1994 Volume 34 Issue 1 Pages 99-107
The mechanism for improving the resistance to the secondary working embrittlement by adding B to extra-low-C, Ti and Nb co-added interstitial-atom free steels with various P contents was studied by investigating the brittle-ductile transition temperature of drawn cups under various drawing ratios, and by evaluating the grain boundary segregation behavior of B and P. The transition temperature was lowered by adding B under all the conditions studied, while it was raised by employing a higher drawing ratio and with increasing P content. The effect of P content on the transition temperature was not affected by B content. By increasing the holding time at 1123 K, the transition temperature was significantly raised irrespective of the B content. It was proved by Auger electron spectroscopy that P atoms segregate to the grain boundary with or without B addition. The results obtained in this study support the mechanism that grain boundary strengthening by segregated B itself was predominant for improving the resistance to the secondary working embrittlement by B addition. However, it was also observed that P segregation was decreased with increasing the B addition. Therefore, it can be concluded that the improvement by B addition to the secondary working embrittlement was predominantly due to grain boundary strengthening by segregated B itself, and additionally by the site competition between B and P at the grain boundary.
