Effects of Laser Shock Peening on the Surface Integrity of 18 % Ni Maraging Steel

Abstract

Maraging steels represent a special group of ultrahigh strength steels which can be hardened by precipitation of intermetallic compounds at temperatures around 480 °C [1]. These steels have a high content nickel, cobalt, and molybdenum, while the content of carbon, considered an impurity, is kept as low as possible. Commercially available maraging steels can reach yield strengths up to 2400 MPa. In addition to high strength, they are characterized by high resistance to thermal fatigue, high fracture toughness, and good weldability [2]. In order to achieve martensitic transformation during quenching, lower cooling rates are sufficient, and there is less probability for cracking to occur. During age hardening there is very little distortion. Therefore, parts can be machined to final dimensions before the aging process. Maraging steels were primarily developed as high strength structural materials, intended for applications in aeronautical and aerospace. Later on, because of their superior mechanical properties, maraging steels started to be used in the manufacturing of tools [3] such as molds and die-casting dies. Maraging steels are used for the manufacturing of mechanical parts and tools which operate in demanding environments and conditions where they are subject to mechanical fatigue, thermomechanical fatigue, corrosion, and wear. These phenomena have a negative effect on fatigue life and may cause an early failure of the mechanical part.Fatigue behavior of highly stressed metallic components can be significantly improved by mechanical surface treatments [4] such as shot peening (SP) and laser shock peening (LSP). LSP is an innovative surface treatment [5] that can increase the fatigue strength of metallic parts by generating compressive residual stresses in the thin layer of the treated surface. During LSP, the surface of the treated component is exposed to nanosecond long laser pulses of intense energy from 5 J to 100 J [6]. The material in the interaction area with the laser beam vaporizes, and by further absorption of laser energy it ionizes and transforms into plasma. The newly created plasma continues to absorb the laser energy and generates pressure on the surface by transmitting shock waves into the treated material, Fig. 1. When shock wave stresses exceed the yield strength, plastic deformation occurs under the interaction zone between the laser beam and the material. The surrounding material prevents dilatation of the irradiated area of the surface layer, generating compressive residual stresses, which can reach depths up to 1 mm [7]. LSP treatment is far Effects of Laser Shock Peening on the Surface Integrity of 18 % Ni Maraging SteelPetan, L. -Ocaña, J. L. -Grum, J. Luca Petan 1 -José Luis Ocaña 2 -Janez Grum 1,* • Surface integrity of untreated and LSP treated maraging steel specimens was analyzed.• LSP generated compressive residual stresses in the maraging steel surface layer.• Strain hardening of the maraging steel surface layer occurred after LSP.• High compressive residual stresses in combina...

Fatigue Properties of Maraging Steel after Laser Peening

“…The interaction between laser beam size and material affected the propagation nature of the shock waves. Smaller-diameter shock waves probably expand like spheres with a higher attenuation rate than larger-diameter shock waves, which behave like planar fronts [15,16,24,25]. This phenomenon, together with a higher overlapping rate between laser spots, may explain our findings.…”

“…They found out the LSP generated highly compressive RSs in the component surface layer. Petan et al [16] have also shown that LSP with relatively low pulse energy can generate compressive RSs in maraging steel at a level of 500 MPa. When they increased laser pulse density (PD), the surface roughness increased.…”

Influence of reverted austenite on fatigue life of 18 % nickel maraging steel

“…Shot peening increases the high cycle fatigue life and helps to reduce the sensitivity to humid environments [2,18,24,27]. Laser shock peening helps in delaying both crack initiation and propagation [8,9]. Nitriding increases the hardness of the surface and induces compressive residual stress in the surface layer which improves the fatigue life [25,28].…”

Evaluation of Residual Stresses after Irregular Interrupted Machining

“…This undesirable effect causes expenses to repair and renovation of parts. Analysis of residual stress is very important [1,2]. Manufacturing process (machining, forming, welding, etc.)…”