Low Alloy Cast Steel Research Articles

Evolution mechanism of inclusions and microstructure in low-alloy cast steel with cerium addition

Rare earth (RE) elements not only modify inclusions but also refine the steel's microstructure. This study investigates the evolution mechanism of cerium on inclusions and microstructure in low-alloy cast steel through experimental and thermodynamic analyses. After cerium is added to the steel, strip-like inclusions transform into spherical ones, accompanied by a reduction in size. The evolution path of inclusions follows MnS + MnS–Al2O3→Ce2O2S–Ce2S3–MnS + CeAlO3–Ce2S3–MnS with cerium addition. Notably, Ce2S3 and Ce2O2S exhibit an orientation relationship, with [1‾ 22]Ce2S3//[01 1‾ 1]Ce2O2S and (02 2‾)Ce2S3//(1‾ 011)Ce2O2S. Compared to Ce-free steel, the Ce-0.06 steel shows a reduced grain size and the absence of needle-shaped Widmanstätten structures, which may be mainly attributed to rare earth inclusions as heterogeneous nucleation of δ-Fe. This work can provide a theoretical basis for improving the overall mechanical properties of low-alloy cast steel by adding cerium.

Particular Features of the Distribution of Nonmetallic Inclusions in a Continuously Cast Low-Alloy Steel Ingot

Particular Features of the Distribution of Nonmetallic Inclusions in a Continuously Cast Low-Alloy Steel Ingot

Effect of zirconium and niobium on the microstructure and mechanical properties of high-strength low-alloy cast steels

The aim of this work is to study the effect of zirconium and niobium on the refinement of grain size and mechanical properties of micro-alloyed cast steels in heat treated conditions. Five micro-alloyed cast steels with different compositions, as steel without microalloying elements and micro-alloyed steel with (i) 0.05% Zirconium (Zr), (ii) 0.05% Zirconium (Zr) and 0.05% Niobium (Nb), (iii) 0.10% Zirconium (Zr), and (iv) 0.10% Zirconium (Zr) and 0.10% Niobium (Nb) were investigated. The heat treated samples are normalized at 1000 °C followed by air cooling and were characterized to study the characteristics of carbide precipitates by SEM and TEM and mechanical properties were evaluated by tensile test as per ASTM A370. Among these five cast steels, steel containing 0.10% Zr and 0.10% Nb showed a higher tensile strength of 1184 MPa and yield strength of 740 MPa with reasonable impact energy of 42 J compared to other steels under the same heat treated conditions. Due to the combined addition of Zr and Nb elements in the micro-alloyed steel, a remarkable improvement of mechanical properties particularly strength and impact energy was observed. As evident from microstructure investigation, these improved mechanical properties in the present steel could be attributed due to the effective refinement of ferritic grain size in the normalized condition.

Resistance to Abrasive Wear with Regards to Mechanical Properties Using Low-Alloy Cast Steels Examined with the Use of a Dry Sand/Rubber Wheel Tester.

This paper focuses on relationship between the mechanical properties and abrasive wear resistance, expressed by the Kb index, using an example of low-alloy cast steels. In order to achieve the aim of this work, eight cast steels of varying chemical composition were designed, cast and then heat treated. The heat treatment involved quenching and tempering at 200, 400 and 600 °C. Structural changes caused by tempering are demonstrated by the different morphologies of the carbide phases in the ferritic matrix. In the first part of this paper, the present state of knowledge about the influence of structure and hardness on the tribological properties of steels is discussed. This research involved the evaluation of a material's structure, as well as its tribological and mechanical properties. Microstructural observations were performed using a light microscope and a scanning electron microscope. Next, tribological tests were carried-out with the use of a dry sand/rubber wheel tester. To determine the mechanical properties, Brinell hardness measurements and a static tensile test were carried out. The relationship between the determined mechanical properties and abrasive wear resistance was then investigated. The analyses also provided information regarding the heat treatment states of the analyzed material in the as-cast and as-quenched states. It was found that the abrasive wear resistance, expressed by the index Kb, was most strongly correlated with hardness and yield point. In addition, observations of the wear surfaces indicated that the main wear mechanisms were microcutting and microplowing.

Effect of Ti addition and cast part size on solidification structure and mechanical properties of medium carbon, low alloy cast steel

In this work, the effect of Ti addition and the cast part size on the solidification structure and mechanical properties of a medium carbon, low alloy cast steel was analyzed. The experimental analysis involved the design of the melts by using Thermo-Calc® software, where different amounts of Ti added to a standard chemical composition of an AISI 13XX steel were simulated. Then, the solidification macrostructure (dendritic pattern and grain size) and microstructure were characterized by using conventional and specific metallographic techniques. Finally, the mechanical behavior in terms of hardness and tensile properties were evaluated. The results show that the addition of 0.12% of Ti promotes a fine dispersion of Ti nitrides and carbides, but when the Ti concentration raises to 0.2%, the size of the Ti nitrides and carbides increases while its amount decreases. Ti nitrides and carbides particles act as nucleation sites for the precipitation of ferrite from austenite, and it was found that the addition of Ti in the higher concentrations refines the solidification macrostructure (dendritic pattern) for both cast part sizes evaluated. Regarding mechanical properties, the addition of Ti does not significantly vary the ultimate tensile strength but reduces the total elongation for cast part sizes

Effect of Boron Accompanied by Chromium, Vanadium and Titanium on the Transformation Temperatures of Low-Alloy Cast Steels

Effect of Boron Accompanied by Chromium, Vanadium and Titanium on the Transformation Temperatures of Low-Alloy Cast Steels

Non-metallic inclusions as an indicator of the impact toughness of carriage castings from steel 20GL

The correlation dependence between impact toughness and non-metallic inclusions (NI) in fractures of specimens made of low-alloy cast steel 20GL produced in open-hearth and electric arc furnaces for carriage castings "bogie side frame" and "bolster beam" is considered. Metallographic and statistical analyzes of NI according to GOST 1778–70 (method L) based on the Vestra image system program were carried out using the method of optical microscopy on samples of low-alloy cast steel 20GL with different impact toughness, with the help of which one of the reasons for the low values of impact toughness (KCV–60 < 2∙102 kJ/m2) — impurity by NI of 20GL steel samples. Using a scanning electron microscope, a combined approach to the study of NI and a metal matrix of fractures in samples of low-alloy cast steel 20GL with different impact toughness was implemented. An X-ray microspectral analysis of NI at the fracture point of specimens melted in open-hearth and electric arc furnaces was carried out, which showed the presence of large accumulations of NI in fractures of specimens made of 20GL steel with low values of impact toughness (KCV–60 < 2∙102 kJ/m2) both in open-hearth and electric arc melts. The use of a scanning electron microscope made it possible to obtain fractograms of fractures in samples with a clearly expressed diverse morphology of NI and various reliefs of the metal matrix. A significant role in the results of impact toughness plays the metal matrix of samples of openhearth and electric arc melts, which is clearly confirmed by the presence of cleavage facets with a stream pattern and tongues at brittle and small depressions at ductile-brittle fractures, as well as the presence of various shapes and sizes of NI. On the basis of X-ray microanalysis, graphs of the weight content of chemical elements contained in NI, metal matrix, fractures of samples of open-hearth and electric arc melts with different impact toughness are given.

Case study of testing different materials for seat belt retractor torsion bar by the means of finite element analysis

This paper examines the use of various materials for the force limiter torsion bar found in an automotive seat belt assembly. We have selected the following materials: carbon steel, cast stainless steel, cast low alloy steel and cast aluminium alloy. The primary method used for this study is finite element analysis (FEA) and the use of the named materials on a 3D model of the torsion bar, constructed using the dimensions of a standard part. The 3D models were created with a 3D CAD program and the FEA analysis was carried out with special software. For the input values, the torsion bar was fixed at one corner and a 360 degree rotation shift at the other corner. A fine mesh of 1.5 mm/element was also set to get a more accurate analysis. The results of this study are in the form of stress, strain, safety factor and displacement plots generated by the FEA analysis software showing the difference between the materials. The main outcome of the study is to determine the best overall material to manufacture the part in terms of performance and cost.

Investigation on compressive strength of a low alloy steel (AISI4140) and plain carbon steel - a novel statistical approach

The prime objective of this work is to investigate the compressive strength of low alloy steel (AISI4140) and compare it with that of plain carbon steel. As cast low alloy steel (AISI4140) and plain carbon steel were considered for this investigation. ClinCalc tool was used to calculate the samples, accordingly 20 samples per group were prepared as per ASTM standards. A CNC laser cutting machine is used for the preparation of specimens as per ASTM standards (E8). By using universal testing machines (UTM) the compressive properties were performed and observed for both groups. According to independent T-test and descriptive statistical analysis, it is observed that there exists a significant (with a significance value of 0.001, i.e., P < 0.05) difference in the compressive strength between low alloy steel (AISI4140) and plain carbon steel. From the compression testing results plain carbon steel shows an average of 13.657 MPa, whereas low alloy steel (AISI4140) exhibits an average compressive strength of 43.564 MPa. Within the limitations of the study, it is found that low alloy steel (AISI4140) has good compression strength when compared to plain carbon steel.

Microstructural parameters as indicators of reliability of car castings made of 20GL steel

The complex influence of grain number, average area and grain hardness on the section of low-alloy cast steel 20GL of car castings &ldquo;Side frame&rdquo; and &ldquo;Truck bolster&rdquo; on the basis of statistical and microstructural analysis of samples obtained after open-hearth and electric arc melting and single and double heat treatment (HT), on increase of the toughness KCV-60 &gt; 2.0. The frequency diagram of the relationship between the number of open-hearth and electric arc melts and the same level of impact toughness in 2018 with the imposition of grain microstructure and different levels of impact toughness (KCV-60 &lt;2.0, KCV-60 &ge; 2.0 and above KCV-60 &gt; 2.0∙102 kJ/m2). The relationship between the number of samples obtained by open-hearth melting and passed the 2nd HT, and the same level of impact strength in 2019 with the imposition of the grain microstructure from samples after the 1st and 2nd HT and different levels of impact toughness (KCV-60 &lt; 2.0 and KCV-60 &gt; 2.0∙102 kJ/m2). Microstructure of samples of low-alloy cast steel 20GL of car castings &ldquo;Side frame&rdquo; and &ldquo;Truck bolster&rdquo; types was studied by optical microscopy in the search for causes of falling toughness (KCV-60 &lt;2.0). Statistical and microstructural analysis of the array of data on the size and average area of grains, their number and hardness in 20GL steel samples after single and double HT indicated different viscoplastic properties of these castings. The authors concluded that the grain size and hardness are the most important indicators of the microstructure of low-alloy steel 20GL and are unique in their effect on toughness.

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 Tempering Process on Microstructure and Mechanical Properties of Low Alloyed Cast Steel

The effect of tempering process on the microstructure and properties of low alloyed cast steel was studied. The results show that tempered at (200~400)°C, the M/A island of the granular bainite decomposes and carbide precipitates. When the tempering temperature rises to (500~600)°C, the M/A island is completely decomposed, and the carbide aggregates and gradually spheroidizes. With the increasing of tempering temperature, the tensile strength increases first and then decreases, elongation and impact energy show a trend of increasing at first, then decreasing and then increasing. The tempering brittleness occurs at 400°C.

Holding Time Influence on the Hot Ductility Behavior of a Continuously Cast Low Alloy Steel

Cracking during the continuous casting process is undesirable and continuous work is being carried out to find further improvements and understand the mechanisms that lead to failure. Investigations on the hot ductility behavior of a continuously cast low alloyed steel using different holding times before straining were done in the present work. Samples were heated to melting temperature in a vacuum atmosphere and then cooled to one of the three test temperatures chosen: 750, 850, and 900 °C. When the desired temperature was reached, the sample was isothermally held for either 10, 90, 300, or 3600 s before the tensile test started, with a strain rate of 10−3 s−1. The reduction of area was measured, SEM images of the fractured surfaces were taken plus LOM images for the analysis of the microstructure. The results show that there was no significant change in the ductility at any of the temperatures until 300 s, with a change in behavior at 3600 s. This was further confirmed with the images and precipitation kinetics simulations. The results are described and compared.

APPLICATION OF THE AOD PROCESS IN THE PRODUCTION OF STEEL CASTINGS TO USE IN EXTREME OPERATING CONDITIONS

Requirements for the use of steel castings in extreme conditions apply to grades from low- to high-alloyed produced with the use of secondary treatment of cast steel in order to obtain very accurate regulation of the chemical composition and to ensure very high purity of the cast steel. The optimal solution for foundry conditions was the use of an AOD converter (for the first time in Poland) for the refining of steel cast from electric arc furnace. In terms of internal quality, low-alloy cast steel castings for low temperature operation, high-alloy martensitic cast steel for high temperature operation and high-alloy duplex casting for high corrosive environments were tested. The application of the AOD process will provide the foundry with a significant increase in its domestic and international portfolio, while increasing the profitability of the foundry’s production.

Influence of Ni content on impact-abrasion wear resistance of medium-carbon low alloy cast steel

Medium-carbon low alloy wear-resistant cast steel with different Ni contents (0.08 mass%, 0.77 mass%, 1.74 mass%, 2.43 mass%) were heat treated at 1050 °C, followed by water quenching and tempering at 250 °C. The influence of Ni content on the microstructure, hardness, impact toughness and abrasive resistance of the cast steel were investigated. The results showed that the Ni contents increasing hindered the transformation of martensite phase by reducing martensite transformation start temperature (Ms) and martensite transformation finish temperature (Mf). The fine martensite phase after quenching improved the hardness, impact toughness and wear-resistance of the cast steel. The cast steel with low Ni content (0.08% or 0.77%) consists of lath tempered martensite, while the microstructure turns to mixed lath martensite and lamellar twin martensite with higher Ni content. The cast steel with 1.74% Ni showed a hardness of HRC49.5, an impact absorbing energy with V-notch impact absorbing energy of 16.7 J, and the best wear resistance among the samples.

Effect of Carbon Content on Abrasive Impact Wear Behavior of Cr-Si-Mn Low Alloy Wear Resistant Cast Steels

The effects of carbon contents on wear resistance were investigated for Cr-Si-Mn low alloy cast steels. The abrasive impact wear behavior was also analyzed. The results showed that, with the increase of carbon content in steels, the metallographic structure partly transformed from lath martensite to acicular martensite gradually, the hardness increased and the impact toughness decreased distinctly, furthermore, wear resistant first increased and then decreased, that was mainly caused by the wear mechanism changed form plastic fatigue wear to brittle fracture wear.

Effect of nickel additions on microstructure evolution and mechanical properties of low-alloy Cr-Mo cast steel

This paper presents investigation of nickel additions on the low-alloy Cr-Mo cast steel which was normalized at temperature of 920 °C. In this experiment, approximately 0.3, 0.5, and 1.0 wt% Ni was added into the Fe-1.0Mn-0.8Cr-0.4Mo cast steel. The microstructure of low-alloy Cr-Mo cast steel was observed by optical microscope and scanning electron microscope, and the phase compositions were identified by EDX analysis. Tensile, hardness, and Charpy impact tests were conducted to investigate correlation between nickel additions to microstructure characteristics and mechanical properties. The results show that increasing nickel from 0.3 to 1.0 wt% on the alloys has improved the strength without sacrificing the impact toughness. Ni addition into low alloy steel increased the austenite stability due to the grain refinement. The strength was found increase linearly with Ni addition which may caused mainly by solid solution strengthening due to Ni dissolved into the ferrite matrix.

Reducing Microsegregation in Next-Generation High-Strength Low-Alloy Cast Steels

The next generation of high-strength low-alloy (HSLA) cast steels is characterized by high levels of strength, as well as increased levels of ductility and impact toughness. The steels discussed in this paper are 4330, Eglin steel, and AF 9628 steel. Microsegregation of alloying elements within these materials, which is the tendency for a higher concentration of alloys to accumulate between dendrite arms, is commonly realized during the cooling stages of casting and can result in substandard mechanical properties. Since this next generation of HSLA cast steels is being utilized for critical commercial and military applications requiring both high levels of strength and ductility, methods of reducing microsegregation through proper heat treatment must be examined. Current methods of reducing microsegregation after casting primarily rely on vacancy diffusion. This effect is typically accelerated through heat treatments of the cast material. Herein, diffusion models are utilized to create a model capable of predicting microsegregation reduction in these high-strength low-alloy cast steels. This model was used to simulate high-temperature heat treatments in order to determine appropriate process parameters for microsegregation reduction of carbide-forming alloying elements in the next generation of high-strength low-alloy cast steels.

Evaluación de la tenacidad a la fractura de anclajes de aceros colados de un puente atirantado por ensayo miniatura de punzonamiento

La evaluación de la vida residual de componentes estructurales en servicio requiere conocer el valor de la tenacidad a la fractura, pero los métodos convencionales para medir la tenacidad demandan remover grandes cantidades de material del componente, lo cual es generalmente impráctico. Sin embargo, el Ensayo Miniatura de Punzonamiento (EMP) (que utiliza especímenes miniatura no estandarizados) ha sido empleado como una alternativa práctica y conveniente para evaluar las características de fractura del material de componentes en servicio. El propósito de esta investigación fue encontrar una relación entre la deformación a la fractura equivalente de EMP εaf y la tenacidad a la fractura JIC de aceros colados de baja aleación procedentes de anclajes de un puente atirantado localizado en el Golfo de México. La tenacidad a la fractura JIC se calculó a partir de los datos experimentales reportados de KIC en un trabajo previo y la deformación a la fractura equivalente se obtuvo mediante el EMP empleando especímenes de 10x10 mm2 por 0.5 mm de espesor. A partir de los resultados de εaf y JIC obtenidos, y correspondientes datos de aceros de baja aleación de la literatura, una correlación lineal fue propuesta para estimar la tenacidad de fractura a partir de la deformación a la fractura equivalente del EMP para los aceros colados pertenecientes a este caso de estudio.

Effect of Tempering Temperature on the Mechanical Properties of Cast L35HM Steel

Abstract A possibility to control the strength, hardness and ductility of the L35HM low-alloy structural cast steel by the applied tempering temperature is discussed in the paper. Tests were carried out on samples taken from the two randomly selected industrial melts. Heat treatment of the cast samples included quenching at 900 °C, cooling in an aqueous solution of polymer, and tempering at 600 and 650 °C. The obtained results showed that the difference in the tempering temperature equal to 50 °C can cause the difference of 121 MPa in the values of UTS and of 153 MPa in the values of 0.2%YS. For both melts tempered at 600 °C, the average values of UTS and 0.2%YS were equal to 995 MPa and 933 MPa, respectively. The values of EL and RA did not show any significant differences. Attention was drawn to large differences in strength and hardness observed between the melts tempered at 600 and 650 °C. Despite differences in the mechanical properties of the examined cast steel, the obtained results were superior to those specified by the standard.