稀土微合金化对5CrNiMo钢组织和性能的影响

以稀土为微合金化元素，在实际生产条件下用常规冶炼工艺，将稀土合金以瞬时密流工艺添加到5CrNiMo钢中，采用金相显微镜、扫描电镜等对5CrNiMo钢微观组织进行了系统研究，并进行了常规力学性能和成分检测。各项试验结果表明：加入微量的稀土元素后，5CrNiMo钢中硫含量降至0．009％和0．005％的高纯度钢数量级。退火组织、淬火组织和淬火后回火组织均显著细化，在硬度、强度相当的情况下，5CrNiMo钢的冲击功与不添加稀土元素的同炉次钢相比，分别提高14J和19J，增幅达5l％和68％。在试样表面达到相同龟裂程度时，试样所需的冷热循环周次比不加稀土的试样分别提高了35％和69％。     

碳化物对H13钢退火软化的影响

利用扫描电镜、物理化学相分析和Ｘ射线衍射方法，测定了不同退火经工艺下Ｈ１３钢中基体的合金元素含量和碳化物类型、尺寸、分布、对对量以及退火硬度。明确了Ｈ１３钢退火后硬度的高低与碳化物粒子的大小、相对量及碳化物的类型的依赖关系。     

C-Curves of Tool Steels for Annealing and Their Application

C curvesoftoolsteelsareusuallyusedforquenching .Theaustenitizingtemperaturemeasuredishigherthanthatofsoften annealingwhichisslightlyaboveAc1,andtheformerissuitedforquenching[1,2 ] .Thekineticcurvesoftoolsteelsarenotusedastheparametersofsoften annealing .TTTdiagrams ,CCTdiagramsandcritical pointsofAmericantoolsteelsH13,S7,S5 ,D2andA6forannealingweremeasuredandinvestigatedbymeansoffull automaticdilatometerinordertomakean nealingtechnologyscientificandobtaineffectivesoftening .Anewsoften ann…     

Carbide Evolution in High Molybdenum Nb-microalloyed H13 Steel during Annealing Process

Based on the Thermo-Calc thermodynamic software,the type of equilibrium precipitated carbides and their contents in high Mo Nb-microalloyed H13steel(NMH13steel)were calculated.The composition,morphology,and distribution of carbides after spheroidal annealing of two forged experimental steels were comparatively examined by means of optical microscopy(OM),scanning electron microscopy(SEM),electron dispersive spectroscopy(EDS)and transmission electron microscopy(TEM).VC,M23C6 and M6C are identified in H13 steel after spheroidizing annealing,while(V,Nb)C,M23C6,M2C and M6C are observed in NMH13 steel.Moreover,it is found that the addition of Nb significantly enhances the stability of MC phase and the high Mo content accelerates the precipitation of small rod-shape M2C phase in NMH13 steel.The amount of the fine carbides in NMH13 steel obviously increased with M2C and M6C precipitated from the ferrite phase,which is in accordance with the results of thermodynamic calculations.     

18CrNiMo7-6齿轮钢带状组织控制及其对力学性能的影响

采用金相显微镜研究了正火冷却工艺对18CrNiMo7-6齿轮钢带状组织的影响.采用显微硬度计、SEM、拉伸试验机、冲击试验机以及金相显微镜研究了不同程度带状组织对淬回火后试验钢显微硬度的均匀性、成分偏析程度和力学性能的影响.试验结果表明：在930℃奥氏体化保温后,采用强风冷却方式快速冷却到610℃,再炉冷到400℃,最后空冷至室温,可以将带状组织降低到1.5级.但若采用连续快速冷却的方式,则会导致大量贝氏体组织的生成;不同带状组织试验钢经850℃淬火、180℃回火热处理后,显微硬度极差值在30~35 HB 之间,硬度分布均匀性及力学性能各向异性程度相当.     

两种高等级管线钢的奥氏体热变形行为

利用MMS300热模拟试验机在温度为850~1 150℃,应变速率为5 s-1,道次间隔时间为1~400 s的条件下进行了X80及X100管线钢双道次压缩变形试验,测定了不同间隔时间、不同变形温度条件下的软化率。研究结果表明：当道次间隔时间相同时,随变形温度升高,X80及X100管线钢静态再结晶分数均增加,再结晶进程加...     

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Effect of normalized cooling treatment on banded structure of gear steel 18CrNiMo7-6 was analyzed through metallographic microscope. Effects of banded structures with different degree on micro hardness uniformity, composition segregation, mechanical properties of test steels after quenching and tempering were analyzed through microhardness tester, scanning electron microscope, tensile testing machine, impact testing machine and metallographic microscope. The results show that, banded structure can be reduced to 1.5 degree after austenizing heat preservation at 930??, Strong wind cooling to 610??, furnace cooling to 400?? and then air cooling. But continuous rapid cooling can result in the formation of a large amount of bainite; Micro hardness range of test steels with different banded structure degree is between 30~35 HB after quenching at 850?? and tempering at 180??. Hardness uniformity and anisotropy of mechanical properties are comparable.     

Microstructure and Properties of Hot Working Die Steel H13MOD

Compared with H13 steel, the influences of different heat treatment process on the microstructure and properties of the new type of hot working die steel H13MOD were studied. The results show that the complete austenitizing temperature of H13MOD is around 1030 °C and the quenching hardness achieves the maximum value at this temperature. While for H13, the complete austenitizing temperature is above 1100 °C and the quenching hardness rise constantly with the quenching temperature increasing. In quenching process, the undissolved MC carbides can prevent the coarsening of grain in both steels. With the rise of quenching temperature, when MC carbides dissolve completely, the grain grows quickly. The hardness and strength of H13MOD at higher tempering temperature (above 570 °C) are nearly the same as those of H13, but its toughness is higher than that of H13. Mo₂ C carbide is the main strengthening phase in H13MOD, which is attributed to the higher content of Mo. The quantity of VC eutectic carbides is reduced because of lower content of V in H13MOD, which plays an important role in enhancing the impact toughness of H13MOD. Under a certain strength condition, H13MOD steel can be used in the environment that higher toughness is required and the service life of die casting mold can be improved.     

Effect of non-metallic inclusions on fracture toughness of tool steels

The aim of these investigations was first of all to evaluate the fracture toughness (K_lc) changes of the hot-work tool steels depending on the non-metallic inclusions (NMI) volume fraction (melting technology). The tests were carried out on two types of the hot-work tool steels, i. e. H13 and H11 according to AISI. As a result of these investigations, supplemented by the detailed fractographic analysis, it has been revealed that uniform arrangement of NMI in the structure can be considered as harmless for the fracture toughness of tool steels. At high steel hardness values, the NMI, because of their action with a very small plastic strain zone, can be treated as natural obstacles in the crack propagation. At low hardness values of tool steels, achieved as a result of tempering at high temperatures, the role of NMI in the process of crack formation of these steels is limited by carbides precipitated from martensite. The micro-voids are formed round these carbides, which, connecting earlier than the voids formed round NMI, set the path of cracking and determine the steel fracture toughness.     

The postweld heat-treatment response of simulated coarse-grained heat-affected zones in a new ferritic steel

The tempering behavior of simulated coarse-grained (CG) heat-affected zones (HAZs) in two ferritic alloy steels, 2.25Cr-1Mo and HCM2S, was investigated. The hardness of HCM2S was found to be stable at longer times and higher temperatures than the 2.25Cr-1Mo steel, even though the “as-welded” hardnesses were approximately equal. Both materials reached a peak secondary hardness after tempering for 5 hours at 575 °C. The increase in hardness of the 2.25Cr-1Mo steel was due to precipitation of Fe-rich M₃C carbides within the prior-austenite grains, whereas the secondary hardening in HCM2S was due to a fine dispersion of intragranular, W-rich carbides. The HCM2S steel retained its hardness at longer times and higher temperatures than 2.25Cr-1Mo steel, because of the precipitation of intragranular, W-rich carbides and V-rich MC carbides that stabilized the lath structure. This study shows that HCM2S should not be heat treated in the same way as 2.25Cr-1Mo steel and also provides a basis for defining the postweld heat treatment (PWHT) of HCM2S.     

退火温度对S700MC强化效果的影响

采用退火试验,结合光学显微镜、扫描电镜、透射电镜和显微硬度计等设备,研究了不同退火温度对S700MC强化效果的影响。结果表明,退火处理能够显著影响碳化物形貌及变形区补充析出的细小铌和钛复合相的尺寸及分布。随着退火温度升高,碳化物及变形区补充析出的铌和钛复合相细化,弥散度提高,试样厚度方向上各检测位置的维氏硬度增大,强化效果显著;当退火温度升高至570 ℃时,碳化物及变形区补充析出的铌和钛复合相粗化,强化效果下降;而当退火温度为510 ℃ 时强化效果最佳。     

退火温度对S700MC强化效果的影响

采用退火试验,结合光学显微镜、扫描电镜、透射电镜和显微硬度计等设备,研究了不同退火温度对S700MC强化效果的影响。结果表明,退火处理能够显著影响碳化物形貌及变形区补充析出的细小铌和钛复合相的尺寸及分布。随着退火温度升高,碳化物及变形区补充析出的铌和钛复合相细化,弥散度提高,试样厚度方向上各检测位置的维氏硬度增大,强化效果显著;当退火温度升高至570 ℃时,碳化物及变形区补充析出的铌和钛复合相粗化,强化效果下降;而当退火温度为510 ℃ 时强化效果最佳。     

20CrNiMo钢球化退火工艺研究

采用亚温球化退火、普通球化退火、等温球化退火对20CrNiMo钢进行热处理工艺试验,利用光学显微镜和布氏硬度计分别对球化后的显微组织进行观察和硬度检测。结果表明,20CrNiMo钢经过普通球化退火、等温球化退火、硬度值≤160HBW,且经过710℃亚温球化退火,随着时间的延长,球化率有所上升,当球化退火时间达25 h以上时,亚温球化退火能获得65%以上的珠光体球化率;采用750℃保温6 h后再以10℃/h的冷却速度缓慢冷却的普通球化退火工艺,能获得83%以上的珠光体球化率;采用750℃保温6 h,经30 min炉冷到650℃保温6 h的等温球化退火,能获得硬度值为145HBW和93%的球化率。     

X45NiCrMo4钢材的软化退火

试验研究了模具钢X45NiCrMo4(0.45C-1.3Cr-4Ni-0.25Mo）的退火工艺参数对硬度的影响,试验结果表明：最佳软化加热温度为860℃,等温温度为640℃。     

正火冷却速度对18CrNiMo7-6齿轮钢组织和硬度的影响

18CrNiM07-6钢(/%:0.17C、0.59Mn、0.24Si、1.56Ni、1.71Cr、0.28Mo)为表面硬化齿轮钢要求正火后钢的组织为铁素体+珠光体和较低的HB硬度值。18CrNiM07-6钢连续冷却后易得到高硬度的贝氏体组织。通过实验室高温箱式电阻炉试验表明,870～900℃1 h-640～660℃4 h炉冷至300℃,空冷,该钢的组织为铁素体+珠光体+贝氏体组织,HB硬度值为340～350;而870～900℃1 h,30℃/h至640～660℃,炉冷至300℃,空冷,该钢的组织为铁素体+珠光体,HB硬度值为190～210:生产试验表明,30 t Φ 180 mm 18CrNiM07-6钢锻材经900℃10 h,≤30℃/h至650℃25 h,30℃/h至500℃空冷,可获得铁素体+珠光体组织。     

TiC含量对激光熔覆TiC增强双相不锈钢复合涂层性能的影响

采用激光熔覆技术在40 Cr Ni Mo基材上制备了TiC增强双相不锈钢复合熔覆层,熔覆层物相主要由奥氏体、马氏体、M₇C₃型碳化物和TiC组成。其中M₇C₃型碳化物主要包括Fe₇C₃、Cr₇C₃或者(Fe、Cr)₇C₃三种,TiC按尺寸可分为熔解后析出的微米级TiC以及粗大的未熔TiC颗粒。析出的TiC颗粒为方块状,随着TiC添加量增加,呈花瓣状长大。未熔TiC颗粒与基材形成了扩散界面,具有很好的界面结合性。当加入30 wt.%TiC时,熔覆层具有最好的耐磨性,硬度可达55.26 HRC,磨损体积为2.54×10^-2 mm³,耐磨性是基材的3.37倍。     

Recrystallization of deep drawing columbium (Nb)-treated interstitial-free sheet steels

The softening response after isochronal annealing of cold-rolled, Cb-treated, vacuum decarburized-deoxidized, interstitial-free steels was investigated by hardness measurements, tension tests, and optical and transmission electron microscopy. Softening after annealing, following cold reduction, occurs by recovery-recrystallization and a reduction in precipitation hardening due to the coarsening of CbC precipitates. The recrystallization start temperature increases markedly with increasing amounts of Cb in solid solution in ferrite. Fine CbC precipitates retard recrystallization to a much lesser degree, and their effects can be eliminated by coarsening prior to cold reduction. Recrystallization initiates at free surfaces. Partially recrystallized structures consist of two layers of recrystallized matrix separated by an unrecrystallized zone. The recrystallized layers thicken with increasing temperature or time. This phenomenon is an inherent characteristic of these steels and not a result of external influences.     

Recrystallization of deep drawing columbium (Nb)-treated interstitial-free sheet steels

The softening response after isochronal annealing of cold-rolled, Cb-treated, vacuum decarburized-deoxidized, interstitial-free steels was investigated by hardness measurements, tension tests, and optical and transmission electron microscopy. Softening after annealing, following cold reduction, occurs by recovery-recrystallization and a reduction in precipitation hardening due to the coarsening of CbC precipitates. The recrystallization start temperature increases markedly with increasing amounts of Cb in solid solution in ferrite. Fine CbC precipitates retard recrystallization to a much lesser degree, and their effects can be eliminated by coarsening prior to cold reduction. Recrystallization initiates at free surfaces. Partially recrystallized structures consist of two layers of recrystallized matrix separated by an unrecrystallized zone. The recrystallized layers thicken with increasing temperature or time. This phenomenon is an inherent characteristic of these steels and not a result of external influences.     

Influence of Partitioning Effects on the Retained Austenite Content and Properties of Martensitic Stainless Steel

The effect of a quenching and partitioning (Q&P) heat treatment with a quenching temperature (T_Q) range from 20 to 190 °C is investigated for two martensitic stainless tool steels X40Cr14 and “X25CrN13”, focusing on microstructural evolution, hardness, and toughness. The influence on the retained austenite (RA) content, when replacing part of carbon with nitrogen, is of core interest. The amount of RA is analyzed by X-ray diffraction and is additionally proved with electron backscatter diffraction, and the RA content is thermodynamically calculated. Subsequently, the effect of the microstructure on toughness and hardness is investigated. For both steels, the toughness maximum is reached in the region of the RA maximum. The “X25CrN13” attains higher toughness at higher RA contents. Higher RA contents do not benefit X40Cr14. Furthermore, the effect of double tempering at higher tempering temperatures after Q&P on the steels is investigated. Besides RA contents and hardness, dilatometer curves are used to evaluate the formation of fresh martensite in the microstructure. The secondary hardness maximum of “X25CrN13” is reached at 500 °C and that of X40Cr14 is at 480 °C. For double tempering temperature at 520 °C, T_Q has little effect on toughness, and “X25CrN13” shows better values.     

Effect of Nitrogen and Niobium on the Structure and Secondary Hardening of Super Hard High Speed Tool Steel

High‐speed steels have been used mostly for multi‐point cutting tools and for plastic working tools. High speed steels are ferrous based alloys of the Fe‐C‐X multi‐component system where X represents a group of alloying elements comprising mainly Cr, W or Mo, V, and Co. The properties of these steels can be improved by modifying their chemical composition or the technology of their production. One of the new trends in modifying the tool steels chemical composition consists in the addition of niobium and nitrogen. In this work, the effects of niobium and nitrogen on morphology of carbides and secondary hardening temperature of investigated high speed tool steels were studied. This experimental work shows that, the conventional ingots have many types of carbides of different shapes and sizes precipitate on the boundary together with thick needle like carbides. On the contrary, for nitrogen steel, the nitrogen alloying leads to form dense, fine and well distributed microstructure. While, on the case of niobium alloying, single carbide (MC), and different types of eutectic carbides were precipitated which have a major effect on the secondary hardening temperature.