Hot Brittleness Research Articles

Metallographic study of non-ferrous metal products from the Maray 1 site of the Baitovo Cul-ture in the Lower Ishim River region

The article examines non-ferrous metal products from the Baitovo Culture materials of the Early Iron Age hillfort of Marai 1. This settlement is located in the forest-steppe of the Ishim River region of Western Siberia. The upper building hori-zon marks the settlement of the Baitovo Culture dating to the 4th–2nd centuries BC. Metallographic analysis of 28 items was carried out using the Axio Observer D1m microscope (Zeiss). As a result, eight technological schemes characteristic for the metalworking activities of the Baitovo population have been identified. The study shows that prevailing were smithing tech-nologies in different temperature regimes for the production of non-ferrous metal objects (16 specimens, 57.2 %). The pref-erence was given to hot forging in the red-heat regime at 600–800°C (7 specimens, 25 %), cold forging with annealing (5 specimens, 17.8 %), as well as incomplete hot forging at 300–500°C (3 specimens, 10.7 %). Casting without further refine-ment was recorded in the microstructures of arrowheads, ingots and splashes (9 specimens, 14.2 %). Casting, followed by a slight degree of deformation (20–30 %), was noted in three cases. This scheme correlates with the metalworking traditions of the Itkul and Krasnoozerskaya Cultures, and it was dominant on the territory of the Tobol-Ishim region during the Early Iron Age. Such a low percentage of items related to it could be explained by the absence in Marai 1 of large items cast in moulds needing further refinement (knives, celts, etc.). A microstructural study confirmed the use of pure oxidized copper by the craftsmen of the Baitovo Culture, with characteristic inclusions of Cu–Cu2O eutectic, associated with the Ural production centres. Arrowheads and an ingot made of pure oxidized copper were probably a direct import from the territory of the Itkul Culture. Low-alloy tin and arsenic bronzes, coming from the metal production centres of Kazakhstan and Altai, were also used to the same extent for production of some tools and jewellery. The correlation between the type of product, composition of raw materials and technology of its manufacture has been revealed, which is most clearly manifested in arrowheads and awls. The use of high temperatures and significant degrees of compression (80–90 %) has been recorded in a number of cases, resulting in the appearance of rejects. Cracks of hot brittleness, as well as of cold brittleness, occurred in the process of technological cycle, carried out with an excess of the tensile strength of the metal.

Study of technological properties of new aluminum-calcium alloys for pistons of internal combustion engines

The results of studies of the casting properties of aluminum-calcium alloys in comparison with known silumins are presented. The alloys were prepared in a resistance electric furnace based on pure components and ligatures. The pouring was carried out at temperatures of 700 and 780 oC for silumins and aluminum-calcium alloys, respectively, obtaining flat ingots for subsequent remelting and casting of samples. All samples were poured with the same superheat above the liquidus temperature of 100 oC. It is shown that alloys with calcium (both eutectic and hypereutectic) are not inferior to widely used silumins in terms of fluidity, hot brittleness, and form fillability. For the first time, the parameters of difficult shrinkage were determined in a T-shaped sample of aluminum-calcium alloys in comparison with silumins. It is shown that eutectic alloys have comparable values of linear shrinkage with eutectic silumins, and the shrinkage of the hypereutectic alloy Al – 6% Ca – 3% Mn exceeds the shrinkage of the hypereutectic silumin AK18 by 1.5 times (1.5 and 1%, respectively). A high deformation plasticity during hot and cold rolling of the Al6Ca3Mn hypereutectic alloy has been established. The overall reduction ratio after applying both rolling methods exceeded 95%. The primary crystals retained their compact size and shape. It has been established that the strength properties of cold-rolled sheets from the Al6Ca3Mn hypereutectic alloy correspond to the strength values of the AD31 industrial aluminum alloy, which allows to consider it promising in those industries where a combination of high manufacturability with reduced thermal and electrical conductivity is required.

Causes of Corner Cracks in Hypoperitectic Microalloyed Steel Billets

Due to the development of continuous casting technology, the incidence of cracks in the continuous casting process has been significantly reduced. However, a few small cracks still appear during the continuous casting of special steel. For instance, cracks often appear at the corner of the billet during the production of hypoperitectic microalloyed steel. Most research on the causes of corner cracks in hypoperitectic microalloyed steel has focused on investigating the hot ductility of steel and not considered the shrinkage characteristics during solidification. Herein, the hot ductility behavior show that cracks are not related to the hot brittleness of steel. The effects of alloy composition on the phase evolution and shrinkage of steel during solidification are focused. Uneven solidification leads to excessive shrinkage of the corners in the billet, and an air gap is generated between the billet and the mold. The return of temperature in the corner of the billet results in the coarseness of the corner grain. Abnormal solidification also results in the severe deformation of the billet, leading to severe wear with the mold, causing Cu to infiltrate into the billet, and further increasing the crack sensitivity of the steel.

Characters of Deformation and Surface Quality and Cutter Wearing at High-Speed Cutting

In this paper, the impact of cutting speed and feed amount on cutting deformation and surface quality and cutter wear have been studied by the test of high manganese steel cutting with metal ceramic tool at high speed. The results show that it is feasible by cutting high manganese steel with cermet tool at high-speed cutting (HSC). Chip changes into succession segment from band in macrostate. Sawteeth can be seen on the top surface of chip while high temperature feature in burning color and cold welding form appear on the bottom of the chip. The model of surface roughness built can be used to predict surface quality at HSC, and provided cutting optimized parameters scheme. Further research indicates that high-speed cutting has its special deformation mechanism and plastic chips exhibit hot brittleness which provides a favorable condition for solving the chip breaking problem in the cutting of high manganese steel.

Effect of tin addition on the microstructure and properties of ferritic stainless steel

This article reports the effects of Sn on the inclusions as well as the mechanical properties and hot workability of ferritic stainless steel. Precipitation phases and inclusions in Sn-bearing ferritic stainless steel were observed, and the relationship between the workability and the microstructure of the steel was established. Energy-dispersive X-ray spectroscopic analysis of the steel reveals that an almost pure Sn phase forms and MnS-Sn compound inclusions appear in the steel with a higher Sn content. Little Sn segregation was observed in grain boundaries and in the areas around sulfide inclusions; however, the presence of Sn does not adversely affect the workability of the steel containing 0.4wt% Sn. When the Sn content is 0.1wt%–0.4wt%, Sn improves the tensile strength and the plastic strain ratio and also improves the plasticity with increasing temperature. A mechanism of improving the workability of ferritic stainless steel induced by Sn addition was discussed: the presence of Sn lowers the defect concentration in the ultra-pure ferritic lattice and the good distribution of tin in the lattice overcomes the problem of hot brittleness that occurs in low-carbon steel as a result of Sn segregation.

Effect of Manganese Sulphide Size on the Precipitation of Tin Heterogeneous Nucleation in as-Cast Steel

AbstractTramp elements in steels such as tin have been thought harmful because of the hot brittleness at grain boundaries and will be enriched in new steels because of difficulty of removal. It has been an important and difficult matter for metallurgist to use these elements. In the present paper, the as-cast steel containing high concentration of tin is prepared in laboratory and tin precipitates at the manganese sulphide inclusions have been found. A theoretical model is established to calculate the size of manganese sulphide inclusions acted as the heterogeneous nucleation site of tin precipitation. The results show that the inclusions with the smaller contact angle between tin precipitate is more advantageous to be the nucleus of tin heterogeneous nucleation. In this experiment, the manganese sulphide inclusions whose size is 2~4 μm in diameter can act as the nuclei of the nucleation of tin precipitation.

Effect of tin on corrosion resistance and formability of tin bearing ferritic stainless steel

The inclusions modification, the morphology of microstructure, the mechanical property at room temperature and the mechanical property at high temperature of tin bearing stainless steel were studied under the experimental condition. The effect of tin on the microstructure of steel matrix and the composition evolution of deoxidisation were analysed. Under experimental conditions, because of the lower defect in ultra-pure ferritic lattice, the well distribution of tin in lattice overcame the problem of hot brittleness happened in low carbon steel by the segregation of tin. Small amount of tin increased the tensile strength, improved its plastic strain ratio and relatively high amount of tin had no adversely effect on the workability. With the increase in temperature, the addition of tin improved the plasticity on the contrary.

Effect of manganese sulfide on the precipitation behavior of tin in steel

Tramp elements such as tin are considered harmful to steel because of hot brittleness they induce at high temperatures. Because tramp elements retained in steel scrap will be enriched in new steel due to the difficultly of their removal, studies on the precipitation behavior of tin are essential. In this study, the effects of different inclusions on the precipitation behavior of tin in steel were studied. The results show that the tin-rich phase precipitates at austenite grain boundaries in an Fe-5%Sn alloy without MnS precipitates, whereas Sn precipitates at the boundaries of MnS inclusions in steel that contains MnS precipitates. MnS is more effective than silicon dioxide or aluminum oxide as a nucleation site for the precipitation of the tin phase, which is consistent with the disregistry between the lattice parameters of the tin phase and those of the inclusions.

Optimization of the Compositions of the High Strength Casting Aluminium Alloys Based on Nickel Eutectic

The phase composition of the AlNiMnFeSiZr system was analyzed with respect to new-generation heat resistant casting aluminum alloys based on a 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 compared with the AlNiMnFe base alloy. Alloys with low silicon content have a sufficiently good casting property, which enables fabrication of thin-walled castings, not inferior to AA356 alloy types widely used to cast complex shapes. Addition of silicon to the AlNiMnFe base alloy sharply deteriorates hot cracks. Silicon greatly decreases the solubility of Zr at (Al), which is reflected on hot brittleness of Al2%Ni1%Mn0,5%Fe-0,2%Zr system alloys.

Hot ductility of eco-friendly low carbon resulphurised free cutting steel with bismuth

The hot ductility of low carbon resulphurised free cutting steel with different bismuth contents was studied using a Gleeble-1500 thermal–mechanical simulator, and the hot brittleness mechanism was analysed with a combination of SEM and energy dispersive X-ray spectroscopy. The results showed that the steels with bismuth contents of 0·12 and 0·17 wt-% both had a good hot ductility (RA, >70%) at 1100–1200°C, which illustrated that the steels might be suitable for the rolling provided the finish rolling temperature does not go <1100°C. However, the hot ductility of the steels deteriorated with the increase in bismuth content at 950–1100°C because of the presence of the low melting point liquid bismuth films at austenite grain boundaries and the delay of the dynamic recrystallisation by Bi additions. At 850–900°C, the steels all had very poor hot ductility, which was mainly attributed to the presence of the ferrite film and the unrecrystallised austenite as well as the presence of the low melting point phases pure Bi and Fe rich (Fe,Mn)S.

Summary of the Function of Sn in Iron and Steel

In the steel industry Sn is always regarded as harmful impurity element, one of "Five harmful elements", which affects the welding property and equality of steel product especially the equality of continuously cast bloom and causes hot brittleness, temper brittleness, crack and fracture. While Sn element also has a vital influence on free-cutting steel, electrical sheet, cast iron and stainless steel. NSSC developed ferritic stainless steel containing low Sn and Ni content improving the corrosion resistance performance and the workability significantly. So the Sn element, as cheap alternative adding element, can substitute for Cr and Ni. It's helpful to study the effect of tin in the iron and steel and develop new stainless steel products of high equality conserving chromium resources. In this way it will promote the variety and technique of stainless steel, ensure the independence on resources and conserve resources remarkably.

Development of a magnesium alloy with good casting characteristics on the basis of Mg–Al–Ca–Mn system, having Mg–Al2Ca structure

Application of calcium as alloying element for magnesium alloys has been considered according to literature data. Mg–7%Al–4%Ca–0.5%Mn casting alloy was offered, which possesses the low propensity to the hot brittleness and good castability. The alloy has the moderate strength (σu = 150 MPa) and the satisfactory percentage elongation (δ = 3%). It is shown, that calcium-containing alloys smelting of Mg–Al–Ca–Mn system is preferable with the application of low-chloride flux FL10 (20%MgCl2; 29%KCl; 12%BaCl2; 23%CaF2; 15%MgF2; 1%B2O3). The alloy smelting in the atmosphere of argon and SF6 mixture results in the increased shelling and waste of calcium. The heat treatment is offered for the developed alloy, which is directed to the Al2Ca phase spheroidizing. The developed magnesium alloy, alloyed with calcium, is perspective for the industry production of low-cost moulding.

Influence of valence electron structures of phase and biphase interfaces of sulfides on hot brittleness in steel

This paper calculates the electron structures of phase of FeS, MnS and their biphase interface electron structures with austenite in steel. The precipitation and the transformation of FeS and MnS are investigated through studying the valence electron pair numbers on the strongest bond n A with the structure formation factor S. The continuity of electron density and its relation with stress are explored in the biphase interfaces with the electron density difference απ Using n A, S, απ we explain the reason why FeS can bring about hot brittleness in steel and the physical mechanism why MnS may eliminate or inhibit hot brittleness, based on which satisfying results are obtained by calculating several rare-earth sulfides.

Influence of Trace Elements on Hot Ductility of an Ultra High Purity Invar Alloy

Like steels, austenitic INVAR alloys Fe-Ni 36 % show a large ductility trough between 500°C and 1100°C. To understand hot brittleness mechanisms and especially trace element effects, synthetic alloys were prepared using ultra-high purity iron and nickel doped with selected amounts of carbon, sulphur, boron, aluminium, and nitrogen. Four kinds of synthetic alloys were studied to establish the intrinsic influence of sulphur, the combined effects of sulphur and precipitates such AIN or BN, and the effect of boron in the presence of sulphur, on ductility and fracture mechanisms. We propose several mechanisms to explain the loss and the recovery of ductility for each of the studied alloys, and then define the field of temperatures where these mechanisms control ductility.

Liquid Eutectic Brittleness in Austenitic Cr-Ni Steels / Versprödung von austenitischen Cr-Ni-Stählen durch niedrigschmelzende Eutektika

Investigations of crack formation in the hot rolling process of hollow blooms of titanium stabilized austenitic steel were carried out. The microscopic and microfractographic observations revealed the melting of lamellar titanium carbide-sulphides and the formation of films on the austenite grain boundaries. This is the main reason for hot brittleness. It was found that for the tested steel sulphur content of 0.011% and lower makes it resistant against hot brittleness caused by titanium carbide-sulphides

High resolution autoradiography for revealing sulphur segregation at austenite grain boundaries

A high resolution autoradiography technique was applied to observe the evolution of sulphur (S) segregation level in a high-purity iron doped with carbon (C), about 30 ppm of S and/or aluminum (Al) and nitrogen (N). The sample radioactivity was 5.6 KBq (0.15 μ Ci) with an exposure time of about 3 wk. The alloys were annealed at 950°C or 1150°C and also deformed at 950°C (in the hot brittleness temperature region). The S segregation revealed on austenite grain boundaries is more pronounced on the deformed specimen containing AIN precipitates. A high S concentration was observed in cracked regions. At 1150°C, the segregation level is smaller. A specimen containing only S deformed at 950°C, exhibits S segregation on dynamically recrystallized boundaries.

Segregation-induced intergranular brittleness of ultrahigh-purity Fe–S alloys

AbstractThe hot ductility of ultrahigh–purity Fe–S alloys doped with 20 to 100 ppm sulphur has been studied by tensile tests at a strain rate of e = 2 × 10−3 S−1. A well defined ductility trough between 850 and 1100°C was found in alloys containing ~50 ppm sulphur. This minimum sulphur content necessary to produce an intergranular embrittling effect is much higher than in steels containing aluminium and nitrogen doped with 10 ppm sulphur. The role of sulphur in reducing hot ductility is explained in terms of the intergranular brittleness caused by the presence of sulphur on grain boundaries, which decrease their cohesion. The intergranular hot brittleness of Fe–S alloys can be attenuated by dynamic recrystallization at low sulphur contents. In this case the dynamic recrystallization rate must be higher than the void nucleation and propagation rate. The hot ductility minimum temperature shifts with increasing sulphur content and seems to change in the same manner as the sulphur solubility limit temperature...

Tendency toward hot embrittlement of St3sp, 14G2, and 15KhSND steels with an increased arsenic content

1. Hot-rolled low-carbon St3sp and low-alloy 14G2 and 15KhSND steels with a ferriticpearlitic structure with phosphorus contents within the limits of GOST 380-71 and GOST 19282-73 and an arsenic content increased to 0.15% possess an increased resistance to hot embrittlement. 2. In the heat-treated condition with a bainitic-martensitic tempering structure 15KhSND steel with an increased phosphorus and arsenic content possesses a reduced resistance to hot brittleness in comparison with hot-rolled steel with a ferritic-pearlitic structure. The primary effect of hot embrittlement of this steel is related to the presence in the steel of an increased (>0.020%) phosphorus content.

Hot brittleness of Mo+30% W

1. The alloy of Mo+30% W is susceptible to hot brittleness at 1400–1800°C. 2. Varying the tungsten content from 28 to 35% has little effect on the susceptibility to hot brittleness. Raising the carbon content from 0.002 to 0.007% sharply reduces the reduction in section in the hot brittleness range. The addition of a small amount of hafnium (∼0.2%) to the Mo+30% W alloy reduces susceptibility to hot brittleness. 3. Increasing the strain rate within the limits of 0.5–3000 mm/min reduces susceptibility to hot brittleness. 4. The hot brittleness of the alloy is due to precipitation of phase of the Mo2C type in the grain boundaries.

Some New Rheological Experiments on Igneous Rocks at Temperatures up to 1120 C

Summary The stress-strain relations and creep behaviour of a dolerite, a microgranodiorite, and a dunite have been determined in uniaxial compression at temperatures up to 1120°C. All three rocks remained brittle at temperatures up to 1050C, with approximately linear stress-strain relations and small fracture strains. Creep tests were carried out at stresses (< 10' Nm-2)* which were low compared to the uniaxial compressive strength at the same temperature. At these stresses and in experiments with a duration of -1 d only transient creep was observed, with the creep strain proportional to a fractional power of the time (Andrade creep), as was observed in earlier experiments at lower temperatures, and the creep rate decreased with the elapse of time. The apparent viscosity, therefore, increases with time, having a value in the range 10I2 - 10'' Nsm-2 after times of 10% and 10- lo2' Nsm-' after times of -3y (by extrapolation)?. The activation energy for creep at a low stress of 130 x lo5 Nm-2 determined for microgranodiorite at temperatures greater than 800°C and for dolerite at temperatures greater than 940°C indicated that the creep was probably diffusion controlled. Using a theory due to Mott, the steady-state creep rate and the corresponding equivalent viscosity were calculated for the conditions of the experiments. The viscosities for pressures on the geotherms of Ringwood were then calculated, by making use of the proportionality between activation energy for diffusion and the absolute melting temperature. For stresses in the range lo6- 10' Nm-' dolerite has a viscosity of 10- lo2' Nsm-2 at at depths of 60-80 kin in oceanic areas, and at depths greater than 120 km in shield areas; and microgranodiorite at the same stresses has a similar viscosity at depths in the range 80-130 km in shield areas. These estimates are in satisfactory agreement with present concepts of the lithosphere. At temperatures above 1050°C the dolerite and microgranodiorite exhibited partial melting. The dolerite remained brittle, with the partial melt being extruded from microfractures, but the microgranodiorite showed some ductility. We can postulate that even rocks deep in the mantle may be brittle if their temperatures are not more than N 1OOOC. A discussion is given of the apparent conflict between the experimental observation of hot brittleness and the geological observation that even some comparatively cool silicate rocks have apparently deformed in a ductile manner.