SURFACE TREATMENT OF METAL SUBSTRATES

Abstract

A process for surface treatment of metal substrates, including the steps of: providing a metal substrate including hydroxyl groups at its surface; bringing the metal substrate into contact with a solution of at least one organophosphorus compound to enable the reaction of the hydroxyl groups at the surface of the metal substrate with the organophosphorus compound to form a monomolecular layer over the surface and a second layer of physisorbed organophosphorus molecules at least preponderantly crystallized, the obtained treated substrate being coated with the organophosphorus compound in the form of a first monomolecular layer coating at least 15% of the surface of the substrate and in the form of a physisorbed second layer at least preponderantly crystallized. A treated metal substrate which may be obtained by the process thereof, corresponding solution and its use for treating metallic substrates to improve their tribological properties during their shaping, in particular their stamping.

Claims

1. A process for surface treatment of metal substrates, 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 the hydroxyl groups at the surface of the metal substrate with the organophosphorus compound to form a monomolecular layer over the surface and a second layer of physisorbed organophosphorus molecules at least preponderantly crystallized, the obtained treated substrate being coated with the organophosphorus compound in the form of a first monomolecular layer coating at least 15% of the surface of the substrate and in the form of a physisorbed second layer at least preponderantly crystallized.

2. A process for lubricating metal substrates according to claim 1, wherein the at least one organophosphorus compound is of formula (I) below ##STR00005## 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, organophosphonic acid, thiol, amine, halogen, cyano or silane, or is absent; and R.sub.1 and R.sub.2 are, 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 claim 1, wherein the solvent comprises an alcohol, and/or water.

4. The process for lubricating metal substrates according to claim 3, wherein the alcohol is an alcohol chosen among methanol, ethanol, propanol, isopropanol and butanol and the mixtures thereof.

5. The process for lubricating metal substrates according to claim 1, wherein the solution has a concentration of more than 1 mM/l.

6. The process for lubricating metal substrates according to claim 1, wherein the solution of the organophosphorus compound is supersaturated.

7. The process for lubricating metal substrates according to claim 1, wherein the treated substrate is made of iron, nickel, cobalt, aluminum, copper, chromium, titanium, zinc, gold, silver, ruthenium, rhodium or any of their alloys.

8. The process for lubricating metal substrates according to claim 1, wherein the organophosphorus compound is of formula (I) where A is a saturated alkyl group and/or a straight alkyl group.

9. A treated metal substrate, wherein it has been obtained by the process according to claim 1.

10. The treated metal substrate according to claim 9, wherein it consists of a substrate made of iron, nickel, cobalt or any of their alloys.

11. The treated metal substrate according to claim 9, wherein it 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 claim 10, wherein it consists of a flat product.

13. A surface treatment solution comprising at least one phosphonic compound of formula (I) below ##STR00006## 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, 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 R.sub.1 and R.sub.2 are, 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, possibly water-added, the concentration of the organophosphorus compound of formula (I) in the solution being of more than 1 mM/l.

14. A method comprising, treating metal substrates in order to improve their tribological properties during their shaping with the solution according to claim 13.

Description

[0119] The invention will be described in more detail by means of the examples which follow, and of the figures, which show:

[0120] 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 organophosphorus compound;

[0121] FIGS. 2 (a) and (b): micrographies obtained by scanning electron microscopy of the surface of a ferritic (grade 1.4509-4441) stainless steel substrate treated according to the example 139 highlighting the existence of a crystallized physisorbed layer;

[0122] FIGS. 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.

[0123] 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), 75 (C) and 76 (D).

[0124] FIG. 5: the friction coefficient 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) 1220-1230) for a ferritic-type (grade 1.4509-4441) stainless steel substrate, treated according to the example 139 (A) and with a conventional chlorinated mineral lubricant (RenoForm ETA-Fuchs) (B);

[0125] FIG. 6: the LDR (Limit Drawing Ratio) of a ferritic-type (grade 1.4509-4441) stainless steel substrate treated according to different configurations: [0126] according to the examples 141 (A), 145 (B), 149 (C), 153 (D), 139 (E) and 139 with surface rinsing of the heaps by ultrasounds (F); [0127] with the lubricant Molykote G-Rapid Plus (G) and the conventional chlorinated mineral oil Fuchs Renoform ETA (H);

[0128] 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);

[0129] 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 1.4509-441) 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 EPSCF (D), and according to the example 153 (E).

[0130] 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 DR136P (A), and according to the example 73 (B).

[0131] FIG. 10: 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).

[0132] FIG. 11: the current density according to the potential for a ferritic-type (4411.4509-441) stainless steel sheet immersed in a hydrochloric acid solution (at 0.3% by weight) non-treated (A) and treated according to the example 139 (B).

EXAMPLES

[0133] Unless otherwise stated, all the tests have been performed at ambient temperature and pressure.

Example A

[0134] Synthesis of the n-Dodecylphosphonic Acid

[0135] 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 5-10 min and the resulting oil is cooled to ambient temperature. The concentrated aqueous hydrochloric acid (12 M, 250 ml) is added and the heterogeneous mixture is brought to boiling under good stirring for 15 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

[0136] Synthesis of the n-Hexadecylphosphonic Acid

[0137] Global synthesis protocol analogous to that of Example A.

Examples A1-A10

[0138] Preparation of the Grafting Solutions

[0139] In a recipient with an adequate volume, equipped with appropriate stirring and heating means, two solutions have been prepared such that:

[0140] 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 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.

[0141] 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 B1-B10

[0142] Preparation of the Grafting Solutions

[0143] In a recipient with an adequate volume, equipped with appropriate stirring and heating means, two solutions have been prepared such that:

[0144] 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 1 below. The solution is stirred until complete solubilization, if appropriate by heating the solution.

[0145] Solution 2: 1000 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.

[0146] Table 1 shows the compositions of the grafting solutions obtained in the different examples A1 to A10 and B1 to B10.

TABLE-US-00001 TABLE 1 Composition of the grafting solutions Concentration EXAMPLES Solution Group A (mol/l) A1 1 C12 straight alkyl 0.001 A2 1 C12 straight alkyl 0.005 A3 1 C12 straight alkyl 0.01 A4 1 C12 straight alkyl 0.05 A5 1 C12 straight alkyl 0.1 A6 2 C12 straight alkyl 0.001 A7 2 C12 straight alkyl 0.005 A8 2 C12 straight alkyl 0.01 A9 2 C12 straight alkyl 0.05 A10 2 C12 straight alkyl 0.1 B1 1 C16 straight alkyl 0.001 B2 1 C16 straight alkyl 0.005 B3 1 C16 straight alkyl 0.01 B4 1 C16 straight alkyl 0.05 B5 1 C16 straight alkyl 0.1 B6 2 C16 straight alkyl 0.001 B7 2 C16 straight alkyl 0.005 B8 2 C16 straight alkyl 0.01 B9 2 C16 straight alkyl 0.05 B10 2 C16 straight alkyl 0.1

Examples 1-160

Grafting on Austenitic (Examples 1-24) and Ferritic (Examples 25-48) Stainless Steel

[0147] A metal substrate, constituted by a 1 mm thick sheet of 189 ED-grade (1.4301-304) austenitic or 441-grade (1.4509-441) ferritic stainless steel respectively, has been treated with the treatment solution prepared as indicated hereinabove according to the following modus operandi.

[0148] 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 1 second, 30 minutes (0.5 h), 2 h and 16 h, respectively.

[0149] The substrate is not rinsed after treatment. Indeed, 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 with a treatment using oils.

[0150] 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 tables 2, 3, 4 and 5 below.

[0151] The substrates thus treated have been characterized as described later on.

TABLE-US-00002 TABLE 2 Treatment parameters of an austenitic stainless steel with the solutions prepared according to the examples A1 to A10. Grafting Grafting EXAMPLES Metal solution time 1-4 Austenitic stainless steel A1 1 s; 0.5; 2 and 189 ED 16 h 5-8 Austenitic stainless steel A2 1 s; 0.5; 2 and 189 ED 16 h 9-12 Austenitic stainless steel A3 1 s; 0.5; 2 and 189 ED 16 h 13-16 Austenitic stainless steel A4 1 s; 0.5; 2 and 189 ED 16 h 17-20 Austenitic stainless steel A5 1 s; 0.5; 2 and 189 ED 16 h 21-24 Austenitic stainless steel A6 1 s; 0.5; 2 and 189 ED 16 h 25-28 Austenitic stainless steel A7 1 s; 0.5; 2 and 189 ED 16 h 29-32 Austenitic stainless steel A8 1 s; 0.5; 2 and 189 ED 16 h 33-36 Austenitic stainless steel A9 1 s; 0.55; 2 and 189 ED 16 h 37-40 Austenitic stainless steel A10 1 s; 0.5; 2 and 189 ED 16 h

TABLE-US-00003 TABLE 3 Treatment parameters of an austenitic stainless steel with the solutions prepared according to the examples B1 to B10. Grafting Grafting EXAMPLES Metal solution time 41-44 Austenitic stainless steel B1 1 s; 0.5; 2 and 189 ED 16 h 45-48 Austenitic stainless steel B2 1 s; 0.5; 2 and 189 ED 16 h 49-52 Austenitic stainless steel B3 1 s; 0.5; 2 and 189 ED 16 h 53-56 Austenitic stainless steel B4 1 s; 0.5; 2 and 189 ED 16 h 57-60 Austenitic stainless steel B5 1 s; 0.5; 2 and 189 ED 16 h 61-64 Austenitic stainless steel B6 1 s; 0.5; 2 and 189 ED 16 h 65-68 Austenitic stainless steel B7 1 s; 0.5; 2 and 189 ED 16 h 69-72 Austenitic stainless steel B8 1 s; 0.5; 2 and 189 ED 16 h 73-76 Austenitic stainless steel B9 1 s; 0.55; 2 and 189 ED 16 h 77-80 Austenitic stainless steel B10 1 s; 0.5; 2 and 189 ED 16 h

TABLE-US-00004 TABLE 4 Treatment parameters of a ferritic stainless steel with the solutions prepared according to the examples A1 to A10. Grafting Grafting EXAMPLES Metal solution time 81-84 Ferritic stainless steel A1 1 s; 0.5; 2 and 441 16 h 85-88 Ferritic stainless steel A2 1 s; 0.5; 2 and 441 16 h 89-92 Ferritic stainless steel A3 1 s; 0.5; 2 and 441 16 h 93-96 Ferritic stainless steel A4 1 s; 0.5; 2 and 441 16 h 97-100 Ferritic stainless steel A5 1 s; 0.5; 2 and 441 16 h 101-104 Ferritic stainless steel A6 1 s; 0.5; 2 and 441 16 h 105-108 Ferritic stainless steel A7 1 s; 0.5; 2 and 441 16 h 109-112 Ferritic stainless steel A8 1 s; 0.5; 2 and 441 16 h 113-116 Ferritic stainless steel A9 1 s; 0.55; 2 and 441 16 h 117-120 Ferritic stainless steel A10 1 s; 0.5; 2 and 441 16 h

TABLE-US-00005 TABLE 5 Treatment parameters of a ferritic stainless steel with the solutions prepared according to the examples B1 to B10. Grafting Grafting EXAMPLES Metal solution time 121-124 Ferritic stainless steel B1 1 s; 0.5; 2 and 441 16 h 125-128 Ferritic stainless steel B2 1 s; 0.5; 2 and 441 16 h 129-132 Ferritic stainless steel B3 1 s; 0.5; 2 and 441 16 h 133-136 Ferritic stainless steel B4 1 s; 0.5; 2 and 441 16 h 137-140 Ferritic stainless steel B5 1 s; 0.5; 2 and 441 16 h 141-144 Ferritic stainless steel B6 1 s; 0.5; 2 and 441 16 h 145-148 Ferritic stainless steel B7 1 s; 0.5; 2 and 441 16 h 149-152 Ferritic stainless steel B8 1 s; 0.5; 2 and 441 16 h 153-156 Ferritic stainless steel B9 1 s; 0.55; 2 and 441 16 h 157-160 Ferritic stainless steel B10 1 s; 0.5; 2 and 441 16 h

[0152] A. Surface Tension

[0153] In 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 B5 (with rinsing) for the (ferritic and austenitic) stainless steel substrates and with the solution A3 (with rinsing) for the aluminum and copper substrates.

[0154] 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 .sub.1.sup.P and dispersive .sub.1.sup.D components are known and disclosed in the table 6.

TABLE-US-00006 TABLE 6 Surface energies of the considered liquids. Details of the polar and dispersive components. .sub.LmJ/m.sup.2 .sub.L.sup.dmJ/m.sup.2 .sub.L.sup.pmJ/m.sup.2 Water 72.8 21.8 51 Ethylene glycol 48 29 19 Diiodomethane 50.8 50.8 0

[0155] Indeed, 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:

.sub.SV=.sub.SL+.sub.LV cos

[0156] 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.

TABLE-US-00007 TABLE 7 Effect of the treatment on the surface tension of the metal surfaces Contact angle Surface tension Metal [] [mJ/m.sup.2] Ferritic Non-treated 92 24.7 stainless steel Treated (EX. 139) 115 18.5 Austenitic Non-treated 15 66.5 Stainless steel Treated (EX. 59) 100 18.5 Aluminum Non-treated 3 47 treated 115 15 Copper Non-treated 96 38.1 treated 125 21.9

[0157] 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.

[0158] 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. FIG. 4 highlights the evolution of said coverage rate in the case of an austenitic stainless steel according to the immersion times, respectively from 1 s to 16 h. Thus, it is set out the fact that 19% of the surface is already covered by a monomolecular layer after an immersion time of 1 s whereas this rate rises to 41%, 85% and 94% for immersion times of 30 minutes, 2 hours and 16 hours, respectively.

[0159] Moreover, it is remarked that the surface tension, different for each of the non-treated substrates, tends to be aligned for the treated substrates, at a value close to 18.5 mJ/m.sup.2, thereby reflecting the sole contribution of the monomolecular layer in the apparent 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.

[0160] B. Friction Coefficient

[0161] In 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.

[0162] In this device, the floating portions are cylindrical and come into lineal (or pseudo-lineal 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. In the tests reported herein, the cylinders are made of a tool steel Z160CD12. They exert an average normal force (perpendicular to the surface of the treated substrate) of 4000 N and are animated at a defined speed of 10 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).

[0163] 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:

[00001]$=\frac{F_t}{2.Math..Math.F_n}$

where Fn is the applied normal force and Ft is the resulting tangential force.

[0164] The evolution of the friction coefficient according to the number of passes (according to the friction distance) is illustrated by FIG. 5. Both concern a ferritic (4441-1.4509) stainless steel substrate. FIG. 5 offers a performances comparison between (curve B) a commonly used industrial oil (oil RenoForm ETA commercialized by Fuchs Lubrifiants France) and (curve A) a treatment of the substrate by the present invention according to the example 139.

[0165] 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 overtime.

[0166] The results highlight a very clear improvement of the tribological properties by the treatment according to the process of the invention. In 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.

[0167] C. Deep-Drawability

[0168] The deep-drawability is a major factor in the shaping of materials. Indeed, 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, . . . ).

[0169] In 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. In 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.sub.max, 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.sub.max/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.

[0170] The obtained results are illustrated through FIGS. 6 and 7.

[0171] Table 8 synthesizes the results thus obtained for austenitic-type (1.4301-304) and ferritic-type (14509-441) stainless steel substrates in various lubrication configurations. It should be noted that the tools themselves are made of non-coated steel Z160CDV12, 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 FIGS. 6 and 7.

TABLE-US-00008 TABLE 8 Effect of the treatment of the invention on the deep-drawability Metal Lubricant LDR Austenitic Treated 2.17 (A) stainless (example 59) steel Non-treated RenoForm ETA 2.10 (C) 304 (Oil commercialized by (FIG. 7) Fuchs Lubrifiants France) Non-treated Molykote G-Rapid Plus 2.18 (B) (Solid lubricating paste commercialized by Dow Corning) Ferritic Treated 2.09 (A) stainless (example 141) steel Treated 2.15 (B) 441 (example 145) (FIG. 6) Treated 2.18 (C) (example 149) Treated 2.24 (D) (example 153) Treated 2.35 (E) (example 139) Treated 2.04 (F) (example 139 + rinsing and removal of the 2.sup.nd layer) Non-treated RenoForm ETA 2.20 (G) (Oil commercialized by Fuchs Lubrifiants France) Non-treated Molykote G-Rapid Plus 2.28 (H) (Solid lubricating paste commercialized by Dow Corning)

[0172] 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 (FIG. 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 141, 145, 149, 153, 139 and 139 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 (FIG. 6). It should be noted that the lubricant Renoform ETA is a chlorinated mineral oil commonly used 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.

[0173] 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. In 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.

[0174] Complementarily to the determination of the LDR levels, a second stamping test has been performed in order to validate the performance of the product following an equibiaxial expansion type loading path: the Erichsen test. In the context of this test, the matter engulfing during the shaping operation is avoided by the application of a sufficient die-cushion 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 Z160CDV12) during the vertical displacement operated by the latter. Table 9 synthesizes the results obtained on a ferritic (14509-441) stainless steel grade treated according to the example 153 or non-treated but coated with different conventional lubricants. The data relate to a ferritic (14509-441) stainless steel and are taken up in FIG. 8.

TABLE-US-00009 TABLE 9 Effect of the treatment of the invention on the deep-drawability Erichsen Metal Lubricant index Ferritic Treated 10.7 (E) stainless (example 153) steel Non-treated RenoForm ETA 9.6 (D) 441 (Oil commercialized by Fuchs Lubrifiants France) Non-treated Molykote G-Rapid Plus 10.0 (A) (Solid lubricating paste commercialized by Dow Corning) Non-treated Martol EP180 9.7 (C) (Oil commercialized by Total) Non-treated Martol EP5CF 9.6 (B) (Oil commercialized by Total)

[0175] 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 10%.

[0176] In 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.

[0177] FIG. 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 DR136P, which is a chlorinated lubricant commonly used on the present production tool (curve A). Said lubricant further necessitates a costly post-stamping degreasing step. It should be noted that a considerable difference exists between the two series of realized parts illustrated by FIG. 9 as regards the initial lubrication conditions before stamping. Whereas in the case of the use of the conventional lubricant MotulTechCadrex DR136P, 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 10%, allows a direct and evident reduction of the energy necessary for the realization of the parts. It 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. In addition, no post-stamping degreasing is herein necessary, thereby inducing an evident direct gain in productivity.

[0178] D. Corrosion Resistance

[0179] In 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 voltammetry in an acid environment. The experimental conditions of this test are compiled in table 10 below.

TABLE-US-00010 TABLE 10 Experimental conditions of the voltammetric test Three-electrode Working electrode Substrate to be tested electrochemical cell Counter electrode Platinum Reference electrode Saturated calomel Solvent HCl 0.5% airy ambient temperature Slew rate 10 mV/s

[0180] The obtained curves correspond to voltammograms indicating the current density according to the potential applied to the metal immersed in the hydrochloric acid solution.

[0181] 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 139 (curves B) as well as on the non-treated corresponding metals for comparison (curves A).

[0182] The obtained voltammograms are illustrated in FIGS. 10 and 11 respectively.

[0183] It is observed that the behavior of the stainless steel sheets is considerably modified by the treatment according to the invention. In 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.

[0184] Hence, the performed studies also confirm the substantial interest of the process of the invention with regard to protection against corrosion.

[0185] Thus, the process of the invention allows access to metal substrates having advantageous characteristics such as a low friction coefficient, an excellent deep-drawability, and in addition, advantageously, a high corrosion resistance.

[0186] The process is simple and rapid to implement and does not require any specific equipment. It 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.

[0187] 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.

[0188] 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.