Brightening and passivation of stainless steel surfaces

Abstract

This invention relates to a composition for the brightening and/or passivating of stainless steel after pickling. The invention is based on the discovery that the presence of organic compounds containing multiple hydroxyl groups with at least 3, but not more than 8 carbon atoms as a further ingredient of passivating and brightening solution significantly increases the desmutting performance of pickled stainless steel surfaces. The compositions of the invention are especially useful for the passivating and brightening of stainless steel grades being alloyed with sulfur. The invention thus further encompasses a passivating and brightening process for pickled stainless steel surfaces wherein the stainless steel is alloyed with at least 0.10 at.-% of sulfur.

Claims

1. A passivating and brightening aqueous composition, comprising water and the following dissolved components: (A) at least one acid which does not contain fluorine; (B) at least one fluorine containing inorganic compound; (C) at least one substance containing a peroxy moiety; and (D) at least one organic polyol compound containing more than two hydroxyl groups with at least 3, but not more than 8 carbon atoms.

2. The composition of claim 1, wherein the at least one acid which does not contain fluorine according to component (A) is selected from the group consisting of sulfuric acid, phosphoric acid, and combinations thereof.

3. The composition according to claim 1 wherein the at least one organic compound according to component (D) is selected from 1,2,3-trihydroxypropane, 1,2,3,4-tetrahydroxybutane, 1,2,3,4,5-pentahydroxypentane, 1,2,3,4,5,6-hexahydroxyhexane.

4. The composition according to claim 1 wherein the at least one organic compound according to component (D) is present in a range from 2 to 15 g/l.

5. The composition according to claim 1 wherein the at least one acid according to component (A) has a pK.sub.a value for a first deprotonation step of less than 3.5.

6. The composition according to claim 1 wherein the at least one acid according to component (A) is present in a range from 0.5 to 100 g/l.

7. The composition according to claim 1 wherein the at least one fluorine containing inorganic compound according to component (B) is selected from free or complex fluorides.

8. The composition according to claim 1 wherein the at least one fluorine containing inorganic compound according to component (B) is present in a range from 4 to 25 g/l, calculated as fluorine content.

9. The composition according claim 1 wherein the at least one substance containing a peroxy moiety according to component (C) is selected from hydrogen peroxide, peroxysulfuric acid, peroxyacetic acid, peroxyboric acid, peroxyphosphoric acid, peroxydiphosphoric acid, and salts thereof.

10. The composition according to claim 1 wherein the at least one substance containing a peroxy moiety according to component (C) is present in a range from 3 to 25 g/l, calculated as hydrogen peroxide content.

11. The composition according to claim 1 further comprising at least one organic compound as component (E), which is different from compound (D) and selected from: (E1) substances constituted of molecules that contain both at least one ether moiety and at least one hydroxyl moiety in each molecule; (E2) substances constituted of molecules that contain in each molecule at least two ether moieties; and/or (E3) substances constituted of molecules that contain in each molecule both at least one ether moiety and one nitrogen atom that is covalently bonded to at least three carbon atoms.

12. The composition according to claim 11 wherein the at least one organic compound (E) is present as component (E1) that is selected from compounds wherein each molecule has a number of carbon atoms that is at least 3 and is not more than 100; and each molecule has a number of hydroxyl groups that is not more than 3; and each molecule has a number of ether moieties that is not more than 50; and at least one oxygen atom in an ether moiety in each molecule is bonded to a terminal monovalent alkyl group that contains at least 2 carbon atoms.

13. The composition according to claim 1 wherein: (A) is present as sulfuric acid in an amount of 0.5 to 100 g/l; (B) is present as a complex fluoride of B, Si, Ti and/or Zr in a range from 4 to 25 g/l, calculated as fluorine content; (C) is present in a range from 3 to 25 g/l, calculated as hydrogen peroxide content; (D) is present as one or more of sorbitol, xylitol, meso-erythritol, glycerol in a range from 2 to 15 g/l; and said composition containing less than 1 g/l of nitrates.

14. The composition according to claim 1, wherein the at least one organic compound according to component (D) is selected from sorbitol, xylitol, meso-erythritol, glycerol and mixtures thereof.

15. The composition according to claim 1 wherein the at least one fluorine containing inorganic compound according to component (B) is selected from complex fluorides of B, Si, and/or Ti.

16. A passivating and brightening aqueous composition for use on stainless steel, comprising water and the following dissolved components: (A) at least one acid which does not contain fluorine, the at least one acid being present in an amount of 10 to 30 g/l; (B) at least one fluorine containing inorganic compound; (C) at least one substance containing a peroxy moiety; and (D) at least one organic polyol compound containing more than two hydroxyl groups with at least 3, but not more than 8 carbon atoms present in an amount sufficient for removal of smut from stainless steel.

17. The passivating and brightening aqueous composition for use on stainless steel of claim 16, further comprising component (E) a stabilizer different from component (D) comprising substances constituted of molecules that each contain 3-100 carbon atoms, 1-50 ether moieties, and 1-3 hydroxyl moieties; wherein at least one oxygen atom in one of the ether moieties in each molecule is bonded to a terminal monovalent alkyl group that contains at least 2 carbon atoms.

18. A process for the brightening and passivating of austenitic, ferritic or martensitic stainless steel grades wherein the stainless steel grade is subsequently after pickling with or without intermediate rinsing step brought into contact with a brightening and passivating composition according to claim 1 for a time and at a temperature sufficient for desmutting the pickled stainless steel grade; wherein temperature is in a range from 15 to 40 C.

Description

EXAMPLES

(1) Wire samples of hot rolled austenitic stainless steel (EN 1.4029; 0.15-0.25 at.-% of S) and martensitic stainless steel (EN 1.4035; 0.15-0.35 at.-% of S) were pretreated with reduction molten salts and then pickled for 26 minutes at 50 C. in hydrochloric acid (170 g/l HCl) and subsequently for 5 minutes at 40 C. in a Cleanox solution (commercialized pickling process of the applicant according to EP-B-582 121).

(2) After the rinsing step the wire samples were completely dark due to the presence of black smut on the surface. The wire samples were then immediately brightened and passivated for 5 minutes at 25 C. in different solutions according to Table 1.

(3) After this step the samples were rinsed with low pressure water spray for 1 minute and dried.

(4) The dried wire samples were evaluated visually to compare surface brightness with an arbitrary scale ranging from 1 to 5, where: 1=very bad (as before brightening) 2=bad (surface partially bleacheddarkening of white paper when rubbed on the surface) 3=acceptable (quite bleached surface but still some residuals after white paper rubbing) 4=good (negligible black residuals rubbing paper on the surface, but poor homogeneity) 5=very good (completely bleached and homogeneous surfaceno black residuals rubbing the surface with paper).

(5) TABLE-US-00001 TABLE 1 Results of the brightening of wire samples of different stainless steel grades Con- Brightness centration EN EN Example Composition g/l 1.4029 1.4035 C1 HNO.sub.3 630 2 2 C2 H.sub.2SO.sub.4/H.sub.2O.sub.2/HF 15/17/2 1 1 C3 H.sub.2SO.sub.4/H.sub.2O.sub.2/HF 15/17/10 1 1 C4 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6 15/17/7 3 3 C5 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6 15/17/14 3 3 E1 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6/ 15/17/14/3.5 5 5 glycerol E2 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6/ 15/17/14/6.9 5 5 sorbitol E3 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6/ 5/17/14/2/2 5 5 glycerol/sorbitol E4 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6/ 15/17/14/5.8 5 5 xylitol

(6) Wire samples of a less noble austenitic grade, such as the sulphur containing alloy EN 1.4305 were pickled for 40 minutes at 40 C. in a Cleanox solution (commercialized pickling process of the applicant according to EP-B-582 121).

(7) After the rinsing step the wire samples were completely dark due to the presence of black smut on the surface. The samples were then immediately passivated and brightened for 5 minutes at 25 C. in different solutions according to Table 2.

(8) After this step the wire samples were rinsed with low pressure water spray for 1 minute and dried. The same arbitrary scale for the assessment of the surface brightness as described above was applied to the dried wire samples of the alloy EN 1.4305.

(9) The effect of the compositions of this invention on the desmutting performance on EN 14305 stainless steel is less pronounced compared to the stainless steel grades of Table. 1. Nevertheless compositions of the invention prove to perform slightly better.

(10) TABLE-US-00002 TABLE 2 Results of the brightening of wire samples of EN 1.4305 austenitic stainless steel with a sulfur content of 0.15 at.-% Con- centration Example Composition g/l Brightness C6 HNO.sub.3 150 4 C7 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6 15/17/7 4 C8 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6 15/17/14 4 E5 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6/ 15/17/14/3.5 4 meso-erythritol E6 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6/ 15/17/14/3.5 5 xylitol E7 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6/ 15/17/14/3.5 5 sorbitol E8 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6/ 15/17/14/3.5 5 sobitol/glycerol E9 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6/ 15/17/14/3.5 5 glycerol

(11) The effect of the concentration of different glycols (polyol according to Description of the invention) was investigated on hot rolled EN 1.4029 following the same sequence of treatment as described for the examples of Table 1 and applying the same arbitrary scale for the evaluation of surface brightness.

(12) TABLE-US-00003 TABLE 3 Effect of the concentration of different polyols on the brightening of hot rolled austenitic stainless steel wire samples (EN 1.4029) with a sulfur content of 0.15-0.25 at.-% Con- centration Example Composition g/l Brightness E10 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6/ 15/17/14/3 5 glycerol E11 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6/ 15/17/14/6 5 glycerol E12 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6/ 15/17/14/9 5 glycerol E13 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6/ 15/17/14/3 5 sorbitol E14 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6/ 15/17/14/6 5 sorbitol E15 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6/ 15/17/14/9 5 sorbitol E16 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6/ 15/17/14/5 5 xylitol E17 H.sub.2SO.sub.4/H.sub.2O2/H.sub.2SiF.sub.6/ 15/17/14/9 5 xylitol

(13) The brightening result conferred by compositions of this invention for the most preferred compounds (D) is very stable in a concentration range from 3-9 g/l (Table 3).

(14) The effect of the concentration of different oxidizing agents (according to Description of the invention) was investigated on wire samples of hot rolled martensitic stainless steel EN 1.4035 following the same sequence of treatment as described for the examples of Table 1 and applying the same arbitrary scale for the evaluation of surface brightness.

(15) TABLE-US-00004 TABLE 4 Effect of different oxidizing agents on the brightening of hot rolled martensitic stainless steel wire samples (EN 1.4035) with a sulfur content of 0.15-0.35 at.-% Con- centration Example Composition g/l Brightness C9 H.sub.2SiF.sub.6/HNO.sub.3 14/50 1 E18 H.sub.2SiF.sub.6/HNO.sub.3/glycerol 14/50/3.5 4 E19 H.sub.2SO.sub.4H.sub.2O.sub.2/H.sub.2SiF.sub.6/HNO.sub.3/ 15/17/14/50/3.5 4 glycerol E20 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6/glycerol 15/3/14/3.5 4 E21 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6/glycerol 15/6/14/3.5 4 E22 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6/glycerol 15/9/14/3.5 5 E23 H.sub.2SO.sub.4/H.sub.2O.sub.2/H.sub.2SiF.sub.6/glycerol 15/17/14/3.5 5

(16) The use of nitric acid as a strong acid according to component (A) of a composition of this invention yields slightly poorer results with respect to the brightness of the treated stainless steel surfaces (E18, E19). Similarly, the brightening effect in compositions of this invention where the amount of compounds with a peroxy moiety according to component (C) does vary in a range from 3-17 g/l is considerably stable in this specific range (E20-E23).