粉末合金鋼添加硼之燒結與機械性質研究

Sintering and Mechanical Properties of the Powder Alloy Steel Adding Boron

林暐珣(Wei-Shun Lin)

指導教授 ： 吳明偉

國立虎尾科技大學/工程學院/材料科學與綠色能源工程研究所/碩士(2013年)

摘要

粉末合金鋼普遍使用於汽機車等相關產業，但因其成品帶有約10%的孔隙率，因此其強度及韌性皆較鑄件要來的差，而有效提升其成品密度成為研究粉末冶金材料的一大課題。本研究先初步探討B元素對於液相燒結與燒結密度的影響，結果顯示當燒結溫度在1120℃以前相對密度約在87%~88%，當燒結溫度提高至1250℃時，則相對密度可提高至94%~95%。而之後探討Mo、Cr、Ni等合金元素於不同溫度燒結下對於含B合金鋼之影響。其中Ni的添加會提升液相生成溫度。
為了解其晶粒內部之元素分佈，本研究也利用EPMA分析探討其元素擴散情形，結果發現Ni在1120℃後開始擴散，且於1200℃後會均勻分佈在晶粒內部。由硼化物之成分分佈可證實Cr、Mo、C皆易與B共同集中在硼化物內。藉由定量分析可確定各合金系統內之硼化物成分不同。在機械性質方面，硼之添加因形成許多硬度約Hv1600~2600之硼化物，因此使合金鋼之硬度相當高，最高可達HRC。但因堅硬的硼化物主要皆位在晶界上，且呈現連續相，故在拉伸過程中極易沿著硬而脆的連續硼化物產生沿晶破斷，因此抗拉強度不佳。

關鍵字

粉末冶金 ； 硼 ； 液相燒結 ； 顯微組織 ； 抗拉強度

並列摘要

Powder metallurgy (PM) steels have been extensively used in the automobile industry. The strength and toughness of PM products are lower than those of wrought ones due to the presence of about 10 vol.% porosity in the PM products. Thus, the method to increase the sintered density is the key issue in the PM field. The aim of this study was to investigate the effect of boron on the liquid phase sintering and sintered density of PM steels. The results showed that, after 1120℃ sintering, the sintered density is only 87%~88%. When the sintering temperature was increased to 1250℃, the sintered density achieve 94%~95%. The influences of Mo, Cr, and Ni on the liquid phase sintering were also examined. Ni is found to increase the temperature for liquid formation.
To investigate the alloying distribution, EPMA was used to analyze the alloying diffusion and homogeneity. The results indicated that Ni atom starts to diffuse into the iron powder after 1120℃ sintering. After 1200℃ sintering, the distribution of Ni in the Fe grain is homogeneous. Furthermore, the distributions of Cr, Mo, and C matched that of B. The compositions of boride in various alloy systems are different, as identified by quantitative analyses. The addition of boron can generate many borides with high microhardness of Hv1600~2600. These borides result in the highest apparent hardness of HRC. However, these borides were continous and located primarily at the grain boundary. During tensile test, the intergranular fracture occurs along the network of boride and results in low tensile strength.

並列關鍵字

powder metallurgy ； boron ； liquid phase sintering ； microstructure ； tensile strength

參考文獻

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