Corrosion of carbon steel in filling material in an urban environment

The corrosion process of carbon steel in soil has been investigated, in particular the influence of the soil of an urban environment. A field test was carried out with test panels buried in trenches. Localized and uniform corrosion rates were evaluated after 1 and 3 years. Soil samples from points adjacent to the panels were analyzed with respect to a number of physical and chemical parameters believed to influence the corrosion process. Corrosion products were analyzed and identified. The study shows that the localized corrosion rate of soil buried constructions may be remarkably high in a filling material in comparison to other soils. The heterogeneity of the soil seems to have a greater influence on the localized corrosion rate than the chemical composition of the soil. However, the uniform corrosion rate was comparatively low in the heterogeneous filling material. Both the high alkalinity in the soil water and the groundwater, and the high total hardness of the soil water in the filling material seem to reduce the uniform corrosion rate. Corrosion rate determinations with commercial probes is also discussed. The linear polarization resistance (LPR), the electric resistance (ER) and the corrosion potential measurement techniques are compared. All probes showed a seasonal variation in corrosion rate. The measurements with commercial probes were associated with some problems, mostly a result of poor contact between the probes and the soil.     

Influence of interface-related parameters on some heat stable salts in the corrosion studies of carbon steel for post-combustion CO2 capture

The effect of flow and temperature on the corrosion behavior of carbon steel in an aqueous methyldiethanolamine solution containing different heat stable salts, such as sodium sulfate, sodium sulfite and sodium thiosulfate, has been studied. The introduction of flow and increase in temperature generally caused an increase in the corrosion rate of carbon steel but the presence of the heat stable salts affected the corrosion behavior to different extents. Sulfate increased the corrosivity of the aqueous methyldiethanolamine solution, thus showed accelerated corrosion behavior in the presence of flow and with increase in temperature when compared with the solution without heat stable salts. The presence of sulfite reduced the corrosivity of the methyldiethanolamine solution due to its oxygen scavenging ability. Although flow and temperature stimulated an increase in the corrosion rate of carbon steel, the corrosion inhibiting effects of sulfite ions increased with the salt concentration. Also, the presence of sodium thiosulfate caused a reduction in carbon steel corrosion. Its inhibition ability is largely the result of the formation of FeS product layer resulting from its disproportionation reaction. This layer offered a slight resistance to the influence of flow and increase in temperature when compared with the system without heat stable salts.     

Integrated laser based pre-tempering at laser welding of AISI 1045 steel by using 3D-scanner optics

Laser-based pre-heating of laser beam welding with a 3D scanning optics, applied to AISI 1045 steel, is studied. Laser beam welding of heat-treatable steel is challenging due to martensitic hardening in combination with defects. Pre-tempering aims the reduction of the cooling rates and martensitic microstructure within the weld seam. An oscillating defocused laser beam was guided over the surface for pre-heating by means of a 3D scanner optics. During pre-heating, the laser power, the scanning speed and the number of cycles were varied. Welding with 4000 W and 2 m/min with a focused laser beam was executed. Thus the resulting temperature profile behind the ongoing laser beam and cooling time T_8|5 between 800 °C–500 °C was significantly extended. Two parameter combinations (15 cycles|600 W|50 mm/s(²) and 10 cycles|800 W|50 mm/s²) succeeded in a microstructure of bainite and martensite. By extending the cooling time T_8|5 to 3.11 s(²) and 4.17 s². Thus, average hardness for laser based pre-tempering of 487 HV 0.5(²) and 455 HV 0.5² was achieved. As a reference, global pre-heating at 400 °C using a heating plate can reduce the average hardness of the weld zone from 729 HV 0.5 at room temperature to 304 HV 0.5 at a cooling time T_8|5 of 5.63 s.     

Carbon and stainless steel in solutions of lithium nitrate in ammonia at moderate temperatures

The lithium nitrate in ammonia solution has been proposed and demonstrated as a thermodynamically attractive working mixture for absorption heat pumps. A literature search failed to find corrosion studies of said solution. The corrosion of carbon and stainless steel in solutions of lithium nitrate in ammonia was studied for a series of concentrations and temperatures from 50 to 150°C. The materials studied were found to be suitable for construction of absorption heat pump process equipment for this working mixture.     

Corrosion inhibition of carbon steel in various water types by zinc gluconate

The effect of zinc gluconate on the corrosion inhibition of carbon steel DIN RSt 37‐2 in various water types has been evaluated using Tafel polarization and scanning electron microscopy techniques. Experiments were performed using 6 types of water, namely, soft tap water from Dubrovnik region, hard tap water from Zagreb region, 3.5% sodium chloride solution, sea water from Dubrovnik region, biologically inert sea water from Dubrovnik region and demineralized water. The concentration of zinc gluconate varied from 0.1 to 3 gl^–1. The results show that substantial corrosion inhibition using zinc gluconate can be obtained with low concentrations in tap waters along with demineralized water and with moderate concentrations in 3.5% sodium chloride solution and sea waters. EDX analysis confirmed the presence of zinc ions which are incorporated in the protective layer of carbon steel specimen. The corrosion inhibition is predominately obtained by anodic mechanism.     

Modellierung der Stängelkristallitbildung beim Hartlöten von Kohlenstoffstählen mit Kupfer

Simulation of columnar crystallite formation in brazed seams of copper‐brazed carbon steels When brazing steels of different carbon content with copper filler metal, columnar crystallites form on the carbon‐rich iron surface if the width of the brazing gap is smaller than 100 μm. Braze seams with such microstructures were described as early as the 1950ies and it was found out, that the strength of such a joint is significant enhanced, if this crystallites penetrate the entire seam. Extensive experimental investigations in recent years confirm, that the final average length of the crystallite increases superproportionally with decreasing brazing gap width and is almost inversely proportional to the difference in carbon content of the joined steels. Although many attempts to explain this phenomenon are known from literature, the mechanism of columnar structure formation has not been clarified properly until now. The aim of the present work was to develop an appropriate physical model, that describes the growth of crystallites as a function of carbon content in the base materials, the initial brazing gap width and the applied process parameters (temperature, time). The model is an appropriate tool for a general choice and development of filler metal‐base material combinations forming columnar crystallites in the braze seam.     

Enhancing the lifetime and corrosion resistance of gears made of carbon steel

Gears for structural machines require high fatigue strength for high performance. Generally, gears made of carbon steel easily corrode, thus, shortening their fatigue life. The aim of this paper is to improve the fatigue strength of carbon steel gears by means of heat treatment method which was nitriding composed of 95 % nitrogen gas as well as 5 % hydrogen gas, and to investigate its properties after nitriding. Therefore, in order to find the optimum nitriding temperature to increase the hardness and corrosion resistance of gears, the gas nitriding process was conducted at two different tube furnace temperatures: low (550 °C) and high (1150 °C), both for four hours. Microstructural and mechanical property evaluation of the low and high temperature nitrided low-carbon steel BS970-080A15 were studied and the results were compared to identify which gear had better performance in terms of hardness as well as corrosion resistance. The results from Vickers hardness test and weight loss analysis proved that high temperature nitrided carbon steel is harder and more corrosion resistant than the low temperature one.     

Carbon dioxide corrosion of carbon steel and corrosion inhibition by natural olive leaf extract

The corrosion of carbon steel in carbon dioxide saturated chloride carbonate solution with and without olive leaf extract at 25 °C and 65 °C has been studied by linear polarization resistance technique, electrochemical impedance spectroscopy, scanning electron microscopy and Fourier transform infrared spectroscopy. In the absence of olive leaf extract, the corrosion products created under the testing conditions within 24 h at both testing temperatures have no significant protective properties. Measurements for uninhibited systems showed high corrosion current densities and low polarization resistances of carbon steel. Both linear polarization resistance technique and electrochemical impedance spectroscopy measurements reveal that olive leaf extract inhibits the carbon steel corrosion. The addition of a low‐concentration olive leaf extract decreases corrosion current densities, increases charge transfer and polarization resistance, resulting in more uniform and smoother steel surfaces. These effects are attributed to the adsorption of olive leaf extract on the carbon steel surface.     

Conventional and in situ tensile test of friction stir welded steel – Optimization of processing parameters

In the present investigation, steel plates were joined at different tool traversing speed by friction stir welding keeping other parameters same. Microstructural characterization was carried out with optical and scanning electron microscopes. At weld nugget pearlite and bainite were present within ferrite matrix. Thermo‐mechanically and heat affected zones microstructure consisted of pearlite and ferrite. Second phase area fraction and matrix grain size at different regions were varied depending on welding parameters. Weld nugget exhibited substantial improvement in microhardness with respect to base metal. In this respect heat affected zone revealed minimum microhardness and was below base metal value. Tensile tests were carried out on standard and miniature specimens in scanning electron microscope. Highest joint efficiency to the tune of ～82 % and ～120 % of that of base metal obtained for standard and miniature specimens, respectively machined from weld fabricated at lowest welding speed. With increment in welding speed assembly strength was reduced for both types of specimens. Standard specimens failed from heat affected zone and miniature specimens failed through centre of weld nugget. Apart from matrix grain size and second phase area fraction, precipitation of microalloyed carbide / carbonitride was responsible for altering the joint strength.     

Effect of quenching temperature on structure and abrasive wear resistance of boron‐containing medium carbon steel

Under the condition of oil cooling, the effect of quenching temperatures on the structure and abrasive wear resistance of medium carbon steel containing 2% B has been studied. The results show that the metallic matrix of Boron‐containing Medium Carbon Steel (BMCS) transforms into the martensite from the mixture of martensite, pearlite and ferrite while quenching at 900°C – 1050°C. The change of boron carbide existing in BMCS is few in different quenching temperature. After quenching the hardness of BMCS excels 56 HRC, and the change of quenching temperature has no obvious effect on the hardness of BMCS. The increase of quenching temperature leads to the increase of impact toughness, and impact toughness has no obvious change when quenching temperature exceeds 1000°C. Moreover, the increase of quenching temperature leads to a slight decrease of weight loss and the abrasive wear resistance of BMCS has a slight increase while increasing quenching temperature. Quenching at 1000°C–1050°C BMCS has excellent comprehensive property.