DE505606T1

DE505606T1 - Process for pickling and passivating stainless steel without using nitric acid.

Info

Publication number: DE505606T1
Application number: DE91113628T
Authority: DE
Inventors: Marco Bianchi
Original assignee: ITB Srl
Current assignee: ITB Srl
Priority date: 1991-03-29
Filing date: 1991-08-14
Publication date: 1994-02-03
Also published as: ES2082063T5; ES2082063T3; DE69114265T2; FI920580A7; EP0505606B2; FI101234B; DE69114265T3; JPH04304391A; EP0505606B1; ATE129753T1; GR3018681T3; DK0505606T3; ITMI910879A0; ITMI910879A1; DE69114265D1; EP0505606A1; JP2655770B2; IT1245594B; FI920580A0

Abstract

A process for pickling and passivating stainless steel using a bath of the following initial composition: H2SO4 at least 150 g/l Fe<3><+> at least 15 g/l HF at least 40 g/l stabilized H2O2 1-20 g/l non-ionic surfactants and acid attack inhibitors 1 g/l, into which an air flow and an H2O2 quantity of between 0.3 and 1 g/l per hour, controlled to maintain the bath Redox potential at >/= 350 mV, are fed in continuously.

Claims

05U5 EP No. 91 113 628.1 60 497 u2/jr Patent claims

1. Process for pickling and passivating stainless steel, consisting in bringing the material to be treated into contact with a bath maintained at a temperature of between 30 and 70 ^° C and preferably between 45 and 55°C and having the following initial composition:

a) H2SO4 at least 150 g/l

b) Fe ³⁺ at least 15 g/l

c) HF at least 4 0 g/l

d) H2O2 (comprehensively known stabilizers) 1-20 and preferably 2 to 5 g/l

(e) additives of the non-ionic surfactant type (emulsifiers, wetting agents, brightening agents) and of the acid attack inhibitor type: approximately 1 g/l in total;

where the following are continuously fed into the bath:

an air flow of at least 3 m ³ /h per m ³ bath, using a suitable distribution device to diffuse the flow into the liquid mass,-

a quantity of stabilized H2O2 of between 0.3 and g/l per hour, controlled on the basis of the redox potential of the bath, which must be maintained at >. 3 50 mV;

and optionally sufficient amounts of components (a), (c) and (e) to maintain their concentration in the bath at optimal levels and the bath pH at less than 1 and preferably between 0 and 0.5.

2. Method according to claim 1,

characterized in that the Fe ^{3 +} ions are introduced into the initial bath in the form of ferric sulphate.

3. Method according to claim 1,

characterized in that H ₂ O ₂ is used which is stabilized with the stabilizer Interox.

4. Method according to claim 1,

characterized in that

a bath of the initial composition is used:

172 g _/ l _H2SO4

48 g/l HF

15 g/l Fe ^{3 +}

5 g/l H ₂ O ₂

1 g/l of non-ionic surfactant and

Acid attack inhibitor additives

2 g/l H ₂ O ₂ - Stabilizer in the form of Interox S

5. Method according to claim 1,

carried out in combination with the previous partial removal of oxides by a known method.