CA1038245A - Process for improving the anti-corrosion properties of steel coated with nickel or cobalt - Google Patents
Process for improving the anti-corrosion properties of steel coated with nickel or cobaltInfo
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- CA1038245A CA1038245A CA221,769A CA221769A CA1038245A CA 1038245 A CA1038245 A CA 1038245A CA 221769 A CA221769 A CA 221769A CA 1038245 A CA1038245 A CA 1038245A
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Abstract
ABSTRACT OF THE DISCLOSURE
A process is provided for coating a ferrous metal article, e.g. steel or iron, with a corrosion resistant surface layer. The process involves first coating the article with a layer of nickel and/
or cobalt, then heating the coated article for a time less than 45 minutes at an austenitizing temperature in excess of 725°C and then applying to the first metal layer an additional layer of at least one of the metals selected from the group consisting of chromium, tin, lead, zinc, copper and cadmium. The coated article so obtained has improved resistance to corrosion.
A process is provided for coating a ferrous metal article, e.g. steel or iron, with a corrosion resistant surface layer. The process involves first coating the article with a layer of nickel and/
or cobalt, then heating the coated article for a time less than 45 minutes at an austenitizing temperature in excess of 725°C and then applying to the first metal layer an additional layer of at least one of the metals selected from the group consisting of chromium, tin, lead, zinc, copper and cadmium. The coated article so obtained has improved resistance to corrosion.
Description
103~5 The present invention relates to a process o~ improving the anti-corrosion properties of ferrous metals, e.g. steel articles, with a surface layer containing nickel andfor cobalt and the article s produced thereby.
It is known to coat steel already coated with a layer of ;
nickel with another metal layer, e.g. zinc or chromium. In this way, ~n improvement in anti-corrosion properties of the steel is obtained.
It is also known to coat steels with a layer of nickel and then to subject the coated steel to a diffusion heat treatment at a temperature in excess of 725C for a relatively short time in order to effect an improvement in the anti-corrosion properties thereof. In this connection, reference is made to U.S. Patent No. 2,731,403.
An object of one aspect of this invention is to provide a process for improving the corrosion resistant properties of a ferrous metal articleg e.g. a steel substrate or article, already coated with a surface layer of nickel andior cobalt. - -An object of another aspect of this invention is to provide a coated steel article characterized by improved resistance to corro--sion.
It has now surprisingly been discovered that a combination of the known processes described above provides a considerably improved effect with respect to the anti-corrosion properties of the steel;
- Accordingly, by one broad aspect the present invention provides for properties of a steel article which process comprises applying to said article a first layer of at least one metal selected from the group consisting of nickel and cobalt, subjecting said coated article to a bonding heat treatment at an austenitizing temperature in the range of 725C - 1000C for a time less than 45 minutes, and then applying as a second layer at least one metal seIected from the A ~
It is known to coat steel already coated with a layer of ;
nickel with another metal layer, e.g. zinc or chromium. In this way, ~n improvement in anti-corrosion properties of the steel is obtained.
It is also known to coat steels with a layer of nickel and then to subject the coated steel to a diffusion heat treatment at a temperature in excess of 725C for a relatively short time in order to effect an improvement in the anti-corrosion properties thereof. In this connection, reference is made to U.S. Patent No. 2,731,403.
An object of one aspect of this invention is to provide a process for improving the corrosion resistant properties of a ferrous metal articleg e.g. a steel substrate or article, already coated with a surface layer of nickel andior cobalt. - -An object of another aspect of this invention is to provide a coated steel article characterized by improved resistance to corro--sion.
It has now surprisingly been discovered that a combination of the known processes described above provides a considerably improved effect with respect to the anti-corrosion properties of the steel;
- Accordingly, by one broad aspect the present invention provides for properties of a steel article which process comprises applying to said article a first layer of at least one metal selected from the group consisting of nickel and cobalt, subjecting said coated article to a bonding heat treatment at an austenitizing temperature in the range of 725C - 1000C for a time less than 45 minutes, and then applying as a second layer at least one metal seIected from the A ~
-2- -~
-~()3~245 group consisting of chromium, tin~ lead, zinc, copper and cadmium to ~aid first layer~ whereby a coated article is obtained characterized by improved resistance to corrosion.
By one variant of this process, the period of heat treatment is less than 15 minutes, preferably less than 5 minutes.
By yet another variant, the first layer is applied at a thickness of over 2 microns and wherein said second mètal layer is also applied at a thickness of over 2 microns.
By a still further variant, the thicknesses of the first layer and of the second layer is 5-25 microns.
By another variant~ the steel is a carbon steel containing up to 0O9~ carbon.
- ~ By still another variant, the steel article contains 0.2%
to 0.6% carDon and wherein following the bonding heat treatment at said austenitizing temperature, the article is rapidly cooled to form a martensitic structure.
By another a,spect of'this invention, a process is provided for improving the corrosion resistance of a steel article which compris-es, applying to said article a first thin layer of at least one metal selected from the group consisting of nickel and cobalt over a thickness range of over 2 to 50 microns, heat treating said coated article at an austenitizing temperature falling within the range of 725C to 1000C at substantially less than 45 minutes, and then applying a second thin layer of at least one metal selected from the group consisting of chromium 9 tin, lead, zinc, copper and cadmium to said first layer of a thickness of o~er 2-50 microns, whereby a coated article is obtained characterized by improved resistance to corrosion.
By a variant thereof, the period of heat treatment is less than 15 minutes, preferably less than 5 minutes.
.
~ ~ -3-. -- . . =
_ _ . . .. . _ _, . .
1038Z~s By another varian~ ther~of, the steel article con~ains up to 0.9~ carbon by weight and wherein following the bonding heat treatment at said austenitizing temperature, the article is rapidly cooled to form a martensitic structure.
By another aspect of this invention, a novel article of manufacture of provided comprising a steel substrate having bonded thereto a first layer of a metal selected from the group consisting of nickel and cobalt at a thickness ranging from over 2 to 50 microns and a second metal layer selected from the group consisting of chromium, tin, lead, zinc, copper and cadmium bonded to said first layer at a thickness ranging from over 2 to S0 microns, said article being heat *reated at a temperature of 725-1000C at which - phase transition to austentic structure of carbon begins before the deposition of said second metal 7 said steel substrate being characteri-zed by markedly improved resistance to corrosion.
By one variant, the steel is a carbon steel containing up to 0.9~ carbon, preferably 0.2 - 0.6% carbon.
The heat treatment of the nickel and/or cobalt layer comprises the first stage of the process of an aspect of the present invention. This heat treatment should take place within such limits with respect to temperature and time that the diffusion of nickel and/
or obalt into the steel substrate is sufficiently inhibited and preferably does not exceed a maximum of a few microns. In this manner, diffusion of iron into the nickel and/or cobalt layer will also be sufficiently inhibited. ThiS is achieved by carrying out the A
-3a-;q F
1038245 ~
heat treatment at a temperature in excess of b7~t 725C for,a time lèss than 45 minutes, Actually, the bèst results are obtained as regards the anti-corrosion properties of the final surface layer if the heat treatment of the steel object,pre- - L
coated with nickel and/ox cobalt is carried out for a time sub-s~antially less than 30 minutes. Thus, it has been found that diffusion of nickel and/or cobalt into the substrate is further ~ -, inhibited if the heat treatment is less than 15 minutes. Tests ~ - - .
have indicated that better anti-corrosion properties are obtained ~
at less,than 15 minutes of heat treatment as compared to heat - ~r-~
treatment tim2s of be~een 15 and 30 minutes and that periods '~
' of heat treatment of even less than ' 5 minutes provide the , i best properties in the final surface layer~ The-time at which -, 'the temperature of treatment of the surface layer amounts to or , ' ,~ .
15' ' exceeds 725C is referred to as ~he period of heat treatment. ~ - -P2rio~s of heat treatment in excess of 45 minutes have been found to cause diffusion of such-an order that the proper-- ties,of the surface layer are markedly deteriorated in one or ' more respects. It has been found th'at heat treatment at a tem-perature belo-~ 725C, i.e. below the temperature at which a phase '' transition to austenitic structure of carbon steels b2gins, does not provide goo~ adhesion of the nickel and/or cobalt surface layer.
It has been observed that a heat treatment at a te~- ~' p~ .
-25 perature in excess of 725C for a time shorter t,han 1 minute t .~ . .
~` 1038z4s provides an excellent product which is quite superior to nonheat treated products and to products which have been treated for a time in excess of 45 minutes.
The article (of steel or iron~ to which the surface layer of nickel and/or cobalt is applied can be of arbitrary form and composition.
Conventional carkon steel in the form of plates, pip~s or bands is suitable for many purposes. According to aspects of the present invention, it has also been found advantageous to apply the surface layers to such finished steel objects as bolts, screws and castings.
Ihe very short time of treatment is believed to be due to the fact that the interlayer between the surface layer and the substrate re-crystallizes very rapidly because of high inherent surface energy and that an atomic bond is achieved to the substrate by this recrystallization. If ; the time of heat treatment is too long, erg~ substantially more than 45 minutes at temperature, diffusion occurs which gradually impaLrs the 0rrosion resistant properties of the surface layer.
In ths electr~lytic coatins of steel with a first layer of nickel or cobalt, a certain amDunt of pores is apt to form passing j through the whole layer and thus expose the steel surface. If a new metal layer, e.g. zinc, is applied on top of this layer, atomic hydrogen is precipitated in the pores ~Ihich diffuses into the steel and causes so-calle . ~ ' .
- G _:
: . .
gen embrittlement. By the heat treatment according to the process of an aspect of the present inven~ion, two positive effects are achieved with respect to avoiding hydrogen embrittlement. For example, the hydrogen, which penetrates the steel during pickling and during the electrolytic coating of nickel or cobalt, is released by diffusion, and the pores formed in the nickel or cobalt layer tend to close themselves so that the steel surface is no longer exposed. This prevents additional hydrogen absorption by the steel during the application of the next metal layer.
The heat treatment according to the process of an aspect of the present invention is usually carried out in a neutral or reducing atmosphere. Such conditions may preferably comprise a - protective gas 9 e.g. argon, or a reducing gas, e.g. hydrogen or carbon monoxide. The heat treatment can, if desired, also be carried out in air, especially if a coloured surface is desired.
In order to assure optimum improvement of the anti-corrosion properties in practice, the temperature during heat treatment should be at least 72soc at` the surface layer, as stated above. A usable range of temperature has been found to be 725c to 1000C. It is preferred that the heat treatment be carried out at a temperature at which there is a complete transformation into austenitic structure. It appears that temperature below 7?5 result in such a slow crystallization in the interlayer that no adhesion occurs, unless longer periods of heat treatment are used. If, on the other hand, long periods of heat treatment are used 7 the properties of the substrate material tend to deteriorate. Thus, a very essential advantage of the process according to aspects of this ~ention is that the substrate material is not changed appreciably by the short time of treatment used. This is of great importance in the manufacture of wire, among other products, as _~ -- r r~
1C~3~Z45 -the microstructure is very importan-t for assuring the desired mechani-cal properties of the wire, e.g. Alasticity and fatigue strength.
One of the advantages of the process of aspects of this invention is that hardenable steels which have been surface coated with nickel and/or cobalt can be hardened in connection with the present heat treatment by cooling the article rapidly following completion of the heat treatment so that an austenitic decomposition product is obtained comprising a martensitic structure, provided that, during heat treatment, the steel arti~le is heated to an austenitizing temperature in excess of 725C. Such steels may contain up to 0.9~ by weight, for example, at least 0.05~ carbon, and preferably 0.2% to 0.6% carbon. The term "steel" used herein is meant to cover iron as well.
The surface layer containing nickel and/or cobalt is `
applied to the article (of steel or iron) in conventional manner by electrolysis or chemically. Plating baths are disclosed in the book entitled Modern Electroplating (Second Edition, 1953) published by John Wiley and Sons, for example on pages 141 to 146, 260 to 263 and 282 to 286.
To the surface layer of nickel and~or cobalt following heat treatment, a thin additional layer of one or more of the metals chromium, tin, lead, zinc, copper and cadmium is then applied. This layer can also be applied in a conventional manner, e.g. by electrolysis, by spraying of molten metal on the steel substrate or by chemical deposition. Such methods are well known to those skilled in-the art.
Markedly improved results have been obtained with the coating of articles characterized by uniform smooth surfaces, for example, steel pipes, steel plates, strip and the like. Thus, an iron pip~ (0.01%C by weig~t) coated inside and outside with nickel in accordance with the process of an aspect of this invention (e.g. a 7 ~ 7_ r~
,q nickel electroplate of 10 ~icrons -thick and heat treated at 870C
for 20 minutes) and then coated with a zinc electroplate of 10 microns exhibited a resistance to corrosion under the salt spray tes.
(ASTM B-117) for a very long period of time as evidenced by the appearance of red rust a~ter 800 to 1000 hours.
In tests conducted on threaded steel articles or other complicated shapes, it has been found that a normal carbon steel (0.4~ carbon) coated with a layer of nickel or cobalt of thi~kness of 10 microns and which has not been subsequently heat treated, exhibited 10 red rust attach after 10 hours in a salt spray test (ASTM B-117). These same articles coated with a zinc layer alone of 10 microns thick exhibited red rust in the same test after 90 to 100 hours. On the ; other hand, when such threaded carbon steel articles were fi~st coated with a nickel layer of 10 microns ~hick and then heat treated accord-ing to the process of an asp,ect'of this invention followed by coating with a zinc layer of 10 microns thick, red rust did not appear until - after 200 to 300 hours under the same testing conditions. This is - unusual for such complicated shapes. Similar improved results are obtainable with cobalt as the first layer closest to the steel and with metals other than zinc as the second or outer layer. Thus, markedly improved properties with respect to resistance to corrosion have been obtained'for the following coating combinations: nickel-cadmium, and nickél-copper. It wilI be observed from these tests that it is very important that the original nickel or cobalt layer be subjected to heat treatment according to the process of aspects of this invention before the second metal layer is applied. It has also been noted that a nickel layer having a thickness of 10 microns and which has not been heat-treated, does not provide the ma~ked improvements of the teachings of aspects of th~s invention as regards anti-corrosion properties, even when a zinc layer is applied to -the nickel layer, .. . .
1038Z4s Si~ilarly~ in cases whcre the nickel layer has been subjected to too long a heat -treatment of more than 45 minutes at a temperature in excess of 725C, inferior properties have been obtained. It is believed that apparently iron diffuses into the nickel ~hich results in red rust appearing much sooner. In the conventional hot-dip coating of zinc,some amount of dissolved ~, _g _ ~03~Z45 ~
iron will a~pear in the zinc lt~yer which has a deteriorating ef-fect on the anti-corrosion properties.
The preferre~ as~ects of the invention will be apparent from the following examples. ~ -Example 1 For comparlson with known techni~ues, the following sur-face coatings were made on a 1.5 ~ (r~ 0O06 inch) steel wirc ~ of carbon steel ( 0O7% carbon)O
; Ao Coating with 1 micron tin layer alone by hot-dip :-. - . _,
-~()3~245 group consisting of chromium, tin~ lead, zinc, copper and cadmium to ~aid first layer~ whereby a coated article is obtained characterized by improved resistance to corrosion.
By one variant of this process, the period of heat treatment is less than 15 minutes, preferably less than 5 minutes.
By yet another variant, the first layer is applied at a thickness of over 2 microns and wherein said second mètal layer is also applied at a thickness of over 2 microns.
By a still further variant, the thicknesses of the first layer and of the second layer is 5-25 microns.
By another variant~ the steel is a carbon steel containing up to 0O9~ carbon.
- ~ By still another variant, the steel article contains 0.2%
to 0.6% carDon and wherein following the bonding heat treatment at said austenitizing temperature, the article is rapidly cooled to form a martensitic structure.
By another a,spect of'this invention, a process is provided for improving the corrosion resistance of a steel article which compris-es, applying to said article a first thin layer of at least one metal selected from the group consisting of nickel and cobalt over a thickness range of over 2 to 50 microns, heat treating said coated article at an austenitizing temperature falling within the range of 725C to 1000C at substantially less than 45 minutes, and then applying a second thin layer of at least one metal selected from the group consisting of chromium 9 tin, lead, zinc, copper and cadmium to said first layer of a thickness of o~er 2-50 microns, whereby a coated article is obtained characterized by improved resistance to corrosion.
By a variant thereof, the period of heat treatment is less than 15 minutes, preferably less than 5 minutes.
.
~ ~ -3-. -- . . =
_ _ . . .. . _ _, . .
1038Z~s By another varian~ ther~of, the steel article con~ains up to 0.9~ carbon by weight and wherein following the bonding heat treatment at said austenitizing temperature, the article is rapidly cooled to form a martensitic structure.
By another aspect of this invention, a novel article of manufacture of provided comprising a steel substrate having bonded thereto a first layer of a metal selected from the group consisting of nickel and cobalt at a thickness ranging from over 2 to 50 microns and a second metal layer selected from the group consisting of chromium, tin, lead, zinc, copper and cadmium bonded to said first layer at a thickness ranging from over 2 to S0 microns, said article being heat *reated at a temperature of 725-1000C at which - phase transition to austentic structure of carbon begins before the deposition of said second metal 7 said steel substrate being characteri-zed by markedly improved resistance to corrosion.
By one variant, the steel is a carbon steel containing up to 0.9~ carbon, preferably 0.2 - 0.6% carbon.
The heat treatment of the nickel and/or cobalt layer comprises the first stage of the process of an aspect of the present invention. This heat treatment should take place within such limits with respect to temperature and time that the diffusion of nickel and/
or obalt into the steel substrate is sufficiently inhibited and preferably does not exceed a maximum of a few microns. In this manner, diffusion of iron into the nickel and/or cobalt layer will also be sufficiently inhibited. ThiS is achieved by carrying out the A
-3a-;q F
1038245 ~
heat treatment at a temperature in excess of b7~t 725C for,a time lèss than 45 minutes, Actually, the bèst results are obtained as regards the anti-corrosion properties of the final surface layer if the heat treatment of the steel object,pre- - L
coated with nickel and/ox cobalt is carried out for a time sub-s~antially less than 30 minutes. Thus, it has been found that diffusion of nickel and/or cobalt into the substrate is further ~ -, inhibited if the heat treatment is less than 15 minutes. Tests ~ - - .
have indicated that better anti-corrosion properties are obtained ~
at less,than 15 minutes of heat treatment as compared to heat - ~r-~
treatment tim2s of be~een 15 and 30 minutes and that periods '~
' of heat treatment of even less than ' 5 minutes provide the , i best properties in the final surface layer~ The-time at which -, 'the temperature of treatment of the surface layer amounts to or , ' ,~ .
15' ' exceeds 725C is referred to as ~he period of heat treatment. ~ - -P2rio~s of heat treatment in excess of 45 minutes have been found to cause diffusion of such-an order that the proper-- ties,of the surface layer are markedly deteriorated in one or ' more respects. It has been found th'at heat treatment at a tem-perature belo-~ 725C, i.e. below the temperature at which a phase '' transition to austenitic structure of carbon steels b2gins, does not provide goo~ adhesion of the nickel and/or cobalt surface layer.
It has been observed that a heat treatment at a te~- ~' p~ .
-25 perature in excess of 725C for a time shorter t,han 1 minute t .~ . .
~` 1038z4s provides an excellent product which is quite superior to nonheat treated products and to products which have been treated for a time in excess of 45 minutes.
The article (of steel or iron~ to which the surface layer of nickel and/or cobalt is applied can be of arbitrary form and composition.
Conventional carkon steel in the form of plates, pip~s or bands is suitable for many purposes. According to aspects of the present invention, it has also been found advantageous to apply the surface layers to such finished steel objects as bolts, screws and castings.
Ihe very short time of treatment is believed to be due to the fact that the interlayer between the surface layer and the substrate re-crystallizes very rapidly because of high inherent surface energy and that an atomic bond is achieved to the substrate by this recrystallization. If ; the time of heat treatment is too long, erg~ substantially more than 45 minutes at temperature, diffusion occurs which gradually impaLrs the 0rrosion resistant properties of the surface layer.
In ths electr~lytic coatins of steel with a first layer of nickel or cobalt, a certain amDunt of pores is apt to form passing j through the whole layer and thus expose the steel surface. If a new metal layer, e.g. zinc, is applied on top of this layer, atomic hydrogen is precipitated in the pores ~Ihich diffuses into the steel and causes so-calle . ~ ' .
- G _:
: . .
gen embrittlement. By the heat treatment according to the process of an aspect of the present inven~ion, two positive effects are achieved with respect to avoiding hydrogen embrittlement. For example, the hydrogen, which penetrates the steel during pickling and during the electrolytic coating of nickel or cobalt, is released by diffusion, and the pores formed in the nickel or cobalt layer tend to close themselves so that the steel surface is no longer exposed. This prevents additional hydrogen absorption by the steel during the application of the next metal layer.
The heat treatment according to the process of an aspect of the present invention is usually carried out in a neutral or reducing atmosphere. Such conditions may preferably comprise a - protective gas 9 e.g. argon, or a reducing gas, e.g. hydrogen or carbon monoxide. The heat treatment can, if desired, also be carried out in air, especially if a coloured surface is desired.
In order to assure optimum improvement of the anti-corrosion properties in practice, the temperature during heat treatment should be at least 72soc at` the surface layer, as stated above. A usable range of temperature has been found to be 725c to 1000C. It is preferred that the heat treatment be carried out at a temperature at which there is a complete transformation into austenitic structure. It appears that temperature below 7?5 result in such a slow crystallization in the interlayer that no adhesion occurs, unless longer periods of heat treatment are used. If, on the other hand, long periods of heat treatment are used 7 the properties of the substrate material tend to deteriorate. Thus, a very essential advantage of the process according to aspects of this ~ention is that the substrate material is not changed appreciably by the short time of treatment used. This is of great importance in the manufacture of wire, among other products, as _~ -- r r~
1C~3~Z45 -the microstructure is very importan-t for assuring the desired mechani-cal properties of the wire, e.g. Alasticity and fatigue strength.
One of the advantages of the process of aspects of this invention is that hardenable steels which have been surface coated with nickel and/or cobalt can be hardened in connection with the present heat treatment by cooling the article rapidly following completion of the heat treatment so that an austenitic decomposition product is obtained comprising a martensitic structure, provided that, during heat treatment, the steel arti~le is heated to an austenitizing temperature in excess of 725C. Such steels may contain up to 0.9~ by weight, for example, at least 0.05~ carbon, and preferably 0.2% to 0.6% carbon. The term "steel" used herein is meant to cover iron as well.
The surface layer containing nickel and/or cobalt is `
applied to the article (of steel or iron) in conventional manner by electrolysis or chemically. Plating baths are disclosed in the book entitled Modern Electroplating (Second Edition, 1953) published by John Wiley and Sons, for example on pages 141 to 146, 260 to 263 and 282 to 286.
To the surface layer of nickel and~or cobalt following heat treatment, a thin additional layer of one or more of the metals chromium, tin, lead, zinc, copper and cadmium is then applied. This layer can also be applied in a conventional manner, e.g. by electrolysis, by spraying of molten metal on the steel substrate or by chemical deposition. Such methods are well known to those skilled in-the art.
Markedly improved results have been obtained with the coating of articles characterized by uniform smooth surfaces, for example, steel pipes, steel plates, strip and the like. Thus, an iron pip~ (0.01%C by weig~t) coated inside and outside with nickel in accordance with the process of an aspect of this invention (e.g. a 7 ~ 7_ r~
,q nickel electroplate of 10 ~icrons -thick and heat treated at 870C
for 20 minutes) and then coated with a zinc electroplate of 10 microns exhibited a resistance to corrosion under the salt spray tes.
(ASTM B-117) for a very long period of time as evidenced by the appearance of red rust a~ter 800 to 1000 hours.
In tests conducted on threaded steel articles or other complicated shapes, it has been found that a normal carbon steel (0.4~ carbon) coated with a layer of nickel or cobalt of thi~kness of 10 microns and which has not been subsequently heat treated, exhibited 10 red rust attach after 10 hours in a salt spray test (ASTM B-117). These same articles coated with a zinc layer alone of 10 microns thick exhibited red rust in the same test after 90 to 100 hours. On the ; other hand, when such threaded carbon steel articles were fi~st coated with a nickel layer of 10 microns ~hick and then heat treated accord-ing to the process of an asp,ect'of this invention followed by coating with a zinc layer of 10 microns thick, red rust did not appear until - after 200 to 300 hours under the same testing conditions. This is - unusual for such complicated shapes. Similar improved results are obtainable with cobalt as the first layer closest to the steel and with metals other than zinc as the second or outer layer. Thus, markedly improved properties with respect to resistance to corrosion have been obtained'for the following coating combinations: nickel-cadmium, and nickél-copper. It wilI be observed from these tests that it is very important that the original nickel or cobalt layer be subjected to heat treatment according to the process of aspects of this invention before the second metal layer is applied. It has also been noted that a nickel layer having a thickness of 10 microns and which has not been heat-treated, does not provide the ma~ked improvements of the teachings of aspects of th~s invention as regards anti-corrosion properties, even when a zinc layer is applied to -the nickel layer, .. . .
1038Z4s Si~ilarly~ in cases whcre the nickel layer has been subjected to too long a heat -treatment of more than 45 minutes at a temperature in excess of 725C, inferior properties have been obtained. It is believed that apparently iron diffuses into the nickel ~hich results in red rust appearing much sooner. In the conventional hot-dip coating of zinc,some amount of dissolved ~, _g _ ~03~Z45 ~
iron will a~pear in the zinc lt~yer which has a deteriorating ef-fect on the anti-corrosion properties.
The preferre~ as~ects of the invention will be apparent from the following examples. ~ -Example 1 For comparlson with known techni~ues, the following sur-face coatings were made on a 1.5 ~ (r~ 0O06 inch) steel wirc ~ of carbon steel ( 0O7% carbon)O
; Ao Coating with 1 micron tin layer alone by hot-dip :-. - . _,
3 coating.
B~ Coating with 15 micron zinc layer alone by hot-dip -coating- k C. Coating with 10 micron nickel layer-by electro-lysis and heat treated. ._~
D. Coating with 10 micron-nickel layer by electro-~- lysis, heat treated at 850C for 4 minutes and then coated with 12 micron zinc layer on top of the nickel layer by electrolysis according to the present invention.
~0 Corrosion attack as evidenced by the appearance of red rust was evaluated a ter testing each specimen in the salt spray r -~ atmosphere according to ASTM B-117 and the following results were ; o~tained:
A. Red rust o-curred after a testing period of ~5 5 hours.
,~ '.
1 0- ~ , ~.
~ . , tt_~
103~24s - B. Red rust occurred after a testin~ period of 35 h~urs.
C. Red rust occurr~d after a testin~ period of 20 hours.
D. `~o attack due to red rust occul-red after a testing period of 300 hours.
As will be noted, markedly improved results are obtained with S the invention ~i.e. D.).
Example 2 Bolts of carbon steel (0.4% carbon) were coated with a 10 micron layer of nickel by electr~lysis by barrel plating in a nickel salt solution (from a Watts Bath at lamp/dm2 and 50C for 50 minutes) and were then hard-ened by heating to 850C for 10 mlnutes and by cooling Ln oil. The bolts were coated with a 10 micron zinc layer electrolytically according to a known process comprising 15 to 20 gPl ~grams per liter) zinc, 25 b~ 45 gpl of sodium cyanide, 80 gpl NaO~, the plating being carried out at a current d~nsity of 1 a~p/dm2 for 60 minutes at rDom temperature. For comparison purposes, the same bolts were hardened without nickel layers and thencoated with a lo micron zinc layer.
- Improved results were obtained with the bolts coated according bo the process of the present invention in that red rust formed after a salt spray testing period of 200 hours; whereas red rust was :
~ ... , . . . ~ _ .. ~ .
, ~ ~
~038Z45 obserYed after a shorter period of 95 hours for the bolts 5 ~, .
electrolytically coate~ with zinc alone in the conventional man-ner. Bolts coa.ed only with a 10 micron nickel layer (followe~
by heat treating at 870CC for 20 minutes) corro~ed after a very short period of 10 hours.
ExamPle 3 Tests were conducted with 100 steel or iron pipe sam- j ples ( 0.01% C) m~asuring 200 mm long and 10 mm in aiameter. ~
The pipes were coated with a 10-micron layer of nickel from a "~ ~ - ~5`7' l Watts Bath at a curren. density of ' - 4 amps/dm2 at room te~- :
perature. The coated pipes were then sub~ected to a bonding heat treatment at 870C for 20 minutes in argon, 50 of the pipe samples being then coated with zinc according- to the process described in Example 2, while the remaining 50 were not. In addi- -: ::
.. . . .
tion, 50 pipe samples without the nickel coating were coated with ` a 10-micron layer of zinc as in Example 2.
-All of the pipes were subjected to a salt spray test referred to as ASTM B-117 and the following results obtained:
- ~ Av~rage Time For Pipe SamPles Red Rust to Appear (1) 50 pipes ~i-coated and heat 7 treated 10 hours (2) 50 pipes zinc-coated only 110 hours r ~3) 50 pipes Ni-coated (heat treated) and then zinc coated 900 hours ~ . j.. _. .
~ -12-.~L
1038Z45 ~`
Broadly speaking, the first coating metal nickel and/or cobalt may be applied at a thickness of at least several microns and may range from over 2 - 3 to 25 or even to SO microns, depend-ing upon the economics of the pro_ess and the configuration of the articles. The second coating metal selected from the group consisting o Cr, Sn, Pb, Zn, Cu and Cd may be applied similarly at a thickness of over several microns and range from over 2 - 3 to 25 or even to SO or more microns depending upon the economics of the process and the configuration of the article. A prefer-red range of thicknesses of the foregoing coatings is 5 to 25 micronsr . i :
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B~ Coating with 15 micron zinc layer alone by hot-dip -coating- k C. Coating with 10 micron nickel layer-by electro-lysis and heat treated. ._~
D. Coating with 10 micron-nickel layer by electro-~- lysis, heat treated at 850C for 4 minutes and then coated with 12 micron zinc layer on top of the nickel layer by electrolysis according to the present invention.
~0 Corrosion attack as evidenced by the appearance of red rust was evaluated a ter testing each specimen in the salt spray r -~ atmosphere according to ASTM B-117 and the following results were ; o~tained:
A. Red rust o-curred after a testing period of ~5 5 hours.
,~ '.
1 0- ~ , ~.
~ . , tt_~
103~24s - B. Red rust occurred after a testin~ period of 35 h~urs.
C. Red rust occurr~d after a testin~ period of 20 hours.
D. `~o attack due to red rust occul-red after a testing period of 300 hours.
As will be noted, markedly improved results are obtained with S the invention ~i.e. D.).
Example 2 Bolts of carbon steel (0.4% carbon) were coated with a 10 micron layer of nickel by electr~lysis by barrel plating in a nickel salt solution (from a Watts Bath at lamp/dm2 and 50C for 50 minutes) and were then hard-ened by heating to 850C for 10 mlnutes and by cooling Ln oil. The bolts were coated with a 10 micron zinc layer electrolytically according to a known process comprising 15 to 20 gPl ~grams per liter) zinc, 25 b~ 45 gpl of sodium cyanide, 80 gpl NaO~, the plating being carried out at a current d~nsity of 1 a~p/dm2 for 60 minutes at rDom temperature. For comparison purposes, the same bolts were hardened without nickel layers and thencoated with a lo micron zinc layer.
- Improved results were obtained with the bolts coated according bo the process of the present invention in that red rust formed after a salt spray testing period of 200 hours; whereas red rust was :
~ ... , . . . ~ _ .. ~ .
, ~ ~
~038Z45 obserYed after a shorter period of 95 hours for the bolts 5 ~, .
electrolytically coate~ with zinc alone in the conventional man-ner. Bolts coa.ed only with a 10 micron nickel layer (followe~
by heat treating at 870CC for 20 minutes) corro~ed after a very short period of 10 hours.
ExamPle 3 Tests were conducted with 100 steel or iron pipe sam- j ples ( 0.01% C) m~asuring 200 mm long and 10 mm in aiameter. ~
The pipes were coated with a 10-micron layer of nickel from a "~ ~ - ~5`7' l Watts Bath at a curren. density of ' - 4 amps/dm2 at room te~- :
perature. The coated pipes were then sub~ected to a bonding heat treatment at 870C for 20 minutes in argon, 50 of the pipe samples being then coated with zinc according- to the process described in Example 2, while the remaining 50 were not. In addi- -: ::
.. . . .
tion, 50 pipe samples without the nickel coating were coated with ` a 10-micron layer of zinc as in Example 2.
-All of the pipes were subjected to a salt spray test referred to as ASTM B-117 and the following results obtained:
- ~ Av~rage Time For Pipe SamPles Red Rust to Appear (1) 50 pipes ~i-coated and heat 7 treated 10 hours (2) 50 pipes zinc-coated only 110 hours r ~3) 50 pipes Ni-coated (heat treated) and then zinc coated 900 hours ~ . j.. _. .
~ -12-.~L
1038Z45 ~`
Broadly speaking, the first coating metal nickel and/or cobalt may be applied at a thickness of at least several microns and may range from over 2 - 3 to 25 or even to SO microns, depend-ing upon the economics of the pro_ess and the configuration of the articles. The second coating metal selected from the group consisting o Cr, Sn, Pb, Zn, Cu and Cd may be applied similarly at a thickness of over several microns and range from over 2 - 3 to 25 or even to SO or more microns depending upon the economics of the process and the configuration of the article. A prefer-red range of thicknesses of the foregoing coatings is 5 to 25 micronsr . i :
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Claims (14)
1. A process for improving the corrosion resistance of a steel article which comprises, applying to said article a first layer of at least one metal selected from the group consisting of nickel and cobalt, subjecting said coated article to a bonding heat treatment at an austenitizing temperature in the range of 725°C - 1000°C for a time less than 45 minutes, and then applying as a second layer at least one metal selected from the group consisting of chromium, tin, lead, zinc, copper and cadmium to said first layer, whereby a coated article is obtained characterized by improved resistance to corrosion.
2. The process of claim 1, wherein the period of heat treatment following the application of said first layer is less than 15 minutes.
3. The process of claim 2, wherein the period of heat treatment following application of first layer is less than 5 minutes.
4. The process of claim 1, wherein said first layer is applied at a thickness of over 2 microns and wherein said second metal layer is also applied at a thickness of over 2 microns.
5. The process of claim 4 wherein the thicknesses of the first layer and the second layer is 5-25 microns.
6. The process of claim 1, wherein said steel is a carbon steel containing up to 0.9% carbon.
7. The process of claim 6 wherein the steel article contains 0.2% to 0.6% carbon and wherein following the bonding heat treatment at said austenitizing temperature, the article is rapidly cooled to form a martensitic structure.
8. A process for improving the corrosion resistance of a steel article which comprises, applying to said article a first thin layer of at least one metal selected from the group consisting of nickel and cobalt over a thickness range of over 2 to 50 microns, heat treating said coated article at an austenitizing temperature falling with the range of 725°C to 1000°C at substantially less than 45 minutes, and then applying a second thin layer of at least one metal selected from the group consisting of chromium, tin, lead, zinc, copper and cadmium to said first layer of a thickness of over 2-50 microns, whereby a coated article is obtained characterized by improved resistance to corrosion.
9. The process of claim 8 wherein the period of heat treatment at said austenitizing temperature is less than 15 minutes.
10. The process of claim 9 wherein the period of heat treatment at said austenitizing temperature is less than 5 minutes.
11. The process of claim 8 wherein the steel article contains up to 0.9% carbon by weight and wherein following the bonding heat treatment at said austenitizing temperature, the article is rapidly cooled to form a martensitic structure.
12. As an article of manufacture, a steel substrate having bonded thereto a first layer of a metal selected from the group consisting of nickel and cobalt at a thickness ranging from over 2 to 50 microns and a second metal layer selected from the group consisting of chromium, tin, lead, zinc, copper and cadmium bonded to said first layer at a thickness ranging from over 2 to 50 microns, said article being heat treated at a temperature of 725 - 1000°C at which phase transition to austenitic structure of carbon begins before the deposition of said second metal, said steel substrate being character-ized by markedly improved resistance to corrosion.
13. The coated steel substrate as in claim 12, said steel being a carbon steel containing up to 0.9% carbon.
14. The coated steel substrate as in claim 13 wherein the carbon content ranges from 0.2% to 0.6%.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE7434125 | 1974-03-14 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1038245A true CA1038245A (en) | 1978-09-12 |
Family
ID=20323177
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA221,769A Expired CA1038245A (en) | 1974-03-14 | 1975-03-11 | Process for improving the anti-corrosion properties of steel coated with nickel or cobalt |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1038245A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2011148242A3 (en) * | 2010-05-24 | 2012-04-05 | Toyota Jidosha Kabushiki Kaisha | Method of plating stainless steel and plated material |
| CN113458937A (en) * | 2021-08-03 | 2021-10-01 | 深圳华美金属材料科技有限公司 | Colored wire-drawing galvanized sheet and preparation method thereof |
| CN115279944A (en) * | 2020-02-28 | 2022-11-01 | 奥钢联钢铁有限责任公司 | Method for producing a hardened steel component with a zinc alloy corrosion protection layer |
-
1975
- 1975-03-11 CA CA221,769A patent/CA1038245A/en not_active Expired
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2011148242A3 (en) * | 2010-05-24 | 2012-04-05 | Toyota Jidosha Kabushiki Kaisha | Method of plating stainless steel and plated material |
| CN102906311A (en) * | 2010-05-24 | 2013-01-30 | 丰田自动车株式会社 | Method of plating stainless steel and plated material |
| CN102906311B (en) * | 2010-05-24 | 2015-07-08 | 丰田自动车株式会社 | Method of plating stainless steel and plated material |
| US9347145B2 (en) | 2010-05-24 | 2016-05-24 | Toyota Jidosha Kabushiki Kaisha | Method of plating stainless steel and plated material |
| CN115279944A (en) * | 2020-02-28 | 2022-11-01 | 奥钢联钢铁有限责任公司 | Method for producing a hardened steel component with a zinc alloy corrosion protection layer |
| CN115279944B (en) * | 2020-02-28 | 2023-09-26 | 奥钢联钢铁有限责任公司 | Method for producing a hardened steel component having a zinc alloy corrosion protection layer |
| CN113458937A (en) * | 2021-08-03 | 2021-10-01 | 深圳华美金属材料科技有限公司 | Colored wire-drawing galvanized sheet and preparation method thereof |
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