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The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyeres. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron...

A model for estimating the upper to lower bainite transition has been developed for the iron–carbon–manganese–chromium–silicon alloy system by comparing the time required to decarburise a supersaturated bainitic ferrite platelet and that needed for the start of cementite precipitation in the ferrite. The problem is treated as a competition between the decarburisation time and the kinetics of cementite precipitation. Lower bainite is induced when the latter process is faster. The time for forming a volume fraction of 0.01 of the equilibrium amount of cementite is taken as the precipitation start time. The model was calibrated using experimental data from the iron–carbon system, and verified with the iron–carbon–manganese–molybdenum system and an experimental steel currently being developed for high-strength applications.

The growth of austenite from a mixture of ferrite and cementite in low-alloy steels can be classified into three temperature ranges above the eutectoid temperature. In the first range, the austenite growth and cementite dissolution are controlled by alloy element diffusion from the beginning. In the second, they are controlled by carbon diffusion and switch to alloy element diffusion control at a later stage. In the third, the cementite dissolution, if the ferrite matrix has transformed to austenite upon heating, is controlled by carbon diffusion until completion. The transition temperatures between these ranges are evaluated in a quaternary alloy containing Mn and Cr by Thermo-calc and DICTRA simulation, and are in essential agreement with earlier experimental results. The proposed simple approach of calculating the transition temperatures may facilitate our understanding of austenitization kinetics and the design of heat treatment, for example, homogenization and soaking, of high-carbon steels.

Nanostructured bainite is extremely resistant to severe tempering making it difficult to reduce its hardness sufficiently to allow certain processing before heat treatment into its final state. An attempt is therefore made to introduce the divorced pearlite reaction that relies on the presence of pro-eutectoid cementite in the austenite in order to produce a microstructure containing spheroidal cementite particles simply by continuous cooling from the two phase austenite and cementite field. It is demonstrated that dramatically reduced hardness values can be achieved using this method.

A study of electric contact surface treatment to ductile iron has been carried out. This technology was based on the application of the contact resistance heating between the electrode and workpiece. For comparison, the experiments of induction hardening to ductile iron were studied. The microstructure, microhardness, surface residual stress and wear properties were investigated using optical microscope, scanning electron microscope, X-ray diffraction, Vickers microhardness and rolling contact wear tests. Electric contact surface treatment resulted in the formation of fine ledeburite (white bright layer) and martensite in the ductile iron surface, in which the hardness in these areas was higher than that of induction hardened surface. The wear test results showed that the ductile iron surface after electric contact surface treatment had better wear resistance owing to the fine microstructure, high hardness and residual compressive stress.

The effects of alloying elements on the kinetics of austenitization from pearlite structure were studied by computer simulation in Fe–C–M ternary alloys, where M is Mn, Cr, Si or Ni, assuming local equilibrium conditions at all transformation interfaces. A thin austenite film was assumed to nucleate at ferrite/cementite interfaces and grow in one dimension. The existence of a partition to no-partition transition temperature (PNTT) was rationalized. Above the PNTT, the growth rate of austenite is governed by the difference in carbon activity between austenite/cementite and ferrite/austenite interfaces; a substitutional element influences the reaction rate by affecting carbon activity. Below the PNTT, redistribution of M is necessary. The PNTT increases with the concentration of all alloy elements except Ni, which has a large segregation tendency in austenite from both ferrite and cementite, as well as repulsive interaction with carbon. The amount of overheating at PNTT from Ae1 increases in the order Si (∼...

When spheroidal graphite iron is cast on a chili, a mottled structure is obtained because of the rapid cooling conditions. More precisely, a microstructure gradient may occur from the outer surface...

The particle distribution in semi-solid slurry under centrifugal field was simulated and the main factors such as fraction of solid, rotation speed, and holding time effecting the particle distributions are discussed. The simulation results showed that primary particles rich zone is produced in radially outer area and these results are in good agreement with the experiment. The centrifugal effect produces the primary particles distribution along the radial direction. Denser particles are concentrated in outside than inner side. For high fraction of solid samples, 'wall' appear in the middle of samples because of high viscosity region making particle difficult to move. Longer holding time gives denser primary particles concentrated more in outside than inner side. Higher rotation speed gives increased gradient of hardness in the radial direction. It is due to that number of primary austenite at inner side at higher rotation speed is less than that at lower rotation one. At higher rotation speed, ledeburite forms more at inner side of specimen than at the other one. It is also shown that semi-solid processing at lower fraction of solid gives higher hardness because smaller number of primary austenite, namely more ledeburite forms in microstructure. The present study gives useful information on producing material with locally changing property by semi-solid processing.

The microstructural evolution of a spheroidised Fe-0.85C wt- steel during heavy cold rolling and post-aging was studied, with the emphasis on cementite. A new morphology of cementite, wavy thin bands nearly parallel to the rolling plane, was found in the specimens subjected to rolling reductions >90. Slip on 001theta planes was observed in the deformed cementite particles. By X-ray diffraction, it was found that the initial spheroidal cementite particles dissolve partially in a solid solution of ferrite by deformation, in a manner similar to that of the lamellar cementite of pearlite. Greater strain age hardening was observed for the spheroidised steel than for a similarly treated pearlitic Fe-0.85C steel. The strain age hardening peak was observed at 573 K for the spheroidite structure, which is 150 K higher than was observed for the pearlite structure. The activation energy for age hardening was estimated to be 122 kJ mol1, which is attributed to carbon atom diffusion from cementite to dislocati...

Grey and white cast irons were surface remelted using a high power CO2 laser with a scanning velocity in the range 0·5–200 mm s-1 and the resulting surface structures were investigated using optical microscopy and X-ray diffraction. The remelted surface of the white iron was composed of austenite dendrites, which decompose to pearlite at low cooling rates and martensite at medium cooling rates. The maximum volume fraction of martensite was obtained at 10 mm s-1. The lattice parameter of the austenite increased with increasing solidification velocity owing to solute trapping of carbon. The remelted surface of the grey iron was composed of cellular ledeburite and X-ray diffraction analyses of the grey specimen indicated the presence of austenite, martensite, graphite, cementite, and ɛ phases. The initial austenite partially transformed to martensite at high cooling rates and to ɛ phase at low cooling rates. The appearance of the ɛ phase is therefore linked to the decomposition of supersaturated aust...

The influence of vanadium addition on the microstructure of high carbon steels has been investigated. A careful examination of the initial stages of austenite decomposi~ion has been made, using a r...

After laser surface remelting of nodular iron 400-12 a modified layer consisting of remelted and hardened layers has been observed. Microscopy of the hardened layer was used to analyse the occurrence of martensite shells and/or ledeburite shells around the graphite nodules in the ferrite matrix. The size of the shells was subsequently supported by diffusion calculations.

In this paper the total driving force for the decomposition of retained austenite and martensite are calculated together with the nucleation and growth characteristics of cementite in the two phases. The results demonstrate that the driving force for the decomposition of martensite is an order of magnitude less than that of austenite. However, the driving force for cementite precipitation in martensite is two orders of magnitude greater than in austenite with a much shorter incubation period. On short term tempering cementite precipitates from martensite whereas on longer term tempering decomposition of retained austenite occurs because of the increase in driving force which is enhanced by the contraction of the martensite on decomposition. It is argued that the precipitation of cementite from the austenite results in tempered martensite embrittlement, a mechanism dependent upon the two related decomposition processes. The segregation of trace impurities or the precipitation of cementite at the gr...

The surface of nodular cast iron was first coated with tungsten carbide powder, then melted by concentrated solar energy to form an alloyed layer on its surface. By scanning a high energy focal point over the surface, a predominantly alloyed surface was created after rapid solidification. The surface of the alloyed layer was quite flat, with a microstructure of very fine ledeburite. This alloyed layer possessed a very high hardness and high tempering resistance, and had greatly improved wear resistance compared to untreated nodular cast iron. In addition, excellent adhesive wear resistance is displayed by the alloyed material.