Various methods are available to reduce the level of residual stresses in welded joints. Heat treatment, overloading, and vibratory treatment can all be used, but the most common method is based on a controlled heating-and-cooling cycle, i. e., thermal stress relief. This technique makes use of the fact that the yield stress of a metal […]

Finally, in our consideration of shrinkage and distortion we must not ignore the impor­tance of heat input. As we have seen in Chapter 2 and 3, the heat from the weld pool during solidification flows into the plate adjacent to the fusion boundary. The width of metal heated to above room temperature is greater than […]

As the weldment is locally heated, the weldmetal and HAZ adjacent to it are at a temperature substantially above that of the unaffected base metal. As the molten pool solidifies and shrinks it causes shrinkage stresses on the surrounding weld metal and HAZ area. In the beginning, the contraction the weld metal applies is small, […]

• Stress relief heat-treatment is defined as the uniform heating of a structure to a suitable temperature, holding at this temperature for a predetermined period of time, followed by uniform cooling (uneven cooling may result in additional stresses). • Stress relief heat treatment is usually performed below the critical range so as not to affect […]

Various thermal and mechanical treatments are often performed on welds to reduce the re­sidual stresses and distortion. They include preheat, postweld thermal treatments, peening, and so forth. These treatments also change the metallurgical properties of weldments. 5.3.1 Reasons for Treatment • To restore the base properties affected by the welding heat. • To modify weld-deposit […]

Among the solid state reactions, the most important phenomenon is the formation of cold cracks or delayed cracks. This type of cracking is confined to steels that can be hardened. These steel contain a hard phase called martensite. The cracks occur after the weld completely cools down, sometimes hours after or even weeks after welding. […]

The absorption of gas from the arc or flame into the weld-pool causes gas-metal reaction (since both the metal and the gas are at higher temperatures). There are two types of such reactions. In the first type the gas may be just dissolved in the liquid metal. In the second type, the gas and liquid […]

Cooling rate increases with welding speed and for a given welding speed the cooling rate in­creases with decreasing weld-pool size. The thermal cycle at any point in the medium is gov­erned by its distance from the moving heat source. As the distance from the heat source in­creases the peak temperature reached decreases and the temperature […]

When SAE 1030 steel is examined under a microscope, it is found to contain mostly ferrite and cementite (alternate layers). Cementite is one of the iron carbides, a hard chemical compound of iron and carbon. When this steel is heated, no change is seen upto Acx temperature. At this temperature, ferrite begins to act as […]

Iron-carbon phase diagram is shown in Fig. 5.4. Steel undergoes definite internal changes when subjected to temperatures above its critical range. If the steel cools naturally from this temperature it returns to its normal condition similar to that found after normalizing. Time needs to be allowed during cooling cycle so that the internal changes that […]