Corrosion Technical Publications
192. Stainless Steel AISA Grades for PM Applications: Applications requiring stainless steels are growing at a rate of about 5% annually. Opportunities for using powder metallurgy (PM) exist, but additional grades not covered by MPIF Standard 35 are required. The American Iron and Steel Institute (AISI) has standards for a broad range of stainless steels that can be used in many applications, but the compositions of these grades must be modified to be conducive to manufacture by conventional PM techniques. Several of these grades have been produced as standard press and sinter powders. The physical properties, mechanical properties and microstructures of these various grades are reviewed to serve as a guideline for PM parts manufacturers and potential applications of these grades are addressed.
191. Development of High Performance Stainless Steel Powders: Advanced melting technology is now being employed in the manufacture of stainless steel powders. The new process currently includes electric arc furnace (EAF) technology in concert with Argon Oxygen Decarburization (AOD), High Performance Atomizing (HPA) and hydrogen annealing. The new high performance processing route has allowed the more consistent production of existing products, and has allowed enhanced properties, such as improved green strength and green density. This paper will review these processing changes along with the potential new products that are being developed utilizing this technology. These include high strength stainless steels such as duplex and dual phase as well as stainless steel powders used in high temperature applications such as diesel filters and fuel cells.
185. Precipitation Hardening PM Stainless Steels: Applications requiring high strength stainless steels are growing rapidally. Precipitation-hardening stainless steels have seen limited use in powder metallurgy despite their high strength. Strengthening of these alloys is achieved by adding elements such as copper and niobium, which form intermetallic precipitates during aging. The precipitation-hardening grades exhibit corrosion resistance levels comparable with those of the chromium-nickel (300 series) grades. The physical properties and microstructures of two precipitation hardening PM stainless powders are presented: 17-4 PH, a high-chromium, martensitic precipitation hardening stainless steel, has been optimized for use in PM applications; and a new low chromium (12 w/o) alloy that utilizes copper in the precipitation reaction. This alloy (410LCu), is considered to be a cost-effective alternative in applications that require high strength and moderate corrosion resistance.
181. Machinability Additives for Improved Hard Turning of PM Steel Alloys: The machining of ferrous PM alloys differs considerably from wrought materials. The role of porosity and heterogeneous microstructures complicates the machining process, often making it more challenging. In addition, the presence of martensite in the microstructure of more highly alloyed and/or sinter-hardened PM components increases tool wear. One advantage of PM is that machinability additives can be easily admixed into the powder and therefore into the final part. Manganese sulfide is a well known additive for improving machinability. A new machining additive, designated MA, has been developed to compliment MnS in PM steels. Hard turning tests were performed to evaluate the effect of both additives on tool wear in different material systems. The MA additive was found to improve machinability beyond that of MnS in sintered compacts containing martensite. It additionally reduced rusting on the part surface. This paper discusses the improvement in machinability with these additives, with an emphasis on sinter-hardenable PM steels.
171. Development of a High-Strength-Dual-Phase PM Stainless Steel: Applications requiring high strength stainless steels are growing at a fast pace. Typical alloys used for these applications are either highly alloyed materials such as 17-4PH or materials that require a secondary heat treatment such as SS-410HT. A new dual-phase stainless steel has been developed as a lower cost option. The microstructure of the dual-phase stainless steel consists of a mixture of ferrite and martensite, the proportions of which are dictated by the chemical composition of the alloy. This unique microstructure results in high strength and hardness, while maintaining ductility. The mechanical properties of this new alloy are compared with those of competing materials such as 17-4PH, SS-409LE and SS-410HT. Potential applications for this new material are reviewed.
152. Production of Stainless Steel Powders by Advanced Steelmaking Technology: Advanced melting technology is now being employed in the manufacture of stainless steel powders. The new process currently includes electric arc furnace (EAF) technology in concert with Argon Oxygen Decarburization (AOD), High Performance Atomizing (HPA) and hydrogen annealing. The new high performance processing route has allowed Hoeganaes Corporation to provide not only a more consistent product, but has allowed enhanced properties, such as improved green strength and green density. This paper will review the potential to use this processing route to provide products with improved properties and performance.
145. Development of Stainless Steel and High Alloy Powders (Improved Stainless Steel Processing Routes): Advanced melting technology is now being employed in the manufacture of stainless steel powders. The new process currently includes electric arc furnace (EAF) technology in concert with Argon Oxygen Decarburization (AOD), High Performance Atomizing (HPA) and hydrogen annealing. The new high performance processing route has allowed Hoeganaes Corporation to provide not only a more consistent product, but has allowed enhanced properties, such as improved green strength and green density. This paper will review the potential to use this processing route to provide products with improved properties and performance.
92. The Influence of Microstructure and Carbide Particles on the Creep Behaviors of PM Alloys: Microstructure, related porosity, and the presence of strengthening inclusions such as carbides are known to influence the strength behaviors of PM alloys. Since an understanding of these relationships will be required if PM alloys are to be successfully used in demanding automotive applications, studies were conducted to evaluate their influence on design properties such as creep. Elevated tensile creep tests at 6770C (12500F) and 35Mpa (5Ksi) were conducted to determine steady state creep rates and deformations of 434L and 304L alloys. While both materials exhibited acceptable behaviors for automotive applications, relatively large differences between creep rupture times were observed. Moreover, a large variance in the creep rupture time was observed for the 304L alloy. It is believed that the observed variations in creep behaviors between the 434L and 304L alloys can be attributed to porosity variations, the existence of a silicon oxide layer along the grain boundaries of the 304L samples, and the presence of chromium carbide within the 434L specimens.