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New Process Speeds up Hot Isostatic Pressing Conventional hot isostatic pressing (HIP) using argon or nitrogen as the pressurizingmedium for the consoli- dation of metal powders tends to run to long cycle times, typically of the order of 3 to 7 hours, which can make the HIP route uneconomic for many applications. There are, therefore, intensive efforts underway to reduce the total HIP cycle time, and researchersat Kobe Steel Ltd's Isost- atic Pressing Center in Kobe, Japan, report that they have succeeded in developing a new pseudo-HIP pro- cess, which has reduced the holding time needed to consolidate tool steel powders from 60 minutes at pressure and temperature to only 1 minute. The process - designated 'Q-HIP' (Quick-HIP) - was described by H. Yutaka and his colleagues in a paper presented at the 1st Japan Internatio- nal SAMPE Symposium as used con- solidate to full density three gradesof gas atomized tool steel powder - Adarniteused in rolls, SKDll used in cold rolling dies, and KHA30 which is a PM high speed steel grade. They stated that in conventional HIPing of such powders to full density tempe- ratures of between 1050 and 1150C and pressures of up to 1000 kg/ern? would be required for a holding time of 60 minutes, with total cycle time varying from 3 to 5 hours. Using the 'Q-HIP' process, the time at tempe- rature and pressure could be reduced to only 1 minute. The 'Q-HIP'process is said to involve the filling of gas atomized powders into a low-carbonsteel capsule which is then vacuum degassedat 300-500C and sealed by welding.The capsule is heated to the desired HIP tempera- ture, charged into a pressure vessel filled with a visco-plastic pressuriz- ing medium (heat resistant grease), and compactedisostaticallybyapply- ing pressuresof 1000to 5000 kgf/cm? to the grease via a stem (Fig.l). The pressure vessel is contained in a 400 ton hydraulic press and has success- fully produced fully dense compacts 65 mm diameter and 100 mm in length in total cycle time of less than 5 minutes. Isostatic pressure of 1000 kgf/cm" used in conventional HIPcycleswas, however, found insufficienttototally eliminate porosity in the tool steel compacts made by the 'Q-HIP' pro- cess, but pressures of 5000 kgf/cm 2 did achieve full density and proper- ties arecomparabletocompactsmade by conventionalHIPas can be seen in Table 1. The shrinkage ratio of the capsule in axial and radial directions was found to be 12 and 15% respec- tively, which is practically the same as in gas HIPing. There was no con- spicuous difference in the microst- ructures of Q- HIPed specimens and those made by conventional HIPing. FIG. 1 The 'Q-HIP' process developed by Kobe Steel for the consolidation of powders in 1 minute Conv. HIPed Q-HIPed KHA30 SKD , Adam i e FIG. 2 Photomicrographs of the structure of 'Q-HIPed' conventional HIPed tool steels Q-HIPing Heating ° GO o :. ... 0 o • · 0 o _ 0 o - 0 o • 0 o - 0 o 0 Degassi 9 Test No Process UTS YS Elongation RA Hardness (kg/mm 2 ) (kg/mm 2 ) (%) (%) (HRC) 1 Q-HIP 114.6 68.1 5.9 6.7 36.8 2 Q-HIP 115.6 71.4 4.3 6.7 37.4 10 Cony. HIP 101.9 68.4 5.9 5.5 33.2 TABLE Tensile strength properties of HIPed adamite tool steel ,.------ --r------ -.------ -.-- - - - - - - - - - -, etal Powder Reporl IS p::b!is,'! !nga special survey onJapan in une 1990. his special Issue will be dlstr ,'buted althe P ""90 ex, '!; ition onJuiy 2-6. -0 a edltoria! synopsis and ache ising detal!s, please contact; F ances B reakwell, ! MPR je t. 0743 64675 Fax. 0743 6 2958 I n y r I t MPR April 1990 247
