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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. Casting technology is very attractive for producing industrial components as well as everyday-life household items. Since castings are manufactured to near-net shape, intensive machining is not required resulting in cost-efficient production of complex-shaped items. The casting process requires specific alloy compositions allowing good form filling, a low defect level as well as achieving the desired target properties after solidification and down-cooling [ 1 ]. Cast iron is a material with long history and tradition.
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Filmed in Hindi , the film revolves around the relationship between a live-in couple caught amidst their busy professional careers. The film stars actors Randeep Hooda and a relative newcomer Shahana Goswami in the leading role. This movie is an adaptation of Junger's film If Only Tara Mishra Shahana Goswami , an aspiring actress and singer, and Nikhil Singh Randeep Hooda , a young professional in an advertising firm have been in a relationship since a few years. Kulbhushan Kharbanda is a taxi driver. Tara wants to cement their relationship by having him meet her parents as a commitment to a marriage. But Nikhil, who is workaholic and professionally ambitious, is always pre-occupied with his work. Saying that he is happy with the way things are between the two of them, he stashes away her proposal for marriage. Trouble brews between them when Nikhil constantly forgets little things about her and their relationship. He begins to take Tara, her family and friends for granted.

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. Casting technology is very attractive for producing industrial components as well as everyday-life household items. Since castings are manufactured to near-net shape, intensive machining is not required resulting in cost-efficient production of complex-shaped items.

The casting process requires specific alloy compositions allowing good form filling, a low defect level as well as achieving the desired target properties after solidification and down-cooling [ 1 ].

Cast iron is a material with long history and tradition. According to the binary iron-carbon diagram, cast irons are alloys having more than 2. Cast irons usually solidify following the stable iron-carbon diagram, thus forming graphite during solidification. Definition of cast iron alloys according to carbon and silicon contents [ 2 ]. Molybdenum alloying is applied in both classes of iron, typically for products with increased property demands. In particular cases, cast irons can be subjected to heat treatment after solidification for property improvement.

The initial ferritic-pearlitic microstructure of the matrix is modified by so-called austempering to become bainitic with a high fraction of metastable retained austenite [ 4 ].

They are manufactured over a large variety of alloy compositions used in a multitude of applications. Thus, a high degree of specialization is involved with steel foundries. It can be stated that steel castings are preferred where manufacturing of a component starting from a wrought or rolled steel semi-product is too costly or too difficult.

The different steel casting alloys can be distinguished according to the following application areas [ 5 ]: general applications unalloyed C-Mn-Si steel , improved weldability and toughness for general purposes, high pressure purposes for use at low temperatures, high pressure purposes for use at room temperature and elevated temperatures, heat resistant steel castings, corrosion resistant steel castings, wear resistant steel castings. Approximately half of the global annual castings output is produced by Chinese foundries [ 3 ].

The increasing demand for high-performance castings is driven by key industries such as the automotive, mechanical engineering and mineral processing sectors. The optimization of casting alloys typically involves a combination of properties to be considered. Applications in the automotive powertrain are demanding an improved combination of strength, heat conductivity and thermal fatigue resistance. In mineral processing optimized wear resistance is targeted, which is related to a suitable combination of hardness and toughness.

The paper addresses the particular role of molybdenum alloying in this respect and highlights current alloy developments in China. Molybdenum is known to act as carbide stabilizer in cast iron. At low addition level it has little effect on castability and chilling tendency.

Free carbides are only formed at higher molybdenum addition. The amount and shape of graphite are not measurably affected by molybdenum additions below 0. The main effect provoked by molybdenum alloying to cast iron is observed during solid state transformations.

With increasing molybdenum alloy content, the pearlite phase field in the continuous cooling transformation CCT diagram is shifted towards longer times. Molybdenum addition up to around 0. Higher molybdenum additions, preferably in conjunction with nickel or copper, promote the transformation from austenite into acicular ferrite. Such irons usually contain at least 0. The actual amount of alloy required depends upon the section thickness. They are more easily machinable at high levels of hardness — HB than unalloyed irons due to the absence of free cementite.

Amongst the typical alloying elements, it is found that Mn and Ni coarsen the interlamellar spacing of pearlite, whereas an increasing content of Cr produces finer pearlite spacing. Si has only a slight influence on pearlite spacing. Molybdenum clearly has the strongest effect in decreasing the interlamellar spacing. The individual effect of these alloying elements on the pearlite interlamellar spacing, S 0 , can be described as [ 9 ]. In pearlitic microstructures, the interfaces between ferrite and cementite act as barriers to dislocation movement [ 10 ].

The critical stress necessary to shift dislocations in ferrite lamellae is related to the macroscopic yield stress. That critical stress rises with the refinement of the pearlitic microstructure, since a decrease of pearlite interlamellar spacing leads to an increase in the resistance to glide according to a Hall-Petch type relationship.

Furthermore, finer pearlite microstructures comprising smaller colony size and shorter interlamellar spacing, show a more ductile fracture character.

Grey cast iron has limited strength and almost no ductility. Nevertheless, pearlitic grey cast iron is the preferred material for applications such as engine blocks, cylinder heads, flywheels or brake discs.

This is reasoned by the low cost, good castability and favorable thermal conductivity of grey cast iron. Demands for higher thermal efficiency and weight reduction enabled by reducing component cross-sections require the development of high-performance grey cast iron with an improved combination of tensile strength and heat conductivity.

However, those features promoting heat conductivity are typically detrimental to strength. The challenge is to find a suitable balance of microstructural design and hence alloy concept. Considering the matrix, ferrite has better heat conductivity than pearlite, yet the latter has higher strength. The heat conductivity of ferrite decreases with increasing alloy content. A higher volume share of graphite increases heat conductivity on expense of strength. From an alloying point of view, it appears favorable reducing the level of solute elements for improving thermal conductivity.

In this respect, silicon is the most critical element. The use of a carbide stabilizer with good solubility and rather large atomic size is considered to be favorable [ 14 ]. Molybdenum exactly fulfils these conditions. Based on various published results it can be estimated that 0. In synergy with other alloying elements such as for instance chromium, vanadium or niobium, the strengthening effect can be even larger. At elevated operating temperature, Mo-alloyed grey cast iron better retains strength and has clearly improved creep resistance [ 6 , 15 ].

The grey iron alloys GJL have higher thermal conductivity and lower strength than vermicular graphite iron grades GJV. Raising the molybdenum content towards the earlier stated limit of 0.

Current grey iron grades according to typical automotive standards are represented in Fig. Niobium is a rather unconventional alloying element providing additional strength to grey cast iron. Unlike molybdenum, niobium affects the solidification structure and graphite morphology.

Niobium additions up to around 0. This alloy concept is being used for the production of vehicle brake discs [ 18 , 20 ]. Systematic alloy variations in laboratory trials have indicated that the tensile strength of grey cast iron can be most efficiently increased by simultaneously refining the eutectic cell size and the pearlite interlamellar spacing see Fig.

In that respect, the combined alloying of molybdenum and niobium has a particularly high strengthening potential. In this combination, molybdenum is providing additional refinement of pearlite interlamellar spacing and promotes precipitation strengthening by niobium. Hypo- and hyper-eutectic alloy concepts of grey cast iron grades and specified mechanical properties according to European automotive standards. Effect of niobium addition on microstructural refinement in grey cast iron [ 18 ].

Effect of microstructural refinement on tensile strength in grey cast iron based on laboratory results provided by Shanghai University [ 21 ]. Nodular iron, in contrast to grey iron, contains graphite in form of isolated spheroids within a matrix consisting of ferrite or pearlite. This results in higher strength, good elongation and increased toughness as compared to iron containing lamellar graphite.

Nodular irons are particularly interesting for manufacturing complex-shaped components used for engine or machine parts subjected to high acceleration or impact loads as well as for pressure pipes and vessels. Like in grey cast irons, molybdenum is added to nodular iron for further enhancing strength and also here additions up to 0. Molybdenum added to nodular irons particularly enhances tensile, creep, and stress-rupture strengths at elevated temperature [ 6 , 7 , 15 ]. Such alloys are typically used for turbocharger housings of diesel engines.

Silicon and molybdenum are complementary alloying elements with silicon providing oxidation resistance and raising the ferrite-to-austenite transformation temperature A 1 while molybdenum increases the elevated temperature strength and creep resistance. Constrained thermal cycling tests of ferritic SiMo nodular iron demonstrated a strong beneficial effect of molybdenum [ 15 ]. It should be noted that molybdenum additions to such austenitic irons have similar effects as in ferritic SiMo alloys. Tensile strength at high temperature for SiMo iron alloys and austenitic cast iron Ni-resist D5S [ 22 ].

The formation of pearlite during cooling must be avoided [ 25 ]. During austempering, an increasing fraction of bainite forms and carbon partitions to the remaining austenite phase. The final microstructure of austempered ductile iron ADI consists of bainite and retained austenite also called ausferrite as well as spherical graphite resulting in very attractive properties. Toughness and elongation are better in ADI as compared to other cast iron materials at comparable strength.

Accordingly, ADI is one of the most attractive construction materials for realizing weight reduction see Fig. The most significant use of ADI is found in vehicle and railway applications see Fig. Some typical examples of truck and trailer components manufactured from ADI are shown in Fig. Comparison of light weighting potential and cost for materials used for manufacturing of massive components [ 25 , 26 ]. Market share of major applications for ADI castings [ 29 ]. Molybdenum alloying is used to avoid pearlitic transformation during cooling to the austempering temperature avoiding the necessity for major capital investment in quenching facilities [ 30 ], especially when casting components with larger section size see Fig.

Manganese is also an effective hardenability agent yet must be kept low max. Larger additions of nickel or copper could supply the required hardenability, but combined nickel-molybdenum or copper-molybdenum alloying is more effective because of the synergetic effects of these elements on hardenability [ 31 ]. The inherently high silicon content inhibits carbide precipitation during austempering and thus helps stabilizing austenite. Heat treatment cycle for austempering and effect of alloying elements on the matrix phase formation [ 25 ].

Recent development activities at Shanghai University are focusing on further improving wear resistance of ADI.



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