轴承钢棒材超快速冷却新工艺的应用研究

 针对国内某钢厂连轧生产线上出现的网状碳化物严重析出问题,提出高温终轧后超快速冷却与缓冷相配合技术,在精轧机后安装超快速冷却器,对60 mm棒材高温终轧后超快速冷却到一定温度后缓冷,从而抑制了网状碳化物的析出,使过冷奥氏体完全发生伪共析转变而得到细片层间距的珠光体型组织-索氏体,并促进珠光体形核减小珠光体球团直径,减小C原子扩散能力细化了珠光体片层间距,得到了利于球化退火的理想组织。     

用超快速冷却新工艺生产GCr15轴承钢

 通过对GCr15轴承钢高温终轧后进行冷却速度大于100 ℃/s的超快速冷却试验,研究了轧后不同冷却工艺制度对组织形态和网状碳化物的影响,结果表明,高温终轧后进行超快速冷却可抑制网状碳化物析出,发生伪共析转变而得到细片层间距的珠光体型组织——索氏体,并促进珠光体形核和减小碳原子扩散能力,达到细化晶粒的目的,得到利于球化退火的预备组织。     

超快速冷却对中碳钢组织和性能的影响

利用超快速冷却装置,通过控制轧后冷却路径,对某中碳钢的显微组织和力学性能进行了系统的研究.结果表明:超快速冷却可以抑制先共析铁索体的生成,破坏原有先共析铁素体的网状分布;超快速冷却显著缩小了珠光体的片层间距;随着超快速冷却后温度的降低,实验钢的强度和室温冲击韧性同时得到了提高.高温终轧+超快速冷却工艺可以使中碳钢获得良好的力学性能,避免了低温轧制带来的轧机负荷大的弊端,提高了轧制节奏.     

微观组织控制对板坯表面横裂纹的抑制

板坯表面横裂纹被公认为是由于薄膜状初生铁素体附近应力集中诱导而形成的,例如沿着奥氏体晶界形成的先共析铁素体。在目前的研究中,通过对连铸坯微观组织控制抑制横裂纹的构想进行了试验。每一个试验进行了3种检测,（11）二次冷却对锭坯微观组织影响测试;（b）微观组织热塑性热拉伸测试;（c）连铸板坯裂纹敏感性连铸试验。测试结果如下：（1）连铸板坯表面微观组织能够通过二次冷却进行控制。表层结构控制（SSC）冷却,在二冷区,出结晶器后的连铸坯强冷却到温度低于A3转变温度,随后连铸坯回温至1250K,形成薄膜状游离铁索体结构。（2）重熔和凝固之后的试样进行的热拉伸测试证明通过微观组织控制能够明显提高钢材的热塑性,钢材塑性凹槽几乎消失了。上述结果也再次证明为了评价微观组织控制对横裂纹敏感性的作用,在热拉伸测试中试样的重熔是必不可少的。（3）连铸测试证明微观组织控制能够减少横裂纹的敏感性。（4）通过SSC冷却,均匀细小的弥散析出相,例如（Ti,Nb）（C,N）,实现了预防横裂纹和微观组织控制的作用。     

过共析钢轨生产工艺研究

过共析钢轨以高耐磨、高强韧性而著称,可以广泛应用在服役条件复杂的小曲线半径上。通过对合金体系设计、纳米相析出和在线热处理协同控制先共析渗碳体析出关键技术的研究,利用微合金化技术、碳化物生成元素、抑制晶界碳化物生成元素添加,抑制奥氏体温区晶界网状二次渗碳体的生成,配合精准的在线冷却工艺控制有效抑制渗碳体的生成,实现了过共析钢的开发与研究。     

轴承钢棒材超快冷却的实际运用研究

针对生产轴承钢棒材产品出现的网状碳化物问题,以国内某厂棒材热连轧生产线为依据,对GCrl5轴承钢轧后进行快速控制冷却的温度场进行模拟研究,并运用于实际生产中,取得了较好的效果。结合现场条件所能采用的各种冷却工艺,利用计算机模拟方法,对冷却工艺进行了优化分析,使得GCr15轴承钢20～60的产品的网状级别≤2.0级,解决了中小规格棒材轴承钢网状碳化物达不到标准要求的问题。     

低合金钢棒材控轧工艺及设备的开发与应用

介绍了在石钢棒材连轧线上采用所开发的中间冷却装置及快速冷却导卫对低合金钢棒材进行控制轧制的原理及实践.采用该技术,使得终轧温度控制在950℃以下,从而达到经控轧后的钢材的室温组织晶粒度比未采用控轧工艺生产的室温组织晶粒度提高至少1个级别.     

加钒对高碳钢内珠光体形核和长大的影响

研究了加钒对高碳钢显微组织的影响，用分辨率高的金相技术仔细地检测了奥氏体分解的初期情况，进一步证实了加钒会促使形成晶界铁素体膜，甚至在共析成份范围内亦然，证明了这种铁素体是共析转变的产物，而不是先共析铁素体。这是因为首次转变是碳化物微粒沿晶界形核，这些碳化物基本上等同于渗碳体。看来，钒的存在改变了晶界渗碳体的形貌和分布，而不是使其形成网状物，这些渗碳体以细小弥散的微粒形态密布于晶界上。认为出现这种     

连铸二冷模式对微合金钢板坯角部表层组织的影响

为减少和预防攀枝花钢钒有限公司P510L微合金钢连铸坯角部裂纹的发生,进行了二冷区不同冷却模式对铸坯角部表层组织及表面横裂纹的影响研究。结果表明:传统弱冷模式下,大量膜状先共析铁素体连成网状,阻碍了奥氏体基体的连续性,降低了铸坯角部的热塑性。在优化冷却模式下,在铸坯角部表层2~3 mm的组织细小、分布均匀,没有出现先共析铁素体膜,有利于控制铸坯表面横裂纹的发生。相对于传统弱冷模式,优化冷却模式可将铸坯角部表面横裂纹指数由3.2降至0.4,裂纹发生率得到了控制。     

优化冷却工艺降低轴承钢网状

提高轴承钢质量关键是提高轴承钢疲劳寿命,轴承钢提高疲劳寿命方法之一就是提高钢材的组织均匀性,降低轴承钢棒材网状是提高组织均匀性关键之一。某钢厂采用235 mm×265 mm连铸坯,通过800连轧机组轧制,采用PCS冷却系统冷却,对GCr15轴承钢Ф50进行水冷试验。通过试验表明,轴承钢棒材轧后不进行水冷网状组织级别较高,单段水冷系统冷却由于最后由心部返温,降低网状效果不明显,采用两段次需要充分考虑水冷段距离,距离较远有充足的返温时间,然后再进行冷却,能够有效降低网状组织。三段水冷全部投入使用能够有效降低网状,最终轴承钢的网状级别可控制在2.5级以内。     

Effect of Ultra-Fast Cooling on Microstructure of Large Section Bars of Bearing Steel

The ultra-fast cooling technology of large section bars and the microstructure for different cooling patterns were studied by optical microscope, transmission electron microscope and energy spectrometer. The results indicated that the large section bars were passed through the zone of secondary carbide precipitation quickly by ultra-fast cooling technology (UFC) at instantaneous cooling rate of about 200 ℃/s and the finishing cooling temperature was higher than M,. The lamellar spacing of pearlite decreased and the microhardness increased with decreasing the re-reddening temperature. The precipitation of network carbide was restrained when rereddening temperature was 690 ℃. And fine laminated pearlite was obtained through transformation of pseudopearlition that induced the reduction of the diameter of pearlite grain and refinement of the lamellar spacing of pearlite, so ideal microstructures of promoting spheroidizing annealing were obtained.     

Effect of Ultra-fast cooling on the microstructure of large-section bars of bearing steel

 The ultra-fast cooling technology of large-section bars GCr15 bearing steel was researched connected with industry practice, the microstructure in different cooling patters were researched by optical microscopy、transmission electron microscopy and energy spectrometer, it was concluded that: the large-section bars of GCr15 bearing steel passed the zone of secondary carbide precipitation quickly through the ultra-fast cooling technology(UFC) the instantaneous cooling rate of which was about 200℃/s, the finishing cooling temperature was higher than Ms, the lamellar spacing of pearlite was thinner and thinner and the micro-hardness was bigger and bigger along with the reduction of re-reddening temperature,the precipitation of network carbide was restrained when re-reddening temperature was 690℃, and fine laminated pearlite was obtained through transformation of pseudopearlition which induced the reduction of the diamond of pearlite grain and refinement of the lamellar spacing of pearlite, ideal microstructures promoting spheroidizing annealing were obtained.     

Hot Rolled Strip Re-reddening Temperature Changing Law during Ultra-fast Cooling

Temperature deviation between surface and the center of hot rolled strip is formed during ultra-fast cooling(UFC). Surface temperature would rise when temperature deviation goes up to an extent, and strip re-reddening phenomenon will appear. Strip re-reddening affects the stability of strip microstructure, property and temperature control precision. Thus, it is necessary to conduct research on re-reddening temperature changing law to improve strip property and temperature control precision. Strip temperature trends for various strip thicknesses and ultra-fast cooling rates were obtained by numerical calculation method. Re-reddening temperature, temperature deviation between surface and center, and boundary layer position changing law were obtained. By comparison, some conclusions were obtained: UFC re-reddening temperature and laminar cooling(LC) re-reddening temperature were linear to ultra-fast cooling rate respectively. Ultra-fast cooling rate affected UFC re-reddening temperature greatly, but it had little effect on LC re-reddening temperature. Equations which were used to calculate UFC re-reddening temperature, LC re-reddening temperature and maximum temperature deviation were obtained. The position of boundary layer stayed in 1/4 strip thickness.     

高碳铬不锈轴承钢孪晶碳化物研究

研究了高碳铬不锈轴承钢“孪晶碳化物”（直线状和链状碳化物）的影响因素及形成原因,结果表明：加热温度达到1140℃,退火后开始出现沿晶界分布的链状碳化物;加热温度≥1160℃,退火后出现大量直线状和链状两种形态的碳化物。材料从高温直接冷却时,温度≥1080℃并且冷却速度≤80℃／h可能析出链状碳化物,并且温度越高冷却速度越慢析出的可能性就越大。直线状碳化物形成原因为：材料加热温度过高．晶粒长大的过程中晶界迁移时偶然发生堆垛错误形成了生长孪晶,在随后的退火过程中碳化物向奥氏体挛晶界面沉淀而形成,是真正意义上的孪晶碳化物。链状碳化物是由于材料过热或者局部过热,在随后冷却过程中碳化物沿奥氏体晶界析出而形成的,本质上是一种网状碳化物。     

热变形工艺对100Cr6轴承钢线材网状碳化物的影响

利用热膨胀仪、热模拟试验机、金相显微镜、场发射扫描电镜等测定了100Cr6轴承钢的CCT曲线，试验研究了热压缩及控轧控冷对网状碳化物析出行为的影响。结果表明：第二道次压缩温度从850℃降低至700℃时，奥氏体再结晶细化向未再结晶转变，二次碳化物逐步由晶界封闭网状向半封闭条状、短杆状再向沿拉长的奥氏体晶界链状转变，750～800℃内变形碳化物细小、分散；Φ10 mm 100Cr6线材采用910℃降至770℃温度控轧+快速冷却工艺，其热轧态、球化退火及淬回火后碳化物分布均匀性逐步提升，奥氏体晶粒由8.0级细化至10.0级，晶界碳化物由封闭网状向断续条状转变，平均厚度从0.54μm降低至0.11μm,网状级别由3.0级占比33%降低至≤2.0级占比100%,可缩短球化退火时间及提高轴承的疲劳寿命。     

400 MPa级縮微合金化抗震钢的控轧控冷工艺实践

在化学成分合理设计的基础上HRB400E钢(/%:0.21～0.25C,0.40～0.65Si,1.40～1.55Mn,≤0.040P,≤0.040S,0.015～0.025Nb,0.005～0.008N),研究了不同加热温度及控轧控冷温度对力学性能、金相组织和钢筋表面时效锈蚀的影响。提出了最佳的轧制温度参数:加热温度为1140～1170℃、开轧温度为1 040～1 060℃,精轧温度为1000～1030℃,终轧后的冷床温度是870～890℃。结果表明,铌微合金化HRB400E钢屈服强度450-475MPa,其析出物主要为粒径大小为300～600nm的Nb(C,N),分布在网状碳化物上、网状碳化物边缘以及晶界附近的晶粒内部。     

Influence of on-line tempering parameters on microstructure of medium-carbon steel

A new process involving ultra-fast cooling(UFC)and on-line tempering(OLT)was proposed to displace austempering process,which usually implements in a salt/lead bath and brings out serious pollution in the industrial application.The optimization of the new process,involving the evolution of the microstructure of medium-carbon steel during various cooling paths,was studied.The results show that the cooling path affected the final microstructure in terms of the fraction of pearlite,grain size and distribution of cementite in pearlite.Increasing the cooling rate or decreasing the OLT temperature contributes to restraining the transformation from austenite to ferrite,and simultaneously retains more austenite for the transformation of pearlite.It is also noted that bainite was observed in the microstructure at the cooling rate of 45°C/s and the OLT temperature of 500°C.Through either increasing the cooling rate or decreasing the OLT temperature,the distribution of cementite in pearlite is more dispersed and grain is refined.Taking the possibility of industrial applications into account,the optimal process of cooling at 45°C/s followed by OLT at 600°C after hot rolling was determined,which achieves a microstructure containing nearly full pearlite with an average grain size of approximately 7μm and a homogeneously dispersed distribution of cementite in pearlite.     

基于超快冷的控轧控冷装备技术的发展

控制轧制与控制冷却技术是钢种开发和改善产品质量的重要轧制工艺技术。介绍了热轧板带钢超快冷技术的发展前沿,重点阐述了国内自主研发超快冷工艺装备的技术特征。在此基础上,进一步介绍以超快冷为核心的新一代TMCP工艺原理以及“轧制-冷却”相结合的“温控-形变”耦合控轧技术研发现状,通过控制轧制与超快冷有效结合,综合利用细晶强化、析出强化、相变强化等多种强化方式,可以充分挖掘钢铁材料的潜力,实现资源节约型、节能减排型的绿色钢铁产品制造过程。     

热轧中厚板超快速冷却过程温度场数值模拟

 超快速冷却工艺作为热轧钢板生产的核心技术,对改善板材产品组织形态、提升产品性能具有重要意义。在中厚钢板的超快速冷却过程中,心部与表面之间的冷却速度差异使得钢板在厚度方向上形成内外温度差,而超快速冷却中钢板表面的换热机制较为复杂,两者综合提升了中厚板冷却机制的界定难度。为提升中厚板超快冷模型计算精度,完善其换热体系,建立了中厚钢板轧后超快速冷却过程中等效换热系数反求法的数学模型。该模型依托离散解析法,基于导热微分方程及物体正规阶段的状态特点,将求得的超越方程根转化为等效换热系数,并将此作为超快冷温度场模型的边界条件。在此基础上,构建了超快速冷却温度场仿真模型,验证了20 mm钢板超快速冷却机制下的温度场。结果表明,等效换热系数反求法的数学模型能够适用于中厚钢板的超快冷工艺。     

20CrMnTiH圆钢精轧后控冷过程温度场有限元分析

通过对20CrMnTiH圆钢精轧后控制冷却过程温度场进行有限元模拟以及现场温度实测,得出了Φ35 mm规格圆钢芯部、1/2半径处和表层温度的分布曲线。分析说明,轧后水冷却过程圆钢表层温度急速下降,而芯部温度下降缓慢,水冷时圆钢芯部与表面的最大温差约为115℃;水冷后的空冷过程使得圆钢芯部和表层温度逐渐一致。20CrMnTiH圆钢精轧后采用快速水冷并配合空冷工艺,有利于抑制奥氏体晶粒长大并获得均匀细小的轧材组织。