Heat-resistant Cast Research Articles

Environmental Load Reduction by Reducing Ni Content of Heat Resistant Cast Alloy

Environmental Load Reduction by Reducing Ni Content of Heat Resistant Cast Alloy

Fe-25Cr-12Ni耐熱鋳鋼の高温酸化について

Fe-25Cr-12Ni耐熱鋳鋼の高温酸化について

An Investigation on the Cracking of Air Tubes of Rotary Kilns in a Sponge Iron Plant

Cracking of an air tube used for supplying air in rotary kiln of a sponge iron plant is investigated in this paper. The material of the air tube is ASTM A297 HK 40, a member of the heat-resistant cast alloy family (H series) steels widely used for enhanced high-temperature properties. Microstructural degradation occurring at high temperature affects mechanical and corrosion-resistance properties of the component. The failure analysis consists of visual observation, chemical analysis, examination of microstructures using optical and scanning electron microscopes, and characterization with energy-dispersive spectroscopy (EDS). Microstructural characterization reveals (i) intergranular corrosion at the cross section of tube wall, (ii) formation of severe chromium carbide network at the grain boundary, (iii) formation of sigma phases along the grain boundary as well as within the matrix, and (iv) generation of crack at the grain boundary filled with oxides. Analyses of these results suggest that formation of carbide network and sigma phases at the elevated service temperature depletes the alloying elements from the surrounding matrix, enhancing intergranular corrosion, which leads to cracking of the air tube.

Effects of working temperature and carbon diffusion on the microstructure of high pressure heat-resistant stainless steel tubes used in pyrolysis furnaces during service condition

In the present study, high pressure heat-resistant cast stainless steels (HP steels) modified with niobium and titanium were investigated in as-cast conditions and after being used in pyrolysis furnaces. Life span of the studied specimens obtained from pyrolysis furnace was 5 years. Microstructural changes were studied via scanning electron microscopy (SEM) equipped with energy dispersive spectrum (EDS), optical microscopy (OM), and X-ray diffraction (XRD). The effect of temperature and carbon diffusion on the microstructure, chromium-rich carbides, the NbC transformation to G-phase and other precipitates formed during service condition were discussed. The results showed that two major phases, namely chromium and niobium carbides, existed in the as-cast specimens. Temperature and carbon diffusion influenced the composition and volume fraction of secondary precipitates. Chromium and niobium carbides were transformed to M 23C 6 and G-phase respectively during service. Higher working temperatures do not always cause coarsening of precipitates. However, factors such as decarburization and carbon diffusion have important roles, too.

Influence of iron and silicon on the phase composition and structure of heat-resistant casting nikalines strengthened by nanoparticles

The phase composition of the Al-Ni-Mn-Fe-Si-Zr system is analyzed as applied to heat-resistant nikalines (aluminum alloys of a new generation based on Ni-containing eutectic), which are strengthened by the Al3Zr (L12) nanoparticles. It is shown that the presence of iron and silicon considerably complicates the phase analysis when compared with the AN4Mts2 base alloy. Silicon strongly widens the crystallization range, which increases the tendency of the alloy to form hot cracks during casting. It is shown that economically doped nikaline AN2ZhMts substantially exceeds the most heat-resistant cast aluminum alloys of the AM5 grade in the totality of its main characteristics (heat resistance and mechanical and production properties).

Investigation of weldability and property changes of high pressure heat-resistant cast stainless steel tubes used in pyrolysis furnaces after a five-year service

High pressure heat-resistant cast stainless steel (HP steel) tubes produced by centrifugal casting are used in petrochemical industries for pyrolysis furnaces. They have appropriate ductility and weldability in as-cast conditions. These steels lose their ductility and weldability after being used in service and, hence, require repair. In the present study, the effect of metallurgical changes on weldability and ductility was investigated. The life span of the studied tubes was 5 years. Using electrodes with a chemical composition close to the base metal analysis, welding was done by gas-tungsten arc welding (GTAW) process. Solution treatment was used to recover the properties of tubes which can be useful, depending on metallurgical changes.

Toughness of Ferritic Heat-Resistant Cast Steels with High Sulfur Contents

Toughness of Ferritic Heat-Resistant Cast Steels with High Sulfur Contents

Failure Analysis of Radiant Tube Burners in Continuous Annealing Line (CAL) of an Integrated Steel Plant

Failure analysis of radiant tube burners (ACI HK 40 with composition ~25 wt.% Cr, ~20 wt.% Ni) removed from a continuous annealing line (CAL) of a cold rolling mill (CRM) of an integrated steel plant was performed using optical microscopy (OM), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and microhardness measurements. Studies revealed that the failures were mainly attributed to combined influences of creep and carburization-assisted localized oxidative attack. A suitable heat-resisting cast austenitic stainless steel was identified as a candidate alloy to replace the previously used ACI HK 40 alloy.

Microstructural degradation of two cast heat resistant reformer tubes after long term service exposure

Microstructural evolution of a gas reformer tube made of the two dissimilar heat-resistant cast alloys, 25Cr–35Ni and 28Cr–48Ni–5W, was studied using light optical microscopy and scanning electron microscopy equipped with energy dispersive spectroscopy point analysis. Specimens were cut from an ex-service, failed reformer tube aged 8 years. The phases and carbides at each section of the reformer tube were determined and compared with as-cast conditions. It was found that the specimens located far from the bottom or the roof of the reformer box had mainly meta-stable phases such as G-phase or M 23C 6 due to exposure to intermediate temperatures. Those inside the reformer box, however, had phases such as M 6C carbides which are more stable than M 23C 6, and NbC due to exposure to high temperatures above 1000 °C.

The Effect of Cu on the Microstructure and the Elevated Temperature Properties of Ferritic Heat Resistant Cast Iron

The effects of copper addition on the microstructure and the elevated temperature properties of ferritic heat resistant cast iron were investigated. The as-cast pearlite formed due to the addition of Cu was fully eliminated by full annealing. As the content of Cu increased, the grain size of ferrite decreased. The grain refinement due to the addition of Cu enhanced the mechanical properties at room temperature, however, those at elevated temperature deteriorated. The addition of Cu diminished the volume change during α→γ transformation. The starting point of α→γ transformation increased with Cu contents under 1.15wt% Cu but this tendency was reversed above this point. This trend can be found also in the case of lattice parameter of ferrite matrix. It is inferred from Fe-Cu phase diagram that the addition of Cu enlarged the coexistence zone of α and γ, so it diminished the volume change during α→γ transformation.

Heat Resistant Ni-Cr-Fe Steels for Superplastic Forming Dies: From Material Microstructure to Die Design

During superplastic forming, dies are subjected to high temperatures and severe environmental conditions. Optimum material grade choice and die design have to take into account all these combined parameters. Microstructure evolution and high temperature mechanical properties are investigated and reported for various Heat Resistant Cast Steels. New die concepts are suggested for energy and cost savings.

KUBOTA ALLOY HL

Abstract Kubota Alloy HL is an austenitic Fe-Cr-Ni heat-resistant stainless steel casting with similar properties to those of HK 40. The higher chromium in the alloy confers better resistance to scaling by oxidizing and sulfur-bearing gases, while also increasing, the resistance to carburization. This datasheet provides information on composition, physical properties, and tensile properties as well as creep. It also includes information on corrosion resistance as well as casting, machining, and joining. Filing Code: SS-1058. Producer or source: Kubota Metal Corporation, Fahramet Division.

Heat Resistant Ni-Cr-Fe Steels for Superplastic Forming Dies: From Material Microstructure to Die Design

During superplastic forming, dies are subjected to high temperatures and severe environmental conditions. Optimum material grade choice and die design have to take into account all these combined parameters. Microstructure evolution and high temperature mechanical properties are investigated and reported for various Heat Resistant Cast Steels. New die concepts are suggested for energy and cost savings.

Microstructural evolution in austenitic heat-resistant cast steel 35Cr25Ni12NNbRE during long-term service

The microstructural evolution of austenitic heat-resistant cast steel 35Cr25Ni12NNbRE during aging and long-term service was investigated using optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The microstructure of the as cast steel consists of the dendritic austenite, the block-like eutectic carbide M 7C 3 spreaded among austenitic dendrite, and a small quantity of M 23C 6 carbide. The microstructure of the steel aged at 600 °C consists of eutectic carbide M 23C 6 transformed from eutectic carbide M 7C 3 and dendritic austenite in which fine secondary carbide particles M 23C 6 precipitated. The precipitated carbide M 23C 6 kept a cubic–cubic orientation relationship (OR) with austenite matrix. There existed a carbide precipitation free zone (PFZ) around the eutectic carbide. For the long-term serviced samples, the secondary carbide precipitated in the austenite strikingly increased and the PFZ disappeared. Part of the M 23C 6 transformed into M 6C, which always kept a twin OR, [ 1 1 4 ] M 6 C / / [ 1 1 0 ] A / / [ 1 1 0 ] M 23 C 6 , with the austenite and the M 23C 6 secondary carbide. In addition, a small quantity of σ phase FeCr and ɛ-Cr 2N were also identified. The effects of alloy composition and service condition on the microstructural evolution of the steel were discussed.

High Temperature Mechanical Properties of HK40-type Heat-resistant Cast Austenitic Stainless Steels

This work characterized HK40-type, cast austenitic stainless steel, as the W content was varied from 0 to 3.6 wt.%. Analysis of microstructure using optical and scanning electron microscopies showed that the alloys contained relatively large amount of Cr-carbide, Nb-compound, and MnS at the austenite grain boundary. The addition of W promoted the formation of Cr-carbide and affected the high-temperature mechanical properties. According to tension tests carried out at room temperature, 400, 600, and 800 °C, the alloys became significantly stronger and brittle as W content increased. The low-cycle fatigue tests showed that fatigue resistance was also increased with W addition, but an excessive amount of W decreased the fatigue resistance. The HK40-type alloys with 2.0 wt.% W exhibited best high-temperature mechanical performances.

High-Temperature Low-Cycle Fatigue Property of Heat-Resistant Ductile-Cast Irons

This study examined the high-temperature degradation behavior of two types of heat-resistant Si-Mo ductile cast iron (Fe-3.4C-3.7Si-0.4Mo and Fe-3.1C-4.5Si-1.0Mo) with particular attention paid to the mechanical properties and overall oxidation resistance. Tension and low-cycle fatigue properties were examined at 600 °C and 800 °C. The mechanical tests and metallographic and fractographic analyses showed that cast iron containing higher Si and Mo contents had a higher tensile strength and longer fatigue life at both temperatures than cast iron with lower levels due to the phase transformations of pearlite and carbide. The Coffin–Manson type equation was used to assess the fatigue mechanism suggesting that the higher Si-Mo alloy was stronger but less ductile than the lower Si-Mo alloy at 600 °C. However, similar properties for both alloys were observed at 800 °C because of softening and oxidation effects. Analysis of the isothermal oxidation behavior at those temperatures showed that mixed Fe2SiO4 layers were formed and the resulting scaling kinetics was much faster for low Si-Mo containing iron. With increasing temperature, subsurface degradation such as decarburization, voids, and cracks played a significant role in the overall oxidation resistance.

Damage of heat-resistant castings in a carburizing furnace

The study reviews typical damages occurring in heat-resistant castings used in box-type carburizing furnaces. The analysis was mainly based on a visual examination of elements withdrawn from operation. Furnace heat-resistant equipment can be divided into construction elements installed permanently in a furnace chamber (e.g. radiant tubs, fans, rollers) and elements utilized to set or load and unload parts to be carburized (e.g. grates, fixtures, basket). Depending on the function performed by a particular casting, its degradation process varies. The final consequence of the wear and tear of a casting is above all a decohesion of its walls that results from an influence of carburizing atmosphere, or from the combined effect of carburizing atmosphere and thermal fatigue. The effect of creep, that may occur in castings during their use as a result of the load of the structure or/and of the carburized parts, was not observed to be a direct cause of the damages.

Degradation of mechanical strength of pyrolysis furnace tubes by high-temperature carburization in a petrochemical plant

Pyrolysis furnace tubes made of HP45 heat-resistant steel casting to handle carbonaceous gases at about 850 °C in a petrochemical plant developed longitudinal cracks after less than one-third of the expected life. Detailed microstructural analysis showed that the cracks were developed by a ductile intergranular mode. This was correlated with high-temperature carburization attack leading to massive precipitation of intergranular carbides and a mixture of carbides and sigma phase within the matrix. Experimental results suggested that the highly reducing nature of the environment precluded the tube material from developing and maintaining a surface protective oxide scale, which facilitated the rapid inward diffusion of carbon.

Failure Investigation of a Furnace Tube Support

A furnace tube support failed after 6 months service at 850 °C. The support was an HK alloy, a member of the heat-resistant cast alloy family (H-Series) steels. The H-series steels are widely used in the petrochemical industry for components requiring enhanced high-temperature properties. Microstructural changes occurring at high temperature clearly affect the mechanical properties. The property degradation in HK-40 steel furnace tube support subjected to high temperature was caused by the formation of sigma phase. The investigation included metallurgical analysis, materials characterization, and mechanical analysis.

Heat-resisting ion-plasma coatings for turbine blades based on rhenium-nickel alloys

Multilayer heat-resisting ion-plasma coatings are considered for protection from high-temperature oxidation in the working blades of turbines made from heat-resisting cast nickel alloys containing rhenium. Metallographic and microprobe data are given for the structure and composition of the coatings, and also for the zone of diffusion interaction at the boundary between the coating and the heat-resistant alloy in the initial state and after oxidation in air at 1100°C for 500 h.