Experimental Study and Thermodynamical Calculation on the Formation of Eutectic Phase of MnS-RE_2S_3 and(Mn,Ca)S-RE_2S_3 in Sulfur-Containing Free-Cutting Steel

The free-cutting phase in RE or Ca-RE treated sulfur-containing free-cutting steel is the eutectic phases of MnS-RE_2S_3 and (Mn,Ca)S-RE_2S_3,respectively.The atomic ratio of RE/S needed to modify all the MnS into the eutectic phase is higher than 1.48 or 1.41-1.37 Ca/S,when RE or Ca-RE is used as the modifiz- er in the sulfur-containing free-cutting steel.Moreover,the thermodynamical calculation shows that the eutectic temperature is lower than the solidifying temperature,which is the key condition for the eutectic phase to keep globual during solidifying.

Simulation of the continuous casting process in a mold of free-cutting steel 38MnVS based on a MiLE method

A new method called mixed Lagrangian and Eulerian （MiLE） method was used to simulate the continuous casting process in a mold of free-cutting steel 38MnVS.The simulation results are basically in agreement with experimental data in the literature,achieving the three-dimensional visualization of temperature distribution,melt flow,shell thickness,and stress distribution of blooms in a mold.It is shown that the flow velocity of steel melt becomes smaller gradually as the casting proceeds.When the flow reaches a certain depth,two types of flow patterns can be observed in the upper zone of the mold.The first flow pattern is to flow downwards,and the second one is to flow upwards to the meniscus.The corner temperature is higher,and the thickness is thinner than those in the mid-face.The effective stress in the corner area is much bigger than that in the mid-face,indicating that the corner area is the dangerous zone of cracking.

Influence of Ca/S and Rolling Reduction on Shape of Sulphide in Free-cutting Steel 5NiSCa

1.IntroductionThe shape of sulphide has a great influ-ence on machinability and transverse prop-erty of steel.It is very important to obtainoval sulphide instead of elongated one forimproving machinability and transverseproperties[1,2].

Influence of cold deformation on microstructure,mechanical properties,and corrosion resistance of high-sulfur free-cutting 316LS stainless steel

In this study,the influence of plastic deformation produced by cold rolling at reduction ratios ranging from 10% to 80% on the microstructure,mechanical properties,and pitting corrosion behavior of high-sulfur freecutting 316 LS austenitic stainless steel was investigated. The results indicate that slipping is the predominant effect and that sulfide inclusions extend along the rolling direction during the cold deformation of 316 LS. The strong austenite stability of 316 LS results in the formation of only a small quantity of deformation-induced martensite. The experimental results reveal that the strength,hardness,and yield ratio increased with increases in the reduction ratio,mainly due to work hardening,whereas the elongation decreased drastically,due to the combined effect of the work hardening and brittleness caused by the numerous sulfide inclusions. Electrochemically active sites on the surface of316 LS increased with an increased reduction ratio,which caused an increased current fluctuation in the passive zone. This also caused the breakdown potential（ E_b） near the pitting zone to exhibit a gradual increase in the zigzag current shift to the left on the polarization curves. The E_b of 316 LS decreased with increases in the reduction ratio,mainly due to the extended sulfide inclusions,the increased dislocation density,and the deformation-induced martensite content.

Analysis on composition and inclusions of ballpoint pen tip steel

Ballpoint pen tip steel, a super free-cutting stainless steel, exhibits excellent corrosion resistance and good machining properties. In this study, inductively coupled plasma spectroscopy, metallographic microscopy, and scanning electron microscopy were used to determine the elemental contents in five ballpoint pen tips and their components, morphologies, and inclusion distributions. The results showed that the steels were all S–Pb–Te super free-cutting ferritic stainless steel. The free-cutting phases in the steels were mainly Mn S, Pb, and small amounts of Pb Te. Mn S inclusions were in the form of chain distributions, and the aspect ratio of each size inclusion in the chain was small. The stress concentration effect could substantially reduce the cutting force when the material was machined. Some of the Pb was distributed evenly in the steel matrix as fine particles（1–2 μm）, and the rest of the Pb was distributed at the middle or at both ends of the Mn S inclusions. The Pb plays a role in lubrication and melting embrittlement, which substantially increases the cutting performance. Pb Te was also usually distributed in the middle and at both ends of the Mn S inclusions, and Te could convert the sulfides into spindles, thereby improving the cutting performance of the steel.

Application of tellurium in free-cutting steels

Te is widely used in iron and steel industry. After adding a certain amount of Te in the steel, many physical and chemical properties can be improved. As a free-cutting element, a small amount of Te can significantly improve the machinability of steel. The existing form of Te in the steel, the modification law of MnS inclusion by Te and the influence rule and mechanism of Te on the machinability of steel are summarized and expounded in detail, providing a reference for further study and development of Te-containing free-cutting steels.

Effect of Free-cutting Additives on Machining Characteristics of Austenitic Stainless Steels

The machinability tests were conducted by using a YD-21 dynamometer on a CA6161A lathe.The experiments were conducted to determine the effect of free-cutting additives on machining characteristics of austenitic stainless steels.The conventional austenitic stainless steel 1Cr18Ni9Ti（steel A） and the free cutting austenitic stainless steel（steel B） were prepared.The results have shown that machinable inclusions were composed of MnS and CuO,and they might be also Ti4C2S2.The presence of Bi in the inclusion was detected by the atom map and electro-probe microanalysis（EPMA）,which might be one of the most important factors to improve the machinability of austenitic stainless steels.The cutting forces for steel B were lower than those of steel A at various cutting speeds;the abrasion depth of the flank of the tool for steel B was less than that of the steel A under the same cutting conditions.The machinability of austenitic stainless steel was visibly improved by adding free-cutting additives,such as S,Cu and Bi.Ultimate tensile,yield strength,and total elongation values of the free cutting austenitic stainless steel were improved due to the addition of these free-cutting additives.

Formation and evolution behavior of inclusions in Al-killed resulfurized free-cutting steel with magnesium treatment

To reveal the formation and evolution behavior of inclusions during magnesium treatment and resulfurization in Al-killed free-cutting steel, both laboratory experiments and thermodynamic calculations were carried out. The extracted samples were polished and analyzed by scanning electron microscopy and energy-dispersive spectroscopy. The results indicated that MgO formed immediately and then transferred to MgO·Al2O3 with the homogenization of [Mg] in steel in the case of low magnesium addition (w[Mg] < 0.0020%). However, MgO would keep stable in the case of high magnesium addition (w[Mg] ≥ 0.0020%). In the process of resulfurization, the addition of sulfur forced the transformation of MgO to MgO·Al2O3 accompanied with the formation of MgS if the mass fraction of [S] in steel was in the range 0.15%-0.70%. MgS precipi-tated as a solid solution containing a quantity of MnS, and the composition of the sulfide solution was calculated to be (Mg0.85Mn0.15)S when the mass fraction of [Mn] was 1.2%. The formation mechanisms of inclusions after magnesium and sulfur additions were discussed comprehensively, and proper models for the evolution of inclusions were set up.

Trial Production of Sulphurous Free-Cutting Gear Steel by Convert-Billet Continuous Casting Process

In consideration of the composition characteristics and quality requirements of sulphurous free-cutting gear steel, the rational measures of sulfur control, calcium treatment and key technologies of continuous casting process are applied in the development of a full-line operation of LD-Billet continuous casting on steelmaking with semi-steel, which suggests an economic production of the steel has been realized. Test results show that the average retrieval rate of sulphurous alloy in the process of RH treatment is 95.3% and sulfur content of products is stability. Otherwise, content of T[O] in casting billet is in the range of 11×10-6 ~ 18×10-6 with average value is 14.7×10-6.Based on this, the billets have good surface quality and internal quality.

Effects of sulfur addition methods and Ca-Si treatment on the microstructure and properties of 30MnVS

The effects of sulfur addition methods and Ca-Si treatment on the microstructure and properties of free-cutting non-quenched and tempered steel 30MnVS were investigated by using optical microscopy, SEM and tensile test methods. The results show that sulfur addition methods influence the morphology of sulfides and the properties of 30MnVS slightly. Ca-Si treatment is beneficial for the formation of complex sulfides which normally have oxide cores, therefore, improving the distribution of sulfides in the tested steel and enhancing its toughness. The two methods, pyrite addition during LF process and S wire feeding during VD process, slightly influence the morphology and distribution of sulfides and the properties of 30MnVS; Ca addition not only promotes the nucleation of sulfides on the cores of calcium aluminate inclusions, but also creates modification effect on MnS, reducing the relative plasticity and hot deformability of sulfides during hot rolling process, thereby reducing the length/width value of sulfides and improving their distribution, and significantly enhancing its mechanical properties, in particular, the impact toughness increased by 30%.

STUDY ON FORMATION MECHANISM OF ADHERING LAYER FORMED ON TOOL FACE

The appearance of adhenng layer formed on tool face, its composition and distributionare analysed when Ca-S free-cutting stainless steel is machined. Cutting temperature field and itsrelation with formation of the layer is also studied. The result shows that, the layer can be formed under proper temperature condition, the stable cutting temperature field keeps the stable layer, itsthickness and composition distribution along rake face depend on the corresponding cutting tem-perature field. The theoretical model of the layer formation is set up.