Grain Size Of Steel Research Articles

Evaluation of the brittleness and viscosity of metals upon tensile testing

The indicators of the brittleness and viscosity of metals calculated from their mechanical properties are considered with allowance for the stress state proceeding from the results of tensile testing of cylindrical smooth and notched samples of perlite 16KhSN, martensitic-aging (maraging) 03Kh11N10M2T, and austenitic 10Kh11N23T3MR steels. Tests were carried out on a UEM-10TM tensile strength testing machine, deformation diagrams developed on a scale of ~50:1 at a deformation rate of 5 mm/min. The sample size before and after testing were measured using a micrometer and an ISA-2 comparator with an accuracy of ±10–3 mm. Pendulum impact bending tests were carried out on a MK15 with the same cylindrical notched samples used to plot the plasticity and viscosity diagrams depending on the Bridgman stress state stiffness index. The new indicators of the brittleness λ = εk/η and viscosity η = (Sk/σb) – 1 (where εk = ln(1/(1 – ψk)) is the true limit plasticity) are proposed proceeding from the testing data. The special feature of the brittleness index λ is growth of the index with increase in the metal strength, e.g., due to pre-deformation or strengthening heat treatment procedures. However, a decrease in the groove radius on the samples, i.e., an increase in the Bridgman stress state stiffness, has almost no effect on the brittleness value λ, but is accompanied by a correlation decrease in the values of the viscosity indices η and the ultimate ductility εk of steels. The curves of the temperature dependences of the mechanical properties of steels 16KhSN and 03Kh11N10M2T show that anomalies in the brittleness indices λ observed at elevated test temperatures can be attributed to the structural transformations like increase in the grain size of 16KhSN steel or in the amount of the residual austenite in 03Kh11N10M2T steel due to reverse martensitic transformation. In this case, the temperature dependences of the viscosity η and brittleness λindicators change in the opposite way.

Effect of boron accompanied by chromium, vanadium and titanium on kinetics of austenite grain growth

ABSTRACT The work was aimed at analysing the effect of boron on austenite grain size of low-alloy cast steels during austenitization in the range between 850°C and 1200°C. The effect of boron was investigated in presence of other alloying additives: chromium, vanadium and titanium. Eight melts with various chemical compositions were subjected to heat treatment started from soaking at eight different temperatures. After quenching, former austenite grain size was determined by a method of quantitative metallography. Influence of boron on austenite grain size, especially in presence of other alloying elements, was evaluated by one-way variance analysis ANOVA and the Kruskal–Wallis tests. The analyses showed a significant influence of boron on austenite grain size, which can be compensated by alloying elements creating stable carbides and nitrides.

Effect of grain size on the corrosion behavior of fully recrystallized ultra-fine grained 316L stainless steel fabricated by high-energy ball milling and hot isostatic pressing sintering

Fully recrystallized ultra-fine grained 316L steel with different grain sizes were prepared by high-energy ball milling followed by hot isostatic sintering. The relationship between grain sizes and the corrosion behaviors in salt water was studied. The results showed that the re-passive ability was always stronger for finer grained samples by formation of much denser and shallower pits, however, the influence of grain size on the pitting potential was insignificant and the passive film even seemed to become susceptible to cathodic polarization when the grains were refined to sub-micron scale. It was notable that there existed many contradictory conclusions in relevant studies. The ambiguity in the relationship between grain size and corrosion behaviors of stainless steels was discussed in detail.

Influence of Boron on Solid-State Phase Transformation Temperatures and Grain Size in IF Steel

The influence of boron on solid-state phase transformation temperatures and grain size in IF steel was investigated. The results show that boron can segregate at the grain boundaries of the IF steel doped with boron during the cooling process. Compared with the specimen without boron, the grain size of specimen with 34-ppm boron is large and its Brinell hardness is relatively small, 216 μm and 59.8HB, respectively. Moreover, the addition of boron in IF steel can rotate the grains toward the [001] orientation, decrease the phase transformation temperature from austenite to ferrite and increase its phase transformation activation energy during the cooling process. According to the experimental results, during the cooling process, the addition of 34-ppm boron in IF steel can reduce the peak temperature of phase transformation by 3.44 K ~ 6.67 K and increase the phase transformation activation energy by 318.59KJ/mol.

Nonmetallic inclusions and secondary structure of continuous casting steels

The article presents the results of a study of the non-metallic inclusions and secondary structure of continuous casting steels It is estimate that main quantity of non-metallic inclusions (»72%) it inputted in steel during the deoxidization and the secondary oxidation, therefore the casting processes need to be managed very well to decrease the quantity of non-metallic inclusions in liquid steel. Reducing the secondary dendrite arms spacing for the strip casting process, in comparison with the conventional continuous casting process of thick slab, will reduce the size of non-metallic inclusion and as result could improve the mechanical properties of steel. Content of the endogenous non-metallic inclusions in stainless steel with Ti, in carbon steel and in electrical steel grades decreases in ladle and tundish in 2.7–3.2 times in comparison with quantity of non-metallic inclusions before pouring from furnace. The increasing of the tundish width decreases in 20 times the quantity of nonmetallic inclusions by sizes from 70 to 80 mm, and in 5–6 times by sizes 220–230 mm. Increasing of the tundish height reduces of the oxygen content in continuous casting of slab It was development the dependence of the secondary dendrite arm spacing with cooling rate. Analysis shown, that the secondary dendrite arms spacing for the strip casting process decreases from 5.91 to 8.31 times in comparison with the conventional continuous casting process of thick slab of thickness 220 mm. Simultaneously non-metallic inclusions sizes to decrease, too. Rapid solidification reduces the number of large non-metallic inclusions: the inclusion number larger than 1 mm is decreased by a ratio of 5 in comparison with the conventional slabs process. It was estimated influence of main parameters on the average grain sizes and the steel microstructure for the strip and conventional casting processes. The dependence of the grain size of carbon and low alloying steels grades (C = 0.08–0.6%, Si = 0.4–0.6%, Mn = 0.4–1.4%, P < 0.03%, S < 0.03%), (C = 0.04–0.6%, Si = 0.11–0.3%, Mn = 0.3–1.12%, P = 0.01–0.035%, S = 0.005–0.035%, Nb = 0.013%, V = 0.001%) and high chromium and stainless steels of type AISI 430 and 304 (C = 0.03–0.12%, Si = 0.83–1.0%, Mn = 0.8–1.0%, Cr = =16.0–18.4%, Ni = 8.47%, N = 0.03%) from casting speed range, final thickness of slab or sheet, reduction, temperature range is estimated by a multi regression analysis. The grain size of steel obtained by the strip casting process, in range 1300 to 1400 oC, is 2.3 time smaller than for the slab casting processes with slab thickness from 50 to 220 mm.

Effect of Niobium and Titanium Addition on Formation of Second Phase Particles in CHQ Steel Using Transmission Electron Microscope

It is common practice that formation of second phase particles such as nitrides or carbides in the steel matrix has significant role to control the grain size of steel. An attempt is made in the present research work to find out the role of nitrogen to form the nitride particles either with Al, Ti, B, Cr or Si. Two steel samples Steel-A and Steel-B with same titanium and aluminum weight percent in the chemical composition were obtained in hot rolled conditions from international market with only the difference of presence of Niobium in Steel-A. Solution heat treatment was performed at 1350°C with 60 minutes holding time in protherm heat treatment furnace available locally was used to dissolve the particles and then steel samples were reheat treated at 800°C with holding time of 60 minutes and water quenched and microstructure was revealed. Transmission electron microscope connected with Ehlers-Danlos Syndrome (EDS) was used to reveal the morphology of second phase particles. Both samples for a high resolution power Transmission Electron Microscopy (TEM) (Jeol JEM 3010) analysis were prepared by using carbon extraction replica method in 5% Nital solution as an etching technique. Both samples were then caught in copper grid of 3mm for using TEM analysis. TEM micrographs clearly revealed the second phase particles in the matrix of steel. The EDS peaks were studied and it was found that the peaks showed the titanium peaks in both the samples A and B and surprisingly there was no any peak found for aluminum. Stoichiometric calculations were carried out and it was found that weight percent nitrogen required for forming TiN is 0.0073, however the total nitrogen present in both the steels A and B is 0.0058 and 0.0061 respectively. That means that all the nitrogen present in the steel matrix was consumed by titanium to form the Titanium Nitride (TiN) so there was no nitrogen remain to fulfil the requirement of aluminum to form the Aluminum Nitride (AlN) particles.

Measurement of Steel Structure Elements in the Specialized Module of the IMAGE-SP Image Processing Software

Grain size is one of the most important characteristics of the microstructure of metals and alloys. Determination of the grain size of steel is regulated by Standart 5639-82 "Steels and alloys. Methods for detection and determination of the grain size". Standart includes determining the grain score by comparison with reference scales, as well as manual measurement methods. The use of image processing software opens up new opportunities for the materials analysis, including for the quantitative metallographic analysis of steels and alloys. The purpose of this work was to test the specialized "Metallography" module to determine the grain score of the image processing software "IMAGE – SP", as well as to check the reliability of the obtained results using the example of ferritic and austenitic steels.In the "Metallography" module, the analysis of standard images of annex No. 3 of Standart 5639-82, as well as real images of the structures of ferritic and austenitic steel, is carried out. It is shown that the results correspond to the definition of the Standart grain score. The divergence in the results is 1 point, which is acceptable.The active development of software products for the quantitative analysis of images in metallography will make it possible to legitimize the methods of computer measurement of parameters of the structures of metals and alloys by creating appropriate standards. Successful testing of the specialized "Metallography" module demonstrates opportunities and prospects for further development of specialized software products for measuring quantitative values of metal and alloy structures. The active development of software for quantitative analysis of the images in metallography will make it possible to legalize methods for measuring parameters of metal and alloy structures by computer techniques.

An Experimental Investigation into The Effect of Treatment Temperature onThe Grain Size of Low Carbon and Microalloyed Steels.(Dept.M)

An Experimental Investigation into The Effect of Treatment Temperature onThe Grain Size of Low Carbon and Microalloyed Steels.(Dept.M)

Effect of Titanium and Boron Microalloying on Sulfide Stress Cracking in C110 Casing Steel.

The effect of Ti and B microalloying on the hardenability, prior austenite grain size (PAGS), mechanical properties, and sulfide stress cracking (SSC) of C110 grade steel was studied by Jominy testing, static tensile testing, an optical microscope (OM), scanning electron microscopy (SEM) and double cantilever beam (DCB) testing. The results show that the addition of 0.015% Ti and 0.002% B into a medium-carbon Fe-Cr-Mo-Nb-V steel increased the hardenability and refined the PAGS and quenched martensite packets, and the size of carbides was reduced. It is believed that these behaviors are responsible for the improvement in the threshold stress intensity factor KISSC.

Metal additive manufacturing of carbon steel with direct laser deposition: computer simulation

Metal 3D printing technology is commercially available, but the quality of the printed product is still a challenging issue that needs to be improved. More research is needed to address the essential technical details of metal 3D printing. Important technical details are the alloy microstructure, imperfections like pores, distortion, surface roughness, and residual stress, which affect the mechanical properties of the printed sample like fatigue performance. This research has computationally studied metal 3D printing for carbon steel to address the parameters that affect the quality of the final product printed by direct laser deposition. Multiscale multiphysics computational algorithms were coding in Microsoft Visual Basics 2015 to simulate the thermal stress, deformation, and austenite grain topology. Energy and force equilibrium equations were numerically solved to simulate the thermal and mechanical history versus print’s adjustable parameters like scan speed, laser power, and rate of metal powders injection through the nozzle. The austenite grain size of steel is an important parameter that is directly related to the local thermal history. A stochastic computational code was developed to simulate grain morphology based on calculated thermal history. The simulation showed the dependence of von Mises stress and thermal history on the rate of metal powders injection, laser power, and scan speed. The simulation showed a rise in von Mises stress by increasing the scan speed and laser power. Print speed and laser power also change the local maximum temperature and the local alloy microstructure. The local austenite grain size increases by reducing scan speed in the heat-affected zone. The simulation showed that the microstructure of the printed part is not uniform, and different layers are distinctive.

Effect of Heat Treatment on Microstructure and Mechanical Properties of New Cold-Rolled Automotive Steels

The effect of austenitizing temperature and aging treatment on the microstructure and mechanical properties of two new cold-rolled automotive steel plates (20Mn2Cr and 20Mn2CrNb) was investigated by using isothermal heat treatment, optical microscope, scanning electron microscope, microhardness tester, and tensile testing machine. The results show that as the austenitizing temperature increased, the original austenite grain sizes of both steels increased. The original austenite grain size of 20Mn2CrNb was smaller than that of 20Mn2Cr. The microhardness of 20Mn2CrNb gradually decreased with increasing aging temperature, while the hardness of 20Mn2Cr varied irregularly. The mechanical properties of 20Mn2Cr were better than those of 20Mn2CrNb under the same heat-treatment process. The effect of heat treatment on microstructure and mechanical properties was related to the martensite content, dislocation density, and precipitation of second-phase particles.

Microstructure and Strengthening/Toughening Mechanisms of Heavy Gauge Pipeline Steel Processed by Ultrafast Cooling

Heavy gauge pipeline steels experience a low qualification in drop-weight-tear test properties because of the low cooling capability of conventional thermomechanical controlled processing. To solve this problem, a new-generation thermomechanical-controlled processing technology based on ultrafast cooling was applied to prepare heavy gauge pipeline steels. The microstructure, strengthening and toughening mechanisms of 25.4 mm X70 and 22 mm X80 pipeline steels that were processed by ultrafast cooling were studied. The microstructures of the 25.4 mm X70 and 22 mm X80 pipeline steels consisted of bainitic ferrite, M-A island and acicular ferrite with a large fraction above 85%. The grain size and high-angle grain boundary fraction of X70 pipeline steel were 2.7 μm and 43%, respectively, whereas those of the X80 pipeline steel were 2.4 μm and 45%, respectively. The strengthening and toughening mechanisms were studied for the ultrafast cooling method. The main strengthening mechanism for 25.4 mm X70 pipeline steel was solution and grain-refining strengthening and precipitation strengthening with contributions of ~456 MPa and ~90.5 MPa, respectively. In the 22 mm X80 pipeline steel, the main strengthening mechanism was the solution and grain-refining strengthening, and dislocation strengthening with contributions of ~475 MPa and ~109.8 MPa, respectively.

Effects of Ce on Microstructure and Mechanical Properties of LDX2101 Duplex Stainless Steel

In the present study, the effects of rare earth metal (REM) Ce on the number, size distribution and type of inclusions, as well as the grain size, tensile and impact properties of LDX2101 duplex stainless steel, were investigated using thermodynamic analysis, optical microscope, image software, scanning electron microscope, tensile and impact testing machines. The results indicate that when the Ce content in steel is 0%, the main inclusions are irregular and large size Al2O3 and Al2O3-MnS. When the Ce content in steel is 0.005% or 0.02%, the inclusions are mainly spherical and small size inclusions CeAlO3, Ce2O2S and Ce2O3. With the increase in Ce content, the proportion of small size inclusions gradually increases; the number of inclusions per unit area decreases from 122 to 58 and the average grain size reduces from 16 ± 0.7 μm to 12 ± 0.3 μm. Moreover, the mechanical properties of steels are improved, and the tensile strength, yield strength and elongation are elevated by 4.69%, 2.83% and 4.9%, respectively. The impact fracture mode of steel without Ce is cleavage fracture, however, the fracture mode is transformed into a mixed fracture of cleavage and dimple after adding 0.005% and 0.02% Ce.

Effect of the Deformation Degree on the Microstructure Evolution of an Austenite Reverted Transformation-Annealed Medium Manganese Steel

An Fe-0.15C-1.2Si-5Mn-0.09Nb-0.08V-0.07Mo (wt.%) medium manganese steel that was subjected to a novel austenite reverted transformation (ART) annealing process. This paper is based on the conventional ART annealing process, and a deformation and ART annealing process is proposed. The influence of the deformation degree on the microstructure and grain size of the medium manganese steel was determined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). The results show that the deformation had a great effect on the microstructure evolution and grain size. The microstructure of the medium manganese steel after the deformation and ART annealing process was consistent with the theory of austenite reverse transformation, i.e., the martensite reverse transformation into austenite occurred during the deformation and ART annealing process. The final microstructure was a mixture of martensite and austenite. As the deformation degree increases, the martensite gradually refines, and carbides precipitate in the lath martensite. The retained austenite is gradually transformed from very large to small and is distributed between the martensite laths. The results show that when deformation occurs in the austenite region, a small deformation can obtain more retained austenite.

The influence of phase distribution and microstructure of the carbon steel on its chloride threshold value in a simulated concrete pore solution

The influence of steel microstructure and phase distribution on the corrosion initiation and chloride threshold value was investigated in a simulated concrete pore solution. Normalizing and cyclic heat-treatment were employed to change the grain size, pearlite, and MnS morphology of the conventional reinforcement carbon steel. The oxidation behavior of obtained microstructures was compared with non-treated steel specimens using the cyclic voltammetry technique. Chloride was added periodically in the solution, and threshold chloride value for each microstructure was determined using potentiostatic electrochemical impedance spectroscopy (EIS). Results revealed that the normalized steel lowered the chloride threshold value while cyclic heat treatment around eutectoid temperature increased the corrosion initiation resistance. Post-corrosion microscopic observation showed that corrosion initiated and propagated preferentially through the pearlite phase, while proeutectoid ferrite was intact. Isolating pearlite and fragmentation of cementite lamella and MnS inclusions through cyclic heat-treatment retarded pit nucleation and slowed down corrosion propagation.

A Unified Model for Plasticity in Ferritic, Martensitic and Dual-Phase Steels

Unified equations for the relationships among dislocation density, carbon content and grain size in ferritic, martensitic and dual-phase steels are presented. Advanced high-strength steels have been developed to meet targets of improved strength and formability in the automotive industry, where combined properties are achieved by tailoring complex microstructures. Specifically, in dual-phase (DP) steels, martensite with high strength and poor ductility reinforces steel, whereas ferrite with high ductility and low strength maintains steel’s formability. To further optimise DP steel’s performance, detailed understanding is required of how carbon content and initial microstructure affect deformation and damage in multi-phase alloys. Therefore, we derive modified versions of the Kocks–Mecking model describing the evolution of the dislocation density. The coefficient controlling dislocation generation is obtained by estimating the strain increments produced by dislocations pinning at other dislocations, solute atoms and grain boundaries; such increments are obtained by comparing the energy required to form dislocation dipoles, Cottrell atmospheres and pile-ups at grain boundaries, respectively, against the energy required for a dislocation to form and glide. Further analysis is made on how thermal activation affects the efficiency of different obstacles to pin dislocations to obtain the dislocation recovery rate. The results are validated against ferritic, martensitic and dual-phase steels showing good accuracy. The outputs are then employed to suggest optimal carbon and grain size combinations in ferrite and martensite to achieve highest uniform elongation in single- and dual-phase steels. The models are also combined with finite-element simulations to understand the effect of microstructure and composition on plastic localisation at the ferrite/martensite interface to design microstructures in dual-phase steels for improved ductility.

A Digital Evaluation Approach for Nodule Size Analysis of Pearlite Mixture Phase Structure in Steel

This study employed a digital evaluation approach for determining the nodule size of a no heat-treatment pearlite structure, as well as the grain size of the ferrite phase via an image morphology process methodology. The grain size of steel has great influence on the mechanical properties of manufactured materials, making it a necessary metallographic inspection item for materials. The properties affected by grain size include hardness, failure life, ultimate stress, electric characteristics, and heat expansion rate. In general, grain size inspection has two approaches: manual comparison and digital computation. In manual comparison, the comparison of standard graphics or the observation of an eyepiece inserted on a microscope can be progressed. For digital computation, planimetric and intercept procedures are applied according to international standards. This study thus applied an image processing algorithm to identify the observed image after undergoing seven times of erosion and dilation operations.

Criteria for achieving the BH effect in ultra-low carbon steels for deep drawing

The authors have investigated key technological parameters of stable production of IF steel sheet with BH-effect. The features of ultralow carbon IF steels and IF steels with BH effect are described. Scheme of IF-BH steel hardening during hot drying of the car body after painting is considered. Data on the chemical composition of IF and IF-BH steels produced at Russian and worldwide enterprises are presented. The authors have analyzed the reasons of appearance of such a defect in the steel sheet as slip bands that arise when the yield area appears on the tensile diagram of steel samples. The requirement on the “shelf life” presented to the IF-BH steel grades is given and disassembled. The article considers the formula for calculating effective carbon content in steel based on the total carbon content in steel, niobium, titanium and nitrogen. The range of carbon effective in steel is given to achieve the optimal value of the BH effect based on previously published works. The results of industrial IF-BH steel production have been analyzed for the conditions of Russian enterprise and recommendations were given on criteria such as the optimum carbon content range in solid solution, the recommended maximum total concentrations of carbon and nitrogen in steel, and the BH effect value guaranteeing a high yield of IF-BH steel sheet in the production. Calculations of various options of microalloying by titanium and niobium for IF-BH steel were done. Criteria are formulated that allow stably obtaining a given value of the BH effect in cold-rolled ultralow-carbon steels. A two-stage scheme for microalloying by titanium and niobium is proposed. The influence of grain size in sheet steel on the presence and value of the BH effect is described as well as on the presence/absence of a yield plateau on the tensile diagram in the sheet metal in the initial state.

Analysis of Tensile Properties of N80Q Steel and 80SH Steel

During heavy oil production, the performance of casing varies with temperature in the service environment. The tensile test of N80Q Steel and 80SH Steel were carried out to evaluate the mechanical properties during the service. The results indicated that the grain size of 80SH steel was relatively uniform and the grain boundary was relatively obvious compared with N80Q steel. A qualitative analysis was performance by relating the tensile properties with different temperature. The results showed that the yield strength, the tensile strength and elongation of N80Q and 80SH steels decreased with increasing temperature, but the degree of decline was limited. The observation of the tensile fracture revealed that the characteristics of the radiation zone of N80Q steel were obvious compared with 80SH steel at 20°C.

DRX behavior and microstructure evolution of 33Cr23Ni8Mn3N: Experiment and finite element simulation

The dynamic recrystallization (DRX) behavior and microstructure evolution of 33Cr23Ni8Mn3N heat-resistant steel were studied by isothermal hot compression experiment within the temperature range of 1000°C–1180°C and strain rate of 0.01–10s−1. Models for the DRX volume fraction and grain size of 33Cr23Ni8Mn3N heat-resistant steel were established, and comparison results showed high consistency for the predicted data from the models and those from scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The model was imported into Deform-3D, and hot compression was simulated by the finite element method (FEM). The simulation and experimental results were highly consistent. Thus, the established DRX model is an important reference for the microstructure evolution in 33Cr23Ni8Mn3N hot deformation behavior.