Upload
thindmanmohan
View
9
Download
1
Embed Size (px)
DESCRIPTION
welding
Citation preview
© 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
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
Turn Pages
SearchChapter(Faster
Download)
SearchDocument(Slower
Download)