Jacek Górka

Analysis of Simulated Welding Thermal Cycles S700MC Using Thermal Imaging Camera

In this paper an influence of simulated thermal cycle on properties and HAZ structure of 10 mm thick S700MC steel plates. The introduction of thermomechanically processed steels with high yield and relatively low carbon equivalent, will significantly reduce the time of welding works by reducing the preheating temperature, or even complete removal of this processing step, furthermore reduction of cross-sectional areas of structural elements, making welded structures with the same capacity will be more slender and lighter. The simulation of thermal cycles was carried out on a specially built test stand equipped with resistive heating source infrared camera VarioCam Head HR with 50 mm lens and a computer with software IRBIS 3 plus. Simulation was prepared for simple and complex thermal cycle. Simulation studies of thermal cycles consisted of resistive heating of samples prepared for the impact test. Single thermal cycles were simulated at temperatures ranging from 400 to 1300 oC, 100 oC and the cycle complex. For each temperature three repeats were carried out. Specimens were tested on impact, strength test and also hardness and metallographical tests. The study showed that there is a possibility to use a purpose built system to simulate simple and complex thermal cycles of S700 MC steel in specific ranges of the cooling time t8/5. Analysis of the results of the study showed that the welding thermal cycle strongly influences the structural changes and phase in the HAZ zone of S700 MC steel. Areas of HAZ heated to high temperatures above 1000 [°C], show a sudden drop of toughness to unacceptable levels of impact strength (27 [J/cm2]). This sharp decrease in toughness is associated with uncontrolled separation processes of MX phases and dissolution of carbides, niobium and vanadium carbonitrides in austenite during heating. The study also showed that the chemical composition of steel and especially titanium and aluminium content is sufficient to bind in the HAZ free nitrogen and reduce the aging process. The control of the amount of heat introduced into the joint area during welding will reduce the adverse separation processes in the weld and HAZ which will ensure adequate toughness of the connection. Precise knowledge of the phenomena occurring in the HAZ during the thermal cycle can impact the ability to control properties and structure of the welded joint.

Repair welding of cast iron coated electrodes

Welding cast iron is a complex production procedure. Repair welding was used to repair damaged or poorly made castings. This is due to a tendency to cracking of the material during welding as well as after it. Welding cast iron can be carried out on hot or on cold. Hot welding requires high heat material and the use of welding material in the form of cast iron. In the case of cold welding, it is possible to use different materials. Mostly used filler metals are nickel and copper based. The work shows the course of research concerning repairmen of ductile iron with arc welding method. For the reparation process four types of ESAB company coated electrodes dedicated for cast iron were used with diameter 3.2 and 4 mm: ES 18-8-6B (4mm), EB 150 (4mm), OK NiCl, EŻM. In the cast iron examined during the testing grooves were made using plasma methods, in order to simulate the removed casting flaws. Then the welding process with coated electrodes was executed. The process utilized low welding current row of 100A, so there would only be a small amount of heat delivered to the heat affected zone (HAZ). Short stitches were made, after welding it was hammered, in order to remove stresses. After the repair welding the part of studies commenced which purpose was finding surface defects using visual testing (VT) and penetration testing (PT). In the second part, a series of macro and microscopic studies were executed witch the purpose of disclosuring the structure. Then the hardness tests for welds cross sections were performed. An important aspect of welding cast iron is the colour of the padding weld after welding, more precisely the difference between the base material and padding weld, the use of different materials extra gives the extra ability to select the best variant. The research of four types of coated electrode was executed, based on the demands the best option in terms of aesthetic, strength and hardness.

The structure and properties of filler metal-free laser beam welded joints in steel S700MC subjected to TMCP

The research-related tests aimed to determine the effect of filer-metal free laser beam welding on the structure and properties of 10 mm thick steel S700MC subjected to the Thermo-Mechanical Control Process (TMCP). The nondestructive tests revealed that the welded joints represented quality level B according to the requirements of standard 13919-1. The destructive tests revealed that the joints were characterised by tensile strength being by approximately 5% lower than that of the base material. The tests of thin foils performed using a high-resolution scanning transmission electron microscope revealed that filler metal-free welding led to the increased amount of alloying microagents (Ti and Nb) in the weld (particularly near fusion line) in comparison with welding performed using a filler metal. The significant content of hardening phases in the welds during cooling resulted in considerable precipitation hardening through finedispersive (Ti,Nb)(C,N) type precipitates (several nm in size) leading to the deterioration of plastic properties. The destructive tests revealed that the joints were characterised by tensile strength being by approximately 5% lower than that of the base material. The increase in the concentration of microagents responsible for steel hardening (Ti and Nb) also contributed to the decrease in weld toughness being below the allowed value of 25 J/cm2.

Diode laser cladding of Co-based composite coatings reinforced by spherical WC particles

A laser cladding system consisting of a direct diode laser with the flat-top beam profile and an off-axis powder injection nozzle has been used to fabricate Co-based (Satellite 6) metal matrix composite coatings reinforced by spherical-shaped WC particles. Non-porous coatings with the WC fraction of about 50 vol.% and a low dissolution of the WC particles in the matrix have been obtained. The heat input level affects the degree of WC dissolution and the matrix mean free path between the embedded WC particles. Comparative erosion tests between the metallic Satellite 6 and composite Satellite 6/WC coatings showed that the composite coatings exhibit a superior erosion resistance only at the oblique impingement condition. Generally, a low erosion resistance of the composite coatings at the normal impingement is mainly attributed to a very smooth interface between the spherical-shaped WC particles and the matrix alloy.

Testing of Flame Sprayed ZrO2 Matrix Coatings Containing CaO

Presented in this article are the properties of flame sprayed ceramic coatings using oxide ceramic materials consisting of a powdered zirconium oxide (ZrO2) matrix with 30% calcium oxide (CaO) applied to unalloyed S235JR grade structural steel. A primer consisting of a metallic Ni-Al-Mo based powder has been applied to plates with dimensions of 5x200x300 mm and front surfaces of ø 40x50 mm cylinders. Flame spraying of primer coating was conducted using a RotoTec 80 torch, and an external surface was coated with a CastoDyn DS 8000 torch. Evaluation of the coating properties was conducted using metallographic testing, phase composition research, measurement of microhardness, abrasive wear resistance (acc. to ASTM G65 standard) and erosion wear resistance (acc. to ASTM G76-95 standard).

Technology of welding hard wearing plates

The technology of welding of abrasion-resisting plates with the use of different filler metals designed for providing high wear resistance of the top layer and good plastic properties of the parent material is presented. To this end, we made test joints which were subjected to metallographic examination, mechanical testing, hardness measurements and testing of wear resistance of the type metal–mineral in accordance with ASTM G65-04 standard. In each case, the weld joining the wear resistant layer was made with the use of an XHD 6710 covered electrode. For making the weld joining of the parent material of the abrasion-resisting plate, we applied austenitic and ferritic–perlitic filler materials in the form of covered electrodes and solid wires for gas shielded arc welding. The tests have shown that the XHD 6710 electrode can be used for joining of top layers of abrasion-resisting plates providing their high wear resistance. For interpasses and filler passes, it is recommended to use austenitic filler metals which are characterized by very good plastic properties. Moreover, they reduce the mixing ratio of the weld metal and the material of the abrasion resistant layer.

Research into GTA automatic soft soldering technology for solar energy collector components

This article presented research into procedures for the development of gas tungsten arc (GTA) automatic soft soldering of solar absorber components, i.e. joining of tubes to copper foil by means of brazing with SolarCast 5 soft self-fluxing solder paste. The brazing process was carried out in two ways: joining of a flat copper foil to the tube, and joining with formation of a semi-circular channel with a diameter equal to that of the tube, inside the copper foil. The properties of the finished joints were determined by means of metallographic examination, hardness measurements, static tensile tests as well as thermal conduction tests. The results of these tests proved the occurrence of an area of GTA brazing parameters which would ensure high-quality absorber joints between the tube and the copper foil.

Properties and Structure of Deposited Nanocrystalline Coatings in Relation to Selected Construction Materials Resistant to Abrasive Wear

Presented in this work are the properties and structure characteristics of MMA (Manual Metal Arc) deposited nanocrystalline coatings (Fe-Cr-Nb-B) applied to an iron nanoalloy matrix on an S355N steel substrate in relation to selected construction materials resistant to abrasive wear currently used in industry. The obtained overlay welds were subjected to macro and microscopic metallographic examinations; grain size was determined by X-ray diffraction (XRD), and chemical composition of precipitates was determined by energy-dispersive X-ray spectroscopy (EDS) during scanning electron microscopy (SEM). The size of the crystalline grains of the Fe-Cr-Nb-B nanocrystalline microstructure was analyzed using an Xpert PRO X-ray diffractometer. Analysis of the test results of the obtained layers of arc-welded Fe-Cr-Nb-B-type alloy confirmed that the obtained layers are made of crystallites with a size of 20 nm, which classifies these layers as nanocrystalline. The obtained nanocrystalline coatings were assessed by hardness and with the use of metal-mineral abrasion testing. The results of the coatings’ properties tests were compared to HARDOX 400 alloy steel.

Application of Time-Frequency Methods for Assessment of Gas Metal Arc Welding Condition

Gas Metal Arc Welding (GMAW) is a popular method of material joining, widely used for a variety of critical industrial structures. Assuring high quality of joints is than a vital task. Welding is a highly dynamic and non-linear process, thus an application of time-domain or frequency-domain methods is often not suitable for evaluation of welded joints quality. To fully describe the correspondence between the geometry of welding arc, parameters that express the quality of joint, and the welding arc current, being the most important steerable parameter of a GMAW, time-frequency methods (TFM) of signal analysis should be applied. In the paper application of ensemble of STFT and EMD (Empirical Mode Decomposition)-based estimators to evaluate the stability of a GMAW process, that results in the quality of joint. Proposed method of feature extraction was applied on the real data taken during several GMAW realizations with different conditions (changes in welding current, arc voltage, shield gas flow, wire feed speed, etc.). In the active experiment process parameters were acquired. Performed investigations revealed that in comparison to traditional as well as separately used TFM, ensemble of TF estimators gave better performance in a GMAW condition assessment.

Properties of thermo-mechanically treated welds of high yield-point steel

The article presents the properties of thermo-mechanically treated welds of steel S700 MC with a thickness of 10 mm, created using various welding methods and with different values of supplied linear welding energy. The metallographic evaluation, tensile strength testing and hardness measurements allowed us to assess the structure and properties of the welds and evaluate the influence of the amount of heat supplied to the welding area on the tensile strength, impact strength and hardness of welds.