新型耐磨球墨铸铁的研究

通过系统地研究以合金元素锰、辅加微量合金元素,取代贵重金属镍、钼、铜,采用不同于等温淬火的冷却方式,获得以针状组织（贝氏体＋马氏体）为主,有一定量奥氏体的新型耐磨球铁。冲击韧度可达9.8J/cm{sup}2以上,硬度可达55HRC。在磨球生产上应用结果表明,耐磨性比中锰球铁磨球提高一倍,冲击疲劳性能比中锰磨球提高7倍,而生产成本与之相当。     

超高强度钢40CrNi2Si2MoVA贝氏体等温淬火工艺

对超高强度钢40CrNi2Si2MoVA进行贝氏体区短时间等温淬火,得到马氏体加下贝氏体和少量残余奥氏体的复合组织,考察了等温时间的变化对材料显微组织和力学性能的影响,并进一步得出了此条件下该钢的最佳热处理工艺.结果表明:当等温时间在100～150 s时,得到以马氏体为主,含20%左右下贝氏体和少量稳定残余奥氏体的组织.     

贝氏体钢的强韧化途径

发现在粒状贝氏体组织中,控制其小岛尺寸、数量和分布,可获良好强性,研制出粒状贝氏体钢。首次用粥的仿晶界型铁素作韧性与粒贝结合,可获优良强韧性,并研制出此类复相钢。通过合金设计,在空冷条件下获得具有超精细结构的无碳化物贝氏体／马氏体复相组织,贝氏体各层次单元由奥氏体膜包围,使贝氏体／马氏体复相组织具有优良的强韧性,并研制出此类高强高韧钢。     

形变和冷却对B1500HS硼钢马氏体相变的影响

利用Gleeble-1500D热模拟试验机,以恒定的应变速率将在900℃奥氏体化的B1500HS硼钢试样分别压缩10%、20%、30%、40%,然后分别以50℃/s、40℃/s、25℃/s的速度对试样进行冷却。研究形变量及冷却速度对B1500HS硼钢的马氏体相变温度、微观组织、显微硬度和残余奥氏体等方面的影响规律。结果表明:相同冷却速度下,马氏体相变开始温度和相变终止温度均随着形变量的增加逐渐升高。随着形变量的增加,马氏体组织越来越细小,而且薄片状马氏体越来越少,板条状马氏体越来越多。形变量和冷却速度的增大,均使B1500HS试样中的残余奥氏体量减小。形变导致B1500HS硼钢的连续冷却转变图左移,避免未变形B1500HS钢试样生成贝氏体组织的临界冷却速度约为25℃/s。当冷却速度为25℃/s时,试样的变形程度达到30%时,微观组织中开始出现贝氏体。     

铸态含无碳化物贝氏体中锰钢

中锰钢（含1.0%～1.8%C,5.0%～9.0%Mn,0.6%～1.5%Si）在铸态下即可得到无碳化物贝氏体相。在冷却的过程中,当冷却速度大于40℃/min时,室温组织为奥氏体与碳化物;当冷却速度小于20℃/min时,室温组织为无碳化物贝氏体、珠光体、奥氏体与碳化物。无碳化物贝氏体主要是在624～200℃之间形成。在砂型中浇注壁厚大于15mm的铸件时,即可行到大量无碳化物贝氏体,该铸钢具有较佳的硬度,韧度与耐磨性。     

冷却速率对直接淬火钢组织和性能的影响

对含微量硼的钢与无硼钢在不同冷速下直接淬火试样的组织进行了观察,分别测定了含硼钢与无硼钢的连续冷却转变(CCT)曲线,以及轧制后不同温度回火试样的拉伸强度.结果表明:硼的添加会使贝氏体转变Bs点降低,生成粗大的针状或板条状贝氏体组织,这种贝氏体组织越多,它的强度就越低;无硼钢在慢冷情况下(15℃/s),Bs点较高,易于形成粒状贝氏体组织,该组织与马氏体形成的混合组织使强度较高.为避免粗大贝氏体区,对于含硼钢,适宜采用快速冷却;而对于无硼钢,应尽量降低冷却速率.     

The wear behaviour of high-chromium white cast irons as a function of silicon and Mischmetal content

The sliding wear behaviour of high-chromium white cast iron (16.8% Cr) has been examined as a function of silicon and Mischmetal alloy additions (1, 2, 3 and 5% Si and 0.1 and 0.3% Mischmetal). Such additions are known to modify the structure, but there is considerable controversy as to the exact effect. Silicon was found to refine the dendritic structure and increased the eutectic carbide volume fraction. However, for contents above 3%, transformation of the austenitic matrix to pearlite occurred in preference to martensite. Mischmetal additions reduced the austenite dendrite arm spacing, but did not have a significant effect on the carbide structure. The wear behaviour was investigated for each alloy in the as-cast (austenitic matrix) and hardened (martensitic) conditions using a block on ring configuration in pure sliding in the load range 42–238 N for a distance of 70 km against a hardened M2 steel counterface. For low loads (42 and 91 N), all the alloys showed a similar wear rate (3×10⁻⁴ to 4×10⁻⁴ mm³/m), associated with the formation of a thin (3 μm) oxide film of Fe₂O₃, the formation of very fine debris and a small depth of deformation below the worn surface (7 μm). For higher loads, wear was a strong function of microstructure, and was associated with a thicker film of the oxides Fe₂O₃ and Fe₃O₄ and greater depths of deformation. The iron with 2% silicon exhibited the best performance with a wear rate of 7×10⁻⁴ mm³/m and this was attributed to its finer structure and the formation of a thicker oxide film. In contrast, the iron with 5% silicon exhibited the worst performance, with a wear rate of 14×10⁻⁴ mm³/m, attributed to the pearlitic matrix. A linear relationship was observed between the depth of carbide fracture and the wear rate. The relationship between microstructure and wear mechanism is discussed.     

LNG用9Ni钢控轧控冷工艺的热模拟研究

采用Gleeble 3800热模拟实验机测定了9N i钢的CCT曲线,进行不同终轧温度变形试验,分析了不同冷却速度对组织的影响,研究了不同终轧温度与组织、晶粒度、性能的关系。结果表明：轧后冷却速度大于5℃/s为马氏体组织,小于3℃/s为贝氏体组织,9N i钢的终轧温度选择800~850℃,晶粒细小,综合力学性能良好。     

退火及回火处理对含Ni塑料模具钢性能的影响

通过研究2种不同成分的预硬型塑料模具钢锻后砂冷、退火及回火等状态下组织及力学性能并进行分析,发现退火组织由粒状贝氏体+下贝氏体+马氏体组成,降低粒状贝氏体量有利于提高材料的韧性和延伸率。残余奥氏体含量较低,对提高韧性作用不大。回火后残余奥氏体几乎全部分解,软相减少,屈服强度提高。Ni的增加降低了马氏体硬度,提高了贝氏体和退火后回火组织硬度。残余奥氏体对硬度的影响不大。     

中锰汽车钢焊接热影响区组织与韧性

热模拟第三代中锰汽车钢热影响粗晶区的焊接热循环,并利用扫描电镜、透射电镜、显微硬度、冲击和电子背散射衍射（Electron back scatter diffraction,EBSD）试验方法研究了焊接热循环对粗晶区显微组织、硬度和冲击韧性的影响。结果表明：中锰钢热影响粗晶区经过焊接热循环后主要为马氏体组织,当冷却速度较快时,马氏体板条间分布着大量的位错团;随着冷速的减缓,组织中有少量的贝氏体生成,且组织逐渐粗化;粗晶区的硬度随着焊后冷速的减缓呈降低的趋势,在t_8/3>33s后硬度下降缓慢;粗晶区组织中有少量的M-A组元,对冲击韧性影响不大;中锰钢粗晶区中的大角度晶界（>15°）即原奥氏体晶界、马氏体板条束界和板条块界均对裂纹有阻碍作用;大角度晶界密度可作为衡量中锰钢粗晶区的韧性指标,其与冲击韧性成正比,均随着冷速的减缓先增加再逐渐降低,在冷却速度t_8/3为8s时,大角度晶界密度最大,获得的冲击韧性相对较好。     

激光冲击处理对曲轴磨损性能的影响

利用激光冲击波对曲轴球墨铸铁进行表面强化处理,利用摩擦磨损试验机研究激光冲击处理球墨铸铁QT700的磨损性能,利用金相显微镜分析激光冲击处理后其表面微结构,同时采用XRD分析激光冲击处理后球墨铸铁表面马氏体与残余奥氏体的含量。结果表明,激光冲击处理后球墨铸铁具有理想的表面形貌和较高的表面硬度,其抗磨性能大幅度提高,有利于提高其疲劳寿命。     

Solidification and abrasion wear of white cast irons alloyed with 20% carbide forming elements

Three different white cast irons with compositions of Fe–3%C–10%Cr–5%Mo–5%W (alloy no. 1), Fe–3%C–10%V–5%Mo–5%W (alloy no. 2) and Fe–3.5%C–17%Cr–3%V (alloy no. 3) were prepared in order to study their solidification and abrasion wear behaviors. Melts were super-heated to 1873 K in a high frequency induction furnace, and poured at 1823 K into Y-block pepset molds. The solidification sequence of these alloys was investigated. The solidification structures of the specimens were found to consist of austenite dendrite (γ); (γ+M₇C₃) eutectic and (γ+M₆C) eutectic in the alloy no. 1; proeutectic MC; austenite dendrite (γ); (γ+MC) eutectic and (γ+M₂C) eutectic in the alloy no. 2, and proeutectic M₇C₃ and (γ+M₇C₃) eutectic in the alloy no. 3, respectively.

A scratching type abrasion test was carried out in the states of as-cast (AS), homogenized (AH), air-hardened (AHF) and tempered (AHFT) using the abrasive paper with 120 mesh SiC and 10 N application load. In all the specimens, the abrasion wear loss was found to decrease in the order of AH, AS, AHFT and AHF states. Abrasion wear loss was lowest in the specimen no. 2 and highest in the specimen no. 1 except for the as-cast and homogenized states in which the specimen no. 3 showed the highest abrasion wear loss. The lowest abrasion wear loss of the specimen no. 2 could be attributed to the fact that it contained proeutectic MC carbide, eutectic MC and M₂C carbides having extremely high hardness. The matrix of each specimen was fully pearlitic in the as-cast state but it was transformed by heat-treatments to martensite, tempered martensite and austenite. From these results, it becomes clear that MC carbide is a significant phase to improve the abrasion wear resistance of white cast iron.     

优化组织球铁的力学性能及其微观断裂行为

根据球铁断裂过程中石墨及石墨-基体界面的微观力学行为,对球铁组织进行优化设计.以强相(马氏体)或强韧相(奥氏体-贝氏体组织)环包围石墨,基体组织为马氏体或奥氏体-贝氏体组织,加上适量的铁素体,并通过快速加热短时保温后淬火或等温淬火获得.实验结果表明,优化组织球铁具有很高的强韧性.采用扫描电镜动态拉伸观察优化组织球铁断裂过程,发现微裂纹在石墨-基体界面萌生并沿界面扩展,马氏体环或奥-贝环阻碍界面裂纹的萌生与扩展,基体中的硬相和软相分别提高球铁的强度和韧性,这些都有利于提高优化组织球铁的强韧性.     

控轧控冷工艺中冷却温度对Q550D高强钢显微组织和拉伸性能的影响

对热轧Q550D钢板进行控轧控冷处理,研究了6组开始冷却(开冷)温度和终冷温度对试验钢显微组织和拉伸性能的影响。结果表明:6组冷却温度下试验钢的基体组织均由贝氏体+铁素体+马氏体/奥氏体(M/A)岛组成;在相同终冷温度下降低开冷温度,试验钢中铁素体含量明显增加,M/A岛含量略微增加,屈强比减小;在相同开冷温度下降低终冷温度,铁素体含量略有减少而M/A岛含量明显增加,屈强比增大;同时降低开冷温度和终冷温度,铁素体和M/A岛含量同步递增,但M/A岛的增加幅度较小,屈强比降低;在开冷温度755℃、终冷温度395℃下,试验钢具有最佳的拉伸性能。     

The effect of additional silicon on the corrosion and erosion-corrosion of low chromium steels

The addition of 1wt.%Si to commercial steel containing 2.5wt.%Cr significantly lowered its erosion-corrosion metal wastage rate at 650 °C. The improved erosion resistance was largely a result of a modified corrosion behavior. Static oxidation studies showed that the normal silicon content 2.5Cr steel developed a duplex, spalling prone, iron-rich scale at 650 °C. However, with the addition of silicon, the scale was almost 50 times thinner, and was chromium-rich instead. Metal wastage was significantly reduced for static and dynamic corrosion as well as for erosion-corrosion. The thin scale that formed on the additional silicon steels cracked and chipped off at a low metal loss rate compared with the thick scale that formed on the normal silicon steels that spalled off at a higher metal loss rate.     

Quantitative analysis of martensite and bainite microstructures using electron backscatter diffraction

In the present work, ultra‐high‐strength steels with multiphase microstructures containing martensite and bainite were prepared by controlling the cooling rate. A new approach was proposed for quantitatively statistical phase analysis using electron backscatter diffraction (EBSD) based on the band contrast which correlates to the quality and intensity of the diffraction patterns. This approach takes advantage of the inherently greater lattice imperfections of martensite, such as dislocations and low‐angle grain boundaries, relative to that of bainite. These can reduce the intensity and quality of the EBSD patterns of martensite, which decrease the band contrast. Thus, combined with morphological observations, Gaussian two‐peak fitting was employed to analyze the band contrast profile and confirm the ranges of band contrast for the two phases. The volume fractions of bainite and martensite in different samples were determined successfully. In addition, the results show that increased cooling rates improve the proportion of martensite and the ratio of martensite to bainite. Microsc. Res. Tech. 79:814–819, 2016. © 2016 Wiley Periodicals, Inc.     

热输入对1 000 MPa级工程机械用钢接头组织性能的影响

采用三种热输入进行1 000 MPa级控轧控冷(Thermo mechanical control process, TMCP)高强钢的熔化极气体保护焊,利用金相显微镜、扫描电子显微镜和透射电子显微镜研究热输入对焊接接头组织和力学性能的影响。研究结果表明,三种热输入焊缝金属组织主要由板条马氏体和板条贝氏体为主、并含有少量残余奥氏体和粒状贝氏体;焊接热影响区粗晶区组织以板条马氏体和贝氏体为主,并含有少量粒状贝氏体。随着热输入的增加,焊缝组织中贝氏体板条粗化,马氏体板条减少,而粒状贝氏体逐渐增多,部分膜状残余奥氏体向块状转变;焊缝金属冲击韧度和硬度、接头强度逐渐降低,而接头热影响区冲击韧度先增后降;当热输入为15 kJ/cm时焊接接头强韧性匹配最佳。     

A study on erosion of upper bainitic ADI and PDI

Ductile iron containing ∼3.5 wt.% C and 2.1–4.2 wt.% Si (2.1, 2.8 and 4.2 wt.%) was studied. Three sets of specimens with differing Si contents were made into austempered ductile iron (ADI) and pearlite ductile iron (PDI) through heat treatment. These specimens were then eroded with Al₂O₃ particles and SiO₂ particles of 275–295 μm grit size to understand the relationship between erosion rate and microstructure. The ADI specimens were upper bainitic matrices that were austempered for different periods of time at 420 °C. The heat treatment of PDI was conducted at 870 or 930 °C for 1 h then forced air cooled or oil quenched to room temperature.Two types of wear curves, single peak curves and double peak curves, were found when plotting the erosion rate figures derived from the experimental results. 2.1 wt.% Si and 2.8 wt.% Si ADI tempered for a long period of time, due to their decreased retained austenite content and increased carbide content, had a single peak erosion rate curve. This embrittlement effect caused the impact angle of maximum erosion rate to increase from ∼30 to ∼45°. Decreasing the interspacing of the lamellae cementite promoted the hardness and improved the low-angle erosion wear resistance of PDI. The high hardness and brittleness of the matrix reduces the high-angle erosion resistance and the peak erosion rate occurs at a higher angle.For 2.1Si-ADI and 2.8Si-ADI tempered for a short duration, increasing the volume fraction of martensite in the matrix increases the erosion rate at an impact angle of 30°, but the maximum erosion rate is found at 75°. This results in a curve with a double peak. The double peak curve was also observed for high silicon ADI tempered for a long duration. The high solid solution hardness of 4.2Si-ADI, due to low retained austenite content and the presence of carbide in the matrix, results in poor erosion resistance. When this material is austempered for a long period, the erosion rate curve shifts from a single peak curve (30°) to a double peak curve (30°; 60°).     

Erosion behavior of high silicon bainitic structures: II: High silicon steels

The erosion behavior of two austempered high silicon (2.5 wt.% Si) steels, one containing 1 wt.% Mn and the other 1 wt.% Ni, has been compared with the mechanical property variations after austempering for various times in the upper bainite temperature range (420 °C). For both steels the erosion resistance is a maximum for austempering times near the end of stage II. The erosion resistance correlates directly with the tensile toughness and with the percentage elongation divided by the percentage reduction in area and inversely with the hardness in all three stages of austempering. It is shown that the strain-hardening coefficient peaks at the minimum erosion rate and that the high strain-hardening character of the retained austenite in these austempered steels is beneficial to erosion resistance. Comparison with the austempered cast irons in Part I of this study shows that the graphite nodules of the cast irons have no significant effect upon erosion rate.     

Friction and wear properties of Ni–Cr–W–Al–Ti–MoS2 at elevated temperatures and self-consumption phenomena

The composites of Ni–Cr–W–Al–Ti–MoS₂ with different adding amount of molybdenum disulfide (6–20 wt.%) were prepared by powder metallurgy (P/M) method. Their mechanical properties and tribological properties from room temperature to 600 °C were tested by a pin-on-disk tribometer. The effects of amounts of molybdenum disulfide, temperature, load, and speed on the friction and wear properties of composite were discussed. Besides, the tribological properties against different counterface materials, such as alumina, silicon nitride and nickel-iron-sulfide alloys were also investigated. Results indicated that the molybdenum disulfide was decomposed during the hot-press process and the eutectic sulfides of chromium were formed. The hardness and anti-bending strength can be improved by adding 6 wt.% molybdenum disulfide due to reinforcement of molybdenum. The friction coefficients and wear rates of composites decrease with the increase of adding amount of molybdenum disulfide until a critical value of 12 wt.%. The composite with 12% MoS₂ shows the optimum friction and wear properties over the temperature range of RT 600 °C. The friction coefficients of composite with 12% MoS₂ decrease with the increase of temperature, load, and sliding speed, while the wear rates increase with the increasing temperature and are insensitive to the sliding speed and load. The friction coefficients of less than 0.20 at 600 °C and mean wear rates of 10⁻⁵ mm³/N m are obtained when rubbing against alumina due to the lubrication of sulfide films and glaze layer formed on the friction surface at high temperature, while a relatively low wear rate of around 10⁻⁶ mm³/N m presents when rubbing against nickel-iron-sulfide alloys. At high temperature, wear rates of composite containing sulfide are inversely proportional to friction coefficients approximately.