- 學位論文
高強度金屬射出成形燒結硬化合金鋼之製程及機械性質研究
Mechanical Properties and Processing of High Strength Sinter-Hardening MIM Steels
摘要
燒結硬化型合金鋼之基本設計概念為在鐵基材料中添加高硬化能元素，如錳、鉻、鎳、鉬、銅等，讓材料具有高硬化能，使其可以不需經過淬火和回火等熱處理製程即可得到良好的機械性質。本研究將以前人所研究開發的燒結硬化型合金鋼，Fe-8Ni-0.8Cr-0.8Mo-0.17Cu合金系統為主，改變鎳含量來觀察鎳含量對機械性質的影響。結果發現，5wt%鎳含量有最高之拉伸強度，可達2055MPa，伸長量為2.8%。由於鎳在鐵中的擴散速率慢，均質化較為困難，故對機械性質影響很大，為了使鎳在燒結後分佈均勻，本實驗嘗試使用Fe-2Ni預合金粉取代羰基鐵粉，然而在1330℃燒結後，經過深冷和回火熱處理，硬度可達48HRC，拉伸強度為1930MPa，結果不如預期。 本燒結硬化型合金之鉻是由水噴霧的17-4PH不?袗?粉提供，本研究嘗試使用Nitronic60不?袗?粉和Nanoflex不?袗?粉。實驗結果分別為，使用Nitronic60不?袗?粉之機械性質和原先之材料相當，而使用Nanoflex不?袗?粉之機械性質則下降許多。 本研究的後續熱處理分別為經過深冷和回火熱處理以及僅經過回火熱處理兩種。深冷處理的前置時間越久會讓殘留沃斯田鐵穩定化而不易變態為麻田散鐵，使得拉伸強度降低，放置1個月後再進行深冷和回火熱處理之強度為1960 MPa。浸在液態氮中進行深冷處理，進行時間最好為30分鐘，此時會有最高的拉伸強度。最適當的回火溫度為200℃，此時之機械性質最佳，衝擊值亦最高，回火溫度不可超過240℃，否則材料會發生回火脆性而使得材料之機械性質下降。 金屬射出成形適合製作高精密度且形狀複雜之小型零件上，配合燒結硬化型合金鋼的優點，相當適合用在3C產品零件，如筆記型電腦、手機的樞紐、轉軸等。此類零件在使用中之受力通常是以扭力為主，本研究中以自行製作之扭力測試機量測材料之扭轉強度。在未經過回火熱處理時之扭轉強度最高，可達到2043MPa，扭轉角度約196度。經過240℃回火熱處理後，扭轉角度可達580度，但扭轉強度降低至1305MPa。
並列摘要
Sinter-hardening steels that contain high hardenability elements, such as Mn, Cr, Ni, Mo and Cu, could attain good mechanical properties without quenching. In this experiment, the Ni content was adjusted in order to find the best composition. The results show that 5wt% Ni can reach a tensile strength of 2055MPa, and the elongation was 2.8%. To improve the homogenization of Ni, Fe-2Ni prealloy powder was used, but the tensile strength can only reach 1930MPa even after sintering at 1330℃. The Cr was usually added by 17-4PH stainless steel. In this study, different stainless steel powders like Nitronic60 and Nanoflex were used. The results show that the mechanical properties of using Nitronic60 are almost the same as those using 17-4PH, and the mechanical properties of using Nanoflex are worse. The cryogenic treatment can transform the retain austenite into martensite and result in higher tensile strength and hardness. The retained austenite usually become stable if the time between the end of sintering and the start of cryogenic treatment is too long. The results show that the tensile strength was 1993MPa when the waiting time was 1 hour, and it decreased slightly to 1960MPa when the waiting time was 30 days. The effect of the cryogenic treatment time is also examined, and 30 minutes is enough. The proper tempering temperature is 200℃. If the tempering temperature is higher than 240℃, temper embrittlement could happen and result in the lower elongation and impact energy. Metal injection molding process has many advantages in making small parts with complicated shapes, such as gears or ratchets, which must sustain high stresses. These parts are usually operating under large torques, so their torsional strength is another important property. However, there are few references and data available. In this study, the torsional strength was also measured by a self-designed instrument. The results show that the highest torsional strength of this alloy system is 2043MPa without tempering and the torsional angle is 196 degrees. After tempering at 240℃, the highest torsional angle can reach 580 degrees and the torsional strength is 1305MPa.