Evaluation of properties and microstructure as a function of tempering time at intercritical temperatures in HY-80 steel castings

Prior work on a failed HY-80 Bridge Access Trunk (BAT) casting indicated the cause of failure to be improper processing techniques. As-received HY-80 casting material showed a non-homogenous microstructure with two distinct microconstituents present: undertempered martensite and a layered martensite–ferrite structure. Heat treatment temperatures from in the intercritical range (721–799 °C) produced microstructures that differ from the desired uniform microstructure of tempered martensite and were similar to those found in the failed casting. In order to further examine the relationship between processing and microstructure, it was decided to vary the time for which the steel was held in the intercritical temperature range. This additional work was warranted by the medium intercritical heat treatment results in the previous study [Holthaus JE, Koul MG, Moran AL. Property and microstructure evaluation as a function of processing parameters: large hy-80 steel casting for a US navy submarine. Eng Fail Anal 2006;13(1):1397–409] and its similarity to the failed casting microstructures. An important finding of this study is that, contrary to normal behavior during tempering, HY-80 steel tempered in the intercritical range demonstrates a severe loss of toughness; which can be exaggerated for longer hold times and higher temperatures. To confirm the hypothesis that the presence of brittle martensite formed by improper heat treatment was the cause of failure, SEM section fractography was employed to directly examine the microstructure underlying the fracture surface and to identify a correlation between microstructure and fracture mode.     

Modelling and simulation of the electric slag remelting guide vane casting (ESRC) process and its application

Modelling and experiment work is carried out for a large stainless steel casting with variable cross-section and a curved surface which is produced by the electric slag remelting casting process. The casting is part of a hydraulic runner generator at a power station of a big river.

Mathematical models of the heat transfer and melted rate from an expendable metallic electrode were established. The melted rate is related to some important parameters, such as electric current and voltage, temperature and the flow rate of the cooling water in a crystallizer. Electrode melting, the moving pattern of the melted pool and the slag pool and the melt solidification in the metal pool were simulated.

In order to make the enmeshment of the variable curved surface of the casting, a co-operation method of extended constructive solid geometry (CSG) from 9 to 21 uniform geometry with B-Spline surface functions is developed. By this method the guide vane casting is enmeshed. The boundary condition between the steel casting and the crystallizer cooled by water was measured.

Based on the above new content the solidification simulation software ESRC3D is developed. Using it to simulate the whole process of ESRC with different parameters, instead of exploring the technological parameters of casting production by the trail-and-error method, the optimized parameters from the simulation for production of the large stainless steel castings with variable cross-section and a curved surface, such as the guide vane castings, have been used to produce them. Economic benefit and good quality of castings are obtained. Guide vane castings are widely applied to the hydraulic runner generator at numerous river power stations.     

Modelling and simulation of the electric slag remelting guide vane casting (ESRC) process and its application

Modelling and experiment work is carried out for a large stainless steel casting with variable cross-section and a curved surface which is produced by the electric slag remelting casting process. The casting is part of a hydraulic runner generator at a power station of a big river.Mathematical models of the heat transfer and melted rate from an expendable metallic electrode were established. The melted rate is related to some important parameters, such as electric current and voltage, temperature and the flow rate of the cooling water in a crystallizer. Electrode melting, the moving pattern of the melted pool and the slag pool and the melt solidification in the metal pool were simulated.In order to make the enmeshment of the variable curved surface of the casting, a co-operation method of extended constructive solid geometry (CSG) from 9 to 21 uniform geometry with B-Spline surface functions is developed. By this method the guide vane casting is enmeshed. The boundary condition between the steel casting and the crystallizer cooled by water was measured.Based on the above new content the solidification simulation software ESRC3D is developed. Using it to simulate the whole process of ESRC with different parameters, instead of exploring the technological parameters of casting production by the trail-and-error method, the optimized parameters from the simulation for production of the large stainless steel castings with variable cross-section and a curved surface, such as the guide vane castings, have been used to produce them. Economic benefit and good quality of castings are obtained. Guide vane castings are widely applied to the hydraulic runner generator at numerous river power stations.     

Failure of steel castings welded to heavy truck axles

Minor changes in steel chemistry can have a significant affect on weld quality. Weld procedures performed in a manufacturing environment are usually developed based on the steel composition required in a material specification. This is done to consistently produce acceptable weld properties without developing a high hardness heat-affected zone (HAZ) in the adjacent base metal. Fatigue cracks were visually detected in cast steel suspension brackets after operators reported noticing looseness in the rear suspension system. These trucks were associated with a particular vocation that resulted in significant loads transferred through the torque rods that position the rear axles. It was discovered that the carbon equivalent (chemistry) in the steel castings had increased slightly over a period of time which ultimately resulted in a higher than expected hardness in the HAZ. Underbead cracks had formed in the HAZ of the casting that subsequently propagated by fatigue that could have resulted in detachment of the castings from the axle housing.     

Stress Response of Magnetic Barkhausen Noise in Submarine Hull Steel: A Comparative Study

The development of magnetic Barkhausen noise methods for rapid detection of residual stress concentrations has implications for integrity assessment of submarine pressure hulls. However, the stress-response of Barkhausen noise in submarine hull steel, HY-80, is complicated by the influence of the material’s martensitic microstructure. The present work sheds light on the stress-dependent behavior of Barkhausen noise in HY-80 by comparing its signal characteristics with those of more common ferrite/pearlite steels. HY-80 and various ferrite/pearlite steel plates were uni-axially stressed up to and beyond the level for plastic deformation. Barkhausen noise measurements, performed using the same sensor under reproducible flux-controlled magnetization conditions, facilitated a direct comparison of material responses. Results showed that with the application of tensile stress, the Barkhausen noise signal of ferrite/pearlite steels linearly increased, reached a peak value and saturated in the elastic region. By contrast, HY-80 demonstrated a linear increase with tensile stress characterized by a transition from a lower to a seven times higher rate of change for stresses above 200 MPa up to its yield point. The different stress-response of HY-80 was attributed to its martensitic microstructure, which modifies the response of the domain structure under tensile stress conditions.     

Failure analysis of a river water circulating pump shaft from a NPP

This paper presents the failure analysis of a river water circulating pump from a Nuclear Power Plant. The failed component was the upper shaft made of martensitic stainless steel. The metallurgical analyses performed include fractography, metallography and energy dispersive spectrometry analysis. Charpy impact, tensile and hardness tests were also performed. The destructive examination carried out revealed that the root cause of the pump shaft failure was an improper thermal treatment of the material that generated a temper embrittlement process. However, in addition, a hydrogen embrittlement process could have contributed to the failure.     

Effects of Process Settings on the Porosity Levels of AM60B Magnesium Die ““Castings

The study examined effect of die casting process parameters on porosity in magnesium alloy AM60B. Porosity is unavoidable in die casting products, but it can be reduced by controlling the process parameters. It is shown in this work that die casting parameters such as plunger stroke, first phase speed, second phase speed and consolidation pressure all have a significant influence on the porosity level of AM60B magnesium die castings. The relationship between the porosity level and the processing parameters has been investigated. The paper also discusses the developing application of magnesium die castings in the microelectronics and automotive industries,     

Dynamic fracture toughness parameters for HY-80 and HY-130 steels and their weldments

Lower bound dynamic fracture toughness parameters for HY-80 and HY-130 steel and their weld metals are identified. Specific values of the parameters K_Id and K_Im obtained from direct measurements are reported together with estimates inferred from the large body of Charpy energy, nil ductility transition temperature and dynamic tear energy measurements. The emphasis is on reasonable lower bound values at 30°F, the lowest anticipated service temperature, for use in elastodynamic analyses of crack growth initiation, propagation, and arrest in ship structures. For these conditions, it has been found that the ratio K_Id/ σ_Y is approximately equal to 2 in^1/2 for HY-80 steel. For HY-130 steel and the HY-80 and HY-130 weld metals under these same conditions, K_Id/ σ_Y is approximately 1 in^1/2. Consequently, HY-80 plate appears to be substantially more resistant to fracture under dynamic loading than are the other three grades examined.     

Failure Analysis of Ethylene Cracking Tube

Radiant tubes of an ethane furnace at a petrochemical plant fabricated from an austenitic heat resistant steel casting (HP grade) failed along longitudinal direction after a fraction of anticipated service life. To study the cause of failure, microstructures of as-received and used tubes were investigated by optical and scanning electron microscopy and the microchemical composition of tubes and precipitated carbide were determined by energy dispersive X-ray (EDS). Also, the morphology of deposited coke particles was determined by SEM/EDS. Finally to measure the extent of carbon penetration, hardness testing was performed on the inner and outer surface of tube. The experimental results show that the improper coking and decoking cycles remove the protective oxide layer (Cr₂O₃) that forms on the exposed surfaces and that, with this layer removed, the coke could easily deposit on inner, non-protected surface. The carbon diffusion into the metal was accelerated with deposited coke and caused microstructural degradation and drastically reduced the ductility of material at high temperatures.     

Effect of Process Parameters on Porosity in Aluminum Lost Foam Process

1.IntroductionLost foam casting process is still a new technology,and is gaining confidence among manufacturers[1].It isexpected to dramatically improve the competitiveness ofthe foundry industry.Many advantages like eliminatingmachining steps,making complex casting without coresand reducing environmental loads can be offered by thisprocess,because molding binder is not added into themold of the lost foam process.Aluminum alloy castings are widely used in the auto-mobile and aerospace industri…     

Verschleißbeständige Fe‐Basislegierungen mit Niobkarbid

Wear Resistant Fe‐Base Alloys with Niobium Carbide Martensitic Fe‐base alloys from the system Fe‐Cr‐C are widely used as chilled cast irons and tool steels. Because of the low hardness of their FeCr‐carbides this paper reports about new alloys with primarily solidified harder niobium carbides. It focuses on a secondary hardenable welding alloy, a coating material for composite castings, a chilled casting and a corrosion resistant cold work tool steel, which are investigated with respect to their process related microstructure and abrasive wear behaviour.     

Life of rolls in a cold rolling mill in a steel plant-operation versus manufacture

Failures of rolls occur due to improper manufacturing and operational parameters. Prematurely failed (spalled) roll samples collected from a reputed steel plant were examined for their chemistry, inclusion content, microstructures, carbide characteristics, hardness and retained austenite content. The residual stresses were also measured on the inner and outer surfaces of the spalled roll pieces. The higher content of retained austenite was primarily responsible for the spalling of indigenous rolls for which subzero treatment has been recommended. Several suggestions have also been made for smooth operation of the mill and consequently for the life extension of work rolls.     

Molybdenum alloying in cast iron and steel

Metal casting is an important manufacturing technology for efficiently producing massive components with complex shape. A large share of industrial castings is made from iron and steel alloys, combining attractive properties and low production cost. Upgrading of properties in cast iron and steel is mainly achieved by alloying and in fewer cases by heat treatment. Molybdenum is an important alloying element in that respect, increasing strength, hardness and toughness. It also facilitates particular heat treatments such as austempering. The paper describes the metallurgical functionality of molybdenum alloying in iron-based castings and demonstrates its effectiveness for applications in the automotive and mining industry.The full text can be downloaded at https://link.springer.com/content/pdf/10.1007/s40436-019-00282-1.pdf     

Efficient and economical manufacture of heavy steel castings

Heavy steel castings, a symbol of the level of heavy industries, are high-tech products assembling materials, metallurgy, casting, etc. The feasible schemes for economizing manufacturing heavy steel castings were analyzed. The effects of riser design, sand mold, oxidation and deformation of casting during heat treatment, machining allowance, etc., on the economizing manufacture heavy steel castings were reviewed. Realization of efficient and economical manufacture of heavy steel castings will improve the output ratio of metal, shorten manufacturing period, save energy and resource, reduce pollution, and improve the competitiveness of enterprises.     

Study of Solidification Shrinkage of Ductile Iron in Dry Sand Molds

1.IntroductionDuctileironshavereceivedmuchattentioninthepastbecausetheyhaveanattractivecombinationofmechanica1properties[1l21.Theshrinkagebehaviorisaprincipalconcernintheproductionofductileironcastings.Thisphenomenonhasbeenthesubjectofconsiderableattentiontothosestudyingductileironssincesoonafteritsintroductiontothecastmetalsindustry.Inthelate195os,Reynoldset.1.[3]investigatedtheeffectsofcarbonandsiliconcontentonshrink-agebehavior,notingthatsoundcastingscouldbeob-tainedinrigidmoldsifthefollow…     

Design considerations with zinc coated steel and zinc castings

Zinc castings and the various types of zinc coated steel all have different design considerations. Thick coatings applied by hot dipping, by sheradizing or by spraying are usually a final operation after fabrication. Continuously coated sheet or wire has virtually the same design flexibility as the uncoated steel but with longer life to first maintenance treatment. With zinc castings, technical development in the pressure die casting process — notably the ability to make thin and complex thin dimensional shapes — means that a zinc die casting can often economically replace an assembly of steel pressings. This article describes some of the design considerations for each group of materials with examples from practice.     

基于全连接神经网络的压铸件质量预测算法

目的 针对复杂压铸制造过程中高精度监控和质量预测问题,构建全连接神经网络,以提高压铸件缺陷分类和预测的准确性及高效性。方法 提出了一种基于全连接神经网络的算法,用于压铸件的质量预测。以汽车发动机下缸体为研究对象,先通过压铸岛采集关键工艺数据,后通过异常值处理和数据归一化进行数据预处理,再采用最小冗余和最大相关性的启发式算法（MRMR）进行特征处理,选出对压铸件质量影响较大的5个参数,该算法以3个压射速度、真空度、动模流量为输入层参数,以铸件质量为输出层参数。最后确定该算法的结构及各个参数,进行模型的训练与构建,并与不同算法进行性能比较。结果 与传统的决策树、SVM算法相比,该算法在相同数据集的分类和预测性能方面均更优,表明全连接神经网络在预测压铸缺陷方面具有优势。结论 该算法在实际应用中具有很大的潜力,证明全连接神经网络在预测能力和精度方面具有优势,可以为数据分类和预测提供更好的解决方案。     

A study on the formation of liquation cracks in the weld heat-affected zone of HY-80 quenched and tempered steel

Liquation cracking of heat-affected zones (HAZs) is often encountered during the welding of HY-80 steels. To reduce the sensitivity of this defect, the content of impurities, such as P and S, must be kept as low as possible. However, in the development of HY-80 steel, HAZ grain boundary liquation is still found even at very low impurity contents. In order to clarify the cause of this defect, the Gleeble hot ductility test and electron probe X-ray microanalysis (EPMA) were carried out. From the results of EPMA, it was evident that the grain boundary liquation in the heat-affected zone of HY-80 steel was due to the low-melting-point eutectic reaction between Cr, Ni and Mn, which had been swept up by the migrating grain boundaries in the welding-heating thermal cycle, and hence enriched at the grain boundary. In addition, the Gleeble hot ductility test results revealed that the HAZ liquation cracking sensitivity of HY-80 steel could be decreased by reducing the C, Ni and Cr contents of base metal, and by decreasing the dwell time at high temperatures during the welding thermal cycle.     

Shrinkage Behaviour of Spheroidal Graphite Cast Iron in Green and Dry Sand Molds for the Benchmarking of Solidification Simulation

［1］C.E.Bates and B.Patterson: AFS Trans., 1979, 87,323. ［2］S.I.Karsay: Ductile Iron: Gating and Risering, QITFeret Titane, 1981. ［3］J.F.Wallace and P.K.Samal: AFS Trans., 1984, 92,765 ［4］K.C.Su, I.Ohnaka, I.Yamauchi and T.Fukusako:Imono, 1986, 58(10), 702. (in Japanese) ［5］M.S.C.Rao and M.N.Srinivasan: AFS Trans., 1988,96, 551. ［6］S.Takamori, E.Niyama and K.Ikawa: Imono, 1989,61(12), 906. (in Japanese) ［7］S.Takamori: Proc. of Cast Iron Ⅳ, MRS, 1990, 455. ［8］Y.Yang and J.Alhainen: AFS Trans., 1992, 100, 129. ［9］S.Takarnori and E.Niyama: Imono, 1992, 64(5), 338.(in Japanese) ［10］S.Takarnori and E.Niyama: Imono, 1993, 65(1), 31.(in Japanese)     

Failure analysis of automatic coupler SA-3 in railway carriages

In the present work, failure analysis of an automatic coupler in railway carriages which failed in service and caused derailment, was carried out. An evaluation of the failed coupler was undertaken to assess its integrity, including visual examination, photo documentation, fractography, chemical analysis, hardness measurement, tensile and charpy impact testing and microstructural characterization. Results show that some casting defects (e.g. mis-run, cold lap, hot crack and inclusion) resulted in poor mechanical properties. Mis-runs were also responsible for fatigue crack nucleation from two different locations. Beach marks can be observed on the fracture surface. According to the results of fracture mechanics, the load of final fracture was not higher than the standard value. In other words, the fracture was not due to employing improper mechanical loads but mostly because of casting defects.