Medium Carbon Low Alloy Steel Research Articles

Effects of Polyethylene Glycol on the Mechanical Properties of Medium Carbon Low Alloy Steel

The effect of polyethylene glycol [H(OCH 2 CH 2 ) n OH] as quenchant was studied with a view to investigate the mechanical properties and microstructural evaluation of steel. The test samples were subjected to a conventional heat treatment process followed by quenching using prepared polymer solution with a definite proportion. The samples were characterized using a microhardness tester and universal tensile machine for the mechanical properties, metallurgical microscope was used in analyzing their structural re-orientation. From the result, it was observed that the hardness increment of the quenched samples conform to literature review as there was also a rise in the tensile properties. This though, was at the expense of their ductility. The micrographs were found to have justified the reason for the increment recorded in some of the mechanical properties, as it displayed a high proportion of the martensitic phase. Keywords: Hardness, Impact Energy, Polyethylene Glycol, Quenching

Formation and corrosion resistance of a phosphate chemical conversion coating on medium carbon low alloy steel

A uniform fine-crystalline structure is obtained upon PCC coating on 35CrMnSi with Fe2+ curing (b).

Hardness Simulation of over-tempered Area During Laser Hardening Treatment

The main problem of laser hardening process is the over-tempered structure with a hardness decrement zone in the overlapped area between different laser tracks, which may not meet the minimum hardness requirements. The over-tempered structure is located at the middle of two overlapped laser tracks or between the beginning and the ending of a closed trajectory.In this paper, the hardness in the overlapped zones is studied by means of numerical simulations and experimental tests during a temperature controlled laser hardening with scanning optics process. Thus, in order to study their difference and to validate the proposed methodology, two steels with very different tempering curves has been used; a cold work tool steel and a medium-carbon low-alloy steel.

Influence of the holding time of the deep cryogenic treatment on the strain hardening behavior of HY-TUF steel

The effect of the holding time of the deep cryogenic treatment on the strain hardening of HY-TUF, a low-alloy medium-carbon steel, and a comparison with strain hardening of conventional heat-treated steel were investigated. For this purpose, a deep cryogenic treatment was done for different holding times of 12, 24, 48, and 72 h. The metallographic results indicate completion of martensitic transformation; η-carbide precipitation and decrement of carbon concentration in martensitic matrix happened while carrying out a deep cryogenic process. Observations of transmission electron microscopy indicate higher density of dislocations within martensite near the cementite compared to that near the η-carbides. The tensile flow stress data for this steel was examined in terms of Hollomon equation. The results show that strain hardening of conventional heat-treated steel takes place in two stages. This evidence is related to the co-deformation of austenite and martensite. The strain hardening takes place in one stage for the deep cryogenic-treated steels, and their strain hardening exponents increase (from ~0.29 to 0.47) with an increasing holding time up to 48 h. A further increase in the holding time of the deep cryogenic treatment is found not to vary strain hardening exponent. The increase of strain hardening exponent and then observation of plateau in this parameter show an optimum value for the holding time of the deep cryogenic treatment (48 h).

Influence of DIT Parameters on the Cementite Spheroidization in a Low-Alloy Medium Carbon Steel

The influence of strain, strain rate, and temperature on deformation-induced transformation (DIT) in a low-alloy medium carbon steel is studied. The strain promotes the nucleation of ferrite (deformation-induced ferrite) and also pearlite (deformation-induced pearlite), this last being characterized by a fine interlamellar spacing and morphological instability. At strains e > 0.5, intragranular nucleation activates and further ferrite nucleation over the newly created α/γ interface takes place, which gives rise to the precipitation of cementite (deformation-induced cementite) at the ferrite boundaries. Soft annealing treatments have been performed on the microstructures obtained by DIT, and the degree of spheroidization has been quantified by image analysis techniques. In comparison to non-deformed conditions, the application of DIT results in a higher degree of spheroidization after soft annealing. Moreover, the EBSD analysis denotes that ferrite grain size refinement is achieved with respect to non-deformed conditions. The degree of spheroidization is highly influenced by the applied strain level and subsequent holding temperature.

Delamination toughening assisted by phosphorus in medium-carbon low-alloy steels with ultrafine elongated grain structures

The effect of phosphorus (P) on delamination toughening was examined for 0.4%C–1%Cr–0.7%Mn–0.2%Mo steels (mass%) comprised of ultrafine elongated grain (UFEG) structures with strong <110>//rolling direction (RD) fiber textures. The UFEG structures evolved through the plastic deformation of tempered martensitic structures by multi-pass caliber rolling at a temperature of 773K (warm tempforming, WTF). The addition of P, up to 0.093% (mass%), had little influence on the evolution of the UFEG structure and the strength of the steels. Although the tensile ductility and upper-shelf energy showed a slight tendency to decrease as the P concentration increased from 0.001% to 0.093%, the delamination perpendicular to the notch orientation of the impact specimens was pronounced over a wider temperature range. As a result of delamination, the 0.093% P-doped steel exhibited a significant inverse temperature dependence of toughness at temperatures from 250K to 350K. The delamination toughening was dominated by the UFEG structure, and further assisted by the phosphorus segregation. It was considered that the formation of distinct P segregation bands, which presented a structure consisting of brittle and ductile layers, may be especially effective in accelerating delamination and improving toughness in the P-doped steel with an UFEG structure.

Effect of Heat Treatment Process on Mechanical Properties of a Medium Carbon Low Alloy Steel

Effect of heat treatment processes on the microstructure and mechanical properties of a medium carbon low alloy steel was studied by means of color metallography, XRD and mechanical tests.The adopted heat treatment processes included air quenching and then austempering in salt bath, watercooling and then austempering in salt bath, as well as directly austempering in salt bath. The results show that after treatments according to the above three processes the steel may exhibited microstructure composed of different amount of bainite and martensite, and better mechanical properties in comparison with the cast ones, i.e. its impact toughness and hardness were increased by 92%-183% and 31%-55% respectively. For the case of air cooling and then austempering in salt bath, the amount of bainite decreased gradually with the increase of air cooling time while the amount of martensite progressively increased, correspondingly its hardness and impact toughness showed a tendency of increase and decrease respectively.The mechanical performance of the medium carbon low alloy steel is closely related to the ratio of bainite to martinsite in the microstructure. It is noted that the steel with a duplex microstructure of 50%-60% bainite and 30%-40% martensite exhibited an optimal comprehensive mechanical performance.

Effect of Deep Cryogenic Treatment on the Microstructure and Mechanical Properties of HY-TUF Steel

This paper analyzes how a deep cryogenic process changes the microstructure and mechanical properties of a medium-carbon low-alloy steel. The light microscopy, microhardness testing, and transmission electron microscopy reveal that η-carbide and martensite are constituent phases of deep cryogenic treated (DCT) steel, while the microstructure of conventional heat-treated (CHT) steel consists of cementite, martensite, and retained austenite. Transmission electron microscopy also shows that the particles of η-carbide have the shape of ultra-fine globules in DCT martensite. The η-carbides grow in a Hirotsu and Nagakura orientation relationship to the martensitic matrix that enables highly coherent interphase boundaries. The results of the mechanical tests, including tensile and Charpy impact tests, show that the deep cryogenic process can improve toughness in terms of elongation (~12.81%), tensile fracture energy (~266 MPa), and the ductile–brittle transition temperature (~−17.2 °C). The results of fractography are also consistent with the improvement in toughness. It is also found that the strength and macrohardness values are increased. Unlike CHT steel, discontinuous yielding is observed in DCT steel. Moreover, there is no change in Young’s modulus due to the deep cryogenic treatment.

Microstructural control and mechanical properties in friction stir welding of medium carbon low alloy S45C steel

Critical control of the welding conditions produced a fine ferrite–martensite duplex structure with the martensite volume fraction of around 33% in friction stir welding (FSW) of medium carbon (0.45wt% C) low alloy steel sheets. This microstructure provides the preferable combination of tensile strength and ductility. The findings were achieved to clarify the effect of the welding speed on the weldability. The fraction of low angle grain boundaries (LAGBs) decrease with increasing welding speed. At the welding speed of 400mm/min, the top region microstructure consists of lath martensite, while the bottom region shows a fine ferrite–pearlite structure. This microstructural variation can be linked with the distribution of the peak temperatures along the thickness of the weld. Additionally, it was shown that a non-contact thermal imaging system can be used as an effective tool for the online monitoring of several kinds of weld decays.

Grain size effect of austenite on the kinetics of pearlite transformation in low- and medium-carbon low-alloy steels

The value of the parameter n from the kinetic Avrami equation is determined for pearlite transformation in low- and medium-carbon low-alloy steels. The grain size effect of austenite on the kinetic curves of pearlite transformation is shown.

Properties optimization through enhanced cooling rate using liquid CO2 in friction stir welding of medium carbon low alloy steel

Properties optimization through enhanced cooling rate using liquid CO2 in friction stir welding of medium carbon low alloy steel

One-Step Quenching and Partitioning Heat Treatment of Medium Carbon Low Alloy Steel

This paper presents the results of novel one-step quenching and partitioning (Q&P) heat treatment conducted on medium carbon low alloy steel sheet. Samples were austenitised at 1193 K followed by interrupted quenching at 473 K for different partitioning times and finally they were quenched in water. Dilatometry was employed for selection of treatment temperatures. Optical and scanning electron microscopy was carried out to examine the microstructural changes. Volume fraction of retained austenite was measured by x-ray diffraction technique. Resulting microstructures were correlated with the mechanical properties such hardness, tensile strength, elongation, impact absorbed energy, etc. The notch tensile and fracture toughness properties of Q&P steels are still lacking therefore notch tensile strength and plain strain fracture toughness tests were conducted and results are reported here. Results of Q&P treatments were also compared with the properties obtained by conventional Quenching and Tempering (Q&T) and normalizing treatments. Optimum strength-ductility balance of about 2000 MPa tensile strength with 11% elongation was achieved in samples quenched at 473 K and isothermally partitioned for 100 s. Higher ductility of Q&P steel was attributed to the presence of 6.8% film-type interlath retained austenite. Fine-grained martensitic structure with high density of interphase boundaries imparted ultrahigh strength. It was further noted that the impact toughness, notch tensile strength and fracture toughness of 1000 s partitioned samples was higher than 100 s partitioned samples. Possible reasons for high toughness are synergetic effect of recovery of dislocations, partial loss of martensite tetragonality and precipitation of fine transition carbides.

Influence of Prior Warm Deformation on Cementite Spheroidization Process in a Low-Alloy Medium Carbon Steel

Warm deformations have been applied to a low-alloy medium carbon steel (AISI 5140) to promote faster spheroidization during soft annealing treatments. The application of warm deformation leads to the fragmentation of cementite lamellae and the formation of defects on both cementite and the matrix. This induces faster lamellae break-up according to a boundary splitting mechanism, which is responsible for the improved spheroidization after annealing. The substructure developed in the matrix enhances pipe diffusion through the sub-boundaries, which helps the lamellae terminations to coarsen and causes lamellae fast splitting and finally yields a coarse cementite particle distribution. When deforming up to e = 0.3, almost fully spheroidized microstructures are obtained after annealing at 993 K (720 °C), independently of the initial pearlite features. By means of the EBSD technique, it has been observed that the applied warm deformation, in addition to enhancing the degree of spheroidization, allows a much finer microstructure to be formed after annealing. Grain refinement takes place as a consequence of a continuous recrystallization process, which is directly related to cementite spheroidization in the long term.

Effect of Initial Microstructure on Impact Toughness of 1200 MPa-Class High Strength Steel with Ultrafine Elongated Grain Structure

A medium-carbon low-alloy steel was prepared with initial structures of either martensite or bainite. For both initial structures, warm caliber-rolling was conducted at 773 K (500 °C) to obtain ultrafine elongated grain (UFEG) structures with strong 〈110〉//rolling direction (RD) fiber deformation textures. The UFEG structures consisted of spheroidal cementite particles distributed uniformly in a ferrite matrix of a transverse grain size of about 331 and 311 nm in samples with initial martensite and bainite structures, respectively. For both initial structures, the UFEG materials had similar tensile properties, upper shelf energy (145 J), and ductile-to-brittle transition temperatures 98 K (500 °C). Obtaining the martensitic structure requires more rapid cooling than is needed to obtain the bainitic structure and this more rapid cooling promote cracking. As the UFEG structures obtained from initial martensitic and bainitic structures have almost identical properties, but obtaining the bainitic structure does not require a rapid cooling which promotes cracking suggests the use of a bainitic structure in obtaining UFEG structures should be examined further.

Changes in magnetic field intensities around fatigue crack tips of medium carbon low alloy steel (S45C, JIS)

Damage of machine components occur when cracks form and continue to grow to a size large enough to cause fracture. In order to understand the crack propagation phenomena, non-destructive evaluation methods that can be correlated to measurements around the fatigue crack tips are necessary. In the present work, we developed a scanning Hall probe microscope (SHPM) equipped with a three-dimensional sensor and observed magnetic fields around fatigue cracks at room temperature in air while they were growing. In order to study the relation between plastic deformations and magnetic flux densities, both as-received non-heat-treated and heat-treated (quenched and tempered) specimens were used. Medium carbon low alloy steel specimens (S45C, JIS) were used in the experiments. The area around the crack tip was magnetized and the changes in the area were observed. The changes in magnetic fields in soft and hard specimens with the same intensity factors were compared. A strong correlation between the changes in the magnet fields and plastic deformation areas was found.

Investigation of Microstructure and Mechanical Properties of Ultra High Strength Bainitic Steel

In this study, medium carbon low alloy steel was used to obtain bainitic structures. The lower bainite and tempered martensite-lower bainite structures were achieved by isothermal austempering and up quenching treatment, respectively. Based on the results obtained these structures showed a very good combination of strength and toughness. Furthermore, it has been shown that austenitization time and temperature, as well as austempering time and temperature play a major role in achieving ultra-high strength bainitic steels.

The Effect of Hot‐ and Cold‐Rolling on the Electropulse‐Induced Microstructure and Property Changes in Medium Carbon Low Alloy Steels

AbstractThe application of electropulse to hot‐rolled and cold‐rolled, medium carbon low alloy steels has generated completely different effects. For cold‐rolled steel samples, electropulsing treatment causes microstructure refinement and, hence, increments in tensile strength, yield strength, and elongation. For hot‐rolled steels, the effect of electropulsing is found to be negligible. This proves the importance of dislocations in the micromechanism of electropulse‐induced microstructure transformation in solids. The optimal electropulse parameters for the improvement of cold‐rolled steels are observed. The experimental observations are explained within the frameworks of thermodynamics and kinetics of microstructure transformation.

Research on Dual Liquid Bimetal Composite Casting Lining Board

Material wear such as abrasiveness, cavitations erosion, and grinding balls with large diameter etc, exists during the usage of ball mill lining board. The effect of the chemical contents, composite casting process and heat treatment parameter on the interface microstructure, mechanical properties and wear resistance were studied by the SEM, EDAX and TEM, etc. The results show that the bimetal interface formed an effective metallurgical bonding boundary without mixing. The impact toughness of the interface is higher than the working face. The bimetal composite lining board has a very good stability. The service life of the bimetal lining board is increased 70% than the medium carbon low alloy steel under the same service conditions and the process yielding is over 95%.

Experimental investigation of laser transformation hardening of low alloy steel using response surface methodology

In this research, a systematic investigation on laser transformation hardening (LTH) process is carried out on high-strength low-alloy medium carbon steel, EN25 using design of experiments (DOE). The effect of input process parameters like laser power, travel speed over the response hardened width (HW), hardened depth (HD), and hardened area (HA) are analyzed. The experimental trials are conducted based on the design matrix obtained from the 3k full factorial design (FFD) using a 2 kW continuous wave Nd:YAG laser power system. A quadratic regression model is developed to predict the responses using response surface methodology (RSM). Based on the developed mathematical models, the direct and interaction effects of the process parameters on LTH are investigated. The optimal hardening conditions are identified to maximize the HW and minimize the HD and HA. The results of the validation test show that the experimental values quite satisfactorily agree with the predicted values of the mathematical models and hence, the models can predict the response adequately.

Study on microstructures and work hardening behavior of ferrite-martensite dual-phase steels with high-content martensite

A kind of medium-carbon low-alloy dual-phase steels with high-content martensite produced by intercritical annealing at 785-830 ºC for 10-50 minutes were studied in aspect of microstructures and work hardening behavior using SEM and tensile testing machine. The experimental results showed that the work hardening of the studied steels obeyed the two-stage work hardening mechanism, whose work hardening exponent of the first stage was higher than that of the second stage. The work hardening exponent increased with increasing the intercritical annealing temperature and time. For series A steel intercritically annealed at 785 ºC with starting microstructure of ferrite plus pearlite, austenite nucleated at the pearlite colonies, so the holding time of only 50 minutes can increase the work hardening exponent obviously. For series B steel with starting microstructure of martensite, austenite nucleated at lath interfaces, lath colony boundaries of primary martensite and carbides, accelerating the formation of austenite, so holding time for 30 minutes made the work hardening exponent increase obviously. High work hardening rate during initial plastic deformation (<0.5% strain) was observed.