Production Experience with New Heavy Plate Grades for Bridges and Shipbuilding Using Microalloying

Alexander D. Wilson

Mittal Steel USA 139 Modena Road

Coatesville, PA 19320 Tel.: 610-383-3105 Fax: 610-383-2175

Email: alex.wilson@arcelormittal.com

Key words: High Performance Steel (HPS), High Strength Low Alloy (HSLA) Quenching and Tempering (Q&T), Thermal-Mechanical-Controlled Processing (TMCP), Microalloy, Weldability, Bridges,

Shipbuilding

INTRODUCTION Over the past decade, research and development activities in the steel bridge and Navy shipbuilding industries have led to the implementation of improved high strength plate steels. With improved weldability and toughness, microalloying additions were an important part of the alloy design of these grades. The development of these new grades started with a requirement of low sulfur levels, as low as 0.002% maximum, with calcium inclusion shape control. This helped provide a basis for improved toughness in all orientations with resistance to lamellar tearing during welding. Plate production of these improved grades also utilized the optimum processing for high strength plate steels using either/or/both quenching and tempering (Q&T) and thermal-mechanical-controlled-processing (TMCP). These processes are schematically shown in Figure 1. The grades that were developed used V, Cb and/or Ti for strengthening and grain refinement characteristics. The grades that were developed were as follows:

Figure 1 - Processes for Producing Plate SteelsConventionalConventional

ProcessingProcessingThermoThermo--MechanicalMechanical

Controlled Processing (TMCP)Controlled Processing (TMCP)

Heat TreatmentHeat TreatmentHotRolling

Air Cool

Normalizing

Air Cool

Air Cool

ControlledRolling

Air or W

ater Cooled

Quenching & Tempering

Water Q

uench

AcceleratedCooling

Water Spray

Air Cool

Tem

pera

ture

, °F

0

2400

400

800

1200

1600

2000

Navy Shipbuilding ASTM A945 Grade 65 (HSLA-65)

- Up to 1-1/4” (32 mm) produced by TMCP from continuous cast slabs - Over 1-1/4” (32 mm) to 2-1/2” (64 mm) Q&T for ingots

Steel Bridges ASTM A709 Grades

- HPS 70W – TMCP to 2” (51 mm); Q&T to 4” (102 mm) - HPS 100W – Q&T to 4” (102 mm)

A separate discussion of the development of these new grades and recent production experience will be provided in the following sections.

NEW NAVY STEELS

The U.S. Navy has been using HSLA-80/100 grades on their surface vessels for over 20 years. These grades were developed to replace HY-80/100 because of improved weldability(1). This is demonstrated in Figure 2 (2). Subsequently, the need for improved weldability to replace the traditional American Bureau of Shipping (ABS) grades was identified. Also, a slightly higher yield strength would be provided by an HSLA-65 grade. This resulted in a call to industry for grades that would satisfy these needs. Existing line pipe grades for X65 were chosen as the initial candidates. These C-Mn steels have varying microalloyed additions of V, Cb, and Ti. Both TMCP and Q&T processing were evaluated. Thin HSLA-65 The final specification for HSLA-65 was developed as a commercial specification as ASTM A945(3). The chemistry for plates to 1-1/4” (32 mm) is shown in Figure 3. A Ti addition was made to improve weldment toughness properties. Although the specification allows alternative processing of HSLA-65, plates in this thickness range are most often produced by TMCP. The tensile properties for the grade are 65 ksi (450 MPa) min. yield strength and 78-100 ksi (540 – 690 MPa) ultimate tensile strength. Recent production data is summarized in Figures 4 and 5. These graphs demonstrate that the tensile strength controls the specification, particularly for thinner plate. Also, the Charpy-V-Notch (CVN) impact toughness requirement of 70 ft-lbs.(95 J) @ -40oF (-40 C) is readily met. The microstructure of HSLA-65 is shown in Figure 6, which shows the ferrite-pearlite structure typical of a control-rolled plate.

.30 .40 .50 .60 .70 .80 .90.00

.10

.20

.30

.40

ZONE 1* Safe Under Most Conditions

ZONE IIDepends onConditions

ZONE IIIHigh Under

All Conditions

Figure 2 Figure 2 -- The Graville Weldability DiagramThe Graville Weldability DiagramSusceptibility to HAZ Cracking of Navy SteelsSusceptibility to HAZ Cracking of Navy Steels

CE = C + Mn + Si Ni + Cu Cr + Mo + V6 15 5

+ +

*High Strength Welding Consumables May Require Additional Care

Carbon %

EH-36HY-80/100A,B,

D,E

HSLA-80/100HSLA-65

FIGURE 2

HSLA-65 TMCP CVN Data

0

50

100

150

200

250

300

350

400

0.000 0.200 0.400 0.600 0.800 1.000 1.200 1.400

Thickness, in.

Avg

. CV

N @

-40

F, f

t-lb

subsized dataconverted to full

320 PlatesAvg. CVN 131 ft-lb

Figure 5 -

HSLA-65 TMCP Tensile Data

55.0

60.0

65.0

70.0

75.0

80.0

85.0

90.0

95.0

100.0

105.0

0.000 0.200 0.400 0.600 0.800 1.000 1.200 1.400

Thickness, in.

Stre

ngth

, ks

i

UTS YS

320 PlatesAvg. YS 77.3 ksiAvg. UTS 86.1 ksi

FIGURE 3

Figure 4 -

Figure 3 – A945 Grade 65 Chemistry (max. if no range shown)

C Mn P S Si Ni Cr Mo Cu V Cb Al Ti N

To 1-1/4” .10 1.10 0.25 .010 .10 .40 .20 .08 .35 .10 .05 .08 .007 .012(32 mm) 1.65 .40 .020

Over 1-1/4” - 2.5” .10 1.10 .055 .010 .10 .50 .20 .08 .35 .10 .05 .08 .007 .012(32 mm) (64 mm) 1.65 .40 1.00 .020

Figure 6 Figure 6 -- HSLAHSLA--65 65 –– thinner plates to 1¼”thinner plates to 1¼”MicrostructureMicrostructure

5/8 “ Thick Plate FIGURE 5

HSLA-65, Q&T 1.5-2.5" Thick, Tensile Data

0

5

10

15

20

25

30

65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87

Strength, ksi

num

ber

of T

ests

73 PlatesAvg. YS 67 ksiAvg. UTS 80 ksi

Yield Strength Ultimate Tensile Strength

FIGURE 6

Figure 7 -

An additional Navy requirement for HSLA-65 that is often added is a “precise weight” or “weight controlled” plate. This requirement dictates that plate thickness is controlled very accurately. This is possible at the Mittal Steel USA Burns Harbor, IN 160” plate mill because of 93 isotope thickness gauges that provide immediate feedback of plate thickness across the plate width. Rolling schedules are controlled to produce campaigns of similar width and thickness plates, so that consistent thickness during a mill run is possible. Thick HSLA-65 The success of the thin HSLA-65 development raised interest in a thicker high strength product to provide weight savings on aircraft carrier construction. Once again, an existing grade was considered for this application. API-2Y-60 is a Q&T grade used in offshore platforms. An existing chemistry for up to 3” (76 mm) was available from ingot cast applications. Ingot casting is required because of the very large plates often required for platforms and ship structures. This grade was evaluated to 2.5” (64 mm) and met the 65 ksi (450 MPa) yield strength requirements, as well as CVN specifications. The chemistry is shown in Figure 3 and is identical to the thinner chemistry - except for the higher nickel level allowed. The tensile and CVN impact properties for recent production are shown in Figures 7 and 8. Consistent tensile properties have been achieved and excellent toughness demonstrated. The microstructure of this grade is shown in Figure 9. A very refined ferrite-pearlite structure is achieved as a result of the Q&T of this Cb containing chemistry. Both HSLA-65 grades are being widely used in the current construction of aircraft carriers and other surface ships.

HSLA-65, Q&T, 1.5-2.5", CVN Data

0

5

10

15

20

25

30

150 175 200 225 250 275 300 325 350 More

CVN @ -40F, ft-lb

Num

ber

of P

late

s

73 PlatesAvg. CVN 243 ft-lb

FIGURE 7

Figure 8 -

Figure 9 Figure 9 -- Thick HSLAThick HSLA--65 to 2½”65 to 2½”MicrostructureMicrostructure

FIGURE 8

NEW BRIDGE STEELS

Similar to the Navy applications, the U. S. steel bridge industry, together with the Federal Highway Administration (FHWA) has been active over the past 15 years in developing high strength steels with high toughness and improved weldability, referred to as high performance steels (HPS) (4). These grades are shown in Figure 10. The improved weldability is demonstrated in Figure 11. More details of these grades are reviewed below. HPS 70W The chemistry of ASTM A709 HPS 70W (3) is shown in Figure 12. The new grade HPS 70W was an improvement upon a former grade 70W. Lower carbon and sulfur levels, as well as tighter chemistry ranges are required, including a significant V addition to help with strength. The chemistry is used to achieve properties to 2” (51 mm) using TMCP and to 4” (112 mm) using Q&T. A ferrite-pearlite microstructure is shown for both processes, as demonstrated in Figures 13 and 14. The mechanical properties using either processing routes are remarkably similar and robust as noted in Figures 15-17. The only major property challenge has been achieving strength for thicker plate as shown in Figure 18. This led to an increase in the allowed Mn level in thicker plates.

Figure 10 Figure 10 -- Property Requirements for Property Requirements for Current HPS GradesCurrent HPS Grades

HPS 50W HPS 70W HPS 100WUp to 4” Up to 4” Up to 2.5” (101 mm) (101 mm) (64 mm)

Yield Strength, ksi (MPa) minimum 50 (345) 70 (485) 100 (690)

Ultimate Tensile Strength, ksi (MPa) 70 min. (485) 85-110 (586-760) 110-130 (760-895)

CVN of 35 ft.-lbs. (48 J) FCM +10oF (-12oC)* -10oF (-23oC) -30oF (-34oC)

* 30 ft-lbs. (41J)

.30 .40 .50 .60 .70 .80 .90

.00

.10

.20

.30

.40

ZONE 1* Safe Under Most Conditions

ZONE IIDepends onConditions

ZONE IIIHigh Under

All Conditions

Figure 11 Figure 11 -- The Graville Weldability DiagramThe Graville Weldability DiagramSusceptibility to HAZ Cracking of HPS Bridge SteelsSusceptibility to HAZ Cracking of HPS Bridge Steels

CE = C + Mn + Si Ni + Cu Cr + Mo + V6 15 5

+ +

*High Strength Welding Consumables May Require Additional Care

Carbon %

Old 70W Old 100W

HPS 70W

HPS 100W

25 mm Plate ASTM No. 12.3 80 mm Plate ASTM No. 11.2

Figure 13 Figure 13 -- Microstructure of ASTM A709 HPSMicrostructure of ASTM A709 HPS--70W 70W Q&T Plate Comparison at Q&T Plate Comparison at QuarterlineQuarterline

Figure 14 Figure 14 -- TMCP HPSTMCP HPS--70W 70W ControlControl--Rolled, Q&T ChemistryRolled, Q&T Chemistry

3/4 in. (19mm) plate 1 in. (25 mm) plate, approx. ASTM No. 9

Figure 12 Figure 12 -- Chemistries for HPS 70WChemistries for HPS 70WSpecification ModificationSpecification Modification

C Mn P S Si Cu Ni Cr Mo V

Old 70W Min. - .80 - - .25 .20 - .40 - .02

Max. .19 1.35 .035 .04 .65 .40 .50 .70 - .10

HPS 70W (1) Min. - 1.10 - - .30 .25 .25 .45 .02 .04

Max. .11 1.35(2) .020 .006 .50 .40 .40 .70 .08 .08

(1) Calcium treated for inclusion shape control, also requires .010 - .040 A1 and .015 N max.(2) Mn max. to increase to 1.50 for plate over 2.5” thick

Figure 15 Figure 15 -- Comparing Q&T and TMCPComparing Q&T and TMCPHPS 70W; .5 HPS 70W; .5 -- 2 2 ““ thickthick

TMCP 1,365 78.6 4.8 96.0 5.3 129 45

Q&T 424 83.9 6.2 95.9 3.9 141 43

YS UTS LCVNNo. ksi s.d. ksi s.d. @-25 ft-lb. s.d.

HPS 70W CV Q&T

-10F CVN Data vs. Thickness

0

50

100

150

200

250

300

350

400

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

thickness, in.

CVN

, ft-

lbs

Average 152 ft-lb1519 plates

FIGURE 15

Figure 16

HPS 70W BH TMCP -25F CVN Data vs. Thickness

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

400.0

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

thickness, in.

CVN

, ft-l

b

Average 148 ft-lb445 plates

FIGURE 16

Figure 17

HPS 100W The development of the HPS 100W grade was again an industry joint activity (5). The development was based upon the Navy work on HSLA-100 using Cu-Ni alloying with other alloy additions. HPS 100W has a Cb addition for grain refinement and V addition to smooth out the tempering curve in this Q&T alloy. Figure 19 shows the chemistry of the specification. A range of microstructures can be found in the alloy ranging from martensite in thin/surface locations and acicular ferrite in the thicker locations, as shown in Figure 20. Figure 21 demonstrates that good properties are achievable through 4” (102 mm). The excellent properties on an initial application for the grade are summarized in Figures 22 and 23.

HPS 70W Yield Strength vs Gauge 2001 thru Sept 2003

y = -1.5889x3 + 11.02x2 - 26.075x + 101.26R2 = 0.419850

60

70

80

90

100

110

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00

Gauge (in)

Yiel

d St

reng

th (k

si)

FIGURE 17

Figure 18

Figure 19 - Comparison of Chemistries forTraditional and HPS Versions of 100W

C Mn P S Si Cu Ni Cr Mo VTraditional 100W (2, 3)

Min. .10 .60 - - .15 .15 .70 .40 .40 .03

Max. .20 1.00 .035 .035 .35 .50 1.00 .65 .60 .08

HPS 100W (1,2,4)

Min. - .95 - - .15 .90 .65 .40 .40 .04

Max. .08 1.50 .015 .006 .35 1.20 .90 .65 .65 .08

(1) Calcium treated for inclusion shape control(2) 2-1/2” (65 mm) max. thickness(3) contains .001B(4) contains .01/.03 Nb, .02/.05 Al and .015 max. N

Figure 20 - Jominy Test Microstructures of Production Heat - As-Quenched

FIGURE 19

Figure 21 Figure 21 -- HPS 100W Production ResultsHPS 100W Production Results

0

20

40

60

80

100

120

140

160

180

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Thickness, in

CVN

@ _

30F,

ft-lb

Heat 1Heat 2

FIGURE 20

Figure 22 Figure 22 -- HPS 100W HPS 100W –– Tensile DataTensile Data

0

5

10

15

20

25

30

100.

0

104.

0

108.

0

112.

0

116.

0

120.

0

124.

0

128.

0

Strength, ksi

num

ber

Yield Stren.U.T.S.

57 plates 0.875” Thick

AveragesYS – 112

UTS – 119Y/T – 0.94

SUMMARY

The value of microalloyinig additions of Cb, V and Ti are shown for new grades of high strength, welded plate steels for uses in U. S. Navy shipbuilding and for steel bridges. The benefits included refined microstructures and improved strength in both TMCP and Q&T produced grades of steel. These grades are all being widely used today throughout the U.S.A. in steel bridges and Navy shipbuilding.

ACKNOWLEDGEMENTS

A portion of the research work reported herein was carried out under the guidance of the FHWA/AISI/Navy High Performance Steel Steering Committee. Some of the research work was reported to the Carderock Division, Naval Surface Warfare Center and was sponsored by the Federal Highway Administration. The commercial plate production was carried out at Mittal Steel USA plate facilities in Burns Harbor, IN, Coatesville, PA and Conshohocken, PA. The author would like to acknowledge the input and assistance of the staffs of the Mittal Burns Harbor, Coatesville and Conshohocken plate mills and Mittal Steel Research Laboratories.

REFERENCES 1. E. J. Czyryca, et.al., “Development and Certification of HSLA-100 Steel for Naval Ship Construction”, Naval Engineers Journal,

May 1990, pp. 63-82. 2. Graville, B.A., “Cold Cracking in Welds in HSLA Steels,” Welding of HSLA (Microalloyed) Structural Steels, ASM, Nov. 9-12,

1976. 3. American Society of Testing and Materials, 2007 Annual Book of ASTM Standards, Vol. 01.04, A945, A709, West

Conshohocken, 2007. 4. Wilson, A. D., “Properties of Recent Production of A709 HPS 70W Bridge Steels”, International Symposium on Steel for

Fabricated Structures, ASM International, 1999. 5. Wilson, A. D., Gross, J. H. Stout, R. D., Asfahani, R. L., Manganello, S. J., “Development of an Improved HPS 100W Steel for

Bridge Applications”, International Symposium on Microalloyed Steels, ASM International, 2002.

Figure 23 Figure 23 -- HPS 100W HPS 100W –– CVN DataCVN Data

0

5

10

15

20

25

30

120 130 140 150 160 170 180 190 200 210 220 230

CVN@-30F, ft-lb

num

ber

57 plates 0.875” Thick

Average 160