Quality Characteristics of SuperDyma

Transcription

1 Flat s Quality Characteristics of SuperDyma Hot dip Zn Al Mg Si Alloy Coated Steel Sheets -- Marunouchi, Chiyoda-ku,Tokyo -87 Japan Tel: SuperDyma Uen f NIPPON STEEL & SUMITOMO METAL CORPORATION

2 Hot dip Zn Al Mg Si Alloy Coated Steel Sheets Technical Documents Spot Weldability.. Test Specimens Table Test Specimens Coating mass/side ( g/m ) Table shows the test specimens applied. The plate thickness is.8 mm, the coating mass/side of is 9 g/m, and the chromium coating mass/side is mg/m. (aluminum-coated sheet of Nippon Steel & Sumitomo Metal) was used as the comparison material. Chromium coating mass/side ( mg/m ).8 t 9 Proto-type product manufactured at commercial line.8 t manufactured at commercial line.. Test Methods Table Welding Conditions Welding pressure Squeeze Up slope Welding time Hold Cooling water 9 kgf cycles cycles 7 cycles cycles /min Electrode applied: Obara DHOM type; Pre-dots: dots Nugget diameter: The button diameter measured through peeling-off was assessed as the nugget diameter. In the case of irregular nugget diameters, the average of the long and short diameters was used. Table Test Conditions for Appropriate Welding Current Minimum welding current.8 mm or more in average nugget diameters Expulsion-generation welding current Of N=, welding current for which at least expulsion is generated Maximum welding current Of N=, welding current for which at least expulsion and strong deposition between electrode and steel sheet are generated Table Test Conditions for Continuous Dotting Property Welding current for continuous dotting ( Minimum welding current + Maximum welding current )/ Judgment of continuous dotting numbers End in.8 mm or under in average nugget diameters Fig. Range of Appropriate Welding Currents Contents Spot Weldability Corrosion Resistance of Spot Welds Corrosion Resistance of Repaired Sections by Spraying Corrosion Resistance of Cylindrically-drawn Sections Corrosion Potentials (Galvanic Corrosion) Acid and Alkali Resistance Ammonia Resistance Protective Film Formed at Cut-End Surface Corrosion-protection Treatment of Cut-end Surface 7 Results of Exposure Test on Cut-end Surface 7 Chemical Conversion Treatment Property 8 Comparison of Corrosion Resistance with Stainless Steel 9 Notice: While every effort has been made to ensure the accuracy of the information contained within this publication, the use of the information is at the reader s risk and no warranty is implied or expressed by Nippon Steel & Sumitomo Metal Corporation with respect to the use of the information contained herein. The information in this publication is subject to change or modification without notice. Please contact the Nippon Steel & Sumitomo Metal Corporation office for the latest information. Please refrain from unauthorized reproduction or copying of the contents of this publication. The names of our products and services shown in this publication are trademarks or registered trademarks of Nippon Steel & Sumitomo Metal Corporation, affiliated companies, or third parties granting rights to Nippon Steel & Sumitomo Metal Corporation or affiliated companies. Other product or service names shown may be trademarks or registered trademarks of their respective owners. SUPER DYMA is the registered trademark of Nippon Steel & Sumitomo Metal Corporation in Japan and other countries. Fig. shows the test for appropriate welding currents. The range of appropriate welding currents for is relatively high compared to that of. The welding current used in the continuous dotting test was set at (minimum welding current + maximum welding current )/. The welding current applied in the test was. ka for and. ka for. Fig. shows the continuous dotting test results. The continuous dotting number was dots for and dots for. 8 Fig. Continuous Dotting Tests Nugget diameter ( mm ) 7 No. of dots Expulsion generation Depositing Range of appropriate welding currents Range of appropriate welding currents 8 Welding current ( ka ) Nugget diameter ( mm ) 7 No. of dots

3 Corrosion Resistance of Spot Welds Corrosion Resistance of Repaired Welds by Spraying... Test Specimens Table Details of Test Specimens Table Welding Conditions Welding pressure Squeeze 9 kgf cycles Table shows the test specimens applied. Coating mass / side ( g/m ) Post-treatment DURGRIP ( Galvannealed ) * WELCOTE ** ( * ) Hot-dip Zn-%Al.8 t.8 t.8 t.8 t.8 t 9 9 Y treatment Y treatment No treatment Organic film coated Y treatment Proto-type product manufactured at commercial line manufactured at commercial line manufactured at commercial line manufactured at commercial line manufactured at commercial line *Hot-dip Zn-Fe ** Organic composite coated sheet ( * ) WELCOTE is a product sold and registered trade mark in Japan... Test Methods Steel sheets of C were spot-welded at two points to sheets of 7C to prepare the test specimens. Table shows the welding conditions. After spot welding, tape sealing was provided on the rear of the specimens and cut-end surface; these specimens were then used for corrosion resistance tests. For the surface of WELCOTE, an organic composite coating was provided. Then a cyclic corrosion test was conducted; one cycle consisted of ❶ salt spraying [SST (%NaCl, ºC, hours )], ❷ drying [ DRY (ºC, % RH, hours )] and ❸ wetting [WET (ºC, 98% RH, hours )]. Up slope cycles Welding time 7 cycles Hold cycles Cooling water l/min Welding current ka Electrode applied: Obara DHOM type; Pre-dots: dots Photo shows the results of the cyclic corrosion tests (up to 9 cycles). The occurrence of red rust was observed on every coated sheet subjected to cycles. and Hot-dip Zn-%Al developed a protective film over the welds as the number of cycles increased, thereby inhibiting further generation of red rust. continued to show red rust at the welds as the number of cycles increased. The entire surface of DURGRIP (Galvannealed) showed red rust. While red rust occurred at the welds of WELCOTE, it occurred only slightly on their periphery. Photo Corrosion Resistance of Welds DURGRIP-Galvannealed WELCOTE Hot-dip Zn-%Al cycles.. Test Specimens Table 7 Test Specimens Fig. Butt Welding Hot-dip Zn-%Al.. Test Methods Repaired section Weld Coating layer Base metal Table 9 Neutral Salt Spray Cyclic Test Method Condition Temperature ( ºC ) ❶ Salt spray ❷ Drying ❸ Wetting Coating composition Zn %Al %Mg.%Si Zn %Al Fig. Corrosion Resistance Assessment Results for Repaired Welds ( Salt Spray Test ).. Coating mass ( g/m ) () Welding and Weld Repair Butt electric-resistance welding was conducted, and the weld was repaired using zinc-rich paint (refer to Fig. ). Table 8 shows the thickness of the paint film used for repair painting. () Corrosion Resistance Tests The corrosion resistance of the repaired welds and base metal was assessed by a salt spray test and a neutral salt cyclic test (JIS H 8: Table 9, Conventional JASO Tests) The corrosion resistance of welds on that were repaired with zinc-rich paint proved remarkably high compared to Hot-dip Zn-%Al (refer to Figs. and ). This high corrosion resistance appears to be attributable to the fact that the resistance to corrosion provided by the protective film, an inherent property of, also worked on the repaired welds. 9 Surface treatment Special chromate treatment Special chromate treatment Table 8 Results of Zn-rich Paint Repairing of repair painting ( m ) Salt spraying test Neutral salt cyclic test 8..8 Hot-dip Zn-%Al Humidity (%) 9 Salt concentration (%). Time hours hours hours 8 hours/cycle Fig. Corrosion Resistance Assessment Results for Repaired Welds (Neutral Salt Cyclic Test) cycles 9 cycles Ratio of red rust occurrence area ( % ) Base metal of Repaired section of Base metal of Hot-dip Zn-%Al Repaired section of Hot-dip Zn-%Al Ratio of red rust occurrence area ( % ) 7 Base metal of Repaired section of Base metal of Hot-dip Zn-%Al Repaired section of Hot-dip Zn-%Al Test hour ( hr ) 7 No. of cycles

4 Corrosion Resistance of Cylindrically-drawn Sections Corrosion Potential (Corrosion due to Contact with Dissimilar Metals).. Test Specimens.. Table Test Specimens Hot-dip galvanized sheet.t.t.. Test Methods Table shows the deep-drawing test conditions. The drawing ratio was set at.. After paint sealing the lower end of the test specimen following deep drawing, a cyclic corrosion test was conducted under the conditions shown in Table. 9 9 Photo shows the surface appearance before and after corrosion tests. Red rust was not observed on the surface of SU- PERDYMA even after applying cycles of cyclic corrosion tests. Mechanical properties YP L ( MPa ) TS L ( MPa ) E L (%) Table shows the test specimens applied. The plate thickness was. mm, the coating mass/side of was 9 g/m, and the chromium coating mass/side was mg/m. Hot-dip galvanized steel sheets were used as the comparison material. 8 9 Table Deep-drawing Test Conditions Photo Surface Appearance before and after Cyclic Corrosion Tests Before test 7 9 Punch diameter Die shoulder Punch shoulder Drawing ratio R.. Blank holder pressure Coating mass/side ( g/m ) 9 R R.. ton Chromate coating mass/side ( mg/m ) Proto-type product manufactured at commercial line manufactured at commercial line Table Cyclic Corrosion Test Conditions ❶ Salt spray ( % NaCl, ºC, hours ) ❷ Drying ( ºC, % RH, hours ) ❸ Wetting ( ºC, 98% RH, hours ). Test Specimens.. Measurement Methods.. Results and Considerations While containing Mg showed a base corrosion potential that was attributable to MgZn just after immersion, the corrosion potential simulated that of other Zn-type coated sheets after the lapse of hour (refer to Fig. ). This phenomenon seems to be attributable to the suppression of anodic dissolution of the coating affected by the hydration film containing Mg that was formed at the initial stage of corrosion. According to the above, it is considered that when makes contact with a dissimilar metal, the phenomenon of corrosion due to contact with dissimilar metals, attributable to corrosion potential, closely simulates that of common Zn-type coated sheets. Cold-rolled steel sheet Hot-dip galvanized steel sheet Hot-dip Zn-%Al alloy coated steel sheet Measurement was made of the corrosion potential of specimens immersed in %NaCl at room temperature employing an Ag/AgCl reference electrode. Surface exposure of the specimens was adjusted to cm by means of tape sealing. Fig. Secular Changes of Corrosion Potentials (% NaCl, room temperature) Corrosion potential ( V vs Ag/AgC ) Acid and Alkali Resistance Time lapse ( hr ) shows exceptionally good alkali resistance. Cold-rolled sheet Hot-dip Zn-%Al alloy coated sheet Fig. 7 Acid and Alkali Resistance of Various Coated Sheets ( hours) Fig. 8 Corrosion Resistance of Various Coated Sheets under Strong Alkali Environment (ph=., hours) After cycles After cycles Corrosion loss ( g/m /side ) 8 ( Z7 ) Hot-dip Zn-%Al ( Y7 ) ( K8 ) GALVALUME STEEL SHEET* ( AZ ) 8 Coating dissolution amount during -hour Immersion in %NaC solution ( ph ) Corrosion loss ( g/m ) 8 ( Z7 ) Hot-dip Zn-%Al ( Y7 ) ( K8 ) Hours of Immersion in %NaC solution ( hr ) * : GALVALUME is the regisgterd trade name of BIEC International Inc.

5 Ammonia Resistance Corrosion-protection Treatment of Cut-end Surface.. Test Methods Ammonia water ranging in solutions from % to % was used for tests. The ammonia resistance of SuperDyma was assessed in terms of corrosion loss after immersion for hours at C... Test Specimens Table Test Specimens.mm Coating mass K8 Surface treatment Special chromate treatment ( Y treatment ).. Test Results showed better ammonia resistance than Hot-dip Zn-%Al alloy coated sheet. Fig. 9 Ammonia Resistance of Various Coated Sheets Corrosion loss ( g/m ) Hot-dip Zn-%A Hot-dip galvanized sheet GALVALUME STEEL SHEET.. Corrosion-protection Agent.. Test Methods The surface of one cut end of the specimen was coated with the corrosionprotection agent and exposed outdoors (refer to Fig. ). Exposure period: From August 8, Exposure site: Ichikawa, Chiba Prefecture (rural environment) Breton R-C (manufactured by Sugimura Chemical Industry) Fig. Test Method No coating of corrosion-protection agent Coating of corrosion-protection agent Set at an angle of 7º to the horizontal plane Protective Film Formed at the Cut-end Surface.. Test Methods.. Observations Test specimen: with thickness of. mm; coating: K equivalent of products manufactured at commercial lines (no treatment) Exposure period: months from September Exposure site: Compound of R&E Center of Nippon Steel & Sumitomo Metal (coastal environment at Futtsu, Chiba Prefecture) The exposed base metal on the cut end of the specimen was covered with corrosion products containing Zn and Mg... Test Results Photo Corrosion-protection Treatment of Cut-end Surfaces (Results of Outdoor Exposure Tests) Exposure time week month months months Coating of corrosion-protection agent No coating of corrosion-protection agent Photo Observation Results Coating drip Exposed base metal Results of Exposure Test on Cut-end Surface possesses excellent corrosion resistance at cut-end surfaces. In the initial stage of outdoor exposure to the environment, the surface of the cut end of the specimen generated a small amount of red rust. However, the surface was soon covered by a stable protective film that almost completely inhibited further development of corrosion for long time. Cl O Al Photo Corrosion-protection Treatment of Cut-end Surfaces (Results of Outdoor Exposure Tests) 8 months Exposure time months Coating mass: g/m /side Hot-dip Zn-%A Coating mass: 9 g/m /side Coating mass: 9 g/m /side GALUVALUME STEEL SHEET ( laboratory-prepared sample ) Coating mass: 9 g/m /side Fe Mg Zn Sample conditions: (. mm ), surface treatment ( no treatment ) Exposure site: Futtsu weathering site, Nippon Steel & Sumitomo Metal ( Cut-end surface was set sideways; photos at left: down side ) 7

6 Chemical Conversion Treatment Property Comparison of Corrosion Resistance with Stainless Steel.. Test Specimens Table shows the test specimens applied..... Phosphate Treatment Methods.. Assessment Methods.. Assessment Results Fig. Measurement Results for Phosphorus Deposit Mass in Chemical Conversion Coating Phosphorus deposit mass ( g/m ) SUPER- DYMA Hot-dip galvanized sheet alloy coated Hot-dip Zn-%Al sheet Table Hot-dip Zn-%Al Coating composition Zn %Al %Mg.%Si Zn Zn %A Table shows the phosphate treatment method. Table Phosphate Treatment Method Step Treatment Degreasing Rinsing Surface adjustment Chemical conversion treatment Rinsing Rinsing ( pure water ) Chemicals applied FC L8 PL ZTH+PL ZN PB L8 The mass of phosphorus deposits on the chemical conversion coating was measured by the fluorescent X-ray method, and its appearance was observed by means of SEM. The mass of phosphorus deposits on the chemical conversion coating of was very similar to that of hot-dip galvanized steel sheet or Hot-dip Zn-%Al alloy coated sheet (refer to Fig. ). It was confirmed that the configuration of the phosphate crystals, as shown in Photo, was of regular needle crystals, as in the case of hot-dip galvanized sheet and Hot-dip Zn- %Al. From the above, it can be judged that possesses favorable chemical conversion treatment properties similar to those of hot-dip galvanized sheet and Hot-dip Zn- %Al Photo SEM Observation Results for Chemical Conversion Coating (,) SEM observation photo Coating mass ( g/m ) 9 9 Treatment time ( sec ). Test Specimens.. Test Conditions Photo 7 shows the data at, and 9 cycles of cyclic corrosion tests. White rust was observed for, but no red rust was seen even at 9 cycles. On the other hand, red rust was observed after only cycles for stainless steel and continued to develop as the number of cycles increased. Table Test Specimens No. ( SD ) Stainless steel ( SUS ) Table 7 Test Conditions Test method Cyclic corrosion test JASO M9 Standards NSDHC Y K8 SUS Configuration Flat sheet sample ( with edge sealing ) Test conditions Test time ❶Salt spray ( % NaCl, ºC, hours ) ❷Drying ( ºC, % RH, hours ), and 9 cycles ❸Wetting ( ºC, 9% RH, hours ) Cyclic corrosion test with one cycle composed of ❶ to ❸ ( 8 hours / cycle ) Photo 7 Assessment Test Results for Corrosion Resistance (Cyclic Corrosion Test: JASO M9 Method) ( Y-K8 ) Stainless steel ( SUS ) cycles cycles 9 cycles Hot-dip Zn-%Al.. Assessment As demonstrated above, showed better resistance to red rust than stainless steel. 8 9