Capsule-free hot isostatic pressing of sintered steel to full density using water atomised iron and Cr-alloyed powder consolidated by cold isostatic pressing

Abstract

Powder metallurgy (PM) steel with enhanced density is essential for meeting the demands on high strength and high-performance applications. In this study, cold isostatic pressing (CIP) is applied for consolidating water-atomised iron and Cr-alloyed steel powder to reach about 95% densification before sintering. Additionally, the effect of the lubricant and graphite addition on the compressibility of the different base powder types was evaluated. The maximum green densities of ≈7.55 g cm −3 for iron powder and ≈7.45 g cm −3 for Cr-alloyed powder were reached after CIP at 800 MPa. The sintering at 1250°C with added graphite allowed to achieve increased densification to ≈7.60 g cm −3 for the iron and ≈7.50 g cm −3 for Cr-alloyed grades, respectively. These levels were sufficient for surface pore closure, which allowed the application of the capsule-free hot isostatic pressing (HIP) after sintering to reach full density. This approach paves the way for manufacturing large-sized PM components.

Consolidation of water-atomized chromium–nickel-alloyed powder metallurgy steel through novel processing routes

“…1,27 The water-atomized Cr-alloyed steel powder with admixed Ni exhibits good compressibility in isostatic pressing, which agrees with previous studies. 26 As explained in the previous study, 28 the densification involves plastic deformation of the metal particles regardless of the high hardness.…”

“…The approach has been demonstrated before on PM-steel alloyed with 3% Cr, 0.5% Mo, and 0.4% C, where full density is reached. 26 In the present study, the scope is extended to processing of PM steel starting from powder, pre-alloyed with 1.8% Cr, and admixed with 2% Ni and 0.3% C. This material is intended for a case-hardened application and the key role of Ni in enhancing sintering and microstructure development is depicted. With the overall goal of achieving full densification through the CIP, high temperature (HT) sintering, capsule-free HIP route, the influences of CIP pressure, sintering temperature, and sintering conditions are explored.…”