GROWTH OF MnS IN Fe-CU-C-MnS SINTERED STEELS WITH ADMIXED MnS

MnS growth in sintered steels with admixed Fe, Cu, C and MnS has been investigated by SEM and X-ray diffraction, MnS in Fe-Cu-C-MnS sintered steels in which MnS has been admixed is not stable and MnS growth may be ascribed to sintering between MnS particles or reaction between MnS and Fe, Cu, C elements.

Evolution of carbides and carbon content in matrix of an ultra-high carbon sintered steel during heat treatment process

DTA, thermal expansion, XRD, and SEM were used to evaluate the effect of quenching temperature on the mechanical properties and microstructure of a novel sintered steel Fe-6Co-1Ni-5Cr-5Mo-1C. Lattice parameters and the mass fraction of carbon dissolved in the matrix of the steel quenched were investigated. It is discovered that the hardness of the steel increases with quenching temperature in the range of 840-900℃ and remains constant in the range of 900 to 1100℃. It decreases rapidly when the temperature is higher than 1100℃. The mass fraction of carbon dissolved in the matrix of the steel quenched at 840℃ is 0.38, but when the quenching temperature is increased to 1150℃, it increases to 0.98. The carbides formed during sintering are still present at grain boundaries and in the matrix of the steel quenched at low quenching temperatures, such as 840℃. When the quenching temperature is increased to 1150℃, most of the carbides at grain boundaries are dissolved with just a small amount of spherical M23C6 existing in the matrix of the quenched steel.

Factors Influencing the Wear Behavior of Sintered Steels

A review was made on the research progress of wear behavior of sintered steels in recent years. Wear is not an intrinsic property of sintered steels, which is strongly influenced by the wear test conditions. However, many other factors that determine the mechanical properties of sintered steels also affect the wear behavior. Porosity has different effects on the wear of sintered steels depending on the application conditions. Under dry sliding condition, higher porosity results in lower wear resistance. The influence of microstructures on wear resistance is in the order: carbide, martensite, bainite and lamellar pearlite. The wear resistance increases with hardness, but this relationship changes with the porosity and microstructures of sintered steels.

Effect of Varying Carbon Content and Shot Peening upon Fatigue Performance of Prealloyed Sintered Steels

The aim of the work was to find out how the modification of surface treatment and microstructures affect the fatigue characteristics of the considered sintered materials. Two different systems were prepared： as-sintered and shot peened prealloyed sintered （Astaloy CrL based） steels with addition of 0.5% and 0.7% C. Sintering was carried out in laboratory tube furnace in an atmosphere of pure gases 75%N2＋25%H2. The sintering temperature was 1180℃ and sintering time was 60 min. Heating and cooling rates were 10℃/min. Fatigue tests were carried out in symmetric plane bending at stress ratio R=-1 with frequency of about 24 Hz. The presented experimental results showed that prealloyed water-atomised steels, with surface modification, exhibit positive effects on the fatigue failure resistance, and for that reason are suitable for high-performance applications.

Investigation of Sintered Maraging Steels

Processing of five grades of sintered maraging steels containing 13% Cr, 9% Ni, 1% Ti and different quantities of Mo, Co is described. Variations of ageing temperatures and ageing holding times had resulted in choosing optimum regime of ageing f T=550℃, T=2.5 h. It allowed to receive mechanical properties of these steels like to them for compact steels; UTS=1200 MPa, EL=5.3%, RA=7%, and Charpy impact =1445 kJ/m2. X-ray analysis had shown phases Fe7Mo6, Fe2Mo in steels containing Co and decreasing of the period 'of or-phase lattice in these steels after ageing.

HEAT TREATING OF SINTERED Fe-1.5Mo-0.7C STEELS AND THEIR SLIDING WEAR BEHAVIOR

The influence of heat treating on mechanical properties as well as on the sliding wear behavior of sintered Fe-1.5Mo-0.7C steels was experimentally studied. The microstruc-tures of sintered steels change from upper bainite to martensite, tempered martensite, pearlite and lower bainite depending on the heat treating conditions. Heat treating increases the hardness of sintered steels but high tempering temperature, i.e. 700℃, causes the hardness to be even lower than that of the as-sintered ones. The impact energy of sintered steels increases with increasing tempering temperature and arrives the highest at 700℃, while the steels tempered at 200℃ have the highest transverse rupture strength. Austempering results in fair good overall properties, such as hardness, impact energy, and transverse rupture strength. When the sintered steels were austempered, oil-quenched or tempered below 400? after quenched, the wear coefficient becomes considerably lower. Fair high hardness, such as HV30 】 380, and structures of martensite, tempered martensite or lower bainite are beneficial to lowering the wear coefficient. Under the wear test conditions given, delamination and oxidational wear are the main wear regimes for sintered Fe-1.5Mo-0.7C steels. Fe3O4 in the wear debris is beneficial to lowering wear coefficient.

Sintering behaviors of porous 316L stainless steel fiber felt

Isothermal sintering experiments were performed on the 316 L stainless steel fiber felts with fiber diameters of 8 μm and20 μm. Surface morphologies of the sintered specimens were investigated by using scanning electron microscopy(SEM) and optical microscopy. The results show that the amount of the sintering necks and the relative densities of the fiber felt increase with the increasing of both the sintering temperature and the sintering time. And the activation energies estimated present a decline at high relative densities for both 8 μm and 20 μm fiber felts. Moreover, the sintering densification of the fiber felts is dominated by volume diffusion mechanism at low temperature and relative densities. As more grain boundaries are formed at higher temperature and relative density, grain boundary diffusion will also contribute to the densification of the specimen.