DBL_4093_2008-06
June 2008
Mercedes-Benz
Supply Specification
Body components manufactured from press-hardened steel sheets
DBL 4093
BQF available Additional DaimlerChrysler Standards required: DBL 7391, DBL 8457, PPAP PWT 4101, MB Special Terms, VDA 621-415
Supersedes Edition: 07.2006
Refer to Section Changes on page 6
Continued on pages 2 to 8
Issued by: Daimler AG
D-70546 Stuttgart
Standardization (GR/EQS)
Technical responsibility (name): H. Bold Department: PWT/VFT
Plant:
050
Phone: 07031/90-2289 HPC: F155 Technical coordination by Central Materials and Process Engineering
Plant 50, Department PWT/VFT Name: H. Hopf Telephone +49(0)703190-7031 90-2562
Confidential! All rights reserved. Distribution or duplication without prior written approval of Daimler AG is not permitted.
In case of doubt, the German language original should be consulted as the authoritative text.
Product versions and examples
Product version Construction Application examples DBL 4093.00
Press-hardened components
made of bright sheet steel Body components for areas not stressed by corrosion 1
DBL 4093.10
Press-hardened components made of sheet steel with hot-dip aluminum finish
Body components such as A-pillars, B-pillars, roof frames and others, as well as side impact beams and cross beams underneath bumpers DBL 4093.20
Press-hardened components made of sheet steel with
continuous hot-dip galvanized finish
As under product version .10
DBL 4093.90 Press-hardened components made of sheet steel with thermal diffusion zinc coating
As under product version .10
Abbreviated designations
On drawings, in the block for material e.g: Steel DBL 4093.10
in more recent drawings, the DBL for finish and delivery shall be entered in the block for material.
1 Field of application, general requirements
This Supply Specification applies to sheet metal parts for the body structure. These are boron-alloyed steels similar to 22MnB5 which are matched to the hardening process in the press die following heat treatment (austenitization) in the furnace under inert gas or air atmosphere.
Press-hardened components are produced by heating metal sheets or preformed components to a temperature of approx. 900°C, followed by forming and quick cooling in the press die.
1
Product version .00 (bright) shall only be used following approval by the specialist corrosion department (EP/CRK).
2 General properties of the materials, raw materials and supply condition
The materials used for press-hardened components are not standardized with regard to their range of analysis and technological parameters. The product version of this DBL determines the technological properties of the components; see Table 2.
The grades described in this DBL are ultrahigh strength steels with tensile strengths of up to R m = 1600 N/mm2. In order to prevent any hydrogen-induced brittle fractures, care shall be taken to ensure that hydrogen absorption is avoided during the complete manufacturing process and during use in the vehicle.
3 Dimensions and tolerances / Form of supply
3.1 Dimensions and tolerances
For the input stock, the thickness tolerances for continuously hot-dip coated steel sheet and strip in accordance with EN 10143 and continuously hot-rolled uncoated plate, sheet and strip in accordance with EN 10051 shall apply.
4 Technical data
4.1 Input stock
4.1.1 Base materials
For all product versions, the base material corresponds to boron-alloyed steel similar to 22MnB5. The designation 22MnB5 describes commercially available grades. It is intended as an example of the manufacturers' grades which fulfilled the requirements of this DBL at the time of going to print.
4.1.2 Coating
Product versions .10 and .20 are protected against scaling and corrosion by their hot-dip refining process. Product version .10 is hot-dip coated with an aluminum silicon coating AS150 in accordance with DIN EN 10327. In this process, the strip is guided through molten aluminum with approx. 8 – 11 % silicon.
Product version .20 is hot-dip coated with a plating of zinc Z200 in accordance with DIN EN 10327. The relevant layer consists of approx. 99% zinc.
The coating shall be determined in accordance with DIN EN 10327 using the single spot test, and possesses the values according to Table 1.
Table 1: Tolerances of the coating of the input stock
Values / side
Product version
Thickness / μm Minimum coating mass / g/m2
.10 19 - 33 58 .20 10 - 20 85
4.2 Heat treatment and forming (press hardening)
The components shall be hardened such that the microstructure is homogenous and uniformly hardened. Hardening and forming shall be performed so as to prevent any cracks from forming in the base material.
For components according to product version .10, coil coated material shall be produced in one forming stage (hot) to prevent any flaking of the layer (direct press-hardening).
For components according to product version .20, the forming stage shall be in cold condition. The components are then heated and hardened in the die (indirect press hardening).
For components according to product versions .00, .90, preformed components may be heated and then hardened and calibrated in the press die.
Maximum thinning of 30% of the original sheet thickness shall not be exceeded. During design, care shall be taken to ensure that the component strength in the ironed areas is not compensated by hardening.
4.3 Punching and blanking
Components can be pre-blanked before hot-forming and hardening. Component contours with critical dimensions as well as holes shall be blanked or punched following hardening, however. Laser beam cutting is also acceptable.
In the case of the indirect die hardening process, the complete cutting and punching process can take place before hardening.
If a cutting fluid is required to support the finish cut with tools in hardened condition, care shall be taken to ensure that it does not result in faults in the downstream production processes. The constituents shall conform to the requirements of material sheet VDA 232-101. The list of approved oils can be accessed from the relevant department.
4.4 Joining methods
4.4.1 Spot welding
For components according to DBL 4093.20, the current range shall be determined on an identical sheet combination within the context of initial sample inspection for each sampled item number. For all components supplied according to DBL 4093.20, care shall be taken to ensure that the current range is ΔI ≥ 1 kA and that the upper spatter limit I max does not drop more than 200 A.
4.5 Materials and technological characteristics
The following technological characteristics shall be determined on the hardened component.
Table 2: Technological characteristics on finished component
Material no.
PV R p0.2 / MPa R m / MPa A30 mm / % Angle of bend /
°
.00, .10, .20 950 – 1250 1300 – 1600> 6 ≥ 50 (t = 1mm) 1.5528
.90 950 – 1250 1150 – 1400> 5* ≥ 70 (t = 1mm) 1.5528
* Product version .90 has a better ductility during crash compared to the other product versions. This is not apparent from the elongation after fracture determined in the tensile test, as this parameter does not correlate with the ductility during crash.
4.6 Coating and finish
PV .00:Press-hardened components made of bright sheet steel
Descaling of components according to product version .00 shall be performed by blasting according to the present status. The blasting process shall ensure a scale-free finish across the complete component surface. PV .10: Press-hardened components made of sheet steel with continuous hot-dip aluminum finish
The layer thickness of the coating on the hardened finished part shall lie between 35 μm and 50 μm, and the surface roughness R z between 15 μm - 25 μm.
No flaking of the layer is permitted. As a result of the production process, parts show various surface colorations due to a thin oxide layer on the AS coat.
PV .20: Press-hardened components made of sheet steel with continuous hot-dip galvanized finish
The thickness of the hot-dip coating on the hardened component shall lie between 25 μm and 35 μm. No flaking of the layer or loss by burning is permitted. The complete component surface of the finished parts shall be free from loosely adhering oxidic coats.
To ensure a reliable process during spot welding, the layer thickness tolerance indicated shall be maintained in the flange / non-ironed areas.
PV .90:Press-hardened components with thermal diffusion zinc coating
The requirements for the finish and coating are specified in DBL 8457 Thermal diffusion zinc coating of steel components. The effect of the temperature during the coating processes above 300°C alters the mechanical properties of press-hardened components, as indicated in Section 4.5 Table 2.
4.7 Surface treatment
In general, the possibility of hydrogen absorption shall be examined very carefully along the process chain and always avoided.
Pickling and the application of electroplated coatings, e.g. electrolytic zinc coating, is not permitted.
The cataphoretic coating process as well as phosphating shall be assessed in each individual case, as compounds of the elements phosphorus, sulfur (also as hydrogen sulfide H2S), arsenic, antimony, selenium, but also cyanides, thiocyanates, and carbon monoxide may act as promoters of hydrogen absorption and should therefore not be present in pretreatment solutions. In case of doubt, the use of substances shall be agreed with Materials Engineering and Finish.
5 Tests
The test frequency for the following tests required to ensure quality shall be specified in the supplier's quality plan.
The test instructions on which this DBL is based are available from the purchasing department.
5.1 Hardness test
In accordance with DIN EN ISO 18265, Table B2, steels for quenching and tempering in quenched and tempered condition, measuring values from hardness testing can be converted into approximate values for the tensile strength. For measuring values higher than 470 HV10, the correlation curve between hardness HV10 and tensile strength may be extrapolated and used for revaluation. Provided that the material strength is sufficient, method HV30 may also be used.
In coordination with Materials Engineering, locations of the component shall be selected on the drawing for testing the hardness. For product versions .10, .20 and .90, the coating shall be ground down to the base material for hardness testing in the area of the measuring point.
Nondestructive hardness testing (e.g. using the eddy current method) is permitted as supplementary in-series production test following agreement with the responsible department.
5.2 Layer thickness measurement
The layer thickness measurement on the hardened component according to product version .01 shall be performed by means of metallographic sections.
For the other product versions, the layer thickness may be determined using different test methods, following agreement with the responsible department. For product version .20, the thickness may also be determined, for example, electrochemically (galvanostatic dissolution) in accordance with DIN EN ISO 2177 (electrolyte: 100 g/l ZnSO4*5H2O and 200 g/l NaCl, current density: 12,7 mA/cm2)
The requirements in accordance with Table 2 shall be fulfilled.
5.3 Corrosion resistance
Requirements for the paint adhesion / corrosion resistance of components conforming to product version .90 are specified in DBL 8457 Thermal diffusion zinc coating of steel components.
Evidence of infiltration at crack c (U/2) of product versions .00, .10, .20 shall be provided according to the following method.
Test part: Component, cataphoretically coated, with scratch
Cataphoretic dip coating in accordance with DBL 7391.54
The components shall be scratched in accordance with test instructions PA PP PWT 3101, Section
3.9.
To check adhesion before testing, a cross-cut test shall be performed according to PBODC361
(permissible rating Gt < 1,0).
Test:Alternating climate test in accordance with test instructions VDA 621-415
Exposure time: 10 cycles
Assessment: Infiltration c (U/2) shall be determined in accordance with test instructions PA PP PWT 3101, Section 3.10.
Requirement for components according to product versions .00 and .10: c (U/2) < 2,0 mm
Requirement for components according to product version .20: c (U/2) < 1,5 mm
To check adhesion, a cross-cut test shall be performed after the test according to PBODC361
(permissible rating Gt < 1,0).
5.4 Pickle test
The pickle test is intended to check the sensitivity to hydrogen embrittlement after the passage through pre-treatment for painting.
The crack test shall not result in any macrocracks in the base material.
Test specification pickle test
Pickling solution 5 % by weight sulfuric acid +/- 0,2% by weight
Temperature 22°C
2°C
+/-
Sample size min. 5 pcs.
Pickling time 10 minutes (then rinse)
Assessment one hour after the end of the pickling time. Check the components for possible cracks in the base material using a stereomicroscope or the magnetic inductive method. In case of larger components, 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 300cm2 component surface shall be tested in 1000 ml acid.
5.5 Bending test
To determine the angle of bend α1mm , remove at least 3 specimens from the hardened component in each testing direction and test according to test instructions PPAP PWT 4101. In exceptional cases, specimens from 3 comparable components may be taken. For the requirement according to Table 2, the mean value of 3 specimens in testing direction shall be used. If the measured angles of bend αm of specimens with bending direction parallel and normal to the rolling direction differ strongly, then both shall comply with the requirements according to Table 2.
If specimen size 60 mm * 60 mm is unsuitable due to the component geometry, specimen size 60 mm * 30 mm may be used following agreement with the Materials Engineering department.
If during measurement of the angle of bend αm the sheet thickness t of the examined specimens deviates from 1 mm, then the angle of bend α1mm which would exist for t = 1mm may be calculated using t m mm
?=αα1.
5.6 Tensile test
To provide evidence of the mechanical properties within the framework of the initial sample inspection, the tensile test in accordance with DIN EN 10002 shall be performed. The yield stress shall be measured at 0.2 % strain of the total measured length and is called R p0.2. For the tensile test within the framework of the initial sample inspection, the sample geometry described in Figure 1 with an initial measuring length of 30 mm shall be used. The elongation at rupture shall therefore be termed A 30 mm .
Figure 1: Specimen geometry for tensile testing
Specimen thickness: t = thickness of finished part Specimen width: b = 5 mm Radius: r = 5 mm
Width of specimen heads: g = 9 mm Length of specimen heads: k ≥ 30 mm Test length: L C = 36 mm
Initial measuring length: L 0 = 30 mm Total specimen length: L t ≥ 106 mm
When removing the tensile test specimen from press-hardened components, length k of the specimen heads shall be selected as large as possible in order to prevent the specimen from slipping during the tensile test.
6 Duties of the supplier
Refer to MERCEDES-BENZ SPECIAL TERMS Nos. 13 and 16
7 Samples
Refer to MERCEDES–BENZ SPECIAL TERMS No. 13 and DBL 4093 Section 15 "Material-related requirements for initial samples“
8 Deliveries
Refer to MERCEDES-BENZ SPECIAL TERMS No. 13.
9 Marking
Refer to MERCEDES-BENZ SPECIAL TERMS Nos. 4, 24 and 27
10 Packaging
Refer to MERCEDES-BENZ SPECIAL TERMS No. 30.
11 Storability
Refer to MERCEDES-BENZ SPECIAL TERMS No. 29 and No. 30
12 Complaints
Refer to MERCEDES-BENZ SPECIAL TERMS No. 16 and Purchase Conditions for Production Materials and Spare Parts for Motor Vehicles.
13 Environmental protection regulations/Industrial safety
Refer to MERCEDES-BENZ SPECIAL TERMS Nos. 30, and 36 and DBL 8585 Negative substance list for material selection.
14 Other applicable standards
DBL 7391, DBL 8457, PPAP PWT 4101, MB Special Terms, VDA 621-415
Changes as against previous edition:
Section 1 "Field of application, general requirements“ supplemented
Section 3 Sheet thickness tolerances added
Section 4.3 "Punching and blanking“ added
Section 4.4 "Joining methods" deleted
Section 4.6 "Coating and finish" added
Section 5.5 "Bending test“ added
Section 5.6 "Tensile test“ added
Section 15 Material requirements for initial sample part supplemented
15 Initial sample inspection
Page 8
Mercedes-Benz
Material-related requirements for initial samples
DBL4093
June 2008
The initial sample inspection report to the receiving MB plant shall include the following information in the form of a target-actual comparison table. Target value
No
Property
PV.00
PV.10
PV.20
PV.90
Test method / Standard
1
Input stock data
Chemical analysis
Similar to 22MnB5
Acceptance test certificate in accordance with DIN EN 10204, min. 3.1
2 Layer thickness on hardened component, incl. transverse section
---------
35 μm – 50 μm 25 μm – 35 μm
DBL 8457
Layer thickness measurement according to Section 5.2 3
Roughness of component surface R Z --------- 15 μm – 25 μm
--------- --------- VDA 2006
R p0,2: R m :
A 30 mm :
950 – 1250 MPa 1300 – 1600 MPa
> 6% 950 – 1250 MPa 1150 – 1400 MPa
> 5% Tensile test in accordance with Section 5.6
Angle of bend α1mm ≥ 50° (t = 1,0 mm)
≥ 70° (t = 1,0 mm) Bending test according to Section 5.5
4 Technological characteristics with
evidence of specimen removal point on component
Hardness test
415 HV10 – 515 HV10
365 HV10 – 460
HV10 Section 5.1 with sketch of
specified component locations 5 Corrosion resistance
c (U/2): < 2,0 mm c(U/2): < 1,5 mm
DBL 8457
Corrosion test according to Section 5.3
6 Insensitivity to hydrogen embrittlement
The crack test shall not result in any macrocracks in the base material.
Pickle test according to Section 54
7
Evidence of current setting range (lower, upper limit)
--------- --------- ΔI > 1kA
---------
Spot welding according to Section 4.4.1