Experimental Research of Impact Toughness of the Kazakhstani Construction Steel— Assessment of Compliance with the Provisions of 1993 Eurocode

Since 2015, the Republic of Kazakhstan has a new regulatory framework for construction on the basis of Eurocode. Many new steel quality requirements have been introduced for steel structures. As a result, Kazakhstan’s steel production almost ceased to be used in construction. Therefore, a series of studies is being carried out to determine the quality of local steel for compliance with the requirements of Eurocode 1993. Impact toughness testing was carried out on 126 samples of 8, 10, 20 mm thick structural steel produced by the “Arcelor-Mittal” company. The experimental study of impact toughness of KCV and KCU at a temperature of +20˚, -20˚, -40˚ degrees were conducted for seven types of structural steel, the most common in the Republic of Kazakhstan, on the experimental experimentation facility of the KazRDICA JSC. The ST RK STB EN 10045-1-2012 techniques were used. In each series of tests, 3 specimens were used. It has been established that in all cases the temperature requirements of Eurocode 1993 (National Annex to SP RK EN1993-1-1: 2005/2011*, Table НП.2*) are met. A regression relationship between the values of impact toughness and temperature was constructed. It has been established that construction steel produced in the Republic of Kazakhstan fully complies with the requirements of 1993 Eurocode. The studies on the dependence of Brinell hardness of steel on the impact toughness of steel at specified temperatures are performed. The correlation dependencies between the values of impact toughness and BH Brinell hardness have been obtained.

Weld Joint Efficiency of the Kazakhstani Constructional Steel

In the Republic of Kazakhstan, the regulatory framework in construction based on Eurocodes has been in force since 2015. However, Kazakhstani produced steel has not been studied for compliance with the requirements of Eurocode 1993. This has resulted in limited use of Kazakhstani structural steel in construction. The feasibility of using structural steel in welded joints has been experimentally investigated. To verify the application of such joints in construction, including earthquake engineering, experimental studies of welded joints made of structural steel produced by Arcelor-Mittal in Temirtau have been carried out. In total, 7 types of structural steel of various thicknesses were selected. Five specimens have been used in each series of tests. The Brinell hardness values of the weld joint, yield strength of steel and tensile strength, relative rupture strain were determined. It was found that for all types of structural steel, the quality of weld joints complied with the requirements of Eurocode 1993—a sample rupture appeared along the plates (main body of the metal), not along the weld joints. It has been established that structural steel produced in the Republic of Kazakhstan fully complies with the requirements of Eurocode 1993. The studies on the dependence of Brinell hardness values of weld joint steel on the yield strength, tensile strength and relative rupture strain have been carried out. The correlation dependences between the values of yield strength of steel and tensile strength, relative rupture strain and BH Brinell hardness were studied. The results of work will allow for significantly increasing the use of Kazakhstani structural steel in seismic and conventional areas of the Republic of Kazakhstan.

Discussion on Construction Technology of Subway Tunnel Expansion under Bridge Foundation

As the urban populations grow,the number and size of subway construction projects are increasing while also meeting higher construction standards.So,subway construction projects must have a better understanding of construction technology.This article focuses on the construction technology of the subway tunnel expansion under the bridge foundation.By analyzing the engineering characteristics of the bridge foundation and using a project as an example,this article provides a detailed discussion of the construction process of tunnel expansion under a bridge foundation.This article aims to serve as a reference for subway tunnel construction in China to ensure the key points of construction technology are understood,thus improving construction quality and laying a solid technical foundation for the sustainable development of urban rail engineering.

Influence of Mo Content on Microstructure and Mechanical Properties of Fire-Resistant Construction Steel

In order to ensure fire-resistant property of the steel under the condition of the least molybdenum content,effects of molybdenum on microstructure and properties of the fire-resistant construction steel,specially on high temperature strength were investigated.The results show that the room temperature and high temperature strength of the steel is enhanced due to increased Mo content but the impact toughness deteriorates at the same time.The fraction of bainite in the microstructure increases with increasing Mo content while the fractions of polygonal ferrite and pearlite decrease.Comparing with the steel of adding Nb alone,it was obvious that combined addition of Mo and Nb could provide better effect in high temperature strengthening.Addition of 0.25mass% Mo in the steel containing Nb could meet fire-resistant requirements of the construction steel and provide better economical effectiveness.

Analysis of the Characteristics of Materials Obtained by Recycling Scrap Metal in Guinea

The aim of this study was to determine the quality of rebar produced from recycled scrap metal collected throughout the country,and imported rebar sold in the Republic of Guinea.To do this,the samples were subjected to various mechanical tests involving traction,bending and microscopic analysis.In the Lambanyi and Casse Sonfonia samples,all the tensile strength values for diameters 12,14 and 16 were above 550 MPa.Conversely,the iron samples from Baillobaye and the 10 mm diameters of the samples from Casse Sonfonio and Lambanyi have less appreciable values.The limits of elasticity were determined.The various values found vary more or less from the conventional yield strength of the NF A35-016 reference supplied by CBITEC,which is 500 MPa.Microscopic analysis gives us an insight into the internal structure of the iron samples used.This study may provide the company and the vendors with an alternative for their improvements.

Microstructures and Mechanical Properties of a New Multi-functional 460 MPa Grade Construction Structural Steel

This article reports a new generation of Q460 multi-functional construction structural steel,which has high strength(yield strength larger than 460 MPa),excellent toughness(higher than 110 J/cm^(2) at-60 ℃),lower yield ratio(lower than 0.8),good fire resistance(yield strength at 600 ℃ larger than two-thirds of its room-temperature yield strength)and better corrosion resistance.The eff ects of finish cooling temperature(FCT)on the microstructure and properties were studied by scanning electron microscopy(SEM),transmission electron microscopy(TEM),emission electron probe micro-analysis(EPMA),electron backscattering diff raction(EBSD),tensile tester,impact tester,periodic immersion cycle acceleration test and electrochemical experiment.The results show that the strength and toughness are simultaneously improved by decreasing the FCT due to more lath-like bainite with large number of dislocations,refined martensite/austenite(M/A)with higher carbon concentration and increased high angle boundaries.In addition,the fire resistance of the newly developed Q460 steel is obviously better than the conventional one,which is mainly due to non-recrystallized lath-like bainite with high dislocation density at elevated temperature.The corrosion resistance of the new Q460 steel is also improved due to the addition of Cu and Cr.

Construction and Application of Quenching Critical Cooling Rate Model

Based on exploring quenching mechanism, three types of quenching critical cooling rate models of mediumcarbon steel and low-carbon steel and low-alloy construction steel were established, as modified Maynier model, Eldis model and isothermal curve model, respectively. During construction process, regression analysis and Newton interpolation method were used for higher calculated precision. Through comparing and analyzing, the superior one was selected to evaluate the full hardening thickness after quenching. According to hardness analyzing, the deviation between predicted hardness distribution and the experimental value is within 6%.