Stainless steels are classified according to their matrix structure. (a) austenitic (b) ferritic (c) martensitic (d) precipitation hardened and (e) duplex. Special features of stainless steels related to welding. 1. Low thermal conductivity (50% of mild steel) results in less heat input for the job and 10% less current is needed for SS electrodes. higher […]

• The most important consideration is the oxide film. • Use of DC reverse polarity (electrode +) is effective for MIG welding while AC is used for TIG welding of Aluminium. • In AC tungsten inert gas (TIG) welding, when electrode is +ve the oxide of plate is cleaned by ionic bombardment and when it […]

Some materials are easily weldable while certain others require special procedures to weld them. These materials are called difficult to weld materials. The welding of the following such materials will be discussed in this chapter. 1. Welding of cast irons 2. Welding of aluminium and its alloys 3. Welding of low carbon HY pipe steels […]

The electrical resistance could be used as a source of heat. It could be (a) contact resistance of interfaces or (b) Resistance of molten flux and slag Resistance of each hemispherical constriction R = p(r2 — r1)/S where p = resistivity of material (r2 — rx) = length of current path S = geometric mean […]

Calculation and comparison of cooling rates require careful specification of conditions, be- cause it varies with position and time. Most useful method is to determine the cooling rate on the center line of the weld at the instant the metal is passing through a particular tempera- ture of interest, Tc. At temperatures well below melting, […]

For this calculation the outer extremity of the HAZ must be clearly identified with a specific peak temperature. For example for most carbon or alloy steels, there is a distinct etching boundary (as observed on polished and etched weld cross-section), corresponding to a peak temperature of 730°C. Now the problem reduces to the determination of […]

An important parameter that needs to be calculated is the peak temperature reached at any point in the material during welding. The cooling rate from this peak temperature will deter­mine the metallurgical transformations likely to take place in the HAZ. л/2ne pcty 1 1 …(1) (Tp T0) — t-‘net where e = base of natural […]

In many situations, in practice, we are interested in determining the minimum heat input rate ‘Q’ in watts required to from a weld of a given width ‘w’ in a ‘V grove as shown in the Fig. 6.1. It can be calculated* for two dimensional heat source or a three dimensional heat source using equations […]

Q h H AEI where Hnet = — There is a simple but important relationship between the weld metal cross-section. Aw energy input : f2 Hnet _ Л f 2 H A.. = Q J/s. Heat required for melting in Joules/mm3 E = voltage supplied in volts. I = current consumed in Amp. v = […]

The amount of heat input to the weld at its rate determines the geometry of the weld bead deposited and the width of the heat affected zone. It also affects the microstructure of the weld and heat affected zone, which in tern affects the mechanical properties of the joints obtained. In the following paragraphs we […]