doi: 10.1111/j.1460-2695.2011.01606.x Effects of several TIG weld repairs on the axial fatigue strength of AISI 4130 aeronautical steel-welded joints M. P. NASCIMENTO 1 , H. J. C. VOORWALD 1 and J. DA C. PAY ˜ AO FILHO 2 1 Univ Estadual Paulista – UNESP/FEG, Department of Materials and Technology – DMT Av. Ariberto Pereira da Cunha, No.333, CEP12516-410, Guaratinguet ´ a, S ˜ ao Paulo(SP), Brazil, 2 Federal University of Rio de Janeiro, Department of Metallurgical and Materials Engineering – PEMM/COPPE/UFRJ, Cidade Universit ´ aria, Centro de Tecnologia, BlocoF, SalaF-210, Ilha do Fund˜ ao, Caixa Postal 68505, CEP21941-972, Rio de Janeiro(RJ), Brazil Received in final form 9 May 2011 ABSTRACT 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. NOMENCLATURE a = 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. E-mail: marcelino.nascimento@gmail.com c  2011 Blackwell Publishing Ltd. Fatigue Fract Engng Mater Struct 35, 191–204 191 Fatigue & Fracture of Engineering Materials & Structures