Physical Simulation of Weldability of Weldox 1300 Steel

In the present study, the investigation of weldability of new ultra-high strength - Weldox 1300 steel has been presented. The thermal simulated samples were used to investigate the effect of welding cooling time t(8/5) on the microstructure and mechanical properties of the heat affected zone (HAZ). In the frame of these investigation the microstructure was studied by the light (LM) and transmission electron microscopies (TEM). It has been shown that the microstructure of the Weldox 1300 steel is composed of tempered martensite, and inside the laths the minor precipitations mainly V(CN) and molybdenum carbide Mo2C were observed. Mechanical properties of parent material were analysed by the tensile, impact and hardness tests. In details the influence of cooling time in the range of 2.5 - 300 s on hardness, impact toughness and microstructure of simulated HAZ was studied by using welding thermal simulation test. The results show that the impact toughness and hardness decrease with the increase of t8/5 under the condition of a single thermal cycle in simulated HAZ. The continuous cooling transformation diagrams (CCT-W for welding conditions) of Weldox 1300 steel for welding purposes was also elaborated. The steel Weldox 1300 for cooling time in the range of 2.5 - 4 s showed martensite microstructure, for time from 4 s to 60 s - mixture of martensite and bainite, and for longer cooling time mixture of ferrite, bainite and martensite. The results indicated that the weldability of Weldox 1300 steel is limited and to avoid the cold cracking the preheating procedure or medium net linear heat input should be used.