Free-cutting Steel Research Articles

Molecular Dynamics Study on Drilling Performance and Cutting Behavior of Fe–Bi Free-Cutting Steel

Molecular Dynamics Study on Drilling Performance and Cutting Behavior of Fe–Bi Free-Cutting Steel

Effect of Gadolinium on Inclusions in a High-Sulfur Free-Cutting Steel and Converting Two-Dimensional to Three-Dimensional Morphology of Inclusions Through Matlab Programming

Effect of Gadolinium on Inclusions in a High-Sulfur Free-Cutting Steel and Converting Two-Dimensional to Three-Dimensional Morphology of Inclusions Through Matlab Programming

Formation mechanism of cracks formed during drilling of a cold drawn prestressing 1215 free-cutting steel

1215 steel is a low-carbon free-cutting steel with the largest production, and its quality issues are complex and diverse. The formation mechanism of cracks formed during drilling of a cold drawn prestressing 1215 free-cutting steel was investigated by means of optical microscopy, scanning electron microscopy, high-temperature laser scanning confocal microscopy, and Thermo-Calc software. The failure was caused by abnormally wide pearlite with large amounts of sulfide nearby. We speculate the abnormal microstructure was related to C and S segregation in columnar-to-equiaxed transition zone during continuous casting process. However, element segregation was an inherent property in the continuous casting process. Reheating was an important process for homogenization to eliminate segregation, but the reheating temperature was lowered to reduce production costs. The lower reheating temperature resulted in incomplete elimination of columnar-to-equiaxed transition zone segregation, ultimately leading to the formation of abnormal microstructure. This batch of 1215 steel wire was not suitable for producing component required transverse plasticity during machining, but could be used to produce circular shaft components. In the future, it is suggested to increase the reheating and hot-rolling temperature, or take effective measures to reduce segregation during continuous casting.

Effect of Bi content and temperature on the shear mechanical properties of Fe-Bi nanocomposites: a molecular dynamics study

In this study, the effects of Bi content and temperature on the mechanical properties of Fe–Bi nanocomposites were investigated using molecular dynamics simulation. The research reveals that the nanocomposite’s shear strength reaches a peak of 3.785 GPa at a Bi content of 0.15%, attributed to the impediment of dislocation movement by twin boundaries during shearing, resulting in a dynamic ‘Hall–Petch’ effect and exceptional shear performance of the material. The abundant twinning induced around Bi phase inclusions introduces orientational disparities within the crystal, leading to grain misalignments, with dislocations in the grains slipping near the twin boundaries. In the nanocomposites, <100> dislocations merely act as initial sites for reactions, reducing their impact on the material’s strength and fracture behavior. The maximum stress decreases with increasing temperature while the magnitude of atomic transformations increases. The proportion of atoms at grain boundaries is higher at higher temperatures, and the arrangement of atoms at grain boundaries is more complex. At a temperature of 100 K, the dislocation density is highest with the smallest variation, forming a reinforced region within the material. The above results have significant implications for the design of environmentally friendly Bi-containing free-cutting steels.

Effects of oxygen content, Mn/S ratio, Cu content, hot-rolling, and annealing on morphology/distribution of MnS inclusions and microstructure/mechanical properties of free-cutting stainless steel

Free-cutting steel, renowned for its exceptional machinability, is susceptible to the impact of manganese sulfide (MnS) and other non-metallic inclusions on the cutting performance and mechanical properties. The composition, morphology, and distribution of these inclusions are influenced by the total oxygen content and doping elements in free-cutting steel. This study focused on three S303 free-cutting steels with different S, Mn, and Cu contents, and the as-received samples were subjected to deoxidation and oxidation remelting, respectively, using a high-vacuum arc melting furnace to control the oxygen content. Thermo-Calc simulations were employed to predict the phases and phase proportions under different processing conditions and to compare with measurements. While the oxygen content was found to subtly affect the distribution and morphology of MnS inclusions, the Mn/S ratio notably affected the size and quantity of MnS inclusions, consequently impacting the mechanical properties of the steel. Higher Cu contents resulted in Cu segregates in the matrix but did not exist in MnS or form CuO; however, it significantly reduced strain hardening. Comparisons between hot-rolled and annealed samples revealed that the most significant changes in mechanical properties resulted from the release of residual stresses. In nanoindentation tests, it was observed that the hardness of MnS inclusion was influenced mainly by residual stresses not doping elements.

Effect of Bismuth Content and Heating Rate on MnS Inclusions in Free-Cutting Steel

In this paper, the influence of bismuth content and heating rate on the morphology of MnS inclusions in bismuth-containing free-cutting steel during heating was investigated through in situ observation experiments and 3D electrolytic corrosion experiments. By observing the microscopic morphology of inclusions in the original sample, it was found that MnS inclusions in the sample were rod-shaped, spherical, irregular, small in size, and mostly clustered at the grain boundary in the form of chains and divergences. With the addition of bismuth, MnS inclusions of a larger size appear in the steel, and the inclusions distributed at grain boundaries are also reduced. When bismuth (0.010~0.020%) is added to the steel, MnS is mainly spherical and uniformly dispersed in the steel matrix. If the bismuth content is too high, the inclusions aggregate. Through in situ observations of the inclusions in the sample, it was found that the addition of bismuth in the heating process delays the appearance of ferrite grain boundaries and contributes to the spheroidization of MnS inclusions. Mn and S elements can fully diffuse slowly in the matrix with a heating rate below 1 °C/s and a long holding time (300 s), which provides the possibility for the spheroidization of MnS inclusions.

Effects of hydrogen permeation on the mechanical characteristics of electroless nickel-plated free-cutting steel for application to the hydrogen valves of hydrogen fuel cell electric vehicles

Electroless nickel plating is a suitable technology for the hydrogen industry because electroless nickel can be mass-produced at a low cost. Investigating in a complex environment where hydrogen permeation and friction/wear work simultaneously is necessary to apply it to hydrogen valves for hydrogen fuel cell vehicles. In this research, the effects of hydrogen permeation on the mechanical characteristics of electroless nickel-plated free-cutting steel (SUM 24L) were investigated. Due to the inherent characteristics of electroless nickel plating, the damage (cracks and delamination of grain) and micro-particles by hydrogen permeation were clearly observed at the grain boundaries and triple junctions. In particular, the cracks grew from grain boundary toward the intergranualr. This is because the grain boundaries and triple junctions are hydrogen permeation pathways and increasing area of the hydrogen partial pressure. As a result, its surface roughness increased by a maximum of two times, and its hardness and adhesion strength decreased by hydrogen permeation. In particular, hydrogen permeation increased the friction coefficient of the electroless nickel-plated layer, and the damage caused by adhesive wear was significantly greater, increasing the wear depth by up to 5.7 times. This is believed to be due to the decreasing in wear resistance of the electroless nickel plating layer damaged by hydrogen permeation. Nevertheless, the Vickers hardness and the friction coefficient of the electroless nickel plating layer were improved by about 3 and 5.6 times, respectively, compared with those of the free-cutting steel. In particular, the electroless nickel-plated specimens with hydrogen embrittlement exhibited significantly better mechanical characteristics and wear resistance than the free-cutting steel.

Behavior of bismuth and manganese sulfide in free-cutting steel

Behavior of bismuth and manganese sulfide in free-cutting steel

Numerical simulation of void elimination in the billet during hot shape rolling processes based on the Gurson–Tvergaard–Needleman model

The presence of voids can compromise the strength and continuity of downstream products. The Gurson–Tvergaard–Needleman model was utilized to obtain the relevant parameters. A 3D finite element model was then employed to investigate the elimination of voids in a porous free-cutting steel 1215MS during the hot shape rolling process. The center distribution of voids in the billet was considered in the finite element model, and the relationships between the void elimination and the pressure stress in the billet were analyzed. The influences of rolling reduction, rotation speed, and friction between the work roller and billet on the void elimination were also discussed. The results revealed that the pass reduction has a significant influence on the ultimate value of void volume fraction, which is beneficial for better material self-healing during the shape-rolling process. These findings suggest that accurate predictions of void elimination in the workpiece can be achieved using the finite element method for successful simulation of the hot shape rolling process.

Insight into compositional dependence of thermophysical properties and structure of Al2O3-SiO2-CaF2-CaO-Li2O melts

Low-fluoride-lime Al2O3–SiO2–CaF2-based slag melts were designed for producing sulfur-bearing free-cutting steels by electroslag remelting. These newly designed slags must maintain the technological parameters, related to viscosity and crystallization characteristics. The structure, viscosity and crystallization of the slag with different CaO/SiO2 mass ratios and Li2O contents were studied. Raman spectroscopy shows that the silicate network is depolymerized and the aluminate network is polymerized as CaO/SiO2 mass ratio or Li2O content is increased. 27Al MAS-NMR spectra demonstrates the presence of small amounts of AlV and AlVI species in the melts with 0 mass% and 1.18 mass% Li2O, whereas Al is present exclusively in AlIV in other cases. The measured viscosity of the melts and the apparent activation energy of viscous flow decrease with increasing CaO/SiO2 mass ratio or Li2O content. Both the crystallization temperature and the crystallization ability of melts increase with increasing CaO/SiO2 mass ratio or Li2O content.

Hydrogen Embrittlement of 11SMn30 Free-cutting Steel

Hydrogen Embrittlement of 11SMn30 Free-cutting Steel

Formation, Aggregation, and Composite with Oxide Mechanisms of Oxysulfide in 1215MS Free-Cutting Steel

Formation, Aggregation, and Composite with Oxide Mechanisms of Oxysulfide in 1215MS Free-Cutting Steel

Characterization of the three-dimensional morphology of MnS precipitate in Ca-treated resulphurized free-cutting steel via fracture surface analysis

ABSTRACT MnS precipitates in resulfurized free-cutting steels are elongated in the rolling direction and then have a large size in length. It is difficult to accurately obtain the characteristics especially full length of MnS by two-dimensional observation. Three-dimensional morphology of MnS in a Ca-treated resulfurized free-cutting steel was investigated by using tensile method and scanning electron microscopy. Compared with the statistical results of MnS in two-dimension, the size in three-dimension was larger. In two-dimension image, the length of MnS was in the range of ~100 μm, and the percent of MnS with size in the rage of 50~100 μm was about 1.15%. In three-dimension image, however, the length of MnS observed was in the range of ~325 μm, and the percent of MnS with size larger than 100 μm was about 5.73%. The results provide an insight into the role of fracture surface analysis in MnS characterization in resulfurized free-cutting steels.

Behaviors of novel manufacturing 1215MS+Bi steel in casting thermal processes

ABSTRACT Currently, the effects of cooling and heating rates on the sizes and morphologies of impurities and grains in the typical Bi-bearing 1215 MS steels in the manufacturing processes have never been studied, so this work aims to deduce their solidification and heating behaviors. The in-situ heating experiments were carried out using a high-temperature laser confocal microscope. Results show that bismuth could refine the dendrite arm spacing. Liquid Bi segregates at the solidification interface of grain boundary and inhibits the growth of grains. The surface tension of Bi-MnS is smaller than Bi-Fe. A big heating rate aggravated the thermal vibration of grains in local areas and resulted in large local temperature difference. Slow heating and heat preservation are helpful for sulfides to absorb heat and for achieving large grains. To sum up, this study broadens the recognition of free-cutting steels and further contributes to the development of new steel grade.

Forms and Roles of Bismuth in Steel: A Review

In article number 2200625, Jian-bo Xie reviews the forms and roles of Bismuth in steel. Bismuth is used in free-cutting steels; however, the morphology of sulfide in steel has an effect on steel machinability. The morphologies of sulfides in as-cast steel were in clustering, spherical, ellipsoidal, and spindle shapes, while just the clustering sulfide has a bad effect on machinability. Most bismuth particles in steel are in isolated form, and others adhere to sulfides.

Effects of h-BN additives on tensile mechanical behavior of Fe matrix: A molecular dynamics study

In this paper, the effect mechanism of h-BN size, strain rate and tensile direction on tensile mechanical properties of Fe matrix in the presence of h-BN inclusions was investigated by molecular dynamics simulations. The results showed that the existence of h-BN inclusions diminished the tensile mechanical properties of Fe, which was attributed to the large variation in Elastic modulus between the inclusions and matrix as well as stress concentration near the interface. When the h-BN inclusions was 1 nm in radius, the results of the CNA analysis showed that the crystal structure changes from ordered to disordered to partially ordered, and the DXA analysis indicated that the dislocation length increased, then decreased, and then increased again. The stress–strain curve showed a double-peak phenomenon. The first peak was caused by the change in the crystal structure, and the second peak aroused due to the regrowth of dislocations. By analyzed the stress–strain curves at different strain rates, it was found that the tensile strength increased with increasing strain rate, while the Elastic modulus was almost unaffected, from the perspective of potential energy, the conclusion was confirmed. The findings of different tensile directions indicated that the material’s tensile strength was affected by the tensile direction. When the h-BN inclusions are parallel to tensile direction, the h-BN inclusions hindered the plastic deformation and a second peak appeared in the stress–strain curve. This study is essential to comprehend the influence of h-BN inclusions on mechanical properties of free-cutting steel.

Effect of Bismuth and Telluride on the Inclusions of Sulfur Free-Cutting Steel

The development of free-cutting steel is inseparable from the development of environmentally friendly alloy elements and the control of inclusions shape. Alloying elements can affect the composition, morphology, size, and distribution of inclusion, which are the main factors affecting the machinability of free-cutting steel. This study selected sulfur free-cutting steel with different chemical compositions as the research object to examine the effects of bismuth and bismuth tellurium on sulfur-containing free-cutting steel through electrolytic corrosion experiments, metallographic microscopy, scanning electron microscopy, energy spectrum, and electron backscattering analyzer. The results showed that the microstructures of free-cutting-steel containing sulfur, free-cutting steel containing sulfur bismuth, and free-cutting steel containing sulfur bismuth tellurium are composed of ferrite, pearlite, and inclusions. The inclusions in sulfur-containing free-cutting steel are chain, cluster, and a few dotted MnS. The inclusions in sulfur-bismuth free-cutting steel are point and a few dotted MnS. After the addition of Te, the number of dotted inclusions is reduced, while the number of chain and cluster inclusions is increased. Most of the inclusions in bismuth-containing free-cutting steel are flake inclusions, and the class II MnS change into class III MnS, which is beneficial for improving the free-cutting property of steel and to reduce anisotropy. With the addition of Te, MnS of other shapes, such as heart, water drop, butterfly, etc. of a length–width ratio of less than 4 also appeared as MnS and MnTe complex inclusions, and the fusiform manganese sulfide accounted for most of the steel. Both Bi and Te had modification effects on MnS.

Comparison of penetrated MnS grains by steel matrix in variously loaded free-cutting steels with/without Pb as one of the workability parameters

The free-cutting steel is one of the essential structural steels in electrical appliance industry and automotive industry. Most of the steel contains Pb, as solid lubricant, chip breaker, tool edge stabilizer and tool life extender. MnS grains also play the same role of Pb. However, Pb is toxic so that it will be prohibited to add to the steel in near future. Steel industry has tried to replace Pb with other element(s) and/or compound(s). The trials are still going on. This study proposes a candidate of the workability parameters for free-cutting steels with/without Pb. Investigated steels were loaded quasi-statically (strain rate: 1×10-3 s-1) and dynamically (1×103 s-1) up to fracture. Half of the specimens were pre-fatigued to form easier slip situation in steel matrix. After fracture, thin steel matrix penetrated into plenty of MnS grains. For the steel with Pb, the ratios of the number of such penetrations to those of total grains maintained almost the same value for all loading conditions. The ratios were varied with the loading conditions for the steel without Pb. These facts meant that Pb was a key element for easier slip of steel matrix. Therefore, this ratio had a feasibility to be one of the workability parameters for the free-cutting steel.

Study on the machinability of high-silicon high-carbon graphite-based free-cutting steel in contour turning

Study on the machinability of high-silicon high-carbon graphite-based free-cutting steel in contour turning

Study on the machinability of high-silicon high-carbon graphite-based free-cutting steel in contour turning

Study on the machinability of high-silicon high-carbon graphite-based free-cutting steel in contour turning