Pearlite

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

Constitutive relationships of hot stamping boron steel B1500HS based on the modified Arrhenius and Johnson–Cook model

Abstract: Constitutive relationship of boron steel is one of the most necessary mathematical models in the numerical simulation of hot stamping; it describes the relationship of the flow stress with strain, strain rate and temperature. In order to attain the constitutive relationship of boron steel B1500HS, four types of samples with microstructure of austenite, ferrite+pearlite, bainite or martensite are prepared by the Gleeble 1500D thermo-mechanical simulator. Isothermal uniaxial tension testings for these specimens are performed at 20–900 °C at the strain rates of 0.01 s –1 , 0.1 s –1 , 1.0 s –1 and 10 s –1 by Gleeble 1500D, and the true stress–strain curves at the relative conditions are gained. The experimental results show that, the flow stress of samples with relative microstructure rises with the decrease of the deformation temperature, and with the increase of the strain rate. The modified Arrhenius model is used to describe the hot deformation of samples with austenite microstructure, and the modified Johnson–Cook model is used to describe the deformation process of samples with ferrite+pearlite, bainite or martensite microstructure. The constitutive equations depending on the strain, strain rate and temperature are attained by the regression analysis for the experimental data of flow stress, strain, strain rate, temperature, etc. The comparison of the computational data and the experimental results shows that, the computational data using the constitutive relationships are well consistent with the experimental data.

A critical-strain criterion for hydrogen embrittlement of cold-drawn, ultrafine pearlitic steel

Abstract: A stress-modified, critical-strain model of fracture-initiation toughness has been adapted to the case of hydrogen-affected pearlite shear cracking, which is a critical event in transverse fracture of cold-drawn, pearlitic steel wire. This shear cracking occurs via a process of cementite lamellae failure, followed by microvoid nucleation, growth, and linkage to create shear bands that form across pearlite colonies. The key model feature is that the intrinsic resistance to shear-band cracking at a transverse notch or crack is related to the effective fracture strain at the notch root. This fracture strain decreases with the logarithm of the diffusible hydrogen concentration (C H). Good agreement with experimental transverse fracture-initiation-toughness values was obtained when the sole adjustable parameter of the model, the critical microstructural dimension (l*), was set to the mean dimension of shearable pearlite colonies within this steel. The effect of hydrogen was incorporated through the relationship between local effective plastic strain (ɛ eff f ) and C H, obtained from sharply and bluntly notched tensile specimens analyzed by finite-element analysis (FEA) to define stress and strain fields. No transition in the transverse fracture-initiation morphology was observed with increasing constraint or hydrogen concentration. Instead, shear cracking from transverse notches and precracks was enabled at lower global applied stresses when C H increased. This shear-cracking process is assisted by absorbed and trapped hydrogen, which is rationalized to either reduce the cohesive strength of the Fe/Fe3C interface, localize slip in ferrite lamellae so as to more readily enable shearing of Fe3C by dislocation pileups, or assist subsequent void growth and link-up. The role of hydrogen at these sites is consistent with the detected hydrogen trapping. Large hydrogen-trap coverages at carbides can be demonstrated using trap-binding-energy analysis when hydrogen-assisted shear cracking is observed at low applied strains.

Frictional Heating and Its Influence on the Wear of Steel

Abstract: High frictional temperatures during the dry or imperfectly lubricated rubbing of steel produce gross structural changes and intense hardening of the surface layers. In consequence of these changes the wear time curve shows a marked inflexion, the wear rate of soft steel on soft steel diminishing by more than an order of magnitude as the hardened skin develops. The protective layer establishes itself more readily as the carbon content of the steel increases, a feature explained by the ease with which eutectoid pearlite transforms to austenite, and thence to martensite, during the rapid temperature cycle. By simulating the hot spots during wear by the thermal action of electric sparks, the hardness change is shown to be intensified by nitrogen or carbon absorbed from the atmosphere or lubricant.

The effect of interlamellar spacing on strength of pearlite in annealed eutectoid and hypoeutectoid plain carbon steels

Abstract: The strength of pearlite in an eutectoid steel with varying interlamellar spacings and in five hypoeutectoid steels with varying volume fraction of the constituent phases, have been studied using microhardness measurements. In the eutectoid steel, the strength of pearlite derived on its proportionality with microhardness, is found to increase with decreasing interlammellar spacings according to existing relations. But the strength of pearlite in the hypoeutectoid steels is found to vary considerably, even when the interlammelar spacings in the pearliticcolonies are almost constant. The variation of the pearlitic strength in the hypoeutectoid steels is explained on the basis of hydrostatic stresses exerted by the presence of ferrite.