Papers by Keyword: Heat Affected Zone (HAZ)

Abstract: High nitrogen austenitic steels are used as structural materials required possessing high strength and fracture toughness. The present study is concerned with the characteristic features (shape, size, properties and structure) of the laser welded joints in Cr-Mn-, Cr-Mn-Mo-high nitrogen steels compared to the ones of Cr-Ni-steel joint. Butt welded joints were made using carbon dioxide laser with a maximum output of 5 kW in the continuous wave mode. The hardness and tensile tests of welded joints in the air and 3.5 vol.%-solution of NaCl, as well as the theoretical studies were carried out by optical and transmission electron microscopy (TEM). The results are achieved by testing that the welded joints of HNS had satisfactory weldability, adequately high mechanical and corrosion properties. The austenite of the investigated HNS retains high stability throughout the welding cycle.

Abstract: Welding is basic part of the most modern assembly and manufacturing operations. Shielded metal Arc Welding process has hard facing and fabrication job application due to low cost electrode, increasing alloy transfer efficiency and low dilution with substrate without losing production capacity. SMAW electrode is coated with metal mixture called flux, which on decompose produce gases to restrict weld contamination, generating deoxidizers to disinfect the weld. The choice of electrode for SMAW lies on a number of factors, like weld material, welding direction and the preferred weld properties. The present paper investigate the microstructure and hardness properties of the Low carbon steel pipe welded using shielded metal arc welding with different electrode combinations.

Abstract: 4330V is a high strength, high toughness, heat treatable low alloy steel for application in the oil, gas and aerospace industries. It is typically used for large diameter drilling parts where high toughness and strength are required. The research describes the effect of preheat temperature, interpass temperature, heat input, and post weld heat treatment on strength, hardness, toughness, and changes to microstructure in the weld joint. Welding with the lower heat input and no post weld heat treatment resulted in optimal mechanical properties in the weld metal. Austempering at 400 °C resulted in optimal mechanical properties in the HAZ. Increasing preheat and interpass temperature from 340 °C to 420 °C did not improve Charpy V-notch values or ultimate tensile strength in the weld metal or heat affected zones. The higher temperature increased the width of the heat affected zone. Austempering at 400 °C reduced HAZ hardness to a level comparable to the base metal. Both tempering and austempering at 400 °C for 10 hours reduced toughness in the weld metal.

Abstract: Magnetic Barkhausen noise measurements on a welded marine steel plate were performed in a line that passes through the weld bead and extends to the base metal from both sides of the weld. The heat affected zone was characterized by a pattern in the peak height as a function of distance from the weld bead. Barkhausen noise profile analysis by extracting relevant parameters like peak position, profile area and profile half width was also performed. The result showed a clear variation in MBN profile parameters in a way similar to that of the profile peak height. It could be concluded that MBN profile parameters superimposed as a function of measurement distance from the weld bead may provide an accurate determination of the affected material near the weld bead. The variation in MBN profile parameters was enhanced by microstructural and mechanical changes along the measurement line. This experiment demonstrates that the Barkhausen noise profile parameters could be used to track various manufacturing and maintenance processes of steel instead of using a single parameter like the root mean square (rms) to eliminate the variability of results and narrow the tolerance of acceptance criterion.

Abstract: Obtaining narrower kerf and smaller heat affected zone (HAZ) is a difficulty in laser cutting carbon fiber reinforced plastic (CFRP) composites. In order to solve this problem, the experiments used a semiconductor UV laser to cut CFRP have been done and how laser parameters (include pulse power, repetition frequency, cutting speed and direction) influent the width and HAZ of kerf have been achieved. In the meantime, compared with infrared laser cutting CFRP, the quality of CFRP cut by different wavelength laser has been investigated. The results show that owing to CFRP has the characteristic of anisotropy, laser cutting direction is the most significant factor that affects the quality of kerf cut by UV laser. The study also found that owing to high single photon energy, the narrower kerf and smaller HAZ around kerf can be get by UV laser cutting CFRP, nevertheless, it can’t be achieved by infrared laser cutting CFRP.

Abstract: This paper deals with the characterization of hardness, microstructure and precipitation processes in homogeneous T24 welds in the as-welded state and after laboratory PWHT at 745°C for 1 and 6 hours, respectively. Tempering of a T24 steel during quality heat treatment is accompanied by intensive precipitation of MX, M₇C₃ and M₂₃C₆ particles in the bainitic matrix. It was found that SAW welding resulted in a pronounced dissolution of minor phases in the base materials close to the joined faces. In the as-welded state microstructure of the CGHAZ was bainitic and the HV10 level in this part of the HAZ reached nearly 400 units. The dominant strengthening mechanism in the CGHAZ was attributed to transformation strengthening due to decomposition of austenite to bainite. Also the HV10 level in the bainitic filler metal (ca 320 HV10) was very close to the maximum acceptable hardness. PWHT at 740°C for 1 hour resulted in a significant decrease of hardness in the weld metal and especially in the CGHAZ. TEM studies revealed that recovery of bainite in the CGHAZ and the weld metal was accompanied by intensive precipitation of MX, M₇C₃ and M₂₃C₆ minor phases. The hardness level in the CGHAZ dropped to approximately 255 HV10. Prolonging of tempering at 740°C to 6 hours resulted in a modest softening in all parts of the weldments due to more pronounced both precipitation processes and recovery of bainite.

Abstract: Nonlinear finite element method is used in this paper to research the ultimate strength characteristics of aluminum stiffened plates under uniaxial tension-compression cyclic loading. This paper focused on the effect of the distribution mode of HAZ, the range of HAZ and different cyclic loading process on the ultimate strength of aluminum stiffened plates. The results obtained have a certain reference value to the design and manufacture of aluminum stiffened plates.

Abstract: The aim of experimental solution was to measure the thermal characteristics at predetermined locations in the experimental samples in HAZ during the welding process. To measure the thermal cycles were used thermocouples of suitable type. Location of thermocouple was settled in the welding process at the bottom of the experimental samples. Measured values were recorded directly into the computer by using a special program of universal measuring system QUANTUM X.

Abstract: 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 t_8/5. 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.

Abstract: Fabrication of various sub assemblies and items from imported austenitic stainless steel material of SA 240 - 304L (32 mm to 85 mm thick) was started in the year 1990 and work on these assemblies was stopped in 1993 due to unavoidable circumstances. Items and sub-assemblies were either in partially welded / machined or formed condition. Sub assemblies / items were stored in open yard for 13 years after applying plastic peal coating compound and covered with tarpaulin. The storage yard was near to the sea (roll on & off Jetty) as well as next to petrochemical industries. Sub assemblies have seen different extreme weathers conditions, saline and corrosive atmosphere for all these years and during this storage time base material and welded joints were subjected to contamination.