【正文】 eel for plastic injection molding. The steel has low carbon content ( wt.%) to promote toughness, medium chromium content (5 wt.%) to provide good resistance to high temperature softening, 1 wt% Si to improve high temperature oxidation resistance, and small molybdenum and vanadium additions (about 1%) that form stable carbides to increase resistance to erosive wear[8]. Composition analysis was performed on H13 tool steel before and after spray , summarized in Table 1, indicate no significant variation in alloy additions.Table 1. Composition of H13 tool steel Element C Mn Cr Mo V Si Fe Stock H13 Bal.Spray Formed H13 Bal. MicrostructureThe size, shape, type, and distribution of carbides found in H13 tool steel is dictated by the processing method and heat treatment. Normally the mercial steel is machined in the mill annealed condition and heat treated (austenitized/quenched/tempered) prior to use. It is typically austenitized at about 1010176。C, quenched in air or oil, and carefully tempered two or three times at 540 to 650176。C to obtain the required bination of hardness, thermal fatigue resistance, andtoughness.Commercial, forged, ferritic tool steels cannot be precipitation hardened because after electroslag remelting at the steel mill, ingots are cast that cool slowly and form coarse carbides. In contrast, rapid solidification of H13 tool steel causes alloying additions to remain largely in solution and to be more uniformly distributed in the matrix [911]. Properties can be tailored by artificial aging or conventional heat treatment.A benefit of artificial aging is that it bypasses the specific volume changes that occur during conventional heat treatment that can lead to tool distortion. These specific volume changes occur as the matrix phase transforms from ferrite to austenite to tempered martensite and must be accounted for in the original mold design. However, they cannot always be reliably predicted. Thin sections in the insert, which may be desirable from a design and production standpoint, are oftentimes not included as the material has a tendency to slump during austenitization or distort during quenching. Tool distortion is not observed during artificial aging of sprayformed tool steels because there is no phase transformation.References[1] R. G. W. Pye, Injection Mould Design, John Wiley amp。 Sons, NY, p. 14, 1989.[2] Rapid Prototyping amp。 Tooling State of the Industry 1998 Worldwide Progress Report, Terry T. Wohlers, Wohlers Associates, Inc., p. 22, 1998.[3] Kevin M. McHugh, “Fabrication of Tooling Inserts Using RSP Tooling Technology,” Proceedings of Moldmaking ‘99 Conference, Communication Technologies, Inc. Columbus, OH, May, 1999, p. 383.[4] B. Hewson, J. Folkestad, and K. M. McHugh, “Qualifying Rapid Solidification Process Tooling: Justifying Cutting Edge Technology,” Proceedings of Rapid Prototyping and Manufacturing ‘99 Conference, The Society of Manufacturing Engineers, Dearborn, MI, April, 1999, .[5] Master Unit Die QuickChange Systems, Greenville, MI[6] Cotronics Corporation, Brooklyn, NY.[7] E. J. Lavernia and Y. Wu, Spray Atomization and Deposition, John Wiley and Sons, New York, NY, p. 291, 1996.[8] Tool Materials, ed. J. R. Davis, ASM International, Materials Park, OH, , 1995.[9] K. M. McHugh, “Microstructure Transformation Of SprayFormed H13 Tool Steel During Deposition and Heat Treatment,” Solidification 1998, Edited by S. P. Marsh, J. A. Dantzig, R. Trivedi, W. Hofmeister, M. G. Chu, E. J. Lavernia, and Chun, The Minerals, Metals, amp。 Materials Society, P. 427, 1998.[10] Kyeong Ho Baik, EonSik Lee, WooJin Park, and Sangho Ahn, “Formation of Eutectic Carbides in Spray Cast High Speed Steel,” Proceedings of the Third International Conference On Spray Forming, Cardiff, UK p. 251, (1996).[11] K. Bhargava and A. N. Tiwari, “Effect of Rapid Solidification and Heat Treatment on D2 Tool Steel,” Internat. J. Rapid Solidification, 7, 51 (1992).