Production Gas Carburising

1. Introduction


2. Reasons for Case Carburising

Bending Fatigue

Contact Damage

Wear


3. The Hardening of Steels

Heat Treatment—Heating

The Effect of Slow Cooling

The Effect of Fast Cooling

Hardness and the Carbon Gradient


4. Hardness and Hardenability

Core Hardness and Hardenability

Material Selection—Jominy Data

Variability

Significance of Core Strength

Case Hardness and Hardenability


5. Residual Stresses


6. Design for Carburising

Alternative Processes

Design Considerations

Material Considerations

Process Considerations

Process Specifications


7. Carburising Theory

Reactions within the Gas Phase

Transport in the Boundary Layer

Reactions at the Gas-Metal Interface

Carburising in CH4:H2 Mixtures

Carburising in CO:CO2 Mixtures

Carburising in CO:H2:H2O Mixtures

Carburising in CO:CO2:CH4:H2:H2O:N2 Mixtures

Diffusion

Summary


8. Carburising Atmospheres: Their Production and Control

Introduction

Generator Practice

Control of Endothermic Generators

Nitrogen-Based Atmospheres

Economics

Cost Comparison of Alternative Atmospheres

Control of Carburising Atmospheres


9. Control of the Carburising Process

Introduction

Determination of Required Carbon Profile

Determination of Process Parameters

Process Control

Atmosphere Control


10. Furnaces and Equipment

Furnace Types

Batch Furnaces

Continuous Furnaces


11. Pre-Carburising and Post-Carburising Heat Treatments

Pre-Carburising Heat Treatments

Softening

Pre-Carburising Quenching Treatment

Post-Carburising Heat Treatments

Austenitising for Hardening

Practical Hardening Treatments

Local Hardening

Effect of Austenitising Temperature on Properties

Effect of Quenching

Tempering

Refrigeration


12. Quality Control

Materials Acceptance

In-process Testing

Final Inspection


13. Distortion

Effect of Phase Changes on the Specific Volume of Steel

Thermal Gradients

Stress Relief

Thermal Stresses

Transformation Stresses

Thermal Stresses and Transformation Stresses

Uniformity of Heating and Cooling and Geometry of the Component

Chemical Composition

Effect of Other Production Variables

Post-Hardening Corrective Treatments


14. Microstructures in Case-Hardened Surfaces

Internal Oxidation

Decarburisation

Carbides

Retained Austenite

Bainite


15. Aspects of Safety

Responsibility

Safety in the Heat Treatment Department—General

First Aid

Hygiene

Protective Clothing and Footwear

Fire-Fighting Equipment

Ventilation and Gas Detectors

Parting Comment


16. Concluding Remarks

Appendices

A. An Example of the Use of Fatigue Test Data

B. Continuous-Cooling Transformation Diagrams

C. Cooling Curves

D. Theoretical Determination of Case Depth

Index