WO1998048080A1

WO1998048080A1 - Method of taking off iron oxides and hydroxides from steel product surfaces

Info

Publication number: WO1998048080A1
Application number: PCT/RU1998/000038
Authority: WO
Inventors: Vadim Alexandrovich Usachev; Nina Eduardovna Kononenko; Jury Gennadievich Pakin; Viktor Alexeevich Odintsov; Alexandr Nikolaevich Ponkin; Stanislav Alexandrovich Maljutin; Jury Dmitrievich Panaev
Original assignee: Zakrytoe Aktsionernoe Obschestvo Tsentr Novykh Te Khnology 'optron'
Priority date: 1997-04-18
Filing date: 1998-02-17
Publication date: 1998-10-29
Also published as: RU2119553C1

Abstract

Method of taking off iron oxides and hydroxides from steel product surfaces, comprising the steps of treating the surfaces by the mixture of mono (alkyl, dioxyalkyl) ethers of carboxylic acids and monoalkyl ethers of sulphuric acid, in which maleic and sulphomaleic acids are used as carboxylic acids, and mono (alkyl, dioxyalkyl) ethers of maleic and sulphomaleic acids, monoalkyl ethers of sulphuric acid are included additionally with the following component ratio, mass %: Maleic acid 0.1 to 4; Sulphomaleic acid 0.3 to 10; Mono (alkyl, dioxyalkyl) ethers of sulphomaleic acid with the number of carbon atoms in the alkylic radical - one, three, four, dioxyalkylic - three 1.0 to 20; Mono (alkyl, dioxyalkyl) ethers of maleic acid with the number of carbon atoms in the alkylic radical - one, three, four, dioxyalkylic - three 0.1 to 2.5; Monoalkyl ethers of sulphuric acid with the number of carbon atoms in the alkylic radical - one, three, four 0.1 to 5.5; Water - the rest; the treatment being executed from 2 to 11 minutes at 50 to 60 °C.

Description

Method of taking off iron oxides and hydroxides from steel product surfaces

This invention relates to the art of chemical treatment of metals and can be used when steel product surfaces are chemically treated for taking off iron oxides (scale) and iron hydroxides (rust) of a different origin as well as for preparing the steel product surfaces to be undergone further technological operations of galvanizing.

It has previously been proposed to take off scale and rust from surfaces of steel products (rolling, forging, stamping), comprising the steps of treating the surfaces in the solution of inorganic concentrated sulphuric (20 to 25%), hydrochloric (10 to 20%) acids, and, in some cases, in their mixtures (see Patent of France M> 2683832, Cl. C23F 1/28).

Disadvantages of this method are as follows:

1) dissolution of the principal metal that can cause overpickling of the surfaces, nonuniform metal take-off, increased microroughness;

2) deterioration of mechanical properties of the metal due to sorption of evolved hydrogen by the metal, resulting in increased brittleness, decreased viscosity and deterioration of elastic characteristics of the product materials;

3) enviroment pollution by toxic vapours of chlorous hydrogen evoluted in the course of the treatment and sulphate "fogs" formed in the working zone air, that requires additional expenditures to provide a system for neutralizating fumes.

It has also been proposed to take off scale and rust from steel product surfaces, comprising the steps of the surface treatment by solutions of concentrated sulphuric, hydrochloric acids containing special additives (so-called corrosion inhibitors) (see Patent of Japan N° 5-24996, Cl. C23G1/06).

This method allows one to protect the treated product surfaces from overpickling due to the inhibitor action, viz., adsorption of inhibitor particles on the metal surface. However, it does not eliminate disadvantages of the prior method in respect to the enviroment pollution because of the application of the same inorganic acids. In addition, the absorption nature of the inhibiting action of additives affects the metal surface state that results in decreased cohesion strength of plating coatings (for example, nickel coatings), further deposed on the treated steel surface.

Additionally, it has been proposed to take off hard thin scale of iron oxides formed in vapour-producing installations, which are made of austenitic stainless steel and contain parts made of low-alloy steel, containing molybdenum, comprising the steps of treating surfaces by the composition containing at least more than one kind of such organic acids as citric, glycolic, gluconic, malic as well as thioglycolic acid with an addition of the mixture containing at least more than one kind of such compounds as hydrazine, L-ascorbic acid, erithorbic acid, and inhibitor of acidic corrosion (see Patent of Japan M> 5-14027, Cl. C23G1/08). Acidic mixed aqueous solution is introduced into the washed equipment. When the pressure is normal or excessive, and the temperature is 100° C, the scale is taken off as a result of soluting. To accomplish the effective washing, it is necessary to have 0.5 to 2% of thioglycolic acid, the part of which is supposed to affect chelately on iron ions that promotes the soluting of the scale. The concentration of the organic acids is 2 to 3%. The affect of free carboxylic groups of acids is likely to promote the soluting of the scale. The organic amine in quantity of 0.5% is used as an acidic corrosion inhibitor. However, the partial decomposition of thioglycolic acid causes the formation of hydrogen sulphide that reacts with molybdenum being contained in the parts of the washed systems made of low-alloy steels. As a result, the insoluble molybdenum sulphide is precipitated on the washed surface. The evolution of hydrogen sulphide also causes the granular corrosion of austenitic stainless steel. The problem of the thioglycolic acid decomposition is solved by the reducing of ions Fe (+III) responsible for oxidation and decomposition of thioglycolic acid up to ions (Fe+II) , when reducing agents (hydrazine, L-ascorbic acid, erithorbic acid) in quantity of 0.1 to 0.3% are introduced into the system. The above method is accepted as a prior art method.

However, this prototype has the following disadvantages:

1. The limited application since it is applied only to take off a hard thin scale from austenitic stainless steel and low-alloy steel containing molybdenum. Nevertheless, the problem of taking off a hard scale of iron oxide is not only vital when boilers and vaporizers are used. The take-off of iron oxides and hydroxides from ferrous metal surfaces is a vital operation of preparing the surfaces for deposition. In addition, in the processes of rolling at high temperatures and heat treatment, a thick nonuniform (by composition) oxide film (scale) is formed. Hence, the vital problem of taking off oxide film relates not only to austenitic stainless steel and low-alloy steel containing molybdenum, but to carbon and other alloy steels.

2. The decomposition of one of the basic components (thioglycolic acid) in the mixture used. Hence, the problem arises how to introduce additionally in the system reducing agents preventing the destruction process of thioglycolic acid, that causes extra expenditures.

3. High temperatures (100°C) of the treatment. 4. The fact, that the inhibitor of acidic corrosion is introduced into the system, indicates that the applied acidic mixed inhibitor-free solution does not solve the problem of protecting steel surfaces from overpickling.

It is an object of the present invention to eliminate the above disadvantages and to provide an enlargement of nomenclature (range of products) of the treated steels as well as to increase quality of the treated surfaces (reduction in metal losses, elimination of overpickling, improvement of the surface state with respect to preparing for further galvanizing, increased resistivity of the cleaned surfaces to oxidation, i.e., the increased storage time, increased possibilities of taking off scale and rust of a different origin), as well as increased workability of the method, since the steel product surfaces are chemically treated at lower temperatures.

The object of the invention is accomplished by the fact that in the well-known method of taking off iron oxides from steel product surfaces, comprising the steps of treating the surfaces by the composition containing at least more than one kind of such organic carboxylic acids as citric, glycolic, gluconic, malic as well as thioglycolic acid with an addition of the mixture containing at least more than one kind of such compounds as hydrazine, carboxylic acids: L-ascorbic acid, erithorbic acid, and inhibitor of the acidic corrosion, the steel product surfaces are treated by means of the mixture in which maleic and sulphomaleic acids are used as organic carboxylic acids, and mono (alkyl, dioxyalkyl) ethers of maleic and sulphomaleic acids, monoalkyl ethers of sulphuric acid are included additionally with the following component ratio, mass %: Maleic acid 0.1 to 4

Sulphomaleic acid 0.3 to 10

Mono (alkyl, dioxyalkyl) ethers 1.0 to 20 of sulphomaleic acid with the number of carbon atoms in the alkylic radical - one, three, four, dioxyalkylic - three

Mono (alkyl, dioxyalkyl) ethers 0.1 to 2.5 of maleic acid with the number of carbon atoms in the alkylic radical - one, three, four, dioxyalkylic - three

Monoalkyl ethers of sulphuric acid 0.1 to 5.5 with the number of carbon atoms in the alkylic radical - one, three, four

Water the rest, the treatment being executed from 2 to 11 minutes at 50 to 60° C. The dominant features indicated in the claims have not been discovered in other well-known proposed methods of taking off iron oxides and hydroxides from the steel surfaces.

In the widely-used carbon and alloy structural qualitative steels (08; 30; 35), spring steels (60S2, 65G), and alloy steels ( 15Kh; 12KhN3A), an nonuniform (by composition and thickness) film of iron oxides and hydroxides is formed. Depending on the quantity of the formed iron oxides and hydroxides and their origin, the concentration and component ratio can be determined in the proposed solution.

The method is performed as follows:

The mixture is poured into a bath, in which the constant temperature of 50 to 60 °C is maintainted. With the help of suspension the steel products are immersed into the bath and kept in the mixture from 2 to 11 minutes (Table 1). The process duration is determined visually by viewing the state of descaling and derusting. After the treatment the surface quality is estimated with the help of stereoscopic microscope MBS-200. By having kept the steel products in the bath for a fixed period, they are removed from the bath, washed by the running warm water and dried in the air.

In the course of the laboratory tests aimed at developing normal operating modes of the proposed method, the authors have discovered the following behavior. If the components are applied within the limits of the above ranges, scale and rust are completely dissoluted for 2 to 1 1 minutes. The influence of temperature on the rate of descaling and derusting is studied. Thus, when temperatures are lower than 50 °C, the process of taking off iron oxides and hydroxides follows 5 times slower, and when temperatures are more than 60 °C, it follows 1.5 to 2 times faster. However, at 65 to 70 °C the water start evaporating that causes the systems disbalance. Hence, the optimal temperature for performing the proposed method ranges from 50 to 60°C. When the total concentration of the carboxylic acids in the mixture is 1.1 to 1.3 mass %, the ferrous metal surface is dark after descaling and derusting that is likely to be attributed to some oxidation of the cleaned surface. It is not desirable to increase the total concentration of carboxylic acids over 10 mass %, since after the treatment the ferrous metal surface is of dark colour. To attain qualitative light surfaces suitable for galvanizing, it is sufficient to have a total concentration of carboxylic acids of about 2 to 8 mass %. In this case, the scale and rust are taken off for 3.5 to 5 minutes. If mono (alkyl, dioxyalkyl) ethers of sulphomaleic acid are added into the mixture, then the process is stimulated, and the quality of surface is improved. If the proposed mixture solution contains mono (alkyl, dioxyalkyl) ethers of maleic acid and monoalkyl ethers of sulphuric acid, the action of other system components is increased. It should be noted, that the use of all the components with concentrations over the upper limits of the above range causes oxidation of the descaled and derusted ferrous metal surfaces. The use of all the components of the system with concentrations below the lower limits causes both oxidation of the cleaned steel surface and inhibition of descaling and derusting. In the present invention, scale and rust are effectively and quickly dissolved at comparatively low temperatures, when all the components of the solution are jointly available.

One can suppose that the iron oxides and hydroxides are effectively dissolved due to the following: strong chelate effect on iron ions by sulphomaleic acid, mobile hydrogen atoms in hydroxylic groups of alcohol, formed in the process of hydrolysis of monodioxyalkyl ether of sulphomaleic and maleic acids at 50 to 60°C, π-electrons of multiple double bonds of maleic, sulphomaleic acids and their derivatives as well as the participation of carboxylic groups of maleic, sulphomaleic acids and their ethers.

The above factors are likely to promote a ten-fold increase in the capacity of the proposed method compared to the commonly-used solutions of inorganic acids (sulphuric, hydrochloric acids and their mixtures ) for descaling and derusting the ferrous metal surfaces.

Along with the effective dissolution of iron oxides and hydroxides, the realization of the proposed method provides the protection of the cleaned metal surface from overpickling that allows one not introduce additionally in the system inhibitor of the acidic corrosion.

In addition, the cleaned by the proposed method steel surfaces are oxidation-resistant that allows one to increase their time storage up to one month and galvanize them without preliminary surface activating (pickling).

The proposed method has the following advantages:

1. Iron oxides and hydroxides of a different origin are taken off from steel surfaces of wide assortment products quickly, effectively, at low temperatures, and at low concentrations of active components of the proposed solution.

2. The provision of protection of the cleaned metal surface from overpickling allows one to reduce metal losses and to expel from the system an inhibitor of acidic corrosion.

3. The increase in resistivity of the cleaned steel surfaces to oxidation allows one to increase their time storage up to one month and galvanize them without preliminary surface activating (pickling).

4. The invention provides a high operating capacity (which is ten times higher than that of the prior solutions of toxic inorganic acids used for descaling and derusting of steel surfaces). 5. The solution is to be in use in the proposed method consists of organic components, so it is possible to utilize wastes by burning. It gives a large economy over the wet treatment method for the solution under utilization and provides the decreased environmental pollution.

6. The proposed invention can be used both for stationary and jetted treatment methods of taking off scale and rust of a different origin from ferrous metal surfaces.

The invention will now be explained in greater detail with reference to embodiments thereof which are represented in the below Table 1.

Table 1

Claims

What we claim is:

The method of taking off iron oxides and hydroxides of a different origin from steel product surfaces, comprising the steps of treating the product surfaces by a mixture of carboxylic acids, mono (alkyl, dioxyalkyl) ethers of the carboxylic acids and monoalkyl ethers of sulphuric acid, characterizing in that maleic and sulphomaleic acids are used as carboxylic acids, and mono (alkyl, dioxyalkyl) ethers of the maleic and sulphomaleic acids and monoalkyl ethers of sulphuric acid are additionally included into the mixture with the following component ratio, mass %: Maleic acid 0.1 to 4

Sulphomaleic acid 0.3 to 10

Mono (alkyl, dioxyalkyl) ethers of 1.0 to 20 sulphomaleic acid with the number of carbon atoms in the alkylic radical - one, three, four, dioxyalkylic - three

Mono (alkyl, dioxyalkyl) ethers of 0.1 to 2.5 maleic acid with the number of carbon atoms in the alkylic radical - one, three, four, dioxyalkylic - three

Water the rest, the treatment being executed from 2 to 1 1 minutes at 50 to 60 ° C.