Pearlite

About: Pearlite is a research topic. Over the lifetime, 6028 publications have been published within this topic receiving 65695 citations.

Low-Stress Abrasive Wear Behaviour of a 0.2% C Steel: Influence of Microstructure and Test Parameters

Abstract: A low (0.2%) carbon steel has been subjected to heat treatment to form varying quantities of ferrite plus martensite in its microstructure. This was achieved by holding the samples in the two-phase (ferrite plus austenite) region at three different temperatures (750, 780, and 810 °C) for a specific duration followed by quenching in ice water. In another exercise, the steel was also subjected to annealing treatment by austenitizing at 890 °C followed by furnace cooling for comparison purposes. The samples were subjected to low-stress (three-body) abrasion tests using an ASTM rubber wheel abrasion test apparatus at different wheel speeds (150, 273 and 400 rpm corresponding to linear speeds of 1.79, 3.26 and 4.78 m/s respectively) for different sliding distances at a fixed load of 49 N. Crushed silica sand particles of size ranging from 212 to 300 μm were used as the abrasive medium. The wear rate of samples decreased progressively with sliding distance until a (nearly) steady-state condition was attained. This was considered to be due to abrasion-induced work hardening of subsurface regions as well as the greater tendency of protrusion of the harder martensite/pearlite phase at longer sliding distances, thereby providing greater resistance to wear. Decreasing wear rate with increasing treatment temperature 750–810 °C could be attributed to the greater volume fraction of the hard martensite phase in the samples containing ferrite plus martensite. The lower wear rate observed in the case of the samples containing ferrite plus martensite over the annealed ones comprising ferrite and pearlite was attributed to the higher bulk hardness of the former. Increasing linear speed from 1.79 to 3.26 m/s led to an increase in wear rate. This could be attributed to greater tendency of the abrasive particles to create deeper scratches and scouping (digging). A reduction in wear rate with a further increase in the linear speed from 3.26 to 4.78 m/s could be due to a change in the mechanism of wear from predominantly sliding to rolling of the abrasive particles in view of the increased plastic deformability characteristics of the specimens due to higher frictional heating. The present investigation clearly suggests that it is possible to attain a desired combination of bulk hardness and microstructure (consisting of ferrite plus martensite) leading to optimum abrasion resistance in low-carbon steels. The quantity of the two phases in turn could be varied by suitably controlling the heat-treatment temperature.

Influence of forging and cooling rate on microstructure and properties of medium carbon microalloy forging steel

Abstract: In view of their capacity to develop high strength following limited alloying and ease of processing medium carbon microalloyed (MA) steels are very cost-effective compared to quenched and tempered steels for the production of automotive components. To be able to substitute quenched and tempered steels, MA steels must be processed to similar strength levels and acceptable toughness [1]. The increased use of microalloyed forging steels in production applications should be supplemented with an increased understanding of not only the strengthening mechanisms that occur in these steels, but also the effects of the composition and forging parameters on these mechanisms. The size and percentage distribution of ferrite and pearlite within the microstructure play an important role on the final mechanical properties. Each of the microstructure variables is highly influenced by the composition of the microalloyed steels, the forging parameters utilized, and the post-forging cooling rate [2–4]. The aim of the present study is to investigate the influence of different cooling rates on structure and properties of MA steel processed through forging route. The chemical compositions of the steels used in this study are shown in Table I. The steels are medium carbon microalloyed steel with different vanadium and aluminum contents. Specimens obtained from steels 1 and 2 were heated at 1100 ◦C for 30 min and forging operation was carried out. Thirty-six percent deformation was applied by repeated strokes in temperature range of 1000–1100 ◦C. Then forged steel samples were cooled either in water, air, or sand. Room temperature tensile strength was measured by using an Instron machine at a crosshead speed of 1 mm/min. The pearlite grain size, volume fraction of ferrite, and pearlite were determined by using mean linear intercept (mli) method and point counting. Hardness measurement was also carried out using the Vickers hardness test. Fig. 1 shows the evaluation of the microstructure for both of the microalloyed steel under various cooling condition. Table II also shows volume fraction of ferrite and pearlite and mli grain sizes of pearlite in as-received,

A model for austenitisation of hypoeutectoid steels

Abstract: In the field of phase transformations in steels, much attention has been paid to the transformation of austenite into diverse product phases but, until recently not much work has been done on the formation of austenite during heating. There are few published models dealing with the transformation of eutectoid or hypoeutectoid steels with a starting microstructure which is a mixture of ferrite and pearlite. The aim of the present work was to use phase transformation theory to develop a model for austenite formation which takes into account the chemical composition and microstructure of the steel studied, and thermal history experienced. Classic nucleation theory and diffusion-controlled growth equations are used to determine the progressive transformation of the different phases into austenite. A phase transformation model with sound physical basis as the one presented in this work can be used to determine the effects of various parameters in the reaction involved, like microstructure (grain size, pearlite spacing), composition, heating rate and others. Another direct application of this model is the generation of CHT (continuous heating transformation) diagrams for specific steels, which are a useful reference in research, as well as in many industrial processes.