Toughness Of Weld Heat Affected Zone Research Articles

Quantitative analysis of Nb in solid solution in low carbon steels by atom probe tomography and inductively coupled plasma mass spectroscopy

The influence of solute drag effects on austenite grain growth in microalloyed steels has been overshadowed by the well-established phenomenon of Zener pinning associated with a dispersion of fine precipitates. Enhanced toughness in the weld heat-affected zone (HAZ) of high Nb steels suggests that microalloying effects are still operative at peak temperatures even beyond known precipitate stability. As the cornerstone for unveiling the solute drag effect, the solute concentration in the matrix should be accurately measured. In this work, we compared inductively coupled plasma mass spectroscopy (ICP-MS) and atom probe tomography (APT) in determining the extent of Nb dissolution as a function of increasing temperature in two commercial American Petroleum Institute steel grades with different levels of Nb and marked variations in weld HAZ toughness. Both techniques demonstrated that the majority of Nb exists in solid solution at the peak temperatures. APT provided a more consistent determination of soluble Nb, in a better agreement with thermodynamic calculations, whilst ICP-MS underestimated the concentration of Nb in the matrix. This work provides valuable insights in determining soluble Nb concentration in steels.

Correlation between microstructure and impact toughness of weld heat-affected zone in 5 wt.% manganese steels

The microstructure in welding heat-affected zones of 5 wt.% manganese steels was studied, and its effect on impact toughness was analyzed. The simulated coarse-grained heat-affected zone (CGHAZ) had the lowest impact toughness of ~ 39 J at − 40 °C because of coarse-grained structure and least volume fraction of retained austenite (RA) of 1.2 vol.%. The impact toughness of simulated intercritical heat-affected zone (ICHAZ) and fine-grained heat-affected zone (FGHAZ) were ~ 165 and ~ 45 J, respectively, at − 40 °C. The effective grain size of simulated FGHAZ was smaller than that of the simulated ICHAZ. Furthermore, microstructural investigation revealed that the simulated FGHAZ and ICHAZ had similarity in volume fraction and stability of RA. However, tempered martensite was present in ICHAZ and absent in FGHAZ. It is proposed that the presence of tempered martensite contributed to good impact toughness in simulated ICHAZ.

Numerical Model for Predicting Charpy Impact Toughness of Weld Heat-Affected Zone of Steels

Numerical Model for Predicting Charpy Impact Toughness of Weld Heat-Affected Zone of Steels

Some Studies on Heat-Affected Zone (HAZ) Toughness Behavior of API 5L X52 Steel

Heat Affected Zone (HAZ) simulation by Gleeble is a useful method for evaluating welding process parameters to improve the toughness of weld HAZ by optimizing process parameters. The HAZ Toughness in low alloy steels is strongly influenced by the welding parameters (as HAZ microstructure is influenced by the heat input and cooling rate). In the present work different regions of weld HAZ of API 5L X52 steel have been simulated by using Gleeble @ 3800 Thermal- Mechanical Simulator. Two cooling rates (t 8/5 ) 10 s to simulate low heat input (LHI) welding conditions without preheating, (t 8/5 ) 40s to simulate high heat input (HHI) welding were used. Charpy V-notch impact tests were conducted on the simulated as well as on the base material at room temperature (25° C) and at -40° C. Results showed that HHI simulated coarse grain HAZ (CGHAZ) region attributed highest Impact energy of 300 J in comparison to 199 J of base material at 25° C. In HAZ regions, lowest room temperature toughness was observed in sub critical HAZ (SCHAZ) for both HHI and LHI conditions. Lowest impact energy at -40° C was observed in fine grained HAZ (FGHAZ) for both HHI and LHI conditions. Hardness test showed that LHI samples exhibited slightly higher hardness than HHI condition and the hardness profile for HAZ regions was similar for both HHI and LHI conditions.

Some Studies on Heat-Affected Zone (HAZ) Toughness Behavior of API 5L X52 Steel

Heat Affected Zone (HAZ) simulation by Gleeble is a useful method for evaluating welding process parameters to improve the toughness of weld HAZ by optimizing process parameters. The HAZ Toughness in low alloy steels is strongly influenced by the welding parameters (as HAZ microstructure is influenced by the heat input and cooling rate). In the present work different regions of weld HAZ of API 5L X52 steel have been simulated by using Gleeble @ 3800 Thermal- Mechanical Simulator. Two cooling rates (t 8/5 ) 10 s to simulate low heat input (LHI) welding conditions without preheating, (t 8/5 ) 40s to simulate high heat input (HHI) welding were used. Charpy V-notch impact tests were conducted on the simulated as well as on the base material at room temperature (25° C) and at -40° C. Results showed that HHI simulated coarse grain HAZ (CGHAZ) region attributed highest Impact energy of 300 J in comparison to 199 J of base material at 25° C. In HAZ regions, lowest room temperature toughness was observed in sub critical HAZ (SCHAZ) for both HHI and LHI conditions. Lowest impact energy at -40° C was observed in fine grained HAZ (FGHAZ) for both HHI and LHI conditions. Hardness test showed that LHI samples exhibited slightly higher hardness than HHI condition and the hardness profile for HAZ regions was similar for both HHI and LHI conditions.

Effects of Al Addition on the Microstructure of Fe-Mn-Si Ultra-Fine Grain Steel Welded Heat Affected Zone

In order to improve toughness of the weld heat affected zone (HAZ) of ultra-fine grained (UFG) steel, a thermal simulation procedure of Fe-Mn-Si UFG steels with different Al addition was conducted and the corresponding microstructure was characterized and investigated. The results indicate that the maximum value on driving force of nucleation is ultra-fine grain steel with wtAl=0.6%, it has been explained in Nucleation kinetics that the grains are fine in UFG2. On the other hand, the bainite ferrite growth orientation has been increased. The toughness was remarkably enhanced in the steel welded heat affected zone. The formation of strie retained austenite and grain refinement of bainite ferrite in Fe-Mn-Si UFG steels with Al additions results in the increasing toughness of weld HAZ.

The effects of PWHT on the toughness of weld HAZ in Cu-Containing HSLA-100 steel

A study was conducted to examine the effects of postweld heat treatment (PWHT) on the impact toughness and microstructures in the weld heat affected zone (HAZ) of Cu-containing HSLA-100 steel. The Gleeble, thermal/mechanical simulator, was used to simulate the weld HAZ. The details between toughness and PWHT of HAZ were studied by impact test, optical microscopy (O.M.), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The decrease of HAZ toughness in the single thermal cycle simulation relative to the base metal's toughness is ascribed to the coarsened-grain formed by heating to 1350°C. While the increase of HAZ toughness in the double thermal cycle simulation relative to that in the single thermal cycle is due to the fine ferrite (α) grain transformed from austenite (γ) by heating to α/γ two phase region. Cu precipitated during aging, which increases the strength of the base metal, is dissolved during the single thermal cycle to 1350°C and remains in the matrix during subsequent thermal cycle simulations. It precipitates by introducing PWHT suggesting that the decrease of toughness in the triple thermal cycle simulation (TP1=1350°C, TP2=800°C and TP3=500°C) does not occur from the Cu precipitation. The behaviors of Cu-precipitates in the weld HAZ are similar to those in the base metal. The PWHT at 550°C shows the highest hardness and the lowest toughness in the HAZ, whereas PWHT at 650°C shows a reasonable toughness and strength combination suggesting the possibility of improving the toughness of HAZ.

Influence of phosphorus on weld heat affected zone toughness in niobium microalloyed steels

Weld heat affected zone microstructures have been simulated in a niobium microalloyed C–Mn steel. These structures have been Charpy impact tested and examined metallographically. Troughs were observed in the plots of Charpy energy against post-weld heat treatment time at 600°C. The explanation for this behaviour is shown to be associated with non-equilibrium segregation of phosphorus to lath boundaries in the steel. Mathematical modelling of non-equilibrium segregation, together with high spatial resolution analytical electron microscopy results, support this contention. Using the predictions of the model, several suggestions are made concerning the alleviation of phosphorus segregation to boundaries and hence the reduction of cracking susceptibility during post-weld heat treatment of the steel.MST/994

Influence of phosphorus on weld heat affected zone toughness in niobium microalloyed steels

Influence of phosphorus on weld heat affected zone toughness in niobium microalloyed steels

Dynamic Fracture Toughness of Weld Heat-Affected Zone in Ductile Cast Iron

Dynamic Fracture Toughness of Weld Heat-Affected Zone in Ductile Cast Iron

Microstructure and toughness of weld heat-affected zone in 785MN m−2HSLA steel

The effect of microstructure on the toughness of the heat-affected zone (HAZ) in a 785 MN m−2 HSLA steel has been investigated with narrow-gap welds. Various microstructure regions, i.e. a coarse-grained austenite region, afine-grained region, a partially austenitized region, and a tempered region, were formed periodically adjacent to the fusion line. This structural change was caused by reheating owing to successive weld-metal deposition. Therefore, specimens produced by simulating the multipass weld thermal cycles were also examined to assess the local microstructure and toughness in the HAZ. The transformation behaviour of simulated HAZs subject to reheating thermal cycles was related to the toughness. The partially austenitized structure, within which carbon enrichment occurred during reheating, was decomposed into high-carbon martensitic islands with poor toughness during subsequent cooling. The ductile–brittle transition properties of the HAZ are controlled by the fraction of the partially transformed structure in the HAZ.