This form of cracking occurs within the base metal at a very short distance away from the fusion line. It occurs in low-alloy and high-alloy steels. The factors responsible for this form of cracking are not, as yet, completely understood. It is known that dissolved hydrogen gas must be present; otherwise underbead cracking does not […]

Many of the defects that occur in pipe welding have, of necessity, already been discussed in previous chapters. In this chapter addi­tional information will be given on the causes of these defects and preventive measures required to avoid their occurrence. The subject will be covered from the point of view of the welder, rather than […]

Distortion caused by welding can seriously affect the alignment and the locational accuracy of a pipe installation unless preventive measures are taken to avoid these problems. While in the last chapter the basic causes of distortion in weld joints were treated, this chapter will show how the distortion in the weld joint can affect the […]

Earlier in this chapter stress was likened to an internal load existing inside of the metal. Stresses in metal are a result of external loads and when the external load is removed, the stresses are relieved. Stresses inside metals can also result from other causes, such as cold working, machining, grinding, heat treating, casting, and […]

During the welding process, the metal adjacent to the weld is also heated. The temperatures existing in a mild steel plate during weld­ing are given in Fig, 11-16. Since the temperatures adjacent to the weld exceed the critical temperatures, the grain size of the metal in this zone is affected. The effect of the welding […]

Cold-working imparts stresses in metals that remain after the cold-working operation is finished. These stresses are called residual stresses. When the cold-working is severe the grains are distorted as a result of this operation (see Fig. 11-17). Machining operations also impart residual stresses in metals as a result of the cold-working effect, the severity depending […]

Alloying elements are added to steel for the following purposes: 1. To increase hardenability 2. To increase strength at ordinary temperatures 3. To improve high-temperature properties 4. To improve toughness 5. To increase wear-resistance 6. To increase corrosion-resistance. When alloys are added in the right amount and in the correct combination, it can be said […]

It is a common experience that metals expand when they are heated. Like any metal, steel will also expand when heated; how­ever, in the region between the critical temperatures, Acb and Ac3, a marked contraction occurs upon heating. This is shown schemati­cally in Fig. 11-14 for a.2 percent carbon steel (AISI 1020). When the steel […]

A slightly modified form of the iron-carbon diagram is shown in Fig. 11 -12. The modification is in the naming of the constituents where, in this case, the names used in this text are inserted in place of the usual Greek names or symbols. The iron-carbon diagram illustrates the temperatures at which the different constituents […]

The constituents in the microstructure of steel determine its prop­erties, to a large extent. Some of the important constituents in steel will now be examined. Ferrite. (Fig. 11-5.) This is a solid solution of a very small percent­age of carbon in iron. It appears at a temperature below 1333F and the iron has a body-centered […]