# Failure Analysis of Gear on Rail Transit

## TL;DR

This paper analyzes gear failures in high-speed trains to identify root causes and suggest solutions for improving gear reliability.

## Contribution

A standardized analytical procedure is applied to four gear failure cases, revealing new insights into root causes and countermeasures.

## Key findings

- Subsurface slag inclusions in raw materials contribute to gear failure.
- Grinding-induced temper burns and hardness drops are identified as failure factors.
- Inadequate heat treatment and insufficient lubrication lead to premature gear degradation.

## Abstract

The gear transmission system is a safety-critical component in rail transit, typically designed for a service life exceeding 20 years. Failure analysis of such systems remains a key focus for railway engineers. This study systematically investigates four representative cases of premature gear failure in high-speed trains using a standardized analytical procedure that includes visual inspection, chemical analysis, metallographic examination, scanning electron microscopy, and hardness testing. The results identify four primary root causes: subsurface slag inclusions in raw materials, inadequate heat treatment leading to a non-martensitic layer (∼60 μm) at the tooth root, grinding-induced temper burns (crescent-shaped "black spots") accompanied by a hardness drop of ∼100–150 HV, and insufficient lubrication. The interdependencies between these factors and failure mechanisms, e.g., fatigue cracking, spalling, and thermal scuffing, are analyzed. This work provides an evidence-based framework for improving gear reliability and proposes targeted countermeasures, such as ultrasonic inclusion screening and real-time grinding temperature control, to extend operational lifespans.