2. Prepared By: Mr. Prashant S. Kshirsagar (Sr.Manager-QA dept.)

3. -: Content :- 1.Cold working 2.Effect of cold working 3.Work Hardening phenomena 4.Importance of annealing 5.Mechanism of annealing by diffusion process (Recovery, recrystallization & grain growth) 6.Importance of Annealing temperature 7.Importance/Benefits of Hydrogen Gas

4. What is Cold Working? Cold working means the working of metals below their recrystallization temperature. During cold working, strain hardening is observed and also the grains become distorted. The mechanical properties are sensitive to structure and hence they get affected. Besides the mechanical properties, many other properties are also affected due to increase in defect density during cold working.

5. Work hardening:-

6. -: COLD WORKING :- Effect of Cold Working on properties of steel :- Property Degree of cold work Electrical resistance Internal Stresses Tensile Strength Hardness Corrosion resistance Ductility

7. -: Importance of annealing :- Purpose:- The main purpose of the annealing is as follows, To relieve the internal stresses induced due to cold working. Internal stresses are not desirable because they lead to premature, sudden, and brittle failures of the components. They also decrease the corrosion resistance. To reduce the hardness and to increase ductility. To increase the uniformity of phase distribution. To refine the grain size.

8. Process:- The process consist of heating the stainless steel wire at 1050˚ to 1100˚C in the reducing/inert atmosphere (i.e. hydrogen gas) to avoid the oxidation and cooling to room temperature in water. Due to heating martensite will transform into austenite & due to rapid cooling to room temperature this avoid the separation of carbides. This makes the steel soft & corrosion resistant. -: Process of Annealing :-

9. -: Mechanism of annealing by diffusion process :- -: Schematic illustration of the effects of recovery and recrystallization on grain structure. Note the formation of small strain-free grains during recrystallization. :-

10. After annealing After drawing -: MICROSTRUCTURAL CHANGES AFTER ANNEALING :-

11. -: Importance of annealing :-  Why are we doing annealing at 1050 to 1100 deg.C temperatures for each zone? - Carbides which present precipitates at temperature between 425 and 900 deg.C, the annealing temperature should be safely above this limit. As, all carbides should be present in the solution before cooling begins and because CrC dissolves slowly. The highest working temperature should be around 1100 deg.C consistent with limited grain growth.

12. Strings of Delta-Ferrite 1) The higher the delta ferrite, the more transformation martensite is formed and the lower the ductility. As the martensite increases, the ductility decreases and the potential for fracture increases. 2) In corrosive environments, the delta ferrite will reduces corrosion resistance. 3) Greater the quantity of delta Ferrite the more the chances of Hydrogen Embrittlement, the alloy may develop microcracks during welding. -: Effect of delta ferrite on properties of stainless steel: -  Why are we not doing annealing above 1100 deg.C temperatures for each zone?

13. -: MICROSTRUCTURAL CHANGES AFTER ANNEALING :- -: Microstructure of Wire Rod :-

14. -: MICROSTRUCTURAL CHANGES AFTER ANNEALING :- -: Microstructure after wire drawing :-

15. -: MICROSTRUCTURAL CHANGES AFTER ANNEALING :- -: Microstructure after Annealing :-

16. -: Benefits of Hydrogen :- GasDensity [kg/m³] Thermal conductivity (W/mK) Specific heat capacity [kJ/kgK] Nitrogen1.13070.025661.041 Hydrogen0.08130.186114.3 Argon1.6130.017820.5216 Helium0.16140.155.1931 -: Benefits of Hydrogen :- Hydrogen has 7 times more thermal conductivity than nitrogen and 13 times more specific heat capacity. Consequently, hydrogen accelerates the transfer of thermal energy to or from the charge being annealed. At the same time, H2 ensures that the entire charge is heated through more evenly. Hydrogen promotes “surface cleaning” & retains brightness for a prolonged period. Hydrogen eliminates scaling, usually a result of conventional annealing process.

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