Stainless Steel

Stainless Steel 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.

172. Pre-Alloyed Boron in Powdered Metal (P/M) Stainless Steels The demand for high-density stainless parts continues to grow as P/M continues to battle conventional stainless. The compressibility and hence the final sintered density of P/M stainless steels are limited due to their high alloy content. The addition of boron allows P/M to produce nearly full density parts that achieve mechanical properties similar to wrought materials. By adding boron to the melt prior to atomizing, the segregation of boron is minimized leading to a more uniform microstructure and properties. The present work will examine the role of pre-alloyed boron in both austenitic and ferritic stainless steels. Experimental work will involve the measurement of green and sintered properties. Using the laboratory experiments as a guide, specimens will be sintered in production furnaces to determine the performance of various grades of boron containing stainless steels. The specimens will be evaluated for density distribution, dimensional stability and mechanical properties.

171. Development of a High-Strength-Dual-Phase P/M 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.

144. Unique Stainless Steel Materials and Processing for High Strength with Reduced Magnetic Performance A new automotive part was designed having property requirements incorporating high yield and tensile strengths with good ductility, while at the same time requiring reduced magnetic performance. This combination of properties precludes the use of iron and low alloy materials because of their intrinsic magnetic response. In an effort to satisfy both requirements, type 200 stainless steel powders were prepared and processed into both mechanical property test specimens and magnetic toroids. Processing of the compacted samples was optimized to give the required strength characteristics with required minimal magnetic response. This paper will detail the types of stainless materials utilized and unique processing developed to accomplish these conflicting requirements. The mechanical and magnetic properties will be presented.

135. Improved Stainless Steel Processing Route 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 these processing changes along with the potential new products that can be made with this technology.

113. Effect of Small Additions of Boron on Mechanical Properties & Hardenability of Sintered P/M Steels Low levels of boron (0.01-0.15w/o) may induce sufficient hardenability and strength in powder metallurgy steels to permit a decrease in the level of the alloying elements, increase powder compressibility and reduce the as-sintered hardness. These lean alloys may be sufficiently ductile to coin and be hardened by subsequent heat treatment. The goal of this study was to identify the boron level in FLN2-4400 (Fe + 0.85w/oMo, 2.0w/oNi, 0.3w/oC) which yields the optimal combination of strength, ductility, and hardenability. Tensile, transverse rupture, hardness, and Jominy end quench tests were performed on this alloy with six different levels of boron added Sintered strength and ductility increase up to 0.05w/oB, but decrease beyond this level, even though sintered density increases significantly. Jominy hardness traces show that the hardenability is not increased substantially until the concentration of boron reaches 0.05w/o. The microstructures of the Jominy bars show that with an increase in boron level, the depth to which martensite is retained increases, but that grain boundary segregation occurs. A level of boron ~ 0.05w/o gives the optimum combination of strength, ductility, and hardenability in FLN2-4400.

92. The Influence of Microstructure and Carbide Particles on the Creep Behaviors of P/M 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.

84. Water Atomized Fine Powder Technology Industry trends indicate the need for economical fine powder grades for a growing number of applications. Particle size, shape and percentage yields are the important characteristics associated with the manufacture of suitable powders. This work identifies our development efforts, corresponding achievements and commercial applications. Various metal injection molding binder formulations, to be used in conjunction with the fine powders, are also reviewed.

71. Studies on the creep and Corrosion Behaviors of Various P/M Stainless Steel Alloys - Technical Paper never published.

70. High Performance P/M Stainless Steels Powder Metallurgy (P/M) automotive exhaust flanges are in volume production for several US automobile and light truck engines. However competing technologies continue to improve and may threaten the anticipated increase in applications of P/M stainless flanges. This paper examines the properties of stainless steel powders, particularly a stabilised ferritic steel that should improve the processing and competitiveness of P/M stainless steels in automotive applications.

64. High Performance P/M Stainless Steels Powder Metallurgy (P/M) stainless steel automotive exhaust flanges are in volume production. However competing technologies continue to improve and may threaten the anticipated increase in applications of P/M stainless steel flanges. This paper examines improvements in powder properties that should improve the processing and performance of P/M stainless steels.

56. Evaluation of P/M Ferritic Stainless Steel Alloys for Automotive Exhaust Applications - Technical Paper not available.

55. The Effect of Service Temperature on the Properties of Ferritic P/M Stainless Steels An area of current development for P/M stainless steel applications is automotive exhaust systems. Recent work in this area has proven the potential application of ferritic stainless steel P/M materials for exhaust flanges to be viable. Lacking in this work, however, is a sufficient database for P/M stainless steels and, in particular, elevated temperature mechanical properties.

A study was undertaken to investigate the effect of service temperature on the mechanical properties of several ferritic P/M stainless steel grades including 410L, 409Cb, 434L and 434Cb. In particular, tensile properties were generated for these alloys and compared with their wrought equivalents. The effect of process conditions and the subsequent microstructure was also considered.

51. Processing Experience of Green Strength Enhanced Material Systems Green strength enhanced material systems have been developed for iron and Low alloy as well as stainless powder metallurgy applications. Relative to normal processing, the increase in green strength is 50-100%. The nature of green strength with respect to both materials and processing conditions is reviewed. The processing variations designed to meet target properties such as apparent density, flow and compressibility are compared with conventional material systems. Manufacturing experience with a mechanical press is presented.

29. Effects of Powder Properties and Processing on Soft Magnetic Performance of 400-Series Stainless Steel Parts With the advent of growth in soft magnetic applications suitable to Powder Metallurgy, powder manufacturers parts fabricators and end users of such parts must gain a better understanding of the relationships between powders, processing and the ultimate performance of soft magnetic P/M parts. Studies have been conducted and valuable data extracted on the subjects of pure iron, iron-phosphorus, iron-silicon and prealloyed iron-nickel alloys as they relate to magnetic properties. With the identification of applications requiring corrosion resistance as well as mechanical and magnetic properties, including the Anti-lock Brake System (ABS) tone wheel, industry is investigating ferritic stainless steel solutions. This study represents an effort to provide some initial answers to questions regarding the "real world" capability of P/M production of high quality, ferritic stainless steel parts that exhibit excellent magnetic properties.

19. Effects of Processing and Materials on the Soft Magnetic Performance of Powder Metallurgy Parts Soft magnetic properties of P/M parts are influenced by materials and processing. This paper will review the magnetic properties of several iron-based materials along with how various processing steps influence magnetic properties. In particular, density, sintering temperature, sintering time and sintering atmosphere effects will be examined. Special attention will be paid to the influence that sintering conditions have on chemistry and the resulting effects on magnetic properties. Materials investigated in the study include pure iron and combinations of iron, phosphorus, silicon and nickel.

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