Ballistic Testing Of SSAB Ultra-High-Hardness Steel For .

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Ballistic Testing of SSAB Ultra-High-Hardness Steel forArmor Applicationsby Dwight D. Showalter, William A. Gooch, Matthew S. Burkins,and R. Stockman KochARL-TR-4632Approved for public release; distribution is unlimited.October 2008

NOTICESDisclaimersThe findings in this report are not to be construed as an official Department of the Army position unlessso designated by other authorized documents.Citation of manufacturer’s or trade names does not constitute an official endorsement or approval of theuse thereof.Destroy this report when it is no longer needed. Do not return it to the originator.

Army Research LaboratoryAberdeen Proving Ground, MD 21005-5069ARL-TR-4632October 2008Ballistic Testing of SSAB Ultra-High-Hardness Steel forArmor ApplicationsDwight D. Showalter, William A. Gooch, and Matthew S. BurkinsWeapons and Materials Research Directorate, ARLR. Stockman KochSSAB Oxelosund ABApproved for public release; distribution is unlimited.

Form ApprovedOMB No. 0704-0188REPORT DOCUMENTATION PAGEPublic reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gatheringand maintaining the data needed, and completing and reviewing the collection information. Send comments regarding this burden estimate or any other aspect of this collection of information,including suggestions for reducing the burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 JeffersonDavis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing tocomply with a collection of information if it does not display a currently valid OMB control number.PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.1. REPORT DATE (DD-MM-YYYY)2. REPORT TYPE3. DATES COVERED (From - To)October 2008FinalApril 2008–August 20084. TITLE AND SUBTITLE5a. CONTRACT NUMBERBallistic Testing of SSAB Ultra-High-Hardness Steel for Armor Applications5b. GRANT NUMBER5c. PROGRAM ELEMENT NUMBER6. AUTHOR(S)5d. PROJECT NUMBERDwight D. Showalter, William A. Gooch, Matthew S. Burkins, and R. StockmanKoch*1L16226188H805e. TASK NUMBER5f. WORK UNIT NUMBER7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)8. PERFORMING ORGANIZATIONREPORT NUMBERU.S. Army Research LaboratoryATTN: AMSRD-ARL-WM-TAAberdeen Proving Ground, MD 21005-5069ARL-TR-46329. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)10. SPONSOR/MONITOR’S ACRONYM(S)11. SPONSOR/MONITOR'S REPORTNUMBER(S)12. DISTRIBUTION/AVAILABILITY STATEMENTApproved for public release; distribution is unlimited.13. SUPPLEMENTARY NOTES*SSAB Oxelosund AB, SE-613 80 Oxelosund, Sweden14. ABSTRACTThe highest-performing U.S. steel alloys for armor-piercing (AP) bullet protection are manufactured to MIL-DTL-46100E,high-hardness armor (HHA) with a hardness range of 477–534 Brinell hardness number (BHN), and to MIL-A-46099C, dualhardness armor (DHA), which is produced by roll bonding a 601–712 BHN front plate to a 461–534 BHN back plate. Whilethese materials still serve their intended applications, monolithic ultra-high-hardness (UHH) steels with a hardness of 600 BHNor greater have been developed. This class of steels increases AP bullet defeat, reduces armor weight, and eliminates themanufacturing difficulties inherent in DHA. Swedish Steel Oxelösund AB (SSAB) produces a number of grades of steel,which have previously been assessed against AP ammunition. However, SSAB has two UHH armor steels designated ARMOX600T and ARMOX ADVANCE that meet this hardness criteria. ARMOX 600T is a nominal 600 BHN steel while ARMOXADVANCE has a nominal hardness of Rockwell C58-63 ( 650 BHN). This report assesses the performance of these steelsagainst two projectiles that will be used to generate a new military specification for UHH steel armor. The performance ofthese UHH steels will be compared to the current HHA MIL-DTL-46100E specification.15. SUBJECT TERMSarmor plate, steel, armor piercing, ultra-high hard17. LIMITATIONOF ABSTRACT16. SECURITY CLASSIFICATION OF:a. REPORTb. ABSTRACTc. THIS PAGEUNCLASSIFIEDUNCLASSIFIEDUNCLASSIFIED18. NUMBEROF PAGES19a. NAME OF RESPONSIBLE PERSONDwight D. Showalter19b. TELEPHONE NUMBER (Include area code)UL52410-278-7308Standard Form 298 (Rev. 8/98)Prescribed by ANSI Std. Z39.18ii

ContentsList of FiguresivList of Tablesv1.Introduction12.ARMOX Steels23.Experimental Procedure24.Test Projectiles45.Results and Discussion46.Conclusions87.References9Appendix A. ARMOX ADVANCE Photographs11Appendix B. ARMOX 600T Photographs15Appendix C. Data Sheets19Distribution List37iii

List of FiguresFigure 1. Production flow diagram at SSAB for ARMOX steel plate manufacture.3Figure 2. The 0.30-cal. APM2 and 0.50-cal. APM2 test projectiles.5Figure 3. ARMOX 600T and ARMOX ADVANCE plate thickness vs. V50 velocity for the0.30-cal. APM2 at 30 obliquity. .6Figure 4. ARMOX 600T and ARMOX ADVANCE plate thickness vs. V50 velocity for the0.50-cal. APM2 at 30 obliquity. .7Figure A-1. ARMOX ADVANCE (0.30 cal.): 4.8 mm (a) front and (b) back.12Figure A-2. ARMOX ADVANCE (0.30 cal.): 5 mm (a) front and (b) back.12Figure A-3. ARMOX ADVANCE (0.30 cal.): 6 mm (a) front and (b) back.12Figure A-4. ARMOX ADVANCE (0.30 cal.): 7 mm (a) front and (b) back.13Figure A-5. ARMOX ADVANCE (0.30 cal.): 8 mm (a) front and (b) back.13Figure A-6. ARMOX ADVANCE (0.50 cal.): 8 mm (a) front and (b) back.13Figure A-7. ARMOX ADVANCE (0.50 cal.): 10 mm (a) front and (b) back.14Figure A-8. ARMOX ADVANCE (0.50 cal.): 12 mm (a) front and (b) back.14Figure B-1. ARMOX 600T (0.30 cal.): 4.8 mm (a) front and (b) back. .16Figure B-2. ARMOX 600T (0.30 cal.): 5 mm (a) front and (b) back. .16Figure B-3. ARMOX 600T (0.30 cal.): 6 mm (a) front and (b) back. .16Figure B-4. ARMOX 600T (0.30 cal.): 7 mm (a) front and (b) back. .17Figure B-5. ARMOX 600T (0.30 cal.): 8 mm (a) front and (b) back. .17Figure B-6. ARMOX 600T (0.50 cal.): 8 mm (a) front and (b) back. .17Figure B-7. ARMOX 600T (0.50 cal.): 10 mm (a) front and (b) back. .18Figure B-8. ARMOX 600T (0.50 cal.): 12 mm (a) front and (b) back. .18iv

List of TablesTable 1. Chemical composition of ARMOX plate. .3Table 2. Mechanical properties of ARMOX plate. .3Table 3. Projectile and obliquity requirements for ordered thicknesses. .4Table 4. ARMOX 600T and ARMOX ADVANCE plate vs. the 0.30-cal. APM2 projectile at30 obliquity. .5Table 5. ARMOX 600T and ARMOX ADVANCE plate vs. 0.50-cal. APM2 at 30 obliquity. .6v

INTENTIONALLY LEFT BLANK.vi

1. IntroductionThe U.S. armor community is currently engaged in accelerated efforts to deliver lightweightarmor technologies that can defeat armor-piercing (AP) projectiles at reduced areal weights thatare available across a large industrial base. While many of these programs involve theapplication of lower-density metals such as aluminum and titanium, the selection of steel alloysis still competitive for many ballistic and structural applications; the ability to fabricate armorcomponents in both commercial and military operational areas with available equipment andpersonnel is a major advantage of steel solutions. To meet these requirements, the U.S. armorcommunity has increased the availability of quenched and tempered armor steels by updatingcurrent steel military specifications—the most important has been the updated MIL-DTL46100E specification for high-hardness armor (HHA) (1). This improved specification wasnecessary to supply the large steel demands for combat operations in Iraq and Afghanistan. ThisHHA specification allows modern continuous processing technologies to be used efficiently andoffers a new class of auto-tempered high-hard steels.Currently, the highest-performing U.S. steel alloys for AP bullet protection are manufactured toMIL-DTL-46100E, HHA with a hardness range of 477–534 Brinell hardness number (BHN),and to MIL-A-46099C, dual hardness armor (DHA), which is produced by roll bonding a 601–712 BHN front plate to a 461–534 BHN back plate (2). The roll-bonded DHA steels arecomplex to produce and have known production limitations. The U.S. Army ResearchLaboratory (ARL), in conjunction with the Institute of Metal Science of Sofia, Bulgaria,examined improved steel technologies to produce these DHA steels by electroslag remeltingprocesses, but producing DHA steels remains difficult (3). While both these metal specificationsserve their intended applications, considerable overseas efforts to develop monolithic ultra-highhardness (UHH) steels with a hardness of 600 BHN or greater have been accomplished, andsignificant advancements in steel metallurgy have been noted in Sweden, Germany, and France.The improved ballistic resistance of steel as a function of increasing hardness is well establishedin the ballistic community, particularly by Rapacki et al. in the 15th Ballistics Symposium (4).This class of steels should increase AP bullet defeat, reduce armor weight, and eliminate themanufacturing difficulties inherent in DHA. This report will document the development of anew class of ballistic UHH steels that will be defined in a new military specification. There areadditional UHH steels known or in development that could meet this specification.Swedish Steel Oxelösund AB (SSAB) produces a number of grades of steel that have previouslybeen assessed against AP projectiles by ARL (5). However, SSAB currently has available twoUHH armor steels designated ARMOX 600T (6) and ARMOX ADVANCE (7) that will form thebasis of this new specification. Limited evaluation of ARMOX 600T was conducted in Rapackiet al. (4), but this work expands upon that data. ARMOX 600T has a hardness of 570–640 BHN1

while ARMOX ADVANCE has a nominal hardness of Rockwell C58–63 ( 650 BHN). Thisstudy assesses the performance of these steels against two projectiles that will be used togenerate a new military specification for ultra hard steel with two hardness classes: class 1(513–640 BHN) and class 2 (over 640 BHN). The performance of the ARMOX steels will becompared to the current ballistic acceptance requirements of MIL-DTL-46100E.2. ARMOX SteelsSSAB develops, manufactures, and markets heavy steel plate and is located south of Stockholm,Sweden, on the Baltic coast. SSAB ballistic plate is manufactured under the designationARMOX and is available in hardness ranges from rolled homogeneous armor steel (280 BHN) toUHH steel ( 640 BHN). ARMOX steels are known for high toughness in relation to thehardness. ARMOX 600T has been available on the market for about 10 years and is mostly usedas appliqué armor in various applications in combination with steel, aluminum, composites, orother materials. ARMOX ADVANCE is the newest member of the ARMOX family and is alsointended for appliqué armor. As weight is a critical factor in many vehicle projects, the aim is tooffer a higher mass efficiency.ARMOX steels are produced from iron-ore-based metallurgy through blast furnaces, steeldeoxidation in an LD converter, and vacuum treatment, thus resulting in very clean steel. Themodern four-high plate mill allows the possibility to roll with large reductions, resulting in afine-grained microstructure. Depending on the hardness/toughness requirements, the steelundergoes various heat treatments to achieve final properties. The continuous casting productionflow and heat treatment line at SSAB are shown in figure 1. The chemical composition andmechanical properties of three ARMOX alloys are shown in tables 1 and 2. ARMOX 500T has ahardness and ballistic performance that meet the current MIL-DTL-46100E specification and isrepresentative of current high-hardness steels.3. Experimental ProcedureThe ballistic performance of ARMOX 600T and ARMOX ADVANCE steel plates wasdetermined by obtaining the V50 ballistic limit for each plate thickness against the correspondingspecified test projectile. The test methodology is described in detail in the MIL-STD-662F (8).The V50 ballistic limit is the velocity at which an equal number of fair impact completepenetration (target is defeated) and partial penetration (target is not defeated) velocities areattained using the up-and-down firing method. Fair impact is defined as occurring when aprojectile with an acceptable yaw strikes the target at a distance of at least two projectile2

Figure 1. Production flow diagram at SSAB for ARMOX steel plate manufacture.Table 1. Chemical composition of ARMOX plate.C max(%)ARMOX 500T0.32ARMOX 600T0.47ARMOX ADVANCE 0.47GradeSiMn max P ��0.71.00.010S max Cr max Ni max Mo max B 70.0050.0051.53.00.70.005Table 2. Mechanical properties of ARMOX plate.GradeARMOX 500TARMOX 600TARMOXADVANCE480–540570–640Charpy-V–40 oC10 10 mm(J)Minimum 25Minimum 120.2%Yield Strength(N/mm2)Minimum ngation(%)Minimum 87aRC58-6314a1600a2250a9aHardness(BHN)aTypical values.3

diameters from a previously damaged impact area or edge of plate. A complete penetration isdetermined by placing a 0.5-mm (0.020-in) 2024T3 aluminum witness plate 152.6 mm (6.00 in)behind and parallel to the target. If any penetrator or target fragment strikes this witness platewith sufficient energy to create a hole through which light passes, the result is considered acomplete penetration. A partial penetration is any impact that is not a complete penetration. Forthe MIL-DTL-46100E (MR) specification, the V50 ballistic limit is defined as the average of sixfair impact velocities comprising the three lowest velocities resulting in complete penetration andthe three highest velocities resulting in partial penetration. A maximum spread of 45.7 m/s(150 fps) shall be permitted between the lowest and highest velocities employed in determiningballistic limits. The data for the two ARMOX steels are compared to the baseline data of MILDTL-46100E.4. Test ProjectilesThe ARMOX plate samples for this report ranged in thickness (nominal) from 0.189 in (4.8 mm)up to 0.472 in (12 mm). The corresponding test projectiles and plate obliquities required foreach thickness under MIL-DTL-46100E are listed in table 3. The 0.30-cal. APM2 steel coreweighs 5.2 g; with the copper jacket and lead filler, the total projectile weight is 10.6 g. Thetotal length of the projectile is 35.6 mm (1.4 in). This projectile is shown in figure 2. The0.50-cal. APM2 also has a steel core along with a copper jacket and lead filler. The steel coreweighs 25.4 g with a total weight of 44.9 g. The total length is 57.5 mm (2.26 in). Figure 2 alsoshows this projectile in detail.5. Results and DiscussionThe V50 ballistic limits and standard deviation, , for each plate thickness against the 0.30-cal.APM2 were determined experimentally for both the ARMOX 600T and ARMOX ADVANCEplates; the data is shown in table 4. Figure 3 plots the V50 velocities vs. the plate thickness forthe ARMOX 600T and ARMOX ADVANCE plates, as well as the velocity specificationTable 3. Projectile and obliquity requirements for ordered thicknesses.Ordered Thickness Nominalmm (in)4.8 (0.189)–8.00 (0.315)8.00(0.315)–12.0 (0.472)Projectilea0.30-cal. AP0.50-cal. APaTwo types of projectiles are required for the nominal thickness 8 mm (0.315 in).4Angle of Obliquity( )3030

Figure 2. The 0.30-cal. APM2 and 0.50-cal. APM2 test projectiles.Table 4. ARMOX 600T and ARMOX ADVANCE plate vs. the 0.30-cal. APM2 projectile at 30 5678ActualThicknessmm (in)4.52 (0.178)5.46 (0.215)6.32 (0.249)7.42 (0.292)8.36 (0.329)4.52 (0.178)5.38 (0.212)6.40 (0.252)7.34 (0.289)8.33 (0.328)ObliquityAngle( )303030303030303030305V50m/s (ft/s)723.0 (2372)760.1 (2494)781.8 (2565)863.2 (2832)891.5 (2925)666.6 (2187)819.0 (2687)859.5 (2820)905.5 (2971)892.4 (2928)StandardDeviationm/s (ft/s)13.4 (44)15.2 (50)10.1 (33)15.2 (50)14.3 (47)14.0 (46)17.4 (57)13.4 (44)17.1 (56)12.2 (40)

31009008002300700600190011000.10500MIL-DTL-46100E (MR)Armox 600T2nd Order Fit2 CurveArmox Advance2nd Order Fit2 Curve15000.150.200.250.30V50 Velocity m/sV50 Velocity (fps)27004003000.35thickness (inches)Figure 3. ARMOX 600T and ARMOX ADVANCE plate thickness vs. V50 velocity for the 0.30-cal. APM2at 30 obliquity.requirements for high-hard steel (MIL-DTL-46100E). The 2 curve (V50 – 2 ) is also plottedfor each steel; this curve accounts for the fact that the V50 only provides the velocity at which thearmor defeats the penetrator 50% of the time. Subtracting 2 from the V50 velocity provides thestatistical velocity at which the armor will defeat the penetrator 98% of the time. The V50ballistic limits and for each plate thickness against the 0.50-cal. APM2 for ARMOX 600T andARMOX ADVANCE plates are shown in table 5. Figure 4 plots the V50 vs. the plate thicknessfor the ARMOX 600T and ARMOX ADVANCE plates, as well as the specificationrequirements for high-hard steel (MIL-DTL-46100E).Table 5. ARMOX 600T and ARMOX ADVANCE plate vs. 0.50-cal. APM2 at 30 minalThickness(mm)8101281012ActualThicknessmm (in)8.36 (0.329)10.41 (0.410)12.25 (0.482)8.33 (0.328)10.29 (0.405)12.24 (0.482)ObliquityAngle( )3030303030306V50m/s (ft/s)691.9 (2270)754.3 (2475)826.0 (2710)725.7 (2381)788.2 (2586)824.7 (2706)StandardDeviationm/s (ft/s)6.5 (28)13.1 (43)14.3 (47)11.0 (36)14.3 (47)13.4 (44)

2800V50 Velocity (fps)24007002200Armox 600T2nd Order Fit2 CurveArmox Advance2nd Order Fit2 CurveMIL-DTL-46100E (MR)200018000.30.40.5V50 Velocity (m/s)80026006000.6thickness (inches)Figure 4. ARMOX 600T and ARMOX ADVANCE plate thickness vs. V50 velocity for the 0.50-cal.APM2 at 30 obliquity.The ballistic advantage of increased hardness can be seen in figures 3 and 4 where both theARMOX 600T and ARMOX ADVANCE are significantly better-performing steels thanstandard high-hard steels. The data points for each thickness are plotted, and a second order fitto the data is shown in the solid lines. The solid lines at the bottom of the graphs are also secondorder fits that define the acceptance velocities under MIL-DTL-46100E for the respectivethickness. These lines already incorporate 2 reduction, which provides an acceptable varianceto allow the high-hard plate to meet the specification. Therefore, the best direct comparisons tothe baseline high-hard acceptance lines are the dashed 2 lines of the ARMOX 600T andARMOX ADVANCE plates over the thickness range tested.The 0.30-cal. data for both ARMOX steels of figure 3 show a performance inflection in the dataat the 4.8-mm thic

while ARMOX ADVANCE has a nominal hardness of Rockwell C58–63 ( 650 BHN). This study assesses the performance of these steels against two projectiles that will be used to generate a new military specification for ultra hard steel with two

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