High-strength Products Research Articles

Machinability Studies of Aluminium-based Hybrid Metal Matrix Composites – A Critical Review

Aluminium composites are being used in many industries like automobiles, aeronautical, signage, cabinetry, cladding and transportation. Aluminium has a lightweight, long lasting, weather resistance, fire resistance and ratio of strength- to- weight is high properties. In today's rapidly developing manufacturing industries, there are many challenges to use metal composites. Also, there is a need to do research on various input parameters, safety parameters and environmental impacts. now, today's era vehicle manufacturing companies are growing up faster. vehicle manufacturing companies are focusing on increasing speed and reducing weight of vehicles so it will be achieved by choosing appropriate metal compositions. For the machining process, a turning operation has been selected. As the material hardness increases cutting forces increase and there is a need to select proper material to cut these composites. For preparing various metal composites stir casting, sand casting, squeeze casting, in-setu method and powder metallurgy process were used. The aim of this study is to give better suggestions and understanding of which material composites should be used? What is the alternative metal by considering operating conditions for machining and performance parameters? Present study is being investigated considering cutting speed, feed rate and depth of the cut while machining and how it affects performance parameters such as high tool wear, hardness, strength, SR, castability and chips production etc. Suggested carbon fibre is an alternative and how it affects the motion of an object and how it adds value in safety by considering certain parameters.

DEVELOPMENT OF CALOTROPIS/COTTON BLENDED YARN AND ITS PROPERTIES

Natural fibres, which are an important part of the human environment, and also valuable raw materials used for textile and non-textile production. The use of natural fibres instead of materials such as glass fibres, carbon, and talc provides several advantages including low density, low cost, good specific mechanical properties, and biodegradability. Blending is the mixing of two or more masses of fibres so that the resulting mixture has the characteristics of the average of the component items. The most important reason for blending is the creation of new and more desirable effects.This study was conducted in Assam in the year 2021. Four different methods were used for the extraction of fibre from the peeled bark of tender stems of Calotropis gigantea plants and among which chemical retting with alkali (NaOH) was selected for the study. The study was carried out by blending Calotropis and cotton in three proportions (25:75, 50:50, and 75:25 ratios) and the properties of blended yarns were investigated. It was observed that the Cotton yarn has given a higher amount of TPI and extension than the blended yarn. Fifty: fifty blended yarn have higher tensile stress, and higher lea strength than the other yarn, and were the finest among the blends.The cotton yarn had a finer count, high lea strength, and more count strength product compared to blended yarns. It was also noticed that 50:50 blended yarn had high count strength product than the other combination.

29Si and 27Al NMR study of the structural transformation of calcined kaolin residue-based geopolymer using low alkali activator content for sustainable construction materials

Geopolymer commercialization efforts in parallel with unconventional research are the only pathway to achieve the large-scale deployment of geopolymer technology. Geopolymers with a low quantity of alkali activator produced by the compression process are one way to bring this technology to industry because of the higher strength and lower efflorescence of the product. In this work, calcined kaolin residue-based geopolymers with a low alkali activator content were synthesized by various Si/Al mole ratios with soluble silicate from Na2SiO3 to adjust the Si ratio. The effects of Si/Al mole ratios on the structural transformation, microstructure, and compressive strength of geopolymers containing low alkali activator content were studied. The structural transformation and microstructure of geopolymers were characterized by NMR, SEM, and BET, and the compressive strength was assessed using a mechanical testing machine. The results present that geopolymer synthesized with various Si/Al mole ratios of precursor materials impacted the change in polymerization degree of silicate species (Qn(mAl)) and aluminate species. The Q4(4Al) and Q4(3Al) structures were transformed into the Q4(2Al) structure, and the content of the AlIV structure decreased when the Si/Al mole ratio of geopolymer was increased to 1.58. However, the contents of Q4(4Al) and AlIV structures increased again when the geopolymer had a Si/Al mole ratio of 1.62. SEM/EDX and BET results of geopolymers presented denser matrices, more amorphous aluminosilicate gels, and higher Si/Al ratios in aluminosilicate gels, while the pore size and pore volume were quite small when the Si/Al mole ratio of precursor materials was increased. In contrast, the highest Si/Al mole ratio of 1.62 showed different properties. The compressive strength of geopolymer was maximized at a Si/Al mole ratio of 1.58, and the decline in compressive strength of geopolymer with higher Si/Al mole ratio was related to the contents of Si–O–Si, Si–O–Al, and Al–O–Al bonds, content of aluminosilicate gels, and properties of the microstructure. The geopolymer synthesis using calcined kaolin residue and low alkali activator content is considered an eco–friendly process, which uses waste materials and less chemicals, and obtains high-strength products.

Fatigue behavior of unidirectional fiber‐reinforced pultruded composites with high volume fiber fraction

AbstractPultrusion is a high‐volume manufacturing process for fiber‐reinforced polymer (FRP) composites ensuring high strength and quality products. However, research studies are very limited on the fatigue behavior of these products, especially with unidirectional fiber alignment. This study investigates the fatigue behavior of the unidirectional pultruded glass FRP (GFRP) composites with high fiber volume fraction ( ). Tension–tension fatigue loading was applied with different levels of applied stress, frequency, and gripping condition until failure. Results showed that the high composites have significantly low fatigue life cycle. Moreover, increasing the frequency showed better fatigue resistance, while the tabs geometry has insignificant effect on the fatigue behavior of the dog‐bone shaped specimens. Comparison with available literature showed that GFRP composites with high have lower fatigue performance than those with low . A fatigue capacity reduction factor is also proposed for unidirectional GFRP composites as a function of the .

Multiscale Characterization at Early Ages of Ultra-High Performance Geopolymer Concrete.

The main obstacle of using geopolymer as a construction repair material is its slow strength development rate, which is the most significant attribute of an early-age opening for traffic and striking-off formwork. Geopolymer technology has recently attracted huge interest as an alternative to traditional cementitious materials with low environmental impact. Thus, this study investigates the feasibility of developing an ultra-high performance geopolymer concrete (UHPGC) with the aim of achieving high early-age strength. For this purpose, UHPGC mixtures activated with different potassium hydroxide molarities and aluminosilicate material types were developed and examined being cured with different curing temperatures. The early strength and durability of the UHPGC after 8 and 24 h were investigated. Experimental results revealed that the optimal mix design of UHPGC corresponds to a KOH molarity of 16 M and a 30% silica fume content. Furthermore, former mixture cured at 100 °C gave superior 8 and 24 h early strength values of 79 and 134 MPa, respectively. Moreover, a superior interaction of slag, silica fume, and activator solution at early age for UHPGC is revealed by the microstructural characteristics examined by a field emission scanning electron microscope (FESEM) with energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy analysis, and thermogravimetric (TGA) techniques. It was also found that the compressive strength results and the results of the microstructure analysis are well coincided. The experimental results obtained in this study emphasize the feasibility of using developed UHPGC as an eco-friendly quick repair materials The development of one-part UHPGC as a quick, cost-effective, and high-strength product for all construction repair maintenance will lead to huge improvements in the structural capacity and durability of structural components.

Achievement of high strength and plasticity product of the nugget zone in friction stir welded high-Mn steel via controlling stacking fault energy

The high Mn steel (Mn ≥ 20 wt.%) is widely applied because of excellent cryogenic properties. In the fusion-welded high-Mn steel joint, the Mn vapor and segregation degrade the joint quality. Friction stir welding (FSW) produces a high-Mn steel joint without defect, but the nugget zone (NZ) exhibits a poor plasticity. In this work, the preheating was subjected to FSW high-Mn steel to improve the plasticity of the NZ. Compared with the as-welded NZ, the as-preheated NZ contained slightly coarser austenite with lower density of dislocations (6.7 × 1014 m−2), and had a lower stacking fault energy (SFE) (47.18 mJ m−2) at room temperature. The lower SFE caused the deformation mechanism of dislocation slip and active twinning-induced plasticity (TWIP) in the as-preheated NZ owing to the lower back stress and critical twinning stress. Subsequently, a high strength and plasticity product of 62 GPa% was achieved in the as-preheated NZ, which was consistent with high strain hardening rate. At cryogenic temperature of −196 °C, the SFE of the as-preheated NZ decreased to 35.66 mJ m−2, but more active TWIP besides dislocation slip was found during tension. Therefore, the as-preheated NZ exhibited excellent strength and plasticity product of 91.9 GPa%. Furthermore, the yield strength of the as-preheated NZ was slightly reduced, which was attributed to the decreased of dislocation density and grain growth.

The relationship between austenite morphology and continuous TRIP effects in forged 4Mn steel

In this study, we developed forged medium-Mn steel (4Mn-3Al-0.38C) with a high product of tensile strength and elongation (PSE) (68.5 GPa·%). The PSE initially increased and then decreased with the quenching temperature. Austenite with various morphologies (including lath, block, flake, and equiaxed types) was obtained in the sample quenched at 730 °C (F730), and it continuously transformed into martensite (67%) during the tensile process. The different austenite morphologies exhibited different stability. The lath and block austenites transformed into martensite in the early deformation stage, followed by the flake and equiaxed austenites. Therefore, transformation induced-plasticity (TRIP) effects occurred continuously in a large strain range to reduce strain localization and stabilize the change of the work hardening rate, providing theoretical guidance for controlling the microstructure of high-PSE medium-Mn steels.

Role of Al element in tailoring the austenite mechanical stability and tensile properties of medium Mn steels

Al is generally employed as a key alloying element to tailor the austenite mechanical stability and mechanical properties in medium Mn TRIP steels. However, the effect of Al on the austenite stability has been limitedly studied, leaving contradictory results without a self-consistent explanation. This study addressed this issue through a systematic study of medium Mn TRIP steels with compositions of 0.2C–8Mn-0/1.5/3Al (wt.%), while providing new insights into the factors influencing austenite stability and mechanical properties. It was found that the variation of the Mn distribution in austenite from non-equilibrium to near-equilibrium state and the weakened strain incompatibility between phases due to sufficient recovery of tempered martensite can be achieved with the addition of Al, which contributed to slowed strain-induced martensite transformation (SIMT) and improved austenite stability in the experimental steels annealed at low temperatures in the two-phases region, resulting in a decrease in ultimate tensile strength (UTS) and an increase in total elongation (TE). Furthermore, fully recovered tempered martensite with the hardness much lower than that of austenite was obtained in the 3Al steel annealed at a high temperature in the two-phase region, which led to a significant reduction in yield strength and thus low UTS. Meanwhile, heterogeneous strain distribution was induced by the remarkable gap in hardness between the two phases, which can be responsible for the relatively high austenite mechanical stability. The varying strain states and variation of Mn distribution in austenite can be achieved for the medium Mn TRIP steels with different Al contents, contributing to a wide range of UTS&TE combination with high strength and elongation product (≥40 GPa·%). And the elucidation of the effect of different strain states also opens a new window to adjust the austenite stability and mechanical properties of medium Mn TRIP steels.

Improved strength performance of rubberized Concrete: Role of ground blast furnace slag and waste glass bottle nanoparticles amalgamation

Production of high strength and sustainable concrete by recycling various industrial wastes in an eco-friendly way to reduce the landfill problems remains challenging. Ever-increasing disposal of million tons of waste tyres worldwide posed serious environmental concern. The reuse of waste tyres in concrete as fine and coarse aggregates was shown to enhance its strength performance and solve the landfills-related environmental issues. Thus, new types of rubberized concrete mixes with improved bond zone and strength performance were produced by combining the waste rubber tyre aggregates (WRTAs), waste glass bottle nanoparticles (WGBNPs) and ground blast furnace slag (GBFS) with ordinary Portland cement (OPC). The designed concrete mixes contained 30% of crumb rubber as substitute of the natural fine and coarse aggregates wherein OPC was replaced by 20% of GBFS and various WGBNPs contents (3, 6, 9 and 12%). The workability performance, microstructures, and strength properties of the proposed mixes were evaluated using various tests. Concrete containing 6% of WGBNPs showed significant enhancement in the bond zone between cement paste and crumb rubber surface wherein the compressive strength was increased by 14% compared to the control specimen. The microstructures analyses of WGBNPs blended concretes displayed the formation of dense gels and less pores with acceptable engineering properties. It was asserted that concretes obtained by blending GBFS, WGBNPs and WRTAs with less OPC can be the potential green construction materials with immense benefits for the environment, thus minimizing the greenhouse gases emission and landfill requirements.

A highly effective strain screened from soil and applied in cementing fine sand based on MICP-bonding technology

Soil cementation based on microbially induced calcite precipitation (MICP) technology is a new research hotspot in the field of biogeotechnical engineering. However, due to the presence of only calcium bonds among particles, MICP-cemented soil shows obvious brittleness, which is the bottleneck of the application of MICP technology in geotechnical engineering. MICP-bonding technology can improve the shortcoming of high brittleness of the calcium bond by increasing the plastic bond among matrix particles. Based on MICP-bonding technology, this study isolated a high-efficiency strain named XR1#, which has the ability to produce both urease and extracellular polysaccharide. Gene sequencing identified the strain as Bacillus oceanicus. The superiority of XR1# bacteria is its ability to induce mineralization and polysaccharide production at the same time. Through the combination of calcium carbonate crystal filling and extracellular polysaccharide bonding, the strength and ductility of the sand column were improved, and the brittle characteristics of traditional MICP technology were reduced. By studying the effect of nutrient elements of the culture medium on calcium precipitation and polysaccharide yield, the two metabolites of XR1# bacteria could be artificially regulated. In an experiment with microbial-cemented fine sand, compared with the traditional Sporosarcina pasteurii, XR1#-cemented sand columns had high production and uniform distribution of calcium carbonate, high strength, and good ductility, and showed obvious advantages. This study provides a new strain with high efficiency and multiple functions for MICP-bonding technology and a new research idea for reducing MICP brittleness.

The activation of compression twin pairs and plasticity improvement of directionally solidified Mg alloy

The <112¯0> orientated Mg-4.70Zn-0.38Y-0.14Zr alloy with high product of strength and elongation (PSE = 5346 MPa•%) was prepared using directional solidification technology. Electron Back Scatter Diffraction (EBSD) and High Resolution Transmission Electron Microscopy (HRTEM) were applied to explore the deformation mechanism and plasticity improvement of experimental alloys. Experiment results showed that the dominant deformation systems were non-basal slipping systems and compression twin pairs (CTPs). High critical resolved shear stress (CRSS) of non-basal slipping system increased the yield strength (180 MPa) and tensile strength (198 MPa). The CTP followed the geometrical relationship of TP1 (twinning plane of variant1)∥TP2 (twinning plane of variant2) and appeared in a wider misorientation range than tensile twin pair which was classified as twinning shear transmission and had high geometric coordination factor (m’). Calculation results showed that the stress concentration at the junction of CTP and grain boundaries was the same as inside the compression twin. 60% of x/<11 2¯ 0> (0°≤x < 180°) grain boundaries in experimental alloy satisfied this geometrical relationship, leading to the general activation of CTP and plasticity improvement (elongation is 27%).

In situ modification of case-hardening steel 16MnCr5 by C and WC addition by means of powder bed fusion with laser beam of metals (PBF-LB/M)

Typical high-strength products are made from carbon-rich steels possessing relatively high carbon content, thus reducing weldability. In this work, preliminary studies on designing and tailoring a low-alloyed steel for the laser-based powder bed fusion (PBF-LB/M) process by adding carbon black (C) nanoparticles and tungsten carbide (WC) particles for enhancing the material properties are provided. First, the base material 16MnCr5 is modified with different concentrations of C and WC. It was found that an increased C and WC content resulted in an elevated material hardness in the as-built state. However, this comes at the cost of a poorer processability as pore formation increased for C-modified and crack tendency increased for WC-modified 16MnCr5. When applying a post-process quenching and optional tempering heat treatment, material hardness in the range of 615 HV can be achieved for C-enriched 16MnCr5 in the tempered state, which would be suitable for bearing and gearing applications. The addition of WC particles favored an improved wear resistance which is twice as high as the one of C-modified material for similar material hardness, showing the enormous potential of WC addition for reducing the wear rate. Complementary SEM and EDX analyses show that both the dilution and bonding zone of the WC particles are affected by the processing conditions and the WC concentration. Furthermore, it was found that a nearly defect-free fabrication of WC-enriched 16MnCr5 was possible for up to 2.5 wt.-% of WC, proving that the occurring defects are highly sensitive to the WC concentration.

The role of SSC cycle in ice hockey off-ice training

The Stretch and shortening cycle (SSC) is one of the most common used mechanism in a human body. The objective of this study was to determine a level of slow and fast stretch-shortening cycle utilization in elite ice hockey players and prescribe some off-ice training recommendations. The sample included 23 professional ice-hockey players of the Slovak Tipos league team HKM Zvolen (2 goalkeepers, 7 defenders, 14 forwards; age 26 ± 4.79 years; height 182.87 ± 6.28 cm; bodyweight 87.22 ± 6.54 kg) in this research. The Depth jump (DJ) test, the Bilateral squat jump test and the Bilateral counter-movement jump test were recorded in order to analyze the players’ ability to use fast and slow SSC cycle in lower limbs. The results showed no correlation between DJ and SJ or CMJ tests. However, Pearson correlation revealed strong correlation between SJ and CMJ (p &lt; 0.01, r2 = 0.949). 1 player achieved better score in CMJ test within the range between 10 – 15 % (11.97 %). 16 players scored better in CMJ test than SJ, but the percentage difference was insufficient (from 1.46 to 8.20 %) and finally higher SJ performance than CMJ performance was measured in 6 players (from 0.47 to 16.3 %). 6 players, who don’t utilize SSC efficiently due to their poor tendon stiffness compared to high explosive muscle strength production were instructed to add more plyometric exercises to their training regimen. On the other hand, 16 players were more prone to injury due to insufficient load bearing capacity compared to their ability to generate power. They were instructed to add more maximal strength exercises and strength exercises with emphasis on eccentric phase of movement in order to build the capacity for decelerative movements. DOI: https://doi.org/10.24040/sjss.2021.7.2.40-48

ABOUT TECHNOLOGICAL FEATURES OF PRODUCTION OF REINFORSING BARS FROM PEARLITE GRADE STEELS

Formulation of the problem. In the production of coiled rolled products from perlite grade steels, metallurgical enterprises encounter with the sorting of some batches of continuously cast billets or commercial products due to non-compliance with regulatory requirements. One of the alternative ways of using such blanks can be their reassignment for the production of thermally hardened reinforcing bars. In accordance with the edition of GOST 5781-82, it was possible to produce hot rolled reinforcing bars from steel grade 80C (carbon content 0,74…0,82 %), and according to TU 14-15-339-94 – thermally hardened with a carbon content of 0,50…0,85 % C. In world practice, reinforcing bars of a strength class similar to classes A800…A1000 (DSTU 3760:2019) are made mainly of high-carbon steels. The main type of stressed reinforcement in the EU, USA, Canada and Great Britain are rods with a nominal diameter of 26…40 mm of strength class 835…1030 MPa and 26…36 mm of strength class 1080…1230 MPa. An analysis of the requirements for reinforcing bars according to various regulatory documents shows that in the standards of Canada, the USA and the UK, the carbon content is not standardized, but according to the standards of Japan and Ukraine it is 0,45…0,80 % and 0,13…0,37 % respectively. According to the requirements of international standards, the minimum values of the yield strength and strength correspond to the reinforcing bar A800 (DSTU 3760:2019). Therefore, for the possibility of producing reinforcing bars from high-carbon steels, it is necessary to establish rational temperature-time conditions for heat hardening modes, which will ensure that the finished metal products comply with the requirements of DSTU 3760:2019. Purpose. Determine the influence of the parameters of the technology of thermal hardening on the features of the formation of the structure and mechanical properties of reinforcing bars made of steels with a carbon content of 0,50…0,90 %. Results. The possibility of producing reinforcing bars of strength classes А800 and А1000 from steels С56DВ, C70DВ, C80DВ and C82DВ (EN 16120-2:2017) using intermittent and interrupted quenching methods has been scientifically proven. In accordance with the results obtained, the industrial production of reinforcing bars of strength classes A800 and A1000 from these steels is expedient, since it will contribute to the improvement of technical and economic indicators in the production of coiled steel from perlite grade steels intended for high-strength products (cold-worked rebar, metal cord, bead wire, spring wire, reinforcing ropes, etc.). Based on the results of industrial experiments, a technical agreement was developed and approved for the production of pilot batches of thermally hardened reinforcing bars of strength classes A800 and A1000 from steels containing 0.50...0.90 % carbon.

Low-temperature superplasticity of ultrafine-grained near β titanium alloy

Studies of the low-temperature superplasticity (SP) of ultrafine-grained (UFG) near β alloy Ti-5Al-5V-5Mo-1Cr-1Fe at a temperature of 823 K (∼0.42 Tm) in the range of strain rates (2.0–6.9)·10−3 s−1 have been carried out. It is shown that for an UFG alloy with an average grain size of d ∼ 0.17 µm, obtained by the method of multi-axial pressing, the value of the relative elongation to failure exceeds 950% at a strain rate of 2·10−3 s−1. Annealing of the UFG alloy at a temperature of 873 K for 1 h does not cause a noticeable increase in the average grain size (d ∼ 0.23 µm), but leads to the transition of a part of grain boundaries to a more equilibrium state and a decrease in elongation to failure by more than 3 times in the range of strain rates. The study of the evolution of the microstructure under tension at a rate of 2·10−3 s−1 showed that in both states of the alloy up to an elongation of 150%, the average size of the elements of the grain-subgrain structure practically does not change, which is due, among other things, to the appearance of new grains less than 100 nm in size during the SP deformation. It is shown that the significantly lower elongation to failure of the UFG Ti-5Al-5V-5Mo-1Cr-1Fe alloy subjected to annealing may be due to the hindered accommodation of grain boundary sliding during the SP deformation by intragranular dislocation slip because of the transition of individual grain boundaries to an equilibrium state. The preservation of the UFG structure of the alloy with high strength characteristics under conditions of low-temperature superplasticity creates good prerequisites for obtaining high-strength products of complex shape in the regime of SP forming.

Comparison between growth performance in two silvopastoral systems comprising trees, short-lived perennial shrub, a forage, and livestock)

We aim to determine the growth performance of two 20-year-old silvopastoral systems comprising two timber trees, a palm tree), a short-lived perennial shrub, a forage and livestock; and to investigate fibre features and certain physical and mechanical properties of two timber trees (Myracrodruon urundeuva and Peltophorum dubium) in two plantation systems. The first system is called MP with two timber trees and the second one is called MPS with two timbers and a palm tree. The studied systems showed that it was possible to successfully combine fast-growing species, animals, forage and woody tree species, with a production cycle of more than 50 years of different goods and services (e.g., ornamentals, palm hearts, landscaping, fruits, seeds, bee pasture, meat, and wood). The height, diameter and volume for M. urundeuva trees in the MP system were greater than in the MPS system, whereas no difference between the systems was observed for P. dubium. By comparison, the growth and volume in P. dubium were greater than in M. urundeuva. For wood properties, it was shown that both systems can be used successfully, but the MPS system performed better than the MP system, in the aim of wood production of high mechanical strength and calorific value. In addition, the MPS intercropping system can yield more goods and services than the MP system, both systems bring returns with short-term (bean seed, forage, pasture), medium-term (forage, palm products, pasture, wood), and long-term (wood) financial returns.

Experimental Investigation of Suitable Cutting Conditions of Dry Drilling into High-Strength Structural Steel.

Dry machining is one of the main ways to reduce the environmental burden of the machining process and reduce the negative effect of the cutting fluid and aerosols on operators. In addition, dry machining can reduce overall machining costs and, in the case of large workpieces, reduce the extra work associated with removing residual cutting fluid from the workpiece and adjacent area. For high-strength structural steel products, it is typical to drill holes with larger diameters of around 20 mm. Therefore, this work is devoted to the investigation of the dry drilling process carried out on a workpiece made of S960QL steel with a helical drill with a diameter of 21 mm. The aim was to find suitable cutting conditions for dry drilling with regard to process stability and workpiece quality. An experiment performed with a coolant served as a comparison base. A dry drilling experiment was performed with cutting speeds from 30 to 70 m·min−1 and feeds from 0.1 to 0.3 mm·rev−1, and with the results of this experiment, the same experiment with flood cooling was performed. During the drilling process, spindle torque values were recorded using the indirect spindle current recording method. The macroscopic chip morphology was studied to understand the cutting process. The chip thickness ratio was measured, as well as the maximum diameter of spiral chips. On the final workpiece, the qualitative and dimensional parameters of the holes were evaluated, such as the diameter, cylindricity and surface roughness, depending on the change in the cutting conditions and cutting environment. Evaluation of the obtained data led to the following conclusions. When drilling the S960QL material, there is only a very small increase in the drilling torque during dry drilling compared to drilling with cutting fluid. The increase in friction demonstrated by the chip thickness coefficient is significant. The influence of the environment on the dimensional accuracy showed a tendency for a slight increase in the holes’ diameters during dry machining. In comparison, the cylindricity of the dry-drilled holes shows a lower deviation than the holes drilled with cutting fluid. The surface roughness of the holes after dry drilling is affected by the increased friction of the outgoing chips, despite the resulting parameters being very good due to the drilling technology standards. This work provides a comprehensive view of the dry drilling process under defined conditions, and the results represent suitable cutting conditions to achieve a stable cutting process and a suitable quality of drilled holes.

Recrystallisation before austenitization for improved microstructure and properties in automotive steel sheets with high product of strength and elongation

This study investigated the effect of recrystallization before austenitizing transformation (i.e., pre-recrystallization) on the microstructure and properties of 22Mn2Cr cold-rolled automotive steel sheets based on continuous annealing at 700 °C for various holding times. Subsequently, the samples were heated to an austenitizing temperature of ∼850 °C, which led to the formation of a fine austenite grains via nucleation at the dislocations during reheating. The austenite grain size was more refined when samples were pre-recrystallized at 700 °C for several minutes compared to those directly heated to 850 °C, which was attributed to combined grain refinement from recrystallization and austenite phase transformation. This refined austenite grain size led to a finer bainite grain size in the cooled final product. The strength of the steel decreased slightly (∼1200 MPa), but the elongation (∼19%) and product of strength and elongation (∼23 GPa%) were significantly enhanced by the pre-recrystallization treatment.

Real-time defect identification of narrow overlap welds and application based on convolutional neural networks

To improve the quality of narrow overlap welds and reduce cost during the high-strength production, it is essential to detect weld defects promptly by identification of the type of defects to provide solution accordingly. This paper proposes an integrated weld defect identification approach combing eddy current detection with 3D laser scanning based on Convolutional Neural Networks (CNN). The detection principle and equipment of the two detection methods are introduced. To fit the training process of CNN, two set of detection signals are preprocessed: a two-dimensional time-frequency diagram for eddy current signals using continuous wavelet transform and for laser images, weld edges are extracted and divided by region using image convolution and combining with integral graph. CNN model VGG16 is trained afterwards with data collected from one local manufacturer in Shanghai. It is discovered that performance of eddy current and laser image identification on different types of weld defects is different, and the accuracy can be increased with the two methods combined. Last, to achieve real-time detection of narrow overlap welding, a two-stage defect recognition model is built which greatly improves the efficiency of weld defect identification without affecting the accuracy of weld defect identification.

Automotive Steel with a High Product of Strength and Elongation used for Cold and Hot Forming Simultaneously.

A low-cost and easy-to-produce C–Mn–Cr automotive steel for both cold and hot forming is presented in this paper. The alloying element Cr was used to replace Mn in medium-Mn steel and instead of B in hot-formed steel, in order to achieve microstructure control and hardenability improvement, replacing the residual austenite-enhanced plasticization with multidimensional enhanced plasticization through multiphase microstructure design, grain refinement, and dispersion enhancement of second-phase particles. The products of strength and elongation for the cold-formed and hot-formed steel were 20 GPa·% and 18 GPa·%, respectively, while the tensile strengths were more than 1000 MPa and 1500 MPa, respectively. This new automotive steel was also characterized by good oxidation resistance. The mechanisms of strength and plasticization of the experimental automotive steel were analyzed.