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Properties of heat treated PM alloy steels
I M P R O V E M E N T OF S I N T E R E D T15 HIGH S P E E D S T E E L BY LASER SURFACE MELTING R. C o l a c o e t al ( I n s t i t u t o S u p e r i o r Technico). The use of laser to fuse t h e surface of sintered T15 HSS, in order to e n h a n c e p r o p e r t i e s by r e m o v a l of p o r o s i t y a n d r e f i n e m e n t of structure, was described. The s t r u c t u r e of t h e as-sintered steel was shown to consist of large carbides, bainite a n d to c o n t a i n significant porosity. The laser m e l t e d alloy h a d reduced porosity a n d h a d a dendritic structure, w i t h martensite, r e t a i n e d a u s t e n i t e a n d carbides. It was r e p o r t e d t h a t Vicker's h a r d n e s s e s u p to 1100 a f t e r l a s e r t r e a t m e n t a n d h e a t t r e a t m e n t a t 525-550°C were a t t a i n e d w h i c h r e s u l t e d in i m p r o v e d c u t t i n g performance. STUDY O F ELECTRIC D I S C H A R G E MACHINING OF METAL MATRIX COMPOSITES P.K. M a d a n et al ( I n d i a n Inst of Technology, Kanpur, India). It was shown t h a t ~he m a c h i n i n g of MMC, c o n t a i n i n g abrasive particle reinforcements, by conventional methods, was difficult. E x p e r i m e n t s using electric d i s c h a r g e t o c u t A1-A1208 w i t h Cu e l e c t r o d e s , w e r e d e s c r i b e d . Effects of p r o c e s s v a r i a b l e s on m a t e r i a l removal, wear a n d m i c r o s t r u c t u r e were reported. It was s h o w n t h a t m a t e r i a l r e m o v a l was increased by increase in discharge c u r r e n t a n d reduced by increase in discharge time. Surface r o u g h n e s s increased with increase in c u r r e n t density. The m a c h i n e d surfaces were characterized by electron microscopy a n d energy dispersive X-ray analysis.
Innovations in forming technology D E N S I F I C A T I O N BEHAVIOUR D U R I N G ROTARY FORMING OF PM MATERIALS G. Pregowski (Rotopress I n t e r n a t i o n a l Inc, USA). Some aspects of cold rotary repressing of s i n t e r e d p r e f o r m s were d i s c u s s e d w i t h respect to densification, d i s t r i b u t i o n of porosity a n d final properties. Results for a range of materials were presented, including iron, stainless steel a n d bronze, to s h o w t h e i m p o r t a n c e of n o n - a x i a l d i s t r i b u t e d loads c o n c e n t r a t e d on small areas. Some applications were outlined. MULTI-LAYERED PM MATERIALS MADE BY REPETITIVE COMPACTION ON CNC COMPACTING P R E S S H. Tsuru a n d T. Nakagawa (University of Tokyo, Tokyo, J a p a n ) . A new compacting press, a c t u a t e d by AC servo m o t o r s u n d e r full c o m p u t e r control a n d with six axes was described. Use of t h e p r e s s for r e p e t i t i v e c o m p a c t i o n , w i t h
42 MPR November 1993
powder additions made for each r e p e t i t i o n , was outlined. P r o d u c t i o n of layered p a r t s was shown to be possible. The t e c h n i q u e w a s r e p o r t e d t o a l l o w a t t a i n m e n t of u n i f o r m density in p a r t s with a high aspect ratio a n d to allow composition variations t h r o u g h t h e part. I n v e s t i g a t i o n of d e n s i t y v a r i a t i o n s a n d interlayer bond strength allowed optimization of process sequences. HOT E X T R U S I O N OF E N C A P S U I ~ T E D POWDERS A T LOW E X T R U S I O N RATIOS N. Rahimi et al (Royal Inst of Technology, Stockholm, Sweden). The use of extrusion for the c o n s o l i d a t i o n of e n c a p s u l a t e d p o w d e r s was discussed a n d was s h o w n to be a viable process for p r o d u c t i o n of bar, tube or wire. A model for compaction was described. Effects of e x t r u s i o n p a r a m e t e r s were considered.
Structure/property relationships in sintered steels P R O P E R T I E S OF HEAT T R E A T E D PM ALLOY S T E E L S R.J. C a u s t o n e t al ( H S e g a n ~ e s Corp, Riverton, New Jersey, USA). The f u t u r e d e v e l o p m e n t of PM steel technology was discussed w i t h regard to the need for mechanical properties approaching those of cast/wrought materials. The p a p e r p r e s e n t e d t h e results of a study of t h e effects of density a n d sintering t e m p e r a t u r e on t h e m e c h a n i c a l p r o p e r t i e s a n d s t r u c t u r e s of q u e n c h e d a n d t e m p e r e d PM alloy steels. EFFECTS OF MANGANESE SULPHIDE ON T H E MECHANICAL P R O P E R T I E S O F PM S T E E L S H.I. Sanderow a n d T. P r u c h e r ( C o n c u r r e n t Technologies Corp, Inc, USA). I n v e s t i g a t i o n s of t h e effects of MnS a d d i t i o n s on t h e m e c h a n i c a l properties of s i n t e r e d steels were described. The a m o u n t of MnS, 0.3, 0.5 or 0.8 wt%, t h e m e t h o d of m a k i n g additions, prealloyed or mixed, density a n d alloy composition were a m o n g t h e p a r a m e t e r s studied. It was r e p o r t e d t h a t MnS d i d n o t r e d u c e t h e i m p a c t s t r e n g t h at low d e n s i t i e s w i t h a small reduction at h i g h e r densities. Some alloys e x h i b i t e d a r e d u c t i o n in i m p a c t with a small reduction at h i g h e r densities. Some alloys e x h i b i t e d a r e d u c t i o n in i m p a c t s t r e n g t h for 0.5% MnS c o m p a r e d with MnS free alloys with no f u r t h e r reduction for 0.8% MnS. E F F E C T S OF PM P R O C E S S I N G A N D H E A T T R E A T M E N T ON FATIGUE BEHAVIOUR OF HIGH DENSITY POWDER F O R G E D ALLOY S T E E L D.W. Smith et al (Michigan Technological University, USA).
An evaluation of cyclic s t r e s s / s t r a i n a n d fatigue crack p r o p a g a t i o n in high s t r e n g t h p o w d e r forged 46XX alloy steels, at various levels of density, sintering t e m p e r a t u r e a n d m i c r o s t r u c t u r e was presented. Low cycle fatigue a n d c o m p a c t t e n s i o n s p e c i m e n s were used to d e t e r m i n e sensitivity of crack initiation a n d growth to these p a r a m e t e r s , i m p u r i t i e s a n d p r o c e s s conditions. The experimental data was compared with t h a t for c a s t / w r o u g h t steels of s i m i l a r compositions.
Heat treatment processes ADVANCES IN ON-SITE N I T R O G E N SUPPLY SYSTEMS FOR T H E PM INDUSTRY D,I. Bowe et al (Air P r o d u c t s a n d Chemicals Inc, Allentown Pennsylvania, USA). Methods for t h e p r o d u c t i o n of N-based a t m o s p h e r e s for use in s i n t e r i n g were reviewed. Cryogenic a n d non-cryogenic N was considered t o g e t h e r with m i x t u r e s of N w i t h H a n d / o r h y d r o c a r b o n s . It w a s r e p o r t e d t h a t on-site p r o d u c t i o n of nonc r y o g e n i c N a n d i t s p u r i f i c a t i o n by a d v a n c e d m e t h o d s yielded a gas suitable for sintering at a cost c o m p a r a b l e with g e n e r a t e d gas. MECHANICAL BEHAVIOUR OF S I N T E R E D A N D A U S F O R M E D 440C STAINLESS STEEL R.A. Queeney a n d C.A. Klinger (Pennsylvania State University, Pennsylvania, USA). It was r e p o r t e d t h a t a s i n t e r e d stainless steel h a d been ausformed by h e a t i n g to 1050°C, q u e n c h i n g t o 2 3 0 ° C i n t h e m e t a s t a b l e austenitic state, deformed at 2 3 0 ° C a n d q u e n c h e d t o 20 °C. T h e p r o p e r t i e s a n d s t r u c t u r e were described and shown to be comparable with marquenched and tempered materials. Applications for t h e alloys were discussed. DIFFUSION THERMOCHROMIZING OF SOME S I N T E R E D S T E E L S G.M.A. Said et al (A1-Azhar University, Cairo, Egypt). T h e r m o c h r o i m i z i n g of s i n t e r e d steels, Fe, Fe-2% Ni a n d Fe-4% Ni a t different porosities was described. C o m p a c t s were H sintered and pack-thermochromized and the depth of the chromized layer d e t e r m i n e d as f u n c t i o n s of t i m e a n d t e m p e r a t u r e . Use was m a d e of statistical techniques. M a t h e m a t i c a l models was used to predict layer thickness. Microstructures a n d h a r d n e s s e s were d e t e r m i n e d a n d t h e results used to optimize t h e process to o b t a i n a specified d e p t h of chromized layer.
IntermetalUc materials COMPACTIBLE G R A D E S OF NICKEL A L U M I N I D E POWDERS R.M. C o o p e r et al
(Pennsylvania State
Innovations in forming technology D E N S I F I C A T I O N BEHAVIOUR D U R I N G ROTARY FORMING OF PM MATERIALS G. Pregowski (Rotopress I n t e r n a t i o n a l Inc, USA). Some aspects of cold rotary repressing of s i n t e r e d p r e f o r m s were d i s c u s s e d w i t h respect to densification, d i s t r i b u t i o n of porosity a n d final properties. Results for a range of materials were presented, including iron, stainless steel a n d bronze, to s h o w t h e i m p o r t a n c e of n o n - a x i a l d i s t r i b u t e d loads c o n c e n t r a t e d on small areas. Some applications were outlined. MULTI-LAYERED PM MATERIALS MADE BY REPETITIVE COMPACTION ON CNC COMPACTING P R E S S H. Tsuru a n d T. Nakagawa (University of Tokyo, Tokyo, J a p a n ) . A new compacting press, a c t u a t e d by AC servo m o t o r s u n d e r full c o m p u t e r control a n d with six axes was described. Use of t h e p r e s s for r e p e t i t i v e c o m p a c t i o n , w i t h
42 MPR November 1993
powder additions made for each r e p e t i t i o n , was outlined. P r o d u c t i o n of layered p a r t s was shown to be possible. The t e c h n i q u e w a s r e p o r t e d t o a l l o w a t t a i n m e n t of u n i f o r m density in p a r t s with a high aspect ratio a n d to allow composition variations t h r o u g h t h e part. I n v e s t i g a t i o n of d e n s i t y v a r i a t i o n s a n d interlayer bond strength allowed optimization of process sequences. HOT E X T R U S I O N OF E N C A P S U I ~ T E D POWDERS A T LOW E X T R U S I O N RATIOS N. Rahimi et al (Royal Inst of Technology, Stockholm, Sweden). The use of extrusion for the c o n s o l i d a t i o n of e n c a p s u l a t e d p o w d e r s was discussed a n d was s h o w n to be a viable process for p r o d u c t i o n of bar, tube or wire. A model for compaction was described. Effects of e x t r u s i o n p a r a m e t e r s were considered.
Structure/property relationships in sintered steels P R O P E R T I E S OF HEAT T R E A T E D PM ALLOY S T E E L S R.J. C a u s t o n e t al ( H S e g a n ~ e s Corp, Riverton, New Jersey, USA). The f u t u r e d e v e l o p m e n t of PM steel technology was discussed w i t h regard to the need for mechanical properties approaching those of cast/wrought materials. The p a p e r p r e s e n t e d t h e results of a study of t h e effects of density a n d sintering t e m p e r a t u r e on t h e m e c h a n i c a l p r o p e r t i e s a n d s t r u c t u r e s of q u e n c h e d a n d t e m p e r e d PM alloy steels. EFFECTS OF MANGANESE SULPHIDE ON T H E MECHANICAL P R O P E R T I E S O F PM S T E E L S H.I. Sanderow a n d T. P r u c h e r ( C o n c u r r e n t Technologies Corp, Inc, USA). I n v e s t i g a t i o n s of t h e effects of MnS a d d i t i o n s on t h e m e c h a n i c a l properties of s i n t e r e d steels were described. The a m o u n t of MnS, 0.3, 0.5 or 0.8 wt%, t h e m e t h o d of m a k i n g additions, prealloyed or mixed, density a n d alloy composition were a m o n g t h e p a r a m e t e r s studied. It was r e p o r t e d t h a t MnS d i d n o t r e d u c e t h e i m p a c t s t r e n g t h at low d e n s i t i e s w i t h a small reduction at h i g h e r densities. Some alloys e x h i b i t e d a r e d u c t i o n in i m p a c t with a small reduction at h i g h e r densities. Some alloys e x h i b i t e d a r e d u c t i o n in i m p a c t s t r e n g t h for 0.5% MnS c o m p a r e d with MnS free alloys with no f u r t h e r reduction for 0.8% MnS. E F F E C T S OF PM P R O C E S S I N G A N D H E A T T R E A T M E N T ON FATIGUE BEHAVIOUR OF HIGH DENSITY POWDER F O R G E D ALLOY S T E E L D.W. Smith et al (Michigan Technological University, USA).
An evaluation of cyclic s t r e s s / s t r a i n a n d fatigue crack p r o p a g a t i o n in high s t r e n g t h p o w d e r forged 46XX alloy steels, at various levels of density, sintering t e m p e r a t u r e a n d m i c r o s t r u c t u r e was presented. Low cycle fatigue a n d c o m p a c t t e n s i o n s p e c i m e n s were used to d e t e r m i n e sensitivity of crack initiation a n d growth to these p a r a m e t e r s , i m p u r i t i e s a n d p r o c e s s conditions. The experimental data was compared with t h a t for c a s t / w r o u g h t steels of s i m i l a r compositions.
Heat treatment processes ADVANCES IN ON-SITE N I T R O G E N SUPPLY SYSTEMS FOR T H E PM INDUSTRY D,I. Bowe et al (Air P r o d u c t s a n d Chemicals Inc, Allentown Pennsylvania, USA). Methods for t h e p r o d u c t i o n of N-based a t m o s p h e r e s for use in s i n t e r i n g were reviewed. Cryogenic a n d non-cryogenic N was considered t o g e t h e r with m i x t u r e s of N w i t h H a n d / o r h y d r o c a r b o n s . It w a s r e p o r t e d t h a t on-site p r o d u c t i o n of nonc r y o g e n i c N a n d i t s p u r i f i c a t i o n by a d v a n c e d m e t h o d s yielded a gas suitable for sintering at a cost c o m p a r a b l e with g e n e r a t e d gas. MECHANICAL BEHAVIOUR OF S I N T E R E D A N D A U S F O R M E D 440C STAINLESS STEEL R.A. Queeney a n d C.A. Klinger (Pennsylvania State University, Pennsylvania, USA). It was r e p o r t e d t h a t a s i n t e r e d stainless steel h a d been ausformed by h e a t i n g to 1050°C, q u e n c h i n g t o 2 3 0 ° C i n t h e m e t a s t a b l e austenitic state, deformed at 2 3 0 ° C a n d q u e n c h e d t o 20 °C. T h e p r o p e r t i e s a n d s t r u c t u r e were described and shown to be comparable with marquenched and tempered materials. Applications for t h e alloys were discussed. DIFFUSION THERMOCHROMIZING OF SOME S I N T E R E D S T E E L S G.M.A. Said et al (A1-Azhar University, Cairo, Egypt). T h e r m o c h r o i m i z i n g of s i n t e r e d steels, Fe, Fe-2% Ni a n d Fe-4% Ni a t different porosities was described. C o m p a c t s were H sintered and pack-thermochromized and the depth of the chromized layer d e t e r m i n e d as f u n c t i o n s of t i m e a n d t e m p e r a t u r e . Use was m a d e of statistical techniques. M a t h e m a t i c a l models was used to predict layer thickness. Microstructures a n d h a r d n e s s e s were d e t e r m i n e d a n d t h e results used to optimize t h e process to o b t a i n a specified d e p t h of chromized layer.
IntermetalUc materials COMPACTIBLE G R A D E S OF NICKEL A L U M I N I D E POWDERS R.M. C o o p e r et al
(Pennsylvania State