Fatigue Life Improvement in Lean Duplex Stainless Steel by Peening Treatments

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The present work studies the effects of shot peening (SP) and laser shock peening without coating (LSPwC) on the low-cycle fatigue life of the lean duplex stainless steel LDX 2101. LSPwC with two pulse densities, 2500 and 5000 pulse/cm2, were considered. To analyze the changes induced by each peening treatment, roughness, residual stress, hardness, quantitative phase analysis, qualitative surface chemical composition and dislocation microstructure were evaluated. This article shows that SP and LSPwC induce in the surface; beneficial compressive residual stresses, increase of hardness and roughness and in the austenite phase a pronounced work hardening. The strong barrier of this hardened austenite phase to microcrack growth can explain the improvement in the fatigue life of LDX 2101 with peening treatments. Moreover, the highest fatigue life is achieved for the LSPwC-treated material with 5000 pulse/cm2 because of the presence of deformation twins in the autenitic phase. https://doi.org/10.1007/s11661-019-05455-y  The Minerals, Metals & Materials Society and ASM International 2019

I.

INTRODUCTION

WITH the objective of turning economic materials into better and more competitive products, the improvement of their properties by surface treatments is usually considered. Among the surface treatments available are the mechanical peening treatments such as conventional shot peening (SP) and emergent laser shock peening (LSP). All mechanical surface treatments induce compressive residual stresses (CRSs) and work hardening on the materials’ surface, enhancing the fatigue life, wear and corrosion resistance. The effectiveness of each surface treatment mainly depends on the roughness levels, achieved work hardening and induced CRS.[1] The first two qualities lower the chance of fatigue crack initiation, and the third one retards crack propagation.[1] However, if the CRSs relax during service, the benefits of surface enhancement are lost.[2] Three mechanisms of CRS relaxation are known: thermal, overload and cyclic loading. In this sense, McClung[3] performed

RENATA STRUBBIA, SILVINA HEREN˜U´, and VALERIA FUSTER are with the Instituto de Fı´ sica Rosario, CONICET-UNR, Bv. 27 de febrero 210 bis, 2000 Rosario, Santa Fe, Argentina. Contact e-mail: strubbia@ifir-conicet.gov.ar GILBERTO GO´MEZ-ROSAS is with the Departamento de Fı´ sica, Centro Universitario de Ciencias Exactas e Ingenierı´ as, Universidad de Guadalajara, Blvd. Marcelino Garcı´ a Barraga´n 1421, 44430 Guadalajara, Jalisco, Mexico. CARLOS RUBIO GONZA´LEZ is with the Centro de Ingenierı´ a y Desarrollo Industrial, Pie de la cuesta 702, Desarrollo San Pablo, 76130 Quere´taro, Qro, Mexico. Manuscript submitted February 23, 2019.

METALLURGICAL AND MATERIALS TRANSACTIONS A

a literature survey to address the stability of surface residual stress fields during fatigue. He found that after relevant fatigue exposures some significant fraction of the induced residual stress often remains. Moreover, it has been reported that surface treatments can significantly improve the metals’

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