Low Temperature Impact Research Articles

Laboratory measurement setup to study thermal physical processes under low temperature impact

Laboratory measurement setup to study thermal physical processes under low temperature impact

Design and Corrosion Resistance Performance of Nano-Multilayer Coatings for the Protection of Breathing Gas Cylinders Used in Diving

Seamless gas cylinders for diving exhibit excellent low-temperature impact performance, lightweight characteristics, and good corrosion resistance, making them widely applicable in underwater activities. However, during use, the peeling of paint or corrosion on the surface of these cylinders poses a significant threat to their safety. In this study, environmentally friendly arc ion plating technology was used to deposit TiBN, CrAlN, and nano-multilayer coatings of CrAlN/TiBN. The surface morphology, tribological properties, and corrosion resistance of these coatings were investigated. The results indicated that both CrAlN and CrAlN/TiBN coatings possess fewer droplets, pinholes, and pits, and the cross-section of the CrAlN/TiBN coating exhibits a denser structure. The preferred orientation for TiBN was identified as TiB2 (101), while that for CrAlN was Cr(Al)N (200), with the preferred orientation for CrAlN/TiBN being TiB2 (101). The friction measurements revealed that the lowest coefficient was observed in the CrAlN/TiBN coating (0.489), followed by CrAlN (0.491) and then TiBN (0.642). Electrochemical tests conducted in artificial seawater demonstrated that the self-corrosion potential was highest for the CrAlN/TiBN coating, followed by CrAlN and lastly TiBN. The developed TiBN-based nano-multilayer coatings hold substantial application value in protecting seamless gas cylinders used in diving.

Development and testing of a remote calibration device for the temperature field of environmental testing equipment

Abstract Temperature is one of the important parameters for the calibration of environmental testing equipment. Due to its special working requirements and large volume and weight, the demand for on-site inspection and calibration of environmental testing equipment has always been high. Conducting research on remote calibration devices for temperature fields in environmental testing equipment is beneficial for improving the testing efficiency of environmental temperature and humidity, reducing the workload of testing personnel, and further reducing customer testing costs. By using ANT Wireless technology and using SHT3X temperature and humidity sensors to create a temperature field calibration device for environmental testing equipment, the above functions can be achieved. After testing, the maximum transmission distance of a single node can reach 70 meters, and the maximum networking distance between multiple nodes can exceed 1,000 meters. It can adapt to high and low-temperature impact tests at -20°C~60°C, and the response speed of temperature and humidity sensors is slightly slower than traditional temperature measurement thermocouples. It is suitable for calibration and detection of environmental testing equipment with good insulation performance.

Initial temperature conduction process and fracture response of rock impacted by ultra-low-temperature fluid: A case study of polymethyl methacrylate

Injecting ultra-low-temperature fluids, such as liquid carbon dioxide (CO2) and liquid nitrogen (LN2), into deep, low-permeability reservoirs for fracturing is an emerging waterless fracturing technology. When these fluids enter the reservoir, they rapidly exchange heat with the fracture walls, triggering intense cold shock, which influences fracture development. Although many scholars have studied the effects of nitrogen freezing and thawing on coal seams, the initial thermal exchange and cold shock process when LN2 first enters the rock mass remains unclear. This paper uses the visualizable material polymethyl methacrylate (PMMA) as the research object, conducting low-temperature impact experiments under different preset temperatures (20 °C, 40 °C, 60 °C, and 80 °C) to investigate the impact of thermal exchange during cold shock on PMMA fracturing. The results show: (1) During LN2 impact, PMMA's temperature changes in three stages: slow cooling (micro-cracks initiation), rapid cooling (formation of long fractures), and temperature recovery (crack formation completion). (2) In prolonged impacts, PMMA temperature decreases linearly, while in short-term cyclic impacts, temperature decreases exponentially with faster recovery, increasing the likelihood of micro-cracks formation. (3) Temperature differences have a dual effect on crack formation and propagation: they significantly enhance internal thermal stress, leading to rapid micro-cracks initiation and expansion, while also causing uneven temperature gradients in the crack propagation region, shifting fracture modes from tensile to complex composite failures and promoting secondary crack formation. However, a significant temperature differential may result in the development of a singular crack propagation path, hindering the formation of complex fracture networks. These findings offer theoretical insights into fracture network formation in waterless fracturing of low-permeability reservoirs.

Effect of Trace Rare Earth Element Cerium (Ce) on Microstructure and Mechanical Properties of High Strength Marine Engineering Steel

In this paper, FH460 special steel with rare earth element cerium (Ce) was selected, and the control group without Ce was set up. By changing the content of Ce, the microstructure, phase transition point, and mechanical properties of the test steel were observed to study the effect of trace rare earth element Ce on the microstructure and mechanical properties of high-strength marine engineering steel. The morphology and energy spectrum of inclusions in three kinds of test steels were observed by SEM, and the morphological changes in inclusions in FH460 high-strength marine engineering steel after adding Ce were investigated. The fracture morphology and energy spectrum analysis were carried out by combining the tensile test at room temperature and the gradient low temperature impact toughness test, and the effect of trace Ce on the mechanical properties of the test steel was comprehensively analyzed. The results show that the addition of Ce changes the phase transformation temperature of Ac1 and Ac3, and refines the original microstructure of the test steel. SEM observation showed that the addition of Ce changed the long strip MnS and polygonal irregular Al2O3 inclusions into ellipsoids, which reduced the size of inclusions. The gradient low temperature impact test shows that with the decrease in temperature, the fracture dimple depth of the three test sheets of steel decreases, and the Ce-containing test steel forms a deep dimple centered on rare earth inclusions, which hinders the crack propagation and significantly improves the low temperature impact toughness of the test steel.

Making large-size fail-safe steel by deformation-assisted tempering process

Synergistically improving the strength and toughness of metallic materials is a central focus in the field of physical metallurgy. Yet, there is a noticeable lack of research in strengthening and toughening large-size metal components, whereas those components are extensively used in the modern industry. In this work, a deformation-assisted tempering (DAT) process was proposed to create a novel microstructure in 1.4 tons low-alloyed plain steel. After DAT treatment, the steel contains low dislocation density but high density of low-angle subgrain boundaries and dispersed spherical nano carbides. Such microstructure enables a much better combination of tensile strength and fracture toughness compared to the small-size quench and temper steels. The significant improvement in low-temperature impact toughness is due to the occurrence of delamination and subsequent large plastic deformation at the notch tip. The DAT process can provides a new strategy for the development of large-size fail-safe steel with excellent strength and fracture resistance.

Study on the Effect of Pressure on the Microstructure, Mechanical Properties, and Impact Wear Behavior of Mn-Cr-Ni-Mo Alloyed Steel Fabricated by Squeeze Casting

ZG25MnCrNiMo steel samples were prepared by squeeze casting under pressure ranging from 0 to 150 MPa. The effects of pressure on the microstructure, low-temperature toughness, hardness, and impact wear performance of the prepared steels were experimentally investigated. The experimental results indicated that the samples fabricated under pressure exhibited finer grains and a significant ferrite content compared to those produced without pressure. Furthermore, the secondary dendrite arm spacing of the sample produced at 150 MPa decreased by 45.3%, and the ferrite content increased by 39.1% in comparison to the unpressurized sample. The low-temperature impact toughness of the steel at −40 °C initially increased and then decreased as the pressure varied from 0 MPa to 150 MPa. And the toughness achieved an optimal value at a pressure of 30 MPa, which was 65.4% greater than that of gravity casting (0 MPa), while the hardness decreased by only 6.17%. With a further increase in pressure, the impact work decreased linearly while the hardness increased slightly. Impact fracture analysis revealed that the fracture of the steel produced without pressure exhibited a quasi-cleavage morphology. The samples prepared by squeeze casting under 30 MPa still exhibited a large number of fine dimples even at −40 °C, indicative of ductile fracture. In addition, the impact wear performance of the steels displayed a trend of initially decreasing and subsequently increasing across the pressure range of 0–150 MPa. The wear resistance of samples prepared without pressure and at 30 MPa was superior to that at 60 MPa, and the wear resistance deteriorated when the pressure increased to 60 MPa, after which it exhibited an upward trend as the pressure continued to rise. The wear mechanisms of the samples predominantly consisted of impact wear, adhesive wear, and minimal abrasive wear, along with notable occurrences of plastic removal, furrows, and spalling.

Mechanism of pore water phase change, freezing expansion, and pore enlargement of coal samples under low-temperature liquid nitrogen action

Liquid nitrogen fracturing, a technology for enhancing coal seam permeability without water, garnering considerable attention due to the intricate network of fractures induced by the low-temperature impact of LN2 on coal reservoirs. The phase transition freezing expansion of water-ice plays a pivotal role in determining the efficacy of coal damage. As direct measurement of water signal change during freezing is impractical, studying the variation in unfrozen water content during coal sample re-warming subsequent to cold shock is beneficial. This approach aids in elucidating the phase transition expansion and pore expansion mechanisms at different pore scales. The findings reveal the sequence of pore ice melting in coal samples frozen by LN2: micropores exhibit initial water appearance, followed by medium-sized pores, with micropores reaching peak levels first. Subsequently, water migrates from micropores to medium-sized pores, leading to their peak levels, before macropores show water presence. The temperature gradient from the coal sample center to the coal wall, owing to thermal resistance, results in the part melting first also freezing first. Analysis indicates that the porosity signal of lignite and bituminous coal increased by 203 % and 467 % during medium-sized pore melting, emphasizing the prominence of the medium-sized pore melting stage. It is further inferred that the phase transition freezing expansion and pore expansion of coal sample water induced by LN2 primarily occur in medium-sized pores.

COMPARATIVE STUDIES ON MICROSTRUCTURE AND TOUGHNESS OF 9 % Ni STEEL JOINTS WELDED BY SMAW AND GTAW

The microstructure and impact toughness of 9 % Ni steel joints welded by shielded metal arc welding (SMAW) and gas tungsten arc welding (GTAW) were investigated. The two kinds of weld metal were mainly composed of cellular dendrites and a granular precipitated phase. The grains and cellular dendrites of the GTAW weld metal were smaller than those of the SMAW weld metal. The precipitates in the SMAW weld metal were stripe-shaped while those in the GTAW weld metal were rod-shaped; the number of precipitates in the GTAW weld metal was lower than in the SMAW weld metal. The low-temperature impact toughness of the GTAW weld metal was better than that of the SMAW weld melt.

Grain misorientation induced low-temperature impact toughness deterioration and its deformation mechanism of Ti6321 titanium alloy

In this study, the impact toughness and deformation mechanism of base metal (BM), heat affected zone (HAZ) and weld zone (WZ) of Ti6321 alloy joint at different temperatures (20 °C, 0 °C, −20 °C, −40 °C, −60 °C and −196 °C) are studied. The microstructure of BM consists of primary α (αp), acicular α and β phase. The HAZ is composed of αp, acicular α, acicular martensite (α′) and β phase. The WZ is composed of acicular α′, lath α′ and β phase. All the BM, HAZ and WZ obtain the highest impact toughness at 20 °C, which are 51 J, 75 J and 72 J, respectively. Under −196 °C, brittle fractures occurs in the BM, HAZ and WZ, and their impact toughness are 18 J, 22 J and 30 J, respectively. Compared with the impact test at −196 °C, the fracture surface of 20 °C by impact test has higher kernel average misorientation and geometrically necessary dislocation. The fracture impact resistance at 20 °C is greater. Grain deformation at 20 °C consumes more energy and the crack propagation path is more tortuous.

Effect of final rolling temperature on the microstructure and properties of high-manganese austenitic low-temperature steel

The effect of final rolling temperature ranging from 962 to 696 °C on as-rolled high-Mn austenitic low-temperature steel was investigated using scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy, and X-ray diffraction. The microstructure of the experimental steel remained austenite without suffering ferrite phase transformation, even when produced with a final rolling temperature as low as 696 °C. A decrease in the final rolling temperature of the steel was accompanied by a decrease in grain size from 20.2 to 6.0 μm, accompanied by an increase in dislocation density from 3.01 × 1014 to 10.9 × 1014 m−2. In addition, M23C6 carbides precipitated at the grain boundaries when the final rolling temperature was below 782 °C. Grain refinement and increased dislocation density significantly enhanced the strength of the material. However, an increase in the intragranular dislocation density compromised grain deformation ability. Moreover, the precipitation of M23C6 reduced the plasticity and toughness of the material. Considering the balance between yield strength and low-temperature toughness, the optimal final rolling temperature was 898 °C; this produced a material with a yield strength of approximately 507 MPa and a low-temperature impact energy absorption of approximately 143 J.

Role of M-A constituents in bainitic microstructure on crack propagation behavior in the ICCGHAZ of HSLA steels for offshore applications

The objective of the study is to understand the effect of martensite-austenite (MA) constituents along with the neighbouring bainitic matrix and its effect on low-temperature impact toughness in the thermo-mechanically simulated inter-critically reheated coarse-grained heat-affected zone (ICCGHAZ) of offshore High Strength Low Alloy (HSLA) steels. ICCGHAZ was simulated using a Gleeble 3500 thermomechanical simulator between the inter-critical temperature near Ac1 (lower ICT) and at a temperature 50 °C higher (upper ICT) for two different steels (steel A and steel B) with predominant microstructures composed of granular bainite (GB) and bainitic ferrite (BF), respectively. MA constituents were observed in the form of necklaces along prior austenitic grain boundaries (PAGB) of simulated ICCGHAZ for both steel A and steel B. Steel A combrised of discrete island MA constituents inside the GB grains and steel B consists of lath shaped MA constituents inside BF grains. Fractographical analysis showed that secondary cracks were initiated at the MA constituents along PAGB and propagated linearly into the GB/BF grains in the ICCGHAZ. The cracks initiated at the bulky MA at grain boundaries of steel A moved towards the pre-cracked or de-bonded discrete MA inside the grains and propagated through the interlinking of microcracks. In contrast, for steel B a notable percentage of cracks were initiated through the necklace-like MA at the grain boundaries and propagated through the BF lath. Pre-cracking of the slender MA present at the lath boundaries facilitated crack propagation in steel B. Furthermore, increasing the inter-critical temperature improved the impact toughness of steel A with a predominantly GB microstructure, whereas impact toughness improvement was limited in steel B with a BF microstructure.

Effect of small amounts of cerium on impact toughness and tensile properties of industrial Al-killed steel Q355D

The influence of cerium (Ce) on the mechanical properties of industrial steel was meaningful. And inclusions, grains, impact toughness, and tensile properties of industrial aluminium-killed Q355D were investigated by adding varying amounts of Ce. It was found that (i) inclusion of the sample without Ce was mainly manganese sulphide (MnS) and Al2O3-Mn(Ca)S, inclusion of the sample with adding 0.0017% Ce was mainly MnS- and Ce-based inclusions of CeAlO3–Ce2O2S–CaS, and inclusion of the sample with adding 0.0025% Ce was mainly MnS- and Ce-based inclusions of CeAlO3–Ce2S3–Mn(Ca)S; (ii) the number of MnS inclusions had decreased and shortened by increasing Ce. Meanwhile, Ce-based inclusions moved in the direction of decreasing size by increasing Ce; (iii) the grains were refined by adding Ce. In particular, fine acicular ferrite was formed by adding 0.0017% Ce; and (iv) the low-temperature impact toughness was best, and yield strength was the highest for the sample with adding 0.0017% Ce, which was attributed to the contribution of fine acicular ferrite and Ce2O2S inclusion.

Tailoring the strength and low-temperature toughness of HSLA structural steel by adding trace Ce

In this study, the trade-off between strength and low-temperature toughness of high-strength low-alloy (HSLA) structural steel was solved by adding trace Ce, which increased yield strength by 5.4 % and Charpy V-notch (CVN) impact energy at −40 °C by 57.9 %. The strengthening and toughening mechanism was revealed by multi-scale characterization. The results show that the strain hardening ability is improved after adding Ce. The grain size is refined and the geometrically necessary dislocation (GND) density increases to ensure the strength improvement. The CVN impact specimens change from cleavage fracture to quasi-cleavage fracture. The grain size, inclusions and high angle grain boundaries (HAGBs) are refined and optimized, which enhances the resistance to impact crack propagation and improves the low-temperature impact toughness.

Stepwise crystallization method combining isotactic polypropylene-based plastic waste film to prepare high-performance polypropylene random copolymer

Upcycling of waste plastic film is increasingly important at the background of energy shortage and environmental crisis. However, direct reuse of the waste plastics as reworked material inevitably downgrades the mechanical properties. Herein, a stepwise crystallization method was used to enable the recycling of waste isotactic polypropylene (iPP) film value-added in iPP-based homocomposites. In detail, the effect of β-nucleating agent (β-NA) and iPP on crystallization behaviors of polypropylene random copolymer (PPR) was investigated at first. The stepwise crystallization procedure was further introduced to promote the β-crystallization of PPR/iPP/β-NA composites in which the crystal structures, polymorph compositions and phase morphologies were systematically researched. At last, impact behaviors of PPR/iPP/β-NA composites were characterized and a penitential toughening mechanism was proposed. It was found that the stepwise crystallization boosted β-crystallization and growth of rubbery phase during the isothermal procedure, resulting in an increase of relative β-crystal content and low temperature impact toughness from 0 % and 2.02 kJ/m2 of neat PPR to 33.4 % and 3.06 kJ/m2 of PPR/iPP/β-NA composites. This work provides a simple, implementable, and effective method for the recycling of waste iPP films and the low-temperature toughening of PPR.

Crystallographic study on microstructure evolution and mechanical properties of coarse grained heat affected zone of a 500 MPa grade wind power steel

The effect of different welding heat inputs on the microstructure and mechanical properties of the simulated coarse grained heat affected zone (CGHAZ) of high-strength wind power steel with yield strength of 500 MPa has been investigated using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Charpy impact tests have demonstrated that there exists an optimum heat input of ∼20 kJ/cm that allows optimum impact toughness to be obtained for the CGHAZ. It was shown that this is related to the refined bainitic structure and the highest density of high-angle grain boundaries (HAGBs) with misorientation angle of more than 45°. In crystallographic visualization studies, it was shown that the weakest variant selection occurs for the bainite transformation in the optimal heat input, leading to the highest density of HAGBs with each Closed-packet group containing two or three Bain groups and showing a staggered arrangement structure. The contribution that can effectively deflect and prevent crack propagation during impact experiments has to come from the block boundary. However, it was also found that the center segregation induced by C and Mn reduces the low-temperature impact toughness of the core sample before and after simulated welding, and affects the fluctuations of impact toughness and fatigue performance of simulated CGHAZ. Mn segregation can have a genetic effect on the welding heat affected zone, inducing a lower temperature martensitic transformation, which in turn leads to a decrease in low-temperature toughness and fatigue crack arrest performance.

Experimental Study on Mechanical Properties of Reinforcement under Low-Temperature Impact

Abstract Ammonia is an important carrier of hydrogen energy, and the large-scale storage of liquid ammonia is the next trend of cryogenic energy storage. At present, the international mainstream liquid ammonia tank is generally about 50, 000 m3. The outer storage tanks generally adopt a metal structure, and the material applied for larger concrete full-capacity tanks is worth doing further research. Steel reinforcement bars (rebar) are an important construction material for full-capacity cryogenic energy storage tanks. The performance of rebar is an important index in the process of designing the strength of building structures. The factors affecting the properties of rebar are diverse, and reasonable control of each influencing factor can improve the performance of rebar used for liquid ammonia storage tanks. This paper carries out the study on the mechanical properties of the steel reinforcement bars from the concrete of the main container under low temperatures for storing liquid ammonia. Through experimental research on the failure of steel used in external tanks, it has been shown that temperature has a significant impact on the ductile-brittle transition. Further treatment can effectively prevent the brittleness of steel bars, improve the safety and reliability of storage tanks at low temperatures, and is of great significance for the design and construction of subsequent large liquid ammonia storage tanks.

Effect of Mo and Cr on the Microstructure and Properties of Low-Alloy Wear-Resistant Steels.

Low-alloy wear-resistant steel often requires the addition of trace alloy elements to enhance its performance while also considering the cost-effectiveness of production. In order to comparatively analyze the strengthening mechanisms of Mo and Cr elements and further explore economically feasible production processes, we designed two types of low-alloy wear-resistant steels, based on C-Mn series wear-resistant steels, with individually added Mo and Cr elements, comparing and investigating the roles of the alloying elements Mo and Cr in low-alloy wear-resistant steels. Utilizing JMatPro software to calculate Continuous Cooling Transformation (CCT) curves, conducting thermal simulation quenching experiments using a Gleeble-3800 thermal simulator, and employing equipment such as a metallographic microscope, transmission electron microscope, and tensile testing machine, this study comparatively investigated the influence of Mo and Cr on the microstructural transformation and mechanical properties of low-alloy wear-resistant steels under different cooling rates. The results indicate that the addition of the Mo element in low-alloy wear-resistant steel can effectively suppress the transformation of ferrite and pearlite, reduce the martensitic transformation temperature, and lower the critical cooling rate for complete martensitic transformation, thereby promoting martensitic transformation. Adding Cr elements can reduce the austenite transformation zone, decrease the rate of austenite formation, and promote the occurrence of low-temperature phase transformation. Additionally, Mo has a better effect on improving the toughness of low-temperature impact, and Cr has a more significant improvement in strength and hardness. The critical cooling rates of C-Mn-Mo steel and C-Mn-Cr steel for complete martensitic transition are 13 °C/s and 24 °C/s, respectively. With the increase in the cooling rate, the martensitic tissues of the two experimental steels gradually refined, and the characteristics of the slats gradually appeared. In comparison, the C-Mn-Mo steel displays a higher dislocation density, accompanied by dislocation entanglement phenomena, and contains a small amount of residual austenite, while granular ε-carbides are clearly precipitated in the C-Mn-Cr steel. The C-Mn-Mo steel achieves its best performance at a cooling rate of 25 °C/s, whereas the C-Mn-Cr steel only needs to increase the cooling rate to 35 °C/s to attain a similar comprehensive performance to the C-Mn-Mo steel.

Effect of Pre-Weld Heat Treatment on the Microstructure and Properties of Coarse-Grained Heat-Affected Zone of a Wind Power Steel after Simulated Welding

The effect of pre-weld heat treatment on the microstructure and low-temperature impact toughness of the coarse-grained heat-affected zone (CGHAZ) after simulated welding was systematically investigated through the utilization of scanning electron microscopy (SEM) and electron back-scattering diffraction (EBSD). The Charpy impact test validated the presence of an optimal pre-weld heat treatment condition, resulting in the highest impact toughness observed in the CGHAZ. Three temperatures for pre-weld heat treatment (690, 720 and 750 °C) were used to obtain three different matrices (Steel 1, Steel 2, Steel 3) for simulated welding. The optimal pre-weld heat treatment is 720 °C for 15 min followed by water quench. Microstructure characterization showed that there is an evident microstructure comprising bainite (B) in Steel 1 and Steel 2 after pre-weld heat treatment, while the addition of martensite (M) with the pre-weld heat treatment temperature exceeds Ac1 by almost 60 °C (Steel 3). These differences in microstructures obtained from pre-weld heat treatment influence the refinement of high-temperature austenite during subsequent simulated welding reheating processes, resulting in distinct microstructural characteristics in the CGHAZ. After the optimal pre-weld heat treatment, Steel 2 subjected to single-pass welding thermal simulation demonstrates a refined microstructure characterized by a high density of high-angle grain boundaries (HAGBs) within the CGHAZ, particularly evident in block boundaries. These boundaries effectively prevent the propagation of brittle cracks, thereby enhancing the impact toughness.

Revealing the mechanism of crack initiation and propagation in CGHAZ of S690QL welded joints through low-temperature impact tests with gradient setting of pendulum angle

As the most brittle areas of welded S690QL high-strength steel structures, coarse-grained heat-affected zone (CGHAZ) was crucial for the structural integrity of components. This paper designed an innovative low-temperature impact testing method with a gradient setting of pendulum angle to investigate the micro-mechanism of crack initiation and propagation in the CGHAZ of S690QL welded joints. The results reveal that continuous blocky M−A constituents were distributed along prior austenite grain boundaries (PAGBs), leading to stress concentration and crack initiation. During low-temperature impact processes, cracks propagate in a transgranular mode along {100} or {110} crystal planes. Due to the interaction between compressive stress and the crack tip, regions with high kernel average misorientation (KAM) such as PAGBs can divert the crack. The coarsening of prior austenite grains in the CGHAZ leads to a diminished hindering effect of PAGBs on crack propagation. The findings elucidate the complex relationship between microstructure and impact toughness of CGHAZ, providing insights into crack behavior and mechanisms in CGHAZ.