In equipment manufacturing, there are occasions that the base metal (BM) need to be hot or cold worked prior to welding. After welding, the components have to be submitted to a normalizing heat treatment in order to recover its original mechanical properties. In this work four different low alloy steel weld metals (WM) both in the as welded condition and after normalizing heat treatment have been studied. Optical and scanning electron microscopy were used to observe the WM microstructure. Tensile and Charpy V toughness testing and microhardness measurements were used to evaluate the WM mechanical properties. Results show that normalizing breaks the original columnar structure in the as welded condition to an equiaxial structure similar to the one of the BM. Due to low carbon content of the WM it was observed a high decrease on the tensile properties specially the yield strength after normalizing. In respect of toughness, the normalizing heat treatment was observed to increase the Charpy V energy, except for one WM where a great content of martensite-austenite-bainite constituent was formed. Opposite to others post weld heat treatments, normalizing modifies significantly the microstructure and the resulting mechanical properties of the WM. Although normalizing is always beneficial to the BM, care must be taken in order to select welding consumables

No abstract

a b s t r a c tIn this work the effect of Gas Tungsten Arc Welding (GTAW) repairs on the axial fatigue strength of an AISI 4130 steel welded joint used in airframe critical to the flight-safety was investigated. Fatigue tests were performed at room temperature on 0.89 mm thick hot-rolled plates with constant amplitude and load ratio of R = 0.1, at 20 Hz frequency. Monotonic tensile tests, optical metallography and microhardness, residual stress and weld geometric factors measurements were also performed. The fatigue strength decreased with the number of GTAW repairs, and was related to microstructural and microhardness changes, as well as residual stress field and weld profile geometry factors, which gave origin to high stress concentration at the weld toe.

A B S T R A C T Welded joints of airframes critical to the flight-safety are commonly repair welded during its operational live. In this study, the effect of up to three weld repairs by gas tungsten arc welding (GTAW) on the axial fatigue strength of AISI4130 steel used in an airframe critical to the flight-safety was investigated. The tests were performed on hot-rolled steel plate specimens, 0.89 mm thick, with load ratio R = 0.1, constant amplitude, at 20 Hz frequency and room temperature. The results obtained indicated that the axial fatigue strength decreased with the GTAW process itself, and with the subsequent repair cycles, as a consequence of microstructural and microhardness changes and of weld profile geometry factors, which induced high stress concentration at the weld toe.Keywords GTAW; heat-affected zone; high strength low alloy steel; microstructure; repair welding; weld metal; weld toe notch. N O M E N C L A T U R Ea = Peterson's parameter for steel BM = Base metal CE = Carbon equivalent CGHAZ = Coarse-grain heat affected zone da/dN = fatigue crack propagation rate (mm/cycle) DC = Direct Current FGHAZ = Fine-grain heat affected zone GTAW = Gas Tungsten Arc Welding HAZ = Heat affected zone HFC = High fatigue cycles ICHAZ = Inter-critical heat affected zone IIS/IIW = Institut International de la Soudure/International Institute of Welding Kf = fatigue-notch factor Kt = Theoretical stress concentration factor LFC = Low fatigue cycles NDT = Non-destructive testing q = notch-sensitivity factor r = notch-root R = Stress or load ratio R a = Roughness average (μm) S = Stress (MPa)Correspondence: M. P. Nascimento.

No abstract