Hydrogen induced brittle crack growth in Cu-strengthened HSLA-100 steels

The annular brittle cracking in notched samples of an HSLA-100 steel has been studied by crack interrupts. The average crack growth rate was found to be geometry and strain rate dependent. Suitable normalisation led to a generalised expression for crack growth rates that was strain rate and geometry independent. The crack growth rates were found to be directly proportional to a ‘critical product’ namely {KIcrack-tip·CHcrack-tip}. The crack initiation threshold for notched specimens showed an inverse exponential relationship with the notch tip hydrogen concentration. The crack tip hydrogen concentration was best represented by a hydrostatic stress equilibrated concentration for shallow notched specimens. Hydrogen deficiency in deep notches necessitated the use of a ‘frozen-in’ concentration approach for determining the crack tip hydrogen.