本研究主要是將AISI 440C高鉻不?袗?粉末添加25、33、40wt%TiC粉末,起始粉末以實驗室混合與工業造粒兩種方式製成後,在1200、1300、1400℃進行燒結,接著再分別施以熱處理(1100℃淬火,520℃回火三次及2.5h/次)、低壓與高壓之熱均壓處理(1250℃、1200bar;1250℃、1500bar)、熱均壓(1250℃、1500bar)+熱處理(200℃回火三次及3h/次)等步驟完成試片製作,最後以視孔隙率、硬度試驗、三點抗彎強度(TRS)試驗、OM與SEM之顯微組織觀察等進行分析,來探討熱均壓製程對於燒結後之胚體強化的效果。 由實驗結果顯示,在TRS方面,燒結後的TRS較高,其中以添加25wt%TiC的混合粉在1400℃燒結之TRS最高,為1502.6MPa;在硬度方面,40wt%TiC之混合粉在1400℃燒結後,經過高壓熱均壓處理(1250℃、1500bar),具有最高的硬度,硬度值為HRA 86.9(HRC 70.7);在顯微組織方面,由於燒結後經過熱均壓處理之基材會析出著細微的針狀組織,對於其硬度能有效的提升;另外,若以硬度為主要考量,添加40wt%TiC之混合粉在1400℃燒結後進行高壓熱均壓處理,由於顯微結構上有許多的針狀組織且高鉻不?袗?基材與TiC分布最均勻,因此硬度最高,硬度值為HRA 86.9(HRC 70.7),TRS為1104.93MPa(160.21×103psi),且比市面上之Ferro-Tic®(HRC 68、TRS 149×103psi )都來得高;最後,造粒粉由於在燒結後,封孔效果較差,因此在經過熱均壓處理後,其硬度與TRS皆較混合粉低。
In this study, we mixed AISI 440C high chromium stainless steel powders with different amounts (25, 33 and 40 wt.%) of TiC powder. The mixing was done by one of following methods, ball milling in laboratory and granulation. The mixed powders were sintered at 1200、1300、1400℃, followed by a series of heat treatments and HIP processes. The heat treatment included quenching at 1100℃, tempering three times at 520℃ for 2.5 hours. The HIP treatments were low and high pressures (1200 bar and 1500 bar at1250℃) with one HIP treatment (1500bar at 1250℃) followed by heat treatment (tempering three times at 200℃ for 3 hours). Various materials characterization techniques were used in order to evaluate the materials properties and microstructures, including apparent porosity, hardness test, transverse rupture strength (TRS) test, OM and SEM. The results show that a high TRS value of 1502.6MPa was obtained when the 25wt% TiC mixed powder was sintered at 1400℃. The 40wt% TiC mixed powder had the highest hardness (HRC 70.7 or HRA 86.9) after sintering at 1400℃ and HIP treatment (1500bar at 1250℃). The microstructural evaluation revealed that the matrix had small needle-like structure after HIP treatment, resulting in increased hardness. For the powder added with 40wt% TiC powder and sintered at 1400℃ followed by HIP treatment, numerous needle-like structures were seen with TiC uniformly dispersed in the high Chromium stainless steel matrix and thus the highest hardness (HRA 86.9 or HRC 70.7) and TRS 1104.93 MPa ( 160.21×103 psi) were achieved. The results were better than those reported for Ferro-Tic® ( HRC 68、TRS 149×103 psi). On the other hand, the powders prepared by the granulation method exhibited poor properties presumably because of the closed-pore effect.
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