Spheroidizing Heat Treatment Research Articles

Evaluation of effect of spheroidization heat treatment on mechanical properties via small punch test

Due to the long time high temperature thermal action, pearlite heat-resistant steel 15CrMo is prone to pearlite spheroidization, which reduces its strength and makes it difficult to meet the actual service requirements. Therefore, quantifying the effect of pearlite spheroidization is an important factor in evaluating the high temperature performance of 15CrMo steel. In this study, the mechanical properties of 15CrMo steel were tested by uniaxial tension (UT), small punch tensile (SPT) test; the microstructure of 15CrMo steel after spheroidization heat treatment (SHT) was obtained by image processing technique to obtain the geometric characteristic parameters of pearlite spheroidization phase (PSP); the influence of spheroidization characteristics and properties were analyzed by mathematical and statistical analysis, and the results showed that the PSP size had the greatest influence on the properties; based on this, the linear relationship models between the spheroidization parameters and the mechanical properties of UT and SPT results were established with high accuracy of prediction.

Spheroidization Heat Treatment Conditions with Data Analysis in Medium Carbon Cr-Mo Steel for Ultra High Strength Cold Heading

The degree to which parameters affect the spheroidization heat treatment of steel was calculated by setting the spheroidization heat treatment conditions of Cr-Mo steel and using data analysis such as S/N ratio and ANOVA. After analyzing the transformation temperatures of the steel, A<sub>c1</sub> and A<sub>c3</sub> , using a DSC, the conditions were set accordingly. The surface hardness was measured for the conditions and used as an evaluation index. The correlation was analyzed by comparing the spheroidized volume fraction and the surface hardness, and the Pearson correlation coefficient was -0.88, proving that a correlation existed between the two values. Using S/N ratio and ANOVA, the degree to which each control parameter affects the decrease in the surface hardness was analyzed, qualitatively and quantitatively. For the S/N ratio, priority affecting the surface hardness for each control parameter was analyzed. The 1<sup>st</sup> heating temperature was found to have a more preferential effect on the surface hardness than the 1<sup>st</sup> heating time and the 2<sup>nd</sup> heating temperature. Using ANOVA, the 1<sup>st</sup> heating temperature was determined to be a very significant factor with the greatest influence, contributing 73.2% to the surface hardness. Intercritical annealing is a suitable spheroidization heat treatment condition, so if the surface hardness of the steel needs to be reduced using Intercritical annealing, the 1<sup>st</sup> heating temperature and time should be designed as the priority.

The Optimization of Spheroidizing Heat Treatment Parameters on SCM440 Alloy Steel Wires Using Taguchi Robust Design

In the fastener industry, SCM440 alloy steel wire is widely used in the production of cold forging parts, such as high-strength steel fasteners, auto parts, hardware supplies, etc. The wire manufacturers use an intercritical process for spheroidized annealing the alloy steel wires. The quality of a spheroidized annealed wire affects the cold forging quality of fasteners. A series of experimental tests on SCM440 alloy steel wires is carried out in a commercial hydrogen furnace. Various parameters such as spheroidized annealing temperature (A), prolonged heating time (E), holding temperature and time (B, C), cooling rate and temperature (D, F) affect the quality characteristics of wires, such as tensile strength, hardness and ductility. The effects of intercritical spheroidized annealing treatment on mechanical properties are investigated using Taguchi robust design to obtain optimal spheroidized annealing conditions to improve the mechanical properties of alloy steel wires for cold forming. It is experimentally revealed that the spheroidized annealing temperature (A), cooling rate and temperature (D, F) significantly affect the quality of spheroidizing annealed SCM440 alloy steel wires. The optimal spheroidized annealing conditions for SCM440 alloy steel wire are spheroidized annealing temperature of 771°C and prolonged heating for 5.0 h, then holding the temperature of 725°C for 1.0 h, and slowly cooling to the temperature of 713°C at the rate of -9°C /h. Therefore, the optimal mean tensile strength of 520.0 MPa, optimal mean hardness of 80.8 HRB, and optimal mean ductility of 0.488 are obtained. The variations of the properties are significantly reduced to achieve a much even quality for annealed wires. The optimal spheroidizing heat treatment parameter settings evidently improve the performance measures and the cold formability of SCM440 alloy steel wires is effectively improved.

Experimental Evaluation of the Effects of Structural Changes on the Vibration Properties of CK35 Steel

Abstract The microstructure of some components which operate in high-temperature conditions (e.g. boiler components, turbine blades used in gas power plants, jet engines and reactors) is subjected to changes in long run, which leads to a degradation in the mechanical properties of these components and consequently, reduces their lifecycle. Therefore, it is so useful to detect the changes in the microstructure of these parts during their operation, employing an easy, fast and non-destructive method to determine their remaining life. In this study, we evaluate the effects of the microstructural changes on natural frequencies and the damping coefficient of CK35 steel, employing the experimental modal test. We aim to use the method for power plant components, if it has significant effects. To do so, we applied spheroidization heat treatment on CK35 steel samples having a primary structure of ferrite-pearlite for 24 and 48 hours. Then, we carried out the experimental modal test on samples having different metallurgical structures, but with the same dimensions and weights. According to the findings, the spherical ferrite-carbide particles in the ferrite structure increase the natural frequencies and damping coefficient. These tests show that the structural changes in this type of steel result in slight changes in the values of natural frequencies; however, it significantly changes the damping frequencies.

Investigation and optimization of surface roughness with experimental design methods by turning of AISI-1050 after spheroidization heat treatment

In this study, surface roughness values that were obtained by turning a medium-carbon steel (AISI 1050) applied to spheroidization heat treatment were modeled with two different optimization methods. The test materials were subjected to spheroidization heat treatment for three different periods as 15, 60, and 180 min. Three different cutting speeds and three different feed rates were used for the turning operations. Surface roughness values obtained from the surface of the workpieces after turning were analyzed by the response surface method (RSM) and Taguchi method (TM). These analyses show that the surface roughness changes directly depending on the feed rate and other parameters have a limited effect on the surface roughness. The regression analysis revealed that in both methods, the R2 values were higher than 0.99, and it showed the effectiveness of these two methods. As a result, these two different experimental design methods showed high stability in solving this engineering problem. Additionally, in the comparison of the methods with each other, the ratio of similarity to the experimental results was evaluated by considering the percentage. The ratio of similarity was obtained by over 90% in both methods. When the ratio of similarity was analyzed, RSM had more effective results than TM.

Effect of spheroidization of cementite in ductile cast iron

The research aims to provide an alternative to austempering treatment of ductile cast iron with a simple and cost-effective heat-treatment process. This goal was accomplished by applying a simple one-step spheroidization heat treatment to the as-cast ductile iron, which would normally possess a coarse pearlitic microstructure to a significant extent. Spheroidization experiments involving isothermal holding below the lower critical temperature (A1) were conducted followed by standard mechanical testing and microstructural characterization for an experimental ductile iron. After improving the spheroidization holding time at a given temperature, the work shows that the ductility and toughness of an as-cast ductile iron can be improved by 90% and 40%, respectively, at the cost of reducing the tensile strength by 8%. Controlled discretization of the continuous cementite network in pearlitic matrix of the ductile iron is deemed responsible for the improved properties. The work also shows that prolonged holding time during spheroidization heat treatment leads to degradation of mechanical properties due to the inhomogenous microstructure formation caused by heterogeneous decomposition and cementite clustering in the material. The main outcome of this work is the demonstration of ductile cast iron’s necking behavior due to spheroidization heat treatment.

Effects of spheroidization heat treatment and intercritical annealing on mechanical properties and corrosion resistance of medium carbon dual phase steel

Spheroidization heat treatment and intercritical annealing and their effects on the mechanical properties and corrosion behavior of CK45 medium carbon steel were studied. Increasing the spheroidization time resulted in the decline of strength and hardness of the initial martensitic steel but improved the tensile ductility and corrosion resistance. Intercritical annealing of the spheroidized steels resulted in the formation of austenite at the expense of cementite particles at short intercritical annealing times, which resulted in the development of dual phase (DP) steels after water quenching. Increasing the holding time at the intercritical annealing temperature led to a remarkable increase in the volume fraction of martensite in the microstructure, leading to poor ductility and corrosion resistance. This processing route, however, made it possible to obtain low martensite contents via short intercritical annealing of spheroidized steels, which resulted in the enhancement of strength-ductility balance while maintaining appropriate corrosion resistance.

A review of recent progress in mechanical and corrosion properties of dual phase steels

New concepts proposed for processing of dual phase (DP) steels as one of the main classes of advanced high-strength steels (AHSSs) to enhance their mechanical properties (strength–ductility combination) and corrosion resistance were introduced. The current review covers (I) the processing routes to obtain the ferritic–martensitic microstructures, (II) parameters of intercritical annealing (IA) treatment, (III) primary thermomechanical treatments, and (IV) post processing. First, the principal heat treatment methods, i.e., step quenching, intermediate quenching, and intercritical annealing of ferritic–pearlitic steel, as well as the partitioning of manganese were critically discussed. Then, the effects of holding time at the intercritical annealing temperature on the austenitization, grain coarsening kinetics, abnormal grain growth, and volume fraction of martensite were summarized. Next, the importance of cold deformation (notably rolling) and heating rate for the development of fine-grained DP microstructures (with chain-networked martensitic islands) through recrystallization and modification of the preferred nucleation sites for the austenite phase was discussed. Moreover, the applications of severe plastic deformation techniques (such as constrained groove pressing), thermal cycling (multi-step or repetitive intercritical annealing), and spheroidization heat treatment were discussed. Finally, the impacts of tempering, quench aging, and bake hardening on the properties of DP steel were reviewed. This short overview shows the opportunities that the conventional and innovative processing routes can offer for the potential industrial applications of DP steels, especially in the lightweight car body for the automotive industry to address the safety, fuel consumption, and air pollution issues.

Mechanism of Cementite Spheroidization from Different Initial Microstructures in Fe-0.65C-2.33Mn Alloy

The spheroidization mechanism from different initial microstructures during spheroidizing heat treatment was studied in Fe-0.68C-2.33Mn alloy. Two types of initial microstructures, i.e. pearlite and martensite, were obtained by varying the cooling rate. The microstructure and property evolution during spheroidizing annealing was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The DICTRA software, assuming local equilibrium conditions, was used to simulate the carburizing process of different initial microstructures through different cooling rate. The results indicate that the spheroidization mechanism of cementite was related to the initial microstructures and the smaller lamellar spacing of pearlite inhibited the coarsening of cementite, resulting in the size of cementite smaller than that of martensite as the initial structure.

Intercritical and subcritical spheroidization of 10B38 cold heading steel

For the production of bolts by cold forging, the hardenable steel has to be in a soft and ductile state. The Cold Heading Quality Steel is achievable by a spherodization heat treatment on the hot rolled material. The scope of this study is a boron bearing medium carbon steel which has many promising properties as bolting material. The experimentations covered two different initial conditions before the spheroidization heat treatment: hot rolled (ferrite-pearlite microstructure) and quenched (martensitic microstructure). In combination, two spheroidization procedures were considered too: subcritical and intercritical heat treatments. Intercritical heat treatment process included heating to 750 °C , holding for 2 h and then cooling to 715 °C and then holding for 12 h. In the subcritical heat treatment proess, the materialwas heated to 715 °C , holding for 12 h followed by cooling in the furnace. To assess the cold formability, a special notched tensile test was employed and the results were supported with metallographic and microhardness measurements. For both subcritical and intercritical heat treatment, higher levels of spheroidizatin were achieved with the quenched samples compared with the hot rolled condition. On the other hand the subcritical heat treatment resulted in higher levels of spheroiization. A practical equation is developed which relates the failure strain of notched tensile specimens with pearlite content and the hardness of the 10B38 steel.

Spheroidization heat treatment and intercritical annealing of low carbon steel

Spheroidization annealing of low carbon steel and its effects on the microstructure and mechanical properties of dual phase (DP) steel were studied. It was revealed that the reduction in strength and hardness of the quenched martensitic microstructure was much more pronounced compared to the fully annealed ferritic-pearlitic banded microstructure with spheroidizing time. This was related to the confinement of spheroidized carbide particles to distinct bands in the latter, and the uniform dispersion of carbides and high-temperature tempering of martensite in the former. During intercritical annealing of the spheroidized microstructures, the tendency to obtain martensite particles as discrete islands was observed. This, in turn, resulted in an inferior strength-ductility balance compared to the DP steel obtained from the intercritical annealing of martensite, which negated the usefulness of the spheroidized microstructures as the initial microstructures for the processing of DP steels.

A Study on Two-Stage Cold Forging for a Drive Shaft with Internal Spline and Spur Gear Geometries

A two-stage cold forging process was proposed to manufacture a drive shaft with an internal spline and spur gear geometries, and this process was mainly composed of a forward extrusion for preform and a forward-backward extrusion for the drive shaft. In the process design, the preform was designed using a volume apportioning scheme from the required target shape, thereafter, the initial round billet was outlined. AISI 1035 carbon steel was selected as the raw material, and a spheroidizing heat treatment was adopted. Using the raw and spheroidizing annealed workpieces, uni-axial tensile and compression tests were carried out to evaluate the effect of the heat treatment and to measure the mechanical properties. Finite element simulations were sequentially performed to assure the suitability of the proposed process design. Considering the results from the process design and the numerical simulations, the related tool components were prepared and applied to a series of experimental investigations. The preform and the drive shaft fabricated by the two-stage cold forging experiments were compared with the required target and the numerically predicted configurations. The results indicated that the two-stage cold forging process proposed in this study could be well applied to the production of the drive shaft with an internal spline and spur gear structures.

Effect of Composition and Heat Treatment Regime on Structural State and Capacity of Special Alloy Steel Round Rolled Product for Cold Upsetting

On the basis of physicochemical prediction of the effect of component content on the phase and structural transformations, it is shown that in order to prepare a favourable ferrite-pearlite microstructure and to ensure the key capacity of round rolled product for cold upsetting, it is preferable to obtain in special alloy steels 40Х, 38KhGNM, 35KhGSA, 30G1R, and 12KhN an element content close to the lower grade limit. A study of the microstructure and hardness of round-rolled specimens from steels 35KhGSA, 38KhGNM, and 40Х establishes that isothermal annealing at 20–50°C below the А1 temperature and nonisothermal annealing at 1–30°C below the А1 temperature are the optimum for spheroidizing heat treatment. In this case, a different fraction of globular pearlite is obtained in the metal microstructure depending on the steel grade: 35KhGSA about 90%, 38KhGNM and 40Х about 30%, and in all cases there are favorable results for cold upsetting tests. The defining effect of surface defects and rolled product structural state on cold upsetting capacity is demonstrated.

Understanding of Processing, Microstructure and Property Correlations during Spheroidizing Heat Treatment of 100Cr6 Steel

In the present study an investigation has been carried out for spheroidization of 100Cr6 bearing steel used in forging industry. Three different spheroidization processes were considered. The first one was the annealing of normalized steel under Ac1 temperature for a long time. The second one was the annealing of normalized steel above Ar1 temperature after heating between Ac1 and Acm for one hour. The third one was the annealing of hardened steel under Ac1 temperature for a long time. For evaluation of cold workability with different spheroidization annealing periods, the yield strength and percentage of reduction in area in uniaxial tension were recorded. The present results indicate that low alloyed carbon bearing steels can be easily processed to achieve unique microstructures and properties.

The Assessment of Cutting Force with Taguchi Design in Medium Carbon Steel–Applied Spheroidization Heat Treatment

In this study, the analysis of cutting forces on medium carbon AISI 1050—to which different spheroidization heat treatments were applied—was conducted by the mixed-level Taguchi orthogonal experiment design method. In the experiments, besides the parameters of feed rate, depth of cut and cutting speed having effect on cutting forces as a factor in orthogonal design, the spheroidization time and temperature parameters were also used. By the performed orthogonal experiment design method, the values of cutting forces were estimated using the five-factor, two- and three-leveled Taguchi L36 (22 × 33) mixed orthogonal experiment design method. The effectiveness of the machining parameters on the cutting force was revealed by performing analysis of variance test. Moreover, the effectiveness rates of the parameters were also determined in the study as per the signal noise rates. Consequently, it has been observed that the feed rate is more effective on the cutting forces compared to other parameters.

Effect of spheroidizing heat treatment on the microstructure, hardness and toughness of high carbon powder metallurgy steel

Effect of spheroidizing heat treatment on the microstructure, hardness and toughness of high carbon powder metallurgy steel

Influence of Spheroidizing Heat Treatment on Mechanical Properties of EN47 Steel

The high temperature phase austenite in steel has the property to transform into a variety of room temperature phases like coarse pearlite, bainite & martensite depending upon the cooling cycle. The machinability and toughness depend upon the shape and distribution of pro eutectoid harder phases. The spherical or oval shapes give lesser resistance for machining process. So it is required to design the heat treatment to tailor the property as required by the application. In this view, it is proposed to study the mechanical and micro structural properties of EN47 steel undergoing Spheroidization. The aim of this work is to test the hardness, toughness and wear property of the steel in spheroidised condition. Hardening treatment improves hardness of the material, a marginal decrease in hardness value with improved ductility is observed in tempering. Hardening and longer duration tempering show better wear resistance compared to other heat treatments. Both mild and severe wear regions are observed. Generally mild wear region is observed above five hours of continuous running of the specimen. Micro structural analysis shows the existence of pearlitic structure in as bought & normalized specimen, lath martensitic structure in hardened specimen.

Study of the Al-Si-X system by different cooling rates and heat treatment

The solidification behavior of the Al-12.6% Si (A1), the hypereutectic Al-20%Si (A2) and the Al-20%Si-1.5% Fe-0.5%Mn (A3) (in wt. (%)) alloys, at different cooling rates is reported and discussed. The cooling rates ranged between 0.93 °C/s and 190 °C/s when cast in sand and copper wedge-shaped molds, respectively. A spheroidization heat treatment was carried out to the alloys in the as-cast condition at 540 °C for 11 hours and quench in water with a subsequent heat treatment at 170 °C for 5 hours with the purpose of improving the mechanical properties. The samples were characterized by optical microscopy, scanning electron microscopy and mechanically by tensile test, in order to evaluate the response of the heat treatment on the different starting microstructures and mechanical properties. It was found that alloys cooled at rates greater than 10.8 °C/s had a smaller particle size and better distribution, also showed a greater response to spheroidization heat treatment of all silicon (Si) phases. The spheroidization heat treatment caused an increase in the ultimate tensile stress (UTS) and elongation when compared with the alloys in the as-cast condition. The highest UTS value of 174 MPa was obtained for the (A1) alloy.

Effect of Hydrogen Charging on Low Cycle Fatigue Life and its Dependence on Cementite Morphology

Hydrogen deteriorates the strength of steel, and it is well known as hydrogen embrittlement. The susceptibility to this embrittlement is generally increased more with higher strength steels under the usual static loading. Meanwhile fatigue strength is more important in structural use; it is desired to clarify the effect of hydrogen on the properties under cyclic loading. Present paper deals with the effects of hydrogen entry on the strain controlled low cycle fatigue properties of low carbon steel (JIS S10C), which is the most basic kind of steels. With the information about hydrogen in steels, the extent of hydrogen damage in fatigue life and its dependence to cementite morphology were discussed. The total hydrogen content of 0.5–1.5 mass-ppm severely degrades the fatigue life of normalized S10C, which is not so strong and almost insusceptible to hydrogen embrittlement under static loading. The fracture surface is accompanied with fish-eye fracture surface. This is originated at inclusion and propagating with quasi-cleavage and vague striation. The hydrogen gas atmosphere formed around inclusion during cyclic loading is claimed to be the major reason for the degradation. Spheroidizing heat treatment makes the steel free from the degradation. The hydrogen claimed for the degradation of fatigue life is what has been trapped by pearlite or cementite/ferrite interface, because this interface is reduced by the spheroidizing treatment. It is not the hydrogen that was trapped by non-metallic inclusion before fatigue test.

Monitoring the Microstructural Evolution in Spheroidized Steels by Magnetic Barkhausen Noise Measurements

The aim of this study is to monitor nondestructively the degree of spheroidization in steels by Magnetic Barkhausen Noise (MBN) method. Various series of specimens consisting of either lamellar pearlite or partially/completely spheroidized carbides were produced from AISI 1060 steel by appropriate heat treatments. All specimens were characterized by metallographic examinations, hardness and MBN measurements. The results show that MBN signals are very sensitive to the variations in the microstructure caused by the spheroidizing heat treatment. The change of microstructure, from coarse lamellar carbides to uniformly dispersed spherical carbides in ferrite matrix, is reflected as higher Barkhausen activity due to less effective pinning of domain walls.