Heat-resistant Cast Steel Research Articles

Constructing high-density dislocations by primary (Nb,Ti)(C,N) to induce massive secondary precipitations in austenitic heat-resistant cast steel

The microstructural evolution and the high-temperature tensile properties of a novel Nb-Ti-N alloyed austenitic heat-resistant cast steel were investigated during the isothermal aging at 900 °C for up to 1000 h. The mechanisms of enhancing strength-ductility synergy and the high-temperature tensile fracture behaviors after the aging process were analyzed in detail through tensile tests at 900 °C. Obtained results show that the high-density dislocation regions and the Cr segregation, formed around the intragranular primary (Nb,Ti)(C,N), provided numerous nucleation sites for submicron-sized secondary M23C6 precipitates. The density of secondary M23C6 significantly increased, while the coarsening rate was notably reduced during the aging process. Simultaneously, the uniform dispersed precipitation of nano-sized secondary (Nb,Ti)C was promoted by massive dislocations, which exhibited high resistance to coarsening during long-term aging. The improvement of high-temperature strength was attributed to the precipitation strengthening effects induced by the submicron-sized M23C6 and nano-sized (Nb,Ti)C particles. Additionally, the enhancement of ductility during aging was mainly due to the more effective stress transmission and the ameliorated interface relationship between primary (Nb,Ti)(C,N) and austenitic matrix, which was facilitated by the abundant precipitation of secondary phases. The current findings indicate that high-density dislocations constructed by the intragranular primary (Nb,Ti)(C,N) induce the extensive dispersion of secondary strengthening phases, which enhanced both ultimate tensile strength of 158 MPa and elongation of 45.3% at 900 °C after isothermal aging for 1000 h.

Synergetic Kinetics of High-Temperature Surface Degradation Processes in Austenitic Heat-Resistant Cast Steels

Synergetic Kinetics of High-Temperature Surface Degradation Processes in Austenitic Heat-Resistant Cast Steels

Enhancing oxidation resistance of a novel nickel-saving dual-phase heat-resistant cast steel based on Mn–N optimized oxide scale

The effect of Mn–N on the oxidation behavior and microstructure evolution of a novel nickel-saving Fe–26Cr–4Ni-0.3C dual-phase heat-resistant cast steel at 900 °C was investigated. After 100 h of oxidation, the H–Mn–N steel (3.14 %Mn-0.232 %N) exhibited approximately three times better oxidation resistance compared to the L-Mn-N steel (0.24 %Mn-0.084 %N). The increase of Mn–N decreased the oxidation rate from 2.30 × 10−2 mg2∙ cm−4∙ h−1 to 3.26 × 10−3 mg2∙ cm−4∙ h−1. The oxide scale structure of L-Mn-N steel consisted of outer Cr2O3, inner (Fe0.6Cr0.4)2O3, and Fe1.4Cr1.6O4, while the oxide scale of H–Mn–N steel (3.14 %Mn) was SiO2, MnCr2O4, and Mn1.5CrO4 from the matrix to the outside. Mn–N increased the proportion of austenite from 40 % to 70 %, which reduced the diffusion rate of oxygen. This hindered the formation of layered oxide Cr2O3 and promoted the formation of a dense layer of SiO2 on the matrix surface, providing a pathway for the enhancement of the trade-off between oxidation resistance and cost.

Changes in Carburized Microstructures and Creep Properties of Nb-Added SCH13A Heat-Resistant Cast Steel due to Different Pouring Temperatures

Changes in Carburized Microstructures and Creep Properties of Nb-Added SCH13A Heat-Resistant Cast Steel due to Different Pouring Temperatures

Influence of Nb Addition on Microstructure and Creep Property of Heat-Resistant Cast Steel in Vacuum Carburizing and Quenching

The relation between microstructure and creep property of austenitic heat-resistant cast steels with and without Nb addition under the condition of repeated vacuum carburizing and quenching was investigated. Cr-carbide scale is formed on the sample surface by a carburizing reaction, resulting in the depletion of Cr in the matrix adjacent to the scale. A carburized layer consisting of various fine carbides is observed below the Cr-depleted layer, and the carburized layer depth is suppressed by Nb addition. When process of vacuum carburizing and quenching is repeated, formation of voids caused by heating and rapid cooling is more remarkable in primary Cr carbides than in primary Nb carbides. As the carburized layer depth increases, creep rupture time of both cast steels shifts to the shorter time side; however, Nb addition is effective for extending creep rupture time at 1303 K.

Development of a Novel Heat-Resistant Austenitic Cast Steel with an Improved Thermal Fatigue Resistance

Development of a Novel Heat-Resistant Austenitic Cast Steel with an Improved Thermal Fatigue Resistance

A high N and W heat-resistant martensitic cast steel with balanced tensile strength and creep resistance achieved by Laves and μ intermetallics

A high N and W heat-resistant martensitic cast steel with balanced tensile strength and creep resistance achieved by Laves and μ intermetallics

Influence of Nb Addition on Microstructure and Creep Property of Heat-Resistant Cast Steel in Vacuum Carburizing and Quenching

Influence of Nb Addition on Microstructure and Creep Property of Heat-Resistant Cast Steel in Vacuum Carburizing and Quenching

Development of Data-Driven Machine Learning Models for the Prediction of Casting Surface Defects

This paper presents an approach for the application of machine learning in the prediction and understanding of casting surface related defects. The manner by which production data from a steel and cast iron foundry can be used to create models for predicting casting surface related defect is demonstrated. The data used for the model creation were collected from a medium-sized steel and cast iron foundry in which components ranging from 1 to 100 kg in weight are produced from wear and heat resistant cast iron and steel materials. This includes all production-relevant data from the melting and casting process, as well as from the mold production, the sand preparation and component quality related data from the quality management department. The data are tethered together with each other, the information regarding the identity and number of components that resulted in scrap due to the casting surface defect metal penetrations was added to the dataset. Six different machine learning algorithms were trained and an interpretation of the models outputs was accomplished with the application of the SHAP framework.

Effect of minor Ce and Zr on the wear property of a nickel-saving austenitic heat-resistant cast steel

ABSTRACT In this work, the effect of Ce and Zr on the wear performance of a nickel-saving austenitic heat-resistant cast steel at room temperature and 900 °C are investigated. The wear mechanism and strengthening mechanism played by the addition of Ce and Zr are also discussed. The enhanced work-hardening rate after adding Ce and Zr strengthens the worn surface during wearing and improves the wear resistance of the nickel-saving austenitic steel at room temperature. The addition of Ce and Zr reduces the dynamic recovery and recrystallisation softening effect, which is the main reason for improving the high-temperature wear performance of the nickel-saving austenitic steel. Besides, the wear-protective glaze layer formed on the worn surface of Ce- and Zr-containing alloys could also reduce the high-temperature wear of the nickel-saving austenitic steel.

Ocena kvalitete izločevalnega žarjenja termično obstojne jeklene litine z uporabo Taguchijeve analize

In this study, the effects of temperature and time on the hardness of heat-resistant cast steel HK30 Nb obtained with centrifugal casting were analysed using the Taguchi method. On the basis of the analysis of the obtained results, we reached reliable conclusions on the improvement of the exploitation properties. The tests showed that precipitation annealing of a HK30 Nb casting can improve the exploitation properties at high temperatures. The defined temperature and holding time comply with the results of the mathematical analysis of the achieved properties, and the presumed research theory from this study can hence be confirmed. The studies showed that the mechanical properties improved during the precipitation-annealing process. During this process, significant transformations of the carbide phase occur in the microstructure, thereby changing its morphology, distribution, size and composition, which was confirmed by testing the microstructure with a scanning electron microscope.

Influence of Pouring Temperature on Microstructure and High Temperature Mechanical Properties of Nb-added Austenitic Heat Resistant Cast Steel

Influence of Pouring Temperature on Microstructure and High Temperature Mechanical Properties of Nb-added Austenitic Heat Resistant Cast Steel

Microstructure evolution and corrosion behavior of Nb-alloyed cast heat-resistant steel during different aging treatments

The microstructure evolution of heat-resistant cast stainless steels aged at 600, 700, 800 and 900 °C for 2 h was investigated by scanning electron microscopy and X-ray diffraction. Potentiodynamic polarization curves were applied to study the effects of Nb addition and aging temperature on corrosion resistance. The results demonstrated that eutectoid decomposition of the ferritic phase (δ → σ + γ2) was observed at 700–900 °C. The content of σ-phase first increased and then decreased in the steels, where the maximum content was obtained at 800 °C, indicating that the highest hardness occurred at 800 °C accordingly. The hardness of Nb-containing steels was significantly higher than that of Nb-free steels. The corrosion resistance of heat-resistant cast steels in various aging temperatures was different due to the formation of σ-phase. Both Cr-rich carbides and σ-phase were harmful to the corrosion resistance, while Cr-rich carbides were the main factor. Nb-containing heat-resistant cast steels exhibited superior corrosion resistance, as Cr-rich carbides were reduced and the corrosion products of Nb-rich slowed down the formation of steady-state pits.

Influence of Pouring Temperature on Microstructure and Elevated Temperature Properties of Heat Resistant Cast Steel

Influence of Pouring Temperature on Microstructure and Elevated Temperature Properties of Heat Resistant Cast Steel

Effect of W Addition on Microstructure and High Temperature Properties of Austenitic Heat Resistant Cast Steel

Effect of W Addition on Microstructure and High Temperature Properties of Austenitic Heat Resistant Cast Steel

Effect of Ce on oxidation behaviour and microstructure evolution of a nickel-saving austenitic heat-resistant cast steel

The effect of Ce on the oxidation behaviour and microstructure evolution of nickel-saving austenitic heat-resistant cast steel in air at 900 °C was investigated by performing the isothermal oxidation tests. After 200 h of oxidation, the oxidation resistance of Ce-containing steel was about 20 % higher than that of Ce-free steel. In addition to its role as a reactive element, alloyed Ce slowed the rate of manganese depletion from the substrate and subsurface ferrite formation, leading to the improvement of the oxidation resistance of Ce-containing steel.

Effect of minor Zr on oxidation resistance and mechanical property of nickel-saving austenitic heat-resistant cast steel

In order to study the effect of minor Zr on the oxidation resistance and the mechanical properties of nickel-saving austenitic heat-resistant cast steel, the oxidation resistance at 900 °C and the tensile properties at room temperature and at 900 °C of Zr-containing and Zr-free steels were carried out. The results showed that the addition of 0.011% Zr could slightly reduce the oxidation rate and improve the oxidation resistance of Zr-containing steel. In addition, the tensile properties of Zr-containing steel at room temperature and at 900 °C were significantly improved. Brittle fracture occurred in two experimental steels at both temperatures, and brittle characteristics appeared in the fractures.

PM-10 Effect of microstructure on creep property of W-added heat resistant cast steel

PM-10 Effect of microstructure on creep property of W-added heat resistant cast steel

The influence of solution annealing on microstructure and mechanical properties heat-resistant cast Steel HK30 modified by Niobium

In this paper, the room temperature mechanical properties, as well as the microstructure of HK 30 Nb steel, were tested in the initial as-cast and solution annealed condition. Results show that tensile properties after the solution annealing have a slightly lower value than as-cast samples. Microstructural analysis of samples after solution annealing showed dissolution of primary carbides present in the initial as-cast condition. The morphology and composition of carbides were changed during a solution annealing. Analysis of microstructure was done by optical microscopy (OM) and scanning electron microscope (SEM), whereas hardness and tensile tests were performed for characterization of mechanical properties.

G-phase formation in twenty-years aged heat-resistant cast austenitic steel reformer tube

HP50M heat-resistant cast austenitic steel tubes are exposed to high temperatures (i.e. 900 °C) for long periods (10 years or longer) in petrochemical reforming plants. Twenty-years aged tubes exhibit microstructural changes such as primary carbide transformation and growth, MC carbide transition to G-phase, and fine secondary M23C6 precipitation. Analytical electron microscopy reveals that silicon tends to segregate at austenite inter-dendritic boundaries in fresh as-cast tubes. Thermo-kinetic simulation of long-term precipitate evolution of the steel is carried out together with Si segregation compositions. The experimentally observed general trend that G-phase forms at the expense of MC carbide is successfully predicted for the Si segregation compositions after a few thousand hours of aging in a temperature range between 700 and 900 °C. This study demonstrates that the Si segregation plays a crucial role in the formation of G-phase in this type of heat-resistant cast steels. Additional heat-treatment experiment confirms that G-phase becomes unstable above 900 °C and the reverse transition to MC occurs.