*Article* **Fatigue Properties of Maraging Steel after Laser Peening**

### **Luca Petan 1, Janez Grum 1,\*, Juan Antonio Porro 2, José Luis Ocaña 2 and Roman Šturm 1**


Received: 30 October 2019; Accepted: 24 November 2019; Published: 28 November 2019

**Abstract:** Maraging steels are precipitation hardening steels used for highly loaded components in aeronautical and tooling industry. They are subjected to thermomechanical loads and wear, which significantly shorten their service life. Improvements of their surface mechanical properties to overcome such phenomena are of grea<sup>t</sup> interest. The purpose of our research was to investigate the influence of pulse density and spot size of a laser shock peening (LSP) process on the surface integrity with the fatigue resistance of X2NiCoMo18-9-5 maraging steel. Surface integrity was analyzed through roughness, residual stress, and microhardness measurements. The tests performed on resonant testing machine confirmed LSP is a promising process for increasing fatigue resistance of a component. Fatigue crack occurs, when the resonance frequency decreases. This moment, when the fatigue crack initiation phase ends and the fatigue crack propagation phase starts, was chosen as the moment of failure. We have proved LSP is a successful method in improving fatigue resistance of maraging steel by appropriate combination of laser spot size and pulse density tested in our research.

**Keywords:** microhardness; residual stresses; resonant fatigue resistance; roughness
