Title of Invention	AN IMPROVED SURFACE TREATMENT PROCESS FOR PRODUCING ENHANCED CORROSION RESISTANT IRON AND STEEL
Abstract	An improved surface treatment process for producing enhanced corrosion resistant iron and steel which comprises in activating the surface of iron or steel either in inhibited hydrochloric acid of concentration ranging from 30 to 50% containing hexamine as inhibitor in the range 0.5 to 1% for a period ranging from 5 to 30 minutes or alternatively in sulphuric acid of concentration ranging from 5 to 25% for a period ranging from 1 - 5 minutes, dipping in copper sulphate solution of critical pH ranging from 1.5 to 5.5 for a period ranging from 60 to 600 seconds and then heat treating at 500 - 900°C for a period ranging from () r> to 5 hours to enhanced corrosion resistant iron or steel

Title of Invention

AN IMPROVED SURFACE TREATMENT PROCESS FOR PRODUCING ENHANCED CORROSION RESISTANT IRON AND STEEL

Abstract

An improved surface treatment process for producing enhanced corrosion resistant iron and steel which comprises in activating the surface of iron or steel either in inhibited hydrochloric acid of concentration ranging from 30 to 50% containing hexamine as inhibitor in the range 0.5 to 1% for a period ranging from 5 to 30 minutes or alternatively in sulphuric acid of concentration ranging from 5 to 25% for a period ranging from 1 - 5 minutes, dipping in copper sulphate solution of critical pH ranging from 1.5 to 5.5 for a period ranging from 60 to 600 seconds and then heat treating at 500 - 900°C for a period ranging from () r> to 5 hours to enhanced corrosion resistant iron or steel

Full Text	The present invention relates to j process for the preparation enhanced corrosion resistant iron and steel. The present invention particularly relates to improvements in or relating to a surface treatment process for enhanced corrosion resistance of structural iron and steel. The main usage of the invention is the considerable enhancement in the durability of iron and steel structural components particularly useful in marine and alkaline environments. Therefore, this invention will have direct impact and application in steel industry. This invention will also directly lead to considerable saving in the construction industry because of the enhanced durability of reinforced concrete structures. It is fairly well known that the structural iron and steel normally have only limited corrosion resistance and they need additional protective treatments when exposed to hostile environments. Reference may be made to B.I.S. standard 8629 - Code of Practice for Protection of Iron and Steel structures from Atmospheric Corrosion wherein no surface treatment at the manufacturer's end for imparting inherent corrosion resistance has been specified. The drawback is the need for effective surface preparation and other protective schemes at the user's end. Reference may be made to the Materials Selector, Second Edition, Edited by Norman A.Waterman and Michael F.Ashby, Chapman & Hall, UK, 1997) wherein diffusional coating based on chromium or nickel has been suggested. The drawback is that chromium or nickel based diffusion process needs controlled atmosphere as well as high operating temperature (1000°C). Another drawback is the durability factor for chromised steel (pack chromising) surface is around 10 while nickel diffusion coated steel has a durability factor of only around 2 and the durability is inadequate. Reference may be made to J.R.Davis, Surface Engineering of Carbon and Alloy Steels in ASM Handbook on Surface Engineering, Vol.5, ASM International, 1994, p 738 wherein for certain industrial applications, nitriding or carburising is recommended. The drawbacks are that nitriding or carburisation process renders the substrate more vulnerable for stress corrosion and corrosion fatigue because of increased hardness and operating temperature is also on the higher side (1000 - 1100° C). Reference may be made to High Strength Low Alloy Steels, Committee on Technology, Brussels, International Iron and Steel Institute, 1997 wherein thermomechanical treatment has also been advocated in conjunction with low alloying with elements like Cr , Cu, Si, Mo, Nb, Ti etc. The drawback is that thermomechanical treatment by itself does not impart corrosion resistance and hence the process is to be complimented with addition of a number of alloy elements. Reference may also be made to RDCIS - SAIL: Extended Abstracts of Completed Projects 96/97, p 88 wherein the durability factor for thermomechanical treatment rebar is reported to be only around 2. The drawback is that the atmospheric corrosion resistance against chloride attack is inadequate. The main object of the present invention is to provide an improved process for preparation of enhanced corrosion resistant iron and steel which obviates the drawbacks as detailed above. Another object of the present invention is to develop a cost effective surface modification method, which is amenable for adaptation at manufacturer's end. Accordingly, the present invention provides an improved surface treatment process for producing enhanced corrosion resistant iron and steel which comprises in activating the surface of iron or steel either in inhibited hydrochloric acid of concentration ranging from 30 to 50% containing hexamine as inhibitor in the range 0.5 to 1% for a period ranging from 5 to 30 minutes or alternatively in sulphuric acid of concentration tanging from 5 to 25% for a period ranging from 1-5 minutes, dipping in copper sulphate solution of critical pH ranging from 1.5 to 5.5 for a period ranging from 60 to 600 seconds and then heat treating at 500 - 900°C for a period ranging from 0.5 to 5 hours to enhanced corrosion resistant iron or steel Hitherto known processes for heat treatment of ferrous substrate and formation of stable oxide coating do not involve any thermally conducting metallic medium with a result that any oxide coating formed on ferrous substrate had only limited corrosion resistance. The novelty of the present invention lies in forming a thermally conducting metallic copper uniformly spread over the entire ferrous substrate. This is achieved by dipping the ferrous substrate in copper sulphate solution for a short period so that a layer of metallic copper is formed on the surface. This is a temporary layer acting as a thermal jacket on the ferrous substrate. During subsequent heat treatment of the ferrous substrate, this metallic copper promotes catalytic reaction for the formation of a highly corrosion resistant oxide film on the ferrous substrate. In an embodiment of the present invention the surface to be treated is first activated by dipping either in hydrochloric acid of concentration ranging from 30 to 50% containing hexamine as inhibitor in the range 0.5 to 1 % for a period ranging from 5 to 30 minutes or in sulphuric acid of concentration ranging from 5 to 25 % for a period ranging from 1 to 5 minutes In another embodiment of the present invention the activated surface is immediately dipped in copper sulphate solution of critical pH 1.5 to 5.5 for a duration ranging from 60 to 600 seconds. In yet another embodiment of the present invention the modified surface is subjected to heat treatment at a critical temperature - time sequence, the temperature ranging 500 to 900 °C and the treatment time ranging from 0.5 to 5 hrs. The invention broadly consists in activating the iron or steel surface either in inhibited hydrochloric acid medium or in sulphuric acid medium followed by dipping in copper sulphate solution of a critical pH ranging from 1.5 to 5.5 for a period ranging from 60 to 600 seconds. The material is then heat treated at a temperature ranging from 500°C to 900°C for a period ranging from 0.5 to 5 hrs. The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention. EXAMPLE -1 The corrosion resistance of the mild steel treated as per this invention was evaluated by anodic polarisation technique as per reference made to K.S.RaJagopalan, K.Venu and K.Balakrishnan, Journal of Electrochemical Society, Vol. 109, 1962, p81 . Plain round mild steel of size 10 mm in dia. and 30 mm in length was activated in 30% concentrated hydrochloric acid containing 10 gms hexamine as inhibitor. Then the surface was dipped in copper sulphate solution of pH 3.2 for 400 seconds. The material was heat treated at 500°C for 4.75 hours. After heat treatment, the specimen was degreased with acetone. An exposed area of 4 cm2 was used for corrosion studies and the remaining portion was lacquered both at top and bottom. The test specimen was kept immersed in 0.04N NaOH solution containing 5000-ppm chloride. The open circuit potential was monitored using high impedance multimeter against saturated calomel electrode. After getting stabilized potential, the test specimen was anodically polarised sat a constant current density of 290 uA/cm using platinum as auxiliary electrode. This optimum current density was required to shift the potential of the specimen to oxygen evolution potential. The potential was monitored for 5 minutes. If the passivity is maintained, the potential remains constant at the oxygen evolution potential value till 5 minutes. If the passivity is broken, the potential drops to more negative values with time. The experiment was repeated on an untreated mild steel specimen of the same dimension in 0.04 N NaOH solution containing 5000 ppm chloride. At the end of the experiment the specimen was taken out and visually observed for rust spots. The results of this study are given below: Steel Visual Observations Steel treated as per this No rust spots Invention Untreated steel Innumerable rust spots It is thus shown that the steel treated as per this invention has very high tolerable limit for chloride as compared to untreated mild steel. EXAMPLE -2 The corrosion resistance of the cold twisted deformed (CTD) rebar treated as per this invention was evaluated by anodic polarisation technique as per reference made to K.S.RaJagopalan, K.Venu and K.Balakrishnan, Journal Electrochemical Society, Vol. 109, 1962,p81. CTD steel of size 10 mm in dia. and 30 mm in length was activated in 50% concentrated hydrochloric acid containing 10 gms hexamine as inhibitor. Then the activated steel was dipped in copper sulphate solution of pH 5.0 for 360 seconds. The material was heat treated at 700°C for 2.25 hours. After heat treatment, the fspecimen was degreased with acetone. An exposed area of 4 cm was used for corrosion studies and the remaining portion was lacquered both at top and bottom. The test specimen was kept immersed in 0.04N NaOH solution containing 10000 ppm chloride. The open circuit potential was monitored using high impedance multimeter against saturated calomel electrode. After getting stabilized potential, the test specimen was anodically polarised at a constant current ^ density of 290 uA/cm using platinum as auxiliary electrode. This optimum current density was required to shift the potential of the specimen to oxygen evolution potential . The potential was monitored for 5 minutes. If the passivity is maintained, the potential remains constant at the oxygen evolution potential value till 5 minutes. If the passivity is broken, the potential drops to more negative values with time. The experiment was repeated on an untreated CTD steel specimen of the same dimension in 0.04 N NaOH solution containing 10000 ppm chloride. At the end of the experiment the specimen was taken out and visually observed for rust spots. The results of this study are given below: Steel Visual Observations Steel treated as per this No rust spots Invention Untreated steel Innumerable rust spots It is thus shown that the treated cold twisted steel as per this invention has very high tolerable limit for chloride as compared to untreated cold twisted steel. EXAMPLE -3 Surface treatment as per this invention was given to thermomechanically treated rebar (TMT) and its corrosion resistance was evaluated by anodic polarisation technique as per reference made to K.S.Rajagopalan, K.Venu and K.Balakrishnan Journal of Electrochemical Society, Vol .109, 1962 p81. TMT steel of size 10 mm in dia. and 30 mm in length was activated in 30% concentrated hydrochloric acid containing 10 gms hexamine as inhibitor. Then the activated steel was dipped in copper sulphate solution of pH 4.7 for 250 seconds. The material was heat treated at 900°C for 1 hour. After heat treatment, the specimen was degreased ri with acetone. An exposed area of 4 cm was used for corrosion studies and the remaining portion was lacquered both at top and bottom. The test specimen was kept immersed in 0.04N NaOH solution containing 10000-ppm chloride. The open circuit potential was monitored using high impedance multimeter against saturated calomel electrode. After getting stabilized potential, the test specimen was anodically polarised at a constant current density of 290 uA/cm2 using platinum as auxiliary' electrode. This optimum current density was required to shift the potential of the specimen to oxygen evolution potential. The potential was monitored for 5 minutes. If the passivity is maintained, the potential remains constant at the oxygen evolution potential value till 5 minutes. If the passivity is broken, the potential drops to more negative values with time. The experiment was repeated on an untreated TMT steel specimen of the same dimension in 0.04 N NaOH solution containing 10000 ppm chloride. At the end of the experiment the specimen was taken out and visually observed for rust spots. The results of this study are given below: Steel Visual Observations Steel treated as No rust spots per this invention Untreated steel Innumerable rust spots It is thus shown that the treated TMT steel as per this invention has very high tolerable limit for chloride as compared to untreated TMT steel. EXAMPLE - 4 The corrosion resistance of the mild steel sheet treated as per this invention was evaluated by anodic polarisation technique as per reference made to K.S.RaJagopalan, K.Venu and K.Balakrishnan, Journal of Electrochemical Society, Vol.109, 1962 p.81. Mild steel sheet of size 40mm x 15 mm x 2mm was activated in 30% concentrated hydrochloric acid containing 10 gms hexamine as inhibitor. Then the activated steel was dipped in copper sulphate solution of pH 3.5 for 300 seconds. The material was heat treated at 700°C for 5 hours. After heat treatment, the specimen was degreased with acetone. An exposed area of 4 cm2 was used for corrosion studies and the remaining portion was lacquered both at top and bottom. The test specimen was kept immersed in 0.04N NaOH solution containing 10,000 ppm chloride. The open circuit potential was monitored using high impedance multimeter against saturated calomel electrode. After getting stabilized potential, the test specimen was anodically polarised -^ at a constant current density of 290 uA/cm using platinum as auxiliary electrode. This optimum current density was required to shift the potential of the specimen to oxygen evolution potential. The potential was monitored for 5 minutes. If the passivity is maintained, the potential remains constant at the oxygen evolution potential value till 5 minutes. If the passivity is broken, the potential drops to more negative values with time. The experiment was repeated on an untreated mild steel sheet specimen of the same dimension in 0.04 N NaOH solution containing 10000 ppm chloride. At the end of the experiment the specimen was taken out and visually observed for rust spots. The results of this study are given below: Steel Visual Observations Steel treated as per No rust spots this invention Untreated steel Innumerable rust spots It is thus shown that the mild steel sheet treated as per this invention has very high tolerable limit for chloride as compared to untreated mild steel sheet. EXAMPLE - 5 The corrosion resistance of the cold twisted deformed steel treated as per this invention was evaluated as per British Standard 1391: 1952 for Performance Tests For Protective Schemes. The test procedure for this ARE salt droplet test is given below: The specimens shall be suspended vertically, by means of hooks of glass insulator passing through the holes in two corners, over large dishes partly filled with water. The distance between the surface of the water and the lower edge of the specimens shall be 2-3 in. and the specimens shall be one behind the other and all face the same way. They shall be a convenient distance (not more than 1 in.) apart to prevent touching when being moved and a dummy specimen shall be placed at each end of each row. Once daily, for 5 days a week, all the specimens, including the dummies, shall be removed temporarily from their position on the rack and sprayed individually on both sides with the synthetic sea water using a hand-operated atomizer. The aim shall be to cover the surface with discrete droplets, by giving a number of puffs with the nozzle at a suitable distance (6-12 in.) from the specimens, the spray being directed, in turn, at different parts of the surface. The spraying shall not be so heavy that the droplets coalesce; in order to avoid this it may prove necessary on occasions, where the surface is still wet from the previous spraying to refrain from applying the full weight of spray specified below. It is essential to keep the specimens covered with droplets. Immediately after spraying, the specimens shall be returned to their positions on the rack and the whole collection shall be covered with a box-like cover of sheet metal or other suitable material, to prevent the drying of the droplets. The temperature throughout the test shall preferably be between 55°F. and 70° F. (say 13° C. and 21°C.) and the test assembly shall be protected against external sources of heat tending to produce local variations in temperature. Cold twisted mild steel rebar (2 nos.) of size 8mm dia. and 50mm in length was activated in 30% concentrated hydrochloric acid containing 10 gms hexamine as inhibitor. Then the activated steel was dipped in copper sulphate solution of pH 5.0 for 420 seconds. The material was heat treated at 700°C for 4 hours. After heat treatment, the specimen was degreased with acetone. An exposed area of 3 cm2 was used for corrosion studies and the remaining portion was lacquered both at top and bottom. The corrosion resistance of the treated CTD steel along with untreated CTD steel was simultaneously evaluated as per the procedure of A.R.E. Salt Droplet Test described above. During the testing period, daily the specimens were examined for corrosion. The corrosion rates for the treated and untreated specimens after 30 days of exposure are given below: Steel Corrosion rate, mg/dm2/day (mdd) Untreated steel 141.19 Steel treated as per this invention No corrosion. The results of this study show that the treated CTD rebar as per this invention passes A.R.E. Salt Droplet Test and the untreated CTD rebar does not pass this test. EXAMPLE-6 The atmospheric corrosion resistance of the mild steel sheet treated as per this invention was evaluated by exposing the specimens in the open atmosphere. 2 mm thick mild steel sheet of size 6" x 4"was activated in 30% concentrated hydrochloric acid containing 10 gms hexamine as inhibitor. Then the activated steel was dipped in copper sulphate solution of pH 3.5 for 300 seconds. The material was heat treated at 700°C for 5 hours. After heat treatment, the specimen was degreased with acetone. Then the treated mild steel sheet specimens along with untreated mild steel sheet specimens were simultaneously exposed to open atmosphere for a period of 30 days. Daily specimens were observed for corrosion. Corrosion has been observed on the untreated mild steel specimens within 4 days whereas no corrosion has been observed on the treated mild steel specimens as per this invention even after 30 days of exposure to the atmosphere. The novelty of this invention lies in utilizing a loosely adherent metallic copper layer on ferrous substrate as a temporary heating jacket to promote a catalytic reaction for forming a tenacious and protective oxide layer in ferrous substrates. This is elaborated as follows: When a ferrous substrate is dipped in copper sulphate solution, the substrate metal atoms at the surface are replaced by cuprous ions from copper sulphate solution, which are reduced at the substrate surface due to the difference in electrode potential of the two metal / ion systems. The extent of the deposition as well as the nature of deposition depend upon the pH of the copper sulphate solution. When ferrous substrate is dipped in the copper sulphate solution, a metallic layer of copper is uniformly adhering to the ferrous surface. This metallic copper layer because of its higher thermally conducting nature is able not only to uniformly distribute the temperature along the entire surface but also to concentrate the temperature closer to the ferrous substrate avoiding heat loss. This thing happens during subsequent heat treatment. That is to say that the copper layer acts as a heating jacket during the heat treatment process and activates the surface. This is hitherto unknown novel process. The critical pH controls the kinetics of reaction. The main advantages of the present invention are: 1. This invention is a simple process consisting of simple dipping and subsequent heating. The process is therefore amenable for adaptation at the steel manufacturing stage itself. 2. The durability factor obtained in this new invention is of the order of 20-40, which is several times more than the hitherto known processes. 3. Another advantage of this invention is that the maximum operating temperature is in the range 500 - 900°C, which results in considerable saving in heat energy. We Claim: 1. An improved surface treatment process for producing enhanced corrosion resistant iron and steel which comprises in activating the surface of iron or steel either in inhibited hydrochloric acid of concentration ranging from 30 to 50% containing hexamine as inhibitor in the range 0.5 to 1% for a period ranging from 5 to 30 minutes or alternatively in sulphuric acid of concentration ranging from 5 to 25% for a period ranging from 1 - 5 minutes, dipping in copper sulphate solution of critical pH ranging from 1.5 to 5.5 for a period ranging from 60 to 600 seconds and then heat treating at 500 - 90()°C for a period ranging from 0.5 to 5 hours to enhanced corrosion resistant iron or steel. 2. An improved surface treatment process for producing enhanced corrosion resistant iron and steel substantially as herein described with reference to the examples.

Full Text

The present invention relates to j process for the preparation enhanced corrosion resistant iron and steel.
The present invention particularly relates to improvements in or relating to a surface treatment process for enhanced corrosion resistance of structural iron and steel.
The main usage of the invention is the considerable enhancement in the durability of iron and steel structural components particularly useful in marine and alkaline environments. Therefore, this invention will have direct impact and application in steel industry. This invention will also directly lead to considerable saving in the construction industry because of the enhanced durability of reinforced concrete structures.
It is fairly well known that the structural iron and steel normally have only limited corrosion resistance and they need additional protective treatments when exposed to hostile environments.
Reference may be made to B.I.S. standard 8629 - Code of Practice for Protection of Iron and Steel structures from Atmospheric
Corrosion wherein no surface treatment at the manufacturer's end for imparting inherent corrosion resistance has been specified. The drawback is the need for effective surface preparation and other protective schemes at the user's end.
Reference may be made to the Materials Selector, Second Edition, Edited by Norman A.Waterman and Michael F.Ashby, Chapman & Hall, UK, 1997) wherein diffusional coating based on chromium or nickel has been suggested. The drawback is that chromium or nickel based diffusion process needs controlled atmosphere as well as high operating temperature (1000°C). Another drawback is the durability factor for chromised steel (pack chromising) surface is around 10 while nickel diffusion coated steel has a durability factor of only around 2 and the durability is inadequate.
Reference may be made to J.R.Davis, Surface Engineering of Carbon and Alloy Steels in ASM Handbook on Surface Engineering, Vol.5, ASM International, 1994, p 738 wherein for certain industrial
applications, nitriding or carburising is recommended. The drawbacks are that nitriding or carburisation process renders the substrate more vulnerable for stress corrosion and corrosion fatigue because of increased hardness and operating temperature is also on the higher side (1000 - 1100° C).
Reference may be made to High Strength Low Alloy Steels, Committee on Technology, Brussels, International Iron and Steel Institute, 1997 wherein thermomechanical treatment has also been advocated in conjunction with low alloying with elements like Cr , Cu, Si, Mo, Nb, Ti etc. The drawback is that thermomechanical treatment by itself does not impart corrosion resistance and hence the process is to be complimented with addition of a number of alloy elements.
Reference may also be made to RDCIS - SAIL: Extended Abstracts of Completed Projects 96/97, p 88 wherein the durability factor for thermomechanical treatment rebar is reported to be only around 2. The drawback is that the atmospheric corrosion resistance against chloride attack is inadequate.
The main object of the present invention is to provide an improved process for preparation of enhanced corrosion resistant iron and steel which obviates the drawbacks as detailed above.
Another object of the present invention is to develop a cost effective surface modification method, which is amenable for adaptation at manufacturer's end.
Accordingly, the present invention provides an improved surface treatment process for producing enhanced corrosion resistant iron and steel which comprises in activating the surface of iron or steel either in inhibited hydrochloric acid of concentration ranging from 30 to 50% containing hexamine as inhibitor in the range 0.5 to 1% for a period ranging from 5 to 30 minutes or alternatively in sulphuric acid of concentration tanging from 5 to 25% for a period ranging from 1-5 minutes, dipping in copper sulphate solution of critical pH ranging from 1.5 to 5.5 for a period ranging from 60 to 600 seconds and then heat treating at 500 - 900°C for a period ranging from 0.5 to 5 hours to enhanced corrosion resistant iron or steel
Hitherto known processes for heat treatment of ferrous substrate and formation of stable oxide coating do not involve any thermally
conducting metallic medium with a result that any oxide coating formed on ferrous substrate had only limited corrosion resistance. The novelty of the present invention lies in forming a thermally conducting metallic copper uniformly spread over the entire ferrous substrate. This is achieved by dipping the ferrous substrate in copper sulphate solution for a short period so that a layer of metallic copper is formed on the surface. This is a temporary layer acting as a thermal jacket on the ferrous substrate. During subsequent heat treatment of the ferrous substrate, this metallic copper promotes catalytic reaction for the formation of a highly corrosion resistant oxide film on the ferrous substrate.
In an embodiment of the present invention the surface to be treated is first activated by dipping either in hydrochloric acid of concentration ranging from 30 to 50% containing hexamine as inhibitor in the range 0.5 to 1 % for a period ranging from 5 to 30 minutes or in sulphuric acid of concentration ranging from 5 to 25 % for a period ranging from 1 to 5 minutes
In another embodiment of the present invention the activated surface is immediately dipped in copper sulphate solution of critical pH 1.5 to 5.5 for a duration ranging from 60 to 600 seconds.
In yet another embodiment of the present invention the modified surface is subjected to heat treatment at a critical temperature - time sequence, the temperature ranging 500 to 900 °C and the treatment time ranging from 0.5 to 5 hrs.
The invention broadly consists in activating the iron or steel surface either in inhibited hydrochloric acid medium or in sulphuric acid medium followed by dipping in copper sulphate solution of a critical pH ranging from 1.5 to 5.5 for a period ranging from 60 to 600 seconds. The material is then heat treated at a temperature ranging from 500°C to 900°C for a period ranging from 0.5 to 5 hrs.
The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention.
EXAMPLE -1
The corrosion resistance of the mild steel treated as per this invention was evaluated by anodic polarisation technique as per reference made to K.S.RaJagopalan, K.Venu and K.Balakrishnan, Journal of Electrochemical Society, Vol. 109, 1962, p81 . Plain round mild steel of size 10 mm in dia. and 30 mm in length was activated in 30% concentrated hydrochloric acid containing 10 gms hexamine as inhibitor. Then the surface was dipped in copper sulphate solution of pH 3.2 for 400 seconds. The material was heat treated at 500°C for 4.75 hours. After heat treatment, the specimen was degreased with acetone. An exposed area of 4 cm2 was used for corrosion studies and the remaining portion was lacquered both at top and bottom. The test specimen was kept immersed in 0.04N NaOH solution containing 5000-ppm chloride. The open circuit potential was monitored using high impedance multimeter against saturated calomel electrode. After getting stabilized potential, the test specimen was anodically polarised
sat a constant current density of 290 uA/cm using platinum as auxiliary electrode. This optimum current density was required to
shift the potential of the specimen to oxygen evolution potential. The potential was monitored for 5 minutes. If the passivity is maintained, the potential remains constant at the oxygen evolution potential value till 5 minutes. If the passivity is broken, the potential drops to more negative values with time. The experiment was repeated on an untreated mild steel specimen of the same dimension in 0.04 N NaOH solution containing 5000 ppm chloride. At the end of the experiment the specimen was taken out and visually observed for rust spots. The results of this study are given below:
Steel Visual Observations
Steel treated as per this No rust spots
Invention
Untreated steel Innumerable rust spots
It is thus shown that the steel treated as per this invention has very high tolerable limit for chloride as compared to untreated mild steel.
EXAMPLE -2
The corrosion resistance of the cold twisted deformed (CTD) rebar treated as per this invention was evaluated by anodic polarisation technique as per reference made to K.S.RaJagopalan, K.Venu and K.Balakrishnan, Journal Electrochemical Society, Vol. 109, 1962,p81. CTD steel of size 10 mm in dia. and 30 mm in length was activated in 50% concentrated hydrochloric acid containing 10 gms hexamine as inhibitor. Then the activated steel was dipped in copper sulphate solution of pH 5.0 for 360 seconds. The material was heat treated at 700°C for 2.25 hours. After heat treatment, the
fspecimen was degreased with acetone. An exposed area of 4 cm was used for corrosion studies and the remaining portion was lacquered both at top and bottom. The test specimen was kept immersed in 0.04N NaOH solution containing 10000 ppm chloride. The open circuit potential was monitored using high impedance multimeter against saturated calomel electrode. After getting stabilized potential, the test specimen was anodically polarised at a constant current
^
density of 290 uA/cm using platinum as auxiliary electrode. This

optimum current density was required to shift the potential of the specimen to oxygen evolution potential . The potential was monitored for 5 minutes. If the passivity is maintained, the potential remains constant at the oxygen evolution potential value till 5 minutes. If the passivity is broken, the potential drops to more negative values with time. The experiment was repeated on an untreated CTD steel specimen of the same dimension in 0.04 N NaOH solution containing 10000 ppm chloride. At the end of the experiment the specimen was taken out and visually observed for rust spots. The results of this study are given below:
Steel Visual Observations
Steel treated as per this No rust spots
Invention
Untreated steel Innumerable rust spots
It is thus shown that the treated cold twisted steel as per this invention has very high tolerable limit for chloride as compared to untreated cold twisted steel.
EXAMPLE -3
Surface treatment as per this invention was given to thermomechanically treated rebar (TMT) and its corrosion resistance was evaluated by anodic polarisation technique as per reference made to K.S.Rajagopalan, K.Venu and K.Balakrishnan Journal of Electrochemical Society, Vol .109, 1962 p81. TMT steel of size 10 mm in dia. and 30 mm in length was activated in 30% concentrated hydrochloric acid containing 10 gms hexamine as inhibitor. Then the activated steel was dipped in copper sulphate solution of pH 4.7 for 250 seconds. The material was heat treated at 900°C for 1 hour. After heat treatment, the specimen was degreased
ri
with acetone. An exposed area of 4 cm was used for corrosion studies and the remaining portion was lacquered both at top and bottom. The test specimen was kept immersed in 0.04N NaOH solution containing 10000-ppm chloride.
The open circuit potential was monitored using high impedance multimeter against saturated calomel electrode. After getting stabilized potential, the test specimen was anodically polarised at a
constant current density of 290 uA/cm2 using platinum as auxiliary' electrode. This optimum current density was required to shift the potential of the specimen to oxygen evolution potential. The potential was monitored for 5 minutes. If the passivity is maintained, the potential remains constant at the oxygen evolution potential value till 5 minutes. If the passivity is broken, the potential drops to more negative values with time. The experiment was repeated on an untreated TMT steel specimen of the same dimension in 0.04 N NaOH solution containing 10000 ppm chloride. At the end of the experiment the specimen was taken out and visually observed for rust spots.
The results of this study are given below:
Steel Visual Observations
Steel treated as No rust spots
per this invention
Untreated steel Innumerable rust spots
It is thus shown that the treated TMT steel as per this invention has very high tolerable limit for chloride as compared to untreated TMT steel.
EXAMPLE - 4
The corrosion resistance of the mild steel sheet treated as per this invention was evaluated by anodic polarisation technique as per reference made to K.S.RaJagopalan, K.Venu and K.Balakrishnan, Journal of Electrochemical Society, Vol.109, 1962 p.81. Mild steel sheet of size 40mm x 15 mm x 2mm was activated in 30% concentrated hydrochloric acid containing 10 gms hexamine as inhibitor. Then the activated steel was dipped in copper sulphate solution of pH 3.5 for 300 seconds. The material was heat treated at 700°C for 5 hours. After heat treatment, the specimen was degreased with acetone. An exposed area of 4 cm2 was used for corrosion studies and the remaining portion was lacquered both at top and bottom. The test specimen was kept immersed in 0.04N NaOH solution containing 10,000 ppm chloride. The open circuit potential was monitored using high impedance multimeter against saturated calomel electrode. After
getting stabilized potential, the test specimen was anodically polarised
-^
at a constant current density of 290 uA/cm using platinum as auxiliary electrode. This optimum current density was required to shift the potential of the specimen to oxygen evolution potential. The potential was monitored for 5 minutes. If the passivity is maintained, the potential remains constant at the oxygen evolution potential value till 5 minutes. If the passivity is broken, the potential drops to more negative values with time. The experiment was repeated on an untreated mild steel sheet specimen of the same dimension in 0.04 N NaOH solution containing 10000 ppm chloride. At the end of the experiment the specimen was taken out and visually observed for rust spots. The results of this study are given below:
Steel Visual Observations
Steel treated as per No rust spots
this invention
Untreated steel Innumerable rust spots
It is thus shown that the mild steel sheet treated as per this invention has very high tolerable limit for chloride as compared to untreated mild steel sheet.
EXAMPLE - 5
The corrosion resistance of the cold twisted deformed steel treated as per this invention was evaluated as per British Standard 1391: 1952 for Performance Tests For Protective Schemes.
The test procedure for this ARE salt droplet test is given below:
The specimens shall be suspended vertically, by means of hooks of glass insulator passing through the holes in two corners, over large dishes partly filled with water. The distance between the surface of the water and the lower edge of the specimens shall be 2-3 in. and the specimens shall be one behind the other and all face the same way. They shall be a convenient distance (not more than 1 in.) apart to prevent touching when being moved and a dummy specimen shall be placed at each end of each row.
Once daily, for 5 days a week, all the specimens, including the dummies, shall be removed temporarily from their position on the
rack and sprayed individually on both sides with the synthetic sea water using a hand-operated atomizer. The aim shall be to cover the surface with discrete droplets, by giving a number of puffs with the nozzle at a suitable distance (6-12 in.) from the specimens, the spray being directed, in turn, at different parts of the surface. The spraying shall not be so heavy that the droplets coalesce; in order to avoid this it may prove necessary on occasions, where the surface is still wet from the previous spraying to refrain from applying the full weight of spray specified below. It is essential to keep the specimens covered with droplets.
Immediately after spraying, the specimens shall be returned to their positions on the rack and the whole collection shall be covered with a box-like cover of sheet metal or other suitable material, to prevent the drying of the droplets.
The temperature throughout the test shall preferably be between 55°F. and 70° F. (say 13° C. and 21°C.) and the test assembly shall be protected against external sources of heat tending to produce local variations in temperature.
Cold twisted mild steel rebar (2 nos.) of size 8mm dia. and 50mm in length was activated in 30% concentrated hydrochloric acid containing 10 gms hexamine as inhibitor. Then the activated steel was dipped in copper sulphate solution of pH 5.0 for 420 seconds. The material was heat treated at 700°C for 4 hours. After heat treatment, the specimen was degreased with acetone. An exposed area of 3 cm2 was used for corrosion studies and the remaining portion was lacquered both at top and bottom.
The corrosion resistance of the treated CTD steel along with untreated CTD steel was simultaneously evaluated as per the procedure of A.R.E. Salt Droplet Test described above. During the testing period, daily the specimens were examined for corrosion. The corrosion rates for the treated and untreated specimens after 30 days of exposure are given below:
Steel Corrosion rate,
mg/dm2/day (mdd)
Untreated steel 141.19
Steel treated as per
this invention No corrosion.
The results of this study show that the treated CTD rebar as per this invention passes A.R.E. Salt Droplet Test and the untreated CTD rebar does not pass this test.
EXAMPLE-6
The atmospheric corrosion resistance of the mild steel sheet treated as per this invention was evaluated by exposing the specimens in the open atmosphere. 2 mm thick mild steel sheet of size 6" x 4"was activated in 30% concentrated hydrochloric acid containing 10 gms hexamine as inhibitor. Then the activated steel was dipped in copper sulphate solution of pH 3.5 for 300 seconds. The material was heat treated at 700°C for 5 hours. After heat treatment, the specimen was degreased with acetone. Then the treated mild steel sheet specimens along with untreated mild steel sheet specimens were simultaneously exposed to open atmosphere for a period of 30 days. Daily specimens were observed for corrosion. Corrosion has been observed on the untreated mild steel specimens within 4 days whereas no corrosion has been observed on the treated mild steel
specimens as per this invention even after 30 days of exposure to the atmosphere.
The novelty of this invention lies in utilizing a loosely adherent metallic copper layer on ferrous substrate as a temporary heating jacket to promote a catalytic reaction for forming a tenacious and protective oxide layer in ferrous substrates. This is elaborated as follows:
When a ferrous substrate is dipped in copper sulphate solution, the substrate metal atoms at the surface are replaced by cuprous ions from copper sulphate solution, which are reduced at the substrate surface due to the difference in electrode potential of the two metal / ion systems. The extent of the deposition as well as the nature of deposition depend upon the pH of the copper sulphate solution. When ferrous substrate is dipped in the copper sulphate solution, a metallic layer of copper is uniformly adhering to the ferrous surface. This metallic copper layer because of its higher thermally conducting nature is able not only to uniformly distribute the temperature along the entire surface but also to concentrate the temperature closer to the
ferrous substrate avoiding heat loss. This thing happens during subsequent heat treatment. That is to say that the copper layer acts as a heating jacket during the heat treatment process and activates the surface. This is hitherto unknown novel process. The critical pH controls the kinetics of reaction. The main advantages of the present invention are:
1. This invention is a simple process consisting of simple
dipping and subsequent heating. The process is therefore
amenable for adaptation at the steel manufacturing stage
itself.
2. The durability factor obtained in this new invention is of the
order of 20-40, which is several times more than the hitherto
known processes.
3. Another advantage of this invention is that the maximum
operating temperature is in the range 500 - 900°C, which
results in considerable saving in heat energy.

We Claim:
1. An improved surface treatment process for producing enhanced corrosion resistant
iron and steel which comprises in activating the surface of iron or steel either in
inhibited hydrochloric acid of concentration ranging from 30 to 50% containing
hexamine as inhibitor in the range 0.5 to 1% for a period ranging from 5 to 30
minutes or alternatively in sulphuric acid of concentration ranging from 5 to 25% for
a period ranging from 1 - 5 minutes, dipping in copper sulphate solution of critical
pH ranging from 1.5 to 5.5 for a period ranging from 60 to 600 seconds and then
heat treating at 500 - 90()°C for a period ranging from 0.5 to 5 hours to enhanced
corrosion resistant iron or steel.
2. An improved surface treatment process for producing enhanced corrosion resistant
iron and steel substantially as herein described with reference to the examples.

Documents:

1557-del-1999-abstract.pdf

1557-del-1999-claims.pdf

1557-del-1999-correspondence-others.pdf

1557-del-1999-correspondence-po.pdf

1557-del-1999-description (complete).pdf

1557-del-1999-form-1.pdf

1557-del-1999-form-19.pdf

1557-del-1999-form-2.pdf

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Patent Number

232084

Indian Patent Application Number

1557/DEL/1999

PG Journal Number

13/2009

Publication Date

27-Mar-2009

Grant Date

15-Mar-2009

Date of Filing

21-Dec-1999

Name of Patentee

COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110 001,INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	NERUR SANKARA NARAYANA RENGASWAMY SOKKIAH RAMU	CENTRAL ELECTRONICAL RESEARCH INSTITUTE, KERAIKUDI,INDIA

PCT International Classification Number

C23F 11/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA