Texture of Rotary-Friction-Welded from Dissimilar Medium Carbon Steels

The purpose of the present study was to investigate the texture in dissimilar medium carbon steels welded by rotary friction technique. The Electron Backscatter Diffraction (EBSD) technique was the main technique used to investigate the effect of welding on grain size and grain crystallographic orientation in the welded joint. Moreover, the effect of isothermal heat treatment at 600°C on welded joint has been studied knowing that this annealing allows to decrease the residual stresses. EBSD results revealed different subzones in welded joint. The texture in the weld is essentially composed of three components: Goss {110} <001>, Rotated Cube {100} <110>, and Rotated Goss {110} <110> orientation. The heat treatments applied on welded material had a slight effect on texture and grain size.

Effects of cooling rate and Al on MnS formation in medium-carbon non-quenched and tempered steels

The effect of Al on the morphology of MnS in medium-carbon non-quenched and tempered steel was investigated at three different cooling rates of 0.24, 0.43, and 200°C·s^-1. The formation mechanisms of three types of MnS were elucidated based on phase diagram information combined with crystal growth models. The morphology of MnS is governed by the precipitation mode and the growth conditions. A monotectic reaction and subsequent fast solidification lead to globular Type I MnS. Type II MnS inclusions with different morphological characteristics form as a result of a eutectic reaction followed by the growth in the Fe matrix. Type III MnS presents a divorced eutectic morphology. At the cooling rate of 0.24°C·s^-1, the precipitation of dispersed Type III MnS is significantly enhanced by the addition of 0.044wt% acid-soluble Al（Als）, while Type II MnS clusters prefer to form in steels with either 0.034wt% or 0.052wt% Als. At the relatively higher cooling rates of 200°C·s^-1 and 0.43°C·s^-1, the formation of Type I and Type II MnS inclusions is promoted, and the influence of Al is negligible. The results of this work are expected to be employed in practice to improve the mechanical properties of non-quenched and tempered steels.

Improvement of Hole-Expansion Property for Medium Carbon Steels by Ultra Fast Cooling After Hot Strip Rolling

The improvement of hole-expansion properties for medium carbon steels by ultra fast cooling （UFC） after hot strip rolling was investigated.It was found that finely dispersed spherical cementite could be formed after ultra fast cooling , coiling and annealing treatment.Tensile strength of the steel after annealing was measured to be about 440MPa.During hole-expansion test , cracks were observed in the edge region around the punched hole because necking or cracking took place when tangential elongation exceeded the forming limit.Cracks were mainly formed by the coalescence of micro-voids.Fine and homogeneous microstructure comprised of ferrite and spheroidized cementite could increase elongation values of the tested sheets by suppressing the combination of the adjacent micro-voids , resulting in the improved hole-expansion property.

PHASE TRANSFORMATION UNIT OF BAINITIC FERRITE AND ITS SURFACE RELIEF IN LOW AND MEDIUM CARBON ALLOY STEELS

The lath-or plate-shaped bainitic ferrite of low and medium carbon alloy steels consists of packets of ferrite sublaths which are composed of many finer and regular ferrite blocks.They are uniform shear growth units of bainitic phase transformation.No carbide is precipitated from them.The bainitic O-carbides are precipitated from γ-α interface or carbon-rich austenite.The mode of arrangement of the units in ferrite sublath packet is in uni-or bi-di- rection.Single surface relief is produced by the accumulation of uniform shear strains with all the ferrite units arranged unidirectionally in a sublath packet,while tent-shaped surface relief is formed by the integration of the uniform shear strains of two groups with ferrite units piling up in two directions and growing face to face;whereas if they grow back to back,the integra- tion will be responsible for invert-tent-shaped surface relief.The interface trace between two groups of ferrite units in a sublath packet is shown as“midrib”.

Ductile Fracture Characterization for Medium Carbon Steel Using Continuum Damage Mechanics

This paper presents the ductility characterization for a medium carbon steel, for two microstructural conditions, that has been evaluated using the continuum damage mechanics theory, as proposed by Kachanov and developed by Lemaitre. Tensile tests were carried out using loading-unloading cycles in order to capture the gradual deterioration of the elastic modulus, which may be linked to the ductile damage increase with increasing plastic strain. The mechanical parameters for the isotropic damage evolution equation were obtained and then used as inputs for a plasticity-damage coupled nu- merical algorithm, validated through numerical simulations of the experimental tensile tests. A comparison between the SAE 1050 steels studied and two carbon steel alloys (obtained from the literature), provided some basic understanding of the influence of the carbon level on the evolution of the damage parameters. An empiric relationship for this set of parameters, which can provide useful data for preliminary studies envisaging prediction of ductile failure in carbon steels, is also presented.

Fretting Wear Behavior of Medium Carbon Steel Modified by Low Temperature Gas Multi-component Thermo-chemical Treatment

The introduction of surface engineering is expected to be an effective strategy against fretting damage. A large number of studies show that the low gas multi-component （such as carbon, nitrogen, sulphur and oxygen, etc） thermo-chemical treatment（LTGMTT） can overcome the brittleness of nitriding process, and upgrade the surface hardness and improve the wear resistance and fatigue properties of the work-pieces significantly. However, there are few reports on the anti-fretting properties of the LTGMTT modified layer up to now, which limits the applications of fretting. So this paper discusses the fretting wear behavior of modified layer on the surface of LZ50 （0.48%C） steel prepared by low temperature gas multi-component thermo-chemical treatment （LTGMTT） technology. The fretting wear tests of the modified layer flat specimens and its substrate （LZ50 steel） against 52100 steel balls with diameter of 40 mm are carried out under normal load of 150 N and displacement amplitudes varied from 2 μm to 40 μm. Characterization of the modified layer and dynamic analyses in combination with microscopic examinations were performed through the means of scanning electron microscope（SEM）, optical microscope（OM）, X-ray diffraction（XRD） and surface profilometer. The experimental results showed that the modified layer with a total thickness of 60 μm was consisted of three parts, i.e., loose layer, compound layer and diffusion layer. Compared with the substrate, the range of the mixed fretting regime（MFR） of the LTGMTT modified layer diminished, and the slip regime（SR） of the modified layer shifted to the direction of smaller displacement amplitude. The coefficient of friction（COF） of the modified layer was lower than that of the substrate in the initial stage. For the modified layer, the damage in partial slip regime（PSR） was very slight. The fretting wear mechanism of the modified layer both in MFR and SR was abrasive wear and delamination. The modified layer presented better wear resistance than the substrate in PSR and MFR; however, in SR, the wear resistance of the modified layer decreased with the increase of the displacement amplitudes. The experimental results can provide some experimental bases for promoting industrial application of LTGMTT modified layer in anti-fretting wear.

INVESTIGATION OF FRACTURE DESIGN FOR MEDIUM CARBON STEEL UNDER EXTRA-LOW CYCLIC FATIGUE IN AXIAL LOADING

The extra-low cyclic fracture problem of medium carbon steel under axial fatigue loading was investigated. Several problems, such as the relations of the cycle times to the depth and tip radius of the notch, loading frequency, loading range and the parameters of fracture design for medium carbon steel on condition of extra-low axial fatigue loading were discussed based on the experiments. Experimental results indicated that the tension-pressure fatigue loading mode was suitable for extra-low cyclic fatigue fracture design of medium carbon steel and it resulted in low energy consumption, fracture surface with high quality, low cycle times, and high efficiency. The appropriate parameters were as follows： loading frequency 3-5 Hz, notch tip radius r = （0.2-0.3） mm, opening angle α = 60°, and notch depth t = （0.14-0.17）D.

Influence of soaking time in deep cryogenic treatment on the microstructure and mechanical properties of low-alloy medium-carbon HY-TUF steel

The influence of soaking time in deep cryogenic treatment on the tensile and impact properties of low-alloy medium-carbon HY-TUF steel was investigated in this study. Microstructural studies based on phase distribution mapping by electron backscatter diffraction show that the deep cryogenic process causes a decrease in the content of retained austenite and an increase in the volume fraction of η-carbide with increasing soaking time up to 48 h. The decrease in the content of retained austenite from ~1.23vol% to 0.48vol% suggests an isothermal martensitic transformation at 77 K. The η-type precipitates formed in deep cryogenic-treated martensite over 48 h have the Hirotsu and Nagakura orientation relation with the martensitic matrix. Furthermore, a high coherency between η-carbide and the martensitic matrix is observed by high-resolution transmission electron microscopy. The variations in macrohardness, yield strength, ultimate tensile strength, and ductility with soaking time in the deep cryogenic process show a peak/plateau trend.

SUBSTRUCTURE AND CRYSTAL MORPHOLOGY OF MARTENSITE IN MEDIUM CARBON IRON ALLOYS

The morphologic,substructural and crystallographic characteristics of martensite in steels 60 and 60Si2Mn have been investigated by means of optical and transmission electron microscopy combined with B-M phenomenological crystallographic theory.The average hab- it plane of martensite in medium carbon iron alloys is{225}_f.Experimental data on the habit plane and the orientation relationship between the austenite and martensite are in agreement with the B-M theoretical calculation of using the Bain strain and lattice invariant shear on (100)[011]_f.

The Study on the Corrosion Behaviour of Welded and Unwelded Medium Carbon Steel in Sodium Chloride(Nacl)Solutions

The research work was based on the study of the corrosion behaviour of the welded and un-welded medium carbon steel in sodium chloride solutions.The Sodium chloride solutions used are 1ml,2ml,3ml and 4ml for both welded and un-welded medium carbon steel in NaCl.The experiments were conducted in two ways,the weight loss analyses of measurements and using the electrochemical analyzer workstation to determine the potential dynamic of the samples.The samples for the weight loss measurements were prepared from rolled products obtained at the foundry shop.Two medium carbon steel materials were sourced with different chemical compositions as sample A and B.The materials were prepared to accommodate the experiments for the determination of welded and un-welded medium carbon steel.A total of sixty-eight(68)samples were produced,prepared and used for the weight loss measurements/analyses the experiments.Thirty-four of the samples each were prepared for both the welded and un-welded experiments.All the samples were produced and prepared through the use of various machining processes with the use of a lathe machine for planning,milling.Thirty-four(34)of the sample preparation were further welded in readiness of the experiments.Sixty-eight breakers were sourced for and used.Ten(10)other samples were used for the determination with the use of the electrochemical analyzer.The chemical compositions of the medium carbon steel were determined with the use of SPECTRO Analytical Instruments.A metallurgical inverted optical microscope was used to determine the microstructures of the materials.The Scanning Electron Microscopy with EDS was used to determine the morphologies of the materials.The thirty-four of the samples were welded this process was performed to determine the effects of welding on the material surrounding the weldments.These materials were made into sizes with the use of power hacksaw(i.e.2cm by 2cm).Other materials were prepared to 1cm x 1cm thickness from the same materials.The Tafel plot experiments and that of the open Circuit Potential Time(OCPT)were carried out with the use of Electrochemical Analyzer/Workstation.The Medium carbon steel materials were exposed for fifty-four(54)days,with an interval of 3days.The corrosion rates analyses were determined and the graphs of the corrosion rates(mm/yr.)and other parameters were used plotted against No of days exposed.

Longitudinal surface cracks of thin slabs

Based on the production practice of medium carbon thin slabs in the CSP plant,the reasons and influencing factors for the formation of longitudinal cracks were investigated,and some industrial measures were taken to eliminate the cracks.The results show that the efficient solutions to reduce longitudinal cracks are improving the performance of the mold powder,stabilizing the mold heat flux,and maintaining a proper taper of the mold during casting.Proper pouring temperature and secondary cooling also play important roles in preventing longitudinal surface cracks.

Multiphase microstructure formation and its effect on fracture behavior of medium carbon high silicon high strength steel

This work investigated the evolution of multiphase microstructure and impact fracture behavior of medium carbon high silicon high strength steel subjected to the austempering treatment at 240,360,and400℃.The results show that martensite,bainite,and retained austenite(RA)are the main microstructural phases.The austempering treatments at 360 and 400℃ caused the formation of carbon-poor ferrite in the matrix,and the transformation of ultrafine bainite into coarse lath bainite and granular bainite,respectively.Thick filmy RA was distributed between bainite laths.The polygonal martensiteaustenite islands and blocky RA formed along the grain boundaries.The average carbon concentration in the matrix decreased with the temperature increase,while the impact toughness initially increased and then dropped with temperature.The quasi-cleavage brittle fracture dominated the impact fracture mechanism of the sample austempered at 240℃ by forming tearing surfaces and tearing steps.The microcracks disappeared in the RA on the prior austenite grain boundaries.On the other side,the fracture surface of the sample austempered at 360℃ exhibited ductile fracture with deep dimples and brittle fracture with cleavage river patterns.The polygonal martensite-austenite islands or blocky RA constrained the microcracks.After austempered at 400℃,the brittle fracture was dominant,showing river patterns,and the microcracks propagated through the granular bainite without any resistance.

Effect of Cyclic Annealing on Microstructure and Mechanical Properties of Medium Carbon Steel

The microstructure and mechanical properties of medium carbon steel after cyclic heat treatment were in- vestigated. The effects of cyclic numbers and long time annealing on the microstructure and mechanical properties of the experimental steel were compared. A short duration （5 min） holding at 1023 K （above A1 temperature） and a short-duration （3 min） holding at 893 K are adopted in each cyclic heat treatment. The spheroidization is accelerated during cyclic heat treatment, and the spheroidizing ratio grows with cyclic numbers. After 12-cycle heat treatments, there are few incompletely spheroidized regions in the specimens, and cementite lamellae mostly change into cement- ite particles. The morphological character of cementite for 12 cycles is similar to that undergoing annealing for 10 h at 973 K. The strength of the experimental steel after 5-cycle heat treatment is the lowest in the following cyclic heat treatment, but it is still higher than that of specimens with subcritical annealing over a long period （10 h）. After 12- cycle heat treatment, the strength of the experimental steel is close to that of the normalized steel, and the plasticity is the best in all heat treated specimens.

New Heat Treatment Technology for Grain Refining of Structural Steel

The application of electrical contact heating （ECH） in austenitic grain refining of ultra-pure 42CrMoVNb steel was introduced. The ECH equipment was designed to reach uniform heating of uniform heat transfer in the sample. The 42CrMoVNb steel treated possesses uniform microstructure with an average austenite grain size of 1.4 μm, higher strength （1 538 MPa） and impact toughness （81J/cm^2）.

Dynamic Recrystallization Behavior of Medium Carbon Cr-Ni-Mo-Nb Steel during Hot Deformation

Hot compression deformation behaviors of medium carbon Cr-Ni-Mo Nb steel were investigated at deformation temperatures ranging from 1223 to 1423 K and strain rates of 0.1, 1 and 5 s^-1. Dynamic recovery （DRV） and dynamic recrystallization （DRX） were observed during the hot compression deformation. For all of the samples, DRX occurred at deformation temperatures above 1323 K at different strain rates, while below 1223 K, no DRX was observed. The activation energy of the tested steel was determined as 386.06 kJ/mol. The ratio of critical stress to peak stress and the ratio of critical strain to peak strain were 0. 835 and 0.37, respectively. Kinetic equations interpreting the DRX behavior of the tested steel were proposed, and the corresponding parameters including the volume fraction and the average grain size were determined. Moreover, the microstructures induced under different deformation conditions were analyzed.

Microstructure and strength in ultrastrong cold-drawn medium carbon steel

Via traditional wire drawing,the medium carbon ferrite-pearlite(MCFP)steel wires can achieve the ultrahigh strength beyond 4 GPa normally for high-carbon pearlitic steel wires,but have a 30-60%lower production cost.The microstructural evolution and mechanical properties of medium carbon ferrite-pearlite steel wires have been investigated by means of scanning electron microscopy,transmission electron microscopy and tensile testing.The tensile strength of medium carbon ferrite-pearlite steel wires increases from 750 MPa up to 4120 MPa when the drawing strain increases up toε=6.4,which represents the highest strength reported so far-to our knowledge for a carbon steel with such low carbon content.At low and medium strains(ε≤1.95),the proeutectoid ferrite forms dense dislocation walls(DDWs)via dislocation activities,including sliding,accumulation,interaction,and tangling.With the drawing strain increase,the reorientation of DDWs to the drawing direction forms the coarse proeutectoid ferrite lamellae.Finally,the proeutectoid ferrite deformed to high strains is characterized by a lamellar morphology and the average lamellar spacing of proeutectoid ferrite is about 55 nm atε=6.4.The interlamellar spacing of pearlite and thickness of cementite decreases with the drawing strain increases.The dislocation density in ferrite lamellae increases with the drawing strain increases,and the dislocation density in ferrite lamellae is 7.8×10^(15)m^(2)atε=4.19.A higher dislocation density of 3.1×10^(16)m^(2)can be obtained atε=6.4 by means of extrapolation and TEM investigations.The stress contributions of proeutectoid ferrite and pearlite to the flow stress are estimated based on quantified structural parameters.Based on the assumption that the stress contributions from different strengthening mechanisms are linearly additive and the general rule of mixtures,a good agreement between the measured and estimated flow stresses has been found in a large range of flow stress.The good application of the general rule of mixture to the medium carbon ferrite-pearlite steel wires indicates the importance of quantitative characterization of microstructural evolution and parameters with the strain.

Vertical Short Crack Initiation in Medium Carbon Bainitic Steel Under Mild Tractive Rolling Contact

To improve the current grinding procedure of the back-up roll of CVC hot rolling mills so that the back-up roll service life can be extended, the crack initiation and propagation behavior of medium carbon bainitic back-up roll steel was investigated, a kind of asperity-scale, surface originated vertical short cracks occurred at 5 × 10^2 -1 × 10^4 cycles. Theoretical analysis indicated that the maximum tensile stress occurring at the back edge of the contact of asperities keeps at above 1 347. 97 MPa, and ratcheting and cyclic plastic deformation take place at such sites within 1 × 10^4 cycles. The early initiation of the vertical short cracks is caused by the asperity contact. According to the crack initiation mechanism, short crack behavior and preventive grinding strategy, steel consumption can be reduced considerably by decreasing the surface roughness and removing the asperity influenced surface thin layer at about 70%-80% of the surface distress life.

Comprehensive Control on Microstructures and Properties of Medium Carbon V-N Microalloyed Steel Seamless Oil-Well Tubes of Hot-Rolling Non-Quenched/Tempered

The relationship between microstructures and mechanical properties of a medium carbon V-N microalloyed steel used for N80 seamless oil-well tubes of hot rolling non-quenched/tempered (non-Q and T) was investigated.The results have shown that volume percentages of upper bainite,modified bainite and ferrite have a decisive influence on impact energies of steel tubes.When the total volume percentage of bainite is larger than 5%,the impact energy of tubes can not satisfy with the industrial criteria.Moreover,if the total volume percentage of bainite is smaller than 5%,then the impact energy of steel tubes enhances with volume percentage of ferrite increasing.The final microstructures have closely relation with tube billet quality,controlled cooling temperature after tube rolling and cooling method after stretch-reduction-diameter.High quality of medium carbon V-N microalloyed steel for non-Q and T oil-well tubes can be produced through comprehensive control of microstructures and mechanical properties in sub-procedures,especially for tube billet quality and controlled cooling parameters.

Influence of Vanadium on Fracture Splitting Property of Medium Carbon Steel

The fracture splitting property of medium carbon steel 37MnSiS microalloyed with V up to 0. 45% was investigated by using simulated fracture splitting test,for the development of new crackable medium carbon steel to manufacture high performance connecting rod. Conventional high carbon steel C70S6 was used for comparison. The results show that the volume fraction of both ferrite and V-rich M（ C,N） particles increases,and the pearlite interlamellar spacing decreases with increasing V content,which in turn results in gradual increase of strength and decrease of ductility and impact energy. The fracture splitting property of the tested steel could be improved significantly due to the increase of V content mainly through the precipitation hardening mechanism of fine M（ C,N） precipitates. The fraction of brittle cleavage fracture in the crack initiation area increases noticeably with increasing V content and full brittle cleavage fracture surface could be obtained when V content was increased to 0. 45%. It is concluded that medium carbon steel with V content higher than about 0. 28% possesses not only comparable or even higher mechanical properties with those of conventional steel C70S6,but also excellent fracture splitting property,and therefore,is more suitable to fabricate high performance fracture splitting connecting rod.