I am comparing the mechanical properties of the HAZ of a welded high strength steel using different makes of electrodes which the elemental compositions for both the steel plate and the different electrodes have been carried out. Now sequel to my mechanical test results, I would have to discuss the effects of each element in the respective composition and how they would affect the mechanical properties of the HAZ.
Normally, the term Heat Affected Zone refers specifically to the region of the parent material that has been affected by the welding process but not fully melted. This is in contrast to the Fusion Zone (FZ) which is melted during the welding process and in which parent/filler material mixing occurs. For this reason there is usually no change in the elemental composition of most of the HAZ.
The mechanical properties of HAZ depend on the grain size, so it is important to keep low heat input. Also, some chemical elements can reduce the grain size in the steel composition.
I coincide with H. Coules: if different consumables of the same type, are used to weld the same base metal, with exactly the same heat input, there will not be differences in the ZACs. If the consumables are of different types, it is important to be sure that the same heat input is used (not exactly the same parameters as the different processes have different perfomances)
You need to avoid martensite building in HAZ. For this to happens you need to choose low-carbon and low-hydrogen consumables and max. 200 degree inter-pass temp as well as implementing slow cold-down. Furthermore heat input not to exceed 1.7kJ/mm. I guess your major concern will be to avoid cold cracking after certain service time. This is almost always related to too high residual stresses in the HAZ. This problem could exist also in gas cut edges is work not done properly. Alternatively and to prevent this problem you could resort to ultrasonic peening to relax residual stresses in high-strength steels avoiding heat and hence protecting the parent plate's excellent mechanical properties ( toughness and hardness).
In the HAZ you must avoid the combination of martensite and hydrogen which are the principal cause of the cold cracks. To prevent the martensite, once you cannot change the composition - reducing the Carbon Equivalent, you have to slow down the cooling rate by pre & post heating; to prevent the hydrogen you have to take care about hydrocarbons like grease & solvents and water (humidity in rust, gases, electrodes,etc.). Concerning the electrode, the ones producing higher volume of slag should be the best once the thick slag cover can slow down the cooling rate. The metallic composition itself shall make no difference, once the composition of the HAZ does not change.
Like Harry Coules said, there is no elemental change in the HAZ but there is significant change in the microstructure of the HAZ when using different electrodes. you can find more help from my work . Where there is elemental composition change is within the fusion zone like Harry inferred.
thanks
Thesis COMPARATIVE STUDY OF THE MECHANICAL PROPERTIES OF THE HEAT A...
Our studies are performed on all-weld metal speciments, then the HAZ is not taken into accopunt.
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