Effect of Welding Process Parameters on the Strength of Dissimilar Joints of S355 and Strenx 700 Steels Used in the Manufacture of Agricultural Machinery

The paper evaluates the possibility of using dissimilar materials joined by welding technology in the construction of agricultural machinery. The desire to design larger and more efficient structures requires designers to combine materials with different mechanical and structural properties. In such a case, it is very important to properly select welding parameters so that, on the one hand, the quality of the joint meets the standard requirements, and on the other, the welding process is not too energy-intensive. In this paper, overlay joints connecting S355 steel with Strenx 700 steel were analyzed in terms of strength for three different values of welding parameters and different thicknesses. The starting point was the reference parameters recommended by the company's welding technologists, which were reduced by 10 and 20% according to the linear welding energy. The study compared the strength, ductility and macrostructure of the joints, as well as the energy intensity of the process. The proposed dissimilar joints achieved approximately a 10% increase in the strength limit of the components in comparison to the previously recommended welding parameters. Additionally, finite element analysis calculations of the improved designs showed significant weight reduction (up to 40%) for the relevant agricultural machinery components.

Experimental and Numerical Analysis of Fracture Mechanics Behavior of Heterogeneous Zones in S690QL1 Grade High Strength Steel (HSS) Welded Joint

The heterogeneity of welded joints' microstructure affects their mechanical properties, which can vary significantly in relation to specific weld zones. Given the dimensional limitations of the available test volumes of such material zones, the determination of mechanical properties presents a certain challenge. The paper investigates X welded joint of S690QL1 grade high strength steel (HSS), welded with slightly overmatching filler metal. The experimental work is focused on tensile testing to obtain stress-strain properties, as well as fracture mechanics testing. Considering the aforementioned limitations of the material test volume, tensile testing is carried out with mini tensile specimens (MTS), determining stress-strain curves for each characteristic weld zone. Fracture mechanical testing is carried out to determine the fracture toughness using the characteristic parameters. The experimental investigation is carried out using the single edge notch bend (SENB) specimens located in several characteristic welded joint zones: base metal (BM), heat affected zone (HAZ), and weld metal (WM). Fractographic analysis provides deeper insight into crack behavior in relation to specific weld zones. The numerical simulations are carried out in order to describe the fracture behavior of SENB specimens. Damage initiation and evolution is simulated using the ductile damage material behavior. This paper demonstrates the possibility of experimental and numerical determination of fracture mechanics behavior of characteristic heterogeneous welded joint zones and their influence on crack path growth.

Oxide Metallurgy Technology in High Strength Steel: A Review

Oxide metallurgy technology plays an important role in inclusion control and is also applied to improve the weldability of high strength steel. Based on the requirements of the weldability in high strength steel, the influencing factors of weld heat affected zone (HAZ) as well as the development and application status of oxide metallurgy technology are summarized in this review. Moreover, the advantages and difficulties in the application of rare earth (RE) oxide metallurgy technology are analyzed, combined with the performance mechanism of RE and its formation characteristics of fine and high melting point RE inclusions with distribution dispersed in liquid steel. With the weldability diversities of different high strength steels, the research status of weldability of high strength steel with high carbon equivalent and the effects of RE on the microstructure and properties of HAZ are discussed, and some suggestions about further research in the future are proposed.

Experimental Investigation of Integrated Circular Triple-Wire Pulse GMAW of Q960E High-Strength Steel for Construction Machinery

Multi-wire welding has received much attention in the machinery industry due to its high efficiency. The aim of this study was to investigate a novel pulse gas metal arc welding (GMAW) that has circular triple-wire electrodes. The effect of the pulse phage angle on arc stability was particularly studied. Research showed that for typical phase angles the arc stability from low to high is 180°, 0°, and 120°, and the arcs are very stable at 120°. The triple-wire welding was used to weld a 9 mm thick Q960E steel, which is typically used for the arm of construction machinery. When the welding heat input was controlled at 1.26–1.56 kJ/mm, the weld zone was dominated by acicular ferrite, and the coarse-grained zone of the heat-affected zone was a mixed structure of lath martensite and lath bainite. The tensile strength of the welded joint reached 85% of the base metal and the impact toughness was above 62 J, which can meet the requirements of construction machinery. This indicates that the triple-wire welding has great potential to achieve efficient and high-quality welding for the construction machinery.

Influence of the Welding Process on the Mechanical Characteristics and Fracture of the S700MC High Strength Steel under Various Types of Loading

This paper focuses on the mechanical properties analysis of the high strength S700MC steel applied in welding joints. The research comprised mechanical tests for checking what the changes of tensile characteristics, mechanical parameters, resistance to impact, and fracture toughness look like in selected regions of the welding joint. Stress-strain curves have shown significant differences in the tensile characteristic shape and the values of Young's modulus, yield stress, ultimate tensile strength, and ductility due to the welding process applied. In the case of Charpy tests, the courses of the accumulated energy, force, deflection, and project velocity are presented, indicating the maximum value of absorbed energy, the same level of force during the first contact of the projectile with the specimens, and the significant variation of the velocity for the impact energy ranging from 50 J up to 300 J. On the basis of the fracture toughness tests, the distributions of the CTOD (Crack Tip Opening Displacement) values are presented for the parent material, HAZ (Heat Affected Zone) and weld. Moreover, the characteristic features of the fatigue pre-crack, transient and crack propagation zones are identified and discussed.

Multiscale Statistical Analysis of Massive Corrosion Pits Based on Image Recognition of High Resolution and Large Field-of-View Images

In the present study, a new multiscale method is proposed for the statistical analysis of spatial distribution of massive corrosion pits, based on the image recognition of high resolution and large field-of-view (montage) optical images. Pitting corrosion for high strength pipeline steel exposed to sodium chloride solution was observed using an optical microscope. Montage images of the corrosion pits were obtained, with a single image containing a large number of corrosion pits. The diameters and locations of all the pits were determined simultaneously using an image recognition algorithm, followed by statistical analysis of the two-dimensional spatial point pattern. The multiscale spatial distributions of pits were analyzed by dividing the montage image into a number of different windows. The results indicate the clear dependence of distribution features on the spatial scales. The proposed method can provide a better understanding of the pit growth from the perspective of multiscale spatial evolution.

Research of the Fatigue Life of Welded Joints of High Strength Steel S960 QL Created Using Laser and Electron Beams

This study investigated the fatigue life of welded joints, in particular, the welds of the high-strength steel S960 QL. The welds were created using unconventional technologies by utilising laser and electron beams. The direct application of the research is intended to be carried out through implementing the results towards the design of tracks for the track-wheel chassis of the demining system Božena 5. The producer’s experience shows the damage found in the current track design. The damage occurred during reversing the vehicle on a sand surface. Our goal was to solve this problem. The information acquired in this research will be a very important input factor for further designs of the track made of the tested material and its welds. The analysis of the residual stresses was also part of this study. The experimental research of the tested material’s fatigue life and welded joints was realised on the specimens loaded using cyclic bending and cyclic torsion. These loads were dominant during the track operation. The fatigue life of the tested material was detected using a device designed by us. The measurement results were processed in the form of the Wöhler’s S–N curves (alternating stress versus number cycles to failure) and compared with the current regulations issued by the International Institute of Welding (IIW) in the form of the FAT curves (IIW fatigue class). The achieved research results indicate that the modern welding technologies (laser and electron beams) used on the high-strength steel had no principal influence on the fatigue life of the tested material.

Transgranular Cracking in a Liquid Zn Embrittled High Strength Steel

Intergranular Zn-assisted liquid metal embrittlement (LME) cracks have been frequently reported in steels, involving austenite grain boundary penetration of liquid Zn at high temperature. In the present study, a Zn-coated high strength steel was deformed at an intercritical temperature, and the characteristics of LME cracking were studied in a mixed microstructure composed of ferrite and austenite. Crack propagation was intergranular in austenite; in contrast, the ferrite exhibited both intergranular LME and transgranular LME. Trace analysis of the crack plane orientation was consistent with cracking along {100} cleavage planes in ferrite.

Development of an Electrical Resistance Sensor from High Strength Steel for Automotive Applications

This work focuses on a demonstration of the monitoring of corrosion processes taking place in high strength steel in automotive applications. This is performed by means of a corrosion sensor, which operates as an electrical resistance sensor. It was developed from the same type of material that is used for the high-strength steel parts produced in the automotive industry. Using the sensor, real time corrosion processes can be measured. It is attached to a location inside the vehicle’s engine and is equipped with a data logger, which enables wireless transfer of the measured data. In this study the development, operation, and evaluation of the monitoring process are presented. Corrosion estimation is verified by means of electrochemical methods. A metallographic investigation was included in order to verify the similarity between the microstructural properties of the sensor and those of the as-received high-strength steel sheet.

Application of Cold Wire Gas Metal Arc Welding for Narrow Gap Welding (Ngw) of High Strength Low Alloy Steel

Narrow gap welding is a prevalent technique used to decrease the volume of molten metal and heat required to fill a joint. Consequently, deleterious effects such as distortion and residual stresses may be reduced. One of the fields where narrow groove welding is most employed is pipeline welding where misalignment, productivity and mechanical properties are critical to a successful final assemblage of pipes. This work reports the feasibility of joining pipe sections with 4 mm-wide narrow gaps machined from API X80 linepipe using cold wire gas metal arc welding. Joints were manufactured using the standard gas metal arc welding and the cold wire gas metal arc welding processes, where high speed imaging, and voltage and current monitoring were used to study the arc dynamic features. Standard metallographic procedures were used to study sidewall penetration, and the evolution of the heat affected zone during welding. It was found that cold wire injection stabilizes the arc wandering, decreasing sidewall penetration while almost doubling deposition. However, this also decreases penetration, and incomplete penetration was found in the cold wire specimens as a drawback. However, adjusting the groove geometry or changing the welding parameters would resolve this penetration issue.

Microstructure Evolution and Mechanical Properties of Underwater Dry and Local Dry Cavity Welded Joints of 690 MPa Grade High Strength Steel

Q690E high strength low alloy (HSLA) steel plays an important role in offshore structures. In addition, underwater local cavity welding (ULCW) technique was widely used to repair important offshore constructions. However, the high cooling rate of ULCW joints results in bad welding quality compared with underwater dry welding (UDW) joints. Q690E high strength low alloy steels were welded by multi-pass UDW and ULCW techniques, to study the microstructural evolution and mechanical properties of underwater welded joints. The microstructure and fracture morphology of welded joints were observed by scanning electron microscope and optical microscope. The elemental distribution in the microstructure was determined with an Electron Probe Microanalyzer. The results indicated that the microstructure of both two welded joints was similar. However, martensite and martensite-austenite components were significantly different with different underwater welding methods such that the micro-hardness of the HAZ and FZ in the ULCW specimen was higher than that of the corresponding regions in UDW joint. The yield strength and ultimate tensile strength of the ULCW specimen are 109 MPa lower and 77 MPa lower, respectively, than those of the UDW joint. The impact toughness of the UDW joint was superior to those of the ULCW joint.

Neutron Diffraction Evaluation of Near Surface Residual Stresses at Welds in 1300 MPa Yield Strength Steel

Evaluation of residual stress in the weld toe region is of critical importance. In this paper, the residual stress distribution both near the surface and in depth around the weld toe was investigated using neutron diffraction, complemented with X-ray diffraction. Measurements were done on a 1300 MPa yield strength steel welded using a Low Transformation Temperature (LTT) consumable. Near surface residual stresses, as close as 39 µm below the surface, were measured using neutron diffraction and evaluated by applying a near surface data correction technique. Very steep surface stress gradients within 0.5 mm of the surface were found both at the weld toe and 2 mm into the heat affected zone (HAZ). Neutron results showed that the LTT consumable was capable of inducing near surface compressive residual stresses in all directions at the weld toe. It is concluded that there are very steep stress gradients both transverse to the weld toe line and in the depth direction, at the weld toe in LTT welds. Residual stress in the base material a few millimeters from the weld toe can be very different from the stress at the weld toe. Care must, therefore, be exercised when relating the residual stress to fatigue strength in LTT welds.

Setting Mechanical Properties of High Strength Steels for Rapid Hot Forming Processes

Hot stamping of sheet metal is an established method for the manufacturing of light weight products with tailored properties. However, the generally-applied continuous roller furnace manifests two crucial disadvantages: the overall process time is long and a local setting of mechanical properties is only feasible through special cooling techniques. Hot forming with rapid heating directly before shaping is a new approach, which not only reduces the thermal intervention in the zones of critical formability and requested properties, but also allows the processing of an advantageous microstructure characterized by less grain growth, additional fractions (e.g., retained austenite), and undissolved carbides. Since the austenitization and homogenization process is strongly dependent on the microstructure constitution, the general applicability for the process relevant parameters is unknown. Thus, different austenitization parameters are analyzed for the conventional high strength steels 22MnB5, Docol 1400M, and DP1000 in respect of the mechanical properties. In order to characterize the resulting microstructure, the light optical and scanning electron microscopy, micro and macro hardness measurements, and the X-ray diffraction are conducted subsequent to tensile tests. The investigation proves not only the feasibility to adjust the strength and ductility flexibly, unique microstructures are also observed and the governing mechanisms are clarified.

Inclusion Rating by Statistics of Extreme Values and Its Application to Fatigue Strength Prediction and Quality Control of Materials

The inclusion rating method by statistics of extreme values (IRMSE) using a r e a of inclusions as the size parameter enables one to discriminate between current super-clean steels. Moreover, IRMSE enables one to predict the size ( a r e a max ) of maximum inclusions contained in domains larger than the inspection domain. The statistical distribution of a r e a max can be used for the quality control of materials and for the prediction of a scatter band of fatigue strength. Practical procedures of inclusion rating and prediction of a scatter band of fatigue strength are shown.