Effect of Boron on the Resistance to Secondary Working Embrittlement in Extra-low-C Cold-rolled Steel Sheet.

Abstract

The mechanism for improving the resistance to the secondary working embrittlement by adding B to extra-]ow-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 11 23 K, the transition temperature was significantly raised irrespective of the B content. It was proved by Auger electron spectroscopy that Patomssegregate to the grain boundary with or without B addition. The results obtained in this study support the mechanismthat grain boundary strengthening by segregated B itse]f 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 improvementby B addition to the secondary working embrittlement was predominantly dueto grain boundarystrengthening by segregated B itseif, and additionally by the site competition between B and P at the grain boundary.