New Process Speeds upHot Isostatic Pressing
Conventional hot isostatic pressing(HIP) using argon or nitrogen as thepressurizingmedium for the consolidation of metal powders tends to runto long cycle times, typically of theorderof3 to 7 hours, which can makethe HIP route uneconomic for manyapplications. There are, therefore,intensive effortsunderway to reducethe total HIP cycle time, andresearchersat KobeSteel Ltd's Isostatic Pressing Center in Kobe, Japan,report that they have succeeded indeveloping a new pseudo-HIP process,which has reduced the holdingtime needed to consolidate tool steel
powders from 60 minutes at pressureand temperature to only 1 minute.The process - designated 'Q-HIP'(Quick-HIP) - was described by H.Yutakaand his colleagues in a paperpresented at the 1st Japan International SAMPE Symposium as used consolidate to full density three gradesofgas atomized tool steel powder Adarniteused in rolls,SKDll used incold rolling dies, and KHA30 whichis a PMhigh speed steel grade. Theystated that in conventional HIPing ofsuch powders to full density temperatures of between 1050 and 1150Cand pressures of up to 1000 kg/ern?
would be required fora holding timeof 60 minutes, with total cycle timevarying from 3 to 5 hours. Using the'Q-HIP' process, the time at temperature and pressure could be reducedto only 1 minute.The 'Q-HIP'process is said to involvethe filling of gas atomized powdersintoa low-carbonsteel capsule whichis then vacuum degassedat 300-500Cand sealed by welding.The capsule isheated to the desired HIP temperature, charged into a pressure vesselfilled with a visco-plastic pressurizing medium (heat resistant grease),and compactedisostaticallybyapply-
ingpressuresof 1000to 5000kgf/cm?to the grease via a stem (Fig.l). Thepressurevessel is contained in a 400ton hydraulic press and has successfully produced fully dense compacts65 mm diameter and 100 mm inlengthin total cycle time of less than5 minutes.Isostatic pressure of 1000 kgf/cm"used in conventional HIPcycleswas,however, found insufficient to totallyeliminate porosity in the tool steelcompacts made by the 'Q-HIP' process, but pressures of 5000 kgf/cm2
did achieve full density and properties arecomparabletocompactsmadebyconventionalHIPas can beseen inTable 1. The shrinkage ratio of thecapsule in axial and radial directionswas found to be 12 and 15% respectively, which is practically the sameas in gas HIPing. There was no conspicuous difference in the microstructures of Q- HIPed specimens andthose made by conventional HIPing.
FIG. 1 The 'Q-HIP' process developed by Kobe Steel for the consolidation ofpowders in 1 minute
Conv. HIPedQ-HIPed
KHA30
SKD ,
Adami e
FIG. 2 Photomicrographs of the structure of 'Q-HIPed'conventional HIPed tool steels
Q-HIPingHeating
°GOo :.... 0o • · 0o _ 0o - 0o • 0o - 0o 0
Degassi 9
Test No Process UTS YS Elongation RA Hardness(kg/mm 2) (kg/mm2
) (%) (%) (HRC)
1 Q-HIP 114.6 68.1 5.9 6.7 36.82 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 ofHIPed adamite tool steel
,.-- - - - - --r-- - - - - -.-- - - - - -.-- - - - - - - - - - -,Li_lI_i n_g_~----f__---_+-------___l
~ etal Powder Reporl IS p::b!is,'!!nga special survey onJapanin une 1990. his special Issue will bedlstr,'buted althe P ""90ex,'!; ition onJuiy 2-6. -0 a edltoria! synopsis andache isingdetal!s, please contact; F ances Breakwell, ! MPRj et. 0743 64675 Fax. 0743 62958
I nyrIt
MPR April 1990 247
