The effectiveness of spheroidization pearlitic steel with regard to the degree of plastic deformation (original) (raw)
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Abstract— Although many heat treatment schemes have been developed for pearlitic steel, in the literature there is still little information about the influence of the different heat treatment parameters on the percentage, properties and morphology of the phases. Neither there is any information on matching the parameters, taking into account the different degree of deformation of the steel wires, the particular applications and operating conditions of the products. The aim of this research was to optimize the parameters of the interoperation annealing used during the cold plastic working of pearlitic steel intended for cold-drawn wires. The results of the mechanical properties and microscopic observations, presented in this paper clearly show that there is no need to apply long recrystallization treatments to small diameter wires. This finding is highly significant from the economic point of view and it clearly shows the importance of the individual matching of heat treatment parameters to specific industrial applications
Deformation Induced Pearlite Transformation and Spheroidization: Effect of Alloying Additions
Advanced Materials Research, 2011
The aim of this research is to investigate the effect of Cr and Al (strong ferrite formers) on the strain-induced γ-to-pearlite transformation in eutectoid steels. The microstructure evolution during the hot deformation of three eutectoid steel grades was investigated using hot torsion testing. More specifically, the steels were deformed to strain levels varying from ε = 0,5 to ε = 1,5 at their specific Ar1 temperature. Hot deformation of the undercooled austenite leads to strain-induced γ-to-pearlite transformation and to the almost instantaneous spheroidization of the formed carbides. The corresponding microstructures consist of submicronic cementite particles and ferritic grains that are 1-5 μm in size. It is shown that 1,5% Cr addition and 0,5% Al addition increase the equilibrium transformation temperature but slower significantly the kinetics of the strain-induced transformation and consequently reduce the kinetics of cementite spheroidization and of ferrite recrystallization.
Pearlitic steels containing from some 0.8 to 0.95% C belong to the group of unalloyed steels of the quality class destined for cold drawing or rolling. At the same time, the steels are characterised with particularly low share of non-metallic inclusions and limited contents of chromium and nickel, which extend the pearlite reaction time. The pearlitic steel in the annealed state has the highest strength in relation to other unalloyed steels, therefore she have found application mainly as wire rods for springs, wires for car tire reinforcement and cables. However one of the issues widely discussed in literature is cracking of pearlitic steel subjected to plastic working, caused by high brittleness of the lamellar precipitations of hard cementite. This issue is extremely important because it affects significantly reduce fatigue strength. The paper presents proposals to modify the process of interoperation annealing in order to eliminate this problem.
Spheroidized Heat Treatment and its Effect on Machinability in Medium Carbon Steels
How spheroidization heat treatments influence on machinability and microstructure of AISI / SAE 1040-1050 steels, under cylindrical turning was investigated, in order to find an optimal tool life as a machinability criterion. Samples were made in the form of bars of 70 and 60 mm in diameter and 125 mm in length. These were subjected to the treatments: T1 = 900 °C / 3 h / oven cooling; T2 = 750 °C / 3 h /-650 °C / 6h / oven cooling and T3 = 700 °C / 24 h /oven cooling. The cutting parameters were: S = 67m / min and 78m / min; f = 0.1 mm / rev; d = 1 mm. The treatments were carried out in a muffle furnace. Hardness was measured on the Brinell scale (HB). A parallel lathe was used for the machinability tests and the Flank wear was measured using a sterographic microscope. The samples microstructure, were revealed at optical level using a high resolution microscope. It was found that the tool life (T) increases to the maximum with the treatment (T2). The maximum life tool, were: For SAE 1040 steel: T = 47.8 min, with treatment (T2). For SAE 1050 steel: T = 35.2 min, with treatment (T2). Material machinability is more affected by cutting speed (S) relative to the other variables. The treated samples (T2) show a lamellar pearlite structure with amounts of spheroidite. In the case of samples with subcritical treatments (T3) a totally spheroidized structure is observed. It is concluded that a combination of laminar pearlite and spheroidite has provided the best life conditions for the tool as a machinability criterion.
Tailoring the Processing Route to Optimize the Strength-Toughness Combination of Pearlitic Steel
Metallurgical and Materials Transactions A, 2022
The present study fine tunes the processing route of a eutectoid steel to shape an optimum strength–toughness combination through appropriate microstructural design. A fully lamellar coarse pearlite microstructure leads to poor strength and toughness. Hot deformation prior to the isothermal treatment breaks down the lamellar pearlite to a spheroidized structure. Moreover, reducing the hot deformation temperature not only refines the pearlite nodule size but also increases the spheroidized pearlite fraction, which thereby improves the toughness of the steel. However, no proportionate increase in yield strength was obtained due to insignificant change in the interlamellar spacing. Remarkable refinement in lamellar spacing and increase in the spheroidization amount was ensured when the hot deformation was carried out just below the eutectoid temperature, owing to the strain-induced pearlite transformation. The presence of a mixed microstructure of fine lamellar pearlite along with spheroidized pearlite constituents simultaneously improves both the yield strength and toughness of the steel. Optimum strength–toughness combination was attained when the hot deformation strain (just below the eutectoid temperature) was increased up to 45 pct. Subsequent increase in strain creates deformation bands and traces of strain-induced bainite in the microstructure, which again deteriorates the tensile elongation of the steel.
Effect of Spheroidization Annealing on Pearlite Banding
Materials Science Forum
The present paper deals with the influence of the duration of isothermal spheroidization annealing on the evolution of pearlite bands in various initial states. In this study, two initial conditions of the steel 16MnCrS5 are considered: a) industrially hot-rolled pearlite structures in their ferritic matrix and b) a specifically adjusted microstructure in the lab condition. Based on the experimental investigations and quantitative microstructural analyses, an empirical model for the prediction of pearlite banding within a broad range of annealing durations could be derived. Both, experiment and model, agree that pronounced pearlite bands in the initial state almost disappear after 25 h of spheroidization annealing. On the other hand, a marginal degree of pearlite banding in the initial state increases slightly during annealing. This fact could be explained by inhomogeneous cementite formation inside and outside the primary segregation regions of manganese.