Introduction

Because welding exposes metal to high temperatures, welders need to understand how metals react to heat. To do this, we examine the properties of metals and how they are measured. Then we investigate the crystalline nature of metals and how heat can cause changes in their crystal structure and properties. We study the effects of alloying elements, the iron-carbon diagram and explain the hardening, tempering, and heat treatment of steel. We also look at steel classification systems and consider the different types of cast iron. With this background, we then look at ways to reduce the negative effects of welding heat on metals.

Fundamentals

What is the difference between metallurgy and welding metallurgy?

Metallurgy is the overall field of extracting and applying metals. Welding metallurgy is a subdivision concerning the behavior of metals during welding, and the effects of welding on the metal's properties.

Why are welders interested in metallurgy and welding metallurgy?

To solve routine fabrication and repair problems, welders must understand:

• Effects of welding on the properties of metals.

• How to correct or minimize the negative effects of welding on metals.

• Hardening, annealing, and tempering of metals, particularly steels.

Mechanical Properties of Metals

What are the four basic types of stresses?

See Figure 12-1.

• Tension

• Compression

• Shear

• Torsion

Figure 12-1: Four types of stress

All stress, however complex, can be described by a combination of two or...