2011 MPIF/APMI International Conference on Powder Metallurgy & Particulate Materials
Microstructure and Mechanical Properties of Microalloyed PM Steels: Microalloying is used in wrought steels to refine grain size during thermo-mechanical controlled processing (TMCP), with an attendant improvement in mechanical properties. With the exception of powder forging (PF), powder metallurgy (PM) does not utilize TMCP. In previous work by the authors, however, it has been shown that in PM steels microalloying elements such as niobium and vanadium can limit austenite grain growth during austenization prior to oil quenching and tempering. By limiting grain growth, the attendant precipitates cause a significant improvement in strength and ductility. In addition the precipitates that form during microalloying can also improve the strength of the pearlite which forms in the sintered condition. The objective of this study was to explore the use and potential benefits of microalloying elements such as vanadium and niobium in PM steels. The resulting mechanical properties and accompanying microstructure of these microalloyed PM steels are evaluated and rationalized.
Mn-Containing Steels for High Performance PM Applications: Alloying with manganese provides good hardenability and cost effectiveness in both wrought and PM steels. Recently introduced ANCORBOND® FLM alloys combine the benefits of Mn with moderate levels of Mo to produce lean alternatives to Ni- and Cu-containing hybrid alloy steels. The good hardenability of these Mn-containing steels makes them interesting candidates for sprocket applications, where martensite formation in components is necessary to impart good wear resistance. The current work assesses the heat treatment response of these alloys compared with FLN2-4405 under production conditions.
Improved Powder Performance Through Binder Treatment of Premixes: Powder mixes used in the PM industry contain ingredients of substantially different particle sizes and specific gravities that have a strong tendency to segregate during handling. Reducing or eliminating this segregation is essential for the part producer to achieve consistent precision and optimum performance. Treating the premixes with various types of binders improves the performance of the premix as a whole. A laboratory study was conducted with various binder/lubricant systems and results relating to segregation, flow and press performance are reviewed. Developments that provide improved flow rates combined with increased green densities and green strengths as well as their impact on overall productivity and performance are outlined.
Fatigue Performance of Molybdenum Prealloyed PM Steels: A versatile range of molybdenum prealloyed PM steels were developed over the years to meet performance requirements in the marketplace. More recently, steels containing 0.3 and 0.5 w/o prealloyed Mo have become commercially available as a result of economic pressures driving cost reduction in manufacturing PM parts. Leaner alloys based on prealloyed Mo are capable of delivering attractive properties for many applications where optimization of performance, design, and cost is desired. The robust nature of these alloys permits the use of secondary processing to enhance their performance over conventional press and sinter properties. This study explores the static and dynamic properties of lean prealloyed Mo steels with admixed copper and nickel, both as sintered and heat treated in mixes with 0.6 w/o graphite. The as-sintered fatigue performance of a 0.3 or 0.5 w/o Mo prealloy is improved with additions of Ni (0.75 w/o) and further enhanced with Cu (0.5 w/o). Heat treating boosts the fatigue limit for all combinations studied in reference to the as-sintered results, and it was found that 0.3 w/o Mo performs as well as 0.5 w/o Mo prealloy when heat treated. Additions of Cu were found to be detrimental to heat-treated fatigue behavior, supporting prior studies on the effects of heat treating Cu-containing PM alloys [1]. Furthermore, this work demonstrates that a composition as lean as, 0.3 w/o Mo + 0.75 w/o Ni + 0.6 w/o Gr, has competitive heat-treated fatigue performance when compared with FN-0205HT and FLN2-4405HT. INTRODUCTION