SURFACE TREATMENT OF METAL SUBSTRATES
[Technicalfield]
The present invention relates to a method for surface treatment of metal substrates,
in particular of stainless steel, in order to improve their properties, in particular the
tribological characteristics during their shaping, in particular by stamping,
[Technologica I background]
Combining durability, good mechanical properties, hygiene and ease of maintenance,
the stainless steel has nowadays become the reference material in numerous fields such as
the car industry, the consumer goods industry, the heavy industry, microtechnology and
electronics,
ln a general manner, the preparation of the finished product requires at least one
forming operation, for example a stamping for flat products. The field in which a metal is
deformed with neither striction nor breakup largely depends on the performances of the
used lubricant.
However, the use of usual stamping oils poses increasing problems. First of all, the
oils, in particular the most performing oils, are not always easy to implement, Their viscosity
may cause application difficulties and the amount required to cover the substrate may be
substantial. Moreover, the use of these oils requires a meticulous cleaning of the sheet
metal as well as the tools and the workstation. Finally, the retreatment of these oils after use
poses serious environmental problems, especially when these consist of chlorinated or
sulfurized oils.
Furthermore, these lubricants do not always provide the required performance,
which may cause substantial costs, lndeed, an insufficient lubrication increases the number
of disposals of shaped products. This may also increase the number of maintenance
interventions (rectifications, polishing,...) and therefore their wearing. ln this respect, the
chlorinated or sulfurized oils are the most satisfactory ones. But, it has been seen that they
pose environmental problems which may become prohibitive given the possible regulatory
evolutions.
[Technical problem]
A purpose of the invention is to propose a method allowing conferring to metal
substrates the properties required to allow their shaping, in particular by stamping, without
the use of any separate complementary lubricant,
Another purpose of the present invention is to propose such a method allowing
improving the tribological properties of a metal substrate during its shaping.
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Another purpose of the present invention is to propose metal substrates having
tribological properties, in particular during their shaping.
Still another purpose of the present invention is to propose a surface treatment
solution which may substitute for existing industrial lubricants, which does not have the
drawbacks mentioned hereinabove, in particular the environmental ones,
IProposed solution according to the invention]
These purposes and others are reached according to the invention by a treatment in
which the surface of the metal substrate is brought into contact with a solution of
organophosphorus compounds so as to form a coating composed of a chemisorbed first
layer at the metallic surface in which the organophosphorus compounds are organized in the
form of a monomolecular layer and of a second layer of physisorbed organophosphorus
molecules at least preponderantly crystallized.
ln general, the first monomolecular layer includes covalent-type bonds with hydroxyl
groups present at the surface of the metal substrate, The organophosphorus compounds
may be considered as being chemisorbed thereon. Thus, the first layer has a strong
adherence to the substrate, ln contrast, the molecules constitutive of the second layer have
weak links with the substrate, of the Van-der-Waals type. The organophosphorus
compounds may be considered as being physisorbed thereon (see Figure 1). This second
layer, at least preponderantly crystallized (that is to say crystallized by at least 50% of its
mass and of its molecules), therefore has a lesser adherence to the substrate.
The process of the invention confers very interesting properties to the metal
substrates, in particular with regard to their tribological properties during their shaping.
lndeed, the inventors have observed that the coating of organophosphorus
compounds formed as previously described has astonishing lubricating qualities, comparable
to and even higher than those of the best lubricants available in the market.
Moreover, advantageously, the coating deposited according to the invention confers
an improved corrosion resistance to the metal substrate.
Hence, the metal substrates treated according to the invention may be lubricated
well before their shaping, which has notable advantages. lndeed, the lubricating coating
contributes to an easy handling, reduces the risk of corrosion, in particular during transport,
and greatly facilitates the subsequent shaping, since it frees from the need of using a
separate complementary lubricant, generally in the form of an oil or of a polymer coating,
while not degrading the lubrication performances and preserving the integrity of the tools
from a premature wearing.
The absence of oil allows a financial saving and the preservation of the environment.
ln addition, it allows cleaning the workstation and the tools by simple dusting, which
constitutes a substantial time saving.
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Hence, the process of the present invention offers a performant solution for
treatment of metal substrates adapted to shaping processes, in particular to stamping, in
both economic and environmental terms.
lndeed, the used organophosphorus compounds are barely toxic and may be
implemented in a barely toxic solvent, in particular an alcohol and/or water, a 1,00%
alcoholic solution (including ethanol, in particular absolute ethanol, is a privileged example)
being preferred. Hence, the implementation of such a solution does not cause regulatory
difficulties, and its withdrawal does not pose risks to the environment.
Moreover, the organophosphorus compounds are used in solution, which reduces
the amount required to confer the pursued properties in comparison with oils, and further
contributes to the economical and ecological interest of the method of the invention.
Also, according to a first aspect, the invention relates to a process for surface
treatment of metal substrates, comprising the steps of:
(¡) providing a metal substrate including hydroxyl groups at its surface;
(ii) bringing the metal substrate into contact with a solution of at least one
organophosphorus compound so as to enable the reaction of said hydroxyl groups at the
surface of the metal substrate with- said organophosphorus compound to form a
monomolecular layer over at least 1-5% of the surface of the metal substrate and, over said
monomolecular layer, a second layer of physisorbed organophosphorus molecules at least
preponderantly crystallized,
the obtained treated substrate being coated with the organophosphorus compound
in the monomolecular form and in the physisorbed form at least preponderantly crystallized,
Preferably, the at least one organophosphorus compound is of formula (l) below
O
z- A-.$--oR,
oR.' (l)
wherein
A represents a hydrocarbon chain, saturated or unsaturated, straight or branched,
comprising 4 to 28 atoms of carbon, the chain may be substituted with one or several
group(s) chosen among hydroxy, amino, cyano, halogen, sulfonic acid, organophosphonic
acid and/or interrupted by one or several atom(s) or group(s) chosen among O, HN or SH;
Z represents one or several terminal functional group(s) chosen among alcohol,
aldehyde, carboxylic acid, phosphonic acid, thiol, amine, halogen, cyano or silane, or is
absenq and
Rr and Rz ârê, independently of each other, a hydrogen or a saturated alkyl, straight
or branched, comprising 1- to 18 atoms of carbon.
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Among these compounds of formula (l) are preferred those in which:
A is a saturated alkyl group; and/or
A is a straight alkyl group.
The organophosphorus compounds are implemented in the process of the invention
in the form of a solution, Preferably, the solvent comprises an alcohol, in particular an
alcohol chosen among methanol, ethanol, propanol, isopropanol and butanol, and/or water.
Advantageously, the used solution of the organophosphorus compound has a
concentration of more than l- mM/l and preferably from L0 to 1000 mM/|, advantageously
from 20 to 500 mM/|, and in particular from 50 to 200 mM/1. Preferably, the solution of the
orga nophosphorus com pound is supersaturated.
ln particular, the substrate treated by the method of the invention may be a
substrate made of iron, nickel, cobalt, aluminum, copper, chromium, titanium, zinc, gold,
silver, ruthenium, rhodium or any of their alloys, in particular the steels such as the stainless
steels, the carbon steels and the electrical steels.
According to a second aspect, the invention relates to a treated metal substrate
which may be obtained by the process of the invention.
ln particular, it may consist of a substrate made of iron, nickel, cobalt or any of their
alloys. Alternatively, it may consist of a substrate made of aluminum, copper, chromium,
titanium, zinc, gold, silver, ruthenium, rhodium or any of their alloys.
ln particular, the metal substrate may be a flat product.
According to a third aspect, the invention relates to a surface treatment solution
comprising at least one organophosphorus compound of formula (l) below
0
z- A-$---oR^
oR.' (t)
wherein:
A represents a hydrocarbon chain, saturated or unsaturated, straight or branched,
comprising 4 To 28 atoms of carbon, preferably L6 atoms of carbon, the chain may be
substituted with one or several group(s) chosen among hydroxy, amino, cyano, halogen,
sulfonic acid, phosphonic acid and/or interrupted by one or several atom(s) or group(s)
chosen among O, HN or SH;
Z represents one or several terminal functional group(s) chosen among alcohol,
aldehyde, carboxylic acid, phosphonic acid, thiol, amine, halogen, cyano or silane or is
absent; and
Rr and R2 âr€, independently of each other, a hydrogen or a saturated alkyl, straight
or branched, comprising 1 to 18 atoms of carbon,
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in a solvent comprising an alcohol, in particular methanol, ethanol, propanol,
isopropanol and butanol, possibly water-added, the concentration of the organophosphorus
compound of formula (l) in the solution being of more than 1 mM/|.
Finally, according to a fourth aspect, the invention concerns the use of such a
solution for the treatment of metal substrates in order to improve their tribological
properties during their shaping, in particular during stamping.
IDetailed description of the invention]
The inventors have unexpectedly discovered that a metal substrate treated according
to the invention has tribological properties during its shaping which are higher than or
equivalent to a substrate treated with conventional lubricating oils. lt has also been
observed, accessorily, that such a treatment is likely to confer a substantially improved
corrosion resistance to the metal substrate.
The obtained results highlight the fact that these particular properties of the coating
result from the presence of organophosphorus compounds both in the chemisorbed form
and in the physisorbed form at least preponderantly crystallized.
lndeed, under the conditions of the process of the invention, the surface of the metal
substrate is first grafted by a very fine monomolecular layer of the organophosphorus
compound. The grafting takes place by reaction of the phosphonic groups with at least part
of the hydroxyl groups present at the surface of the metal. This results in that the first layer
is linked to the substrate by covalent-type bonds, and firmly adheres to the metallic surface.
Furthermore, the monomolecular layer may be self-assembled. But this is not mandatory at
all, thereby enabling rapidity and simplicity of implementat¡on of the treatment in terms of
time and number of steps, An advantage of the process according to the invention, in an
industrial application, is actually that it does not necessitate allowing time for the
monomolecular layer to be self-assembled, and even it does not necessitate that the
monomolecular layer coats the entire surface of the substrate. A coating of at least 1,5% of
the surface of the substrate is already sufficient, lt is possible to proceed to the shaping
almost immediately after the coating of the substrate, as soon as the solvent has
evaporated, On the other hand, it becomes preferable to work with high concentrations of
the organophosphorus compound in the solvent, optimally in supersaturation.
By < self-assembled monolayer >, is meant a layer which may be defined as a
molecular assembly which is formed spontaneously over time by immersion of a substrate in
a solution containing an active surfactant, until the formation of a perfectly arranged
monolayer,
According to the invention, the coating of the metal substrate further includes,
disposed over said monomolecular layer, a second layer of physisorbed molecules of the
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organophosphorus compound at least preponderantly crystallized. By ( at least
preponderantly >, is meant that at least 50% of the compound is in the crystallized form,
This second layer is clearly thicker in comparison with the first layer. Most often, it is
possible to detect its presence with the naked eye, Since the underlying monomolecular
layer covers at least 1,5% of the reactive sites, the second layer is not linked everywhere to
the substrate by strong covalent-type bonds, this is all the more as the second layer is at
least preponderantly crystallized, Hence, the adhesion of the second layer results from other
bonds, for example of the Van der Waals type, in particular with the underlying
organophosphorus molecules grafted to the metal. This second layer may be considered as
physisorbed. Furthermore, in the second layer, the molecules of the organophosphorus
compound are at least preponderantly crystallized. ln orderto preserve the superficial layer
and to ensure the pursued effect, it is therefore important that the process of the invention
does not include subsequen.t steps likely to eliminate at least the second layer, or is not
followed by such steps before the shaping of the product, or, in a general manner, before
any operation during which the presence of the second layer would be advantageous.
IProcess]
The present invention mainly concerns a process for treating metal substrates
allowing improving their tribological behavior during their shaping, and possibly also their
corrosion resistance.
ln its widest definition, this process is characterized by the deposition on the
substrate of a coating of an organophosphorus compound with the particularity that the
compound is provided in a double form.
lndeed, the coating includes a first monomolecular layerwhich is not necessarily selfassembled,
which is in contact with at least 15% of the surface of the substrate, and is linked
to the substrate by means of covalent-type bonds, and, above this first layer (and above the
substrate in the areas where it is not covered by the first layer, if any), it includes a second
layer in which the compound is both in the physisorbed form and, at least preponderantly,
crystallized, with a low adherence of the second layer on the first surface, and also on the
substrate in the possible areas not covered by the first layer.,
It is the presence of the organophosphorus compound in these two distinct forms
which allows the obtainment of the desired technical effects, without the need to add other
compounds to the treatment solution, or of an additional layer of any product on the surface
of the material to be shaped.
As mentioned hereinabove, according to a first aspect, the invention concerns a
process for surface treatment of metal substrates, comprising the steps of :
(¡) providing a metal substrate including hydroxylgroups at its surface;
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(ii) bringing the metal substrate into contact with a solution of at least one
organophosphorus compound so as to enable the reaction of said hydroxyl groups at the
surface of the metal substrate with said organophosphorus compound so as to form a
chemisorbed monomolecular layer, not necessarily self-assembled, over the surface, and a
second layer of physisorbed organophosphorus molecules at least preponderantly
crysta llized,
the obtained treated substrate being, ultimately, coated with the organophosphorus
compound in the chemisorbed form (the monomolecular layer) and in the physisorbed form
at least preponderantly crystallized (the second layer).
The process of the invention may be used on substrates with various natures and
sha pes.
Nevertheless, the metal must be oxidizable, spontaneously or not, and therefore
likely to present hydroxyl groups at its surface. Thus, it may consist of substrates based on
iron, nickel, cobalt, aluminum, copper, chromium, titanium, zinc, gold, silver, ruthenium,
rhodium or based on one of their alloys such as stainless steels, carbon steels or still
electricalsteels.
The metal substrate may be a-substrate made of massive metal or, possibly, a
composite substrate, but it will include a surface which is made of metal at least partially,
ln order to dispose hydroxyl groups at the surface, it is not generally necessary to
subject the metal substrate to a particular treatment, lndeed, with the exception of certain
metals or alloys, the ambient conditions suffice to oxidize the surface, thereby creating the
hydroxyl groups whích react with the phosphonic function.
The metal may be a pure metal but most often it wìll consist of a metallic alloy. Are
particularly concerned in the process of the invention, the steels, in particular the stainless
steels, the carbon steels, the electrical steels (Fe-Si) but also the ferrous alloys with high
added value (Fe-Ni, Fe-Co). Nonetheless, it may also consist of non-ferrous metals such as
aluminum, copper, chromium, nickel, cobalt, titanium, zinc, gold, silver, ruthenium and
rhodium or the alloys thereof.
The shape of the substrate may be very variable. Thus, it is possible to use as a
substrate, for example, flat products intended, in particular, to be deep-drawn, with a
thickness comprised between 0.04 mm and 20 mm, with a preference for a thickness
comprised between 0.4 and 2.5 mm, tubes, wires, or still products intended to cutting (in
particular for substrates the thickness of which is less than 4 mm).
Nonetheless, it is also possible to consider implementing the process of the
invention, to also treat the products which will be shaped, in particular in order to ensure
the corrosion resistance during the transport or before the surface treatment,
Preferably, the at least one organophosphorus compound is of formula (l) below
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o¡¡ -ORa Z-A-P{t
ofi' (r)
10
wherein
A represents a hydrocarbon chain, saturated or unsaturated, straight or branched,
comprising 4 lo 28 atoms of carbon, preferably L6 atoms of carbon, the chain may be
substituted w¡th one or several group(s) chosen among hydroxy, amino, cyano, halogen,
sulfonic acid, phosphonic acid andlor interrupted by one or several atom(s) or group(s)
chosen among O, HN or SH;
Z represents one or several terminal functional group(s) chosen among alcohol,
aldehyde, carboxylic acid, phosphonic acid, thiol, amine, halogen, cyano or silane, or is
absent; and
Rr and Rz ârê, independently of each other, a hydrogen or a saturated alkyl e, straight
or branched, comprising 1- to 1-8 atoms of carbon.
Among these compounds of form.ula (l) are preferred those in which:
Rr and Rz are hydrogen;
Rr and/or Rz are methyl, ethyl, propyl, isopropyl, isobutyl, tert.butyl or nbutyle;
Z is absent;
Z is an halogen, in particular fluoro, chloro, bromo or iodo;
Z is the carboxylic acid;
Z is thiol;
Z is silane;
Z is not the phosphonic acid;
A is a saturated alkyl group;
A is a straight alkyl group;
A does not carry a phosphonic acid;
A is an alkyl group including 4 to 20 atoms of carbon;
A is an alkyl group including L4 to 18 atoms of carbon; and/or
A is an alkyl group including l-6 atoms of carbon.
The tests on stainless steel have concluded that a length of the chain A of l-6 atoms of
carbon would lead to an optimum implementation of the process according to the invention,
at least in this case.
The preferred organophosphorus compounds of formula (l) are those in which Z
represents a functional group chosen among the carboxylic acid, thiol or silane or in which Z
is absent.
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Are particularly preferred the compounds of formula (l) in which the chain A is
straight and saturated and includes only C and H atoms, and therefore those where Z is
a bse nt.
ln the event where they are not avaÌlable in the market, these compounds may be
easily synthesized by adapting the procedure described in the article of M.M. Moine& al.
(2013) titled < Grafting and characterization of dodecylphosphonic acid on copper: macrotribological
behavior and surface properties > (Surface & Coatings Technology).
The organophosphorus compounds include portions with different polarities. Thus,
the end comprising the phosphonic group is polar and has an affinity for the hydroxyl
groups. The phosphonic group reacts by an acid/base reaction with the surface oxide of the
substrate and forms a strong semi-covalent bond between the molecule and the substrate.
Hence, the organophosphonic end is fixed on the metallic surface.
At their other end, the organophosphorus compounds may include a less polar
group, for example a carbon chain possibly substituted tending to confer a preferred
orientation thereto with respect to the metallic surface.
This preferred orientation ultimately leads to a perfectly arranged self-assembled
monolayer. The resulting order is also called self-assembly. However, as has been said, this
characteristic is not mandatory, and the material may be shaped industrially before reaching
this self-assembly state.
The grafting of the organophosphorus compounds on the metal surface may be
performed by simple contact between the metallic surface and the solution.Thus, the step
(ii) of the process allows bringing the metallic surface into contact with the
organophosphorus compounds in solution. This step may be performed by different
conventional means, for example by the Langmuir Blodgett technique, by immersion in a
solution bath, by spraying of the solution, by roller application or still by spreading also
called spin coating.
According to a preferred embodiment, the contact is performed by spraying the
solution containing the organophosphorus compounds over the metal substrate, This
contact mode is particularly advantageous because it is rapid and therefore compatible with
an industrial production rate, Unexpectedly, it has been observed that the quality of the
formed coating is sufficient to improve the tribological properties in a significant manner.
The time of contact necessary to obtain an optimum result in tribological terms may
vary depending on the reactivity of the substrate and of the chosen organophosphorus
compounds. lt may also depend on other parameters such as the temperature and the
concentration of the solution. However, the reaction is generally considered as sufficient
after a contact for a duration which may be as short as one or a few seconds.
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Thus, the duration of contact of the metal surface with the solution of
organophosphorus compounds is preferably from l- second to 600 minutes, still better from
1- to 60 seconds.
The process of the invention does not require any heavy and costly equipment. lt is
rapid and may be performed on large-sized surfaces.
IModified metal substrates]
It has been highlighted by different characterization techniques and in particular by
contact angles measurement, by X-ray photoelectron spectroscopy (XPS), and by infrared
spectroscopy that the treated substrates are coated with a layer of organophosphorus
compounds. ln general, the preponderantly crystallized physisorbed second layer is visible to
the naked eye.
The treated metal substrates have characteristics different from the non-treated
substrates, in particular in terms of tr¡bological properties during their shaping. These
characteristics allow considering their shaping without the use of an additional conventional
lubricant, in particular without a lubricant in the form of an oil or polymer.
Advantageously, such substrates further have a better corrosion resistance, in
particular during storage and transport.
According to a second aspect, the invention therefore concerns a treated metal
substrate which may be obtained by the process of the invention.
The absence of lubricant during the subsequent shaping step is advantageous since it
frees from the need of cleaning the substrates and the tools which is often very costly and
time-consuming. Thus, a non-negligible time saving is possible on the steps subsequent to
the shaping, in particular the stamping step. Moreover, the performance of the associated
lubrication preserves the tooling, subjected to a severe wearing in the case of an
ina ppro priate a nd/or i neffective I u brication.
[Solution]
The grafting of the surface of the metal substrate is performed by contact with a
solution of an organophosphorus compound.
lndeed, one of the advantages of the process lies in the effectiveness of the
organophosphorus compounds. Moreover, considering their good solubility in water and/or
in common alcohols, it appears advantageous to implement the compound in the form of a
solution.
Most of the organophosphorus compounds of formula (l) are soluble in water and/or
one of the alcohols chosen among methanol, ethanol, propanol, isopropanol and butanol.
The non-aerated absolute alcohol is a privileged example, because of its low cost, its low
evaporation temperature and its moderate toxicity. The absence of oxygen dissolved in the
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solvent is not requisite, since the duration of exposure of the organophosphorus compounds
to the solvent may be short, and since the dissolved oxygen then has no time to denature
them.
ln certain embodiments of the process, the concentration of the solution of
organophosphorus compounds may have an impact on the amount of the physisorbed
compound formed atthe surface of the metal, That being said, the process is not limited to a
specific concentration range. lt should only be ensured that the amount of the
organophosphorus compound deposited on the metal surface is sufficient to form both a
chemisorbed monomolecular layer and a physisorbed second layer at least preponderantly
crysta llized.
Thus, the treatment solution comprises more than L, and preferably from l-0 to 1000,
advantageously from 20 to 500 and in particular from 20 to 50 mM/l of the
organophosphorus compound of formula (l) hereinabove. Preferably, in order to ensure the
success of the treatment, a supersaturated solution of the organophosphorus compound(s)
is used, bearing in mind that in the range from 20 to 50 mM/|, for the considered preferred
molecules, this supersaturation is already reached.
According to a third aspect, the invention concerns a treatment solution comprising
at least one organophosphonic compound of formula (l) below
o
z- A-$---oR"
oR.' (t)
wherein:
A represents a hydrocarbon chain, saturated or unsaturated, straight or branched,
comprising 4 To 28 atoms of carbon, preferably L6 atoms of carbon, the chain may be
substituted with one or several group(s) chosen among hydroxy, amino, cyano, halogen,
sulfonic acid, phosphonic acid and/or interrupted by one or several atom(s) or group(s)
chosen among O, HN or SH;
Z represents one or several terminal functional group(s) chosen among alcohol,
aldehyde, carboxylic acid, phosphonic acid, thiol, amine, halogen, cyano or silane or is
absent; and
Rr and Rz ârê, independently of each other, a hydrogen or a saturated alkyl, straight
or branched, comprising 1 to 18 atoms of carbon,
in a solvent comprising an alcohol, in particular methanol, ethanol, propanol,
isopropanol and butanol, possibly water-added, the concentration of the organophosphorus
compound of formula (l) in the solution being of more than 1 mM/1.
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t2
10
Of course, the solution mayfurther contain other additives common in the field such
as preservatives, emulsifiers, pigments or still additives for withstanding high pressures.
The solution of organophosphorus compounds may be prepared in a conventional
manner. ln principle, the organophosphorus compounds are introduced in the solvent,
although the reverse way may also be performed. ln order to accelerate the dissolution of
the organophosphorus compounds, it is possible to stir and if appropriate heat the solution,
IUse of the lubricating solution]
Finally, according to a fourth aspect, the invention concerns a use of such a solution
for the treatment of metal substrates in order to improve their tribological properties during
their shaping, in particular during stamping.
The invention will be described in more detail by means of the examples which
follow, and of the figures, which show:
Fig. 1: a schematic diagram of a coated metal substrate which may be obtained by
the process of the invention, including a monomolecular layer of an organophosphorus
compound and a second layer of preponderantly crystallized molecules of the
orga nophosphorus com pound;
Fig. 2 (a) and (b): micrographies obtained by scanning electron microscopy of the
surface of a ferritic (grade 1.4509 - 44411 stainless steel substrate treated according to the
example 139 highlighting the existence of a crystallized physisorbed layer;
Fig. 3 (a) and (b): micrographies obtained by scanning electron microscopy of the
surface of a ferritic (grade 1.4509 - 441) stainless steel substrate treated according to the
examples 141 (a) and 153 (b) respectively highlighting the influence of the concentration of
organophosphorus molecules on the existence of a crystallized physisorbed layer.
Fig. 4: the determination of the blocking rate performed by cyclic voltammetry of
austenitic (grade 1.4301- 304) stainless steel substrates treated according to the examples
73 (A), 74 (B),7s (C) and 76 (D).
Fig. 5: the friction coefficient p during a test on a twin-disc tribometer (described in
Roizard et al, < Experimental device for tribological measurement aspects in deep drawing
process >, Journal of Materials Processing Technology,209 (2009) 1220-1,230) for a ferritictype
(grade 1.4509 - 444I) stainless steel substrate, treated according to the example 1-39
(A) and with a conventional chlorinated mineral lubricant (RenoForm ETA - Fuchs) (B);
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Fig, 6: the LDR (Limit Drawing Ratio) of a ferritic-type (grade 1.4509 - 4441.) stainless
steel substrate treated according to different configurations:
according to the examples 141 (A), 145 (B), 149 (C),153 (D), 139 (E) and L39
with surface rinsing of the heaps by ultrasounds (F);
with the lubricant Molykote G-Rapid Plus (G) and the conventional chlorinated
mineral oil Fuchs Renoform ETA (H);
Fig. 7: the LDR (Limit Drawing Ratio) of an austenitic-type (grade 1.4301. - 304)
stainless steel substrate according to the performed lubrication treatment: with the
lubricant Molykote G-Rapid Plus (B), the conventional chlorinated mineral oil Fuchs
RenoForm ETA (C), and according to the example 59 (A);
Fig. 8: the Erichsen index (equal to the reached maximum depth (in mm) by stamping
for equibiaxial expansion type loads) of an austenitic-type (grade 1.4509 - 44I) stainless
steel substrate according to the performed lubrication treatment: with the lubricant
Molykote G-Rapid Plus (A), the conventional chlorinated mineral oil Fuchs RenoForm ETA
(B), the chlorinated mineral oil Total Martol EP180 (C), the non-chlorinated mineral oil Total
Martol EP5CF (D), and according to the example 153 (E).
Fig. 9:the evolution of the applied maximum punch force according to the number of
parts during a phase of series production on a saucepan-type geometry from austenitic-type
(grade 1,4301) stainless steel substrates treated with the chlorinated mineral oil
MotulTechCadrex DRL36P (A), and according to the example 73 (B).
Fig. L0: the current density according to the potential for an austenitic-type (grade
1-.4301-304) stainless steel sheet immersed in a hydrochloric acid solution (at 0.3% by
weight) non-treated (A) and treated according to the example 59 (B).
Fig. L1:the current density according to the potential for a ferritic-type (4411.4509 -
44L) stainless steel sheet immersed in a hydrochloric acid solution (a|0.3% by weight) nontreated
(A) and treated according to the example 139 (B),
IEXAMPLESI
Unless otherwise stated, all the tests have been performed at ambient temperature
and pressure.
EXAMPLE A
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t4
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Svnthesis of the n-dodecvlphosphonic acid
The halogenated derivative z-A-Br (200 mmol) is heated to 200"C (oil bath) and the
triethylphosphite (210 mmol) added drop-by-drop at this temperature for 30 minutes, while
the formed bromoethane is continuously distilled (temperature of the vapor below 40"C),
Afterwards, the mixture is brought to 220-250"C and maintained at this temperature during
20 minutes. The excess triethylphosphite is eliminated under 50-100 mmHg during 5-L0 min
and the resulting oil is cooled to ambient temperature. The concentrated aqueous
hydrochloric acid (t2 M, 250 ml) is added and the heterogeneous mixture is brought to
boiling under good stirring for 1-5 h. After cooling to ambient temperature, the semi-oily
mixture crystallizes. The solid is filtered and water-washed until neutral. Afterwards, it is
dried under suction at 20"C. The phosphonic acid may be recrystallized in cyclohexane so as
to result in plates with an off-white color.
EXAMPLE B
Svnthesis of the n-hexadecvlphosphonic acid
Global synthesis protocolanalogous to that of Example A.
EXAMPLES A1 - A1O
Preparation of the grafting solutions
ln a recipient with an adequate volume, equipped with appropriate stirring and
heating means, two solutions have been prepared such that:
Solution 1: 850 ml of absolute ethanol and L50 ml of ultrapure water are introduced.
Afterwards, in this hydroalcoholic solvent, the organophosphorus compound prepared at
example A is introduced in the amount indicated in the table L below. The solution is stirred
until complete solubilization, if appropriate by heating the solution,
Solution 2: 1000 ml of absolute ethanol are introduced. Afterwards, in this alcoholic
solvent, the organophosphorus compound prepared at example A is introduced in the
amount indicated in the table 1" below. The solution is stirred until complete solubilization, if
appropriate by heating the solution.
EXAMPLES 81- B1O
Preparation of the grafting solutions
ln a recipient with an adequate volume, equipped with appropriate stirring and
heating means, two solutions have been prepared such that:
Solution 1: 850 ml of absolute ethanol and 150 ml of ultrapure water are introduced.
Afterwards, in this hydroalcoholic solvent, the organophosphorus compound prepared at
example B is introduced in the amount indicated in the table L below. The solution is stirred
until complete solubilization, if appropriate by heating the solution,
15
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15
Solution 2: L000 ml of absolute ethanol are introduced. Afterwards, in this alcoholic
solvent, the organophosphorus compound prepared at example B is introduced in the
amount indicated in the table 1- below. The solution is stirred until complete solubilization, if
appropriate by heating the solution.
5 Table 1 shows the compositions of the grafting solutions obtained in the different
examples A1 to 4L0 and 8L to 8L0,
EXAMPLES Solution Group A
Concentration
(mol/l)
A1 1 CL2 straisht alkvl 0.00L
A2 1 Cl-2 straieht alkvl 0,005
A3 1 C1-2 straieht alkvl 0,01
A4 1. C12 straisht alkvl 0.05
A5 1 Cl2 straisht alkvl 0.L
A6 2 C1-2 straisht alkvl 0.001
A7 2 C1-2 straieht alkvl 0.00s
A8 2 C12 straieht alkvl 0.01
A9 2 C12 straight alkyl 0.05
410 2 C1-2 straieht alkvl 0.L
B1 1 C16 stra¡sht alkvl 0.001
82 1, C16 straisht alkvl 0.00s
B3 1. C16 stra¡ght alkyl 0,01
B4 t c16 straisht alkvl 0.0s
B5 t CL6 straisht alkvl 0.1
B6 2 C]-6 stra¡sht alkvl 0.001_
87 2 C16 straight alkyl 0.00s
B8 2 C16 straisht alkvl 0.0L
B9 2 C16 straisht alkvl 0.05
810 2 C16 straieht alkvl 0.1
Table 1: Composition of the grafting solutions
10
EXAMPLES 1- 160
Grafting on austenitic (examples l--24) and ferritic (examples 25-48) stainless steel
A metal substrate, constituted by a L mm thick sheet of 189 ED-grade (1.a301-30a)
austenitic or 441-grade (1.4509-441) ferritic stainless steel respectively, has been treated
15 with the treatment solution prepared as indicated hereinabove according to the following
modus operandi.
First, the substrate is degreased and cleaned by immersion in absolute ethanol and
treatment by ultrasounds for 5 minutes. Second, the substrate thus prepared is immersed in
the chosen treatment solution for a time period of L second, 30 minutes (0.5h), 2h and 16h,
20 respectively.
16
The substrate is not rinsed after treatment. lndeed, this would result in eliminating
the layer of physisorbed organophosphorus compound preponderantly crystallized
preserving only the monomolecular layer. The improvement of the tribological properties
would then be insufficient, and the process would not be a viable solution in comparison
5 with a treatment using oils.
The process has been performed with the different prepared treatment solutions, by
varying the time of contact. The treatment parameters of the different samples are indicated
in the tables2,3,4 and 5 below.
The substrates thus treated have been characterized as described later on,
10
EXAMPLES Metal G rafting
solution
Grafting
time
r-4 Austenitic stainless steel
189 ED
A1
Ls;0.5;2and
16h
5-8
Austenitic stainless steel
189 ED
A2
1- s ; 0.5 ;2 and
16h
9-12
Austenitic stainless steel
L89 ED
A3
1s;0.5;2and
L6h
13-16
Austenitic stainldss steel
189 ED
A4
1s;0.5;2and
16h
17-20
Austenitic stainless steel
189 ED
A5
1s;0.5;2and
16h
21,-24
Austenitic stainless steel
189 ED
A6
1s;0.5;2and
16h
25-28
Austenitic stainless steel
L89 ED
A7
1s;0.5;2and
16h
29-32
Austenitic stainless steel
189 ED
A8
1s;0.5;2and
16h
33-36
Austenitic stainless steel
189 ED
A9
Ls;0.55;2
and 1-6 h
37-40
Austenitic stainless steel
189 ED
A10
1"s;0.5;2and
16h
Table 2:Treatment parameters of an austenitic stainless steel with the solutions prepared
according to the examples A1 to 410.
17
EXAMPLES Metal G rafti ng
solution
G rafti ng
time
4I-44
Austenitic stainless steel
189 ED
BL
1s;0.5;2and
16h
45-48
Austenitic stainless steel
189 ED
B2
L s;0.5 ;2and
16h
49-52
Austenitic stainless steel
189 ED
B3
1- s; 0.5 ; 2 and
16h
s3-56
Austenitic stainless steel
189 ED
B4
Ls;0.5;2and
16h
57-60
Austenitic stainless steel
189 ED
B5
Ls;0.5;2and
16h
61,-64
Austenitic stainless steel
189 ED
B6
1"s;0.5;2and
16h
6s-68
Austenitic stainless steel
189 ED
87
1s;0.5;2and
16h
69-72
Austenitic stainless steel
189 ED
B8
1s;0.5;2and
16h
73-76
Austenitic stainless steel
189 ED
B9
Ls;0.55;2
and 16 h
77-80
Austenitic stainless steel
189 ED
810
1s;0.5;2and
1_6 h
Table 3: Treatment parameters of an austenitic stainless steel with the solutions prepared
according to the examples 81 to B10,
EXAMPLES Metal
Grafting
solution
Grafting
time
81-84
Ferr¡tic stainless steel
441
A1
1s;0.5;2and
16h
85-88
Ferritic stainless steel
441,
A2
1s;0.5;2and
16h
89-92
Ferritic stainless steel
441.
A3
1s;0.5;2and
16h
93-96
Ferritic stainless steel
441.
A4
Ls;0.5;2and
16h
97-1_00
Ferritic stainless steel
44L
A5
Ls;0.5;2and
16h
101-104
Ferritic stainless steel
44r A6
1- s ; 0.5 ;2 and
16h
105-108
Ferritic stainless steel
44r A7
Ls;0.5;2and
16h
1.O9-1.1.2
Ferritic stainless steel
441_
A8
1s;0,5;2and
1_6 h
L1,3-1,16
Ferritic sta ¡ nles-s steel
441
A9
1s;0.55;2
and 16 h
1,1,7-120
Ferritic stainless steel
441,
A10
Ls;0.5;2and
L6h
Table 4: Treatment parameters of a ferritic stainless steel with the solutions prepared
according to the examples Al to 410.
10
EXAMPLES Metal
Grafting
solution
Grafting
time
1,21,-124
Ferritic stainless steel
44'L
B1
Ls;0.5;2and
16h
125-128
Ferritic stainless steel
441
B2
1s;0.5;2and
16h
129-1,32
Ferritic stainless steel
441
B3
Ls;0.5;2and
16h
133-136
Ferritic stainless steel
441,
B4
1s;0.5;2and
16h
1,37-r40
Ferritic stainless steel
441_
B5
l- s ; 0.5 ;2 and
16h
1,41-144
Ferritic stainless steel
441.
B6
l- s ; 0,5 ;2 and
1"6 h
145-148
Ferritìc stainless steel
44L
87
Ls;0,5;2and
16h
1,49-152
Ferritic stainless steel
441,
B8
Ls;0,5;2and
16h
1s3-156
Ferritic stainless steel
441
B9
Ls;0.55;2
and L6 h
1,57-1,60
Ferritic stainless steel
441.
81"0
1s;0.5;2and
16h
Table 5: Treatment parameters of a ferritic stainless steel with the solutions prepared
according to the examples 81 to 810.
A. Surface tension
ln order to highlight the presence of the coating and more specifically of the
monomolecular layer, the samples have been specially rinsed upon completion of the
treatment in order to remove the physisorbed layer. Afterwards, the surface tension has
been assessed before and after the treatment of the substrate with the solution 85 (with
rinsing) for the (ferritic and austenitic) stainless steel substrates and with the solution A3
(with rinsing) for the aluminum and copper substrates.
The surface tension of the different metal substrates has been assessed according to
the methods of Owens and Wendt, from contact angles obtained with three distinct liquids
(diiodomethane, ethylene glycol, water) whose polar yrP and dispersive yrD components are
known and disclosed in the table 6.
YtmJ/mz vr dmJ/m2 vlPmJ/m2
Water 72.8 21_.8 51
Ethylene glycol 48 29 1.9
Diiodomethane s0.8 50.8 0
Table 6: Surface energies of the considered liquids.Details of the polar and dispersive
components.
20
15
10
lndeed, the measurement of the contact angle enables the calculation of the total
surface tension (as well as the polar and dispersive components) based on the following
Young's formula:
YSv = Ysl * yLV COS 0
The measurement and calculations results are compiled in the table 7 below, For all
samples, the treatments (immersion in the solution) have lasted 2 h.
Metal
Contact angle
["1
Surface tension
lmJ/m'zl
Ferritic
stainless steel
Non-treated 92 24.7
Treated (EX.
13e)
115 18.5
Austenitic
Stainless steel
Non-treated 15 66.5
Treated (EX. 59) 100 1"8.5
Aluminum
Non-treated 3 47
treated 115 15
Copper
Non-treated 96 38.1
treated 125 21.9
Table 7: Effect of the treatment on the surface tension of the metal surfaces
These tests have allowed confirming the presence of an active species at the surface
of the treated substrates. Moreover, they have allowed validating the possibility of treating
different metal substrates by means of the process of the invention.
By analyzing the results, a very clear decrease of the surface tension is noted,
indicating a more polar and therefore a more hydrophobic nature of the surfaces (increase
of the contact angle), The very homogeneous results for different samples and sites on the
surfaces reveal the obtainment by the process of the invention of a complete and
homogeneous coverage of the treated surface for the long exposure durations, and a
sufficient coverage, even though not complete, for the short, and even very short (1- s),
exposure durations. Figure 4 highlights the evolution of said coverage rate in the case of an
austenitic stainless steel according to the immersion times, respectively from l- s to 1"6 h.
Thus, it is set out the fact that 1,9% of the surface is already covered by a monomolecular
layer after an immersion time of l- s whereas this rate rises to 4I%, 85% and 94% for
immersion times of 30 minutes, 2 hours and L6 hours, respectively.
Moreover, it is remarked that the surface tension, different for each of the nontreated
substrates, tends to be aligned for the treated substrates, at a value close to 18.5
mJfmz, thereby reflecting the sole contribution of the monomolecular layer in the apparent
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25
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10
surface tension of the tested sample when the immersion time justifies the existence of a
sufficient monomolecular layer to obtain this effect, said immersion time may be of 2 h, and
even lesser, according to the given experimental results,
B. Friction coefficient
ln order to assess the effect of the treatment process of the invention on the
tribological properties of the metal, the treated samples have been characterized by means
of a twin-disc tribometer, representative of the stamping conditions.
ln this device, the floating portions are cylindrical and come into lineal (or pseudolineal
when considering a Hertz contact pressure) direct contact with the substrate to be
tested via two arms forming a clamp, actuated by a pneumatic cylinder, ln the tests reported
herein, the cylinders are made of a tool steel 2160CD12. They exert an average normalforce
(perpendicular to the surface of the treated substrate) of 4000 N and are animated at a
defined speed of 1-0 mm/min. The small contact surface obtained thanks to this particular
geometry of the tool (in comparison with a plane/plane contact) enables access to a finer
study of the friction, in particular allowing obtaining a more accurate evolution of the
friction coefficient according to the friction distance (discretization of the friction = n passes
depending on the desired friction distance).
Through the measurement of the tangential force resulting from the displacement of
the cylindrical tools rotatably fixed on the treated metal substrate, the friction coefficient
has been calculated according to the following formula:
F,
where Fn is the applied normal force and t-, ,Ín{î"rulting tangential force.
The evolution of the friction coefficient according to the number of passes (according
to the friction distance) is illustrated by Figure 5, Both concern a ferritic (4441. - 1,4509)
stainless steel substrate. Figure 5 offers a performances comparison between (curve B) a
commonly used industrial oil (oil RenoForm ETAcommercialized by Fuchs Lubrifiants France)
and (curve A) a treatment of the substrate by the present invention according to the
example L39,
Upon completion of a treatment preconized by the present invention, the measured
friction coefficient is in the range of 0.05 and turns out to be constant during the different
passes. This denotes a very good tribological behavior, which, what's more, is without any
substantial alteration over time.
The results highlight a very clear improvement of the tribological properties by the
treatment according to the process of the invention, ln particular, the metals treated
according to the invention have a friction coefficient lower than that obtained by treatment
with a high-performance oil according to the state of the art.
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22
15
C. Deep-drawability
The deep-drawability is a major factor in the shaping of materials, lndeed, a metal
having a good deep-drawability enables the use of severe stamping industrial conditions
allowing in particular minimizing the number of passes required to confer the desired shape
to the substrate. This deep-drawability is a complex combination of the elastoplastic
mechanical properties of the matter, of the lubrication conditions and of the used process
parameters (tools type, tools kinematics,...).
ln order to assess the effect of the treatment process on the deep-drawability, the
treated substrates have been characterized by stamping following a restricted-type
deformation path through the determination of the LDR (< Limit Drawing Ratio >) for
different lubrication conditions. ln this test, an initial disc with a diameter D is deep-drawn
by a punch with a fixed diameter d (d = 33 mm). As soon as the operation is considered as
successful (realization of the part without breakup), the diameter D of the deep-drawn disc
is increased by successive steps of 4 mm and this, until obtaining the first broken-up part.
The maximum diameter, denoted D'u,, of the last deep-drawn disc before breakup of the
material is then collected to allow the calculation of the limit stamping ratio defined as the
ratio LDR = D."*/d. This ratio is characteristic of each metal substrate and of the associated
lubrication conditions, Hence, the comparison between a sheet metal lubricated with a
common industrial oil and a sheet metal treated by the present invention allows
characterizing the effectiveness of the lubricant herein proposed, at strictly equivalent
matter properties and process parameters. The higher is the obtained LDR value, the better
is the lubricity of the used lubricant.
The obtained results are illustrated through figures 6 and 7.
Table 8 synthesizes the results thus obtained for austenit¡c-type (1.4301 - 304) and
ferritic-type (14509 - 441,) stainless steel substrates in various lubrication configurations. lt
should be noted that the tools themselves are made of non-coated steel Z1,60CDVI2,
without any modification during the different tests, The data relating to the ferritic (1.4509 -
441-) and austenitic (1,4301- 304) stainless steels are taken up respectively by figures 6 and
7.
25
30
10
Metal Lubrica nt LDR
Auste n itic
sta in less
steel
3oa Gie.7)
Treated
(example 59)
2.r7 (ANon-treated
RenoForm ETA
(Oil commercialized by Fuchs
Lubrifiants France)
2.10 (c)
Non-treated
Molykote G-Rapid Plus
(Solid lubricating paste
commercialized by Dow
Cornine)
2.18 (B)
Ferritic
sta in less
steel
aa1 (Fig.6)
Treated
(example 141)
2.0e (A)
Treated
(example 145)
2.ls (B)
Treated
(example 149)
2.18 (c)
Treated
(example 153)
2.24 (D)
Treated
(example 139)
2.3s (E)
Treated
(example 139 + rinsing
and removalof the 2nd
laver)
2,04 (F)
Non-treated
RenoForm ETA
(Oil commercialized by Fuchs
Lubrifiants France)
2,20 (G)
Non-treated
Molykote G-Rapid Plus
(Solid lubricating paste
commercialized by Dow
Cornine)
2.28 (H)
Table 8: Effect of the treatment of the invention on the deep-drawability
A first series of tests has been conducted on an austenitic 304 stainless steel grade
according to the example 59 or non-treated according to the invention but coated with
different conventional lubricants (Figure 7). Complementarily to this first series of tests, a
second series has been performed on a ferritic 441 stainless steel grade treated according to
different examples, namely the examples L41-, 1,45,1,49, L53, 1-39 and L39 with the addition
of an intentional post-treatment rinsing in order to remove, for this last configuration, the
second layer of molecules of the organophosphorus compound at least preponderantly
crystallized. Complementarily to these treatments, in a manner similar to that which has
been done for the austenitic 304 stainless steel grade, tests have been carried out on a sheet
metal non-treated but coated with different conventional lubricants (Figure 6), lt should be
noted that the lubricant Renoform ETA is a chlorinated mineral oil commonly used
24
10
industrially whereas the solid lubricating paste Molykote G-Rapid Plus is a product used at a
laboratory scale (or for a non-automatized production of a small-series) with a very high
lubricity rarely equalled by conventional industrial oils.
It is observed from the results of these tests that the substrates obtained according
to the invention have stamping characteristics, equivalent to and even higher than those
obtained using high-performance lubricants, A clear effect of the initial concentration of
organophosphorus molecules on the performance is set out by these results: a higher
concentration induces a much better performance of the product. ln addition, the test
performed according to the example 139 with the removal of the second layer of molecules
of the organophosphorus compound (F) reflects the necessity of preserving this second layer
of physisorbed molecules at least preponderantly crystallized in order to enhance the
performance of the product, and this, although the monomolecular layer obtained by the
treatment of the example 139 induces a considerable coverage rate.
Complementarily to the determination of the LDR levels, a second stamping test has
been performed in orderto validate the performance of the productfollowing an equibiaxial
expansion type loading path: the Erichsen test. ln the context of this test, the matter
engulfing during the shaping operation'is avoided by the application of a sufficient diecushion
force (10 kN) so that no slip has occurred under the gripping of the tools, The only
slips encountered in the context of this test are localized between the sheet metal and the
hemispherical punch with a 20 mm diameter (made of tool steel Z1-60CDV12) during the
vertical displacement operated by the latter. Table 9 synthesizes the results obtained on a
ferritic (14509 - 44I) stainless steel grade treated according to the example 153 or nontreated
but coated with different conventional lubricants. The data relate to a ferritic (14509
- 441.) stainless steel and are taken up in Figure 8.
Metal Lu brica nt
Erichsen
index
Ferritic
sta in less
steel
441.
Treated
(example 153)
10.7 (E)
Non-treated
RenoForm ETA
(Oil commercialized by Fuchs
Lubrifiants France)
e,6 (D)
Non-treated
Molykote G-Rapid Plus
(Solid lubricating paste
commercialized by Dow
Cornine)
1o.o (A)
Non-treated
Martol EP180
(Oil commercialized by Total)
s.7 (c)
Non-treated
Martol EPSCF
(Oil commercialized bv Total)
e.6 (B)
Table 9: Effect of the treatment of the invention on the deep-drawability
15
25
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It is observed from the results of these tests that the substrate obtained according to
the invention has stamping characteristics and performances clearly higher than those of the
equivalent substrates non-treated but coated with more conventional lubricants dedicated
to the production of large or small series. The performance gain inherent to a treatment
according to the present invention is estimated herein to be l-0%,
ln order to definitively validate the effectiveness of the present invention in an
industrial scale, tests have been carried out on an industrial press under production
conditions, at a production rate of more than 4 parts per minute. The realized part
corresponds to a saucepan with a 240 mm diameter, The latter may be considered as
difficult to manufacture considering the induced forces, in all cases greater than 800 kN, All
of the used tools are integrally coated with a TiCN coating in order to minimize the frictions
generated during the stamping phase,
Figure 9 illustrates the results obtained on an austenitic (1.4301- 304) stainless steel
substrate treated according to the example 73 (curve B) or non-treated but coated with an
industrial lubricant MotulTechCadrex DRL36P, which is a chlorinated lubricant commonly
used on the present production tool (curve A). Said lubricant further necessitates a costly
post-stamping degreasing step. lt should be noted that a considerable difference exists
between the two series of realized parts illustrated by Figure 9 as regards the initial
lubrication conditions before stamping. Whereas in the case of the use of the conventional
lubricant MotulTechCadrex DRI-36P, the tools themselves are coated with the lubricant
before the stamping of the first part as is usually practiced, said tools turn out to be clean
and dry at the beginning of the production in the case of the substrates coated according to
the example 73 of the invention. Nevertheless, it appears very clearly that no deterioration
of the performance is observed during the stamping of said first parts, Still furthermore, a
significant decrease of the maximum force applied by the press is clearly observable on the
entire series of 20 parts herein produced via the treatment proposed by the present
invention. This force decrease, in the range of L0%, allows a direct and evident reduction of
the energy necessary for the realization of the parts. lt further allows considering realizing
parts for which the machine capacity may initially appears insufficient considering the forces
necessary for their realization through the use of a conventional lubricant. ln addition, no
post-stamping degreasing is herein necessary, thereby inducing an evident direct gain in
productivity.
D. Corrosion resistance
ln order to assess the effect of the treatment process of the invention on the
corrosion resistance of the metal, two treated sheet metals have been characterized by
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10
voltammetry in an acid environment. The experimental conditions of this test are compiled
in table 1-0 below,
Three-electrode
electrochemical cell
Workins electrode Substrate to be tested
Counter electrode Platinum
Reference electrode Saturated calomel
Solvent HCl0.s% airv am bient tem oerature
Slew rate 1"0 mV/s
Table 1-0: Experimental conditions of the voltammetric test
The obtained curves correspond to voltammograms indicating the current density
according to the potentialapplied to the metal immersed in the hydrochloric acid solution.
The measurements have been performed on austenitic-type (1.4301- - 304) and
ferritic-type (1.4509 - 441,) stainless steels treated respectively according to the examples 59
and L39 (curves B) as well as on the non-treated corresponding metals for comparison
(curves A).
The obtained voltammograms are illustrated in Fig, L0 and LL respectively.
It is observed that the behavior of the stainless steel sheets is considerably modified
by the treatment according to the invention, ln both studied cases, for an equivalent applied
potential, the treatment according to the invention significantly reduces the current density,
Thus, it is possible to define blocking rates thereof ,99% and 95% respectively, corresponding
to a marked corrosion inhibitory effect of our invention,
Hence, the performed studies also confirm the substantial interest of the process of
the invention with regard to protection against corrosion,
Thus, the process of the invention allows access to metal substrates having
advantageous characteristics such as a low fríction coefficient, an excellent deep-drawability,
and in addition, advantageously, a high corrosion resistance.
The process is simple and rapid to implement and does not require any specific
equipment. lt implements small amounts of barely toxic and low-cost compounds. The
avoidance of the use of a lubricating oil during the transformation allows substantial savings,
including on indirect costs (workforce, degreasing apparatuses...), and avoids the production
of wastes potentially dangerous for the environment.
The metal substrates treated by the process of the invention have substantial
advantages since they greatly facilitate, thanks to their pre-lubrication, their subsequent
shaping and are also protected against corrosion.
Hence, the surface treatment of metal substrates according to the invention, by
deposition of a coating of organophosphorus compounds in different forms, brings in a real
improvement of the tribological properties of the material without requiring a classical
lubricant in addition to said coating,

We claim:
1. A process for surface treatment of metalsubstrates, comprising the steps of:
(i) providing a metal substrate including hydroxyl groups at its surface;
(ii) bringing the metal substrate into contact with a solution of at least one
organophosphorus compound so as to enable the reaction of said hydroxyl groups at the
surface of the metal substrate with said organophosphorus compound to form a
monomolecular layer over the surface and a second layer of physisorbed organophosphorus
molecules at least prepondera ntly crystallized,
the obtained treated substrate being coated with the organophosphorus compound
in the form of a first monomolecular layer coating at least 1,5% of the surface of the
substrate and in the form of a physisorbed second layer at least preponderantly crystallized.
2. A process for lubricating metalsubstrates according to claim 1", wherein the at
least one organophosphorus compound is of formula (l) below
o
z- A-$-'-oËt
oR.'(t)
wherein
A represents a hydrocarbon chain, saturated or unsaturated, straight or branched,
comprising 4 T.o 28 atoms of carbon, preferably l-6 atoms of carbon, the chain may be
substituted with one or several group(s) chosen among hydroxy, amino, cyano, halogen,
sulfonic acid, organophosphonic acid and/or interrupted by one or several atom(s) or
group(s) chosen among O, HN or SH;
Z represents one or several terminal functional group(s) chosen among alcohol,
aldehyde, carboxylic acid, organophosphonic acid, thiol, amine, halogen, cyano or silane, or
is absent; and
Rr and Rz âre, independently of each other, a hydrogen or a saturated alkyl, straight
or branched, comprising 1 to 18 atoms of carbon.
3. The process for lubricating metal substrates according to any of claims L or 2,
characterized in that the solvent comprises an alcohol, and/or water,
4. The process for lubricating metal substrates according to claim 3,
characterized in that said alcohol is an alcohol chosen among methanol, ethanol, propanol,
isopropanol and butanol and the mixtures thereof.
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28
5. The process for lubricating metal substrates according to any of claims Lto 4,
wherein the solution has a concentration of more than l- mM/l and preferably from l-0 to
1"000 mM/1, advantageously from 20 to 500 mM/|, and particularly from 20 to 50 mM/|.
6. The process for lubricating metal substrates according to any of claims 1- to 5,
wherein the solution of the organophosphorus compound is supersaturated,
7. The process for lubricating metal substrates according to any of claims L to 6,
10 wherein the treated substrate is made of iron, nickel, cobalt, aluminum, copper, chromium,
titanium, zinc, gold, silver, ruthenium, rhodium or any of their alloys, in particular the steels
such as the stainless steels, the carbon steels and the electricalsteels.
8. The process for lubricating metal substrates according to any of claims 1,1o7,
15 wherein the organophosphorus compound is of formula (l) where A is a saturated alkyl
group and/or a straight alkyl group.
9, A treated metal substrate, characterized in that it has been obtained by the
process according to any of claims 1 to 8.
20
10. The treated metal substrate according to claim 9, characterized in that it
consists of a substrate made of iron, nickel, cobalt or any of their alloys.
1,1,. The treated metal substrate according to claim 9, characterized in that it
25 consists of a substrate made of aluminum, copper, chromium, titanium, zinc, gold, silver,
ruthenium, rhodium or any of their alloys.
12. The lubricated metal substrate according to any of claims L0 to !!,
characterized in that it consists of a flat product,
30
13, A surface treatment solution comprising at least one phosphonic compound
of formula (l) below
0
z-A-Ëín*'
o-R "' (l)
35
wherein:
29
10
15
20
25
A represents a hydrocarbon chain, saturated or unsaturated, straight or branched,
comprising 4 to 28 atoms of carbon, preferably 1-6 atoms of carbon, the chain may be
substituted with one or several group(s) chosen among hydroxy, amino, cyano, halogen,
sulfonic acid, phosphonic acid and/or interrupted by one or several atom(s) or group(s)
chosen among O, HN or SH;
Z represents one or several terminal functional group(s) chosen among alcohol,
aldehyde, carboxylic acid, phosphonic acid, thiol, amine, halogen, cyano or silane or is
absent; and
Rr and Rz âíê, independently of each other, a hydrogen or a saturated alkyl, straight
or branched, comprising 1to L8 atoms of carbon,
in a solvent comprising an alcohol, in particular methanol, ethanol, propanol,
isopropanol and butanol, possibly water-added, the concentration of the organophosphorus
compound of formula (l) in the solution being of more than 1 mM/1.
t4. A use of a solution according to claim L3 for the treatment of metal substrates
in order to improve their tribological properties during their shaping, in particular during
stamping.