In general, the surface quality of a hot-rolled finished steel product should be checked, but scale is generated on the surface of the hot-rolled steel product, so that surface defects are accurately determined; the scale must first be removed. The conventional method of metallurgical plants is to remove the oxide skin on the surface of carbon steel and alloy steel by a chemical pickling process.
The principle of the existing chemical pickling process is as follows: the acid reacts with the FeO to partially dissolve the scale, and at the same time the acid reacts with the iron matrix, whereby the mechanical action of the hydrogen gas causes the Fe-containing iron, which is still undissolved but rather loose2O3And Fe3O4The scale of (2) is peeled off. In either pickling process, dissolution and exfoliation are effective, but the extent varies greatly depending on the type of steel, the concentration of the acid solution and the temperature. (chemistry of acid pickling of iron and steel materials, early written by Tokyo, P8, 9, 10, science publishers, 1993), (production of wire by high-speed rolling mill, written by group, P391-410, publication of metallurgy industries, 1995).
For alloy steel hot rolled bar and wire, especially Cr-Ni stainless steel, the main component of oxide skin is CrO3And NiO, which is selected from chromium spinel (FeO. Cr)2O3) And nickel spinel (NiO. Cr)2O3) The oxide scale has the advantages of compact and tough structure, firm combination with a matrix, difficult removal by common acid cleaning, 50 minutes forremoval even if sulfuric acid, hydrochloric acid and nitric acid are adopted, and more than 20 minutes for removal of the oxide scale when a strong corrosive hydrofluoric acid and nitric acid mixed acid solution is adopted. And the pickling solution needs to be heated. For this reason, the above-mentioned pickling methods for removing scale all have the following common disadvantages: firstly, the required pickling time is longer, the productivity is low, the cost is high, secondly, the pickling solution needs to be heated, the environmental pollution is serious, and thirdly, the loss of the pickled steel is large.
The invention aims to provide a method for removing oxide skin on the surface of alloy steel, which has the advantages of obvious effect on removing oxide skin on the surface of alloy steel, high removal speed and no pollution.
Aiming at the purposes, the invention adopts the following technical scheme:
the method for removing the oxide skin on the surface of the alloy steel is carried out on a conventional electrolysis device, and the device comprises an electrolysis bath, a direct current power supply, a current reversing switch, a sample clamp and related circuits.
The method for removing the oxide skin on the surface of the alloy steel can adopt three methods, namely an anode electrolytic pickling method, a cathode electrolytic pickling method and a cathode-anode alternate electrolytic pickling method. The three methods are now described as follows:
1. an anodic electrolytic pickling method is adopted, and the process steps are as follows:
(1) placing steel to be treated in an electrolytic bath filled with electrolyte;
(2) electrolyzing by taking steel to be treated as an anode, a conventional lead plate as a cathode and a direct-current power supply as an electrolysis power supply;
(3) the technological parameters during electrolysis are as follows:
current density of 80-300A/dm2
The temperature of the electrolyte is 20-50 DEG C
The electrolysis time is 1-5min
(4) The electrolyte consists of a sulfuric acid aqueous solution and a surfactant, and the ratio (weight percent) of the electrolyte is as follows: 99.996-99.999% of sulfuric acid aqueous solution and 0.001-0.004% of surfactant;
the proportion (weight percent) of the sulfuric acid aqueous solution is as follows: 15-45% of sulfuric acid and 55-85% of water;
the surfactant consists of sodium dodecyl benzene sulfonate, alkylphenol polyoxyethylene and water, and the proportion (weight percent) is as follows: 60-77% of sodium dodecyl benzene sulfonate, 5-20% of alkylphenol polyoxyethylene and the balance of water;
(5) after electrolytic pickling, the steel is taken out, washed clean by water and then dried, and the pickling process is completed.
The surfactant in the electrolyte can accelerate the electrolysis process and improve the electrolysis speed, and is a good acid mist inhibitor which can inhibit acid mist generated when steel and the electrolyte react.
The anode electrolytic pickling method is suitable for high-alloy steel such as Cr-Ni stainless steel and the like. The steel immersed in the electrolyte is used as an anode, the surface of the steel has low oxide scale conductivity but has a plurality of small holesThe flow can be directed to the base metal surface through small holesValence oxide Cr2O3Is oxidized into high-valence CrO3And easily dissolved in acid to become loose, and a large amount of oxygen generated at the anode rapidly peels off the scale. But at high current densities the base metal surface is rapidly in a passive state.
Anode electrode reaction formula:
2. adopts a cathode electrolytic pickling method, and comprises the following process steps:
(1) placing steel to be treated in an electrolytic bath filled with electrolyte;
(2) electrolyzing by taking steel to be treated as a cathode, a conventional lead plate as an anode and a direct-current power supply as an electrolysis power supply;
(3) the technological parameters during electrolysis are as follows:
current density of 80-300A/dm2
The temperature of the electrolyte is 20-50 DEG C
Electrolyzing for 1-5 min;
(4) the electrolyte consists of a sulfuric acid aqueous solution and a surfactant, and the ratio (weight percent) of the electrolyte is as follows: 99.996-99.999% of sulfuric acid aqueous solution and 0.001-0.004% of surfactant;
the proportion (weight percent) of the sulfuric acid aqueous solution is as follows: 15-45% of sulfuric acid and 55-85% of water;
the surfactant consists of sodium dodecyl benzene sulfonate, alkylphenol polyoxyethylene and water, and the proportion (weight percent) is as follows: 60-77% of sodium dodecyl benzene sulfonate, 5-20% of alkylphenol polyoxyethylene and the balance of water;
(5) after electrolytic pickling, the steel is taken out, washed clean by water and then dried, and the pickling process is completed.
The cathode electrolytic pickling method is suitable for carbon steel such as carbon steel, carbon spring steel and the like. Using a sample immersed in the electrolyte as a cathode, and leading current to the surface of the base metal through oxide skin pores to cause hydrogen ion discharge on the surface of the cathode so as to ensure that insoluble high-valence oxygen is generatedCompound Fe2O3And Fe3O4Reducing the iron into low-price FeO and pure iron, generating volume change to cause loose oxide skin and simultaneously generating a cathodeA large amount of molecular hydrogen generated on the surface permeates into the oxidation skin to be rapidly peeled off, and the reaction formula is as follows:
3. the anode and cathode alternative electrolytic pickling method comprises the following process steps:
(1) placing steel to be treated in an electrolytic bath filled with electrolyte;
(2) firstly, taking steel to be treated as a cathode, a conventional lead plate as an anode and a direct-current power supply as an electrolysis power supply to carry out cathodic electrolysis pickling, and switching the current direction after electrolysis for 1-3 minutes, namely taking the steel to be treated as the anode and the conventional lead plate as the cathode to carry out anodic electrolysis pickling; the cathodic electrolytic pickling method and the anodic electrolytic pickling method are alternated once.
(3) The technological parameters during electrolysis are as follows:
current density of 80-300A/dm2
The temperature of the electrolyte is 20-50 DEG C
Electrolyzing for 1-5 min;
(4) the electrolyte consists of a sulfuric acid aqueous solution and a surfactant, and the ratio (weight percent) of the electrolyte is as follows: 99.996-99.999% of sulfuric acid aqueous solution and 0.001-0.004% of surfactant;
the proportion (weight percent) of the sulfuric acid aqueous solution is as follows: 15-45% of sulfuric acid and 55-85% of water;
the surfactant consists of sodium dodecyl benzene sulfonate, alkylphenol polyoxyethylene and water, and the proportion (weight percent) is as follows: 60-77% of sodium dodecyl benzene sulfonate, 5-20% of alkylphenol polyoxyethylene and the balance of water;
(5) and taking out the steel after electrolytic pickling, washing the steel clean by using clear water, and drying to finish the pickling process.
The cathode-anode alternative electrolytic pickling method is suitable for removing the oxide skin of the medium-low alloy steel containing the alloy elements such as Si, Cr, Mn, Mo and the like, and integrates the effects of the cathode electrolytic pickling method and the anode electrolytic pickling method. The sample is firstly treated with cathodic electrolytic pickling, the current direction is switched and then the sample is treated with anodic electrolytic pickling, and the surface of the sample is treated with O2And H2Accelerate the scaling off of the oxide scale.
Compared with the prior art, the invention has the following advantages:
firstly, the effect of removing the oxide skin on the surface of the alloy steel is obvious.
Secondly, the oxide skin is removed quickly, and the steel can be cleaned only in 1-5min, so that the requirement of on-line quick surface inspection of the steel is met, the labor productivity is improved, and the cost is reduced.
Thirdly, the metal matrix is dissolved in a very small amount in the electrolytic process, and the loss is low. Can objectively and truly reflect the surface quality condition of the steel.
Fourthly, the equipment is reasonable in design, small in size, convenient and safe to operate and easy to master.
Fifthly, the electrolyte has good conductivity, wide applicability and no environmental pollution.
Sixthly, the electrolyte consumption is low, the service life is long, and the cost is low.