New mathematical tools for microstructure characterization of welded metallic structures (original) (raw)

Modelling of Microstructure Evaluation of Welding by using Finite Element Method (FEM)

MSc Thesis, 2013

In the present study, arc welding of the AISI 1045 steel is modelled by using 2D-FEM for three types of welding groove; V, double V and U. The temperature distribution, microstructure, grain growth, and the hardness of the heat affected zone (HAZ) of the welding are simulated. The experimental work is carried out to validate the FE model. The very close value between the simulation and experimental results show that the FE model is very effective for predicting the microstructure, the phase transformation, the grain growth and the hardness. The effect of preheating temperature on the martensite formation is analysed. It is shown that 225oC, 300oC and 350oC preheatings eliminate completely the martensite formation for 12 mm thick, V, U and double V-shaped butt welding of AISI 1045 steel. Among the welding grooves, the Vshape is providing the lowest martensite formation and the lowest preheating temperature for martensite elimination.

STUDY THE MICROSTRUCTURE OF WELDING JOINT OF DISSIMILAR METALS

STUDY THE MICROSTRUCTURE OF WELDING JOINT OF DISSIMILAR METALS, 2011

The aim of this work is to study the microstructure of welding joint of dissimilar metals, stainless steel to low carbon steel that is thickness (mm) for both by using the metal active gas (MAG) spot welding process. The welding wire (E80S-G) is used and have (1.2mm) diameter depend of (AWS), and Co gas is used as shielded gas with flow rate (7L/min) for all times used in this work. In this work, we select many samples from the welding joints from welding region and heat effective zone, these samples will change in there welding from the welding time, current and the wire feed. A different region that represents regions of joint interface between the two metals, and heat effected zone we noted that. The ratio of pearlite in low carbon steel more than in base metal and the ratio of ferrite is less than in parent metals. Furthermore, the microstructure of stainless steel has no change as compact with low carbon steel because most of heat concentrated in the low carbon steel.

Wear characterization by fractal mathematics for quality improvement of machine

Purpose -The objective of the present work is to find an alternative approach for gearbox condition monitoring using wear particle characterization incorporated with image vision systems. Design/methodology/approach -It is a quite well-known phenomenon that wear generates whenever two metallic bodies have contact with each other; hence the present work tries to investigate the effect of improper lubrication in the gearbox due to wear particle generation between gear wheels. Since the identification of wear for machine condition monitoring needs much expertise knowledge and is time-consuming using the conventional process, fractal mathematics with image morphological analysis has been utilized to overcome this situation in the present work. Findings -The type of wear has been found for the present method by utilizing the lubricant used in the system ferrographically and a great deal of image processing has been done to characterize the type of particle so that the proper maintenance strategy can be undertaken. Originality/value -Wear particle characterization is a quite common method in maintenance engineering, especially when fault diagnosis of any equipment is concerned. In the present work, the CCD acquisition of the images has been done for different particles, but one analysis amongst them has been shown in this paper. Among all other methodologies, the new technique of fractal mathematics has been used in the present work to minimize the imaging hazards and to make the system more user-friendly.

Image analysis application in metallurgical engineering and quality control

Computational Methods and Experiments in Materials Characterisation IV, 2009

Image analysis (IA) is widely used in different areas of science such as medicine, biology and engineering. Quantitative measuring by image analysis has also found application in metallurgical engineering, especially in analyzing metallographic microstructures. The measuring of different microconstituents dimensions based on image analysis, performed in metallurgical investigations is presented in the paper. Determination of the brittle phase content in the function of the heat treatment temperature for the heat resistant Ni-Cr-Co-W alloy, with the aim of obtaining optimal microstructure for repair welding are presented. Results have shown that the best effect of the brittle phases dissolving is obtained at the temperature of 1250 o C. Investigation of the effects of Si (1-10%) and Cu (0.5-4.5 %) content, in the cast Al alloy for automotive application, on secondary dendrite arm spacing (SDAS) in the structure was performed. Results have shown that the higher silicon and copper contents reduced the size of the SDAS, which directly enable better mechanical properties of the cast product. The effect of different energy inputs, in the steel arc welding process, on the dimensions and geometry of the zones in a cross section of the welded joint was investigated. The heat affected zone (HAZ) of the welds is critical for the mechanical properties and weld quality and it is directly dependent on the energy input. The area and width of the HAZ for different heat inputs, from 0.4 to 1.4 kJ/mm, were measured by the IA. The obtained results have shown direct dependence of the measured dimensions from the energy input. The applied methodology enables weld quality control in the case of the automatic welding processes. All presented experimental results are based on a large number of measurements. A statistical analysis was performed and a high correlation of the results was obtained. For the each of the presented investigations and analyzed phenomenon, a statistical mathematical model is suggested with the boundary conditions defined by the investigated intervals of variables.

Heat Affected Zone Microstructure of Weld Joint Preparation in Artificial Manner

2019

This paper presents two possibilities of martensitic (fine grain and coarse grain) microstructure preparation. These microstructures are present as sub-zones in the heat-affected zone of welded joints. Due to the narrow region of HAZ in a real weld, only a few tests are possible to perform such as micro-hardness. Welding simulator and laboratory furnace were used as methods for the preparation of the specimens. The material used in this study was a Nickel Molybdenum alloy steel (18CrNiMo7-6). Investigation of the mechanical properties of sub-zones of the HAZ of this particular alloy steel, were done by applying proper thermal cycles. Hardness and diameter of grain size were measured, tensile strength is calculated and Charpy instrumented test of both microstructures were performed in room temperature. The difference in Impact toughness was remarkable due to the difference in microstructure, energy for initiation and propagation were calculated by comparing (F-t and E-t) diagrams for...

Using Fractals to Analyze Metallic Microstructures

Expressions relating box counting and lineal analysis are developed. Both methods are used for fitting the spacing distribution of a real microstructure. The relation to grain size distribution is discussed.

The Object Segmentation from the Microstructure of a FSW Dissimilar Weld

Materials, 2022

Friction stir welding (FSW) is an environmentally friendly, solid-state welding technique. In this research work, we analyze the microstructure of a new type of FSW weld applying a two- stage framework based on image processing algorithms containing a segmentation step and microstructure analysis of objects occurring in different layers. A dual-speed tool as used to prepare the tested weld. In this paper, we present the segmentation method for recognizing areas containing particles forming bands in the microstructure of a dissimilar weld of aluminum alloys made by FSW technology. A digital analysis was performed on the images obtained using an Olympus GX51 light microscope. The image analysis process consisted of basic segmentation methods in conjunction with domain knowledge and object detection located in different layers of a weld using morphological operations and point transformations. These methods proved to be effective in the analysis of the microstructure images corrupted b...

Fractal model of structure-properties effect of low carbon steel

Fractal theory has been used for predicting of microstructure (ferrite, pearlite and nonmetallic inclusions) effect on mechanical properties (KCV-60 , 0.2, B, ) of S355J2 steel. The fractal model which has been obtained may be considered as additive database. The database can be complemented by different treatment modes and microstructure. It has been stated that good response of structure-properties has been obtained for strength characteristics (0.2, B) of S355J2 steel and fractal size of lamellar pearlite. Also, correspondence of elongation to fractal size of ferrite has been obtained. As it has been determined the better correspondence of fractal size of non-metallic inclusions defined to impact toughness of S355J2 steel. The results have been confirmed by effect of low carbon steel microstructure on mechanical properties of the steel. The histogram of microstructure and non-metallic inclusions effect on mechanical properties of S355J2 steel has been plotted.

Zone wise local characterization of welds using digital image correlation technique

The process of welding is associated with high and varying thermal gradients across the weld, resulting in inhomogeneous material properties surrounding the weldment. A proper understanding of the varying mechanical properties of the weld and surrounding materials is important in designing and modelling of components with weld. In the present study the characterization of different zones such as fusion zone, heat affected zones and unaffected base material of a deposited weld is carried out using digital image correlation (DIC) technique. A methodology using the micrographic observation and image processing is proposed for accurate identification of various weld zones. The response of welded samples in the elastic and plastic region is compared with the virgin sample. Full range stress-strain curves are obtained for each zone using the whole field strain measurement involving DIC. The parameters investigated are Young's modulus, Poisson's ratio, yield stress, strain hardening exponent and strength coefficient. A study regarding the variation of properties with respect to varying weld currents of 100 A, 130 A and 150 A is carried out. The Vickers microhardness measurement is also conducted to obtain the variation in hardness across weldment. Fusion zone of all the welded samples have reported lower Young's modulus and higher yield strength compared to virgin samples. The Vickers hardness values obtained for fusion and heat affected zones are in line with the yield stress variation obtained zone wise.

Thermo-Mechanical Properties and Microstructural Characterization of Welded Steel Plates

International Journal of Novel Research in Engineering and Science, 2023

The study focused on thermo-mechanical properties of steel weld. A mild steel stock selected from the SAE10XX class was used to fabricate four pairs of rectangular plates, each measuring 200 mm × 100 mm × 6 mm. Mechanical tests were conducted on the welded samples and their microstructures analysed using scanning electron microscope. The results suggest that a good combination of the operational variables guarantees stable welding operation which in turn assists in achieving a quality welded joint. Hence, from the results it is recommended that maintaining low but sufficient high welding power helps to minimize excessive temperature rise in the base metal and improves stress distribution along the welding line, which in turn mitigates degradation of mechanical properties. The result also showed that a coarse structure is formed in the fusion zone while fine structure is formed in the heat affected region.