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© COPYRIGHT 1999 THE ESAB GROUP, INC. LESSON I, PART A depending on the material being tested, the shape of the indenter and the load applied, the conversion tables may differ. For example, a material listed as having a hardness of Rb or Rc means its hardness has been determined from the Rockwell "B" scale or the Rockwell "C" scale. 1 . 6 . 11 Coefficient of Expansion All metals expand when heated and contract when cooled. This dimensional change is related to the crystalline structure and will vary with different materials. The different expansion and contraction rates are expressed numeri cally by a coefficient of thermal expansion. When two different metals are heated to the same temperature and cooled at the same rate, the one with the higher numerical coeffi cient will expand and contract more than the one with the lesser coefficient. 1 . 6 . 12 Thermal Conductivity Some metals will absorb and transmit heat more readily than others. They are categorized as having high thermal conductivity. This characteristic contributes to the fact that some metals will melt or undergo transformations at much lower temperatures than others. 1.7 EFFECTS OF THE ALLOYING ELEMENTS Alloying is the process of adding a metal or a nonmetal to pure metals such as copper, aluminum or iron. From the time it was discovered that the properties of pure metals could be improved by adding other elements, alloy steel has increased by popularity. In fact, metals that are welded are rarely in their pure state. The major properties that can be improved by adding small amounts of alloying elements are hardness, tensile strength, ductility and corrosion resistance. Common alloying elements and their effect on the properties of metals are as follows: 1 . 7 . 1 Carbon Carbon is the most effective, most widely used and lowest in cost alloying element available for increasing the hardness and strength of metal. An alloy containing up to 1.7% carbon in combination with iron is known as steel, whereas the combination above 1.7% carbon is known as cast iron. Although carbon is a desirable alloying element, high levels of it can cause problems; therefore, special care is required when welding high carbon steels and cast iron. 1 . 7 . 2 Sulphur Sulphur is normally an undesirable element in steel because it causes brittleness. It may be deliberately added to improve the machinability of the steel. The sulphur causes the machine chips to break rather than form long curls and clog the machine. Normally, every effort is made to reduce the sulphur content to the lowest possible level because it can Lesson 1 The Basics of Arc Welding Lesson 2 Common Electric Arc Welding Processes Lesson 3 Covered Electrodes for Welding Mild Steels Lesson 4 Covered Electrodes for Welding Low Alloy Steels Go To Test Lesson 5 Welding Filler Metals for Stainless Steels Print Lesson 6 Carbon & Low Alloy Steel Filler Metals GMAW,GTAW,SAW Glossary Lesson 7 Flux Cored Arc Electrodes Carbon Low Alloy Steels Lesson 8 Hardsurfacing Electrodes Lesson 9 Estimating & Comparing Weld Metal Costs Lesson 10 Reliability of Welding Filler Metals Current Chapter Table of Contents Turn Pages Search Chapter (Faster Download) Search Document (Slower Download)

Lesson 1 - Basics of Arc Welding

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Page 1: Lesson 1 - Basics of Arc Welding

© COPYRIGHT 1999 THE ESAB GROUP, INC.

LESSON I, PART A

depending on the material being tested, the shape of the indenter and the load applied, the

conversion tables may differ. For example, a material listed as having a hardness of Rb or

Rc means its hardness has been determined from the Rockwell "B" scale or the Rockwell

"C" scale.

1.6.11 Coefficient of Expansion All metals expand when heated and contract when

cooled. This dimensional change is related to the crystalline structure and will vary with

different materials. The different expansion and contraction rates are expressed numeri

cally by a coefficient of thermal expansion. When two different metals are heated to the

same temperature and cooled at the same rate, the one with the higher numerical coeffi

cient will expand and contract more than the one with the lesser coefficient.

1.6.12 Thermal Conductivity Some metals will absorb and transmit heat more readily

than others. They are categorized as having high thermal conductivity. This characteristic

contributes to the fact that some metals will melt or undergo transformations at much lower

temperatures than others.

1.7 EFFECTS OF THE ALLOYING ELEMENTS

Alloying is the process of adding a metal or a nonmetal to pure metals such as copper,

aluminum or iron. From the time it was discovered that the properties of pure metals could

be improved by adding other elements, alloy steel has increased by popularity. In fact,

metals that are welded are rarely in their pure state. The major properties that can be

improved by adding small amounts of alloying elements are hardness, tensile strength,

ductility and corrosion resistance. Common alloying elements and their effect on the

properties of metals are as follows:

1.7.1 Carbon Carbon is the most effective, most widely used and lowest in cost

alloying element available for increasing the hardness and strength of metal. An alloy

containing up to 1.7% carbon in combination with iron is known as steel, whereas the

combination above 1.7% carbon is known as cast iron. Although carbon is a desirable

alloying element, high levels of it can cause problems; therefore, special care is required

when welding high carbon steels and cast iron.

1.7.2 Sulphur Sulphur is normally an undesirable element in steel because it causes

brittleness. It may be deliberately added to improve the machinability of the steel. The

sulphur causes the

machine chips to break rather than form long curls and clog the machine. Normally, every

effort is made to reduce the sulphur content to the lowest possible level because it can

Lesson 1The Basics of Arc

Welding

Lesson 2Common Electric

Arc WeldingProcesses

Lesson 3Covered Electrodes

for WeldingMild Steels

Lesson 4 Covered Electrodesfor Welding Low Alloy

Steels

Go To Test

Lesson 5Welding Filler Metalsfor Stainless Steels

Print

Lesson 6 Carbon & Low AlloySteel Filler Metals GMAW,GTAW,SAW

Glossary

Lesson 7Flux Cored Arc

Electrodes CarbonLow Alloy Steels

Lesson 8HardsurfacingElectrodes

Lesson 9 Estimating &

Comparing WeldMetal Costs

Lesson 10Reliability of Welding

Filler Metals

CurrentChapter Table ofContents

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