Hot deformation behaviors and flow stress model of GCr15 bearing steel

The hot deformation behaviors of GCr15 bearing steel were investigated by isothermal compression tests, performed on a Gleeble-3800 thermal-mechanical simulator at temperatures between 950 ℃ and 1 150 ℃ and strain rates between 0.1 and 10 s-1. The peak stress and peak strain as functions of processing parameters were obtained. The dependence of peak stress on strain rate and temperature obeys a hyperbolic sine equation with a Zener-Hollomon parameter. By regression analysis, in the temperature range of 950-1 150 ℃ and strain rate range of 0.1?10 s?1, the mean activation energy and the stress exponent were determined to be 351kJ/mol and 4.728, respectively. Meanwhile, models of flow stress and dynamic recrystallization (DRX) grain size were also established. The model predictions show good agreement with experimental results.

WEAR AND LIFE OF PCBN TOOLS WHEN DRY-CUTTING BEARING STEEL GCr15

The wear forms and reasons of PCBN tools when dry-cutting bearing steel GCr15are studied systematically. The effect law of the workpiece hardness on PCBN tools is gained andtool wearing with the quickest speed at the workpiece critical hardness is proved. The life equationat two kinds of workpiece hardness demonstrates that the effect of the cutting speed on the PCBNtool life is less than that of carbide tools and ceramic tools.

Wear Performance of Laser Surface Hardened GCr15 Steel

In order to assess the new tribological properties of laser surface hardened GCr15 steel, the wear resistance between specimens treated with laser and those of conventionally hardened under dry sliding conditions was compared. The change of wear mechanisms in laser hardened GCr15 resulted in a distinct difference in wear rates. The results showed that quenched zones not only had sufficient depth of hardening and higher hardness, but had more retained austenite and finer carbides because of a higher degree of carbide dissolution. Laser surface hardened GCr15 steel specimens exhibited superior wear resistance to their conventionally hardened specimens due to the effects of the microstructure hardening, high hardness and toughness. The wear mechanism for both the laser quenched layer and conventionally hardened layer was highly similar, generally involving adhesive, material transfer, wear-induced oxidation and plowing. When conventionally hardened block specimens rubbed against the laser hardened specimens, the surface of conventionally hardened block specimens was polished. The microstructural thermal stability was increased after laser surface treatment.

Microstructural evolution of GCr15 steel during austenitizing and quenching considering C and Cr content

Microstructural evolution of GCr15 steels with different C and Cr contents during austenitizing and quenching was studied. Thermodynamic analysis of cementite dissolution was implied to obtain the critical temperature. The coordination number x in Fe_xCr_(3-x)C and the volume fraction of undissolved cementite were computed according to element conservation and equilibrium phase diagram. The M_S(martensite transformation temperature) was calculated by using empirical formula. The retained austenite content was calculated with further consideration of quenching temperature. The results showed that the coordination number and the undissolved cementite content were promoted by the austenitizing temperature and carbon content of the steel. Increasing Cr element reduced the coordination number.GCr15 steels with different components had nearly the same M_S when austenitization at 830 °C to 860 °C. The interaction of C and Cr complicated the evolution of M_S and retained austenite content. The results were in good agreement with the literature, which could guide to obtain specified retained austenite and/or carbides.

Alloying Effect of Lanthanum in GCr15 Bearing Steel with Tin and Antimony

Effect of tin and antimony on hot ductility of GCr15 bearing steel as well as interaction between lanthanum and tramp elements, were studied by simulator Gleeble-1500 and the fractures for the tested steels were analyzed using SEM and EDS. The results show that with increasing contents of tin and antimony elements, the hot ductility of GCr15 bearing steel was decreased. Lanthanum can reduce the harmful effect of tramp elements on the hot ductility of GCr15, which can react with antimony to form compound and segregate at grain boundary in steel. Lanthanum can refine the recrystallized austenite grains after deformation and subsequent martensite structure.

Effects of Suspension Casting on Solidification Process of GCr15 Steel Ingot

The mechanism of inoculation in the case of suspension casting process has been studied through solidification kinetics. The effect of suspension casting process on temperature field, solidification rate, temperature gap of crystallization, effective distribution coefficient of solute and nucleation frequency during solidification process in steel ingot were discussed on the base of experiments. It has been found that the suspension casting process can increase both cooling at and solidification rate of steel ingot, improve the temperature field and solute distribution, narrow the temperature gap of crystallication, and increase the nucleation frequency. Thus, the solidification time can be shorten, the solute can be well distributied, the shrinkage porosity can be reduced and the grain of crystallization can be fined.

The microstructural nanoindentation characteristics of different phases in precision annealed GCr15 steel

This study characterizes the mechanical properties and volume fractions of the different phases in precision annealed GCr15 steel using nanoindentation technology. Experimental results indicate that the nanoindentation hardness of cementite grains is between 14.15 GPa and 17.61 GPa,with a mean value of 15.40 GPa. This hardness is much higher than the hardness of ferrite grains. The nanoindentation hardness of ferrite is between 2.78 GPa and 4.89 GPa, with a mean value of 3.35 GPa. The volume fractions of the different phases were also determined using nanoindentation technology, and the volume fraction of cementite in the steel was identified as 15%.

热处理工艺对GCr15钢碳化物球化效果的影响

分别采用常规球化退火、循环球化退火和1050℃高温固溶+700℃高温回火三种不同的预热处理工艺处理后,再用840℃淬火+150℃回火工艺处理了GCr15钢试样,研究了经上述三种工艺处理后GCr15钢试样的金相组织和硬度,分析了实验结果和球化机理。结果表明:GCr15钢试样经1050℃高温固溶+700℃高温回火+840℃淬火+150℃回火的热处理工艺,具有工艺过程简便、可操作性较强、生产周期较短、能耗较低和强韧性较好的特点,其热处理后的金相组织为回火马氏体+细小、圆整、比较均匀弥散分布的碳化物。

GCr15轴承钢的再结晶规律研究

采用阶梯试样的方法并半定量统计了不同工艺条件下的GCr15轴承钢的再结晶晶粒个数,确定了其再结晶百分数,绘制了GCr15轴承钢再结晶区域图,研究了变形温度及变形量对GCr15轴承钢的再结晶规律。结果表明:当变形温度低于900℃、变形量小于30%时,奥氏体处于完全未再结晶区;当变形温度超过1050℃、变形量大于50%时,奥氏体位于完全再结晶区。

喷吹工艺对轴承钢GCr15断裂力学性能影响的研究

通过金相、电镜等手段对SL(钢包喷吹Ca-Si粉)工艺和CAB(钢包吹氧)工艺GCrl5钢中的非金属夹杂物进行了分析和测试;应用断裂力学的方法对两种工艺的GCrl5钢K_(IC)和△K_(th)进行了测定。结果表明:采用SL工艺的GCrl5钢中夹杂物体积分数下降,大颗粒夹杂显著减少;K_(IC)和△K(th)均有所提高。

GCr15钢摆线轮断裂分析

应用化学成分分析,金相组织分析,非金属夹杂物及碳化物检测等方法对GCr15钢摆线轮断裂原因进行了综合分析。结果表明:摆线轮断裂属于脆性断裂,钢中点状不变形夹杂及网状碳化物超标是摆线轮脆性断裂的主要原因,并在生产中得到验证。

Effect of electromagnetic stirring on metallurgical quality of GCr15 electroslag ingot

To further improve the metallurgical quality of electroslag remelting,remove the large inclusions in electroslag ingot and refine the solidification structure of electroslag ingot,an electroslag remelting furnace with electromagnetic stirring was designed,and the influence of different magnetic induction intensities on metallurgical quality of GCr15 electroslag ingot was studied.Inclusions with different sizes and types were analyzed by an ASPEX scanning electron microscope,and the morphology and composition of inclusions were further observed by a JSM-6510LV scanning electron microscope.The distribution of alloying elements on the cross section of electroslag ingot was analyzed by original position analysis(OPA).The results show that whether or not electromagnetic stirring is used,the inclusions in electroslag ingot are mainly composed of Al_(2)O_(3),MnS,MnS-oxide and other oxides,among which Al_(2)O_(3) is the most.Compared with an electroslag ingot without electromagnetic stirring,the number of inclusions decreases considerably,and the proportion of small inclusions increases while the proportion of large inclusions decreases when the electromagnetic stirring with remelting current of 1.1 kA and magnetic induction intensity of 62 Gs is applied.However,excessive electromagnetic force will cause the number and diameter of inclusions to increase again.Electromagnetic stirring has different effects on the segregation of different elements.Under the experimental conditions,the weak electromagnetic force with 1.1 kA and magnetic induction intensity of 108 Gs has little effect on the segregation of C,but decreases the segregation of P,and the excessive electromagnetic force aggravates the segregation of alloy elements.

Rolling contact fatigue life of ion implanted GCr15

Presents an experimental research into the rooling contact fatigue life of GCr15 steel with Ti xN, Ti xN+Ag and Ti xN+DLC layers ion implanted using the plasma ion implantation technology on a ball rod style high speed contact fatigue tester, and concludes with test results that the fatigue life increases to varying degrees with Ti xN, Ti xN+Ag, and Ti xN+DLC layers implanted, and increases 1.8 times with Ti xN+Ag layer implanted, hairline cracks grow continuously into fatigue pits under the action of shear stress in the superficial layer of material, and ion implantation acts to prevent initiation of cracks and slow down propagation of cracks.

Effect of Prior Cold Deformation on the Stability of Retained Austenite in GCr15 Bearing Steel

In this work, the effect of prior cold deformation on the stability of retained austenite in GCr15 bearing steel was investigated after quenching and tempering treatment. The thermal stability was evaluated by calculating thermal activation energy for decomposition of retained austenite using differential scanning calorimeter. The mechanical stability was investigated according to the strain-induced martensitic transformation behavior of retained austenite under the standard compression testing. It is found that the prior cold deformation not only accelerates the carbide dissolution during the austenitization process but also contributes to the carbon partitioning in the tempering stage due to the higher density of phase boundaries, which results in the improvement of the thermal stability of retained austenite. Due to the enhanced carbide dissolution, the higher carbon content in the prior austenite will intensify the isotropic strain of martensitic transformation. As a consequence, the film-like retained austenite is likely to form under a higher hydrostatic pressure and thus shows a higher mechanical stability. Additionally, it is noteworthy that the benefits of the prior cold deformation to the stability of retained austenite would be saturated when the cold deformation degree is larger than 40%.

Hot Deformation Behavior of GCr15 Steel

Hot deformation behavior of GCr15（ASTM 52100） steel was investigated using single-hit compression tests on Gleeble-1500 simulator at the temperature range of 850-1 100 ℃ and strain rate range of 0.1-10 s-1.The flow stress constitutive equation of GCr15 steel during hot deformation was determined by stress-strain curves analysis on the basis of the hyperbolic sine equation.And the models of dynamic recrystallization fraction and dynamic recrystallization grain size of GCr15 steel were established by the measured curves and microstructure observation in different experimental conditions.The mean activation energy and the time exponent of dynamic recrystallization kinetics equation in the range of experimental conditions were determined to be 356.2 kJ/mol and 2.12,respectively.Meanwhile,the flow stress model was also established by the method of allocating flow stress curve with three main stress values,the saturation stress,the steady state stress and the stress when strain is 0.1.The flow stress curves predicted by the developed models under different deformation conditions are in good agreements with the measured ones.

Effect of Mg addition on TiN inclusions in GCr15 bearing steel

Compared with the original GCr15 bearing steel,TiN inclusions are greatly reduced by the effect of Mg addition,and many different types of non-metallic Mg-containing inclusions were observed in Mg-treated GCr15 bearing steel which includes MgO,MgS·MnS,MgO–MgS·MnS,MgAl_(2)O_(4)–MgS·MnS,MgO–TiN,MgS·MnS–TiN,and MgO–MgS·MnS–TiN.The inclusion size distribution based on automatic inclusion analysis software shows that the number of inclusion with the size ranging from 1 to 3μm increases obviously because a large amount of MgO,MgS·MnS,TiN inclusions containing Mg with smaller sizes are massively generated.In situ observation on the experimental steel by high-temperature confocal laser scanning microscopy confirms that MgO can provide nucleation sites for TiN.In addition,the MgS·MnS and MgO–MgS·MnS inclusions can also provide positions for the nucleation of TiN.Thermodynamic calculations indicate that after Mg addition to liquid steel,a large number of fine MgO inclusions are generated in the liquid steel because of the strong reactivity of Mg and O.At the same time,MgS precedes TiN precipitates in the solid–liquid two-phase region;thus,MgO and MgS·MnS can provide sites for TiN nucleation.At last,two possible formation pathways for the above various TiN inclusions containing Mg are discussed.

Effect of axial static magnetic field on cleanliness and microstructure in magnetically controlled electroslag remelted bearing steel

The effect of the axial static magnetic field(ASMF)on cleanliness and microstructure in magnetically controlled electroslag remelted GCr15 bearing steel ingots was investigated experimentally.The results show that a magnetically controlled spin-vibration induced by the interaction of the ASMFs and the remelting current exists at the consumable electrode tip,resulting in thinner liquid melt film and smaller droplets.With the increase in magnetic flux density,the optimization effect of ASMFs on electroslag remelting process increases and reaches the peak with a 40 mT ASMF,then decreases.The cleanliness of the ingots was improved,and the count of inclusions larger than 5μm was reduced.The microstructure of the ingots processed with a 40 mT ASMF was significantly refined.The depth of the metallic molten pool was reduced from 45.2 to 17.5 mm with the application of 40 mT ASMF.The tensile strength,impact toughness,and Rockwell hardness of the ingots obtained under the 40 mT ASMF were significantly improved.The mechanisms of the spin-vibration occurring at the electrode tip end were interpreted in detail to elucidate the effect of ASMFs.

Titanium nitride deposition by high-power density plasma at room temperature

Titanium nitride films are of many excellent properties, such as high hardness,high wear resistance, high corrosion resistance and beautiful golden color.It has wide application in industry. However, several present techniques, such as chemical vapor deposition, physical vapor deposition and ion beam, have their disadvantages which limit the range of using titanium nitride films. These shortcomings are high deposition temperature, weak adhesion of films to substrate and lower deposition rate.