Study of the Catalytic Strengthening of a Vacuum Carburized Layer on Alloy Steel by Rare Earth Pre-Implantation.

Li Li,Xing Xing,Guo Guo,Liu Liu,Huang Huang,Wang Wang

doi:10.3390/ma12203420

Abstract

Conventional carburizing has disadvantages, such as high energy consumption, large deformation of parts, and an imperfect structure of the carburizing layer. Hence, a rare earth ion pre-implantation method was used to catalyze and strengthen the carburized layer of 20Cr2Ni4A alloy steel. In this study, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive microanalysis (EDS), transmission electron microscopy (TEM), and Rockwell/Vickers hardness testing were used to analyze the microstructure, phase composition, retained austenite content, hardness, carburized layer thickness, and carbon diffusion. The results showed that lanthanum and yttrium ions implanted into the 20Cr2Ni4A steel formed solid solutions of rare earth ions and a large number of dislocations, which improved the diffusion coefficient of carbon elements on the carburized surface and the uniformity of the carbon distribution. Simultaneously, rare earth ion implantation improved the structure and hardness of the vacuum carburized layer. Compared to the lanthanum ion implantation, yttrium ion implantation caused the structure of the carburized layer to be finer, and the carbon diffusion coefficient increased by 1.17 times; in addition, the surface hardness of the carburized layer was 61.8 HRC.

Highlights

Since 20Cr2Ni4A alloy steel has excellent surface properties after carburization, it has been widely used for gears and bearings in heavy-duty equipment that is frequently exposed to harsh conditions, such as heavy loads, elevated working temperatures, high frequency vibrations, and high rotational speeds [1,2]
Studies showed that the introduction of rare earth (RE) ions in the carburizing heat treatment of steel or other parts reduces the treatment temperature and increases the carbon activity and the carbon diffusion coefficient during the carburization process; it can improve the structure of the carburized layer [9,10]
The results showed that the addition of RE elements obviously improved the hardness of the carburized layer and decreased the hardness gradient

Summary

Introduction

Since 20Cr2Ni4A alloy steel has excellent surface properties after carburization, it has been widely used for gears and bearings in heavy-duty equipment that is frequently exposed to harsh conditions, such as heavy loads, elevated working temperatures, high frequency vibrations, and high rotational speeds [1,2]. Failures such as wear, pitting, and contact fatigue damage, are more likely to occur on the surface of gears and bearings [3,4,5]. Yan et al [11,12]

Methods

Results

Discussion

Conclusion