity metal oxide, etc., but the basic principles are similar to those of the PM route. Examples of such routes are: the compacted sheet process, spray rolling, centrifugal spray deposition, the direct steel process, and the direct strip process. They are described together with their advantages, disadvantages, and applications. The present industrial scenario and the future outlook of all the processes are discussed briefly.