Date of Award

31-8-2024

Document Type

Thesis

School

School of Mechanical Engineering

Programme

Ph.D.-Doctoral of Philosophy

First Advisor

Dr.S.Venugopal

Second Advisor

Dr.R.Chandramouli

Third Advisor

Hot Compression Test, Low Carbon Steel, Processing Maps, Heat Treatment, Low Cycle Fatigue Test

Abstract

EN353 is a low carbon alloy steel, predominantly used in the manufacturing of heavy-duty gears, shafts, and pinions, especially crown wheel and pinions. It is usually carburized, hardened, and tempered to produce a hard, wear-resistant case. Heat- treated EN353 steel exhibits enhancement in ductility, toughness, strength, and hardness as the internal stresses get relieved in the material. Spheroidizing of medium and high carbon steel is a method of prolonged heating at a temperature below the eutectoid temperature, where pearlite, the lowest energy arrangement of steel, gets converted to ferrite and cementite.

The graphite content of steel assumes a spheroidal shape, and after prolonged heating the pearlite layers are broken down, and spherical lumps of cementite or spheroidite are found. The structures in spheroidite are much larger than those of pearlite and are spaced further apart, making the steel extremely ductile. However, for low-carbon steels, which are soft and ductile in nature, pre-heat treatment enhances the workability. In this work, EN353 steel billets which are used as preforms for the cold forming process are heat treated to possess properties that meet the service demands through microstructure evolution.

Hot compression test is carried out over a broad processing spectrum and the influence of the processing parameters on flow stress is assessed. Using the experimental data, the safe and unsafe processing domains for EN353 steel is identified using Dynamic Material Modeling technique which needs to be integrated with the ideal processing parameters. An Artificial Neural Network model and a mathematical model are developed to predict the flow behavior of the steel in the preferred processing spectrum. Also, the effect of heat treatment on the material’s fatigue behaviour is studied using low cycle fatigue test.

The heat treatment cycle is designed to integrate the preform preparation and the cold forming process for heat treated EN353 steel. The heat-treated steel became softer with improved ductility and toughness without considerable grain coarsening. Grain sizes of the steel after heat treatment were found to be ranging from ASTM number 5 to ASTM number 8 (i.e. average grain diameter of 0.022 mm to 0.062 mm). The fatigue life of EN353 steel has improved significantly (increased by 50%) but at the expense of its strength. The ideal high temperature processing domains for the EN353 steel were identified to optimize the preform preparation for the orbital cold forming process.

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