Papers by Keyword: Impact Toughness

Abstract: Nickel alloying element has been known to play a role in controlling the formation of microstructures in the weld metal (WM). This experiment aims to study the relationship between nickel addition to the microstructure evolution and toughness of shielded metal arc welded SS400 low carbon steel plates. Three welded samples, Ni-01, Ni-03 and Ni-09 were fabricated using electrodes containing different nickel: <0.1% Ni, 0.3% Ni, and 0.95% Ni, respectively. Microstructure of WM was examined using an optical microscope and scanning electron microscopy, and mechanical properties were measured in strength and toughness. The results showed the impact toughness increased when the nickel content of electrodes increased. From the three experimental welded samples, WM of Ni-09 which using electrodes containing 0.95% Ni demonstrated the best result for the impact toughness. It may caused Ni-09 has more AF and finer grains size compared to Ni-01 and Ni-03. It seems with nickel addition in the WM, finer grain size and acicular ferrite (AF) formation were developed.

Abstract: The effect of ten different combinations with various amounts of niobium (0-0.6 wt.%) and chromium (1-4 wt.%) on weldability and mechanical properties of thermomechanically rolled and direct-quenched low-carbon (0.035 wt.%) microalloyed bainitic steel were investigated. Two compositions were alloyed with boron to increase the hardenability, and two with titanium to improve the toughness properties in heat affected zone. The target of the study was to produce steel with 700 MPa yield strength combined with good impact toughness. Coarse grained heat affected zone (CGHAZ) simulations were performed using the Gleeble 3800 thermomechanical simulator to evaluate the weldability of the investigated steels using cooling time from 800 °C to 500 °C (t_8/5) of 5 s and 15 s to simulate different heat inputs in actual welding procedure. Microstructures were characterized using light optical microscopy, and hardness profiles of simulated heat affected zones were determined as well as Charpy-V impact toughness at-40 °C and-60 °C. Shorter t_8/5 time (5 s) produced generally better impact toughness properties compared to longer t_8/5 -time (15 s). Steels with 4 % Cr had the highest impact energies. Generally, more softening occurred with longer t_8/5-time (15 s). However, Cr and Nb alloying decreased the amount of softening in the CGHAZ region, especially with longer t_8/5 -time. These results indicate that even with higher t_8/5 -time, it is possible to achieve strength properties equivalent to the base material in the CGHAZ region by Cr and Nb alloying.

Abstract: The aim of this work is to study the effect cold forming rate (CFR) on the mechanical properties and microstructure of a conventional TMCP and a direct-quenched steel in 420 MPa strength level. The microstructure was characterized using FESEM-EBSD. Tensile properties and Charpy-V impact toughness were determined. As the CFR increased, the yield and tensile strength raised quite linearly with both steels. Yield strength values increased from 450 MPa (as-rolled material) to 700 MPa (25 % CFR). However, tensile strength increased less compared to yield strength. Uniform elongation decreased linearly till about 10 % CFR and total elongation till about 15 – 20 % CFR. The impact values decreased quite linearly in -40 °C and -60 °C test temperature when the cold forming rate increased. In longitudinal direction (L-T) the impact values were at high level at -40 °C and -60 °C with both steels with all CFR. In transverse direction (T-L) the impact results were lower. Impact energies were enhanced by direct quenching compared to conventional steel in every CFR stage. EBSD results showed no major difference between steels in the grain sizes in generally. However, cold forming decreased the grain size and increased low-angle grain boundaries in correlation with increasing CFR. Small size of the coarsest grains (d_90%) usually indicate better toughness, however in this case the impact values were decreased even with smaller grain size as cold deformation occurs. On the other hand, the strength level increased with forming rate. Therefore, a brief discussion of the microstructural features controlling the impact toughness is given.

Abstract: The study was conducted to evaluate the impact toughness of flux-cored arc welded of SM570-TMC steel joint under different heat inputs, 0.9 kJ/mm (low heat input) and 1.6 kJ/mm (high heat input). Welding wire containing 0.4%Ni was selected on this experiment. Multi-pass welds were performed on SM570-TMC steel plate of 16 mm in thickness with a single V-groove butt joint on flat position (1G). The evaluation consists of observations on microstructure using an optical microscope and SEM-EDS, and mechanical properties including tensile, microhardness Vickers and Charpy V-notch (CVN) impact test at temperatures of 25, 0 and-20 °C. Results showed that the impact toughness of the base metal (BM) was higher than the weld metal (WM) at all test temperatures. Hardness and impact toughness of WM at low heat input was observed higher than when applied a high heat input. The welded samples at low and high heat inputs had high of tensile strength, and the fracture seemly occurs on the BM. Microstructure observation showed that at a high heat input, larger grains and microsegregation were observed. It might affect on decreasing their impact property.

Abstract: The purpose of the study was to inspect microstructure, mechanical properties and impact toughness of ductile cast iron grade FCD450 produced by austempering process. The study focused on austempering parameter, which effected impact toughness of material at low temperature. The FCD450 was initially temperature austenized at 885°C (1625˚F) for 2 hours. Austempering was carried out at three different temperatures of 271°C (520˚F), 313°C (560˚F) and 357°C (675˚F). The austempering temperature were varied at 1.5, 2.5 and 3.5 hours. X-ray diffraction was showed that the austempered ductile cast iron (ADI) microstructure consists of austenite and ferrite. The results showed that when austempered at 357°C (675˚F) for 2.5 hours has highest hardness and impact energy at low temperature. The dimple ductile fracture of ADI fracture surfaces was revealed by scanning electron microscope (SEM).

Abstract: The life extension of the reactor requires the improvement of the material performance, especially the radiation resistance. At present, some data about the irradiation hardening and embrittlement behavior of reactor pressure vessel steel have been obtained, mainly the standard tensile properties, standard impact properties and so on. However, to understand the service behavior of materials at higher doses, higher neutron fluence radiation tests are needed. The problem is that because of the large size of the standard sample, if the irradiation dose continues to increase, the surface dose of the irradiated sample will be larger, and it is difficult to test after irradiation. In addition, if the irradiation sample can be replaced by smaller sample, the utilization space of the radiation channel will be greatly improved. The high-throughput characterization for irradiation performance of reactor pressure vessel steel can be achieved. Therefore, in this work, the small punch test of reactor pressure vessel material A508-3 steel was carried out at the temperatures ranging from -150 °C to room temperature. The performance data, such as tensile characteristics, yield strength and fracture energy, were obtained from load-deformation curves. Comparing the results of small punch test with the data obtained by standard tensile and impact test, the correlation on the performance data was established for A508-3 steel.

Abstract: The paper deals with the impact toughness and fracture mode of the low-alloy 09G2S steel in the as-delivered state and in the condition after equal-channel angular pressing (ECAP) and annealing at impact bending in the temperature range of 293-203 [K]. The results on impact toughness KCV and fracture mode of Charpy test specimens made of the 09G2S steel in the as-delivered state and in the condition after hardening are presented. There is a decrease in the steel impact toughness in the examined temperature range after annealing at 673 [K], ECAP, and ECAP with annealing compared to the corresponding value for steel in the as-delivered state. For the 09G2S steel treated with various techniques, the temperature-KCV plot drop occurs smoothly, without abrupt changes, in the examined temperature range, in contrast to the behavior of this value with the upper threshold of the fracture appearance transition temperature for the steel in the as-delivered state.

Abstract: This work investigated microstructure and impact toughness of multi-pass flux-cored arc welded SM570-TMC steel. A comparison was made between weldments fabricated with average heat input of 0.9 kJ/mm and 1.4 kJ/mm, respectively. SM570 steel plate with 16 mm nominal thickness and 1.2 mm diameter of E81-Ni1 flux-cored wire were selected in this experiment. Multi-pass flux-cored arc welding (FCAW) was performed using carbon dioxide shielding gas. Then the weldments were observed using optical microscopy, scanning electron microscope (SEM) and electron probe micro analyzer (EPMA). The steel joint strength was measured via tensile test, and Charpy impact test was performed at three different test temperatures. The microstructure observation exhibited the base metal mainly consist of ferrite and pearlite features, while the weld metal contained the acicular ferrites, polygonal ferrites and M-A constituent at both different heat inputs. The impact toughness of base metal is superior than weld metals. The weld metals fabricated at average heat input of 0.9 kJ/mm have a higher low temperature impact toughness than using heat input of 1.4 kJ/mm. The acicular ferrites amount that significant reduced at the higher heat input may degrade the toughness at low temperature.

Abstract: In the research, the mechanical behavior of duplex stainless steels SAF 2205 and 2507 subjected to Normalized thermal treatments at temperatures at temperatures of 900, 950 and 1000oC for a time of 7 minutes for SAF 2205 and 15 minutes for SAF 2507 were evaluated. It was determined that the mechanical strength increased considerably the higher value was found at 900 °C. It was determined that the K_IC values for the normalized conditions of 900 oC and 950oC, reduce strongly in both steels with respect to the original condition. However, it is clearly reflected that for the normalized condition at 1000 °C the K_IC is fully recovered, and for the temperature range of 700 °C to 900 °C, the values of impact toughness suffer a drastic decrease, caused by the appearance of intermetallic phases.

Abstract: The results of impact testing of welded joint specimens taken from a welded plate made of P460NL1 steel are presented in this paper, and analysed with regards to the cooling time t_8/5, that was previously calculated. The aim was to determine how the cooling times that were measured, some of which were below the minimum required values, affected the toughness, in terms of total impact energy and its components, crack initiation and crack propagation energy. In addition, this analysis included the effects of temperatures measured at the opposite ends of the plate during the welding process, since this had also affected the cooling times for each welding pass. After observing the differences in total, crack initiation and propagation energy between the tested specimens taken from different parts of the welded plate, it was determined that the specimens from the part where the higher temperatures were measured had shown better, more uniform results, whereas the average total impact energy for specimens from both groups were very similar. It was also noticed that the ratio of crack propagation to crack initiation was more favourable (greater) in the case of specimens from the second group (with higher temperature), as the values of crack initiation energy decreased slightly and the crack propagation energy increased.