Niobium in Fire Resistant Structural Steels David K. Matlock and - - PowerPoint PPT Presentation

David K. Matlock and John G. Speer

Advanced Steel Processing and Products Research Center* Colorado School of Mines Golden, Colorado

Steven G. Jansto

CBMM Reference Metals Bridgeville, Pennsylvania

Niobium in Fire Resistant Structural Steels

Niobium in Structural Steels Armourers’ Hall, London July 6, 2012 *An NSF Industry/University Cooperative

Research Center - Est. 1984 http://aspprc.mines.edu/

Acknowledgements

This presentation based primarily on the following theses: Matthew S. Walp, “Fire-Resistant Steels For Construction

Applications,” MS Thesis, Colorado School of Mines, 2003.

Justin C. Cross, “Effects of Microstructure On The Fire-

Resistant Properties Of HSLA Structural Steels,” MS Thesis, Colorado School of Mines, 2006.

Ryan W. Regier, “Thermomechanical Processing Effects

• n the Elevated Temperature Behavior of Niobium Containing

Fire-Resistant Steel,” MS Thesis, Colorado School of Mines, 2008.

Fire Resistance in Structures

Coatings Design Fire Resistant Structural Materials Cost Effective Fire Resistant (FR) Steels Sprinkler Systems

Tokoname Gymnasium

www.armorfirepro.com Design of Steel Frames to Eliminate Fire Protection, Nippon Steel Corp., 1993.

Background: Fire Resistant (FR) Steels

• Significant Japanese Developments….
• Applications require specifications and building

code acceptance

• Requirement:

Guarantee 2/3 of room temperature yield strength at 600°C

• Enhanced

performance due to microstructural stability; alloy with Mo, Nb, Cr, …..

• R. Wildt (2005)
• R. Wildt, Fire Resistant Steel – A New Approach to Fire Safety, Proceedings of the

7th World Congress, CTBUH, Council on Tall Buildings and Urban Habitat: Renewing the Urban Landscape, New York, 2005. ISBN: 978-0-939493-22-7.

Recent Research at ASPPRC

• Microstructure/alloying parameters of interest
• Starting microstructure
• Hot rolled: ferrite-pearlite
• Control cooled: bainitic, martensitic
• Thermomechanically processed
• Microalloy precipitation
• Prior to fire exposure
• During exposure
• Evaluate testing methods for FR steels
• High temperature tensile
• Constant load test – developed at ASPPRC

Experimental Methods

Tensile Testing = f(T)

(conventional approach)

• Impose constant strain

rate

• Vary heating rate to test T

Constant Load “Accelerated Creep”

(newly developed test)

• Impose constant load
• Heat at constant rate =

100 to 1200 oC/hr

ε σ

Increase Temperature

T3 T2 T1 ε σ

Increase Temperature

T3 T2 T1

Elastic Limit

Temperature or Time Displacement or Strain

Fail Elastic Limit

Temperature or Time Displacement or Strain

Fail

Steel Alloys Alloying elements & Composition (wt%) Base 0.1C - 1.0Mn - 0.2Si - 0.01N Nb Base + 0.02Nb Mo + Nb Base + 0.5Mo - 0.02Nb V + Nb Base + 0.05V - 0.02Nb Cu 1.0Cu - 0.75Ni - 0.51Cr - 0.5 Mo - 0.06V - 0.02Nb

Alloy Matrix

Base alloy V + Nb alloy

0.1 0.2 0.3 0.4 0.5

Plastic Eng. Strain

20 40 60 80 100

• Eng. Stress (ksi)

200 400 600

• Eng. Stress (MPa)

Base Alloy 25°C 100°C 200°C 300°C 400°C 500°C 600°C 700°C 600°C 300°C 500°C 400°C 200°C 100°C 25°C 700°C

0.1 0.2 0.3 0.4 0.5

Plastic Eng. Strain

20 40 60 80 100

• Eng. Stress (ksi)

200 400 600

• Eng. Stress (MPa)

V+Nb Alloy 25°C 100°C 200°C 300°C 400°C 500°C 600°C 700°C

600°C 300°C 500°C 400°C 200°C 100°C 25°C 700°C

Tensile Data - Examples

• M. Walp, MS Thesis, 2003

Strain Rate = 3.9x10-3 s-1 Heating Rate = 600 oC/hr 15 minute hold @ T

Strain Rate = 3.9x10-3 s-1 Heating Rate = 600 oC/hr 15 minute hold @ T

200 400 600

Temperature (°C)

20 40 60 80 100

• Eng. Stress (ksi)

200 400 600

• Eng. Stress (MPa)

400 800 1200

Temperature (°F)

Nb V+Nb Nb Base V+Nb Base Mo+Nb Mo+Nb

Temperature Dependent Tensile Data

• M. Walp, MS Thesis, 2003

Heating Rate Effects – Tensile Data

• M. Walp, MS Thesis, 2003

Mo + Nb Alloy

3.9x10-3 s-1 15 minute hold

400 800 1200

Heating Rate (°C/Hr)

20 40 60 80

• Eng. Stress (ksi)

200 400

• Eng. Stress (MPa)

500 1000 1500 2000

Heating Rate (°F/Hr)

200°C 100°C 400°C 500°C 600°C 300°C

Yield Stress (ksi) Yield Stress (MPa)

Vary heating rate 100 to 1200 oC/hour

550 600 650 700 750 Temperature (°C)

• 0.1

0.1 0.2 0.3 Plastic Displacement (in)

50% YS @ 1200°C/Hr Base Nb Mo+Nb V+Nb

• 0.1

0.1 0.2 0.3 Plastic Eng Strain 1000 1100 1200 1300 1400 Temperature (°F) Mo+Nb Base V+Nb Nb

Constant Load – Accelerated Creep

• M. Walp, MS Thesis, 2003

100 nm

Nb alloy Mo + Nb alloy

• TEM Replicas
• Tested at 50% of room temp. yield stress of Nb alloy
• Heating rate = 300°C/hr

Microstructure after Accelerated Creep

• J. Cross, MS Thesis, 2006

Precipitation during Heating

• M. Walp, MS Thesis, 2008
• 1 % Cu Steel – three

heat treat conditions:

• Normalized (N)
• Maximum precipitation

potential during test

• Peak Aged (P)
• Distribution of fine ppts
• Overaged (O)
• Coarse ppts
• minimum precipitation

potential

500 550 600 650 700 750 Temperature (°C)

• 0.1

0.1 0.2 0.3 Plastic Displacement (in)

50% YS @ 600°C/Hr Cu N Cu P Cu O

• 0.1

0.1 0.2 0.3 Plastic Eng Strain 1000 1100 1200 1300 Temperature (°F) Cu P Cu O Cu N

1% Cu steel

Normalized

Speer, et al., HSLA- 2005.

Importance of Base Microstructure

• C-Mn Alloy: Three heat treat

conditions

• Ferrite-Pearlite (F/P)
• Limited substructure in ferrite
• Bainite (B)
• Martensite (M)
• Result:
• Substructure contributes to

FR properties

• Improvement less than by

using Nb-alloy

560 600 640 680 720

Temperature (°C)

0.025 0.05 0.075 0.1 0.125 0.15

Plastic Strain

1100 1200 1300

Temperature (°F)

F/P

300°C/hr 50% Nb RT YS

Martensite Bainite

• J. Cross, MS Thesis, 2006

• Nb Alloy
• Laboratory Rolled
• Vary Finishing Temperature, 650 to 900 oC

Evaluate Substructure Control by TMP

• R. Regier, MS Thesis, 2003

60 min @ 1100C

) Time (min)

25% @ 1000C 900C 800C 750C 700C 650C Air Cool 10% @

A3 A1

Temperature (oC)

RD

900°C 650°C

TMP: Microstructures – Nb Alloy

Electron Back Scattered Diffraction Images (Combined IQ, IPF, and Misorientation Plots)

• R. Regier, MS Thesis, 2003

50 µm 50 µm

Test T = 25°C 600°C

TMP: Tensile Properties – Nb Alloy

• R. Regier, MS Thesis, 2003

600 700 800 900 Finish Rolling Temperature (°C) 350 400 450 500 550 600 Stress (MPa) 55 65 75 85 Stress (ksi) 1200 1350 1500 1650 Finish Rolling Temperature (°F) UTS YS

• A1

A3 α α+ γ γ 600 700 800 900 Finish Rolling Temperature (°C) 200 250 300 Stress (MPa) 1200 1350 1500 1650 Finish Rolling Temperature (°F) 30 35 40 45 Stress (ksi) YS UTS

• A1

A3 α α+ γ γ

Heating rate = 600 oC/hr UTS UTS YS YS

Effect of Finishing Temperature: 650 to 900 oC

Identical Applied loads

500 550 600 650 700 Temperature (oC)

• 0.1

0.1 0.2 0.3 Plastic Eng Strain 1000 1100 1200 Temperature (oF)

50% Nb RT YS @ 600oC/Hr

900

• C

650

• C

750

• C

800

• C

700

• C

1% offset strain

TMP: Constant Load – Nb Alloy

• R. Regier, MS Thesis, 2003

Effect of Finishing Temperature: 650 to 900 oC

Enhanced properties with sub-critical finishing temperature Finish Rolling Temp. YS Ratio (°C) (%) 650°C 63.1 700°C 57.1 750°C 53.1 800°C 57.6 900°C 59.1

TMP: Constant Load – Nb Alloy

• R. Regier, MS Thesis, 2003

Closing Comments: Fire Resistant Steels

• Mo + Nb steels = improved FR properties with

suitable manufacturabilty

• Substructural refinement leads to improved FR

properties

• Bainite
• Warm worked ferrite
• Precipitation during heating may provide

“active” fire protection

• Precipitate stability in Mo + Nb alloys is under

consideration in ongoing ASPPRC research

Current Status: United States

• New ASTM Standard Approved - 2012
• A1077/A1077M-12 Standard Specification for

Structural Steel with Improved Yield Strength at High Temperature for Use in Buildings

• Codes need to recognize FR steels in design

guidelines.

M.S. Walp, J.G. Speer, and D.K. Matlock, “Fire-Resistant Steels,” Advanced Materials and Processes, Vol. 162, No. 10, October 2004, pp. 34-36. J.G. Speer, S.G. Jansto, J.C. Cross, M.S. Walp, and David K. Matlock, “Elevated Temperature Properties of Niobium Microalloyed Steels for Fire-Resistant Structural Applications,” Proceedings of the Joint International Conference of HSLA Steels 2005 and ISUGS 2005, Iron and Steel Supplement, The Chinese Society for Metals, Beijing, China, Vol. 40, 2005, pp. 818-823. R.W. Regier, J.G. Speer, D.K. Matlock, A.J. Bailey, and S.G. Jansto, “Thermomechanical Processing Effects on the Elevated Temperature Behavior of Niobium Bearing Fire-Resistant Steel,” in CD STEEL: Recent Developments in Steel Processing, Proceedings of Materials Science and Technology (MS&T’07), edited by Matthew J. Merwin, Detroit, MI, USA, (2007), pp 255-266; also published in Proceedings of Steel Properties and Applications Conference, edited by L.C. Oldham, AIST, Warrendale, PA, 2007, pp. 803-814. John G. Speer, Ryan W. Regier, David K. Matlock, and S. G. Jansto, “Elevated Temperature Properties of Nb-Microalloyed ‘Fire Resistant’ Constructional Steels,” Proceedings, New Developments on Metallurgy and Applications of High Strength Steels, edited by Teresa Perez, published by Tenaris, Ternium, and Argentina Association of Materials, Buenos Aires, Argentina, 2008, Paper #117, 13 pages; also published by TMS, Warrendale, PA, 2008, pp. 399-412. R.W. Regier, J.G. Speer, D.K. Matlock and S.G. Jansto, “Ferrite Substructure as an Elevated Temperature Strengthening Mechanism for Fire-Resistant Structural Steel,” Materials Science and Technology (MS&T) 2008, 2008, pp. 1571-1581. J.G. Speer, R.W. Regier, D.K. Matlock, and S.G Jansto, "Nb-Microalloyed Fire Resistant Constructional Steels," Niobium Bearing Structural Steels, ed. by S.G. Jansto and J. Patel, TMS, Warrendale, PA, 2010,

• pp. 139-155.

http://aspprc.mines.edu/

Selected References