https://scholars.lib.ntu.edu.tw/handle/123456789/73987
Title: | 高強度 316L 不?袗?之金屬射出成形製程研究 The Study of High-Strength Powder Injection Molded 316L Stainless Steel |
Authors: | 鄭禮輝 Cheng, Li-Hui |
Keywords: | 射出成形;晶粒細化;固溶強化;熱處理;粉末冶金;Powder injection molding;316L stainless steel;grain refinement;solid-solution strengthening;heat treatment;powder metallurgy | Issue Date: | 2011 | Abstract: | 316L為常用於射出成形的不?袗?材料,可製作具有良好抗腐蝕性之精密零件,但其沃斯田鐵之結構導致其強度不高,限制了316L在工業界的應用,本實驗利用晶粒細化、氮固溶強化、熱處理及添加合金元素等方式,增加316L不?袗?之硬度及強度,以提升316L不?袗?之競爭力,實驗中亦分析了不?袗?中氮化鉻之形成機制,並提供其消除方法,以改進其硬度、強度及抗腐蝕性質。 一般射出成形316L需利用高溫燒結才能達到高密度,而高溫燒結易導致晶粒成長使強度下降,若以低溫的1120℃於裂解氨下燒結細316L不?袗?粉( D50=4.1 μm)兩小時,由於細粉具有較大的燒結驅動力,其密度可達7.70 g/cm3、晶粒尺寸約10 μm、氮含量約0.3 wt%、硬度約95 HRB、拉伸強度約740 MPa;相對地,一般粒度之 316L粉(D50=12.0 μm)試片在經過1370℃以真空燒結二小時之後。其密度約7.50 g/cm3、晶粒尺寸約64 μm、硬度約52 HRB、拉伸強度約450 MPa。此外,若將裂解氨燒結之316L不?袗?置於氮氣中進行熱均壓製程,可將氮含量增加至0.8 wt%,於1120℃燒結的細粉316L之硬度及拉伸強度分別可再提升至110 HRB (約37 HRC)及820 MPa,而以1370℃裂解氨燒結之一般粒度316L粉試片之硬度及拉伸強度則由72 HRB增加至100 HRB (約24 HRC)及530 MPa增加至730 MPa。將1370℃真空燒結兩小時之一般粉316L試片,以500℃低溫滲碳24小時,2.85 mm厚之試片滲碳層可達約40μm,表面硬度可達810 HV,由於滲碳之後並無碳化鉻生成,所以仍具有良好的抗腐蝕性,且仍可依一般之製程研磨拋光,製作成外觀件。將低溫滲碳處理應用於乾壓成形不?袗?,利用其內部具有連通孔之特性,滲碳過程碳可進入工件心部而強化,能有效提高不?袗?之硬度及強度。 Powder Injection Molded (PIM) 316L stainless steels are widely applied in the industry for making small components with complicated shapes, but its austenitic structure and poor strength limit its applications. The methods of grain refinement, solid-solution strengthing by nitrogen, carburizing treatments, and alloying were used in this study to improve the mechanical properties of 316L. In order to attain high sintered density, 316L is generally sintered at high temperatures, which causes significant grain growth. To circumvent this drawback, fine (D50 = 4.1 μm) 316L powder was sintered at a low temperature of 1120℃ for 2 hrs in dissociated ammonia. A high sintered density of 7.70 g/cm3 was obtained, the nitrogen content reached 0.3 wt%, and the hardness and tensile strength achieved were 95 HRB and 740 MPa, respectively. Sintering regular (D50 = 12.0 μm) 316L powder at 1370℃ for 2 hrs in vacuum can reach only 7.50 g/cm3 density, 52 HRB hardness, and 450 MPa tensile strength. With hot isostatic pressing in nitrogen, the nitrogen content in the fine 316L specimen that was sintered in dissociated ammonia for 2 hours can be further increased from 0.3 wt% to 0.8 wt% and the hardness and tensile strength of fine 316L specimen were improved to 110 HRB and 820 MPa, respectively. After being low-temperature carburized (LTC) at 500℃ for 24 hrs, the surface hardness of 316L reached 810 HV. The corrosion resistance remained the same because no Cr23C6 formed during carburization. The hardness and tensile strength of powder metallurgy 316L and 304L can also be increased by LTC obviously, since carbon can diffuse into the center of the specimen through interconnected pores. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/251675 |
Appears in Collections: | 材料科學與工程學系 |
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ntu-100-D96527015-1.pdf | 23.54 kB | Adobe PDF | View/Open |
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