Heat Affected Zone and Weld Metal Properties in Welding of Steels Oct01

Heat Affected Zone and Weld Metal Properties in Welding of Steels...

Heat Affected Zone and Weld Metal Properties in Welding of Steels There are many factors which control the properties of the weld metal and heat affected zone (HAZ) while welding of carbon (C) and low alloy steels. The weld metal and HAZ are frequently referred as steel weldments. The welding processes, welding consumables, and welding parameters have also influence on these properties. Properties of steel weldments are also influenced by the corrosive atmospheres and cyclic loading to which they are frequently being subjected. Heat affected zone During the selection of steels, the characteristics of the HAZ are more important than the weld metal. This is since the metallurgical and mechanical properties of the HAZ are directly linked to the selected steel. However, these properties can be adjusted by welding parameters and post weld heat treatment (PWHT). Also the metallurgical and/or weldability issues related with the HAZ characteristics are more difficult to tackle than those connected with the weld metal. Welding issues which usually occur in the weld metal can frequently be overcome by changing the welding electrode and/or other welding consumables. In comparison, difficulties with the HAZ can often be resolved only by changing the base steel, which is generally a very costly measure, or by changing the heat input. Different empirical C equivalents (CE) have been developed and utilized to evaluate the weldability and the tendency of hydrogen (H2) induced cracking (HIC) of the base steels. The most frequently used equation for CE which is also being used by the International Institute of Welding (IIW) is CE = % C + % Mn/6 + (% Cu + % Ni)/15 + (% Cr + % Mo + % V)/5. In Japan, the Ito-Bessyo composition characterizing parameter, Pcm, is more widely used. Pcm is considered...

Welding of Carbon and Low Alloy Steels and Hydrogen Induced Cracking Sep23

Welding of Carbon and Low Alloy Steels and Hydrogen Induced Cracking...

Welding of Carbon and Low Alloy Steels and Hydrogen Induced Cracking Arc welding is a process by which steels are joined by coalescence. Normally the process uses a compatible filler material. Before a well-bonded joint is produced, the joint surface is to be heated above the melting temperature in order to completely fuse with the weld metal. Though the metallurgical reactions which involve melting, solidification, and solid-state transformation are not unusual, the temperatures and cooling rates observed are severe. Active gases also are present and can dissolve in the fused steel. Fluxes are introduced to alloy with and protect the weld metal. Generally, joints are rigid and restrain dimensional changes caused by shrinkage and solid-state transformations, producing residual stresses of yield-strength (YS) magnitude. Since the metallurgical changes do not occur under equilibrium conditions, and since the stresses are high, many of the reactions can take place in either or both the weld metal and the heat affected zone (HAZ) of the steel and can produce defects that weaken their soundness. Because of the tremendous variability of the welding processes, it is difficult to provide much detail about the exact mechanisms involved or the corrections that can be made. Furthermore, many corrective measures are obvious once most defects are explained. One problem, which relates to hydrogen (H2), is not simple. Since this problem is becoming more relevant as more high-strength, low-alloy (HSLA) steels are being welded, the subject of hydrogen-induced cracking (HIC) is very important. Carbon (C) and low alloy steels are welded since they have widespread application and good weldability. This usefulness is mainly due to the metallurgical characteristics of the iron (Fe) base system. The characteristic includes the ability to undergo allotropic (microstructural) transformation which allows the opportunity for hardening and strengthening through...