Pearlite

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

Effects of cooling rate on microstructure, mechanical properties, and residual stress of Fe-2.1B (wt%) alloy

Abstract: The continuous cooling transformation (CCT) curve of an Fe-2.1B (wt%) alloy is obtained using a Gleeble 1500D thermomechanical simulator. The microstructure, mechanical properties, and residual stress of alloy specimens with various cooling rates are examined. The results reveal that the cooling rate has a great influence on the matrix microstructure of the Fe-2.1B (wt%) alloy. Pearlite is formed at the cooling rate of 0.1 K/s, pearlite and martensite are formed in the cooling rate range of 0.2–0.5 K/s, and only martensite remains in the matrix when the cooling rate exceeds 0.5 K/s. In addition, as the cooling rate increases, the dislocation density in the matrix increases, and this, in turn, leads to an increase in the volume fraction of the M23(B, C)6 phase. The precipitation of M23(B, C)6 causes the decrease in the (B + C) contents of the matrix, which, in turn, reduces the microhardness of the matrix to some extent. Meanwhile, the large residual compressive stress of the alloy increases with increasing cooling rate. The maximum residual compressive stresses induced by the cooling rates of 0.5 and 30 K/s are approximately 18% and 36%, respectively, higher than that induced by the cooling rate of 0.1 K/s. Moreover, when the cooling rate increases from 0.1 K/s to 0.5 K/s, the macrohardness and bending stress increase significantly owing to an increase in Vm/Vpr (where Vm represents volume fraction of martensite, Vpr is the volume fractions of pearlite and austenite). When the cooling rate exceeds 0.5 K/s, the macrohardness and bending stress decrease gradually because of the decrease in the (B + C) contents of the matrix and an increase in the residual stress. The critical cooling rate (0.5 K/s) may be the optimal cooling rate of Fe-B alloys.

Predicting properties and minimizing residual stress in quenched steel parts

Abstract: Quenching refers to the process of rapidly cooling metal parts from the austenitizing or solution treating temperature, typically in the range of 845 to 870°C (1550 to 1600°F) for carbon and low alloy steels, for the purpose of forming martensite. Several factors determine whether a particular part can be successfully hardened, including the type, molecular weight, and thermal characteristics of the quenchant, the quenchant use conditions (such as velocity, temperature, and polymer concentration, etc.), section thickness of the part, and the transformation characteristics of the specific alloy being quenched. Successful hardening usually means achieving the required hardness, strength, or toughness while minimizing residual stress, distortion, and the possibility of cracking. Heat removal from parts during quenching can be described in terms of the effective interface heat transfer coefficient. A quenchant must impart a sufficiently high interface heat transfer coefficient to produce a cooling rate that will minimize transformation of austenite to ferrite or pearlite and yield the desired amount of martensite. A quench factorQ has been devised that interrelates quenching variables and transformation kinetics of steel to provide a single number indicating the extent to which a part can be hardened at various locations within the part. The quenchant and the quenchant operating conditions should be selected to provide the proper quench factor while minimizing thermal gradients that can cause distortion or cracking. Cooling curves, interface heat transfer coefficients, quench factors, and thermal gradients produced by a variety of quenchants are presented.

Microstructure and mechanical properties of V–Ti–N microalloyed steel used for fracture splitting connecting rod

Abstract: A new kind of V–Ti–N high strength microalloyed medium carbon steel has been developed, which is used for fracture splitting connecting rod. In this article, the characteristics of this carbon steel and its production process were studied. The microstructure, precipitated phases and their effects on mechanical properties were investigated by optical microscope, SEM, and TEM. The results showed that the steel was constituted of ferrite and pearlite. By reducing the finish rolling temperature and accelerating the cooling rate after rolling, microstructure with fine grain ferrite and narrow lamellar space pearlite could be obtained in V–Ti–N microalloyed medium carbon, and a large number of precipitated phases distributed over ferrite. These led the tensile strength to be more than 1000 MPa, yield strength (YS) more than 750 MPa. The impact fractograph showed typically brittle fracture characteristic.

Method for manufacturing high strength bolt excellent in resistance to delayed fracture and to relaxation

Abstract: A method for manufacturing a high strength bolt excellent in the resistance to delayed fracture and to relaxation, characterized in that a steel product having a chemical composition, wherein C: 0.50 to 1.0 % , Si: 0.5 % or less, Mn: 0.2 to 1 %, P; 0.03 % or less and S: 0.03 % or less, and having a structure, wherein the total area percentage of pro-eutectoid ferrite, pro-eutectoid cementite, bainite and martensite is 20 % or less and the balance is pearlite structure, is subjected to heavy wire drawing, the resulting wire is subjected to a cold heading to make a product having a bolt form, and the product is subjected to a blueing treatment in a temperature range of 100 to 400°C, thereby to manufacture a bolt form product having a tensile strength of 1200N/mm2 or higher and also being excellent in the resistance to delayed fracture and to relaxation.