Steels_ Metallurgy and Applications, Third Edition

Low-carbon strip steels 83

7

A

E

~6

._==

~= 4

.O

9 ~ =i 3

1000

9 - ...... , ; -. ' ,~ ....... 9 ...... ,. , ,,

300 ~ Tempedng

300 ~ Temp.: ~

4oo ~~176 X

X

["O"O '15 (3 0,4 S~1 5 Mn! ""~-- ' "" ""

IO o 15 o--o 4 si-d Mn-O.oi5 Nbl

]A 0.18 C-0.47 SI-2 Mn-O.03Nb ]

112 0.2 C.0.25 S,.~2.4Mn--O.O3Nbl ' , , , ,

1100 1200 1300 1400 1500 1600 1700

Tensile strength (MPa)

Figure 1.94 Effect of tempering temperature on the balance of bendability and tensile
strength of various steels (After Hosoya et al. l~)

104

10 3

o

I ' ' Temp=edngtemperature ' '"1 .....

"~ 100~ ~o

1348 MPa -',,,,,,~o C

D

136~MPa ~

• oooc
  Tensile strength 1346 M~

(^102) 0.35 0.40 ' " O. (^45) 0.50 ' " 0.55 ' 0.60 ' ' 0.65 ' 0.70
Ceq (%)
Ceq = C +Si/24 + Mn/6
Figure 1.95 Effects of carbon equivalent and tempering temperature on time to fracture
of 4-point bent samples (After Hosoya et al. l~)
minimum in bendability (maximum in minimum bend radius) for tempering
temperatures close to 300~ Figure 1.94 shows that for the highest carbon
equivalent studied, values of tensile strength up to above 1600 N/ram 2 could
be obtained, but that for each chemistry, the minimum bendability occurred at
the intermediate values of tensile strength. For a given tensile strength close to
1350 N/mm 2, it was also found (Figure 1.95) that the time for delayed fracture
decreased with increasing carbon equivalent and increasing temperature used. It
was considered that controlling the carbide distribution within the grains was