CHRYSLER LLC Document Number:  MS-11418<S> Material Standard Date Published:  2008-10-02 Category Code:  B-1 Change Level:  A EASL Requirement:  Yes
RESTRICTED:  No
PRESS-HARDENED STEEL FOR BODY PARTS
1.0  GENERAL
1.1  Purpose ***
This standard applies to press-hardened sheet steel and parts for the body structure made of boron manganese alloyed steels.  There are two ways these parts can be processed:  (1) Austenitized sheet  blanks are formed and hardened in the press simultaneously (direct press-hardening), or (2) cold formed parts are austenitized and hardened (indirect press-hardening).  In case of coated steel option (2) may not be used if corrosion protection from the Al-Si coating is needed.
1.2  Coverage of this Standard
This standard covers the mechanical properties, weldability, paintability, and surface requirements of this
ultra high strength steel in the hardened condition.  Requirements for in-coming coil steel are also covered in this standard.
1.3  Recycled Content
All procedures, processes, components or systems using this material must conform to current regulatory (Governmental) requirements regarding regulated substances and recyclability.
2.0  MATERIAL CHARACTERISTICS
2.1  Materials Description
This Chrysler engineering standard defines the material designation, steel product type, grade and coating.  The steel product type can be cold rolled or hot rolled.  The yield and tensile strengths for press-hardened steel are designated in megapascals (MPa).  The steel grades will correspond to the requirements shown in Section 3.  Coating designation specifies the type of coating and coating weight for both sides of the sheet.  All of the press-hardened parts for the body structure are unexposed.
3.0  REQUIREMENTS
Additional requirements and restrictions not specified in this document may be imposed depending on the application, and will be listed on the drawing.
3.1  Requirements of the Raw Material
3.1.1  Chemical Composition***
Base metal chemical composition shall conform to the requirements listed in Table 1.  All compositions are wt. % unless noted otherwise.
TABLE 1:  CHEMICAL COMPOSITION OF BORON-MANGANESE STEEL FOR PRESS-
HARDENING
C Mn P S Si Cr Mo B Ti Al N
Element
(%) 0.20 1.0 - - 0.15 - - .0005 - 0.01 - Min
Max (%) 0.26    1.4 0.030 0.0100.35 0.35  0.35 0.004 0.07  0.06 0.009
3.1.2  Coating***
Steel for press-hardening can be protected against scaling and corrosion through the use of hot-dip aluminized coating.  The aluminized (aluminum-silicon) coating will be applied by immersing the sheet steel in a molten bath composed of aluminum and 5-11% silicon.  The coating is designated as the nominal coating mass in grams per square meter per side, indicated separately for each side of the sheet. The coating mass shall be determined using the single spot method in accordance with ASTM A90 with the exception that the coating weight measurement shall be performed on each side of the sheet.
The coating tolerances in Table 2 will apply to the sheet material prior to the press hardening process.
TABLE 2:  TOLERANCES OF COATING MASSES
AND THICKNESSES OF RAW MATERIAL COATING
REQUIRED
Coating
Required values per side
Designation Mass /g/m² Thickness /μm
AL60/60 60 - 100 19 - 33
Examples:
MS-11418<S> AL60/60-1300T:  Hot dip aluminized with minimum coating wt. of 60 g/m2 each side.
MS-11418<S> 1300T:  Uncoated steel
3.1.3  Thickness Tolerances of Raw Materialxposed
The specified thickness on the drawing will be the minimum thickness of the raw material prior to press-hardening and will meet Chrysler standard PS-5570.
3.2  Heat Treatment and Forming (Press-Hardening)
For parts employing AL60/60-1300T, only the direct press-hardening shall be used to prevent any flaking of the coating.
3.3  Mechanical Properties of Press-Hardened Parts
3.3.1  Tensile Test***
Tests are performed per ASTM A370.  The yield stress shall be measured as the 0.2 % yield strength. The total elongation will be measured by using a fixed extensometer gauge length of 50 mm.
A smaller specimen size described in FIGURE 1 is also allowed for tensile testing.  The total elongation in this case will be measured by using a fixed extensometer gauge length of 30 mm.
FIGURE 1:  CHRYSLER SUBSIZE TENSILE TEST SPECIMEN GEOMETERY FOR PRESS-HARDENED
PARTS.
Test Piece Thickness: t = Part Thickness
Test Piece Width: b = 5 mm
Radius: r = 5 mm
Width of Grip Ends: g = 9 mm
Length of Grip Ends: k ≥ 30 mm
Parallel Length: LC = 36 mm
Original (extensometer) Gauge Length: L0 = 30 mm
Overall Specimen Length: Lt ≥ 106 mm
The press-hardened part shall meet the mechanical properties as specified in Table 3.
TABLE 3:  MECHANICAL PROPERTIES OF PARTS MADE OF PRESS-HARDENED
STEEL (PHS)
Grade Coatings Yield Strength / MPa Tensile Strength / MPa Total Elongation/% in 50mm or 30mm
BH 0-Index / MPa 1300T Uncoated and AL60/60
950-1250 1300-1600 ≥ 6 50
3.3.2  Bake-Hardening
The hardened parts shall meet a minimum BH 0-Index of 50 MPa.  Standard test specimens will be taken from as hardened material per ASTM A-370.  These specimens will be divided into two sets.  One set of specimen is subjected to bake treatment before tension testing.
The BH 0-Index shall be determined as follows:
BH 0  = C – B,
Where,
B = 0.2% offset yield strength of hardened steel.
C = 0.2% offset yield strength after the heat treatment of hardened steel (baking @ 177 degrees C for 30 minutes).
3.4  Microstructure of Press-Hardened Parts
The parts must be heated in the furnace and hardened during cooling in the die such that the microstructure is homogenous and uniformly hardened.  Hardening and forming must be performed so as to prevent any cracks from forming in the base material.  To prevent hydrogen embrittlement, hydrogen absorption must be avoided along the process chain. Pickling and the application of electroplated coatings, e.g. electrolytic zinc coating, is not permitted.
3.4.1  Pickle Test
The pickle test is intended to check the sensitivity to hydrogen embrittlement after the passage through pre-treatment for painting.
No cracks shall occur during the pickle test.
Test specification for pickle test:
Pickling Solution 5 % by Weight Sulfuric Acid +/- 0.2% by Weight
Temperature 22°C +/- 2°C
Sample Size Min. 5 Samples
Pickling Time 10 Minutes and then Rinse
Assessment of samples is conducted one hour after the end of the pickling time.  Check the parts for possible cracks using a stereomicroscope or the magnetic inductive method.  In case of larger parts, the test can also be performed on sections determined in coordination with Materials Engineering (the focus shall be on areas with the largest deformation).  Note that the pickling solution shall be prepared fresh for each test cycle and no more than 300 cm² part surface shall be tested in 1000 ml acid.
3.5  Coating and Surface of Press-Hardened Parts***
3.5.1  Hot-Dip Aluminized (AL60/60)
After forming, the layer thickness shall be between 30 and 50 μm, and the surface roughness Rz between 15-25 μm.  To prevent any flaking of the layer, hot-dip aluminized material shall be produced by only direct press-hardening.  No flaking of the coating is permitted.  As a result of the production process, coloration may occur due to a thin oxide layer on the AlSi coating.
The coating thickness measurement on the hardened part shall be performed by means of metallographic sections.
TABLE 4:  TOLERANCES OF COATING THICKNESSES AND
SURFACE ROUGHNESS OF HARDENED PART.
Coating Thickness
(μm) Surface Roughness, Rz ((μm)
AL60/60 30 - 50 15 - 25
3.5.2  Uncoated
For uncoated parts, descaling is performed by shot blasting.  If no additional part requirements exist, the blasting process must ensure a scale-free surface across the entire part surface.
3.6  Corrosion Resistance
Evidence of the corrosion resistance of press-hardened parts shall be provided according to the followi
ng specifications.
Test Part:  Part, cataphoretically electrocoated, and scribe
E-coated in accordance with MS-PB-45-1
Test:  Corrosion test in accordance with test instructions
(LP-463PB-52-01, Chipping Corrosion Test)
Exposure time: 60 cycles
The undercutting, creepback from scribe, is determined in accordance with test
instructions LP-463PB-52-01
TABLE 5:  MAXIMUM CREEPBACK AFTER CORROSION TESTING
Steel Grade Creepback from Scribe (mm)
AL60/60-1300T < 2.0
2.0
1300T < 4.0  QUALITY
Refer to CS-9801 for general quality requirements.
5.0  DEFINITIONS/ABBREVIATIONS/ACRONYMS
ADRESS.  An acronym for "Automated Document Retrieval and Engineering Standards System."
PHS.  An abbreviation for Press-Hardened Steel
6.0  GENERAL INFORMATION
Three asterisks “***” after the section/paragraph header denotes single or multiple technical changes to
the section/paragraph.
Certain important information relative to this standard has been included in separate standards.  To assure the materials submitted meet all of Chrysler requirements, it is mandatory that the requirements
in the following standards be met.
CS-9800 - Application of this standard, the subscription service, and approved sources
CS-9003 - Regulated substances and recyclability
Within Engineering Standards, the Regulatory (Government-mandated) requirements are designated by
<S> and <E> which correspond to Safety and Emission Shields respectively.  The Chrysler-mandated requirements are designated by <D> and correspond to the Diamond symbol respectively.
For specific information on this document, please refer to the contact person shown in the "Publication Information" Section of this document.  For general information on obtaining Engineering Standards and Laboratory Procedures, see CS-9800 or contact the Engineering Standards Department at
engstds@chrysler.

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