Hardfacing on high-strength steels: Properties of multiple times heated heat-affected zones

The use of high-strength steels as base materials for hardfacing is becoming increasingly important, particularly in applications subjected to frequent dynamic loads (e.g., demolition shears). The heat-affected zone (HAZ) of hardfaced components is significantly more complex than that in conventional welded joints. Adjacent hardfacing layers lead to the formation of HAZ subzones that undergo multiple thermal cycles, and these zones have not been thoroughly investigated before. High-strength steels are more sensitive to thermal cycles, and the properties of the HAZ subzones fundamentally determine the load-bearing capacity of hardfaced parts. In this study, S690QL, S960QL, and S1100QL base materials were used. Hardness testing identified the subzones subjected to three thermal cycles as the most critical. These specific subzones were reproduced using a Gleeble physical simulator by applying three successive thermal cycles. Instrumented impact tests were performed on the simulated specimens, and the results were analyzed statistically. Fractographic analysis was also conducted, revealing clear differences between fractured specimens through quantitative evaluation. For S690QL, the impact properties of the critical subzones did not show significant changes. In contrast, for S960QL, the subzones exposed to three thermal cycles demonstrated improved impact energy with reduced impact force. Surprisingly, the HAZ subzones of S1100QL exhibited impact energies more than three times higher than those of the base material. These results clearly indicate that the subzones subjected to three thermal cycles are softer, yet their impact properties are equal to or better than those of the base material.