Controlled Atmospheres for Heat Treatment

1 Heat Treatment in Controlled Atmospheres

1.1 Interaction Between Metals and Gas Atmospheres

1.2 Gaseous Constituents of Controlled Atmospheres

1.2.1 Oxygen

1.2.2 Nitrogen

1.2.3 Carbon Monoxide and Carbon Dioxide

1.2.4 Hydrogen

1.2.5 Water Vapor

1.2.6 Hydrocarbons

1.3 Chemical Effects of the Individual Atmosphere Constituents on Metals and Alloys

1.3.1 Equilibrium Conditions between Controlled Atmospheres and Metals

1.3.2 Interpretation of the Equilibrium Constant and Its Application in Controlled-Atmosphere Technology

1.3.3 Oxidation

1.3.4 Calculation of Principal Oxidizing Reactions

1.3.5 Decarburizing Reactions

1.3.6 Calculations for Reactions Involving Decarburization

1.3.7 Reactions Resulting in Sulphide Formation

1.3.8 Controlled Oxidation Effects

1.4 Interchange of Elements Between Atmosphere and Metals and Alloys


2 Methods of Heat Treatment in Controlled Atmospheres and the Principal Atmospheres Employed

2.1 Principal Controlled Atmospheres

2.1.1 Endogas Atmospheres

2.1.2 Exogas Atmospheres

2.1.3 Prepared Nitrogen Base or Monogas Atmospheres

2.1.4 Resume of the Chemistry of Atmosphere Preparation

2.1.5 Dissociated Ammonia

2.2 Controlled Atmosphere Generating Plant

2.3 Main Characteristics of Controlled Atmospheres

2.3.1 Composition, Dew Point and Fields of Application

2.3.2 Relative Usage of Protective Atmospheres

2.3.3 Relative Costs of Producing Protective Atmospheres

2.4 Classification of Annealing Treatments Carried out in Controlled Atmospheres

2.4.1 Bright Annealing

2.4.2 Reducing Annealing

2.4.3 Scale-Free Annealing

2.4.4 Low-scale Annealing

2.5 Classification of Atmospheres According to Their Effects

2.5.1 Inert Atmospheres

2.5.2 Neutral Atmospheres

2.5.3 Active Gas Atmospheres


3 Inert-Gas Atmospheres and Vacuum

3.1 Argon and Helium

3.2 Nitrogen

3.3 Hydrogen

3.4 Vacuum as an Atmosphere


4 Exogas Atmospheres

4.1 Properties of Exogas Atmospheres

4.2 Construction and Operation of Exothermic Gas Generators

4.2.1 Oxygen Removal

4.2.2 Sulphur Removal

4.3 Advantages, Disadvantages and Typical Applications of Exothermic-Base Atmospheres

4.4 Production of Exothermic-Base Atmospheres from Hydrocarbons


5 Prepared Nitrogen-Base or Monogas Atmospheres

5.1 Properties

5.2 Prepared Nitrogen-Base or Monogas Generators

5.2.1 Modern Methods of Monogas Production

5.3 Advantages and Disadvantages of Prepared Nitrogenbase or Monogas Atmospheres and Typical Applications

5.3.1 Applicability as a Function of Temperature

5.3.2 Advantages and Disadvantages of Monogas

5.4 Limitations on the Application of Monogas

5.5 Evaluation of Monogas


6 Endogas Atmospheres

6.1 Theoretical Considerations

6.2 Fuel Gas Bases for Endogas Production

6.2.1 Natural Gas

6.2.2 Propane

6.2.3 Town Gas

6.2.4 Hydrocarbon-Steam Reaction

6.3 Design and Operation of Endogas Generators

6.3.1 Catalysts

6.4 Advantages and Disadvantages of Endogas Atmospheres and Fields of Application

6.5 Production of Endogas from Liquid Hydrocarbons

6.6 Exo-endogas Atmospheres


7 Ammonia-Base Atmospheres

7.1 Types of Ammonia-Base Atmospheres

7.2 Properties of Atmospheres Obtained by the Dissociation of Ammonia

7.3 Design and Operation of Ammonia Crackers

7.3.1 Cylinder Battery

7.3.2 Preparation of Controlled, Protective Atmospheres from Liquid Ammonia

7.3.3 Auxiliary Equipment

7.3.4 Safety Precautions

7.3.5 Handling of Protective Atmospheres Consisting of H2 + N2

7.4 Advantages and Disadvantages of Dissociated/Cracked Ammonia and Typical Applications

7.5 Burnt Ammonia

7.5.1 The "Nitroneal" Process


8 Special Gas Atmospheres

8.1 Steam Atmospheres

8.1.1 Steam Generating Plant

8.1.2 Advantages of Steam Treating

8.2 Gas Atmospheres Prepared by Cracking Organic Liquids

8.2.1 Principles of Preparation

8.2.2 Organic Liquids used to Prepare Controlled Atmospheres

8.2.3 Operating Conditions of the Equipment

8.2.4 Controlled Atmospheres Produced Externally


9 Heat-Treatment Furnaces and Heat-Treatment Processes

9.1 Selection of a Gas Atmosphere

9.2 Annealing of Acid and Heat-Resistant Steels

9.3 Heat Treatment of Electrical, Silicon Steels

9.4 Patenting of Steel Wire

9.5 Hardening of High-Speed Steels

9.6 Heat Treatment of Malleable Cast Iron

9.6.1 Heat Treatment of White-Heart Malleable Cast Iron

9.6.2 Heat Treatment of Black-Heart Malleable Cast Iron

9.6.3 Heat Treatment of Pearlitic Malleable Cast Iron

9.7 Hardening and Tempering

9.7.1 Hardening and tempering of springs

9.7.2 Heat Treatment of Engine valves

9.7.3 Hardening and Tempering of Ball Races

9.7.4 Hardening and Tempering of Mass-Produced Parts

9.8 Bright-Annealing of Copper

9.9 Heat Treatment of Brass Products

9.9.1 Oxidation of Brass

9.9.2 Annealing of Brass Strip and Wire

9.9.3 Tower-Type Furnaces for Heat-Treating Brass Strip

9.10 Annealing of Bronze Wire

9.11 Heat Treatment of Nickel Silver

9.12 Heat Treatment of Aluminum Alloys

9.13 Vacuum Heat Treatment

9.13.1 Equipment for Vacuum Hardening

9.13.2 Hardening of High-Alloy Tool Steels

9.13.3 Vacuum Hardening of Low-Alloy Steels

9.13.4 Heat Treatment of Transformer Sheets

9.13.5 Combined Application of Vacuum and Protective Gas in the Heat Treatment of Copper Wires


10 Heat Treatment of Powder Metallurgical Products in Controlled Atmospheres

10.1 Principles of Powder Metallurgy Processes

10.2 Principal Powder Metallurgical Products

10.3 Production of Metal Powders

10.4 Pre-treatment of Metal Powders

10.5 Pressing of Metal Powders

10.6 Sintering of Powder Metallurgical Products

10.7 Post-treatment of Sintered Products


11 Brazing of Metals in Controlled Atmospheres

11.1 Principles of Brazing

11.2 Technology of Brazing

11.2.1 Brazing Materials

11.2.2 Surface Preparation of Joints

11.2.3 Methods of Heating

11.3 Brazing in Controlled Atmospheres

11.3.1 Box-Type Batch Furnaces

11.3.2 Continuous Brazing Furnaces

11.3.3 Atmospheres Used for Brazing


12 Analysis and Control of Furnace Atmospheres

12.1 Absorption Gas Analyzers

12.1.1 The Orsat (Analyzer) Apparatus

12.1.2 Analyzers Based on the Change in Conductivity of Solutions

12.2 Analyzers Based on the Measurement of Thermal Conductivity

12.3 Analyzers Based on the Measurement of Heat Evolved from Specific Reactions

12.3.1 Instruments Employing the Catalytic Oxidation Technique

12.3.2 Instruments Based on the Measurement of Heat Absorption

12.4 Analyzers Based on Calorimetric Measurements

12.4.1 Instruments Measuring the Calorific Value

12.4.2 Instruments Measuring the Wobbe Number or Index

12.5 Paramagnetic Oxygen Analyzers

12.6 Gas Chromatography

12.7 Analyzers Based on Color Change Reactions (Colorimetry)

12.8 Galvanic Cells as Gas Analyzers

12.9 Analysis and Control of Carbon Potential

12.9.1 Direct Measurement of the Carbon Potential

12.9.2 Indirect Measurement of the Carbon Potential

12.10 Accessories for Measuring Instruments

12.10.1 Sampling

12.10.2 Cooling

12.10.3 Filtering and Dust Removal

12.10.4 Drying

12.10.5 Removal of Corrosive Gases

12.10.6 Gas Pumps

12.10.7 Automatic Change-over Valves

12.10.8 Signal Delay

12.10.9 Flow Meters

12.10.10 Calibration of Gas Analyzers


13 Safety Precautions

13.1 Introduction

13.2 Dangers Associated with Controlled Atmospheres

13.2.1 Danger of Asphyxia—Lack of Oxygen

13.2.2 Danger of Poisoning

13.2.3 Danger of Fire and Fire Hazards

13.2.4 Formation of Hazardous Gas-Air Mixtures

13.2.5 Danger of Explosion Hazards

13.2.6 Dangers Associated with Specific Controlled Atmospheres

13.3 Technical Precautions to Prevent Accidents

13.3.1 Techniques for Purging Furnace Chambers

13.4 The Storage of Gases

13.5 Special Safety Equipment

13.5.1 Safety Equipment for Gas-Generators

13.5.2 Observations Regarding Gas-Fired Furnaces

13.5.3 Lighting of Fuel-Burning Appliances

13.6 General Comments on Safety

13.6.1 Equipment

13.6.2 Personnel

13.6.3 Organization

13.7 First Aid

13.7.1 First Aid in the Case of Burns

13.7.2 First Aid in the Case of Poisoning

References and Bibliography

Index