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ODS superalloys improve steel making
ODS superalloys improve steel making O
ne of the m a n y developm e n t p r o g r a m m e s to improve t h e economics of steel making currently u n d e r way in J a p a n is t h e evaluation of new materials for skid rails for the walking b e a m type furnaces used to r e h e a t steel slab or billet. Operating t e m p e r a t u r e s are rising as high as 1350°C in p u r s u i t of energy efficiency a n d higher output. There is also t h e wish to e x t e n d t h e service life of furnace components, to e x t e n d times between overhaul, to reduce m a i n t e n a n c e costs, a n d increase productivity. Conventional skid rails, m a d e of c a s t h e a t - r e s i s t i n g
production. Daido Steel is promoting this improved t e c h n i q u e to m a j o r steel-makers a r o u n d t h e world. There are significant benefits to be o b t a i n e d from a switch from cast to mechanically alloyed skid rails. The increased s t r e n g t h p e r m i t s t h e design of t a l l e r rails, e l i m i n a t i n g cold spots from the slab/billet, t h u s improving product quality. Slab/billet chilling is reduced because t h e oxide dispersion s t r e n g t h e n e d alloy rails hold t h e work f u r t h e r away from t h e cooling water. The skid rail height was increased from 150 to 200 m m at t h e C h i t a Works of D a i d o Steel, r e s u l t i n g in a
which t h e original h i g h e r investm e n t can soon offset t h e e x t r a c o s t in t e r m s o f i n c r e a s e d efficiency, l o n g e r service life, a n d a n increased o u t p u t of a higher quality steel product. Inco invented t h e mechanical alloying powder metallurgy process, originally to produce oxide dispersion s t r e n g t h e n e d superalloys for aircraft gas turbine engine components. This skid rail application in t h e steel-making process is a classic e x a m p l e of t h e spin-off of m a t e r i a l s t e c h n o l o g y from aerospace into t h e r m a l processing. •
I o(}o
200 IOO
••INCONEL iIIoy MA 7EM
50 20 t
~
IO
INCONEL alloy MA 758
Cast I~lR-res/stlng alloy
2 I
The tips of the mechanically alloyed skid rails in this furnace heatcan be seen as the dark lines running horizontally across the picture.
05
treating steel bar 02
ol
i
I IOO
I 1200
I
1300
1400 Mechan/ca~y alloyed skid raft
Temperature, "C
0.025% per hour creep strength data for ODS superalloys and cast Cr-CoNi-Fe-W heat-resisting alloy.
alloys, have a typical life expectancy of a r o u n d six m o n t h s to two years, d e p e n d i n g on t h e o p e r a t i n g c o n d i t i o n s . In o n e d e v e l o p m e n t programme, Daido Steel of Nagoya, h a s established t h a t t h e use of t h e oxide dispersion s t r e n g t h e n e d (ODS), mechanically alloyed products, s u p p l i e d t h r o u g h Daido Inco Alloys Ltd, Tokyo a n d Osaka, h a s doubled t h a t performance, eliminating one of the a n n u a l maintenance shutdowns, and t h u s o b t a i n i n g a n e x t r a week's
d e c r e a s e of t h e t e m p e r a t u r e difference within t h e billet from 56 to 18°C. T h e r m a l efficiency is improved because the higher allowable metal temperatures p e r m i t cooling r e q u i r e m e n t s to be reduced, a n d because t h e rail assembly e x t r a c t s less h e a t from t h e system. The m e c h a n i c a l l y alloyed p r o d u c t s are intrinsically more expensive than conventional, cast heat-resisting alloys. This is, however, a case in
cue is steel)
re
pipe steel)
CooUng
wate~
This sketch shows a typical skid rail assembly. The tip of the mechanically alloyed skid rail, where it is in contract with the steel produt passing through the furnace, is 45mm (1.8in) wide, and it stands 270mm (lO.6in) clear of the center of the cooling water.
M P R April 1993 15
ne of the m a n y developm e n t p r o g r a m m e s to improve t h e economics of steel making currently u n d e r way in J a p a n is t h e evaluation of new materials for skid rails for the walking b e a m type furnaces used to r e h e a t steel slab or billet. Operating t e m p e r a t u r e s are rising as high as 1350°C in p u r s u i t of energy efficiency a n d higher output. There is also t h e wish to e x t e n d t h e service life of furnace components, to e x t e n d times between overhaul, to reduce m a i n t e n a n c e costs, a n d increase productivity. Conventional skid rails, m a d e of c a s t h e a t - r e s i s t i n g
production. Daido Steel is promoting this improved t e c h n i q u e to m a j o r steel-makers a r o u n d t h e world. There are significant benefits to be o b t a i n e d from a switch from cast to mechanically alloyed skid rails. The increased s t r e n g t h p e r m i t s t h e design of t a l l e r rails, e l i m i n a t i n g cold spots from the slab/billet, t h u s improving product quality. Slab/billet chilling is reduced because t h e oxide dispersion s t r e n g t h e n e d alloy rails hold t h e work f u r t h e r away from t h e cooling water. The skid rail height was increased from 150 to 200 m m at t h e C h i t a Works of D a i d o Steel, r e s u l t i n g in a
which t h e original h i g h e r investm e n t can soon offset t h e e x t r a c o s t in t e r m s o f i n c r e a s e d efficiency, l o n g e r service life, a n d a n increased o u t p u t of a higher quality steel product. Inco invented t h e mechanical alloying powder metallurgy process, originally to produce oxide dispersion s t r e n g t h e n e d superalloys for aircraft gas turbine engine components. This skid rail application in t h e steel-making process is a classic e x a m p l e of t h e spin-off of m a t e r i a l s t e c h n o l o g y from aerospace into t h e r m a l processing. •
I o(}o
200 IOO
••INCONEL iIIoy MA 7EM
50 20 t
~
IO
INCONEL alloy MA 758
Cast I~lR-res/stlng alloy
2 I
The tips of the mechanically alloyed skid rails in this furnace heatcan be seen as the dark lines running horizontally across the picture.
05
treating steel bar 02
ol
i
I IOO
I 1200
I
1300
1400 Mechan/ca~y alloyed skid raft
Temperature, "C
0.025% per hour creep strength data for ODS superalloys and cast Cr-CoNi-Fe-W heat-resisting alloy.
alloys, have a typical life expectancy of a r o u n d six m o n t h s to two years, d e p e n d i n g on t h e o p e r a t i n g c o n d i t i o n s . In o n e d e v e l o p m e n t programme, Daido Steel of Nagoya, h a s established t h a t t h e use of t h e oxide dispersion s t r e n g t h e n e d (ODS), mechanically alloyed products, s u p p l i e d t h r o u g h Daido Inco Alloys Ltd, Tokyo a n d Osaka, h a s doubled t h a t performance, eliminating one of the a n n u a l maintenance shutdowns, and t h u s o b t a i n i n g a n e x t r a week's
d e c r e a s e of t h e t e m p e r a t u r e difference within t h e billet from 56 to 18°C. T h e r m a l efficiency is improved because the higher allowable metal temperatures p e r m i t cooling r e q u i r e m e n t s to be reduced, a n d because t h e rail assembly e x t r a c t s less h e a t from t h e system. The m e c h a n i c a l l y alloyed p r o d u c t s are intrinsically more expensive than conventional, cast heat-resisting alloys. This is, however, a case in
cue is steel)
re
pipe steel)
CooUng
wate~
This sketch shows a typical skid rail assembly. The tip of the mechanically alloyed skid rail, where it is in contract with the steel produt passing through the furnace, is 45mm (1.8in) wide, and it stands 270mm (lO.6in) clear of the center of the cooling water.
M P R April 1993 15