Metallurgical Processes and Defects in Steel Products...

Metallurgical Processes and Defects in Steel Products Defects in steel products are defined as deviations in appearance, shape, dimension, macro-structure / micro-structure, and/or chemical properties when compared with the specifications given in the technical standards or any other normative documents in force. Defects are detected either through visual inspection or with the help of instruments and equipments. There are four main metallurgical processes for the manufacture of finished steel products where the steel products can pick up defects. The defects picked up during these processes are (i) casting defects, (ii) rolling defects, (iii) forging defects, and (iv) welding defects. (Fig 1).These defects are described below. Fig 1 Metallurgical processes and steel product defects Casting defects Casting is a forming process which converts liquid steel into a solid product. In foundries liquid steel is cast into complex shapes by pouring of liquid steel into a mould in which it sets to the required shape. In steel plants, liquid steel is normally continuously cast in the form of slab (either thick or thin), bloom or billets. Casting defects are defined as those characteristics which create a deficiency or imperfection exceeding quality limits imposed by design and service requirements. Defects in foundry cast steel products There are in general three broad categories of defects in the foundry cast steel products. These are (i) the major or most severe defects which result in scraping or rejection of castings, (ii) intermediate defects which permit salvaging of castings through necessary repairs, and (iii) minor defects which can be easily repaired. Common defects which generally occur in castings are given below. Porosity – It consists of the spherical holes of varying size, with bright walls, usually evenly distributed and formed due to the gases in the liquid steel. The larger holes...