Metallurgical Considerations in Hot Metalworking Bi-Metal Materials

1. Metallurgical Considerations in Hot Metalworking Bi-Metal Materials John Banker Vice President Customers & Technology Dynamic Materials Corporation Boulder, CO, USA

2. Introduction • Explosion Welding is a proven, robust technology for manufacture of flat clad plates and concentric cylinders • Fabrication of these clad components into industrial equipment often requires high temperature metalworking operations • Controlling these procedures to simultaneously assure metallurgical quality of the cladding layer, base layer and interface in the fabricated equipment can be challenging

3. Hot Cylinder Forming • Commonly used for clad steel >100mm thick • Typically performed at approximately- 650 C to 900 C Dependent upon steel composition and thickness

4. Hot Head Forming • Commonly used for clad steel >25 mm tk • Typically performed at approximately- • 500C to 1100 C Dependent upon clad combination, steel type, and thickness

5. Hot Plate Rolling“Bang and Roll” • Typically used to produce clad plates <20 mm tk from thicker clad slabs • Performed at approximately- 750 C to 1150 C Dependent upon clad combination, steel type, and thickness

6. Base Metal Metallurgical Concerns • Steels are the dominant clad base metal • Steel is selected for mechanical strength and toughness • Base metal must meet Specification Requirements after hot working, heat treating, and all fabrication work (UTS, YS, Impacts, etc)

7. Typical Steel Hot Working Ranges Austenitic Hot Working Range Ferritic Hot Working Range Typical Structural Steel Carbon Level

8. Typical Steel Heat Treatments to Achieve Required Properties 900 Austentize Temperature (°C) Normalize (still air cooling) 650 Water Quench Cooling + Temper 20 Time (min)

9. Cladding Metal Metallurgical Concerns • Corrosion Resistant Alloy (CRA) clad • Cladding metal is selected for specific corrosion resistance • Cladding metal is rarely considered in design strength calculations • High temperature operations must be controlled to assure corrosion performance • Key Factors: temperature, time at temperature, heating and cooling rates • Time-Temperature-Sensitization Curves show relationships of Corrosion Properties vs Heat Treatments

10. CRA Groups from Hot Working Perspective • Stainless Steels: • Basic austenitic stainless steels- 304, 316, 321, 347, 317 • Super austenitic stainless steels- >= 5% Mo • Duplex stainless steels • Nickel Alloys • Reactive metals- Ti & Zr • Refractory metals – Ta & Nb

11. Secondary Phases of Concern in Stainless Steels and Nickel Alloys

12. Austenitic Stainless SteelsCarbide Formation Major Concern

13. Increased Alloying – Other Phases

14. Duplex Stainless Steels

15. Nickel Alloys • Some Alloys Very Slow or No High Temperature Sensitization • Nickel 200: Unalloyed Ni • Alloy 400: 60 Ni – 40 Cu • Alloy 625: 61 Ni + 22 Cr + 4 Fe + 3.6 Cb + 9 Mo • Alloy 825: 42 Ni – 22 Cr – 32 Fe + 2.2 Cu + 3 Mo • Others Complex secondary phase development- Example Alloy C Family

16. Nickel Alloy C Family Ni-Cr-Mo

17. Nickel Alloy C Family Ni-Cr-Mo (alt)

18. Reactive & Refractory Metals • Commonly used Reactive and Refractory metals exhibit no significant phase changes that affect corrosion performance • Titanium alloys Grades 1, 2, 16, 17 • Zr alloys 700 & 702 • Tantalum and Ta-2.5W

19. Effects of Hot Working on Clad Interface Properties Stainless Steels & Nickel Alloys • Diffusion w/in +/- 0.5mm of interface • No continuous brittle intermetallics formed • Slight decrease in shear strength due to recovery of Cold Work at interface • Interface retains toughness • Extremely difficult to disbond

20. Reactive Metal Clad InterfaceConcerns during Hot Working • Ti-Fe, Zr-Fe form several brittle intermetallic compounds • Exposure to Elevated Temperatures can Degrade Clad Interface Properties

21. Shear Strength of Titanium-Steel

22. Larson-Miller ParameterTitanium – Steel Clad

23. Shear Strength of Zirconium-Steel

24. Reactive Metal Clad SteelHot Working Considerations • Optimum temperature range for Heat Teating and Hot Working Reactive Metal Clad is between 550oC – 700oC • Avoid unacceptable degradation of interface properties • Reduction in base metal yield strength at forming temperature • Below steel lower critical temperature • Minimize changes to base metal structure and mechanical properties

26. Typical Segmental Ti Clad Head9 m Diameter x (80 + 3) thick

27. Hot Working Refractory Alloy Clad Tantalum • Readily oxidizes in air above 300C • Cold working is typical • If hot working is mandatory, tantalum must be protected from air • Some success with encapsulation in steel

28. Bang & RollStainless Steels & Nickel Alloys • Typical rolling at 1100 C to 900 C • Single slab rolling for clad thickness <10% of total thickness • Pack rolling for greater clad % • Reliable clad thickness uniformity • Reliable product yields • Some cladding alloys not possible to achieve both cladding metal and base metal properties • Examples: Duplex, Some C-family alloys

29. Bang & RollTitanium – Steel Clad • Considerable tonnage of titanium clad has been produced by single slab Bang & Roll • Slabs up to 150mm thick, rolled product down to 5mm thick • Good thickness uniformity and rolling control up to 15% clad ratio • Difficult to achieve both good bond strength AND base metal of Pressure Vessel Quality • Test work by Hardwick indicates that a Nb interlayer may allow higher temperature rolling, possibly reducing the steel quality issues

30. Conclusions • Explosion Clad plates can be formed and fabricated into reliable industrial equipment by Hot Metalworking • With Proper Selection of Alloys & Procedures, no compromise in • Cladding Metal Corrosion Properties • Base Metal Mechanical Properties • Clad bond quality • With the Wrong Procedures, it is easy to make expensive trash quickly