From Sintered Iron to High Performance PM Steels

Abstract

Keywords: powder metallurgy steels, low alloyed steels, high performance, master alloys.Abstract. Since low alloyed sintered steels were introduced in the market of the structural parts, we have followed the evolution of a material with poor mechanical properties and any uniformity (in the sense of reproducibility) to materials that today are produced with high reliability and performance. The working efficiency could be equivalent in many cases with the best wrought steel, and maintaining a good margin in terms of cost and competitively. In this paper a complete review of the topic is accomplished, from the early times when the first parts were made by plain iron or iron-carbon, going through the different alloying systems: Fe-Cu, Fe-P, Fe-Cu-Ni-Mo, and more recently Fe-Cr-Mo and Fe-Mn. The development in processing routes has been considered too. The main milestones in the field of new alloying systems have been: 1) the introduction of Cu in 60-70"s, 2) the new complex systems with Cu-Ni-Mo in the 80"s and 3) the introduction of alloying elements with high oxygen affinity (in the late 90"s). Regarding the milestones in processing could be considered: 1) the development of new mixing procedures, 2) the warm compaction and high velocity compaction, 3) the improvements in sintering control and high temperature sintering. Several decades of research and innovation, acting on the processing system (mixing, pressing, sintering, post-sintering operations,…) and on the alloying system (from the earliest times with plain iron to complex systems used today), has allowed us to have a highly competitive materials, in terms of performance, and processes in terms of cost. The future is still open to new developments. First sintered steels.Iron based powder metallurgy (PM), were developed in the previous years to the II World War, being the absence of raw materials the pushing effect, and it was the origin of a new materials family (PM Steels) that today can be considered a high performance materials. The first sintered part was introduced in the car industry by General Motors in 1937 and was an oil gear for oil pump [1]. One of the first components introduced was one iron part for an electrical engine in 1945 [2].Till late 60"s were manufactured by PM simple parts, that were based on Fe-C and Fe-Cu-C systems. The knowledge of these systems was developed from works that analyze the possible formation of liquid phase during sintering with the aim of improving the densification and to promote sintering activation [3] as well the diffusion mechanisms in plain systems and selfdiffusion of Fe [4,5]. To analyze and to understand the sintering steps were use iron wires that can reproduce the sintering model based on spheres [6].Looking for the improvement in the mechanical properties, at that time considering the available technology two basic requirements for new alloying systems were stated: poor or null affinity for the oxygen -sintering atmospheres were not enough dried [7]-and the possibility of controlling dimensionally the s...

Integrated product and process development of powder metallurgy hub for automotive clutch

“…However, for parts such as clutch hubs that require higher strength and hardness, pure iron-based powder materials are not sufficient to meet their performance requirements. The alloying of the material is usually performed by adding alloying elements such as C, Cu, Ni, Mo, P and Mn to the iron matrix so as to significantly improve the performance of the iron-based powder metallurgy material [24,25]. Carbon can dissolve into iron to form an interstitial solid solution and play the role of solid solution strengthening.…”

New Opportunities for Low Alloy Steels—Master Alloys for Liquid Phase Sintering

“…To reach this objective, different strategies have been developed to improve the processing route, for instance, in the pressing step, the warm compaction process or the high velocity compaction and in the sintering step, the use of high temperature sintering [8][9][10][11][12]. But the development of new alloying systems is no doubt one of the most explored alternatives.…”

Carbon Co-Deposition During Gas Reduction of Water-Atomized Fe-Cr-Mo Powder

“…However, the high cost of these traditional alloying elements has created a need for cheap and efficient alternatives in order to reduce overall product costs. One such alternative is chromium (Cr), which is low in cost, relatively abundant, easy to recycle and offers good resistance to temper softening [1][2][3]. It is also particularly effective in improving sinter-hardenability [4], which is a process of transforming the whole part or some specific region to martensite by controlling the cooling rate during sintering.…”

“…This offers many economic benefits as a onestep manufacturing process for achieving a good combination of strength, toughness and hardness [4]. Yet despite all these benefits associated with Cr, it is not currently being used to its fullest potential because of its very high affinity for oxygen [1][2][3][4][5].…”