Question of the corrosion effect on the reinforcement quality of continuous casting workpiece in period before assembly began pressing with the development of modern metallurgy and construction.
The transition to the production of reinforcement from continuous casting workpiece has not had a negative impact on the level of mechanical properties, provided the required surface quality of products, as well as improve the performance of mills [1]. However, the repeatedly observed deterioration of corrosion resistance, expressed in the presentation of the damage and the formation of corrosion products in the atmospheric conditions in reinforcement rods of continuous casting workpiece.
Reinforcing steel is unstable to acidic conditions. The main factors determining the corrosion resistance of the reinforcement and its resistance to rust, are the chemical composition of steel, production technology and a corrosive environment [2 ... 4]. Hot rolled reinforcement is less prone to corrosion than heat-treated, because accelerated cooling reduces the formation of scale, which is a protective layer against corrosion.
At Yenakiyevo Steel Plant (YSP) using accelerated cooling in the production of reinforcement steel St. 3 with a subsequent self-tempering surface. This mode provides a soft core with a structure of ferrite and pearlite and the hard surface with a structure of martensite tempering due to self-tempering after accelerated cooling, the hardness of the cross section of reinforcement, respectively, varies from HB 250 on the surface to HB180 in the center section. This reinforcement has a good weldability, and σv = 600 N/mm2, σt = 500 N/mm2, δ = 14%, but lower overall corrosion resistance, manifested by the corrosion of period before assembly.
The purpose of this work was to assess the propensity to general corrosion of the reinforcement of the continuous-cast workpiece production YSP in acid solutions.
For research samples were taken valves profile № 10 and № 12 production YSP. Tests were conducted on the electrochemical corrosion of reinforcement in 1, 5, 10% aqueous solution of H2SO4 for one hour with the help of gas-measuring burette.
For the analysis of the data was calculated rates of corrosion. Their analysis showed that the end part of the samples subjected to corrosion attack stronger than the lateral surface.
Kinetics of gas evolution during corrosion attack of acid solutions of H2SO4 on the reinforcing steel is shown in Fig. 1 ... 2, and after computer processing of the results - in Table. 1. For the calculation of dependency used the program TCWIN.
Figure 1. Kinetics of hydrogen release in electrochemical corrosion of the reinforcement at 10% solution H2SO4 (1 - lateral surface of the profile № 10; 2 - lateral surface profile № 12; 3 - end surface profile № 12, 4 - end surface profile № 10)
Figure 2. Kinetics of hydrogen release in electrochemical corrosion of the reinforcement, depending on the percent H2SO4 in aqueous solution (1 - lateral surface profile № 12; 2 - lateral surface of the profile № 10; 3 - end surface profile of № 10; 4 - end surface profile № 12)
Table 1. Analytical dependence of the volume of gas (ml), evolved during the time of the electrochemical corrosion of the samples
We have seen that the dependencies are not linear, and inhibition of corrosion in the short-term exposure to acidic media isn’t observed. The volume of gas evolved during the time of the electrochemical corrosion of the samples, has a power dependence, namely the power law 2 and the 3 order.
1. The surface of the reinforcement, reinforced by rapid cooling with subsequent self-tempering, less prone to acid corrosion than the core, that is bare ends of the rods will corrode first.
2. With increasing concentration of acid solution process of inhibition of corrosion in the short-term exposure does not occur.
3. Production of reinforcement from continuous casting process does not prevent corrosion of finished products in period before assembly.
The author expresses his gratitude to the supervisor, professor, dr. habil. Alimov Valery for methodological assistance in the conduct of work and discussion results.