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Surface roughness is affected by the tool geometry, feed rate, overcutting by built-up edge, and tool vibration in the depth of the cut direction. However, dividing the roughness value into each component is difficult. Therefore, a new prediction method for the position of the tool contour on the roughness curve is proposed to divide the measured roughness value into components. This proposed method consists of two processes. In one, the roughness curve is divided into the roughness curve formed during each revolution of the work material regardless of the clarity of the feed marks. The other is the process that predicts the vertical position of the tool contour. If the vertical position of the tool contour can be predicted, the vibration and overcutting components of roughness can also be predicted. In this study, the transition of roughness components such as the theoretical roughness, vibration width, and overcutting is studied with the increase in the cutting distance in the turning of chromium molybdenum steel, JIS SCM435. When supplying a 10% emulsion mist, the measured Rz is smaller than that of the dry condition. In both the dry and mist supply conditions, the measured Rz increases from the beginning of cutting then decreases and then increases again with the increase in the cutting distance. The largest component of the total roughness in both the dry and mist supply conditions is the theoretical roughness Rth. The ratio ranges between 50.3% and 78.7%. Regardless of the cutting conditions, the vibration width in the depth of the cut direction is relatively constant. The overcutting slightly increases after the start of cutting, then decreases when the maximum contact length exceeds approximately 0.1 mm. The proposed method verifies the ratio of the surface roughness components and is an effective method for improving the surface roughness. [ABSTRACT FROM AUTHOR]

Welded structures, specifically their fusion and heat-affected zones, are majorly prone to embrittlement and enhanced corrosion due to the induced residual stresses resulting from the complexity of the heating and cooling cycles during welding. In this work, TIG welding of AISI 4140 alloy steel (chromium–molybdenum steel) was done using the filler wire ER80S-B2 (AWS A5.28) followed by post-weld heat treatment. A comparison of base metal, as-welded, and post-weld heat-treated samples is made based on residual stresses, corrosion resistance, and mechanical properties. Due to the presence of stresses and the formation of unstable martensitic structure, the as-welded samples depicted the highest corrosion rate (8.982 mpy) as compared to the post-weld heat-treated sample (5.707 mpy) which is closer to that of base metal (5.627 mpy). Post-weld heat treatment relieves the residual stresses which results in the enhancement of corrosion resistance. The tensile strength for the base metal, as-weld and PWHT samples come out to be 739, 763, and 744 MPa, respectively. Ductility, on the other hand, is restored by post-weld heat treatment which was compromised in the as-welded samples. [ABSTRACT FROM AUTHOR]

The presented publication is focused on increasing the productivity and efficiency of machine production of precision holes. Considerable attention was paid to the influence of the pre-preparation and drilling technology on the quality of the reamed hole. The material selected for machining was chromium-molybdenum steel 42CrMo4 QT. The cluster analysis is implemented to evaluate the experimental results obtained by measuring the cylindricity and surface roughness of the drilled and reamed holes. The factor of hole pre-preparation technology was selected in two quality levels, and the factor of drilling technology in four quality levels. The constant factors were carefully controlled during the experiment, i.e., other possible influences were excluded or minimised. Under constant cutting conditions, the experiment of the subject machining process was carried out. The cutting process parameters investigated were the cylindricity and the roughness of the machined surface Ra. The novelty and contribution of this research lie in confirming the assumption that drilling technology influences hole quality primarily, whereas hole pre-preparation technology has a secondary effect. [ABSTRACT FROM AUTHOR]

[Display omitted] • Excessive internal scale growth led to a change of corrosion mode from general to localized. • The localized sulphidation and grooving is interpreted as a form of stress-assisted corrosion. • Overheating promoted a synergy among corrosion mechanisms at the internal corrosion zone. • Overheating and carburization led to internal carbide coarsening and material softening. • Improper design temperature calculation was a key factor in the premature failure. The failure of a few 9Cr-1Mo steel tube sections, used at the floor section of a radiation coker furnace to preheat bitumen (with approx. 5% sulphur), was investigated. The tubes exhibited both circumferential and longitudinal depressions/grooves as well as cracks on the hot side after only four years of service. Metallurgical failure analysis revealed how a synergy among several damage mechanisms including carburization, oxidation, sulphidation, softening, cyclic damage, metal loss (general and localized) and creep compromised the high-temperature strength of the tubes prematurely. Two main factors in the failure were: (1) lack of consideration for general metal loss in maximum metal temperature calculation (i.e. a design factor) that led to overheating, and (2) inadequate internal scale removal (i.e. a maintenance factor) that led to scale cracking and grooving (i.e. a form of localized corrosion). Discussion on the premature life of the tube and the metal loss mechanism (identified as a form of stress-assisted corrosion) is presented with reference to the applicable API recommended practices and standards. The article should be of interest to petrochemical and oil refining industries throughout the world as premature failures of heater tubes is a global issue. [ABSTRACT FROM AUTHOR]

This study aims to establish fundamental knowledge for online non-destructive inspection in the laser quenching process utilizing acoustic emission. Acoustic emission is the transient elastic wave phenomenon due to release of strain energy in a solid material. And it is well known that the martensitic transformation can induce the acoustic emission. In this study, the acoustic emission monitoring of martensitic transformation during laser quenching experiment was conducted with the chromium molybdenum carbon steel (SCM440 in Japanese Industrial Standards) as the specimen. The experiment was carried out with seven kinds of laser irradiation power for different volume generation of heat-affected zone. After experiment, the martensite structure was confirmed at the heat-affected zone and the volume of the martensite structure within the zone was estimated. Only the specimen irradiated by the lowest laser power had no martensite structure. The acoustic emission waves were analyzed using parameters that showed the generation time duration and scale of source phenomenon. As a result, the relationship between the volume of martensite structure and information of acoustic emission was positive. It was suggested that the acoustic emission monitoring have application for the online non-destructive inspection for the laser quenching process. [ABSTRACT FROM AUTHOR]

Chromium-molybdenum steel (16Mo3) is widely used in petroleum, gas, automotive, and construction industries due to its good oxidation resistance and mechanical properties at moderately elevated temperatures. The aim of the research was to evaluate the corrosion susceptibility of 16Mo3 steel in hot rolled and aluminized states. Aluminization was performed by diffusion pack aluminization process at 900 °C / 2h and 730 °C / 4h, respectively. Electrochemical corrosion testing included measuring open circuit potential (EOCP), linear polarization resistance (LPR), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) in potassium phosphate buffer (KH2PO4, pH = 7). Optical microscopy (OM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS) were used for surface layer microstructure characterization before and after corrosion tests. It was demonstrated that corrosion resistance of aluminized steel increased substantially. Corrosion properties were related to the structure and properties of intermetallic phase (FeAl, FeAl2 and Fe2Al5) that formed on the surface of 16Mo3 steel. [ABSTRACT FROM AUTHOR]

Oil and gas production casing and compression pipes used for structures in oil and gas deposit structures contaminated with a high concentration of hydrogen sulfide should have alongside high strength and cold resistance good sulfide stress corrosion cracking resistance. Medium carbon steels alloyed with chromium and molybdenum are used extensively for such products. After quenching and tempering in the temperature range 680–720ºC these steels possess increased yield and tensile strengths along with good ductility. Alloying with molybdenum and vanadium provides a marked increase in sulfide stress corrosion cracking resistance with an increase in tempering temperature in the range indicated. [ABSTRACT FROM AUTHOR]

Featured Application: Feature Applications: This paper proposes a data-driven approach based on convolutional neural networks to measure the Vickers hardness value directly from the image of the specimen to get rid of the requirement of the manually generation of indentations for measurement. Hardness testing is an essential test in the metal manufacturing industry, and Vickers hardness is one of the most widely used hardness measurements today. The computer-assisted Vickers hardness test requires manually generating indentations for measurement, but the process is tedious and the measured results may depend on the operator's experience. In light of this, this paper proposes a data-driven approach based on convolutional neural networks to measure the Vickers hardness value directly from the image of the specimen to get rid of the aforementioned limitations. Multi-task learning is introduced in the proposed network to improve the accuracy of Vickers hardness measurement. The metal material used in this paper is medium-carbon chromium-molybdenum alloy steel (SCM 440), which is commonly utilized in automotive industries because of its corrosion resistance, high temperature, and tensile strength. However, the limited samples of SCM 440 and the tedious manual measurement procedure represent the main challenge to collect sufficient data for training and evaluation of the proposed methods. In this regard, this study introduces a new image mixing method to augment the dataset. The experimental results show that the mean absolute error between the Vickers hardness value output by the proposed network architecture can be 10.2 and the value can be further improved to 7.6 if the multi-task learning method is applied. Furthermore, the robustness of the proposed method is confirmed by evaluating the developed models with an additional 59 unseen images provided by specialists for testing, and the experimental results provide evidence to support the reliability and usability of the proposed methods. [ABSTRACT FROM AUTHOR]

Simufact Forming covers the complete spectrum of working on forming technologies like rolling, forging, and sheet metal forming. In this paper, finite element comparative analysis was performed on two chromium- and molybdenum-alloyed steel billets, namely 42CrMo4 and 16CrMo4 alloyed steels, using multi-step forming process of hot closed die forging process using Simufact Forming software. 42CrMo4 alloy steel is most commonly used in making of automobile components, and 16CrMo4 alloyed steels are commonly utilised in the area of ship building, airplanes, etc. While working with these materials, with the help of forging process, lot of stresses, strains and temperatures will develop. In this paper, three state variables, namely effective plastic strain, equivalent stress and temperature, for two materials at the end of multi-step forming processes like chamfering, preforming and final forging stages are evaluated and compared. In cooling process, the initial temperature of billet is maintained at 1250°C for both materials. Finally, comparative analysis of two alloyed steel billets was done by considering three-state variables. [ABSTRACT FROM AUTHOR]

• FCG tests on ausformed and non-ausformed JIS-SCM440 were conducted in 90 MPa H 2. • Ausforming improved FCG resistance in H 2 , even at a higher strength level. • Suppression of intergranular cracking enhanced hydrogen embrittlement resistance. • Modified grain morphology and cohesive strength changes influenced FCG resistance. Ausformed specimens of the chromium-molybdenum steel JIS-SCM440 were subjected to fatigue tests in both air and 90 MPa hydrogen gas. The results were compared with those of non-ausformed specimens of the same material with similar tensile strengths (≈ 950 MPa and ≈ 1050 MPa). The ausformed materials demonstrated excellent resistance to hydrogen-induced acceleration of fatigue crack-growth (FCG), effectively reducing the crack propagation rate under cyclic loading in hydrogen environments compared to their non-ausformed counterparts. They maintained an acceleration ratio (i.e., relative FCG rate in hydrogen with respect to that in air) within 10 to 40 times, an order of magnitude lower than that of the non-ausformed counterparts. Despite their high strength levels (i.e., tensile strengths greater than 900 MPa), the FCG rate in the ausformed materials was almost independent of loading frequency at a stress intensity factor range of 20 and 30 MPa·m1/2. Fractographic observations revealed that no intergranular fracture occurred in the ausformed materials, unlike in the non-ausformed ones. These findings suggest that two factors possibly caused the mitigation of FCG rate in hydrogen: (i) modification of the microstructure morphology, i.e., refinement and elongation, and (ii) an increase in the cohesive strength of interfaces under the influence of hydrogen. [ABSTRACT FROM AUTHOR]

An externally restrained stress relief cracking test was developed and demonstrated in testing susceptible and resistant to cracking welds in Cr–Mo steels. Compared to other externally restrained tests, it simultaneously applies stress and compensates thermal expansion during heating to post-weld heat treatment temperature and utilises digital image correlation for quantification of key characteristics of the stress relaxation and stress relief cracking phenomena. In contrast with resistant to stress relief cracking materials, susceptible materials experienced lower levels of stress relaxation, strain absorption, and sustained mechanical energy, with accelerated kinetics of strain accumulation and strain localisation leading to failure. The processes of stress relief cracking and stress relaxation were quantified as low strain – slow strain rate – low energy phenomena. [ABSTRACT FROM AUTHOR]

Increase the demand to produce complex shapes with high quality and dimensional accuracy such as production aerospace, cars, die sinking has been leading to increase the demand to use the non- traditional cutting operations such as wire electro-discharge machine (WEDM) rather than using the traditional operations. An idea to understand the effect of wire diameter, wire feed, pulsing (on/off) time on surface roughness, and metal removal rate of Cr-Mo steel during wire electrical discharge machining was investigated. Two Steel alloy samples with dimensions of (60 x50 x 20)mm were cut into four rectangular spaces with (5x10x20)mm at one side of each sample using wire cut (EDM) machine with a wire diameter of 0.25 mm and feeding rate 2 m/min for sample 1 and a 0.3 mm diameter and 3 m/min feeding rate for sample 2. Pulse (on, off) time was (110, 50), (112, 52), (115, 55), (116, 57) corresponds to space 1, space 2, space 3, and space 4 in both steel block. Surface roughness and metal removal rate measurements were estimated. The results showed that wire diameter, feeding rate, and pulse (on, off) time is proportional with metal removal rate, while reversed with surface roughness. The wire diameter of 0.3 mm and a feeding rate of 3m/min enhanced better surface quality and productivity. Pulse (on, off) time is the most effective parameter. Best duration time was recorded at the values (116, 57)

The current study comprises thermal-induced stress distribution in submerged arc welded chromium-molybdenum (Cr-Mo) steel plate and its mitigation through pre- and post-weld heat treatment. Single-sided single-pass square butt weld joints were investigated for three different cases of welding, post-weld heat treatment (PWHT) and preheating and PWHT. Deep hole drilling (DHD) was employed to estimate the residual stresses across the plate thickness in the two most thermally instigated sections, i.e., FZ and HAZ of the welded joint. Finite element modeling was also carried out for welding and heat treatments. The volumetric double ellipsoidal heat source, element birth and death technique, solid-state phase transformation and creep phenomenon were incorporated in FE modeling. Post-weld heat treatment was found efficient in controlling residual stresses in both FZ and HAZ. However, post-weld heat treatment on preheated weld efficiently mitigated the residual stresses for much lower tensile values in FZ. Preheating also improved the uniformity of the residual stress distribution across the weld thickness in the post-weld heat-treated weld. The fair agreement was achieved in predicted and measured residual stresses results. It was also discovered that holding time does not affect the degree of stress relaxation in PWHT. [ABSTRACT FROM AUTHOR]

[Display omitted] • Choline chloride and propylene glycol DES for anodic treatment of 316 alloy steel. • Significant increase in corrosion resistance was found at 65 °C and 40 mA cm−2. • According to SEM analysis micro-irregularities on the steel surface were reduced. • Selective and excessive leaching of Fe from the surface in selected DES. • High corrosion resistance thanks to surface enrichment with oxidized Cr and Mo. AISI 316 alloy steel was polarized anodically in a deep eutectic solvent based on choline chloride and propylene glycol (1:2 M ratio) at the temperature range of 35–75 °C and the current density range of 10–60 mA cm−2. At certain parameters (i.e., 65 °C, 40 mA cm−2), a significant increase in corrosion resistance and surface gloss were found compared to the "raw" steel, but without a spectacular reduction in the roughness of the samples after the polarization process. The SEM analysis carried out allowed us to determine that despite the increase in roughness, micro-irregularities on the steel surface were reduced. Thanks to the ICP-AES tests, it was found that the increase in the overall roughness of the samples could be caused by the excessive leaching of iron from the surface in selected variable process parameters. XPS showed that the anodic polarization process increased the content of chromium and molybdenum compounds on the steel surface. In conclusion, this liquid may be a future replacement for the standard acid baths used for the AISI 316L electrochemical polishing process, but the optimal process conditions (as well as the use of appropriate bath additives) have yet to be determined. [ABSTRACT FROM AUTHOR]

High-quality materials should always meet the requirements of industrial or consumer applications with the development of advanced technologies. In recent years, high-entropy alloys (HEAs) have been developed as new alloy materials due to their superior mechanical properties. Besides, difficult-to-cut materials have been also widely used in many different industrial applications. (AlCrNbSiTiV)N coatings as HEAs have been usually grown on tool, engine parts, MEMS processing components, and thermoelectric materials using vacuum arc and mechanical alloy methods. Hence, in order to improve the performance of tools and surface quality of workpieces in coolant-free turning process, a high-power impulse magnetron sputtering (HIPIMS) system was used to deposit (AlCrNbSiTiV)N films on the tool surface. In this study, the film thickness, deposition rate, and surface morphology at different substrate temperatures in turning chromium-molybdenum steel were investigated. The (AlCrNbSiTiV)N films coated in this study was homogeneous and very compact and showed good adhesion strength. Experimental results showed that increasing the substrate temperature from 100 to 400 °C during sputtering process indeed could improve the mobility of the atomic surface, the density of the films, and the hardness of the films. The maximum hardness and the elastic recovery rate (Re) of (AlCrNbSiTiV)N films were found to be 41.07 GPa and 80.21%, respectively, when the substrate temperature was increased to 400 °C. In addition, the performance of coated tools by (AlCrNbSiTiV)N film was comparatively much better than that of uncoated tools, which possessed broad application prospects in the future. [ABSTRACT FROM AUTHOR]

When designing ballistic shields, it is of significance to know how materials behave at high strain rates. The paper presents results of the experimental investigation into the influence of the strain rate on the dynamic yield point of 40HM chromium-molybdenum steel. The behaviour of a material differs depending on impact speed, even if the impact energy remains the same. Dynamic tests were conducted on two specimens using two testing stations: a station equipped with a rotary hammer for testing at a speed reaching 40 m/s and a station accelerating the specimen to a high speed (160 to 270 m/s) and launching it to impact a hard, non-deformable shield. The dynamic yield point was determined by using the Taylor theory. To determine the impact speed, an optical measurement method and a digital high-speed camera were used. The impact speed was determined on the basis of the analysis of recorded images using a specialized software program. The impact speed was adjusted experimentally depending on the behaviour of the specimen material. The basic criterion for selecting the impact speed was that the requirement was fulfilled that the cylinder - as a result of the impact - succumbs to an evident plastic deformation without a visible material integrity infringement. The questions of plastic deformation, temperature influence, strain rate and stress-strain relation require an analysis of the formation and effects of dislocations. The unified constitutive law called Johnson-Cook's law describes the relations between the material's tension and strengthening ratio, and between strain rate and temperature. The tests indicated that a strain rate increase considerably improves strength properties of 40HM steel. [ABSTRACT FROM AUTHOR]

This study considers an innovative coolant nozzle that enables a remarkable reduction in grinding fluid consumption in cylindrical plunge grinding of chromium molybdenum steel (ISO 34CrMo4 / JIS SCM435) using a vitrified-bonded cubic boron nitride (CBN) wheel. This coolant nozzle has a simple structure consisting of ordinary nylon or polypropylene fiber brushes and an acrylic resin oil pool. This flexible brush-nozzle is suitably placed in contact with the wheel surface, and the grinding fluid is supplied along the brush to the wheel surface to form a fluid film to the wheel surface, while simultaneously scraping the "air belt." Thus, the grinding fluid adheres to the whole wheel surface by the "Coandă effect," and grinding fluid consumption is reduced to 0.5 L/min or less without causing any thermal damage to the ground surface. The cooling effect of this coolant nozzle is examined mainly by a grinding temperature measurement by means of a fiber-coupled two-color pyrometer. The nylon fiber brush is more effective than the polypropylene brush because of its high elasticity and good water absorption rate, which is related to the wettability. Even with such an extremely small amount of grinding fluid, the grinding force, surface roughness, and grinding temperature are nearly the same as those in the case of the conventional wet grinding. [ABSTRACT FROM AUTHOR]

The microalloying of low-alloyed steels with Nb can improve the strength-to-toughness balance. Such an effect of Nb is usually ascribed to the refinement of the grain structure occurring in the austenite regime during hot forming. In the present work, we report that Nb enhances the impact toughness of a low-alloyed Cr-Mo steel by a mechanism which has not been appreciated so far. The lower impact toughness in the Nb-free Cr-Mo steel is due to segregation of Mo to boundaries, which facilitates the formation of fine Mo-rich ξ-phase carbides lining up along the boundaries. This further promotes the nucleation and propagation of microcracks. The addition of Nb leads to the formation of Mo-enriched NbC particles. The interfaces between these particles and the matrix supply new preferential sites for precipitation of Mo-rich ξ-phase carbides upon subsequent tempering. In this way, Nb additions result in a decrease of Mo segregation to boundaries, significantly reducing the precipitation of ξ-phase carbides on grain boundaries, thus leading to improved impact toughness. In addition to the classical microstructural explanation (grain size effect), this chemical role of Nb sheds new light on the design strategies of advanced low-alloyed steels with optimized strength-to-toughness ratios. [ABSTRACT FROM AUTHOR]

Abstract The causes of through-thickness cracking in a continuous casting steel slab with low carbon and high alloys were investigated by observation of the fractured surface and microstructures of a fractured slab, and analysis of phase transformation through a continuous cooling transformation (CCT) diagram. Intergranular brittle fracture and ductile fracture were observed on the surface of the slab and inside the slab, respectively. A bainite and martensite microstructure was transformed in the vicinity of the slab surface where intergranular fracture occurred due to excessive water-cooling during continuous casting, and ferrite and pearlite were transformed inside the slab due to a slow cooling rate and relatively high temperature. Immediately after continuous casting, the temperature and the cooling rate for the surface of the slab were 300–450 °C and about 0.1 °C/s, respectively, and thus bainite and martensite on the surface of the slab were tempered simultaneously during transfer to the slab yard. As a result, the tempered bainite and martensite on the surface of the slab and the mixed microstructure of ferrite and pearlite inside the slab were transformed. However, segregation of P and S at grain boundaries was observed in the tempered bainite and martensite at the surface of the slab. The segregation of P and S at grain boundaries could occur by tempering at the temperature between 300–450 °C and the cooling rate as slow as 0.1 °C/s at the surface of the slab, and is a critical cause on 'temper embrittlement'. Therefore, it is believed that the intergranular fracture at the surface of the slab was due to the temper embrittlement, and ductile fracture occurred inside the slab having a mixed microstructure of ferrite and pearlite, which is ductile. Highlights • The surface and the inside of the slab were fractured in intergranular brittle fracture and in ductile fracture, respectively. • The surface of the fractured slab was transformed to bainite and martensite due to water-cooling during continuous casting, while ferrite and pearlite were formed inside the slab resulting from slow cooling. • Temperature between 300–450 °C and a very slow cooling rate of 0.1–0.2 °C/min during transfer to the slab yard after continuous casting contributed to temper embrittlement due to the segregation of P and S at the surface of the fractured slab with bainite and martensite, resulting in intergranular brittle fracture. [ABSTRACT FROM AUTHOR]

The effect of cooling rate on martensitic structure and carbides precipitation behavior was investigated based on Cr-Mo alloy steel with different quenching media of oil, water and 10% NaCl-water, respectively. The influence mechanism of martensite structure and carbide precipitates on mechanical properties was also studied. The results showed that martensite packets and blocks were refined with water quenching, however, they were coarse with oil or 10% NaCl-water quenching. Martensite laths were refined and dislocation density increased with increasing cooling rate. The carbides in tempered steel were coarse obviously with 10% NaCl-water quenching. The impact toughness deteriorated significantly with 10% NaCl-water quenching due to coarsening of martensite structure and carbides. [ABSTRACT FROM AUTHOR]

Highlights • Crack growth is predicted following alternatives of distinct complexity and accuracy. • Local stresses should be computed analytically in the uncracked body. • Failure assessment diagram is indispensable for detecting final failure accurately. • Remeshing technique yields similar predictions comparing to analytical algorithms. Abstract The objective of this work is to establish pertinent criteria allowing an optimal alternative to be chosen for calculating the inputs needed to make Run/Repair/Replace decisions and to program inspection plans for cracked wind turbine bearing rings. With this aim, the growth of a hole-edge through-crack was predicted analytically, simulated and measured in a 42CrMo4 steel plate subjected to mode-I cyclic loading. Different alternative procedures according to BS 7910:2013 fitness-for-service code were implemented. Unexpectedly, the numerical calculation of the local stresses in the uncracked body did not improve the estimations of the critical crack length and the number of cycles to failure performed following purely analytical alternatives. That alternative underestimated the critical crack length by 50%. Among the alternatives studied, the one based on numerically calibrated stress intensity factors and crack growth coefficients characterized at the corresponding stress ratios proved to be the most suitable one. Following that alternative, the fatigue life was found to be overestimated by 3.96% in the best scenario whereas the critical crack length was underestimated with an error less than 3%, determined using the Failure Assessment Diagram (FAD) as a failure criterion. [ABSTRACT FROM AUTHOR]

The continuous cooling transformation (CCT) behavior of eight 2¼Cr-1Mo steels from a statistically designed matrix was determined. These steels contained two levels of carbon (0.07 and 0.16 wt.%), manganese (0.35 and 0.85%), chromium (1.5 and 2.8%), and molybdenum (0.3 and 1.25%). Each steel was tested in a quenching dilatometer at five to six cooling rates between 725 and 1.2 °C/min. For each CCT sample, the change in length, microstructure, and macrohardness were determined. The ferrite content was also measured for samples cooled near the ferrite nose. Pearson correlation and multiple regression analyses were performed for various CCT diagram parameters. The correlation analysis showed that carbon and chromium contents significantly affected the critical temperatures and the bainite and martensite transformation temperatures. Increasing carbon content significantly increased the hardness for the bainite and martensite range of cooling rates, but hardness at slower cooling rates was unaffected by alloying elements. Regression equations were obtained for the critical temperatures and the ferrite nose cooling rate. [ABSTRACT FROM AUTHOR]

Abstract Due to the high material utilization and the associated resource and energy efficiency, production processes from the field of cold forging of steel are of great importance. At present, environmentally harmful lubricants have to be used to ensure process stability as well as low wear and friction. Due to environmental, economic and legislative aspects, there is an increased research potential to reduce or to completely substitute lubricants. To achieve the goal of lubricant free dry cold forging of steel, physical vapor deposition (PVD) coatings with self-lubricating properties are applied on forming tools. Promising for this application are PVD coatings on the basis of a (Cr,Al)N hard phase with embedded molybdenum and sulfur which simultaneously meet the requirements of high wear resistance and friction reduction. In the presented work, three self-lubricating coatings (Cr,Al)N+Mo:S deposited with varying bias voltage were investigated. The hybrid PVD technology, consisting of direct current and high power pulse magnetron sputtering dcMS/HPPMS, was used for the coating deposition in an industrial coating unit. Two different steels AISI D2 (DIN 1.2379) and AISI M2 (DIN 1.3343) were used as substrate materials. The influences of substrate material and heat treatments at T = 250 °C were investigated. The samples were analyzed with respect to the universal hardness HU and modulus of indentation E IT using nanoindentation. To determine the interfacial adhesion of the compound coating/substrate, Rockwell indentation and scratch tests were carried out. For the analysis of the tribological behavior, unhardened AISI 5115 (DIN 1.7131) was used as counterpart material. The influence of the elevated temperature on the friction and wear behavior was investigated by Pin-on Disk (PoD) at T = 250 °C and T = 23 °C. The wear of the basic bodies as well as the counterparts were analyzed by confocal laserscanning microscopy. The investigations have shown that the high temperature has a significant influence on the friction and wear behavior. The wear rate of the counterparts decreases by up to a factor greater than x = 100 compared to the test at T = 23 °C. Furthermore, the wear rates of the basic body of the uncoated reference specimen increase rapidly at tribological stress at high temperatures. The examined coatings exhibit high wear resistance at elevated temperatures. The contact surface was studied by Raman spectroscopy after the tribological tests. PoD tests have shown, that the applied coatings led to a significantly reduction in friction most likely due to the tribo-chemically induced formation of self-lubricating MoS 2 reaction layers. Highlights • Hybrid dcMS/HPPMS deposition of (Cr,Al)N+Mo:S coatings with varying bias voltage • Sulfur content as a function of bias voltage due to resputtering effects • Improved friction and wear behavior due to self-lubricating PVD coatings • Formation of tribo-chemically induced reaction layers • Tribo-oxidation in sliding contacts at varying temperatures [ABSTRACT FROM AUTHOR]

Microstructure and mechanical properties after induction hardening have a significant effect on the wear resistance performance and lifetime of 55CrMo steel ball screw. In the paper, the dilatometric curves were recorded at the different heating rate by a Gleeble-1500D thermo-mechanical simulator to determine the effect of heating rate on the austenitizing temperature of 55CrMo steel. Heat treatment of some specimens was performed by the Gleeble-1500D thermal simulator at the different heating temperature, holding time and cooling rate to investigate the effect of induction hardening parameters on the phase transformation, microstructure and microhardness of 55CrMo steel. Microstructure of specimen was analyzed using an optical microscope and a scanning electron microscope. Volume fraction of retained austenite was measured using an x-ray diffractometer. The mechanical properties were evaluated by a microhardness tester. The results show that the austenitizing temperature of 55CrMo steel increases with the increasing heating rate. Increasing the heating temperature, holding time and cooling rate of specimen is helpful in obtaining a uniform cryptocrystalline martensite. Volume fraction of retained austenite is less as the heating temperature is in the range of 900-950 °C. In the induction hardening of 55CrMo steel, the heating temperature should be in the range of 900-1000 °C. [ABSTRACT FROM AUTHOR]

The hot ductility of a low alloyed Cr-Mo steel has been investigated to evaluate the surface cracking sensitivity within the straightening or unbending regime during the continuous casting process. Tensile samples were subjected to various thermal treatments, including melting and solidification, and were tested at deforming temperatures ranging between 600 and 1100 °C using a strain rate of 10−3 s−1. Hot ductility was evaluated based on reduction in area measurement and metallographic investigations. The investigated steel exhibits a drop in ductility at around 800 °C due to intergranular cracking. Microstructural examinations and supplementary thermokinetic computer simulations were carried out to describe the evolution of the microstructure during solidification and cooling. [ABSTRACT FROM AUTHOR]

This work aimed to investigate the martensitic transformation and precipitation of CoCrMo alloys fabricated by selective laser melting (SLM) under aging heat treatment. SLM-fabricated CoCrMo alloy was a mixture of γ-phase and ε-phase, and the content of γ-phase was about 70%. The content of ε-phase increased with the aging time. A nearly pure ε-phase was achieved by aging at 900 °C for 10 h in the SLM-fabricated part. After aging treatment for a short-time, the microhardness of the parts decreased comparing to the AS-SLM probably due to the disappearance of the honeycomb precipitates. The EDS results showed that those granular precipitates in SLM900 and SLM750 are M 23 C 6 . The content of M 23 C 6 increased with aging time. The M 23 C 6 precipitates and martensitic transformation enhanced the microhardness. Specimens with highest microhardness were obtained by aging at 900 °C for 10 h. This result established the relationship between the heat treatment process, microstructure and microhardness. [ABSTRACT FROM AUTHOR]

The influence of hydrogen on the mechanical behaviour of a 42CrMo4 tempered martensitic steel was investigated by means of tensile tests on both smooth and circumferentially-notched round-bar specimens pre-charged with gaseous hydrogen in a pressurized reactor. Hydrogen solubility was seen to decrease with increasing tempering temperature. Moreover, hydrogen embrittlement measured in notched specimens was much greater in the grades with higher hardness, tempered at the lowest temperatures, where a change in the fracture micromechanism from ductile in the absence of hydrogen to intermediate and brittle in the presence of hydrogen was clearly observed. Results were discussed through FEM simulations of local stresses acting on the process zone. [ABSTRACT FROM AUTHOR]

To improve the performance of the steel for brake discs, like mechanical properties and thermal fatigue resistance, Nb is added to the steel. In this paper, the effects of Nb and tempering time on the microstructure and mechanical properties of the steel have been studied. The investigation of precipitation behaviors is based on Thermo‐Calc software and transmission electron microscopy. The results show there is a negative linear relationship between the yield strength and the logarithm of time, and tempering time should not exceed 2 h. V‐rich M8C7 and NbC occur during austenitizing, while (Mo,V)C, M23C6, and M7C3 precipitate during tempering. (Mo,V)C has a strong strengthening effect at the early stage of tempering, but it grows faster than M8C7. With 0.025% Nb addition, the yield strength and impact energy increase simultaneously due to the refinement of martensite; the addition of 0.045% Nb promotes the tempering stability due to the suppression of precipitation and coarsening of Cr carbides and the precipitation strengthening of M8C7 and NbC, therefore, the addition of 0.025–0.045% Nb is conducive to improving the performance of the steel. Moreover, the suppression of Cr carbides with 0.045% Nb addition makes up for the damage of large NbC to toughness. [ABSTRACT FROM AUTHOR]

Metastable-state alloy powders are usually synthesised by milling and occur as products of mechanical alloying (MA), but they are rarely used as starting materials for other MA processes. In this work, metastable-state alloy powders, including supersaturated solid-solution Cr(Mo)s and amorphous Cr(Mo)a were prepared in advance. Then, the Cr(Mo)s/Cr(Mo)a powder mixture was mechanically alloyed with elemental Cu to form Cu-Mo-Cr alloy. The effects of the metastable-state powder Cr(Mo)s/Cr(Mo)a on MA of the immiscible Cu-Mo-Cr system were evaluated. Phases and microstructures of the milled powders were analysed by XRD and TEM, respectively. The results show that amorphous Cu-60wt.%Cr(Mo) and supersaturated solid-solution Cu-20wt.%Cr(Mo) alloy powders can be synthesised by MA. It is concluded that MA of the Cu-Mo-Cr ternary alloy system is significantly promoted when elemental Cu powder is milled with metastable-state alloy powder Cr(Mo)s/Cr(Mo)a. Furthermore, the promoting effect of amorphous Cr(Mo)a on MA the Cu-Mo-Cr alloy system is much greater than that of supersaturated solid-solution Cr(Mo)s, during the milling process. [ABSTRACT FROM AUTHOR]

The dynamic recrystallization (DRX) behavior of 42CrMo steel was studied by hot compressive tests and cellular automaton (CA) simulation. The experimental results showed that initial grain size besides deformation parameters has an obvious influence on dynamic recrystallization (DRX) behavior. It is found that the initial grain size not only influences the number of DRX nucleation site, but also the work-hardening (WH) coefficient, dynamic recovery (DRV) coefficient, DRX nucleation rate and grain boundary (GB) mobility. Moreover, the relationships between the WH coefficient, DRV coefficient, DRX nucleation rate, GB mobility and initial grain size can be well described by the power function. Based on the findings, the traditional CA model was extended to describe the effect of initial grain size on DRX behavior. The comparison between experimental and simulated results showed that the microstructural evolution of 42CrMo steel with different initial grain sizes during hot deformation can be accurately simulated by the extended CA model. [ABSTRACT FROM AUTHOR]

The hot cracking at circular welding joints of quenched and tempered 42CrMo steel were studied. The flow of the molten pool and the solidification process of weld were observed with a high-speed video camera. The information on the variations in the weld temperature was collected using an infrared (IR) thermal imaging system. The metallurgical factors of hot cracking were analyzed via metallographic microscope and scanning electron microscope (SEM). The result shows that leading laser laser-metal active gas (MAG) hybrid welding process has a smaller solid–liquid boundary movement rate ( V SL ) and a smaller solid–liquid boundary temperature gradient ( G SL ) compared with leading arc laser-MAG hybrid welding process and laser welding process. Additionally, the metal in the molten pool has superior permeability while flowing toward the dendritic roots and can compensate for the inner-dendritic pressure balance. Therefore, leading laser laser-MAG hybrid welding process has the lowest hot cracking susceptibility. [ABSTRACT FROM AUTHOR]

In the present work conventional heat treatment like normalizing (bainitic microstructure) and tempering of the alloys has been performed. The materials used in this study were two steels, one the laboratory prepared experimental low alloy Cr-Mo steel in comparison to typical commercial 10CrMo9-10 steel. The determined carbon concentrations of the residual austenite at the different temperatures of bainite transformation supports the hypothesis that the growth of bainitic ferrite occurs without any diffusion with carbon being partitioned subsequently into the residual austenite. It was found that bainitic reaction has stopped when average carbon concentration of the untransformed austenite is close to the T0 line and supports formation of bainitic ferrite by a shear mechanism, since diffusionless transformation is not possible beyond the T0 curve. Normalized samples were air cooled down to room temperature before tempering at various temperatures in the range of 500-750°C. Samples have been austenitized at 980°C for 0.5 hour air cooled and tempered at 500, 550, 600, 650, 700 and 750°C for 1 hour. After heat treatment, the assessment in the microstructure and phase precipitation was made using the samples prepared for metallographic and transmission electron microscope (TEM) on thin foils analysis. Quantitative X-ray analysis was used to determine the retained austenite content after heat treatment like normalizing and tempering and the total volume fraction of the retained austenite was measured from the integral intensity of the (111)γ and (011)α peaks. The changes observed in the microstructure of the steel tempered at the higher temperature, i.e. 750°C were more advanced than those observed at the temperature of 500°C. Performed microstructural investigations have shown that the degradation of the microstructure of the examined steel was mostly connected with the processes of recovery and polygonization of the matrix, disappearance of lath bainitic microstructure, the growth of the size of M23C6 carbides, and precipitation of the secondary M2C precipitates. The magnitude of these changes depended on the temperature of tempering. [ABSTRACT FROM AUTHOR]

Hot forming as a coupled thermo-mechanical process comprises of numerous material phenomena with a corresponding impact on the material behavior during and after the forming process. Within the subsequent heat treatment, possible rapid cooling of the hot formed parts leads to the diffusionless decomposition of austenite into martensite. In this context, in addition to the elastic, plastic and linear thermal strain components, complex isotropic as well as anisotropic transformation strains can occur. Irreversible anisotropic transformation strains account for the plastic deformation at the phase boundary between the emerging and the parent phase and are related to the transformation induced plasticity (TRIP or TP) phenomena. Moreover, TRIP strains can be reduced or amplified by varying the current stress state. These phenomena significantly contribute to the final residual stress state and may be responsible for the cost-intensive component defects arising due to thermal shrinkage. This study aims at developing an FE-based material model in order to describe and quantitatively visualize stress dependence of the transformation induced anisotropic strains for a typical forging steel 42CrMo4. The developed material model as well as the aspects of its implementation in a commercial FE-system (Simufact.forming) is presented. Consequently, the discussed material model is tested by comparison of experimental and numerical results with respect to resulting dilatation under various stress states. [ABSTRACT FROM AUTHOR]

The influence of Laves phase in the microstructure on the creep strength of a modified 9Cr-1Mo tempered ferritic steel, F91, is investigated in this research. Through additional aging heat treatment up to 5000 h, a pronounced increase of Mo-rich Laves phase is found around Cr-rich carbide M 23 C 6 , which is pinned on the prior-austenite grain boundaries and martensitic lath boundaries. This secondary precipitation hardening provided by the Laves phase is rapidly offset by its coarsening into large clusters during long-term thermal exposure and under creep conditions, leading to earlier creep rupture than the pristine material. Uniaxial constant-load creep tests are conducted on both aged and non-aged coupons under the same creep conditions. The creep rupture behavior of both materials is rationalized with the assistance of a deformation-mechanism-based true-stress creep model that was developed in the previous work. The effects of Laves phase on the creep strength of F91 are related to its influence on the well-recognized existing deformation mechanisms: dislocation glide, dislocation climb, and grain boundary sliding. [ABSTRACT FROM AUTHOR]

Producing predictions of the probabilistic risks of operating materials for given lengths of time at stated operating conditions requires the assimilation of existing deterministic creep life prediction models (that only predict the average failure time) with statistical models that capture the random component of creep. To date, these approaches have rarely been combined to achieve this objective. The first half of this paper therefore provides a summary review of some statistical models to help bridge the gap between these two approaches. The second half of the paper illustrates one possible assimilation using 1Cr1Mo-0.25V steel. The Wilshire equation for creep life prediction is integrated into a discrete hazard based statistical model--the former being chosen because of its novelty and proven capability in accurately predicting average failure times and the latter being chosen because of its flexibility in modelling the failure time distribution. Using this model it was found that, for example, if this material had been in operation for around 15 years at 823 K and 130 MPa, the chances of failure in the next year is around 35%. However, if this material had been in operation for around 25 years, the chance of failure in the next year rises dramatically to around 80%. [ABSTRACT FROM AUTHOR]

The cross wedge rolling (CWR) method was used to produce laminated shafts of chromium-molybdenum steel (42CrMo). The effect of the rolling temperature on interface properties of composite 42CrMo/Q235 laminated shaft were explored, for example, the interface micro-structure, chromium diffusion, micro-hardness, bonding strength, and tensile fracture morphology. Results indicate that after rolling, the core material (Q235) and the clad material (42CrMo) combined effectively and formed a notable interface. Under high tem-perature rolling and composite binding, the chromium dif-fused near the interface. By rising the rolling temperature, the diffusion depth of chromium from the clad material to the core material increased. Near the interface of 42CrMo/Q235, the micro-hardness changes gradient. By rising the rolling temperature, the micro-hardness of same location decreased. The maximum interface bonding strength is 1100 °C, the maximum tensile strength is 532.0 MPa, and the maxi-mum shear strength is 422.3 MPa. Scanning electron microscope (SEM) images display the tensile fracture with a typical ductile dimple fracture pattern. Raising the rolling tempera-ture, the size of the dimple increased and the oxide at the bottom of the dimple decreased. At a rolling temperature of 1100 °C, the interface bonding strength should be the highest, which correlated with the interface bonding strength test results. [ABSTRACT FROM AUTHOR]

In this paper, the results of the complex examination of the 42CrMo4 steel samples are presented. The samples were taken from the metallurgical forging prepared for the production of the wind turbine main shaft. The samples underwent Mössbauer spectroscopic analysis, as well as the measurement of its mechanical characteristics such as hardness and strength are analysed. Conversion electron Mössbauer spectrometry confirmed phase purity and isotropy of the investigated 42CrMo4 steel. The method provided accurate results, proving Mössbauer spectrometry to be an effective tool for the wind turbine main shaft analysis. [ABSTRACT FROM AUTHOR]

The method for assessing residual life and disposable residual life of the material of Cr-Mo-V low-alloy cast steel elements after long-term service under creep conditions is presented in the paper. The research included performing the tests, in literature referred to as the short-term creep tests, at the constant level of stress of the test corresponding to the operating one and, at the temperature higher than the preset design one, as well as the creep tests with and without the measurement of elongation during the test. The test results presented in the paper confirmed the possibility of applying the short-term creep tests and the tests with elongation measurement in order to determine the time of further safe service of the material of elements after long-term operation made of low-alloy Cr-Mo-V cast steel types. [ABSTRACT FROM AUTHOR]

Cr–Mo steel high-pressure vessel made of 4130X is a promising economical candidate for hydrogen storage and transport in hydrogen refueling stations. However, the mechanical properties of 4130X in hydrogen gas and the hydrogen-enhanced fatigue life of a 4130X vessel with a design pressure higher than 45 MPa are not completely understood. In this work, the tensile and fatigue properties of 4130X at different positions of a manufactured vessel in 92 MPa hydrogen gas were studied. The fatigue life prediction for the 4130X vessel was performed using fracture mechanics method. The influences of initial crack size and outside diameter on the fatigue life were also investigated. Results indicate that the 4130X from the shoulder area attains a lower relative reduction of area (RRA) and higher fatigue-crack growth rate (FCGR) in hydrogen gas than those of the specimens from the cylinder and juncture. The FCGR measured in hydrogen increases with increasing hydrogen pressure, and the FCGR in 92 MPa hydrogen gas is 30–50 times of the FCGR in air. As the initial crack size increases, not only the fatigue life of the hydrogen storage vessel decreases, but also the hydrogen-induced fatigue life loss is aggravated. Furthermore, the influence of outside diameter on the fatigue life of the hydrogen storage vessel is minimal. [ABSTRACT FROM AUTHOR]

A deformation-mechanism-based true-stress creep model is proposed for studying the creep behavior of modified 9Cr-1Mo steel in this research. Constant-load creep test is conducted on modified 9Cr-1Mo steel in forged form (F91). The creep data obtained in the present study and those reported from the National Institute for Materials Science (NIMS, Japan) on modified 9Cr-1Mo steels processed by different means are analyzed. It is revealed that the relationship of minimum creep rate versus applied engineering stress exhibits distinct power exponent n in three stress regions, which are associated with different deformation mechanisms. The proposed model considers three well recognized deformation mechanisms: dislocation glide, dislocation climb, and grain boundary sliding. The analyses of the experimental data show that this deformation-mechanism-based model can describe fairly well the entire creep deformation process consisting of primary, steady-state, and tertiary creep. [ABSTRACT FROM AUTHOR]

In this study, AISI 4140 steel was subjected to box boronizing treatment at 1123 K, 1173 K and 1223 K for 2h, 4h, and 6h with commercially EKabor 2 powders. Friction and wear behaviour of the boronized and following worn AISI 4140 have been examined. After the wear tests, surface profilometer image analysis and EDS analysis were done. Also wear track area, wear track volume and wear rate were calculated based on the surface of the worn materials. In the AISI 4140 steel and in the boronized samples for 2 h severely plastic deformation wear mechanism was determined, whereas in the samples boronized for 4h and 6h micro-ploughing wear mechanism was determined. Properties of boride layers have an effect on the type of wear mechanism. The boronized samples showed up to 27.3 times higher wear resistance than non-boronized AISI 4140 steel. [ABSTRACT FROM AUTHOR]

In investment casting, the separation of cast components composed of strong, hard materials from the gating system is a delicate operation, which can incur considerable costs in terms of labor and tools. In this study, we substituted conventional grinder cutting with vibration-induced fatigue failure to facilitate the separation of chromium-molybdenum (CrMo) alloy steel components from an investment casting tree. This process involves the creation of V-shape notches on the ingate structure as well as modifications to component layout within the pattern tree. Vibration-excited dynamic experiments were performed to examine the effects of notch designs on stress concentration and cutting off at the ingates. Mold flow analysis was used to optimize the design of the pouring system to ensure casts of high quality. Finite element method (FEM) and experimental modal analysis (EMA) were conducted to predict the efficacy of the model and vibration characteristics. The application of harmonic response analysis to a casting tree model determined the maximum and minimum principal stresses at ingate notches. Once the stress values at the ingate notches were sufficient to ensure failure conditions, the same parameters were used to perform a final experiment for verification. Experiment results revealed that the breaks indeed occurred at the notches of the ingate. The proposed approach could be used as an alternative to conventional cutting using a grinding wheel as a means of reducing labor costs, increasing safety, and enhancing production efficiency. [ABSTRACT FROM AUTHOR]