The research and development of new type of ferro-base heat-resistant alloy

Nickel-base superalloys are high performance materials subject to severe operating conditions in the high temperature turbine section of gas turbine engines.Turbine blades in modern engines are fabricated from Ni-base alloy single crystals which are strengthened by ordered g’ precipitates.Turbine disks are made from polycrystal line Ni-base alloys because these components have higher strength requirements(due to higher stresses).By increasing the upper temperature limit for the next generation of disk materials,the aviation industry will see significant environmental as well as cost benefits. Researchers in the High Temperature Materials Center of the National Institute of Materials Science of Japan have recently completed their work on a new kind of disk alloys.The new disk alloys,a kind of nickel-coble-base superalloys processed by a normal cast and wrought(C & W) route,can withstand temperatures in excess of 725 degree centigrade,a 50-degree increase over C&W disks currently in operation. In this presentation,the author shows the design idea,workability and properties of these Ni-Co-base superalloys. Furthermore,the evaluation of the processing and microstructure on a full-scale processing of Ni-Co-base superalloy turbine disk are described,which demonstrated the advantages and possibility of the Ni-Co-base disc alloys at the component level.     

Recent Advances in Steels for Coal Fired Power Plant: A Review

The current status of the development of materials for advanced ultra supercritical power generation technology is considered in the light of changes in the priorities and opportunities worldwide for high efficiency power plant fired by coal. These include the slower economic growth, the emphasis on renewable sources, and technical setbacks with the new materials necessary for high temperature operation. Currently martensitic steels are restricted to about 620 °C and since Ni-base alloys cannot be used economically below about 700 °C, the utility industry has had to abandon the traditional incremental approach to the increasing of steam temperature. The major theme of the paper will be the potential of further materials research to identify steels with “Gap Closing” potential i.e. with sufficient strength to operate between the current limit for martensitic steels and the lowest temperature at which the Ni-base alloys become viable. Alloys with some potential in this regard are mentioned and representative properties described.     

Fatigue crack growth in some PM low alloy steels consolidated by rotary forging and sintering

Abstract

Fatigue crack propagation rates under plane strain conditions have been investigated for three PM low alloy steels consolidated to high densities by rotary compaction followed by sintering and heat treatment. It is shown that the densities and properties are intermediate between those of pressed and sintered materials and of powder forged materials. Threshold stress intensities compare satisfactorily with those for wrought counterparts, but resistances to crack growth are inferior to those of wrought steels. Possible reasons for the properties of the rotary compacted materials are considered in the light of their microstructures and the behaviour of other PM materials.     

On the Precipitation-Strengthening Contribution of the Ta-Containing Co3(Al,W)-Phase to the Creep Properties of γ/γ′ Cobalt-Base Superalloys

Metallurgical and Materials Transactions A - The creep strength of single-crystalline Co-based superalloys was found to be comparable to first-generation Ni-base superalloys. However, considerable...     

A New Oxide Morphology Map: Initial Oxidation Behavior of Ni-Base Single-Crystal Superalloys

Predictions for oxidation behavior of Ni-base superalloys become more difficult than before because of the complex alloy composition. In this study, we focus on the initial oxidation behavior of Ni-base superalloys, and we suggest a new diagram to predict the initial oxide morphology of Ni-base superalloys with 63 binary, ternary, and multicomponent Ni-base single-crystal superalloys at 1373 K (1100 °C). As a comparison of observed and calculated weight changes after one cycle at 1373 K (1100 °C) obtained by a regression analysis, 63 alloys demonstrated two distinct behaviors, which are divided heretofore into group A and group B. Microstructural observation revealed that an oxide layer in the group A alloys consists of Al₂O₃ and/or spinel or complex oxide, whereas an oxide layer in the group B alloys consists of a thick NiO layer with an Al₂O₃ internal subscale. Thermodynamic properties can reflect more effects of alloy elements in Ni-base superalloys, and Al and Cr activities, calculated by Thermo-Calc, were used as factors to predict initial oxidation morphology. Groups A and B alloys can clearly be divided according to Al and Cr activities. This was suggested as a new diagram to predict the initial oxide morphology of Ni-base superalloys, and possibly it can apply for any generation of Ni-base superalloys.     

高流速辉光放电质谱法检测镍基高温合金中痕量元素及其深度分布

为了制造效率更高,输出功率更大,同时散热更少的飞机引擎,需要燃料的燃烧温度也越来越高,因此航空发动机的生产商和涡轮发动机的制造者对材料和部件提出了新的要求。在较高的温度时,为了维持材料的机械性能和提高合金部件的控制能力,需要继续改进原有的高温合金或者开发新一代高温合金,同时制造者也在建立更加严格的规格界限和质量控制规程。本文主要描述具有高流速离子源的辉光放电质谱仪,这种仪器的分析速度快,灵敏度高,非常适合于高温合金的分析。仪器除了可以做搜索分析和基材的杂质元素含量的检测之外,其直接进样的方法可以更好地检测出各种元素在产品高温受热之后的分布情况,以及痕量元素在保护层和界面的纵向分布。     

FATIGUE BEHAVIOUR OF SINTERED METALS AND ALLOYS

Abstract

Published information on the fatigue behaviour of sintered materials is reviewed.

Porous sintered materials exhibit similar fatigue characteristics to cast and wrought materials, including fatigue limits in ferrous materials. Their endurance ratios are slightly lower than those of similar wrought materials and they may depend on porosity content. In some cases fatigue data for sintered materials show less scatter than those for similar wrought materials. The total porosity content, which is mainly determined by compacting conditions, is the most important factor influencing fatigue behaviour. Endurance limit decreases as the porosity content increases. In the copper- and iron-base materials investigated, fatigue behaviour is influenced only slightly by powder characteristics, sintering temperature, atmosphere, and time, and by post-sintering treatments. Environmental and surface conditions seem to influence the fatigue behaviour in the same manner as pore-free materials. However, notches have a less severe effect than on pore-free materials. Fatigue fracture appears to occur in the same manner as in pore-free materials. Fatigue cracks tend to start at the free surface of the specimen in preference to the internal surfaces of pores, in agreement with theoretical predictions. Sintered low-alloy steels can be heat-treated to give a wide range of fatigue strengths, and they are less notch-sensitive than pore-free steels. The fatigue properties of sintered and pore-free materials are compared and sintered materials are shown to possess fatigue strengths in the same range as cast and wrought materials.     

Niobium in Engineering Steels for Automotive Applications

In the last decade, the European niobium consumption in automotive strip and sheet has more than tripled. The development of high strength and advanced high strength steel grades for strip and plate products focused upon constantly increasing strength levels combined with excellent fatigue properties as well as formability and weldability. Until now, the high potential of microalloyed steel has not been used to the same extent in forgings and springs. This paper reviews automotive components as transmissions, suspensions and springs highlighting new material solutions for special steels having optimized processing and in‐use properties. Special consideration is given to the metallurgical background as well as to examples for the processing and application of niobium microalloyed steel in forgings and springs from low carbon and higher carbon containing steels. Niobium metallurgy permits the reduction of carbon to meet more stringent end‐user requirements demanding high strength combined with improved toughness, fatigue strength and weldability at a competitive manufacturing cost.     

Intrinsic stage i crack growth of directionally solidified Ni-Base superalloys during low-cycle fatigue at elevated temperature

Strain-controlled low-cycle fatigue tests of cylindrical smooth specimens of two kinds of directionally solidified Ni-base superalloys, RENé 80+Hf and CM 247LC, were carried out at a temperature of 873 K, and the successive process from the crack initiation to small crack propagation was investigated by employing a replication technique. Both materials exhibited typical features of stage I fatigue fracture; that is, the fracture occurred on the crystallographic 111 planes, the most important slip planes in face-centered cubic (fcc) materials. It was found that the rate of stage I crack growth, when not influenced by a nearby grain boundary, proportionally increased with the crack length. However, as the crack tip neared a grain boundary, the rate rapidly decreased. It was also shown that the crack growth rate fell when the crack deflection occurred due to secondary slip. Comparison was also made between the stage I crack growth rate and the long crack growth rate in polycrystalline Ni-base superalloys.     

A COMPARISON OF THE MECHANICAL PROPERTIES OF SOME POWDER-FORGED AND WROUGHT STEELS

Abstract

The tensile, impact, and fatigue properties of a range of powder-forged steels have been examined. A relationship has been found between the content of non-metallic inclusions and the fatigue performance. The properties of powder-forged steels at 900 N/mm² strength were compared with those of En16 wrought steel at the same level. The properties of wrought steel are demonstrably extremely variable, depending on the degree of hot work imparted during processing and on the relationship of the test-piece axis to the principal direction of working. The properties of powder-forged steel lie between the highest and lowest that can be expected in wrought steel; comparisons between the two types of material can be made only after careful consideration of their specific characteristics. Powder-forged steels were shown to be capable of developing useful properties over wide ranges of composition.     

The effect of protective coatings on the high temperature properties of a gamma prime-strengthened Ni-base superalloy

The present study examined the influence of chrome-aluminide coatings on the creep and stress rupture properties of a wrought Udimet-520 nickel-base superalloy used in gas turbine blade applications. Creep and stress rupture tests were conducted at 802 °C (1475 °F) on coated and uncoated wrought bars in the fully heat treated condition. The tests showed that the application of the chrome-aluminide coatings caused a marked deterioration in rupture strength and ductility. Masking procedures used to protect the turbine blade roots during coating of the Ni-base superalloy also affected the rupture strength or rupture ductility. The mechanical behavior in the coated creep resistant alloy was correlated with the microstructure and is discussed in terms of possible controlling processes.     

METHODS OF EXTENDING THE APPLICABILITY OF SINTERED STEELS

Abstract

It is a common opinion among users of structural parts that applications for sintered steels are limited to those where requirements for strength are low to moderate. Furthermore, sintered steels of moderate strength are thought to be very brittle. It is the object of this paper to draw attention to significant improvements which have been achieved in the last few years. These are basically a result of powder developments which are based partly on traditional alloying additions, such as Cu, Ni, Mo, and C, and partly on unique combinations of iron powders and phosphorus or on combinations of iron powders, phosphorus, carbon, and/or copper. Unusually favourable combinations of strength and ductility can be achieved with diffusion-alloys based on iron and phosphorus. Components of high-duty sintered steels capable of replacing components of conventional wrought steels can be produced from partially prealloyed combinations of iron, copper, nickel, molybdenum, and carbon. For many applications these materials can also be an alternative to powder-forged steels. All the above powder combinations show consistent and low dimensional changes during sintering so that close tolerances of intricately shaped components can be maintained. Material and processing costs are such that the improved properties can be achieved economically.     

Possibilities for raising the strength classification of ultralow-carbon steels exhibiting the BH-effect

One of the main trends in the development of materials for the body and other parts of automobiles is the greater use of high-strength steels, this being done in order to make the vehicle safer and lighter. The need for this change stems from the continual tightening of standards on tailpipe emissions. The largest metallurgical companies that presently make automobile sheet have been working with the main Russian automobile manufacturers to develop steels with improved commercial properties. This article presents results from studies conducted to optimize the technology used to make rolled products of high-strength, ultralow-carbon steels 01YuTB an 01YuPTB for the automotive industry. The optimized technology includes heat treatment in a continuous annealing furnace. Emphasis should be given to developing technical recommendations on how to optimally combine strength, stampability, and a guaranteed level of the BH-effect (BH₂ ≥ 30–40 N/mm²) in the production of automobile sheet of strength class K180, as well as BH steels of strength class K220 or higher. __________ Translated from Metallurg, No. 1, pp. 67–70, January, 2006.     

Recent progress related with ultra-steels at NIMS

Ultra - steel Project performed at National Institute for Materials Science(NIMS) 1997 -2005 proposed "Breakthroughs for innovation by steel science".The main concepts were composed of decreasing the environmental load,no or less special alloying elements and safer infrastructure with reduced the total life cost.Four "double strength and double life" steels were developed as follows:①800 MPa-class ecologically beneficial steels for welded structures,②1 500 MPa steels with high resistance to fracture,③advanced ferritic steels for 650C-USC boilers and④Ultra-steels for structures in marine and offshore environments.World steel society is still growing with threatening limits of resources and energy.Application of the ultra-steel ideas would be increasingly helpful for the global sustainability.The talk will introduce the recent progress in steel research at NIMS,based on the project accomplishments.     

THE EFFECT OF DEFORMATION ON TENSILE AND IMPACT PROPERTIES OF HOT PM-FORMED NICKEL-MOLYBDENUM STEELS

Abstract

Hardenability, tensile, and impact properties have been determined for two nickel-molybdenum powder-formed steels. The compositions of the two steels were Fe-1·8% Ni?0·5% Mo and Fe ?0·5% Ni ?0·6% Mo; carbon contents studied for both materials were 0·2, 0·3, and 0·4%. Preforms (50 × 50 × 127 mm) were pressed and then sintered for 1 h in a dissociated ammonia atmosphere at 1120°C, to provide a density of 6·5 g/cm³. Preforms were hot formed to full density by upsetting (plane strain) at 980°C or by re-pressing (uniaxial strain) at 1040°C.

Standard 25 mm-dia. × 100 mm-long Jominy end-quenched tests were made to determine hardenability. Room-temperature tensile properties were determined using 6·4 mm-dia. specimens with a 25 mm gauge-length. Standard Charpy V-notch specimens were used to determine the impact properties at ?40, 0, 22, and 100°C. Triplicate tests were made in the as formed as well as the quenched-and-tempered conditions.

The additional flow that was realized by upsetting provided higher tensile and impact strengths than re-pressing. Tensile ductility was the same for both processing conditions. Tensile yield strength (heat-treated to ～26 HV) increased with increasing carbon content for the slack quenched material and levelled off for fully martensitic structures. Room-temperature impact strength also increased with increasing carbon content owing to a decrease in the amount of ferrite in the slack quenched structure. Increasing carbon content caused a decrease in impact strength once fully martensitic structures were achieved.

Impact strength at ?40°C ranged from ～20 to 40 J. Room-temperature impact strength ranged from ～20 to 50 J. These properties were obtained for materials heat-treated to a UTS level of ～850 N/mm². At the lower carbon contents the hardenability curve was found to fall within the AISI ‘H’ band for 4620 wrought steel. At the higher carbon level (0.4% C) the Jominy curves were close to the lower limit of the ‘H’ band for the 4640 wrought steels.     

Nickel-base superalloys for USC power plants

The advanced ultra-supercritical power plants of the future will utilize steam pressures and temperatures that are too high for traditional ferritic steels,thus requiring austenitic materials.Older nickel-base superalloys such as 263 and 617 were initially evaluated under the European THERMIE project beginning in the 1990s.An entirely new age-hardened alloy 740 which possesses exceptional fireside corrosion resistance and creep strength was also developed for boiler tubing capable of serving at 700C.Subsequently,interest in the USA considered other product forms such as steam header piping and steam turbine forgings for service as high as 760C.A more stable and weldable alloy version now called 740H was developed to meet these more demanding conditions.This paper summarizes the current status of work on alloys 740 and 740H.     

Microstructural Stability and Hot Deformation of γ–γ′–δ Ni-Base Superalloys

Nickel-base superalloys exhibit excellent high-temperature mechanical and physical properties and remain the first choice for structural components in advanced gas turbine engines for the aerospace propulsion and power generation applications. In response to the increasing demand for more efficient solutions and tighter requirements linked to gas turbine technologies, the properties of nickel-base superalloys can be improved by modification of their thermo-mechanical and/or compositional attributes. Recent investigations have revealed the potential use of ternary eutectic γ–γ′–δ Ni-base superalloys in advanced gas turbines due to high temperature mechanical properties that are comparable to state-of-the-art polycrystalline Ni-base superalloys. With properties largely dependent on microstructural strengthening mechanisms, both the composition and thermo-mechanical processing parameters of this novel class of alloys need to be optimized concurrently. The hot deformation characteristics of four γ–γ′–δ Ni-base superalloys with varying levels of Nb were evaluated at temperatures and strain rates between 1353 K and 1433 K (1080 °C and 1160 °C) and 0.01 to 0.001/s, respectively. Evidence of dislocation-based plasticity was observed following deformation at low temperatures and high strain rates, while high temperatures and low strain rates promoted superplasticity in these alloys. The extent of the microstructural changes and the magnitude of the cavitation damage which occurred during deformation was found to vary as a function of the alloy composition.     

Soldification segregation in ruthenium-containing nickel-base superalloys

Ruthenium-containing multicomponent Ni-base superalloys with large variations in refractory alloying elements (Re, Ru, Ta, and W) have been investigated with respect to solidification, segregation characteristics, and the tendency to develop grain defects during directional solidification. Phase transformation temperatures and the effects of alloy composition on the liquidus temperature were determined by differential thermal analysis (DTA). The liquidus temperatures for most Ru-containing superalloys are generally higher than those of current commercial single-crystal superalloys. The partitioning behavior of individual constituents under the influence of alloy chemistry was characterized using a quantitative segregation mapping technique combined with a Scheil-type analysis. Whereas ruthenium partitioned preferentially to the dendrite cores during soldification, segregation of Ru is much less pronounced than Re and W. A higher degree of rhenium segregation was observed in Ru-containing superalloys. For the fixed processing conditions and moderate levels of Ru+Re, single-crystal solidification occurred without freckle formation or convection-induced breakdown of the solidification front. However, with high levels of Ru (9.6 ∼ 14.1 wt pct) and Re (7.2 wt pct), grain defects or the complete breakdown of single-crystal solidification was observed. Results from segregation and DTA analyses were used to estimate the corresponding Rayleigh numbers present during solidification of the experimental alloys. The Rayleigh criterion is effective for predicting the conditions under which the grain defect formation occurs during directional solidification of Ru-containing superalloys.     

高强度汽车渗碳齿轮钢的发展及应用

渗碳齿轮钢是汽车用主要结构钢之一，国内主要汽车生产厂家的高强度齿轮钢材料一直使用不同国家多个牌号的渗碳钢。随着技术和应用的发展有必要开发新品种的高强度齿轮钢。分析了高强度汽车渗碳齿轮钢在国内外的发展及应用现状，并根据我国合金材料的特点展望了其发展趋势。     

Impact forging of sintered steel preforms

Abstract

The results of a fifteen year research and development programme on the application of forge hammers to the impact powder forging of 46xx steel preforms are reviewed and assessed. The main topics are suitability of forge hammers to powder forging; effects of forging strain and forging pressure on core residual porosity; importance of pressure dwell or contact time in determining residual porosity near the surfaces and corners of powder forgings; dependence of tensile ductility, toughness, and fatigue strength on high strength, impact powder forged 46xx steel on lateral strain, residual porosity, oxygen, and sulphur contents; and inclusion volume fraction and spacing. It is shown that impact forged steels can achieve mechanical property parity at very high strength levels with high quality wrought steels. State of the art forge hammers have significant technical and economic advantages over presses in powder forging applications and are best suited to powder forging processes for which the forging strains and energy requirements are small.