Thermal State Simulation of Welded Steel Plates under Laser Welding Conditions

The article describes a method for determination of the welded parts temperature pattern under laser welding conditions. An algorithm is engineered to solve the non-stationary heat conduction problem by finite element method. The boundary conditions are determined by the molten pool parameters and depend on the welding regime characteristics. The dependencies for determining the molten pool geometric dimensions for laser welding conditions are proposed. Calculations of the temperature pattern change during the steel plates joint by laser welding are carried out. It is shown that the proposed model adequately describes the heat transfer process in the welding region.

FEM Analysis of the Welding Seams Geometry in Case of Fillet Welds

The role of the welding seam is to achieve the non-removable joint between two or more parts. In principle, three geometric profiles of the welding seams can be obtained: straight profile; concave profile and convex profile. In practice, this geometric shape of the weld seam profile is very important, both in terms of the resistance of the joint to static stresses and in terms of its fatigue life. There are many factors that can influence the geometric shape of the weld seam: the welding process; welding regime; the nature of the filler materials used, the rehabilitation techniques applied and others. Often, this geometric shape of the weld bead is neglected, which is particularly dangerous due to the fact that an improper geometric shape can generate low mechanical strength in static loads or poor fatigue strength in variable loads. An optimum of the geometric configuration of the welding must be found, which reconciles both situations: the mechanical resistance in case of static stresses and also the fatigue resistance in case of variable loads. In this paper, an analysis will be made with finite elements for the straight and convex profile of the welding seams in the case of fillet welds subjected to fatigue. Several elements will be considered such as: damage; total deformation; fatigue sensitivity versus loading history; equivalent von Misses stress; safety factor.

The optimization of welding regimes for obtaining corrosion resistant welded constructions

Most of the technological equipment has welded metal structures in its composition, which are strongly affected by the corrosion phenomenon. In order to achieve a reduction of the corrosion phenomenon it is very important that the welded joints are made using optimal parameters of the welding regime. In the research were made 6 different welded specimens, respectively 3 for the welded T-shaped joint and 3 for the cross-welded joint. The welded joints were made of 10 mm thick using S 355JR steel by the MAG welding process and using welding wire G4 Si 1 as an additive. For the 6 specimens were made analyzes of the metallographic structure thus observing what are parameters of the welding regime that allows to obtain the welded joints with high corrosion resistance.

Corrosion of Welded Metal Structures of Mining Equipment

Mining equipment made of welded metal structures is strongly affected by the corrosion phenomenon due to the working conditions. Initial research has shown that the corrosion phenomenon is most pronounced in the area of cross-welded joints and welded T-shaped joints. In the researches, there was made a chemical analysis of the welded construction material used respectively of the new material and it was observed a reduction in carbon concentration in the material used, but also a substantial increase in the sulfur concentration compared to the new material. The pronounced corrosion of the metallic structure is influenced by the chemical composition change because the sulfur is a grafitizing and weakening element, and the decrease in carbon concentration causes a decrease in corrosion resistance. Also, the pronounced corrosion is due to the action of sulfurous acid (H2SO3) and hydrogen sulfide (H2S), elements that are present in the working environment of welded constructions. In order to achieve a reduction in the corrosion phenomenon, it is very important that the welded joints are made using the optimal parameters of the welding regime so as to obtain metallographic structure with finer granulations.

Minimization of the Thermal Impact in the Laser Welding of Dissimilar Stainless Steels

Laser welding of dissimilar stainless steels is of interest when mechanical, corrosion, or esthetical requirements impose the use of a high-performance stainless steels, while production-cost requirements prevent using expensive materials in all the parts of a given device. The compromise may lead to the use of the most expensive material in critical areas and the cheapest one in the remaining. Their union can be materialized by laser-pulsed welding. It has intrinsic difficulties derived from the different physical and chemical properties of the steels, and from the need of preserving the protective passive layer. The present work achieves a welded joint with minimum thermal impact by means of laser pulses, capable of preserving the corrosion resistance of the involved stainless steels. The influence of the parameters to define static and dynamic pulses on the material and on the welding regime, keyhole, or heat conduction, is studied. It is used to calculate the overlapping factor of the pulses on the basis of the real dimensions of the melted area. A continuous joint has been built with dynamic pulses. The corrosion resistance of it has been checked showing a similar behavior to the non-heated material. The microstructure of the optimized joint is associated with a reduced HAZ while its mechanical behavior is suitable for its real application.

Application of the High Strength Steel HARDOX 450 for Manufacturing of Assemblies in the Military Industry

The problems related to welding of the high strength steel, aimed for manufacturing of welded structures operating in the prominent wear conditions, is considered in this paper. The paper presents an analysis of possibilities and prescribing the technology for welding the high strength steel HARDOX 450. The methodology for estimate the weldability of this steel was established in the theoretical part of the paper, as well as calculations of the welding parameters, while the hardness was investigated in details and the macro and micro structures of the individual welded joint zones were estimated in the experimental part. Obtained experimental results could be usefully applied for selecting and establishing the optimal welding technology for structures made of this steel. The technology thus established and the GMAW welding regime can enable successful execution of the welded joints and reduce the possibility for appearance of flaws and cracks to a minimum.

Contributions Regarding Working Environment Impact of Submerged Arc Welding

Paper presents the main pollutants of the working environment at welding under flux, methodical determination which the main chemical reactions resulting in pollution and pollution coefficient calculation. A number of welding working regime in order to achieve a coefficient of minimal pollution. The experimental results demonstrate that the process of welding under flux is less polluting than manual arc welding and coated electrode but more polluting than the process of welding in protective gas environment. It shows the influence of welding regime parameters for the most important gas pollutants.

Modeling by Finite Element Method of Thermal Field when Coating with Stellite Welding of Valvetype Parts

The paper presents the optimization results of coating by welding technology of the sealing surfaces of a rod-valve and seat assembly by using finite element programs. The assemblies - rod, valve and seat - are used for closing or opening track heat from heating systems used in power plants. The heat is given by steam that is found at a pressure of 400-450 atm and a temperature range of approximately 500°C. These values determine the use of materials of steels grades that are thermo resistant, alloyed with Cr and Mo, and work surfaces are coated with materials out of stellite grades (Co). To optimize parameters of the welding system and decrease heat loss, by conduction and convection, there were used programs of finite element to simulate the propagation of heat gradient acording to the parameters of welding regime.