PM steels with improved properties

PM steels with improved properties

Problems of dimensional control during sintering were discussed. Solutions to the problems, including powder selection, a t m o s p h e r e control an...

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Problems of dimensional control during sintering were discussed. Solutions to the problems, including powder selection, a t m o s p h e r e control and heating cycle were o u t l i n e d with r e s p e c t to chemical and physical factors. E x a m p l e s were given. Q U A N T I T A T I V E P R E D I C T I O N OF D I M E N S I O N A L C H A N G E IN IRONC O P P E R - C A R B O N ALLOYS

R M. German et al. (Pennsylvania State niversity, Pennsylvania, USA). Fe Cu-C a l l o y s , u s e d f o r a g o o d c¢~mbination of e a s y p r o d u c t i o n a n d p~'ope~%ies, was discussed with regard to dimensional tolerances. Work to establish a r e L L t i o n s h i p b e t w e e n Fe p o w d e r s,~rfa,e area a n d green d e n s i t y was described. A control parameter, pore s lrfaco area in the green body, related to green density, was developed. It is shown t!cat il is possible to predict dimensional (hang~,s from powder characteristics a n d (:)mpaction conditions.

Metal injection moulding F A T I G U E S T R E N G T H OF CASE HARDENED INJECTION MOULDED I RON-NICKEL ALLOY

M.K. Bulger, A.R. Erickson (Flomet Inc, 1SA) It was r e p o r t e d in earlier work the l:ttiguo strength of Fe-7%Ni was the same ~ i t h or w i t h o u t 0.5%C. Case h a r d e n e d specimens were r e p o r t e d to have fatigue s*rength e n h a n c e d by a factor of 3. MICROSTRUCTURE AND MECHANICAL P R O P E R T I E S OF I N J E C T I O N MOULDED STAINLESS STEEL

TJ. M:'Cabe et al. (Concurrent Technologies ('orp, USA). Use of MIM for the m a n u f a c t u r e of precipitation h a r d e n i n g 17-4PH stainless steel was d i s c u s s e d with r e s p e c t to properties. Effects of sintering environments at a range of t e m p e r a t u r e a n d effects of d e n s i t y on m e c h a n i c a l properties and microstructure after H1P and heat t r e a t m e n t were described. CARBON C O N T R O L IN I N J E C T I O N M O U L D E D TOOL S T E E L S J Oakes et al. (Teledyne Advanced Materi-

als, USA). The applications of MIM to tool steel was discussed with regard to t h e i m p o r t a n c e of control of C content. To attain this oxides (,n particle surfaces m u s t be reduced before p o r e closure begins. D e n s i f i c a t i o n was shown to d e p e n d on the presence of a C rich liquid p h a s e and without a d e q u a t e C c o n t e n t control densiflcation may be poor.

P r e s i n t e r i n g in H after d e b i n d i n g was r e c o m m e n d e d but in such a way as to e n s u r e t h a t only r e s i d u a l C from t h e b i n d e r is a f f e c t e d leaving t h e p o w d e r %C u n c h a n g e d , w i t h v a c u u m s i n t e r i n g to follow. A S P E C T S OF P R O D U C T I O N OF 4 3 4 0 S T E E L BY I N J E C T I O N M O U L D I N G

G. Fridman, T. Zimring (Metalor 2000, Israel). Attention was drawn to the loss of C during debinding of steel and m e t h o d s of limiting this, use of a debinding a t m o s p h e r e with controlled C c o n t e n t or one which limits decarburization. Influence of powder type and process conditions on %C and p a r t properties were investigated and discussed. M E T A L I N J E C T I O N M O U L D I N G OF POWDER M I X T U R E S E Q U I V A L E N T TO M2 H I G H S P E E D S T E E L

I.H. Moon et ah ( H a n y a n g University, Korea). An e x p e r i m e n t a l comparison M2 high speed steel, made from mixed elemental p o w d e r s or mechanically alloyed m i x e d powders was described. The MA powders were r e p o r t e d to be inferior in respect of mouldability and sintering to full density. T h e MA p o w d e r s s h o w e d i m p r o v e d sintering by repressing after debinding. The e x p e r i m e n t a l results were discussed. ADVANCES IN STAINLESS STEEL P O W D E R S L E A D I N G TO IMPROVED YIELD OF P A R T S

C.P. A s h d o w n et al. (Ultraflne Powder Technologies, Ayre, Maryland, USA). Process i m p r o v e m e n t s , l e a d i n g to i m p r o v e d yield of MIM s t a i n l e s s steel p a r t s were reported. These were outlined as changes in p a r t shape, use of sintering enhancers and use of changes in O content to control %C a n d were s u p p o r t e d by production experiences.

Advanced mechanical properties A D V A N C E D P R O P E R T I E S OF H I G H D E N S I T Y F E R R O U S PM M A T E R I A L S

AJ. Rawlings et al. (Hoeganaes Corporation, Riverton, New Jersey, USA). It was r e p o r t e d t h a t the introduction of a new process h a d enabled higher densities to be a t t a i n e d from a single press/single sinter process route. Effects on properties were described. Other process such as high t e m p e r a t u r e sintering were also considered. P R O P E R T I E S OF D I F F U S I O N B O N D E D ALLOYS P R O C E S S E D TO H I G H DENSITIES

U. E n g s t r o m et al. (H5gan/is AB, HSgan~s, Sweden).

It was shown t h a t diffusion b o n d e d alloys exhibit good properties. Advances in single compaction technology were shown to yield d e n s i t i e s above 7.3 gm.cm 3. The c a p a b i l i t i e s of t h e t e c h n i q u e were d e m o n s t r a t e d for a range of diffusion bonded alloys in high t e m p e r a t u r e sintered and heat treated conditions to illustrate the process flexibility. PM S T E E L S WITH IMPROVED PROPERTIES

T. Hillskog et al. (Uddeholm Corp, Hagfors, Sweden). It was r e p o r t e d t h a t a new process had given cleaner high speed and o t h e r tool steels with resultant improved properties. Comparison was made with other commercial s t e e l s m a d e by o l d e r t e c h n o l o g y . E x a m p l e s of a p p l i c a t i o n s were given.

Hot isostatic processing and density E X P E R I M E N T A L CALIBRATION OF A M O D E L FOR HOT I S O S T A T I C P R E S S I N G OF METAL P O W D E R S

J.J. Conway et al. (Crucible Compaction Metals, Oakdale, Pennsylvania, USA). C o m p u t e r modelling of HIP processing was d i s c u s s e d a n d t h e i m p o r t a n c e of e x p e r i m e n t a l calibration of constitutive c o m p a c t i o n models was e m p h a s i z e d . E x p e r i m e n t a l studies of Ti powder at 250950°C and strain rates of 10 5 to 10 -2 sec z were described. Factors considered were s p e c i m e n d e s i g n , HIP c o n d i t i o n s for i n t e r r u p t e d tests, analysis and effects of t e m p e r a t u r e gradients, shielding effects, m e a s u r e m e n t of thermal properties and d e t e r m i n a t i o n of c o n s t i t u t i v e f u n c t i o n s and parameters. O B S E R V A T I O N OF EARLY S T A G E S OF D E N S I F I C A T I O N IN TITANIUMALUMINIUM-VANADIUM ALLOYS

D.P. de Lo, G.R. Piehler (Carnegie-Mellon University, Pittsburg, Pennsylvania, USA). A s t u d y , in w h i c h Ti-6%A1-4%V powders were HIPed, with interruptions, in t h i n wall c o n t a i n e r s to d e t e r m i n e changes in density, porosity and particle packing, was described. Most of the densification occurred early in t h e HIP cycle before a t t a i n m e n t of m a x i m u m t e m p e r a t u r e a n d p r e s s u r e . Microscopy revealed systematic variations in density related to container geometry and p r o c e s s d y n a m i c s . It w a s s u g g e s t e d t h a t m o d e l s , b a s e d on s t e a d y s t a t e conditions require modification to allow for t r a n s i e n t effects.

MPR December 1995 55