Effect of enhanced cooling on mechanical properties of a multipass welded martensitic steel

Abstract The effect of forced cooling using heat sinks on the mechanical properties and interpass waiting time of two-pass welds has been studied for a martensitic steel with a yield strength of 960 MPa when the interpass temperature was 100 °C. Cross-weld tensile and − 40 °C Charpy-V impact toughness properties were examined. The use of heat sinks is shown to result in a beneficial increase of the cross-weld yield strength but at the expense of the yield-to-tensile strength ratio. Due to its particularly detrimental effect on the heat-affected zone (HAZ) toughness of multipass welds, special attention was given in the Charpy-V toughness of the intercritically reheated coarse-grained HAZ (ICCGHAZ) by also testing simulated ICCGHAZs. It is shown that forced cooling has a beneficial effect in respect of the toughness of this simulated subzone and on the Charpy-V toughness of the HAZ of the actual welds. The interpass cooling time during the two-pass welding was reduced by 37%. The results indicate that, in the case of high-strength steels, it may be possible to simultaneously improve both welding productivity and mechanical properties by using forced cooling down to 100 °C to reduce waiting time between weld passes

Effect of enhanced weld cooling on the mechanical properties of a structural steel with a yield strength of 700 MPa

Abstract In this study, we present the effect of enhanced cooling on the mechanical properties of a high-strength low-alloy steel (having a yield strength of 700 MPa) following a single-pass weld process. The properties evaluated in this study include uniform elongation, impact toughness, yield, tensile and fatigue strengths alongside the cooling time of the weld. With the steel used in this study, the enhanced cooling resulted in a weld joint characterized with excellent cross-weld uniform elongation, yield and fatigue strength. The intensified cooling reduced the time it takes for the weld to reach 100 °C by around 190 s. Not only the fusion line of the weld was less pronounced, but also the grain size of the CGHAZ was greatly refined as a result of the enhanced cooling. The results indicate that combining external cooling to the welding processes can be beneficial for the studied high-strength steel

Effect of forced cooling after welding on CGHAZ mechanical properties of a martensitic steel

Abstract The effects of forced cooling, meaning forced cooling rate and forced cooling finish temperature, on the tensile and impact toughness properties of simulated weld coarse-grained heat-affected zones have been studied for a commercial grade martensitic steel with a yield strength of 960 MPa. The simulations were done by using a Gleeble 3800 to give forced cooling finish temperatures of 500, 400, 300, 200, and 100 °C and forced cooling rates of 50 and 15 °C/s. For the steel studied, strength significantly increased with no significant negative effects on impact toughness when the steel was cooled rapidly to 200 or 100 °C at 15 °C/s. The results indicate that it may be possible to improve welding productivity and mechanical properties of the steel by using forced cooling down to 100 °C to reduce waiting time between weld passes

Effect of forced cooling on the tensile properties and impact toughness of the coarse-grained heat-affected zone of a high-strength structural steel

Abstract The effects of forced cooling, i.e., forced cooling rate and forced cooling finish temperature, on the tensile and impact toughness properties of simulated weld coarse-grained heat-affected zones has been explored in the case of a low-carbon thermomechanically processed steel with a yield strength of 700 MPa. The forced cooling finish temperatures that were studied were 400, 300, 200, and 100 °C and the forced cooling rates were 50 and 15 °C/s. Coarse-grained heat-affected zones were simulated using a Gleeble 3800 thermomechanical simulator. For the steel concerned, strength and impact toughness improved significantly when the steel was cooled rapidly to 200 or 100 °C. The results indicate that it may be possible to substantially improve welding productivity by using forced cooling to reduce interpass times

Effect of heat sinks on cooling time to weld interpass temperature

Abstract In high- and ultrahigh-strength steel welding, interpass cooling time is an important factor affecting productivity and welding costs. Usually, welding heat input is restricted to meet the relatively short recommended cooling times between 800 and 500 °C (t8/5), which are prescribed by the need to meet weld strength and toughness properties. This, in turn, leads to the need for multipass welding with the interpass waiting times needed for the weld to cool to a sufficiently low interpass temperature. Welding productivity is affected by both the number of passes and the interpass waiting time. With a view to minimizing the total number of passes needed for a given preparation, it is beneficial for the interpass temperature to be as low as possible as this permits higher heat input for a given t8/5. On the other hand, low interpass temperature requires longer interpass waiting times. Therefore, this research concerns the potential of introducing copper heat sinks adjacent to the weld to reduce the time it takes for the weld to cool down to the interpass temperature. It is demonstrated that, in the case of a butt weld in a 6 mm thick base plate MAG welded with a weld energy of 1 kJ/mm and an interpass temperature of 100 °C, copper heat sinks almoust halve the interpass waiting time. This can have a marked effect on the overall productivity when welding highand ultrahigh-strength steels and increase their attractiveness for steel construction

A coupled temperature-microstructure model for the heat-affected zone of low alloyed high strength steel during two-pass arc welding

Abstract A coupled temperature-microstructure model was developed in order to simulate the evolution of the microstructure in the heat-affected zone during two-pass gas-metal arc welding. The model is developed to serve the steel industry’s need to evaluate the weldability of new steel grades. Heat transfer and heat input models were used for modelling the arc welding and the temperature changes in the heat-affected zone. A microstructure model was fully coupled with the temperature model, including latent heat of transformation as well as the dependence of thermophysical properties on temperature and phase fractions. The microstructure model simulates phase transformations and grain growth including a simplified model for the effect of fine particles. The modeled temperature paths are in good agreement with the measured ones. The final phase fractions and grain size distribution obtained from the model correspond to the actual microstructure and the model predicts the shapes of the heat-affected zone and fusion zone with relatively good accuracy