preparation and characterization of 304 stainless steel q235 carbon steel composite material

RINP 517 No of Pages 6, Model 5G 11 January 2017 Results in Physics xxx (2017) xxx–xxx Contents lists available at ScienceDirect Results in Physics journal homepage: www.journals.elsevier.com/results-in-physics Preparation and characterization of 304 stainless steel/Q235 carbon steel composite material Wenning Shen a,⇑, Lajun Feng a, Hui Feng b, Ying Cao a, Lei Liu a, Mo Cao a, Yanfeng Ge a 11 10 12 15 16 17 18 19 20 21 22 23 24 25 26 a b School of Materials Science and Engineering, Xi’an University of Technology, No South Jinhua Road, Xi’an 710048, China Shaanxi Institute of Zoology, Xi’an 710032, China a r t i c l e i n f o Article history: Received October 2016 Accepted 28 December 2016 Available online xxxx Keywords: Stainless steel Carbon steel Anti-corrosion Conductivity Electrochemical EIS a b s t r a c t The composite material of 304 stainless steel reinforced Q235 carbon steel has been prepared by modified hot-rolling process The resulted material was characterized by scanning electron microscope, threeelectrode method, fault current impact method, electrochemical potentiodynamic polarization curve measurement and electrochemical impedance spectroscopy The results showed that metallurgical bond between the stainless steel layer and carbon steel substrate has been formed The composite material exhibited good electrical conductivity and thermal stability The average grounding resistance of the composite material was about 13/20 of dip galvanized steel There has no surface crack and bubbling formed after fault current impact The composite material led to a significant decrease in the corrosion current density in soil solution, compared with that of hot dip galvanized steel and bare carbon steel On the basis polarization curve and EIS analyses, it can be concluded that the composite material showed improved anti-corrosion property than hot-dip galvanized steel Ó 2016 Published by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/) 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 Introduction 44 Using grounding materials in substation is the important measure to guarantee safe running of power system and electrical equipment, and to ensure personal safety [1–4] However, power system fault occurs frequently in China, due to the corrosion of grounding materials As a result, it has to excavate the substation grounding grids again and lay new grounding materials, resulting in increased cost [5] In order to prevent the corrosion of the grounding materials, copper material is usually used as grounding materials internationally Nevertheless, China is facing the problem of copper scarcity, which has lead to high cost Moreover, the released copper ions easily pollute groundwater These disadvantages have restricted the application of copper materials as grounding materials in our country [6,7] Several researches have shown that hot dip galvanized steel materials exhibited high corrosion resistance, good conductive ability and lower price Therefore, they are often used as grounding materials in our country [8–10] Since the grade of transmission line voltage has increased, it needs to improve the anti-corrosion property of the grounding materials As a result, hot dip galvanized steel materials for extra high voltage grounding grid are hard to meet the design require- 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 ⇑ Corresponding author E-mail address: shenwenning@qq.com (W Shen) ment [11,12] It has been found that stainless steel exhibits superior anti-corrosion property and heat resistance [13–15] Moreover, it has the same material with other devices connected with grounding grid such as drop line, which can’t produce microcell corrosion Thus, stainless steel material can be used as effective substitution of hot dip galvanized steel However, the resistance of stainless steel is very high When used as grounding material, it can’t conduct current in time In addition, its cost is higher Therefore, they are disadvantages for the application of stainless steel grounding material In this work, we prepared stainless steel/carbon steel composite materials by modified hot-rolling process, using 304 stainless steel as the cladding material and Q235 carbon steel as the substrate Thus, the prepared composite materials can not only exhibit the excellent corrosion resistance of stainless steel, but also present good conductive ability of carbon steel, which can be used as potential grounding materials And their bonding interface, corrosion resistance, and electrical conductivity were estimated 64 Experimental 82 Materials 83 Stainless steel type 304 (in wt%: C 0.039, Si 0.44, Mn 1.21, P 0.018, S 0.002, Ni 8.09, Cr 18.23, Ti 0.042 and N 0.039) and carbon 84 http://dx.doi.org/10.1016/j.rinp.2016.12.050 2211-3797/Ó 2016 Published by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Please cite this article in press as: Shen W et al Preparation and characterization of 304 stainless steel/Q235 carbon steel composite material Results Phys (2017), http://dx.doi.org/10.1016/j.rinp.2016.12.050 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 85 RINP 517 No of Pages 6, Model 5G 11 January 2017 W Shen et al / Results in Physics xxx (2017) xxx–xxx 90 steel type Q235 (in wt%: C 0.22, Si 0.05 max, Mn 0.48, P 0.012 and S 0.022) were used as the clad layer material and substrate respectiviely for the preparation of stainless steel/carbon steel composite material Hot dip galvanized steel bar and bare Q235 carbon steel were used as control 91 Preparation of stainless steel/ carbon steel composite material 92 107 In order to ensure the discharging efficiency of grounding materials, their cross sectional area has to be larger than 300 mm2 based on grounding grid design Thus, Q235 carbon steel rods (U100 mm  1000 mm) were used as substrate, and 304 stainless steel tubes (U100 mm  mm  1010 mm) were used as clad layer material in this work The stainless steel/carbon steel composite material was prepared by modified hot rolling process Specifically, the carbon steel bar was put into stainless steel tube Our preliminary experiment results suggested that the length of the tube should be longer than the bar, so as to avoid the cracking of cladding layer in the rolling process As a result, the two ends of the tube have an allowance of mm Subsequently, the two ends were closed by welding Thus, cracks would not appear in the ends It was then heated up to 1200 °C and hot rolled for six times After that, the composite material with a diameter around 22 mm was obtained 108 Interface characterization 109 117 The composite material rod was cut into a cylinder with a height of cm and its cross surface was polished by waterproof abrasive paper Its macroscopic feature was recorded by digital camera The treated sample was then etched by nitric acid alcohol solution (4 wt%) Subsequently, GX71 metallography microscope was used to study the microstructure of the interface, and JSM6700F scanning electron microscope (SEM) was used to observe the interfacial morphology The components of the interfacial transition zone were analyzed by line scan 118 Grounding resistance testing 119 121 MS2302 grounded resistance measuring instrument was used to test the grounding resistance of the samples The test objects were those underground in 10–55 cm 122 Thermal stability measurement 123 135 The grounding materials must have high anti-thermal shock resistance, since large quantity of heat can be produced when large short circuit current flowing through the grounded conductor In this work, fault current impact method was used to study the anti-thermal shock resistance of the grounding material based on GB3048.7 Specifically, two composite material rods (U22 mm  1000 mm, marked with sample and sample respectively) were selected They were then impacted by fault current of 24.8 KA for three times Subsequently, the changes of the sample surface were observed After that, the resistance in per unit length of the samples was measured using direct current bridge method when cooling to room temperature The impact time was s 136 Corrosion resistance analysis 137 The soli solution from a substation in Shaanxi Province was used as corrosion medium The basic preparation procedures were as follows, the soil retrieved from the soil layer of 80 cm was mixed with deionized water in a ratio of 1:5 Subsequently, the super- 86 87 88 89 93 94 95 96 97 98 99 100 101 102 103 104 105 106 110 111 112 113 114 115 116 120 124 125 126 127 128 129 130 131 132 133 134 138 139 140 natant used as testing medium was obtained after 24 h standing Its contents are shown in Table The three-electrode system was applied to study the electrical potential and the corrosion current of the composite material Hot dip galvanized steel and Q235 carbon steel were used as control The sample was working electrode, platinum electrode was auxiliary electrode, and saturated calomel electrode (SCE) was the reference electrode The test area was cm2 and the soak medium was the soil solution The polarization curve was measured by CS350 electrochemical workstation with a scanning speed of Mv/ S Electrochemical impedance spectroscopy (EIS) was used to study the anticorrosion performance of the composite material Hot dip galvanized steel and Q235 carbon steel were used as control In the test, samples were immersed in the soil solution for 30 The alternating current (AC) impedance spectra were measured by CS350 electrochemical workstation Acquisition parameters including: the AC excitation signal, sine wave with the amplitude of 10 mV and frequency, 0.01–100 kHz 141 Results and discussion 160 Interface analysis of the composite material 161 Fig shows the macro morphology and clad layer thickness of the stainless steel/carbon steel composite material As shown in Fig 1, the composite material exhibited an obvious clad layer There was no gap between the interface and the layer combined closely with the carbon steel substrate The clad layer was uneven and the thickness was in the range of 0.8–1.9 mm The metallographic microstructure of the composite material interface is shown in Fig It can be observed from Fig that the interface along rolling direction showed approximately linear shape The interface was composed of the substrate, transition zone and clad layer The substrate microstructure was ferrite and pearlite The carbon potential of the substrate in heating is higher, due to its larger carbon content than that of stainless steel As a result, the smaller carbon atoms can diffuse to stainless steel by the interstitial diffusion mode Thus, it was found that the decarbonized phenomenon existed in the near vicinity of the interface (carbon steel side) in the composite material, and ferritic transition zone with a thickness of about 90 lm has been formed In cladding material zone, there was no microstructure observed, because it can’t be corroded by nitric acid alcohol solution SEM micrograph and line scanning result of the composite material interface after nitric acid alcohol solution erosion are shown in Fig The SEM morphology also indicated that the interface of the composite material contained matrix microstructure, transition tissue and cladding tissue Microzone composition analysis showed that the elements both in stainless steel and carbon steel diffused on different degree, so the diffusion layer formed It can be seen from the changes of component curve that the diffusion was continuous The diffusion ranges of element Cr, Ni, Mn near interface led to little difference, which were around lm When the sample was high temperature rolled, the element concentration gradient existed in both sides of the interface So, it made these alloy elements diffuse under heat and force The results of interface microstructure and microzone composition analysis suggested that a metallurgical bonding was formatted between the cladding and the substrates, resulting in strong bonding force in the composite material Therefore, the prepared composite material can meet the requirement of grounding material 162 Please cite this article in press as: Shen W et al Preparation and characterization of 304 stainless steel/Q235 carbon steel composite material Results Phys (2017), http://dx.doi.org/10.1016/j.rinp.2016.12.050 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 RINP 517 No of Pages 6, Model 5G 11 January 2017 W Shen et al / Results in Physics xxx (2017) xxx–xxx Table Contents of the prepared soil solution Elements Na+ K+ Mg2+ Ca2+ Fe2+ Al3+ ClÀ SO24 Contents/(mg/L) 1.47 0.38 6.83 41.01 0.09 0.57 4.09 76.86 Fig Macro morphology (a) and the clad layer thickness (b) of the stainless steel/carbon steel composite material Grounding resistance of the composite material 200 In order to confirm the prepared composite material can be used as grounding material, the grounding resistances of the composite material and hot dip galvanized steel in the soil around a substation in Shaanxi Province were measured, and the results are shown in Fig It can be seen from Fig that the grounding resistance of the composite material was much less than that of hot dip galvanized steel The grounding resistance of the two samples decreased with increasing depth of burial and then became stable It might be caused by the increased touch area and close contact between the sample and soil with the increase of the depth The average grounding resistance of the composite material was 89.64 X, which was about 13/20 of hot dip galvanized steel These results proved that the conductive property of the composite material was much better than that of hot dip galvanized steel, which can fulfill the requirement of conductivity for grounding material The good conductive ability of the composite material mainly arose from the large amount of conductive carbon steel 201 Thermal stability of the composite material 218 After the impact by fault current of 24.8 KA for s, the tested surface temperature of the stainless steel/carbon steel composite 219 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 Fig The microstructure of the interface of the composite material Fig SEM micrograph (a) and line scanning results (b) of the interface in the composite material Please cite this article in press as: Shen W et al Preparation and characterization of 304 stainless steel/Q235 carbon steel composite material Results Phys (2017), http://dx.doi.org/10.1016/j.rinp.2016.12.050 220 RINP 517 No of Pages 6, Model 5G 11 January 2017 W Shen et al / Results in Physics xxx (2017) xxx–xxx Fig The grounding resistance of the composite material and hot dip galvanized steel 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 material was 1100 °C After cooling to 800 °C, the macroscopic detection results showed that there was no crack, pit, and bubble appeared in the surface of the composite material, and no change in interface could be observed It indicated the prepared composite material exhibited good thermal stability, which can resist high current impulse Table shows the electrical resistivity of the composite material before and after fault current impulse As shown in Table 2, the resistivity of sample decreased after the fault current impact, while that of sample increased by 11.5% According to Q/GDW 465-2010 standard, the increase of the resistivity of grounding material can’t exceed 15% after the impact of fault current Therefore, the composite material can meet the demands for grounding material The good thermal stability in the composite material might be caused by the metallurgical bonding formed in the hot rolling process The formed transition region made the stainless steel layer closely combined with the substrate Thus, the composite material could not be damaged during the impact of fault current 240 Corrosion resistance analysis 241 The corrosion protection efficiency of the composite material in soil solution was confirmed by the comparison of the potentiodynamic polarization curves of bare Q235 carbon steel and hot dip galvanized steel with that of the composite material and the values of potentiodynamic polarization curves after Tafel fit, displayed in Fig and Table The corrosion potential of the composite material in soil solution was higher than that of bare carbon steel, while its current density was order of magnitude lower than that of 242 243 244 245 246 247 248 Fig Potentiodynamic polarization curves of the composite material, hot dip galvanized steel, and Q235 carbon steel recorded in soil solution Table The values of electrochemical potentiodynamic polarization curves after Tafel fit Samples Q235 carbon steel Hot dip galvanized steel Composite material Corrosion rate/ (mm/a) Corrp/V Corri/(A/cm2) 0.133 0.116 0.00978 À0.749 1.14  10À5 À0.931 7.653  10À6 À0.275 8.452  10À7 bare carbon steel It means that the composite material had higher corrosion resistance than bare carbon steel, which can provide protection for bare steel According to the electrochemical tests, the protection performance against corrosion in soil solution can be established in the following order: the composite material > hot dip galvanized steel > Q235 carbon steel It suggests that the composite material exhibited much improved anticorrosion property than hot dip galvanized steel The galvanized coating has provided cathodic protection for carbon steel substrate by acting as sacrifice anode Galvanized coating was corroded through anodic dissolution in the solution containing Na+ and ClÀ However, 304 stainless steel showed self-passivation in salt solution, due to the addition of passive alloy elements such as Cr and Ni [16] In the measured curves, the anodic polarization curve of galvanized steel hasn’t presented an obvious passivation region, proving that galvanized coating was corroded in the active state of anodic dissolution Nevertheless, the anodic polarization curve of the composite material existed evident passivated region It can limit corrosion ions to the carbon steel substrate Thus, the passivative property of stainless steel could effectively improved corrosion resistance than galvanized coating Table The grounding resistance of the composite materials at 21 °Cbefore and after the impact of fault current Samples Test length/cm Average resistance/mX Average resistivity/ mXÁm Sample before impact Sample after impact Sample before impact Sample after impact 66.0 0.57 0.00027 68.0 0.58 0.00026 77.5 0.65 0.00026 77.5 0.73 0.00029 Fig Equivalent circuit used for impedance data modeling Please cite this article in press as: Shen W et al Preparation and characterization of 304 stainless steel/Q235 carbon steel composite material Results Phys (2017), http://dx.doi.org/10.1016/j.rinp.2016.12.050 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 RINP 517 No of Pages 6, Model 5G 11 January 2017 W Shen et al / Results in Physics xxx (2017) xxx–xxx 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 The two time constant equivalent electric circuit [17] shown in Fig was used to follow and model the evolution of impedance data and is adequate for interpreting the spectra for bare Q235 carbon steel, hot dip galvanized steel and the composite material during 0.5 h immersion in soil solution Rsol is the electrolyte resistance R1 and C correspond respectively to the coating resistance and capacitance, both linked to the barrier properties provided by the coating R2 and CPE are the charge transfer resistance and the double layer capacitance, related to the corrosion process The electrochemical characteristics of the composite material were studied using EIS, recorded after 0.5 h of immersion in soil solution Fig shows the complex plane impedance and the Bode plots (log Z and h vs logf) for bare carbon steel, hot dip galvanized steel and the composite material Compared with bare Q235 carbon steel and hot dip galvanized steel, the composite material showed at least order of magnitude higher impedance, reaching about kX in soil solution (Fig 7b) For the composite and hot dip galvanized steel, the phase angle dependence (Fig 7c) showed two time constants, which correspond to the corrosion activity due to the metal Fe dissolution and oxygen reduction or metal Zn dissolution The time constant appearing at high frequency is associated with the responses of the electrolyte/layer interface, which has described the dielectric and barrier properties of the layers The time constant at lower frequencies relates to the corrosion process at the electrolyte/substrate interface[18,19] The appearance of second time constant indicated the outer layer of the composite material and hot dip galvanized steel has been damaged by the electrolyte The values of EIS circuit parameters fitted according to the electrical equivalent circuit are displayed in Table The data clearly revealed that the composite material had higher anti-corrosion property than bare carbon steel and hot dip galvanized steel The corrosion resistance can be established in the following order: the composite > galvanized steel > carbon steel The higher corrosion resistance of the composite material than galvanized steel may be caused by the following facts The zinc plating layer protected carbon steel substrate through the dissolution of metal Zn After that, carbon steel experienced active corrosion And the dissolution of metal Fe into Fe2+ was the main anodic reaction However, the stainless steel layer protected carbon steel substrate by its self-passivation in soil solution The diffusion of oxygen across the solution boundary layer played an important role in the cathodic process 297 Conclusions 314 The stainless steel/carbon steel composite material was prepared by modified hot-rolling process The 304 stainless steel closely combined with Q235 carbon steel through metallurgical bonding, leading to the formation of transition region in the composite material The composite material showed superior electrical conductivity to hot dip galvanized steel underground Moreover, 315 Fig Complex plane impedance (a), modulus impedance (b) and phase (c) plots of the composite material, hot dip galvanized steel and bare Q235 carbon steel after 0.5 h exposure to soil solution Please cite this article in press as: Shen W et al Preparation and characterization of 304 stainless steel/Q235 carbon steel composite material Results Phys (2017), http://dx.doi.org/10.1016/j.rinp.2016.12.050 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 316 317 318 319 320 RINP 517 No of Pages 6, Model 5G 11 January 2017 W Shen et al / Results in Physics xxx (2017) xxx–xxx Table Parameters of the electrical equivalent circuit for bare carbon steel, hot dip galvanized steel and the composite material Samples Q235 carbon steel Hot dip galvanized steel Composite material Rsol C R1 CPE n R2 159.9 5.099  10À9 385.2 3.113  10À4 0.76639 2282 190.8 57.307  10À9 254.5 9.173  10À5 0.39766 8539 134.8 1.273  10À8 222.3 4.831  10À5 0.79325 3.188  106 331 the composite material had good thermal stability without any surface crack and bubbling after fault current impact From the electrochemical measurements, it was found that the corrosion resistance of carbon steel was significantly improved by the stainless steel layer in soil solution The composite material had an average grounding resistance of 89.64 X, an impedance value of about 3.09  104 X and a corrosion rate of 9.78  10À3 mm/a, order of magnitude lower than that of hot dip galvanized steel Thus, stainless steel/carbon steel composite material could be used as grounding materials, to potentially substitute hot dip galvanized steel 332 Acknowledgments 333 338 This work was supported financially by Dr Start-up funds of Xi’an University of Technology, Science Research Project of Xi’an University of Technology (2015TS001), Key Laboratory Project of Education Department of Shaanxi Province (15JS080), and Science and Technology Co-ordination & Innovation Key Laboratory Project of Shaanxi Province (2014SZS09-Z02) 339 References 321 322 323 324 325 326 327 328 329 330 334 335 336 337 340 341 342 [1] Khan Y, Pazheri FR, Malik NH, Al-Arainy AA, Qureshi MI Novel approach of estimating grounding pit optimum dimensions in high resistivity soils Electr Power Sys Res 2012;92:145–54 [2] He JL, Zeng R Grounding technology of electric power system Beijing: Science Press; 2007 [3] Lim SC, Gomes C, Kadir MZAA Electr Power Energy Sys 2013;47:117–28 [4] Kostic VI, Raicevic NB 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381 382 383 384 385 386 387 388 389 390 ... layer material and substrate respectiviely for the preparation of stainless steel/ carbon steel composite material Hot dip galvanized steel bar and bare Q235 carbon steel were used as control 91 Preparation. .. (a) and the clad layer thickness (b) of the stainless steel/ carbon steel composite material Grounding resistance of the composite material 200 In order to confirm the prepared composite material. .. bare carbon steel, hot dip galvanized steel and the composite material Compared with bare Q235 carbon steel and hot dip galvanized steel, the composite material showed at least order of magnitude