Brittle Fracture Behaviors of Large Die Holders Used in Hot Die Forging

Weifang Zhang,Jingyu Zhang,Wei Dai,Hongxun Wang,Yuanxing Huang

doi:10.3390/met7060198

Abstract

Brittle fracture of large forging equipment usually leads to catastrophic consequences. To avoid this kind of accident, the brittle fracture behaviors of a large die holder were studied by simulating the practical application. The die holder is used on the large die forging press, and it is made of 55NiCrMoV7 hot-work tool steel. Detailed investigations including mechanical properties analysis, metallographic observation, fractography, transmission electron microscope (TEM) analysis and selected area electron diffraction (SAED) were conducted. The results reveal that the material generated a large quantity of large size polyhedral M23C6 (M: Fe and Cr mainly) and elongated M3C (M: Fe mainly) carbides along the martensitic lath boundaries when the die holder was recurrently tempered and water-cooled at 250 °C during the service. The large size carbides lead to the material embrittlement and impact toughness degradation, and further resulted in the brittle fracture of the die holder. Therefore, the operation specification must be emphasized to avoid the die holder being cooled by using water, which is aimed at accelerating the cooling.

Highlights

Forging is one of the major production processes in the mechanical industry
The die holder needs to be preheated to 240 ◦ C by using heating rods
The inner bottom of the die holder would directly contact with the die where the temperature is about 250 ◦ C

Summary

Introduction

Forging is one of the major production processes in the mechanical industry. It is an advanced manufacturing technique that provides important engine components. Forging technology is widely used to produce high-performance mechanical parts in both military and civil fields, such as engine blades that are manufactured by hot die forging. The expense of hot forging equipment is quite high, which usually takes a proportion of 8–15% of all the productive task costs. If considering the failures of hot forging equipment and manufacturing loss during the production, the expense will increase to 30–50% [1,2]. Avoiding the failures of hot forging equipment is one of the most significant tasks for the forging industry

Methods

Results

Conclusion