Experimental investigation of creep crack growth behavior in the heat affected zone of boron added modified 9Cr?1Mo steel weld

This study aims to quantify the improvement in the creep crack growth (CCG) resistance in the heat-affected zone (HAZ) of boron added modified 9Cr?1Mo (P91B) steel weld at 898 K. The crack growth rates in the HAZ of P91B weld have been compared with the crack growth rates in HAZ of without boron P91 steel weld. The creep crack growth rates are estimated as per ASTM E1457 using 7 mm thick compact tension specimens with a notch in the HAZ and test duration 248h-11,000 h. The CCG rate (a?) vs. C* correlation, commonly expressed as a? = D(C*)?, has been established. In comparison, the crack growth rate in the HAZ of P91 weld is found to be threefold as compared to HAZ of P91B weld; with the difference in CCG rate increasing towards a higher C* range. Creep damage assessment study has been done in the vicinity of creep crack in HAZ of a P91B weld specimen tested for 11,000 h. The extent of cavitation, cavities link-up, and micro-crack formation in HAZ of P91B weld is found to be relatively lower than HAZ of P91 weld. Most of the cavities appear to be discrete in nature. This testifies improvement in the creep crack growth resistance in the HAZ of P91B weld due to controlled boron addition of about 100 ppm to modified 9Cr?1Mo steel.

Automated summary

This study quantifies the improvement in creep crack growth resistance in the heat-affected zone of boron-added modified 9Cr-1Mo steel welds at high temperatures. It demonstrates that the addition of boron can significantly reduce crack growth rates, decrease creep damage, and enhance resistance to creep crack growth.