Abstract No. 12. Surface chemical and tribological investigation of hot dip galvanized steel sheets coated with a sulfate based layer

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1 Abstract No. 12 Surface chemical and tribological investigation of hot dip galvanized steel sheets coated with a Christian Timma 1,2, Thomas Lostak 1, Stella Janssen 1, Jörg Flock 1, Christian Mayer 2 1 AG, Technology, Innovation & Sustainability, Duisburg, Germany 2 University of Duisburg-Essen, Faculty of Chemistry, Universitätsstraße 7, Essen, Germany Proposed for: Oral Presentation Providing low friction properties in deep drawing processes of hot dip galvanized () steel sheets is especially important in the automotive assembling industry. Therefore zinc phosphate is mainly used as solid lubricant to prevent metal to metal contact in sheet forming processes. Due to arising phosphate containing wastewaters and sludges in phosphatation processes, alternative systems have to be developed. In the field of solid lubrication, coatings based on earth alkali sulfates (CaSO4, BaSO4, SrSO4) has been studied for use as high temperature solid lubricants (e.g. in molds) on raw steel material [1]. Generally sulfate salts are easy-to-use chemical compounds and mostly non-toxic whereby they are predestinated for industrial usage. Creating s on zinc and zinc coatings can be performed by treatment with solutions containing such salts [2]. In this work a sulfate containing solution is used to create a solid layer on skin passed steel sheets. Surface chemistry is investigated by Confocal Raman Microscopy (CRM) and scanning electron microscopy (SEM). Via Raman imaging a lateral distribution of different sulfates on the coated sample due to a reaction of the solution with the surface is shown. In addition SEM-

2 Abstract No. 12 images indicate a heterogenous layer mainly appearing in the rolling marks of the substrate. The sliding behavior of the formed layer is compared to an untreated -sample in a Pin-on-Disk Test. The results show a lower friction coefficient for substrates coated with a sulfate layer. Furthermore a strip drawing test (simulating an industrial stamping process) also reveals a low friction coefficient. In conclusion the lubrication effect of the sulfate layer is discussed. References: [1] P.J. John, J.S. Zabinski, Tribology Letters 7 (1999) pp [2] H. Tanaka, Y. Takeuchi, T. Ishikawa, T. Nakayama, Corrosion Science 53 (2011) pp

3 Surface chemical and tribological investigation of hot-dip galvanized steel sheets coated with a Jörg Flock, Stella Janssen, Thomas Lostak, Christian Mayer, Christian Timma, CETAS 20/05/2015 Introduction Phosphatation of zinc coated steel as a commonly used process for increasing of formability Reducing friction during various forming operations Zinc phosphate as no classic solid (dry) lubricant Sulfate based systems (M x+ (SO 4 ) y ) as an alternative to reduce friction on steel material* * P.J. John, J.S. Zabinski, Tribology Letters 7 (1999) pp * T. Murakami, J.H. Ouyang, K. Umeda; S. Sasaki, Materials Science and Engineering A 432 (2006) 2 Thinking the future of steel tool workpiece Phosphated steel surface F N Friction, adhesion, wear

4 Introduction 3 Materials & Methods Deposition procedure Application roll Substrate Transport roll Deposition procedure & Surface analysis forming a on hot-dip galvanized steel Surface analysis by different methods (SEM, Raman Spectroscopy Tribological performance Pin-on-Disk Test Dry and liquid environment Conclusion Lubrication mechanism Evaluation 4 Application roll Metering gap Metering roll Coating solution sulfate 37 mg sulfur /m² 26 mg sulfur /m² 11 mg sulfur /m²

5 Results & Discussion Surface layer morphology (SEM) uncoated areas + 26 mg sulfur /m² (Mx(SO4)y) Alkaline cleaned 20 µm Skin-passed areas 20 µm primarily deposited in skin-passed areas 5 S TA Results & Discussion Surface layer chemistry (SEM & Raman-Spectroscopy) + 26 mg sulfur /m² (Mx(SO4)y) = 488 nm } CE 20 µm 6

6 Results & Discussion Deposition behaviour (Raman-Spectroscopy) = 488 nm 7 } Results & Discussion Deposition behaviour (Raman-Spectroscopy) = 488 nm 8 } + Optical Image 250 µm + = 250 µm 26 mg sulfur/m² 1 spectrum /µm

7 Results & Discussion Deposition behaviour (Raman-Spectroscopy) = 488 nm 9 37 mg 27 mg 11 mg 37 mg sulfur / m² sulfur / m² sulfur / m² sulfur / m² 10 } µm Results & Discussion Tribological performance obtained in a Pin-on-Disk Test Friction coefficient Squalan sulfate e sulfate Squalan e = = = Spherical pin duration 37 mg sulfur/m² 26 mg sulfur/m² 11 mg sulfur/m² Pin-on-Disk Test 600 s / 1 rpm force 30 N temperature 60 C sample

8 Results & Discussion Lubrication mechanism Friction coefficient 11 Conclusion Squalan sulfate e steel Liquid conditions sulfate steel Dry conditions 12 Wear track after 60 seconds (under liquid conditions) Wear particles Wear track after 600 seconds (under liquid conditions) 1 µm Crushed/deformed sulfate coating Deposition procedure & Surface analysis 1 µm Sulfate based lubricant mostly deposited in skin-passed areas Tribological performance reduces friction in liquid environment Friction coefficient depending on sulfate amount on surface Evaluation Wear particles are essential for lubricious behaviour