Effect of roll gap adjustment on exit cross sectional shape in groove rolling—Experimental and FE analysis

We machined work roll with groove worn down as well as groove with no wear. We then performed a pilot hot rod rolling test at temperature of 1000 °C using plain carbon steel (0.1% C) as the roll gap decreases from reference roll gap (6.5 mm) to 3.5 mm. To understand better the effect of roll gap (i.e., section height) adjustment on the exit cross sectional area (ECSA) variation of workpiece in a two-stand groove rolling process with wear is considered, we carried out a series of three dimensional finite element analysis. Results reveal that variation of ECSA is almost linearly proportional to roll gap change while the roll gap decreases from reference roll gap (6.5 mm) to 3.5 mm. In oval groove rolling, the exit cross sectional shape and area predicted by FEA is in a good agreement with those measured. In round groove rolling, however, some deviations between FEA and experiment are observed because of roll groove geometry coupled with cross sectional shape of incoming workpiece. In the two-stand groove rolling, the effect of roll gap adjustment at each stand on the exit cross section of workpiece is somewhat different, in comparison with single-stand groove rolling. The roll gap adjustment at the previous stand has a more influence on the ECSA of workpiece than that of the next stand.     

Hot rolling of gamma titanium aluminide foil

Metal flow and microstructure evolution during the thermomechanical processing of thin-gage foil of a near-gamma titanium aluminide alloy, Ti–45.5Al–2Cr–2Nb, with an equiaxed-gamma microstructure was investigated experimentally and theoretically. Foils of thickness of 200–250 μm were fabricated via hot rolling of sheet in a can of proprietary design. The variation in gage of the rolled foils was ±15 μm except in very sporadic (local) areas, with variations of approximately 60 μm relative to the mean. Metallography revealed that the larger thickness variations were associated with large remnant colonies lying in a hard orientation for deformation. To rationalize these observations, a self-consistent model was used to estimate the strain partitioning between the softer (equiaxed-gamma) matrix and the remnant colonies. Furthermore, the efficacy of pre- or post-rolling heat treatment in eliminating remnant colonies was demonstrated and quantified using a static-spheroidization model. The elimination of remnant colonies via spheroidization prior to foil rolling gave rise to improved gage control.     

Sliding behavior and wear mechanism of iron and cobalt-based high-temperature alloys against WC and SiC balls

The sliding behaviors of two typical high-temperature alloys of GH2132 and GH605 against WC and SiC balls were investigated at environments from room temperature to 800 °C with a sliding speed of 50 to 125 m/min under a load of 10 to 20 N. The wear performances of high-temperature alloys, WC and SiC balls were rated and their mechanisms were discussed. The four sliding pairs exhibited the markedly different sliding behaviours, in which the GH2132/WC sliding pair had the maximum friction coefficient with 125 m/min under 10 N at room temperature. The variation trends of ball wear rates with the ambient temperature were at odds with those of friction coefficient. The higher friction coefficient did not always lead balls to suffer from the higher wear rate. The maximum worn depth approximated to 250 μm for the GH2132/WC sliding pair with higher friction coefficient. The GH605/WC sliding pair exhibited the lower friction coefficient and lower worn depth of plate. Whether at room temperature or high temperature, the GH605/SiC sliding pair significantly exhibited good wear resistance with a minor damage of ball and plate despite of its higher friction coefficient.     

冷轧机轧制过程中的轧辊振动研究

以冷轧机轧辊垂直振动为研究对象,在分析冷轧机振动机理的前提下,建立轧机垂直振动简化模型,运用数值仿真方法,分析了轧制压下量、摩擦系数及辊缝阻尼的轧制工艺参数对轧机垂直振动的影响。分析结果表明:减小轧机压下量有利于提高轧机振动临界速度;增加辊缝摩擦系数有利于减小轧辊的振动位移;增加辊缝阻尼能够有效降低振动幅值。在此基础上提出了抑制冷轧机垂直振动方法为:优化各道次压下量,以使轧制临界速度由1340 m·min-1提升到1520 m·min-1;适当降低乳化液浓度,以使辊缝摩擦系数增大,此调节过程应考虑窜流现象;增设液压衬板减震器或多孔阻尼减震器,以增加辊缝阻尼。     

Measurements of friction during hot rolling of aluminum strips

In order to establish the dependence of the coefficient of friction on rolling speed and the reduction, commercially pure aluminum strips were rolled at 500°C, using a 2% oil/water emulsion as the lubricant. The roll separating forces, roll torques, the forward slip, the roll pressure and the interfacial shear stress were measured as a function of the reduction and the rolling speed. The coefficient of friction was determined from the shear stress and the roll pressure distributions and its magnitude was validated independently. The coefficient of friction was found to increase with reduction and, in general, decrease with rolling speed. The adhesion theory of friction has been used to explain the observations.     

The bonding properties and interfacial morphologies of clad plate prepared by multiple passes hot rolling in a protective atmosphere

SUS304 stainless steel and plain carbon steel were first bonded by hot rolling in an argon atmosphere and were subsequently hot-rolled by multiple passes in air. Shearing and peeling tests were performed according to appropriate standards to evaluate the bonding results. The interfacial microstructures, composition diffusion and peeling fractographies of the clad plate samples were used to examine the bond quality. The effects of bond parameters on the bond properties of clad plate were studied. The experimental results indicate that the shear strength reaches 266 MPa, and the peel strength is up to 322 N/mm at 1323 K in the first pass, representing a reduction of 24.3%. Both the shear strength and the peel strength increase with increases in bonding temperature and total reduction ratio. The maximum shear strength reaches 361 MPa, and the peel strength is up to 510 N/mm at 1323 K after six passes with a total reduction ratio of 74.8%. Both the dimension and number of interfacial pores decrease rapidly with increasing rolling passes. Multipass hot rolling generates a number of local embedments at the interface and improves the interfacial bonding strength.     

Effect of hot rolled grain size on the precipitation kinetics of nitrides in low carbon Al-killed steel

The precipitation of nitrides plays a general role in the industrial processing of deep drawing quality Al-killed low carbon steels. In this paper, the effect of hot rolled grain size on the precipitation of nitrides has been analysed. To evaluate the effect of grain size on the nitride precipitation kinetics, thermoelectric power based investigations have been performed on hot and cold rolled specimens.In the hot rolled state, the precipitation of nitrides occurs more intensively in the fine grain size microstructure (average grain size = 9 μm) than in the large grain size microstructure (average grain size = 23 μm) until the precipitated fraction of nitrides reaches about 70%. In the cold rolled state the effect of grain size is much less significant; probably the precipitation process occurs simultaneously at the grain boundaries and along dislocations. According to the simulation results, significant differences can be found between the precipitated fraction of nitrides in fine and large grain size sheets coiled in the temperature range 550–650 °C. In this interval, the precipitated nitride fraction is about two times larger in a fine grain microstructure (9 μm) than in sheets with 23 μm average grain size. The local position in the coil also affects significantly the precipitated fraction of nitrides. In the outer ring of the coil, less than 20% precipitated fraction is predicted in coiling temperature range 550–700 °C. However, in the middle ring of a hot rolled coil, the precipitated fraction changes from 5% to 85% with increasing coiling temperature from 550 to 700 °C.     

Creation of a fine-grained and deformed structure with fine carbide particles in a Fe3Al–Cr–Mo–C alloy

A thermomechanical process has been performed to create a fine-grained and deformed structure with a large amount of fine carbide particles in a Cr, Mo and C containing Fe₃Al-based alloy. By hot rolling at 800 °C to a reduction of 65%, high local misorientation of 8–10 degree per μm was frequently produced in the matrix around large M(Cr, Mo, Fe)₂C particles of which volume fraction is 2.6%. A homogeneous recrystallised structure with average grain size of 70 μm and almost random texture was obtained by particle stimulated nucleation after a subsequent annealing between 900 and 1100 °C for 10 min. Annealing at 1100 °C dissolved 60% of the large carbides into the matrix. A subsequent hot deformation during cooling from 1100 °C led to the formation of a deformed matrix with fine M₂C carbide particles.     

Grinding performance and workpiece integrity when superabrasive edge routing carbon fibre reinforced plastic (CFRP) composites

Data is presented for wheel wear, cutting forces and workpiece integrity when high speed routing 10 mm thick CFRP laminates using single layer electroplated diamond and CBN grinding points as opposed to standard end milling tools. A 60,000 rpm retrofit spindle was utilised to accommodate the 10 mm diameter wheels having grit sizes of 76, 151 and 252 μm employed under either roughing or finishing parameters. Wear of CBN points exhibited a near two-fold increase over diamond with a similar ratio for cutting forces. Despite use of flood cooling, point geometry when roughing compromised life and integrity due to excessive clogging.     

Grain size–wear rate relationship for titanium in liquid nitrogen environment

This paper presents the results of sliding wear experiments conducted on high-purity titanium (Ti) against bearing-steel in liquid nitrogen (LN₂; boiling point: 77 K) environment. Ti samples of three different grain sizes (9, 17 and 37 μm) were used to study the effect of hardness, derived from grain refinement as well as cryogenic test temperature, on the wear properties of Ti. In our experiments, a constant load of 10 N and sliding speeds of 0.67, 1.11 and 4.19 m s^?1 were used. The coefficient of friction (COF) for this tribo-couple varied between ～0.25 and ～0.50. While a steady state was always achieved, a peak in the COF was always noted in case of coarse-grain (37 μm) Ti tested at a sliding speed of 4.19 m s^?1. Under the investigated sliding conditions, the wear rate was found to be of the order of 10^?3–10^?4 mm³ N^?1 m^?1. The lowest wear rate was recorded in the fine-grain (9 μm) Ti at the highest sliding speed of 4.19 m s^?1. The critical analysis of the worn surface topography reveals that the reduced wear rate was due to the formation of adherent and strain-hardened tribolayer. In order to show various dominant wear mechanisms of Ti, a qualitative map was developed in sliding speed–grain size space. Substructure evaluation revealed the formation of a dense array of deformation twins because of the plastic deformation, which often resulted in the subdivision of grains.     

Hydrogen quantification of magnetron sputtered hydrogenated amorphous carbon (a-C:H) coatings produced at various bias voltages and their tribological behavior under different humidity levels

Hydrogenated amorphous carbon (a-C:H) films have extraordinary tribological properties under dry conditions since the C-atoms at the surface are hydratized and not available for any bonding with the opposing material. Under wet conditions water molecules are weakly absorbed by the a-C:H-coatings so the interaction between the coating surface and the tribological counterpart changes to a dipole-like interaction which is disadvantageous for the tribological performance. According to this, the hydrogen-content plays an important role in the wear and friction behavior of diamond-like carbon (DLC) coatings under different humid conditions.This work focuses on the quantification of the hydrogen content of differently bias a-C:H top layered coating systems and their influence on the tribological behavior under different humidity conditions. By means of a magnetron sputter device DLC-coating systems with an a-C:H-top layer have been deposited at bias voltages between ? 75 and ? 200 V. In order to quantify the hydrogen content of the layers Nuclear Reaction Resonance Analysis (NRRA) was used. In combination with the results of the tribological tests under different humid conditions using a ball-on-disk-tester, correlations between the hydrogen content, the bias voltage and the wear and friction performance were made. A clear relationship between the bias voltage and the hydrogen content has been observed, since the values decrease consistently from 27.2 at.% at ? 75 V to a minimum of 19.9 at.% at ? 200 V bias voltage. Furthermore the different humidity levels show a strong influence on the tribological performance, while the bias voltage effects mainly the wear and friction results of the samples tested under wet conditions.     

Effect of different cooling rates on thermomechanically processed high-strength rebar steel

The present article is dealing with 0.2% C, 0.1% V and 0.02% Nb steel. Billets with 130 mm × 130 mm cross-section were austenitized and hold at 1080 °C. The billets were hot rolled to 22 mm bar diameter. Hot rolling was finished at 980–1000 °C. The final bars were air-cooled. On a parallel way, an experimental hot deformation investigation, on the same steel, was carried out at deformation temperature range 1200–800 °C with the same amount of deformation (97% reduction in area). However, cooling regimes after deformation were air cooling, water quenching to 600 °C followed by air cooling, and water quenching to room temperature. Microstructure investigation was done using both optical and scanning electron microscopes. Further evaluation was done using mechanical testing. The industrial trial has unsatisfied results with poorer yield strength with higher ultimate strength. Bainitic aggregates are detected in the hard phases islands. Air cooling after pilot hot deformation creates banded ferrite–pearlite microstructure with 9.11 μm ferrite grains. However, quick water quenching to 600 °C followed by air cooling develops tempered and softened coarse bainite phase. On the other hand, water quenching to room temperature develops fine bainite texture. Water quenching to 600 °C followed by air cooling is the best regime creating accepted mechanical properties.     

Effect of initial particulate and sintering temperature on mechanical properties and microstructure of WC–ZrO2–VC ceramic composites

Owing to improving the mechanical properties of cemented carbides in high speed machining fields, a new composite tool material WC–ZrO₂–VC (WZV) is prepared from a mixture of yttria stabilized zirconia (YSZ) and micrometer VC particles by hot-press-sintering in nitrogenous atmosphere. Commercial WC, of which the initial particle sizes are 0.2 μm, 0.4 μm, 0.6 μm and 0.8 μm, is mixed with zirconia and VC powder in aqueous medium by following a ball mill process. The sintering behavior is investigated by isostatic pressing under different sintering temperature. The relative density and bending strength are measured by Archimedes methods and three-point bending mode, respectively. Hardness and fracture toughness are performed by Vickers indentation method. Microstructure of the composite is characterized by scanning electron microscopy (SEM). The correlations between initial particles, densification mechanism, sintering temperature, microstructure and mechanical properties are studied. Experimental results show that maximum densification 99.5% is achieved at 1650 °C and the initial particle size is 0.8 μm. When temperature is 1550 °C and particle size is 0.4 μm, the optimized bending strength (943 MPa) is obtained. The best hardness record is 19.2 GPa when sintering temperature is 1650 and particle size is 0.8 μm. The indention cracks propagate around the grain boundaries and the WC particles fracture, which is associated with particle and microcrack toughening mechanism.     

辊缝油膜承载力对冷轧机振动的影响

针对某冷轧厂在线轧制过程中轧机的振动问题,从辊缝油膜承载力的角度分析其对轧机振动的影响,得出轧制过程中辊缝间距的减小导致辊缝油膜需提供更大的承载力来维持轧机稳定。从乳化液浓度、轧辊转速、乳化液金属微粒含量方面探讨了增强辊缝油膜承载力的方法,得出乳化液浓度与轧辊转速在增强油膜承载力的同时减小了辊缝的摩擦系数,也易导致轧机振动。通过试验得出,调节乳化液金属微粒含量能够在原有摩擦系数的基础上增强辊缝油膜承载力,从而保证轧机的稳定运行。     

The effect of lubrication on mill loads during hot rolling of low carbon steel strips

Hot rolling experiments have been conducted, using low carbon steel strips. The effects of water, oil/water emulsions, neat oil and dry conditions at the roll/strip surface, on the resulting loads and temperatures were examined. The 1 : 1000 oil-to-water mix appeared to lower the mill loads the most. Doubling the oil volume was found to have a deleterious effect and did not create any further load reductions.     

Equilibrium shape of prismatic dislocation loops under uniform stress

The rolling, recrystallization and cooling of AgCl containing 1–5 μm glass spheres generates thermal misfit dislocations. Under stress, prismatic loops elongate in the glide cylinder defined by their line sense and Burgers vector. Using optical microscopy, the shape of dislocation loops under an applied stress of 2.3 MPa is measured. The measurements are corrected for a friction stress of 0.34 MPa and compared with a model which incorporates the orientation dependent line tension (ODLT) of a dislocation. The measured data show considerable scatter; after averaging, good agreement between theory and experiment is obtained.     

Application of shallow circumferential grooved wheels to creep-feed grinding

A single-point diamond dressing tool was used to cut shallow circumferential groove on aluminum oxide grinding wheels. Creep-feed grinding experiments were then carried out to compare the performance of these grooved wheels with a non-grooved wheel. The results showed that, for the conditions used in this research, a grooved wheel could remove twice as much material as a non-grooved wheel before workpiece burn occurred. The results also showed that a grooved wheel can improve grinding efficiency by reducing the consumed power by up to 61%. Although the use of grooved grinding wheels caused the workpiece surface roughness to increase slightly when compared to a non-grooved wheel, the grooved wheel enabled up to 37% more material to be removed while still maintaining workpiece surface roughness values below 0.3 μm (“fine quality” surface finish), and up to 120% more material to be removed while still maintaining workpiece surface roughness values below 1.6 μm (“average quality” surface finish).     

Texture evolution of high purity tantalum under different rolling paths

Deformation behavior and texture evolution of the material can be significantly affected by strain path change. For this reason, two rolling methods, unidirectional rolling (UR) and clock rolling (CR), were employed to manufacture tantalum plates. Texture evolution during unidirectional rolling and clock rolling was studied respectively by orientation distribution function (ODF). Related annealed microstructures were investigated by orientation image map (OIM). Usually, unidirectional rolling led to a strengthening of the main texture component with increasing strain, but for tantalum dominant texture component {0 0 1} θ-fiber was stable after 70% deformation, while minor texture component {1 1 1} γ-fiber was enhanced with increasing strain. In clock rolling, both of the two fibers were not stable any more for their intensity varied with rolling pass. After the final deformation, a similar texture was produced by the two rolling methods. However, recrystallization texture revealed a big difference. Such different texture development was contributed to microstructural change resulted from rolling path change.     

Friction and wear mechanisms in MoS2/Sb2O3/Au nanocomposite coatings

Fundamental phenomena governing the tribological mechanisms in sputter deposited amorphous MoS₂/Sb₂O₃/Au nanocomposite coatings are reported. In dry environments the nanocomposite has the same low friction coefficient as pure MoS₂ (～0.007). However, unlike pure MoS₂ coatings, which wear through in air (50% relative humidity), the composite coatings showed minimal wear, with wear factors of ～1.2–1.4 × 10^?7 mm³ Nm^?1 in both dry nitrogen and air. The coatings exhibited non-Amontonian friction behavior, with the friction coefficient decreasing with increasing Hertzian contact stress. Cross-sectional transmission electron microscopy of wear surfaces revealed that frictional contact resulted in an amorphous to crystalline transformation in MoS₂ with 2H-basal (0 0 0 2) planes aligned parallel to the direction of sliding. In air the wear surface and subsurface regions exhibited islands of Au. The mating transfer films were also comprised of (0 0 0 2)-oriented basal planes of MoS₂, resulting in predominantly self-mated “basal on basal” interfacial sliding and, thus, low friction and wear.     

Microstructure,texture and magnetic properties of strip casting Fe–6.2 wt%Si steel sheet

An Fe–6.2 wt%Si strip with equiaxed grains and mild {0 0 1}〈0 v w〉 fiber texture was produced by twin-roll strip casting process. Then the as-cast strip was treated with or without the hot rolling prior to the warm rolling and annealing. When the hot rolling was not introduced, a fine and heterogeneous warm-rolled microstructure was produced and led to a fine recrystallization microstructure and very weak {0 0 1}〈0 v w〉 fiber texture in the annealed sheets. When the hot rolling was introduced, a coarse and homogeneous warm-rolled microstructure was produced and led to a very coarse recrystallization microstructure and much stronger {0 0 1}〈0 v w〉 fiber texture in the annealed sheets. The annealed sheets with hot rolling showed a higher magnetic induction and a higher core loss than those without hot rolling.