Papers by Keyword: Impact Toughness

Abstract: A study of the mechanical properties of the finished metal products was carried out. All types of metal products are subjected to continuous quality control, both on the production output at the manufacturer of billets, and on the production entrance at the consumer of metal. Control subject are: strength characteristics (tensile strength σ_в and yield stress σ₀₂ and the characteristics of plasticity (relative elongation δ and relative necking ψ). The pipe steels have another important controlled characteristic: the impact toughness КСU-60. All the test methods are the destroying ones and are characterized by high complexity. The task of reducing the types of tests, the introduction of a comprehensive indicator of product quality is an urgent technical task. The purpose of this work is to study the regularities of changes in the indicators that determine the quality of the sheet metal from the pipe steel.

Abstract: Specimens of pipe steel of increased strength grade type K56-K60, with different values of impact toughness (KCV) were investigated: a metallographic examination of the specimens’ structure was carried out by optical and electron scanning microscopy methods. The interrelation of the microstructure with mechanical properties, in particular with impact toughness and their influence on the nature of fracture pattern is established.

Abstract: Review focuses on describing of mechanical properties of the components manufactured via direct laser depositionfrom cold resistant steel material. The results of tensile and impact testing are presented and microstructures of the fractures are shown. The process of laser deposition of cold-resistant steels, the formation of structures, as well as the mechanical properties of these samples are poorly understood. The results of tensile and impact tests are presented, and microstructures are shown. Mechanical tests for impact strength were carried out at a temperature of -40˚С, with different laser radiation powers. The results are given using the as-received powder, as well as used powder with a different mixing ratio, and the results are analyzed. As a result of the study, it was found that the fractional composition of the 09XH2MD alloy powder affects the mechanical characteristics of samples obtained by direct laser deposition. The effect of recycled powder on the mechanical properties of the obtained samples is given, the optimal laser deposition regimes are selected

Abstract: HY-80 is the high yield steel that commonly used for naval ship and submarine. Arc welding operations are critical stage in fabrication of this steel. During welding, the problem may occur in the heat affected zone due to the high temperature makes the microstructure suddenly changes. Coarse grain heat affected zone (CGHAZ) develops close to the fusion line, steel become brittle and the impact toughness decrease. This research investigated the microstructure of HY-80 weldment, impact toughness at sub-zero temperatures, and hardness distribution along cross-section of the welded joint. ER100S welding wire, Ar+10%CO₂ shielding gas mixture and single V-groove butt joint with an angle of 60° were selected prior to welding. 12 mm thick of HY-80 steel plate that used in this experiment was multipass welded by gas metal arc welding (GMAW). Impact toughness at sub-zero temperature, hardness and microstructure evolutions of base metal (BM), heat affected zone (HAZ) and weld metal (WM) were observed. The result shows at a temperature of-80 °C, the lowest impact toughness was measured at WM (61 J) as compared to fusion line (101 J) and BM (217 J). The hardness measurement shows the maximum hardness was measured in CGHAZ followed WM and BM. Vickers hardness test result of weld joint at bottom area are higher than top area. It may caused of the low heat input of back weld compared to other passes. The lower heat input, cooling rate increased and initiate the formation of hard phase. The microstructure of WM shows acicular ferrites and non-metallic inclusions, these inclusions may deteriorate the impact toughness.

Abstract: In this present work, the effects of recycled aluminum scraps on the impact and hardness properties and microstructures with a melting process are studied. The method was conducted to determine an impact toughness by Charphy pendulums; hardness materials by Vickers's test; and chemical composition by spectroscopy. Four types of aluminum scraps have been recycled using a metal casting process. They are beverage cans, aluminum profile bar waste, gasoline engine piston, and scrap pans. The results show that the maximum hardness obtained is 54.13 VHN on the material of the gasoline engine piston. The lowest hardness is 26.88 VHN which is obtained for pan aluminum recycle. The highest impact test result is obtained on an aluminum pan material which is 40.3 J/mm² in average and the lowest value obtained is on the gasoline engine piston material which is 1.7 J/mm² in average. The microstructure of the gasoline piston shows finer compared to the pans after cast.

Abstract: Weld samples imitating the inservice girth welds in station (L245 straight pipe jointed to WPHY-70 tee joint and L415MB straight pipe jointed to WPHY-80 tee joint) were prepared. Tensile, bending, impact toughness and hardness of the joints were investigated. Results show that under tensile or bending load, failure occurred from the side with lower grade and smaller wall thickness. Relatived to the lower grade side, the weld seam is strong match. Significant change of impact toughness can be found in weld seam center and the heat affected zones (HAZ). The impact energy of seam center is the lowest in the weld joint. The impact energy show a trend of increase from seam center to base metal. In HAZ zone, impact toughness of the fusion line is the lowest. Impact toughness of higher grade side is higher than that of the lower grade side. Hardness of positions in HAZ zones are different distinctly. From coarse grained region to fine grained region, the hardness decrease. For the in-station girth welds jointed with different materials, lower grade and samller wall thickness side should be intensive monitored.

Abstract: High strength and sufficient toughness are key requirements for modern high-performance structural steels. In an attempt to develop a suitable estimation of impact toughness transition temperatures for as-quenched steels, we investigated the determiners of low-temperature toughness with a group of thermomechanically rolled direct-quenched steels with varying martensite contents. These were produced by altering chemical composition, finish rolling temperature and reduction below the non-recrystallization temperature, i.e. austenite pancaking, and characterised in terms of microstructural constituents, grain size distributions, texture and fractography. Provided the finish rolling temperature is high enough to avoid the formation of granular bainite on subsequent cooling, high levels of austenite pancaking yield the best combinations of low-temperature toughness and strength by effectively refining the size of the coarsest grains and randomizing the texture. While absolutely no direct correlation is found within as-quenched steels between the impact toughness transition temperatures and yield strength alone, T_28J and T₅₀ do closely follow a dynamic reference toughness, i.e. the opening stress intensity factor defined by yield strength and the size of the coarsest grains in the effective grain size distribution. This parameter reflects the transition temperatures – the lower the temperature, the lower the reference toughness needed to cause a local brittle fracture. Finally, we show that the impact toughness transition temperatures T_28J and T₅₀ of as-quenched steels can be accurately estimated, irrespective of the test specimen orientation, by utilizing just the dynamic reference toughness and the fraction of {100} cleavage planes within ± 15° of the specimen notch plane.

Abstract: This study presents how Nb addition allowed improving the Charpy impact toughness of a martensitic stainless steel by comparing a conventional AISI410 (12%Cr-0.1%C) and a 12%Cr-0.1%C-0.1%Nb steel after the same austenitization and quenching heat treatment. Adding niobium decreased the ductile-to-brittle transition temperature by 100°C with respect to the Nb-free steel. To identify quantitative fracture criteria for the two materials, the values of critical cleavage fracture stress were determined by the local approach to fracture, combining low temperature tensile tests on notched specimens and mechanical analysis by the finite element method. The main effects of niobium were to refine the grain size and to promote retained austenite films, resulting in a similar resistance to cleavage crack initiation but in a strong improvement of the ductile-to-brittle transition behavior by increasing the resistance to cleavage crack propagation.

Abstract: The reheat furnace process step has a profound effect on the TMCP performance, final hot rolled steel quality and mechanical property consistency during the production of hot rolled steels. The uniformity of heating applied across the entire width and length of the slab or billet is critical in the achievement of customer properties regardless of the chemistry. The resultant ferrite grain size in the final hot rolled product is significantly governed by the initial prior austenite grain size. Numerous reheat furnace process metallurgy and combustion parameters in actual operation affect mill productivity, microstructure, austenite grain size, scrap rate and diverts. This reheating step in the steelmaking process often receives low priority in the evaluation of product quality and mechanical property performance, especially the toughness through the plate thickness. Heat transfer conditions of radiation, convection and conduction affect furnace heating efficiency. In laboratory studies, the furnace heating step is typically quite uniform resulting in a homogeneous and fine prior austenite grain size. During production, it is much more difficult to control the uniformity of heating and heat transfer consistency along the entire length and through the thickness of the work piece. The furnace conditions are correlated to product quality via furnace process variables such as the air to gas ratio, furnace burner condition, furnace pressure, energy efficiency, adiabatic flame temperature (AFT) and furnace refractory condition. Operational practice recommendations are presented to minimize inhomogeneous heating which results in inferior product quality, hot rolling model anomalies and toughness variations in the through-thickness-direction.

Abstract: The welding thermal simulation of 2507 Super Duplex Stainless Steel (SDSS) was investigated using Gleeble-3800 thermo-mechanical simulator. The morphology evolution of austenite and ferrite under different t_8/5 and t_12/8 were observed and compared. The impact tests and pitting corrosion tests under different t_8/5 and t_12/8 were conducted. The results showed that the austenite content increased and the austenitic morphology changed from allotriomorphic structure to strip or coarse-blocky structures with the increase of t_8/5 and t_12/8. The effect of t_12/8 on the microstructure of welding Heat Affect Zone (HAZ) was more distinct than that of t_8/5. The impact toughness of HAZ with the increase of t_12/8 was improved due to higher austenite content, while that with the increase of t_8/5 was slightly decreased due to the formation of intermediate phase, such as σ phase. The corrosion tests showed that the pitting resistance of HAZ was improved with the increase of t_8/5 and t_12/8, while the effect of t_12/8 was especially evident.