燒結氣氛及合金元素對粉末冶金鋼碳含量之影響

粉末冶金（Powder Metallurgy）及金屬射出成形（Metal Injection Molding, MIM）製程產品在工業界有相當的競爭力，因其具有多種優勢，如：多孔性、可製作高熔點金屬、製作具複雜形狀產品及低成本。在鐵系材料中，常添加碳以及合金元素，是改善其機械性質最普遍的方法，其中碳含量最重要，它與材料的強度、硬度和延性息息相關。所以若能有效的控制以及找出對材料性能最佳的碳含量，是重要的課題。在前人的研究指出，燒結時氣氛、流量以及添加的合金元素皆會改變碳含量以及組織均勻性。此外，由於鎳也是粉末冶金中常添加的元素，它能有效提升材料密度、強度及延性，但是卻容易造成含碳基材的組織不均勻性，所以希望藉由此實驗能了解並改善此問題。結果顯示，以MIM製成的Fe-1.75Ni-0.5Mo-0.5C合金鋼（MPIF-4605合金鋼）中，在N2-H2混合氣體下燒結時隨著氫含量之增加碳含量能維持穩定，直至氫含量超過40%才急速降低，而高流量氣氛下燒結的工件雖然得到較高的密度，但材料強度、硬度及碳含量皆比較差。在碳含量在0.6~0.8wt%、鎳含量8wt%時，能得到較好的硬度，但是鎳與碳有排斥效應，且鎳含量過高時，會使得材料中的碳在升溫時無法固溶到基地中，造成碳聚集的現象。若添加1.5wt%鉻在合金系統中可使鎳的擴散更均勻，主要是因為鉻降低了合金系統中鎳與碳的化勢，使鎳及碳能更均勻的分散在組織中，增強材料的機械性質。

關鍵字

粉末冶金；碳；鎳；燒結氣氛；均質化

並列摘要

Powder metallurgy (PM) process has been used widely in the industry due to its capability of making net shape products economically. Similar to most wrought steels, carbon is the most important alloying element for PM steels and is usually added in the graphite powder form. The graphite powders are homogenized during sintering. Previous studies have shown that the composition and flow rate of the atmosphere and the alloying elements are critical in determining the final amount of the dissolved carbon. These effects are further investigated in this study. The results show that the highest carbon content of Fe-1.75Ni-0.5Mo-0.5C (MPIF-4605 alloy) steel is obtained using a N2-40H2 atmosphere with a low flow rate. When the amount of Ni increases, the distribution of C becomes less uniform. This is because C and Ni have a repulsion effect as is demonstrated by the carburization and Ni coating experiments. As the Ni content increases to 15% and above, the repulsion effect becomes so strong that graphite phase forms. To improve the C and Ni distribution, the addition of 1.5wt% Cr was shown to be beneficial and the mechanical properties were enhanced. These experimental results are supported by the Thermo-Calc program analysis.

並列關鍵字

powder metallurgy ； carbon ； nickel ； sintering atmosphere ； homogenization

參考文獻

[2] R. M. German, “Wear Applications Offer Future Growth for PIM,” Metal Powder Report, 1999, Vol.54, No. 6, pp. 24-28.

[3] K. M. Kulkarni, “Dimensional Precision of MIM Parts Under Production Conditions,” International Journal of Powder Metallurgy, 1997, Vol. 33, No. 4, pp. 29-41.

[4] R. M. German, “Technological Barriers and Opportunities in Powder Injection Molding,” International Journal of Powder Metallurgy, 1993, Vol. 25 No. 4, pp. 165-169.

[5] K. S. Hwang and K. H. Lin, “Lubricant Removal in Metal Powder Compacts,” International Journal of Powder Metallurgy, 1992, Vol. 28, No. 4, pp. 353-360.

[7] T. S. Yoon, S. Ahn and C. Park, “Carbon Control During the Debinding of CIP-Polyamide Mixture Using Mixed Gases,” Powder Metallurgy, 1994, Vol. 20, pp. 1173-1176.

國際替代計量

燒結氣氛及合金元素對粉末冶金鋼碳含量之影響

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