Interstitial-Free Steel in Hydroforming Applications

Transcription

1 Great Designs in Steel, Feb Interstitial-Free Steel in Hydroforming Applications Mike Thorpe Product Applications, Stelco

2 Outline Introduction Steel Production Comparison of Production Processes Strain Ageing Facility Photos Tube Making Tube Bending Hydroforming Evolution of Properties Conclusion

3 Introduction What is IF steel? Is this a new product? What are its properties? Yield Strength Tensile Strength Elongation r-value n-value HyForm 27 ksi 44 ksi 47% (IF) 186 MPa 303 MPa P-A 28 ksi 45 ksi 43% MPa 310 MPa

4 Comparison of Production Processes Conventional Steel IF Steel BOF BOF Continuous Casting Hot Rolling Pickling Cold Rolling Continous Galvanizing Line Batch Anneal Precipitate Fe3C Temper Roll SHIP RHOB Vacuum Degasser Remove carbon (<0.005%) Add Ti and/or Nb Continuous Casting Hot Rolling Pickling Cold Rolling Continous Galvanizing Line & In-Line Temper Mill SHIP

5 Strain Ageing Symptoms include increase in yield strength and loss of ductility after long storage times. Phenomenon is accelerated by application of small amounts of strain and heat. Free carbon is the main culprit it accumulates at dislocations inhibiting plastic deformation. A larger problem with hot dip coated steel because of the relatively high cooling rate after the zinc pot, leaving free carbon. Strain ageing can be prevented by eliminating free carbon.

6 Strain Ageing The Production of Conventional Steel The Production of IF Steel BOF BOF Continuous Casting Hot Rolling Pickling Precipitate the carbon as Cold Rolling Fe 3 C using a long annealing cycle. Continous Galvanizing Line Batch Anneal Precipitate Fe3C Temper Roll SHIP RHOB Vacuum Degasser Remove carbon (<0.005%) Add Ti and/or Nb Continuous Casting Remove as much carbon as possible. Hot Rolling Precipitate the Pickling rest as TiC or NbC (stable at subsequent Cold Rolling annealing temperature). Continous Galvanizing Line & In-Line Temper Mill SHIP

7 Facility Photos: Charging the BOF

8 Facility Photos: RHOB Vacuum Degasser

9 Facility Photos: Continuous Casting

10 Facility Photos: Continuous Casting

11 Facility Photos: Hot Rolling

12 Facility Photos: Hot Rolling

13 Facility Photos: Pickling

14 Facility Photos: Cold Rolling

15 Facility Photos: Galvanizing

16 Facility Photos: Galvanizing

17 Facility Photos: Batch Annealing

18 Facility Photos: Shipping

19 Facility Photos: Tube Making Conditions for Strain Ageing: Strain from roll forming and sizing Heat generated during forming Heat from welding Heat from normalizing / annealing

20 Tube Making Weld Characteristics No HAZ softening on either material Narrower HAZ on HyForm (IF) Lower peak hardness on HyForm (IF)

21 Tube Bending J. Gillanders: Pipe and Tube Bending Manual, 2 nd Edition

22 Tube Bending J. Gillanders: Pipe and Tube Bending Manual, 2 nd Edition

23 Tube Bending Better strain distribution on HyForm (IF)

24 Hydroforming Degree of required formability varies with the part and the hydroform process Zones of large expansion Extruded shapes Distance from the tube ends and obstructions to material flow, such as bends Sharpness of radii

25 Evolution of Properties

26 Evolution of Properties

27 Evolution of Properties

28 Conclusion Tube Making is NOT a Problem Better Strain Distribution Significant Work Hardenability Similar Final Part Strength IT WORKS!!!