ADVANCE WELDING: Welding Metallurgy Unit 3 Part 2 Notes

Que3.8. Write short note on weld solidification rate. Answer 1. Weld solidification rate is principally the rate at which weld solidifies in welding. 2. Weld essence solidification rate influences metallurgical structure, parcels and soundness of the weld. 3. The weld solidification time is given by, Where, St = Solidification time, the time lapse from morning to end of solidification at a fixed point in the weld essence, sec. L = Heat of emulsion, J/ mm3 Tm = Liquids temperature of the essence being welded. Que3.9. bandy in brief about the welding metallurgy. Answer 1. The study of welding metallurgy is veritably important because the overall mechanical parcels of a weldment are determined by the characteristic parcels of the individual microstructure present in the weld deposit and the weld heat affected zone. 2. It has long been honored that one of the major problems associated with fabrication by welding arises from the incapability to gain invariant mechanical parcels throughout the weldment. 3. Welding metallurgy is concerned with Melting of electrode and parent essence, ii. Solidification of weld essence, iii. Gas immersion and gas essence responses, iv. Slag essence responses, face marvels, and vi. Solid state responses. 4. Temperature change and change in microstructures introduce volume changes in the area girding the weld and hence beget straining, plastic inflow, residual stresses or indeed cracking. 5. Parent essence is subordinated to a complex thermal cycle with a temperature grade extending from the melting range to ambient temperatures and followed by a cooling cycle convinced by the girding cold essence. Que3.10. Explain the weld essence solidification process. Answer 1. In all metallic systems, solidification is accompanied by the elaboration of heat. 2. In a pure essence the rate of growth is determined solely by the rate of heat birth from the solid- liquid interface. This situation, still, is of purely academic interest in welding, since this position of chastity is noway achieved. 3. The position of chastity in welding operations is similar that isolation always occurs on solidification. 4. As the amalgamation cools through the solidification range, solute is rejected at the solid- liquid interface. 5. Since veritably little mechanical mixing of the liquid occurs in the immediate vicinity of the advancing interface, the rejected solute must be redistributed in the liquid by prolixity. 6. The freezing process is so rapid-fire that diffusional processes can not effectively remove the redundant solute near the interface. Hence, solute enrichment occurs at the moving interface until a dynamic equilibrium is reached. 7. The performing dynamic equilibrium provides an excess of solute in the liquid near the interface with the solute content dwindling to the nominal liquid composition at some distance from the interface. 8. As a result, the effective liquidus temperature varies with distance from the interface. Que3.11. bandy in brief about endothermic gas essence response. Answer 1. In physical( endothermic) result, no emulsion is formed. Advance Welding 3 – 13 H( ME- Sem- 5) 2. It doesn’t inhibit emulsion, but can affect in porosity. 3. Porosity may be caused Due to super achromatism of the molten weld essence with a gas similar as hydrogen, nitrogen or oxygen. ii. By response between two feasts. 4. Heat affected zone may also get embrittled in some cases. 5. The medium of endothermic response is Gas is absorbed up to the maximum solubility and is distributed throughout the weld pool by essence rotation. ii.Fig.3.11.1 shows the solubility of hydrogen in colorful accoutrements at different temperatures. iii. response takes place between gas and essence and between two feasts, , 4Cu O2 2Cu2O G1 2H O2 2H2O G2 Where, G1 and G2 are the free energy changes for two responses. iv. elaboration of gas dissolved in weld pool 1. The gas which has been dissolved in the high temperature portion of the weld pool and is also transferred to cooler regions will form a supersaturated result and will typically be evolved. 2. For gas elaboration to take place there should be a minimal degree of supersaturation and the presence of suitable capitals. 3. The gas bubbles if they come entangled in the fast freezing essence, it’ll give rise to porosity. Que3.12. Explain the mechanics of sediment essence responses. Answer 1. The nature of sediment essence responses is largely determined by the composition of the flux or electrode coating. 2. The form of electrode tip in shielded essence bow welding is illustrated in 3.12.1. The coating forms a cone within which a liquid drop forms. Interaction between sediment and essence takes place originally at the junction between cone and liquid. 3. still, they dissolve at If alloying rudiments are added through the coating. this point and are mixed well enough for the drop, when it detaches, to be nearly homogeneous. 4. This indicates rapid-fire rotation in the drop, due to electromagnetic goods or drag from the gas evolved by the coating. At the same time, the liquid essence is hotted
to a high temperature. 5. In practice the drop profile is by no means as regular as shown in 3.12.1. It’s in a state of constant movement, as is the bow root. This does not, still, affect the introductory figure of the arrangement. 6. In submerged bow welding the bow operates in a depression of liquid sediment and the liquid essence drops constantly transfer through the sediment depression or sometimes around the depression wall. 7. formerly again, because of the high temperature and the large face- tovolume rate of the drop, it’s likely that significant sediment essence responses take place. 8. The deep penetration specific of submerged bow welding may also be applicable to sediment essence responses. Que3.13. Write down the colorful factors affecting changes in microstructure and mechanical parcels of HAZ. Answer colorful factors affecting changes in microstructure and mechanical parcels of HAZ are as follows 1. Welding process used. 2. padding rod composition and the composition of flux in case of carpeted electrodes. 3. The conditions under which the weld is made, i.e., the quantum of oxygen and nitrogen present. 4. The chemical composition of base essence. Que3.14. Write short note on micro and macro structures in weld essence and HAZ. Answer 1.Fig.3.14.1 shows the structure of a weld section. 2. It may be noted that columnar( long stretched) chargers are formed near emulsion faces due to directional cooling of weld towards the centre. 3. Since the inner part of weld cools more slightly it results in an enlarged but regular crystal clear structure. 4. face of weld being in contact with air cools veritably fast and small and slightly stupefied crystal clear structure can be noted there. 5. The parent essence in heat affected zone gests grain growth. 6. In case of thick plate, several passes of weld would be needed and the structure of former weld would be meliorated by the heat in the posterior welding. 7. For single pass welding, post weld heat treatment is desirable to upgrade the weld essence structure.

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