EPNM 2012EPNM 2012

Metallurgical Considerations in Hot Metalworking Bi-Metal

Materials

John BankerVice President Customers & Technology

Dynamic Materials CorporationBoulder, CO, USA

EPNM 2012EPNM 2012Introduction

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

EPNM 2012EPNM 2012

Hot Cylinder Forming

Commonly used for clad steel >100mm thick

Typically performed at approximately-650 C to 900 CDependent upon steel composition and thickness

EPNM 2012EPNM 2012

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

EPNM 2012EPNM 2012Hot 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

EPNM 2012EPNM 2012

Base Metal Metallurgical Concerns

Steels are the dominant clad base metalSteel is selected for mechanical

strength and toughnessBase metal must meet Specification

Requirements after hot working, heat treating, and all fabrication work (UTS, YS, Impacts, etc)

EPNM 2012EPNM 2012

Typical Steel Hot Working Ranges

 

Figure 4. Iron-Carbon Phase Diagram  

Typical Structural Steel Carbon Level

Austenitic Hot Working Range

Ferritic Hot Working Range

EPNM 2012EPNM 2012Typical Steel Heat Treatments to

Achieve Required Properties

900

650

20

Tem

pera

ture

(°C

)

Time (min)

Austentize

Water Quench Cooling + Temper

Normalize (still air cooling)

EPNM 2012EPNM 2012Cladding Metal Metallurgical Concerns

Corrosion Resistant Alloy (CRA) cladCladding metal is selected for specific corrosion

resistanceCladding metal is rarely considered in design

strength calculationsHigh temperature operations must be controlled

to assure corrosion performanceKey Factors: temperature, time at temperature,

heating and cooling rates Time-Temperature-Sensitization Curves show

relationships of Corrosion Properties vs Heat Treatments

EPNM 2012EPNM 2012CRA Groups from Hot Working

Perspective

Stainless Steels:Basic austenitic stainless steels- 304, 316, 321,

347, 317Super austenitic stainless steels- >= 5% MoDuplex stainless steels

Nickel Alloys Reactive metals- Ti & Zr Refractory metals – Ta & Nb

EPNM 2012EPNM 2012

Secondary Phases of Concern in Stainless Steels and Nickel Alloys

(Cr,Fe,Mo)23C6 600 – 950° C Cubic

(Cr,Fe,Mo,Cb)6C 600 – 950° C Cubic

(Cr,Fe,Mo)7C6 950 - 1050° C Orthorhombic

Nitrides (Cr,Fe)2N 650 – 950° C Hexagonal

Sigma σ (Cr,Fe,Mo,Ni) 550 – 1050° C Tetragonal

Laves η (FeCr)2(Mo,Nb,Ti,Si) 550 – 900° C Hexagonal

Chi χ Fe36Cr12Mo10 600 – 900° C Cubic

Carbides

Phase Composition Temperature Range Structure

EPNM 2012EPNM 2012

Austenitic Stainless SteelsCarbide Formation Major Concern

EPNM 2012EPNM 2012

Increased Alloying – Other Phases

EPNM 2012EPNM 2012

Duplex Stainless Steels

EPNM 2012EPNM 2012

Nickel Alloys

Some Alloys Very Slow or No High Temperature Sensitization Nickel 200: Unalloyed NiAlloy 400: 60 Ni – 40 CuAlloy 625: 61 Ni + 22 Cr + 4 Fe + 3.6 Cb + 9

MoAlloy 825: 42 Ni – 22 Cr – 32 Fe + 2.2 Cu + 3

Mo

Others Complex secondary phase development- Example Alloy C Family

EPNM 2012EPNM 2012

Nickel Alloy C Family Ni-Cr-Mo

EPNM 2012EPNM 2012

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

EPNM 2012EPNM 2012

Reactive & Refractory Metals

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

EPNM 2012EPNM 2012Effects of Hot Working on Clad

Interface Properties

Stainless Steels & Nickel AlloysDiffusion w/in +/- 0.5mm of interfaceNo continuous brittle intermetallics

formedSlight decrease in shear strength due

to recovery of Cold Work at interfaceInterface retains toughnessExtremely difficult to disbond

EPNM 2012EPNM 2012Reactive Metal Clad InterfaceConcerns during Hot Working

Ti-Fe, Zr-Fe form several brittle intermetallic compounds

Exposure to Elevated Temperatures can Degrade Clad Interface Properties

EPNM 2012EPNM 2012Shear Strength of Titanium-Steel

EPNM 2012EPNM 2012Larson-Miller Parameter

Titanium – Steel Clad

EPNM 2012EPNM 2012Shear Strength of Zirconium-Steel

EPNM 2012EPNM 2012Reactive Metal Clad Steel

Hot Working Considerations

Optimum temperature range for Heat Teating and Hot Working Reactive Metal Clad is between 550oC – 700oCAvoid unacceptable degradation of interface

propertiesReduction in base metal yield strength at

forming temperatureBelow steel lower critical temperature

• Minimize changes to base metal structure and mechanical properties

EPNM 2012EPNM 2012

EPNM 2012EPNM 2012Typical Segmental Ti Clad Head9 m Diameter x (80 + 3) thick

EPNM 2012EPNM 2012

Hot Working Refractory Alloy Clad

TantalumReadily oxidizes in air above 300C Cold working is typicalIf hot working is mandatory, tantalum must be protected from airSome success with encapsulation in steel

EPNM 2012EPNM 2012Bang & Roll

Stainless 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 propertiesExamples: Duplex, Some C-family alloys

EPNM 2012EPNM 2012Bang & Roll

Titanium – 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

EPNM 2012EPNM 2012

Conclusions

Explosion Clad plates can be formed and fabricated into reliable industrial equipment by Hot Metalworking

With Proper Selection of Alloys & Procedures, no compromise inCladding Metal Corrosion PropertiesBase Metal Mechanical PropertiesClad bond quality

With the Wrong Procedures, it is easy to make expensive trash quickly