• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.578-579
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• 2006

We investigated that the effect of $CaCO_3$ based compound on machinability of two types of PM steels. One is a copper steel which is selected as a general PM steel, and the other is a diffusion alloyed steel selected as a high strength PM steel. It is found that $CaCO_3$ based compound addition improves machinability in drilling of both of the PM steels. Although the compound addition degrades the mechanical properties of PM steels, it is considered that decrease of the properties can be compensated by increasing density.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.393-394
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• 2006

Highly compressible Ni-Mo steels are attractive materials for PM due to high sinter density and ease of processing. Extra-fine Ni admixed PM steels have demonstrated improved mechanical properties and rolling contact fatigue resistance due to a more uniform microstructure and increased Ni diffusion during sintering. Sinter densities of single press single sinter XF Ni-Mo steels can approach $7.5\;g/cm^3$ at moderate compaction pressures. Leaner alloys based on extra-fine Ni powder are possible depending on the performance requirements of the PM steel part. Extra-fine Ni steels are particularly attractive for the growing market of high performance PM gears and sprockets.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.299-300
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• 2006

Machining of sinter-hardened PM steels provides a challenge for part makers. To facilitate machining of these materials, a new additive (MA) has been developed to increase tool life during the machining process. Hard turning tests were performed to evaluate the effect of this new additive. Sintered compacts with the MA additive were compared to compacts without a machining aid and to compacts that contained the MnS additive. This paper discusses the improvement in machinability with this new additive in sinter-hardenable PM steels.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.566-567
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• 2006

The characteristics of residual stresses occurring in PM steel based nickel (FLN2-4405) was investigated. The measurements of residual stresses were carried out by electrochemical layer removal technique. The values and distributions of residual stresses occurring in PM steel processed under various densities and heat treatment conditions were determined. In most of the experiments, tensile residual stresses were recorded in surface of samples. The residual stress distribution on the surface of the PM steels is affected by the heat treatment conditions and density. Maximum values of residual stresses on the surface were observed sinter hardened condition and $7.4\;g/cm^3$ density. Minimum level of recorded tensile residual stresses are150 MPa and its maximum level is 370 MPa.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.209-212
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• 2009

It has been widely reported that carbide-free bainitic steels or super-bainite WP (SB-TRIP) steels for the automotive industry are a new family of steels offering a unique combination of high strength and ductility. Hence, it is important to exactly evaluate the volume fraction of RA and to identify the 3-D morphology of constituent phases, because it plays a crucial role in mechanical properties. Recently, as electron back-scattered diffraction (EBSD) equipped with focused ion beam (FIB) has been developed, 3-D EBSD technique for materials science are used to these steels. Moreover, newly developed atom probe tomography (APT) technique can provide the exact distribution and chemical concentration of alloying elements in a sub-nm scale. The APT analysis results indicate exactly the distribution and composition of alloying elements in the austenite and bainite phases of SB-TRIP steels with the atomic-scale resolution. And thus, no partitioning of aluminum and manganese atoms was showed between the austenite containing $7.73{\pm}0.39$ at% C and the bainitic ferrite associated with $0.22{\pm}0.06$ at% C in the SB-TRIP steel.

• Transactions of Materials Processing
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• v.19 no.1
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• pp.44-49
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• 2010

It has been widely reported that carbide-free bainitic steels or super-bainite TRIP (SB-TRIP) steels for the automotive industry are a new family of steels offering a unique combination of high strength and ductility. Hence, it is important to exactly evaluate the volume fraction of RA and to identify the 3-D morphology of constituent phases, because it plays a crucial role in mechanical properties. Recently, as electron back-scattered diffraction (EBSD) equipped with focused ion beam (FIB) has been developed, 3-D EBSD technique for materials science are used to these steels. Moreover, newly developed atom probe tomography (APT) technique can provide the exact distribution and chemical concentration of alloying elements in a sub-nm scale. The APT analysis results indicate exactly the distribution and composition of alloying elements in the austenite and bainite phases of SB-TRIP steels with the atomic-scale resolution. And thus, no partitioning of aluminum and manganese atoms was showed between the austenite containing $7.73{\pm}0.39$ at% C and the bainitic ferrite associated with $0.22{\pm}0.06$ at% C in SB-TRIP steel.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.409-410
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• 2006

New applications for PM have resulted in a substantial market growth during the last decades. The clue to these components lies in the utilization of new powders and component production processes. In order to reduce development time and increase the probability for success it is essential to work in close cooperation within the whole chain from powder supplier to component supplier and component user.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.407-408
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• 2006

Dimensional precision is a critical parameter in net shape processing of ferrous PM components. Sinter-hardening alloys undergo a transformation from austenite to martensite. Martensite formation expands the sintered compact, while tempering hardened steels results in shrinkage. In addition, martensitic regions with high Cu and C contents may contain large amounts of retained austenite. The presence of martensite and retained austenite, in addition to the tempering step, all play a role in the final dimensions of a component. This paper investigates the dimensional and microstructural changes to two sinter-hardening grades through different post-sintering thermal treatments.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.561-562
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• 2006

The effect of chemical composition of the sintering atmosphere on density, microstructure and mechanical properties of Fe-3%Mn-(Cr)-(Mo)-0.3%C steels is described. Pre-alloyed Astaloy CrM and CrL, ferromanganese and graphite were used as the starting powders. Following pressing in a rigid die, compacts were sintered at 1120 and $1250^{\circ}C$ in atmospheres having different $H_2/N_2$ ratio and furnace cooled to room temperature. It has been found that the atmosphere composition has negligible effect on the as-sintered properties of the investigated materials.

• Journal of Powder Materials
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• v.9 no.5
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• pp.303-306
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• 2002

P/M high speed steels with various Co contents were fabricated by gas atomization and Canning/HIP process. As Co content in P/M high speed steel increased, hardness, transverse rupture strength and yield strength in compressive testing increased due to solid solution hardening of Co in matrix. Especially, PM high speed steels with Co have high deformation resistance to repeated compressive loading.