Research on Cold Crack Sensitivity of High- Strength Wear-resistant Steel Nm360 after Welding

Article history: Received: 21.04.2014. Received in revised form: 02.07.2014. Accepted: 14.07.2014. Due to the high amount of carbon and diffusible hydrogen, high-strength wear-resistant steel NM360, which is widely used on excavating machinery, always tends to develop cold crack after welding. Heat affected zone (HAZ) is the weakest part in a welding joint and is the most probable location for the generation of welding cold crack. In this paper, the effects of preheating temperature and heat input on welding cold crack sensitivity of NM360 steel have been studied by using implant tests. It is found that the preheating temperature and interlayer temperature during CO2 arc welding of NM360 steel should be 100 °C or 125 °C to prevent the occurrence of welding cold crack. The critical rupture stress and rupture time under high stress can be improved significantly with a high enough preheating temperature. However, heat input increase has little effect on critical rupture stress. Fracture analysis after performing implant test s indicates that the fracture in HAZ is typical hydrogeninduced cracking under high stress (≥ σcr). In addition, NM360 steel in HAZ has an intercrystalline quasi-cleavage fracture mode. The area ratio of brittle fracture is increased by increasing test stress.