Effect of silicon on the wear resistance of high-carbon steels with the structures of isothermal decomposition of austenite during friction and abrasive action

The hardness and wear resistance during sliding and abrasive friction of 80S2 (0.83% C, 1.66% Si) and U8 (0.83% C) steels subjected to the isothermal γ → α decomposition in the temperature range 330–650°C and additional 5-min annealing at 650°C are compared. The optimum decomposition temperature is found to be 550°C. At this temperature, fine lamellar pearlite with the maximum hardness and wear resistance as compared to other pearlitic and bainitic structures forms in the silicon steel. The silicon-alloyed fine lamellar pearlite of 80S2 steel is found to have high hardness and abrasive wear resistance as compared to the similar structure in plain U8 steel; however, this pearlite has no advantages in the wear resistance under conditions of sliding friction on a steel plate. Silicon alloying of the bainitic structures in the eutectoid steel leads to a noticeable decrease in the wear resistance during sliding friction and abrasive action. Friction oxidation is shown to negatively affect the abrasive wear resistance of the silicon steel.     

夹杂物对Cr-Ni系高强度钢耐蚀性能的影响

对比研究了2种Cr-Ni系高强度钢在人造海水条件下耐蚀性能差异,采用ASPEX自动扫描电镜分析了钢中夹杂物种类、数量和分布,利用金相显微镜对夹杂物引发腐蚀的过程开展了原位分析,并利用扫描电镜(SEM),观察了腐蚀后样品的微观形貌。全浸腐蚀实验结果表明,A钢虽然合金含量较高,但其腐蚀速率要大于B钢;夹杂物分析及其原位腐蚀实验研究表明,B钢通过Ca处理获得了良好的夹杂物改性效果,将钢中对耐蚀性提高不利的MnS夹杂物改性为CaS复合夹杂物,降低了B钢的点蚀敏感性,提高了B钢的耐蚀性能。     

Effect of heat treatment on mechanical and stirring wear properties of low temperature bainite steels

One- step and two- step isothermal low temperature bainitic transformation were designed. The effects of heat treatments on the microstructures, mechanical properties and stirring wear resistance of low temperature bainite were discussed. The results show that the microstructures of samples under different heat treatments all consist of micro- and nano- scale bainite lath and austenite. The size of bainite lath decreases from 95 nm to 65 nm with the decrease of isothermal temperature from 300?? to 250?? under the one- step isothermal bainitic transformation. Moreover, the volume fraction of austenite likewise decreases from 28??1% to 19??9%. The unstable block austenite is apparently refined by the two- step isothermal bainitic transformation. The optimal balance between the tensile strength (1857MPa) and elongation (10??59%) is obtained in the sample treated by two- step isothermal bainitic transformation. Also, the V- notch impact absorbed energy of the sample treated by two- step isothermal bainitic transformation reaches 11J. Compared with the one- step isothermal bainitic transformation (300, 250??), the sample treated by two- step isothermal bainitic transformation shows the optimized wear resistance and increases by 11??8% and 31??4%, respectively, which is attributed to the better ductility and toughness.     

Formation of the microgeometry of the wear surface of electrometallized coatings during sliding friction

The laws of wear are experimentally studied in the course of the sliding friction of gas-thermal coatings formed by spraying during electric-arc metallization using powdered wires. The microgeometry of the wear surfaces of these coatings is found to correctly reflect the stages of wear. A theoretical probabilistic approach is proposed to describe the microgeometries of the electrometallized coatings and the counterbody material under steady-state wear conditions. According to this approach, the structure of the wear surface is described by the root-mean-square and the arithmetical-mean deviations of the surface profile from a plane determined by the average linear wear.     

Effect of heat treatment on mechanical properties and structure of high-strength pipe steels with a ferrite-bainite structure*

The effect of heat treatment on mechanical properties and microstructure of high-strength low-alloy ferrite-bainite pipe steels is studied. Specimens are heated in a laboratory furnace up to a temperature in the range 100?C850°C. Dependences for the change in mechanical properties on heating temperature and the main features of steel structure are determined. TEM is used to study excess phase precipitation, including Nb and V carbonitrides, during heating. Unfavorable temperature ranges are determined for heating pipe steels with a ferrite-bainite structure. The results obtained may be used in industrial production and during development of new technology for thermomechanical treatment.     

热处理对钢结硬质合金TLMW50覆层抗磨性的影响

为了提高烧结态钢结硬质合金TLMW 50覆层材料的抗磨性能,进行1050℃和1100℃淬火、150℃～250℃回火热处理。利用SEM和TEM对热处理后的试样覆层组织演变进行分析。通过磨粒磨损试验测试覆层试样的抗磨损性。结果表明:热处理后钢结硬质合金TLMW 50覆层中粘结相组织发生明显转变,由片状珠光体组织转变为针状马氏体。1050℃淬火150℃回火工艺处理后的SBCTC试样的磨损量最少,较其他5种工艺对提高SBCTC抗磨性更优越。     

Cyclic creep and cyclic deformation of high-strength spring steels and the evaluation of the sag effect: Part I. Cyclic plastic deformation behavior

The cyclic creep and cyclic plastic deformation behavior of two commercial suspension spring steels of high hardness levels, namely, SAE 9259 and SAE 5160, were studied under different testing conditions of cyclic peak stress and cyclic stress ratio. The experimental results indicate that both the cyclic stress ratio and cyclic peak stress have strong, but complicated, effects on the cyclic creep and cyclic plastic deformation behavior of these materials. It has also been found that the addition of silicon can increase the resistance of these steels to cyclic creep and cyclic plastic deformation, although the extent of this increase is also related to other cyclic deformation conditions. A transition in the relationship between the total plastic strain range and the cyclic stress ratio (R) has been detected at approximately R=0.5. The mechanism of such a transition is explained by the operation of cross-slip during the unloading process of cycling. Moreover, a cyclic softening behavior of these spring steels in the quench-tempered condition was also detected and is attributed to the activation and reorganization of obstacle dislocations introduced into the steels during the process of martensitic transformation. More importantly, this study has indicated that parameters such as the cyclic creep strain, the cyclic creep rate in the secondary creep stage, and the total cyclic plastic strain range can better reflect, and should be used to depict and characterize, the sag behavior of spring steels as well as other materials. Finally, the effect of silicon on sag behavior, in comparison with the results from the Bauschinger-effect test, has also been discussed through the influence of Si on carbide formation and distribution.     

Effect of texture and microstructure on resistance to cracking of high-strength hot-rolled Nb-Ti microalloyed steels

Significant texture gradient in the through-thickness direction was observed in high-strength hot-rolled 560 and 770 MPa Nb-Ti microalloyed steels, characterized by polygonal ferrite and ferrite bainite microstructures, respectively. {113}〈110〉 was the most intense deformation texture in the two high-strength grades of Nb-Ti steels and was dominant in the midthickness region compared to 10 and 25 pct depth below the surface. The recrystallization texture of austenite, {100}〈001〉, transformed into {100}〈011〉 component in the ferrite and indicated an increase in the intensity with increase in depth for the Nb-Ti microalloyed steels. The {100}〈011〉 texture has a detrimental effect on the edge formabiity of steels. However, the midthickness plane contained considerable intensity of desired texture, {332}〈113〉, which is expected to offset the undesirable {100}〈011〉 texture resulting in superior edge formability and impact toughness of Nb-Ti steels, consistent with experimental observations.     

Precipitation reactions during the heat treatment of ferritic steels

The precipitation reactions in two ferritic steels, 9Cr-lMo-V-Nb and 12Cr-lMo-V-W, were studied. Analytical electron microscopy, optical microscopy, electrolytic extractions, and hardness measurements were used to determine the types, amounts, and effects of precipitates formed as a function of the heat treatment. The effect of variations in the austenitizing treatment was ascertained. In addition to variations in the austenitizing time and temperature, different cooling rates after austenitization were also used. Air cooling after austenitization (normalization) resulted in little precipitation in both alloys. Precipitation in the 12Cr-lMo-V-W alloy after furnace cooling was found in all cases examined. Under certain conditions precipitation was also found after furnace cooling the 9Cr-lMo-V-Nb alloy. However, when compared to the amount of precipitate in the fully tempered state, the 9Cr-lMo-V-Nb showed a much greater variation in the degree of precipitation following furnace cooling. In addition, the matrix microstructure of the 9Cr-lMo-V-Nb alloy was very sensitive to cooling rate. The precipitation reactions during tempering after a normalizing treatment were followed as a function of tempering treatment. Tempering temperatures were varied from 400 to 780 °C. The carbide precipitation was essentially complete after one hour at 650 °C for both alloys. Analytical microscopy was used to identify the precipitates. In the 9Cr-lMo-V-Nb alloy, a combination of chromium-rich M₂₃C₆ and vanadium-niobium-rich MC carbides was found. The carbides in the 12Cr-lMo-V-W alloy were identified as chromium-rich M₂₃C₆ and vanadium-rich MC. The results give an indication of the sensitivity of these alloys to heat treatment variations. This paper is based on a presentation made at the “pcter G. Winchell Symposium on Tempering of Steel” held at the Louisville Meeting of The Metallurgical Society of AIME, October 12-13, 1981, under the sponsorship of the TMS-AIME Ferrous Metallurgy and Heat Treatment Committees.     

Mechanical properties of a nitrogen-bearing austenitic steel during static and cycle deformation

The mechanical properties of a nitrogen-bearing corrosion-resistant austenitic steel containing 0.311% nitrogen have been studied during static and cyclic deformation. It is found that the steel having an ultimate strength of 930 MPa exhibits a plasticity of 33%. The endurance limit under repeated tension at 10⁶ loading cycles is 400 MPa. The propagation of a fatigue crack at low and high amplitudes of cyclic deformation follows a ductile fracture mechanism with the presence of fatigue grooves.     

钛含量对铜基粉末冶金摩擦材料摩擦磨损性能的影响

采用粉末冶金方法制备铜基摩擦材料,研究钛的添加量对材料的摩擦磨损性能的影响。结果表明:随着钛质量分数由3%增加到12%,铜基摩擦材料的相对密度提高,硬度增加。钛的添加导致晶格畸变,材料硬度提高。随着摩擦速度增加,材料的摩擦因数减小。钛添加到铜基摩擦材料中,降低了铜基摩擦材料的摩擦因数和磨损量,原因在于钛提高了材料的硬度,增加了表面微凸体强度,减少了犁削程度,从而降低了摩擦面的损伤程度,提高了材料的耐磨性。     

Microstructural changes during wear by plastic deformation of cemented carbide and cermet cutting inserts

The microstructure of one WC-Co and two Ti(C,N)-WC-Co cutting inserts has been studied before and after plastic deformation, caused by high-speed turning. It was found that after deformation, the binder phase had infiltrated some of the grain boundaries and formed lamellae between the hard phase grains. The infiltration of grain boundaries was assumed to occur by a stress-induced dissolution along the grain boundaries of the hard phase grains as a wide front of binder phase, rather than gradually by Co grain boundary diffusion. Some localized dissolution of the hard phase could also be seen as faceting of grains in WC-Co and at triple points in cermets. It was concluded that the plastic deformation occurs by grain boundary infiltration with simultaneous grain boundary sliding. The rate of deformation is controlled by grain boundary infiltration through dissolution of the hard phase grains.     

Ferritic-bainitic structure and ductile fracture resistance of high-strength pipe steels

The formation of the products of bainitic transformation in pipe steels of strength classes K60 (X70) and K65 (X80) during thermomechanical treatment is considered. It is shown that the structural factors that affect the ductile-fracture resistance of steel are the bainite morphology and the carbon distribution over structural constituents.     

Numerical simulation of three-dimensional heat transfer and plastic flow during friction stir welding

Three-dimensional visco-plastic flow of metals and the temperature fields in friction stir welding have been modeled based on the previous work on thermomechanical processing of metals. The equations of conservation of mass, momentum, and energy were solved in three dimensions using spatially variable thermophysical properties and non-Newtonian viscosity. The framework for the numerical solution of fluid flow and heat transfer was adapted from decades of previous work in fusion welding. Non-Newtonian viscosity for the metal flow was calculated considering strain rate, temperature, and temperature-dependent material properties. The computed profiles of strain rate and viscosity were examined in light of the existing literature on thermomechanical processing. The heat and mass flow during welding was found to be strongly three-dimensional. Significant asymmetry of heat and mass flow, which increased with welding speed and rotational speed, was observed. Convective transport of heat was an important mechanism of heat transfer near the tool surface. The numerically simulated temperature fields, cooling rates, and the geometry of the thermomechanically affected zone agreed well with independently determined experimental values.     

Effect of prestrain on stretch-zone formation during ductile fracture of Cu-strengthened high-strength low-alloy steels

The effects of prestrain on the ductile fracture behavior of two varieties of Cu-strengthened high-strength low-alloy (HSLA) steels have been investigated through stretch-zone geometry measurements. It is noted that the ductile fracture-initiation toughness of both the steels remained unaltered up to prestrains of ∼2 pct, beyond which the toughness decreased sharply. A methodology for estimating the stretch-zone dimensions is proposed. Fracture-toughness estimations through stretch-zone width (SZW) and stretch-zone depth (SZD) measurements revealed that the nature of the variation of ductile fracture toughness with prestrain can be better predicted through SZD rather than the SZW measurements. However, for the specimen geometries and prestrain levels that were investigated, none of these methods were found suitable for quantifying the initiation fracture toughness.     

差温热处理工艺对Cr5钢摩擦磨损性能的影响

 运用扫描电镜观察Cr5钢在不同淬火温度下的显微组织,通过洛氏硬度计和摩擦磨损试验机分析淬火温度对Cr5钢摩擦磨损性能的影响。结果表明：Cr5钢淬火后的基体组织是马氏体,基体上会分布有未溶碳化物。随着淬火温度提升,未溶碳化物逐渐减少,淬火组织逐渐均匀化,但淬火温度达到一定值(1 050～990 ℃)时,碳化物基本溶解完全,组织较均匀,硬度值最大,为54.7HRC,磨损失重量最小,磨损表面相对较平整,耐磨性相对较好;继续升高淬火温度,马氏体组织粗大化,使得硬度有所降低,耐磨性下降。     

Effects of austenitisation heat treatment on the fracture resistance and temper embrittlement of MnMoNi steels

The resistance to ductile and brittle fracture of four experimental melts of MnMoNi steel containing varying levels of sulphur, copper and phosphorus has been examined as a function of austenitisation heat treatment, with and without subsequent ageing at 500°C following tempering at 650°C. Fracture resistance was assessed by Charpy impact tests, fracture modes were studied using the scanning electron microscope, grain boundary segregation was quantified from Auger spectroscopy, and boron distribution determined by boron autoradiography. The results indicate that austenitisation heat treatment strongly influences the ductile-brittle transition temperature (DBTT) and upper shelf fracture energy (USE) in the quenched and tempered condition. The subsequent susceptibility to temper embrittlement is also markedly affected, high austenitisation temperatures being detrimental in all respects. Phosphorus segregation has been shown to occur during air cooling from tempering and during isothermal ageing, the degree of segregation increasing with austenitisation temperature, resulting in an increase in DBTT and a reduction in USE. Changes in DBTT and USE on isothermal ageing have been attributed to phosphorus segregation in all four composition melts. Microstructures susceptible to embrittlement have also shown enhanced levels of boron or boron-containing particles at prior austenite grain boundaries.