© COPYRIGHT 1999 THE ESAB GROUP, INC. LESSON I, PART A





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
Lesson 5
Welding Filler Metals for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
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
1.1.0.6 The basic operation of the blast furnace is to reduce iron oxide to iron metal and to remove impurities from the metal.  Reduced elements pass into the iron and oxidized elements dissolve into the slag.  The metal that comes from the blast furnace is called pig iron and is used as a starting material for further purification processes. 1.1.0.7 Pig iron contains excessive amounts of elements that must be reduced before steel can be produced.  Different types of furnaces, most notably the open hearth, electric and basic oxygen, are used to continue this refining process.  Each furnace performs the task of removing or reducing elements such as carbon, silicon, phosphorus, sulfur and nitrogen by saturating the molten metal with oxygen and slag forming ingredients.  The oxygen reduces elements by forming gases that are blown away and the slag attracts impurities as it separates from the molten metal. 1.1.0.8 Depending upon the type of slag that is used, refining furnaces are classed as either acid or basic.  Large amounts of lime are contained in basic slags and high quantities of silica are present in acid slags.  This differential between acid and basic slags is also present in welding electrodes for much of the same refining process occurs in the welding operation. 1.1.0.9 After passing through the refining furnace, the metal is poured into cast iron ingot molds.  The ingot produced is a rather large square column of steel.  At this point, the metal is saturated with oxygen.  To avoid the formation of large gas pockets in the cast metal, a substantial portion of the oxygen must be removed.  This process is known as deoxidation, and it is accomplished through additives that tie up the oxygen either through gases or in slag.  There are various degrees of oxidation, and the common ingots resulting from each are as follows: 1.1.1 Rimmed Steel - The making of rimmed steels involves the least deoxidation.  As the ingots solidify, a layer of nearly pure iron is formed on the walls and bottom of the mold, and practically all the carbon, phosphorus, and sulfur segregate to the central core.  The oxygen forms carbon monoxide gas and it is trapped in the solidifying metal as blow holes that disappear in the hot rolling process.  The chief advantage of rimmed steel is the excel- lent defect-free surface that can be produced with the aide of the pure iron skin.  Most rimmed steels are low carbon steels containing less than .1% carbon. 1.1.2 Capped Steel - Capped steel regulates the amount of oxygen in the molten metal through the use of a heavy cap that is locked on top of the mold after the metal is allowed to reach a slight level of rimming.  Capped steels contain a more uniform core composition than the rimmed steels.  Capped steels are, therefore, used in applications

 

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