Weldability of Steels...

Weldability of Steels There are several factors which control the weldability of carbon (C) and low alloy steels in electric arc welding. A good understanding of the chemical and physical phenomena which occurs in the weldments is necessary for the proper welding of the different steels. Operational parameters, thermal cycles, and metallurgical factors affecting the weld metal transformations and the susceptibility to hot and cold cracking are some of the factors which have marked influence on the weldability of steels. There are also some common tests which determine the weldability of steel. The C and low alloy steels represents a large number of steels which differ in chemical composition, strength, heat treatment, corrosion resistance, and weldability. These steels can be categorized as (i) plain C steels, (ii) high strength low alloy (HSLA) steels, (iii) quenched and tempered (QT) steels, (iv) heat treatable low alloy (HTLA) steels, and (v) pre-coated steels. To understand weldability of steels, it is necessary to have knowledge about the various weld regions. Characteristic features of welds Single pass weldments In the case of a single pass bead, the weldment is generally divided into two main regions namely (i) the fusion zone, or weld metal, and (ii) the heat affected zone (HAZ) as shown in Fig 1. Within the fusion zone, the peak temperature exceeds the melting point of the base steel, and the chemical composition of the weld metal depends on the choice of welding consumables, the base steel dilution ratio, and the operating conditions. Under conditions of rapid cooling and solidification of the weld metal, alloying and impurity elements segregate extensively to the centre of the inter-dendritic or inter-cellular regions and to the centre parts of the weld, resulting in significant local chemical in-homogeneities. Therefore, the transformation behaviour of...