Strength and Deformation Properties of Low-Alloy Steel Bolts with Electroless Ni-P Coating: An Investigation of Two Ther
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JMEPEG https://doi.org/10.1007/s11665-020-05066-4
Strength and Deformation Properties of Low-Alloy Steel Bolts with Electroless Ni-P Coating: An Investigation of Two Thermal Routes K.S. Correia, L.G. Greca, L. Sopchenski
, P. Soares, F.L. Amorim, and R.D. Torres
(Submitted October 10, 2019; in revised form July 24, 2020) Low-alloy steel bolts are used in applications where high strength is needed, although they presented low corrosion resistance, limiting their application in harsh environments. Ni-P coatings could be an alternative to protect low-alloy steel bolts against corrosion. However, Ni-P coatings must be submitted to an interdiffusion post-heat treatment, which provokes severe microstructural changes in the steel substrate, lowering its strength. This research aims to investigate two new thermal routes to obtain Ni-P coatings on lowalloy steel bolts, aiming to preserve the steel substrate’s resistance and deformation properties, addressing the ASTM A320/L7 requirements. The first route proposed consists of obtaining the Ni-P coating on an austempered steel substrate, instead of a quenched/tempered one. This approach resulted in less microstructural changes during the post-heat treatment, although poor impact properties were achieved. The second thermal route consists of Ni-P coating on a quenched substrate, followed by a single-step postheat treatment aiming to temper the substrate and promote the coatings’ interdiffusion at the same time. The single-step post-heat treatment performed at 600 °C for 4 h resulted in appropriated mechanical properties while assuring the creation of a proper coating/steel interdiffusion layer, showing the feasibility to use Ni-P coatings in low-alloy steel to be used in harsh environments. Keywords
ASTM A320/L7, heat treatment, low-alloy steel, Ni-P coating, strength
1. Introduction Low-alloy steel bolts are widely used in applications where high strength is required, such as valves, fittings, and flanges. However, they cannot be applied in harsh aggressive environments, as subsea oil exploration, due to its vulnerability to corrosion (Ref 1). Low-alloy steel is prone to environmentally assisted failures, as the stress corrosion cracking in the presence of H2S, which might catastrophically affect the component performance (Ref 2, 3). Among several coating techniques applied in harsh environments, nickel-based coatings attract considerable attention in the past years due to its excellent wear/abrasion resistance (Ref 4-6). Electroless Ni-P coatingsÕ properties can be tailored
K.S. Correia, Department of Innovation, CISER, R. Cachoeira, 70, Joinville, SC 89205-070, Brazil; and Department of Mechanical Engineering, Polytechnic School, Pontifı´cia Universidade Cato´lica do Parana´, R. Imac. Conceic¸a˜o, 1155, Curitiba, PR 80215-901, Brazil; and L.G. Greca, L. Sopchenski, P. Soares, F.L. Amorim, and R.D. Torres, Department of Mechanical Engineering, Polytechnic School, Pontifı´cia Universidade Cato´lica do Parana´, R. Imac. Conceic¸a˜o, 1155, Curitiba, PR 80215-901, Brazil. Cont
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