Fracture and fatigue in M-50 and 18-4-1 high speed steels
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The l i t e r a t u r e on the f r a c t u r e t o u g h n e s s of high speed s t e e l s is not e x t e n s i v e . E r i c k s o n 4 has m e a s u r e d Kic for M-2 (at 66 Rc) , M-7 (at 68.5, 64, 58.5, and 51.5 Rc), M-42 (68.5 Rc) , STORA-30 (at 68.5 R c) and A S P - 3 0 (at 69 R c ) . J o h n s o n 5 has m e a s u r e d Kic v a l u e s of M - 2 and M - 7 for v a r i o u s heat t r e a t m e n t s . We have i n v e s t i g a t e d the f r a c t u r e t o u g h n e s s and fatigue c r a c k propagation r a t e s of 52100 b e a r i n g s t e e l (1.0 C, 1.5 Cr) which is a l s o used in m a i n s h a f t gas t u r b i n e b e a r i n g s and in other high p e r f o r m a n c e a p p l i cations .8 In this study we have o b s e r v e d the effects of heat t r e a t i n g v a r i a b l e s on the c r i t i c a l s t r e s s i n t e n s i t y f a c t o r s , on the fatigue c r a c k p r o p a g a t i o n r a t e s and on the t e n s i l e p r o p e r t i e s of M-50 and 1 8 - 4 - 1 . The M-50 was a t y p i c a l heat of VIM-VAR s t e e l f r o m an A m e r i c a n m i l l and we followed the u s u a l heat t r e a t i n g p r o c e d u r e s used h e r e . The 18-4-1 was an ESR heat f r o m an E n g lish m i l l and we followed the heat t r e a t i n g p r o c e d u r e s used in the production of E n g l i s h b e a r i n g s . We thus have a c o m p a r i s o n of the two m a t e r i a l s p r o c e s s e d in a c c o r d a n c e with the e s t a b l i s h e d p r a c t i c e s .
E X P E R I M E N T A L PROCEDURE M a t e r i a l s and Heat T r e a t m e n t s The M-50 s t e e l (0.80 C, 4.26 Mo, 4.14 Cr, 0.99 V, 0.27 Mn, 0.19 Si, 0.05 Ni, 0.04 W, 0.04 Cu, 0.01 Co, 0.008 P, and 0.003 S) was supplied by A l l e g h e n y L u d l u m Steel C o r p o r a t i o n as 80 m m d i a m b a r . The s t e e l had b e e n v a c u u m induction melted and v a c u u m a r c r e melted (VIM-VAR). It was approved for use in a i r c r a f t m a i n s h a f t b e a r i n g s , and had a c l e a n l i n e s s r a t i n g shown in T a b l e I. A f t e r rough m a c h i n i n g , the s p e c i m e n s were a u s t e n i t i z e d at 1095~ (2000~ in an e n d o t h e r m i c a t m o s p h e r e . The t i m e at heat was e s t i m a t e d at a p p r o x i m a t e l y 30 m i n . As each load was r e m o v e d f r o m the f u r n a c e , the s p e c i m e n s were dumped and s p r e a d out on an expanded m e t a l grate, a i r cooled to r o o m t e m p e r a t u r e , and then t e m p e r e d 3 t i m e s , for 2 h at heat each t i m e , at 510~ (950~ 530~ (985~ 540~ (1000~ 550~ (1025~ and 565~ (1050~ Tem-
ISSN 0360-2133/ 79/0911-1265500.75/ 0 9 1979AMERICANSOCIETYFOR METALSAND THE METALLURGICALSOCIETYOF AIME
VOLUME10A, SEPTEMBER 1979 1265
Table I. Jernkontoret Cleanliness Ratings of M-50 Steel
Table I I. Undissolved Carbides, Vol Pct
A Sulfide
B Alumina
C Silicate
D Oxide
0.0 0.0
0.0 0.0
0.0 0.0
1.0 1.0
Thin
Heavy
M-50 18-4-1
M6C 0 14.9
MzC 1.8 0
MC 0.8 0.3
Total 2.6 15.2
Table III. Compositions of Mart
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