GCr15轴承钢热处理过程中碳化物的析出与演变行为

采用定量金相的方法研究GCr15轴承钢在球化退火、奥氏体化淬火、低温回火等不同热处理工序后其碳化物的演变行为,通过ThermoCalc软件进行数值模拟计算分析碳化物尺寸和成分对其在奥氏体化时固溶动力学的影响。结果表明:球化退火处理后形成的碳化物粒子尺寸呈多峰分布,奥氏体化和回火后的碳化物粒子尺寸分布为单峰分布,奥氏体化后碳化物中Cr含量略有增加;Cr含量高的碳化物粒子具有较大尺寸;球化退火形成的碳化物在奥氏体化时大量固溶形成了富碳奥氏体,淬火后转变为高碳马氏体并导致高硬度;奥氏体化时碳化物固溶发生Cr的配分导致碳化物中Cr含量增加;直径200nm的碳化物即使其Cr含量接近基体成分,也不能在奥氏体化热处理时完全固溶,未溶的碳化物颗粒将影响后续回火过程的碳化物析出。     

模具钢固溶循环热处理下的机械性能研究

本文对于ＣｒＷＭｎ冷作模具钢的四种不同预处理方法，对比了它们的碳化物粒子尺寸和分布，钢的奥氏体晶粒度大小及强韧化效果。说明：采用循环退火完全能够代替常用的等温球化工艺，可缩短生产周期性约１／３，节省能耗近一半；如何先进高温固溶处理或再加上几次循环淬火，经退火后可获得高度弥散的极细的碳化物，最终热处理的实际晶粒度达１２￣１３级超细化程度，有利于改善模具钢的强韧化效果和耐磨性，延长使用寿命。     

低碳Cr-Mo系深冲双相钢组织与织构演变

通过组织观察以及TEM与XRD技术研究了低碳Cr-Mo系深冲双相钢组织与织构演变规律。结果表明:奥氏体未再结晶区终轧有利于形成{112}〈111〉织构,冷轧过程中{001}〈110〉,{112}〈110〉与{223}〈110〉织构稳定增加,退火过程中形成有利于深冲性能的〈111〉//ND以及{554}〈225〉与{332}〈113〉织构;820℃与860℃临界区退火后γ纤维织构密度差异较小,但是高温退火增大{111}〈110〉与{111}〈112〉织构的取向密度差值,归因于贝氏体中的固溶碳以及贝氏体相变时的变体选择;高温卷取能诱发热轧板中Mo基碳化物粒子析出,并在退火保温过程中回溶,既能发展再结晶织构,又能促进第二相形成。     

等温球化处理过程中球状碳化物的Ostwald长大现象

为Ｔ８Ａ钢和Ｔ１２Ａ钢在等温球化过程中碳化物的球化长大规律进行了研究，结果表明碳化物是以大粒子吞食小粒子和短棒状碳化物分断或棒端溶解自身球化的方式球化长大的。其特点是碳化物尺寸逐渐增大，数目逐渐减少而含量保持不变，长大规律符合Ｏｓｔｗａｌｄ熟化规律。     

硼对M2高速钢凝固组织的影响

研究了微量硼对Ｍ２高速钢的凝固组织以及热处理过程中共晶碳化物团球化的影响及其机理。发现,硼促进层片状Ｍ２Ｃ碳化物的形成;促进共晶碳化物的偏析,使碳化物量增加,层片变粗;促进共晶碳化物在高温加热时的断网和团球化,在高速钢中硼主要偏聚在晶界共晶碳化物上。     

4Cr14Ni14W2Mo钢中的碳化物

本文研究了4Cr14Ni14W2Mo 钢中碳化物的性态,溶解和析出规律及其对性能的影响。指出,该钢中存在球形、立方体形和六方柱体形等多种形态碳化物,但均为 M_(2(?))C_6。较低温度时效析出的碳化物为立方体形,细小弥散,与基体共格,有明显强化作用。未溶碳化物和较高温度二次固溶后析出的碳化物多为球状和六方柱体形,尺寸较大,与基体不共格,强化作用有限。二次固溶沿晶界择优析出的粗大链状碳化物和时效沿晶析出的网状碳化物易导致沿晶断裂。     

铸造过热度和热处理对CoCrMo合金显微组织的影响

研究了CoCrMo合金普通壳型铸造工艺下过热度和高温固溶热处理对显微组织的影响。结果表明:CoCrMo合金在铸态下碳化物主要以大块状共晶状M23C6碳化物存在;随着过热度的增加,碳化物共晶团的尺寸增大,导致室温拉伸性能降低。CoCrMo合金经过高温固溶热处理后,大部分大块状共晶碳化物发生溶解和分解,以细小的颗粒状M23C6碳化物析出并均匀分布于基体,抗拉强度、屈服强度和伸长率得到很大的提高。均匀细小分布的碳化物有利于提高CoCrMo合金的室温拉伸性能。     

高温固溶热处理对HIP态FGH96合金中碳化物影响规律的体视学研究

利用金相显微镜,扫描电镜和透射电镜并结合体视学基本原理,对在不同固溶温度和冷却方式(空冷和炉冷)下热等静压(HIP)态FGH96合金中碳化物的数量、空间分布及尺寸分布等进行了定量表征和对比研究。结果表明:HIP态FGH96合金中碳化物主要为富Nb和Ti的MC,在原始颗粒边界(PPB)上分布的碳化物主要为块状,在PPB区域以外分布的碳化物主要由块状和花状MC组成。在1180℃以下进行固溶热处理时,碳化物含量增加并且加剧了合金中的PPB;当固溶温度达到1180℃以上时,随着固溶温度的升高,合金中碳化物数量减少,PPB逐渐消失。1200℃固溶后炉冷,固溶在基体中的碳主要以非PPB碳化物形式重新析出,会导致合金中PPB碳化物数量的降低,即使合金中的碳化物总量与固溶热处理前几乎相同。另外,空冷合金中PPB碳化物尺寸为单峰分布,而炉冷合金中则表现为双峰,后者与炉冷过程中碳化物能够重新析出密切相关。     

ZG35Cr25Ni12NNbRE钢中黑斑组织的成因探讨

ZG35Cr2 5Ni12奥氏体耐热铸钢经固溶时效后的显微组织由初晶奥氏体、共晶碳化物 ,以及在奥氏体基体上时效析出的二次碳化物组成 ;使用 3.5a(年 )后二次碳化物增多 ,共晶碳化物附近的“无析出区”消失 ,并在许多共晶碳化物内部形成黑斑组织。研究表明 ,黑斑组织是富含稀土元素的氮碳化物ε (Cr ,Fe) 2 (N ,C)相 ,是在长期高温过程中通过消耗共晶碳化物形成的     

固溶温度对8Cr4Mo4V轴承钢的中温相转变和力学性能的影响

在不同温度对8Cr4Mo4V钢固溶处理后在260℃盐浴中发生相转变而生成贝氏体组织,测定了钢的硬度和冲击韧性。使用扫描电镜、电子探针和光学显微镜等手段观察钢的微观组织,分析了合金元素扩散、贝氏体形核及贝氏体尺寸与固溶温度的关系,研究了固溶处理温度对力学性能的影响。结果表明,在1050℃和1065℃固溶处理后钢中的点状碳化物仍有剩余,阻碍了晶粒的长大;在1095℃和1110℃固溶处理后点状碳化物溶解,晶粒平均尺寸增大。固溶处理促使含Cr和V的碳化物溶解,但对含Mo碳化物的影响较小;高温固溶处理后Mo元素仍然存在于碳化物中,在基体中则较少。高温固溶处理使更多的Cr和V元素溶入基体中,降低了碳元素在基体中的扩散系数和贝氏体形核数目以及贝氏体的最终生成量,使贝氏体的组织粗化;随着固溶温度的提高,钢的硬度提高,而冲击韧性降低。     

Inhomogeneous Distribution of Second Phase Particles in Grain Oriented Electrical Steels

The second phase particles were observed during the whole manufacturing process of conventional grain oriented electrical steels, exhibiting that the areal density of particles in the center was obviously higher than that on the surface at each manufacturing stage. After hot rolling, the approximately equiaxed grains formed upon recrystallization were present on the sheet surface while the deformation structures were retained in the central part. Thus, the dislocation density on the surface was evidently lower than that in the center and this trend became more noticeable after the first cold rolling. Since new precipitates were mainly nucleated at dislocations during both hot rolling and annealing following cold deformation, the difference in dislocation density resulted in the inhomogeneous distribution of particles through the thickness of sheet. According to this, Goss grains, which were usually found near the surface, tended to grow up more easily during the secondary recrystallization treatment.     

Influence of intermediate annealing on final Goss texture formation in low temperature reheated Fe-3%Si steel

The precipitation behavior of inhibitors and their influence on final Goss texture formation in grain-oriented electrical steels produced by compact strip processing technology with a reheating temperature lower than 1200 °C were investigated under two distinct intermediate annealing methods: conventional intermediate recrystallization annealing and a new intermediate decarburizing and recrystallization annealing method without final decarburizing after the second cold rolling. The initiation of secondary recrystallization, the distributions of second phase particles, the final Goss texture, and the grain structure were observed. The new technology could maintain higher inhibitor densities because the deformed matrix could provide higher site densities for inhibitor nucleation before secondary recrystallization, resulting in a relatively higher inhibition effect of the second phase particles. The new technology could also compensate for the disadvantages of fewer inhibitors induced by fewer dissolved Mn and S elements in the matrix during lower reheating temperature for hot rolling. The final sheet produced after the secondary recrystallization annealing obtained stronger Goss texture, larger grain size, and better magnetic properties.     

Modelling dislocation assisted tempering during rolling contact fatigue in bearing steels

Rolling contact fatigue in bearing steels is manifested by dark-etching regions, which are attributed to deformation induced tempering. In order to quantitatively explain this phenomenon, a model is suggested for martensite tempering assisted by dislocation glide during rolling contact fatigue. In the model, dislocations transport carbon from the matrix to carbide particles, provided that the carbon is located at a certain distance range from the dislocation contributing to the tempering process. By calculating the amount of carbon in the matrix, the kinetics of carbide thickening and hardness reduction are computed. It is found that the dark-etching region kinetics can be controlled by both bearing operation conditions (temperature and deformation rate) and microstructure (type, size, and volume fraction of carbides). The model is validated against tested bearings, and its limitations are discussed.     

Effect of Cold Rolling on Morphology of Carbides and Properties of 7Cr17MoV Stainless Steel

The evolution of the carbides and mechanical properties of 7Cr17MoV stainless steel used as cutlery material during cold rolling was investigated in this study. The results demonstrate that the microstructure of the rolled steel is composed of pearlite and spheroidal carbides. After cold rolling, the aggregation of carbides was no longer evident, and the carbides appeared to be small in size and uniformly distributed, whereas carbides in hot-rolled strips are clearly aggregated. Decreasing the thickness of the cold-rolled strips decreased the size of the carbide particles while increasing their number, which improved the particle distribution. A large number of fine, even nano-scaled carbides were observed in the material. The carbide phase, which primarily consisted of M₂₃C₆, did not change during cold rolling and annealing. The tensile strength and yield strength first decreased and then increased, and the elongation increased as the thickness of the cold-rolled strips decreased. Dimples and inclusion particles were readily observed upon tensile fracture. The inclusions are identified to be primarily carbides and oxide inclusions.     

The important role of titanium microalloying in refining austenite grain of heavy-duty H-beam steel during rough rolling produced by a new technology

A new technology of austenite grain refinement, fine austenite enhanced ferrite transformation, is proposed for heavy-duty hot-rolled H-beam steels in this work. Titanium microalloying is very important and necessary for the new technology. The effect of titanium on the prior austenite grain size of steels during simulated rough rolling was investigated. The results show that the prior austenite grain sizes of specimens with titanium and niobium elements are much finer than those of specimens with niobium but without titanium deformed at the same parameters. For the alloying composition of studied steels, titanium nitride particle maybe precipitated in specimens with titanium at above 1,200 °C, however, niobium carbide particles can't form in specimens without titanium at above 1,150 °C. The thermodynamically stable titanium nitride particles can impede the grain growth at high temperature for example furnace heating before rough rolling and bring the epitaxial growth of niobium carbide on pre-existing themselves which induces a large number of titanium nitride-niobium carbide composite precipitates. These fine precipitates can pin austenite grain boundaries effectively and ensure austenite grain refinement.     

Deformation and fracture of polymer/metal composites subjected to cold rolling

Cold rolling of a sandwich composite with a metallic strip inclusion in a polymeric matrix can produce a range of outcomes, including deformation and fracture of the inclusion. Using different material combinations under the same processing parameters, the results ranged from minor deformation, to folding and/or loss of adhesion, and fracture of the inclusion, with fracture particles varying in size and shape. Comparisons are made between the resulting structures after cold rolling of the polymer/metal composite to geological formations. In particular, the fracture particles obtained resemble rock structures known as boudins. The phenomena of boudinage and folding encountered in the cold rolling of polymer/metal composites is similar to that seen in geology formations although the time and size scale of these events are several orders of magnitude apart. The experimental results reported show that cold rolling applied to a polymer/metal sandwiched composite induces deformation and fracture behaviors that depend on the mechanical properties of the constituents, deformation behavior of the polymeric matrices, interfacial adhesion, and process parameters such as rollers speed and nip-gap.     

冷轧压下率及初始高斯晶粒取向度对超薄取向硅钢织构演变与磁性能的影响

以不同高斯取向度的取向硅钢成品板为初始原料,采用一次冷轧法制备0.06~0.12mm厚的取向硅钢薄带。利用EBSD取向成像技术研究冷轧压下率以及初始高斯晶粒取向度对超薄取向硅钢织构演变与磁性能的影响。结果表明:随着冷轧压下率增大和厚度减小,退火后再结晶织构增强,当压下率为70%时,再结晶织构中RD∥〈001〉织构最锋锐,磁性能最佳;初始样品高斯取向度越高,制备的薄带样品磁性能越好;因此,生产高性能的取向硅钢薄带应选用初始高斯晶粒取向度较高的成品板。     

圆珠笔头用新型易切削不锈钢的组织与力学性能

对圆珠笔头用新型高铬硫系铁素体易切削不锈钢冷拉线材的微观组织与力学性能进行了研究.结果表明,钢中易切削相为MnS、Pb及其与Te形成的复合夹杂物,均呈细小球状或椭球形沿拉拔方向断续、串链状分布.MnS夹杂物大小横向约1μm,纵向约10μm.钢中Cr、Mo的碳化物对改善MnS夹杂物形态有显著作用.该钢成品线材基体组织为细小铁素体晶粒,晶粒度约为10级,力学性能与进口同类钢线材相近,作为替代进口材料,其用于制造圆珠笔头,具有良好的切削性能,能满足生产加工和使用要求,填补了国内空白.     

奥氏体不锈钢热轧加工性能的数学模型研究

钢的热加工性能是钢的热轧工艺设计的基础.奥氏体钢在热加工中涉及到众多的物理现象,如动态回复、动态再结晶、静态回复、亚动态再结晶、静态再结晶和晶粒长大.一个优秀的描述钢的热加工性能的数学模型可以优化热轧工艺,提高生产效率,改善产品质量.综述了奥氏体不锈钢在热加工中发生的各类物理现象及其相对应的数学模型,讨论了变形温度、变形参数与流变应力、再结晶以及再结晶晶粒度之间复杂的关系,并分析了在工业多道次轧制工艺中,如何应用这些数学模型模拟和预测轧钢过程中残余应变和其内部组织的演变过程.     

The influence of sulphur content on the static recrystallisation of cold worked low carbon aluminium-killed strip steels

The static recrystallisation (SRX) after cold work was studied in four low carbon Al-killed steels with varying sulphur content ranging from 2 to 140 ppm. The sulphur had an indirect but significant effect on the SRX behaviour by the presence of coarse MnS particles on which the AlN precipitated heterogeneously during coiling after hot rolling. The mean size of the AlN/MnS compound particles was generally too coarse to be effective for Zener-pinning of moving boundaries during recrystallisation thereby rendering the AlN ineffective in influencing the SRX process. In the low sulphur content steels, however, with virtually no MnS present, very fine AlN nucleated homogeneously in the matrix or heterogeneously on grain boundaries or dislocations during coiling, with size often less than 30 nm in diameter. These AlN particles were more effective in Zener-pinning of dislocations and moving recrystallisation fronts, thereby retarding the start of SRX by up to 100 times at low coiling temperatures of about 600 °C.