Grain Growth In Heat Affected Zone Research Articles

Monte Carlo simulation of grain growth in heat-affected zone during welding process of cast steel joint and optimization of welding process

Monte Carlo simulation of grain growth in heat-affected zone during welding process of cast steel joint and optimization of welding process

Friction stir welding of severely deformed copper sheets: microstructure and mechanical properties

Friction stir welding (FSW) was performed at different tool rotation speeds of 1250 and 1600 rev min−1 on both annealed, and severely plastic deformed copper sheets via constrained groove pressing (CGP). Also, the effects of water cooling during FSW on weld properties of CGP-treated samples were investigated. It is found that the heat-affected zone (HAZ) has a lower hardness value than the corresponding base metal due to the large grain growth. While the stir zone (SZ) shows a finer grain size with a higher hardness. Moreover, the results proved that in-process water cooling can effectively reduce grain growth in HAZ of CGPed samples and improve the weld strength by increasing the minimum hardness to about SZ hardness of the annealed sample.

Influence of the Mg content on the austenite grain growth in heat-affected zone of offshore engineering steels considering TiN particle pinning and Mo solute drag effects

The submicrometre and nanometre particle characteristics, soluble element contents, and austenite grain growth behaviors in heat-affected zone of offshore engineering steels with 0.0002 (2Mg) and 0.0042 (42Mg) wt.% Mg during the simulated welding process were studied. With increasing the Mg content in steel from 0.0002 to 0.0042 wt.%, the submicron particles are decreased in number and size with their compositions evolved from TiN to TiN + MgO capped with Mo carbides, and the number density of small-sized nanoparticles increases and large-sized nanoparticles decreases. When the temperature is below 1250 °C, the grain growth rate of two steels is not much different due to the larger Mo solute drag effect in 2Mg and larger pinning force in 42Mg. When the temperature is 1250–1300 °C, the small-sized nanoparticles in 42Mg is more than that in 2Mg, resulting in the larger pinning force and smaller grain growth rate in 42Mg. When heated to 1300–1350 °C and soaked at 1350 °C for 300 s, since large quantities of particles smaller than the critical size (dcr) are dissolved, the grain growth rate in 2Mg is smaller than that in 42Mg due to the greater amount of the effective pinning particles and larger pinning force in 2Mg.

Effect of Heat Input on Microstructure and Hardness Distribution of Laser Welded Si-Al TRIP-Type Steel

This study is concerned with issues related to laser welding of Si-Al type TRIP steels with Nb and Ti microadditions. The tests of laser welding of thermomechanically rolled sheet sections were carried out using keyhole welding and a solid-state laser. The tests carried out for various values of heat input were followed by macro- and microscopic metallographic investigations as well as by microhardness measurements of welded areas. A detailed microstructural analysis was carried out in the penetration area and in various areas of the heat affected zone (HAZ). Special attention was paid to the influence of cooling conditions on the stabilisation of retained austenite, the most characteristic structural component of TRIP steels. The tests made it possible to determine the maximum value of heat input preventing the excessive grain growth in HAZ and to identify the areas of the greatest hardness reaching 520 HV0.1.

PREDICTION OF GRAIN GROWTH IN HYBRID WELDING HAZ OF TCS STAINLESS STEEL

According to the formula of grain growth under isothermal condition, the kinetics equation of ferritic grain growth in heat affected zone (HAZ) was obtained, which was combined with the calculated thermal cycles to predict the grain growth in HAZ of TCS stainless steel under the new-type welding procedure-hybrid welding. The grain sizes in HAZ of TCS stainless steel have been calculated for three welding conditions. Simulation results are validated by the average grain sizes measured on the metallographic images of the welding joint of TCS stainless steel. Preliminary discussion has been made on correlation of the grain growth with the thermal cycles and the effect of local variation in thermal cycles on the grain growth.

Monte Carlo simulation of grain growth in heat-affected zone of 12 wt.% Cr ferritic stainless steel hybrid welds

The grain structure in the heat-affected zone (HAZ) of 12wt.% Cr ferritic stainless steel under laser+pulsed gas metal arc welding (laser+GMAW-P) hybrid welding was studied experimentally and theoretically. First, an adaptive combined volumetric heat source model was used to calculate the temperature field in laser+GMAW-P hybrid welding. Then a three dimensional Monte Carlo method using the computed thermal cycles was applied to simulate the evolution of grain structure in the hybrid welding HAZ of the ferritic stainless steel. The predicted fusion zone geometry and the mean grain size agree with the measured results for different welding conditions in laser+GMAW-P hybrid welding of ferritic stainless steel. The simulate results showed that in hybrid welding the width of coarse grain heat-affected zone and the grain structure varied dramatically along the fusion line direction, the maximum mean grain size near the top surface was much larger than that close to the weld root.

A Study of the Microstructure and Grain Size at the Welding Heat Affected Zone of an Industrial Pure Aluminum

In this paper, Monte Carlo (MC) technology with welding experiments and thermal simulation experiments were introduced to simulate the grain growth process in welding heat affected zone(HAZ) of 1060 industrial pure aluminum. First, a kinetic model was defined by both experimental and statistics method. Then the thermal cycle was calculated and at the same time the simulation program was worked out based on MC technology. Thirdly, the grain growth process in HAZ was simulated during different welding heat input, which has great influence on grain growth in HAZ. The result of the simulation demonstrates the grain growth process dynamically and embodies the “thermal pin effect”. Good agreement between MC simulation results and the experimental results was obtained which can provide a reliable evidence for evaluating the welding craft and the weldability.

A stochastic model for austenite phase formation during arc welding of a low alloy steel

Modeling the microstructure of heat-affected zone (HAZ) in weld area can be useful in predicting mechanical behavior of the weldment. A multi-scale model is proposed to calculate the temperature distribution and to predict the microstructure evolution within the HAZ. Finite difference method was used to develop a computer model for studying the cooling curves during welding, and a stochastic method to analyze the austenite formation and its grain growth in HAZ. The droplet of liquid metal detached from electrode in manual arc metal welding is an important concern in studying the temperature distribution and the austenite grains growth. Both heat content of liquid metal detached from electrode and heat generated by electrical arc were used in calculation of temperature distribution. The stochastic model simulates the austenite phase formation and its growth during welding based on the kinetics of these processes. With this model, it is possible to visualize the topology of austenite phase. This multi-scale model was applied to the welding of low alloy steel. The observed morphology was in good agreement with that predicted by the model.

Three-dimensional Monte Carlo simulation of discontinuous grain growth in HAZ of stainless steel during GTAW process

The Monte Carlo (MC) simulations of grain growth in the heat affected zone (HAZ) of titanium alloys and ultra fine austenite steels are widely used. In single-phase alloys, the pinning effect of the grain boundary precipitates is one of the important factors to influence grain growth. However, it has not been considered in most of the simulations. In this study, both thermal pinning and precipitates pinning effects were taken into account to simulate grain growth in HAZ of austenite stainless steel SUS316 during gas tungsten arc welding (GTAW) process. By using heat transfer and fluid flow model, the thermal process of welding that influences grain structure evolution is obtained as well. The results of the simulation agree with the experiment and demonstrate that the grains in HAZ grow discontinuously when a large amount of carbides lie on the grain boundary.

Laser-TIG hybrid welding of ultra-fine grained steel

For improving the weldability of ultra-fine grained (UFG) steel, detailed experiments of laser-tungsten inert gas (TIG) hybrid welding were carried out on this material to investigate the effects of welding parameters on weld shape, microstructure, grain growth in heat-affected zone (HAZ) and mechanical performance. For the hybrid welds, increasing energy ratio of laser to arc (ER LA) can narrow weld width, reduce the tendency of grain growth and ferrite grain coarsening in HAZ and also make the microstructure of fusion zone gradually change from coarse pearlite to fine martensite and bainite. The hybrid weld with low ER LA has obvious softening zone in HAZ; while that with high ER LA has no softening zone because of the low line energy. Compared to laser weld, under appropriate welding parameters hybrid weld with high ER LA can obtain higher welding speed, better weld shape and more sound mechanical performance including similar tensile strength and higher toughness. These results demonstrated that laser-TIG hybrid welding is an effective process for UFG steel.

Three Dimensional Monte Carlo Simulation of Grain Growth in HAZ of Stainless Steel SUS316

The stainless steel SUS316 grain growth process in heat affected zone (HAZ) of gas tungsten arc welding (GTAW) process is studied with Monte Carlo (MC) simulation. The heat transfer and fluid flow model provides the thermal history and thermal distribution of the weldments for MC grain growth simulation. The grain growth evolution is simulated both in isothermal and in HAZ environment. The simulating results show clearly the “thermal pinning” effect on the grain growth evolution in HAZ compared with the isothermal results.

HAZ microstructure simulation in welding of a ultra fine grain steel

In the present work the evolution of grain structure in the weld HAZ (heat affected zone) under welding thermal cycle was simulated. Especially the grain growth in the HAZ of a SS400 ultra fine grain steel was investigated. An integrated 3-D Monte Carlo (MC) simulation system for grain growth of the weld HAZ was developed based on Microsoft Windows. The results indicate that MC simulation is an effective way to investigate the grain growth in weld HAZ. The method not only simulates the non-isothermal dynamics process of the grain growth in the weld HAZ, but also visualizes the austenite grains realistically. Moreover, the thermal pinning effect can be easily included in the simulation process. The grain sizes of the CGHAZ (coarse grain heat affected zone) obtained from MC simulation are basically in agreement with the experimental measurement of the real welded joints under different heat input. Furthermore, the simulation indicates that the grain growth degree is higher for the SS400 ultra fine grain steel compared to conventional steel. With the increase in the heat input, the grain growth of the CGHAZ rapidly increases. Because the activation energy of the grain growth is lower for the SS400 ultra fine grain steel, austenite grains can grow at a relatively lower temperature, hence the range of the CGHAZ becomes wider.

Prior austenite grain growth in heat-affected zone of a O.5Cr-Mo-V steel

AbstractA weld thermal-simulation technique has been used to produce prior austenite grain sizes similar to those observed in the heat-affected zones (HAZs) of O.5Cr-Mo-V welds. Grain-size measurements have been used to develop an Arrhenius equation for grain growth in artificial HAZs. This equation is in reasonable agreement with an ‘impurity drag’ theory for grain growth. In applying the equation to weld HAZs it was found that the steep thermal gradients present resulted in a ‘thermal pinning’ effect which inhibited growth. A final expression has been obtained which describes prior austenite grain growth in manual metal arc weld HAZs in 0.5 Cr-Mo- V steel as a function of heat input. The practical implications of this equation are discussed in terms of grain-size control in the HAZ during welding and these indicate that finegrained HAZs can be produced by low heat inputs and a suitable weld-bead overlap technique. In principle, the approach described