Pearlite

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

Microstructures and mechanical properties evolution during friction stir welding of SK4 high carbon steel alloy

Abstract: Stir-in-plate welds were produced on 2 mm thick plates of SK4 high carbon steel alloy (0.95% C) using a load controlled friction stir welding (FSW) machine. The welding was carried out at a constant welding speed of 100 mm/min and different rotation speeds varied between100 and 400 rpm. The microstructure and mechanical properties of the weld metals were investigated. When FSW was carried out at 100 rpm, a duplex structure of spheroidal cementite and fine ferrite was formed and homogenously distributed in the entire stir zone. On the other hand, when the FSW was carried out at a rotation speed higher than 100 rpm, very fine pearlite and martensite structures were formed in the upper part of the stir zone and increased with the increasing rotation speed. Thin film of retained austenite was found in the microstructure of the weld metal stirred at 200 rpm and its volume fraction increased with further increasing in the rotation speed. Hardness values measured in the stir zone formed at 100 rpm were slightly higher than that of the base metal and homogenously distributed throughout the entire stir zone. Increasing rotation speed more than 200 rpm led to a sharp increase in the hardness values of the stir zone and maximum values around 800–820 Hv were attained at 400 rpm below the tool shoulder. Yield and ultimate tensile strengths of the weld metals increased with the increasing rotation speed, while elongation decreased. Fracture surface of the weld metal formed at 100 was similar to the base metal (BM) and exhibited only a microvoid coalescence dimple fracture, while that formed at 200–400 rpm showed a mixed mode of quasi-cleavage transgranular fracture and ductile dimple fracture mode.

High strength wire rod excellent in delayed fracture resistance, its production, and high strength bolt

Abstract: PROBLEM TO BE SOLVED: To provide a high strength wire rod having excellent delayed fracture resistance as well as ≥1200 N/mm 2 tensile strength, a useful method for obtaining a high strength wire rod like that, and a high strength bolt having the above characteristics. SOLUTION: This wire rod is composed of a steel containing 0.5-1.0% C, and the area ratio of a pearlitic structure having a pearlite nodule size of No.7 or above by grain size number is regulated to ≥80% by inhibiting the formation of structures of one or ≥2 kinds among pro-eutectoid ferrite, pro-eutectoid cementite, bainite, and martensite and also strength is regulated to ≥1200 N/mm 2 by means of heavy wire drawing. Moreover, the steel is heated to 800-1000°C, cooled rapidly down to 520-650°C, and isothermally held at the temperature, by which the formation of structures of one or ≥2 kinds among pro- eutectoid ferrite, pro-eutectoid cementite, bainite, and martensite is inhibited to regulate the area ratio of a pearlitic structure having a pearlite nodule size of No.7 or above by grain size number to ≥80%. Then, strength is regulated to ≥1200 N/mm 2 by means of heavy wire drawing. COPYRIGHT: (C)1999,JPO

Engineering tensile properties by controlling welding parameters and microstructure in a mild steel processed by friction stir welding

Abstract: In order to evaluate the effects of welding parameters on microstructure and tensile properties, a mild steel was stir welded under various conditions. The results revealed that carrying out the friction stir welding (FSW) process in lower rotation speeds or higher welding speeds due to lack of heat input and low flow-ability of the welding material, tunnel defect and flaky surface is appeared. In contrary, in higher rotation speed or lower welding speed, the temperature of stir zone (SZ) reached to single austenite region owing to significant increment of heat input. Consequently, refined microstructure involving ferrite and pearlite transformed from new fresh austenite can be formed. Tensile behavior of the FSW processed specimens exhibited relatively higher amount of yield strength and limited uniform elongation in comparison with the starting material. But, the samples has tunneling defect or any other welding defects showed very limited uniform elongation.

Interphase boundary structures associated with diffusional phase transformations in Ti-base alloys

Abstract: Interphase boundary structures generated during diffusional transformations in Ti-base alloys, especially the proeutectoid α and eutectoid reactions in a β-phase matrix, are reviewed. Partially coherent boundaries are shown to be present whether the orientation relationship between precipitate and matrix phases is rational or irrational. Usually, these structures include both misfit dislocations and growth ledges. However, grain boundary α allotriomorphs (GBA’s) do not appear to develop misfit dislocations at partially coherent boundaries. Evidently, these dislocations can be replaced by ledges which provide a strain vector in the plane of the interphase boundary. The bainite reaction in Ti-X alloys produces a mixture of eutectoid α and eutectoid intermetallic compound. Both eutectoid phases are partially coherent with theβ matrix, and both grow by means of the ledge mechanism, though unlike pearlite the ledge systems of the two phases are structurally independent. Even after deformation and recrystallization, the boundaries between the eutectoid phases and theβ matrix, as well as between these phases, are partially coherent. Titanium and zirconium hydrides have partially coherent interphase boundaries with respect to theirβ matrix. The recent observation of ledgewise growth of γ TiH within situ high-resolution transmission electron microscopy (HRTEM) suggests that, repeated suggestions to the contrary, these hydrides do not grow by means of shear transport of Ti atoms at rates paced by hydrogen diffusion.

Effect of pearlite morphology on impact toughness of eutectoid steel containing vanadium

Abstract: The effect of a change in the morphology of the pearlite colonies on the Charpy impact energy of a fully pearlitic steel containing 0·76%C, 1·20%Mn, and 0·085% V was examined over the range of testing temperatures from −50 to 200°C. The change from a multicolony nodular pearlite structure produced from austenite of grain size 185 μm to a structure composed of individually formed colonies produced from austenite of grain size 25 μm caused a decrease in the transition temperature of 75 K and an almost 100% increase in the Charpy impact energy measured at room temperature. It is proposed that the impact toughness of pearlitic steel can be affected by pearlite morphology, at constant interlamellar spacing, only at temperatures above the ductile–brittle transition temperature of the ferrite, when local plastic deformation in the pearlitic ferrite at high angle boundaries can arrest propagating brittle cracks.MST/730