Microcracks Reduction in Laser Hardened Layers of Ductile Iron

Eduardo Hurtado-Delgado,Álvaro Aguirre-Sánchez,Argelia Miranda-Pérez,Lizbeth Huerta-Larumbe

doi:10.3390/coatings11030368

Abstract

A study of surface hardening of Ductile Iron (DI) with and without austempering heat treatment was developed. The chemical composition of the material contains alloying elements such as Cu and Ni, that allow to obtain a Ductile Iron Grade 120-90-02, based on ASTM A536, which was heat treated to be transformed to Austempered Ductile Iron (ADI). Specimens of 10 × 10 × 5 mm3 were obtained for application of surface hardening by Nd:YAG UR laser of 150 W maximum power. The parameters used were advance speed of 0.2 and 0.3 mm/s and power at 105, 120, 135 and 144 W; the departure microstructures were fully pearlitic in the samples without heat treatment, and ausferrite for austempered samples. Microstructural characterization of hardened samples was performed were analyzed and martensite and undissolved carbides were identified in the pearlitic samples, while in ausferrite samples it was found finer martensite without carbides. The depth of hardened surface to different conditions and their respective microhardness were measured. The results indicate that the surface hardening via laser is a suitable method for improving wear resistance by means of hardness increment in critical areas without compromising the core ductility of DI components, but the surface ductility is enhanced when the DI is austempered before the laser hardening, by the reduction of surface microcracks.

Highlights

The results indicated that surface melting reduced the wear rate of the Austempered Ductile Iron (ADI) by approximately 37%
The microstructure was measured by image analysis with Image Pro Software and NIS Element coupled to the OM; for the ADI samples (Figure 4b), it was present ausferrite, graphite nodules and austenite islands, and the segregated zones disappeared with the austempering
Surface hardening by laser treatment is reliable, but cracks are generated during the solidification if not properly applied

Summary

Introduction

Characteristics of the Ductile Iron and the Austempered Ductile Iron. Ductile Iron (DI) is commonly used in many engineering applications, like sheet forming dies and rolling mills, as reported in literature [1,2]. Their high manufacturability and machinability represent an excellent combination of economic application performances [1,3,4]. By subjecting the DI to heat treatment, it transforms to Austempered Ductile Iron (ADI), which is essentially a spheroidal graphitic iron with ausferrite microstructure comprising mainly low carbon ferrite (α) and high carbon retained austenite (γ).

Objectives

Results

Conclusion