Pearlite

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

Cyclic deformation of pearlitic eutectoid rail steel

Abstract: Cyclic deformation behavior in pearlitic eutectoid steel strongly depends on the interlamellar spacing with cyclic softening in fine pearlite, cyclic hardening in coarse pearlite, and both cyclic softening and hardening depending on the strain amplitude in medium pearlite. Dislocations in cyclically softened specimens were uniformly distributed, while dislocation cells were observed with cyclic hardening. The cell size decreased with increasing strain amplitude. Using the cell size to interlamellar spacing ratios, conditions for cell formation were quantified. Based on dislocation structure observations, mechanisms for cyclic softening and hardening were proposed. Both monotonic and cyclic yield stresses follow Hall-Petch type relations when plotted against interlamellar spacing. Surface fatigue microcrack initiation usually occurred in the ferrite matrix associated with extrusions and intrusions. Most microcracks were almost parallel to the cementite lamellae and oriented between 30 and 90 deg with respect to the tensile axis. Little influence of MnS inclusions on microcrack initiation was noticed.

Effects of chemical composition, rolling and cooling conditions on the amount of martensite/austenite (M/A) constituent formation in low carbon bainitic steels

Abstract: To understand the controlled-rolled granular bainite structure, a series of high-strength low-alloy steels was specially designed and investigated. The effects of the chemical composition, the finish-rolling temperature, and the cooling rate on the amount of martensite/austenite (M/A) constituent formation in the as-rolled alloy steels were evaluated. It was found that for steels containing the same addition of Nb (0.045 wt.%), the granular bainite transformation was retarded with an increased carbon content ranging from 0.021 to 0.056 wt.%. As the carbon content was raised, more niobium combined with carbon to form carbide, and the austenite therefore became niobium-depleted. This effect significantly influenced the granular bainite transformation for the steels studied. It is also shown that the effects of Mn and Mo on the formation of second phases are different from that of carbon. These alloying elements tend to promote the M/A constituent and depress pearlite formation. As to the effect of rolling temperature, it is shown that as the finish-rolling temperature is lowered, the larger strain accumulated in austenite enhances polygonal ferrite formation along the previous austenite grain boundaries, and reduces the amount of M/A constituent. Furthermore, based on a thermodynamic analysis, it is indicated that the granular bainite transformation terminates as the carbon content of austenite reaches the TO curve. The critical carbon content increases with the decrease of the granular bainite transformation temperature. It was also found that the amount of M/A constituent formation decreases with the increase in cooling rate. This result is not consistent with that reported by Shiga et al., Tetsu-to-Hagane, 68 (1982) A227 and Bufalini et al., Accelerated cooling of steel,

Stress shielding and fatigue crack growth resistance in ferritic–pearlitic steel

Abstract: The effect of pearlite morphology on stage IIb (Paris regime) fatigue crack growth behavior in ferritic–pearlitic steel was investigated. Networked and distributed pearlite structures were prepared. Constant-Δ K fatigue crack growth tests were performed in situ in a scanning electron microscope. The results revealed that a distributed pearlite structure had better fatigue crack growth resistance than a networked pearlite structure. From the in situ observations, the distributed pearlite structure indicated a tortuous crack path, which induced crack interlocking as well as crack closure. For the networked pearlite structure, some crack branching was found on the crack path. The crack growth curves for the two microstructures, plotted using the effective stress intensity factor range Δ K eff , where crack closure behavior is taken into consideration, did not coincide. The crack growth curves plotted using the crack tip effective stress intensity factor range Δ K eff,tip , where crack tip shielding behavior as well as crack closure are taken into consideration, successfully coincided on one line.