Influences of Austenization Temperature and Annealing Time on Duplex Ultrafine Microstructure and Mechanical Properties of Medium Mn Steel

A duplex ultrafine microstructure in a medium manganese steel(0.2C-5Mn)was produced by austenite reverted transformation annealing(ART-annealing).The microstructural evolution during annealing was examined by scanning electron microscopy(SEM),transmission electron microscopy(TEM)and X-ray diffraction(XRD).Based on the microstructure examination,it was found that some M3 C type carbides appeared in the martensitic matrix at the beginning of the ART-annealing.But with further increasing annealing time,these carbides would be dissolved and finally disappeared.Meanwhile,the austenite lath was developed in the ART-annealing process and the volume fraction of austenite increased with the increase of the annealing time,which resulted in a duplex microstructure consisting of ultrafine-grained ferrite and large fraction of reverted austenite after long time annealing.The mechanical property examinations by uniaxial tensile tests showed that ART-annealing(6h,650 ℃)resulted in a superhigh product of strength to elongation up to 42GPa·%.     

钼钨钒合金化热作模具钢高温回火组织演变

为适应热冲压技术的发展需求,开发了一种新型高热导率高耐磨性能热冲压用模具钢材料。采用扫描电镜（SEM）、透射电镜（TEM）等检测手段对钼钨钒合金化新型模具钢的高温回火性能与组织特征进行了研究。阐明了新型热冲压模具钢回火过程碳化物析出与演变规律。实验结果表明:实验用钼钨钒合金化模具钢材料具有良好的回火二次硬化性能,在500～600 ℃温度区间回火时,回火组织硬度上升;在600 ℃回火出现二次硬化峰值;当回火温度超过600 ℃后,组织软化程度明显,回火硬度开始下降。实验模具钢在高温回火过程中的硬度变化与其合金碳化物的偏聚、析出和聚集长大密切相关。当在560 ℃以下回火时,实验钢组织中未有合金碳化物析出;当回火温度大于560 ℃时,回火组织中开始析出M₂C型碳化物;当回火温度高于600 ℃后开始析出MC型碳化物;当在620 ℃长时间回火后M₂C型碳化物转化为M₆C型碳化物,此时实验钢硬度开始明显下降;而当回火温度高于660 ℃时,新型实验钢组织中主要为M₆C和MC型合金碳化物。      

Thermomechanical Control Process and Its Effect on Structure and Properties of High Strength Low Alloy Steels

Low carbon steels microalloyed with small amount of carbide and/or nitride forming elements such as Nb,Ti and V with Thermomechanical controlled processing (TMCP) can give fine grained ferrite structure with high strength and superior toughness.The present study was aimed at identifying rolling parameters as well as microstructural characterization for accomplishing high yield strength and high charpy impact property at-60℃ by controlling hot rolling parameters and microstructure Grain size distribution was also monitored and related to mechanical properties of steel.     

Microstructural model for hot strip rolling of high-strength low-alloy steels

The microstructural evolution during hot-strip rolling has been investigated in four commercial high-strength low-alloy (HSLA) steels and compared to that of a plain, low-carbon steel. The recrystallization rates decrease as the Nb microalloying content increases, leading to an increased potential to accumulate retained strain during the final rolling passes. The final microstructure and properties of the hot band primarily depend on the austenite decomposition and precipitation during run-out table cooling and coiling. A combined transformation-ferrite-grain-size model, which was developed for plain, low-carbon steels, can be applied to HSLA steels with some minor modifications. The effect of rolling under no-recrystallization conditions (controlled rolling) on the transformation kinetics and ferrite grain refinement has been evaluated for the Nb-containing steels. Precipitation of carbides, nitrides, and/or carbonitrides takes place primarily during coiling, and particle coarsening controls the associated strengthening effect. The microstructural model has been verified by comparison to structures produced in industrial coil samples.     

Formation of AlN Nano Particles Precipitated in St-14 Low Carbon Steel by Micro and Nanoscopic Observations

In low carbon steels, dissolution and precipitation of the second phases such as carbides and nitrides during annealing cycles can affect the final structure and properties of the materials. The interaction of above processes depends on parameters such as reheating temperature, heating rate, annealing temperature, soaking time and finishing temperature in hot rolling stage before cold rolling. The effects of heating rate and annealing temperature on the microstructure and hardness were investigated. Two heating rates for annealing temperatures of 550, 610 and 720℃ were applied on cold-rolled specimens and St-14 low carbon steel, which were immediately quenched after isothermal annealing. The intercept method was used tO measure average grain sizes. However, resulted microstructures are dif- ferent for the two heating rates. While pancaked structures were observed in specimens annealed with low heating rate, in samples annealed with high heating rate, equiaxed microstructures were observed. Vickers micro-hardness values decreased at all temperatures, which were more significant at higher temperatures. At longer annealing time, signs of increase of hardness values were detected. All results and observations consistently suggest that a precipitati- on process has occurred concurrently with restoration processes during annealing. In addition, the energy dispersive spectroscopy analysis resulted from transmission electron microscopic micrographs have proved that the nano particles precipitated in grain boundaries are AlN.     

热处理工艺对Fe-Mn-Al-C钢组织和性能的影响

利用SEM、XRD、EPMA等试验方法,对不同退火、固溶以及时效工艺下Fe-Mn-Al-C钢的组织演变规律和力学性能进行研究。结果表明,900～1050℃退火温度对试验钢的组织与性能影响较大,随着退火温度的升高晶粒尺寸增大、碳化物逐渐回溶,强度降低、塑韧性提高,在1050℃保温2 h空冷时抗拉强度为1036 MPa,断后伸长率为39%,冲击功41 J,强塑积40 GPa·%;经1050℃保温2 h水冷固溶后时效处理,试验钢组织为奥氏体+铁素体+κ碳化物,随着时效温度的增高,κ碳化物逐渐析出,使试验钢的强度增加、塑韧性降低。600℃时效时,抗拉强度1145 MPa、断后伸长率22%、冲击功28 J,综合力学性能全部满足设计要求。     

Improved Cold Formability by Thermo‐Mechanical Rod Rolling

Usually, unalloyed medium carbon steels and 1% chromium steels for cold heading applications are produced by hot rolling, subsequent controlled cooling and soft annealing. It is shown that by thermomechanical rod rolling and slow air cooling at the loop cooling conveyor the tensile strength can be lowered to such an extent so that cost‐intensive soft annealing procedures are not required. The effects of the processing parameters on the microstructural evolution and final mechanical properties of steel grades 23MnB4 and 1% Cr‐steels like 32CrB4, 37Cr4 and 41 Cr4 are tested by a Gleeble machine. Using a microstructural process model, called CAROD, the entire rolling and cooling process has been optimized.     

Relation between manganese oxide inclusions and microstructure of low-carbon rimmed steel sheet

The influence of manganese oxide inclusions on the microstructure of cold-rolled low-carbon rimmed steel sheet containing 0.30 pct Mn and a high level of oxygen was studied in the laboratory by annealing full-hard samples in the 1200‡ to 1400‡F range. Microprobe results showed that the oxide inclusions deplete the surrounding matrix of its manganese and thereby permit sulfur to remain in solid solution after prior hot rolling. It was found that the dissolved sulfur precipitates during subsequent annealing after cold rolling and produces bands of fine grains in the inclusion area. It was determined that the manganese oxide inclusions, which are generally concentrated toward the center of the sheet cross section, establish a gradient of manganese in solid solution between the surface and center of the steel samples studied. As demonstrated by the electron microprobe and photomicrographic evidence, this manganese gradient caused carbon to diffuse to the sheet surfaces during annealing. The resulting size, shape, and distribution of carbides at the sheet surfaces depended largely on the annealing treatment.     

摩擦对IF钢铁素体区热轧和退火织构的影响

采用X射线衍射仪分析IF钢铁素体区热轧织构以及退火织构的演化,在实验室热轧机上进行了IF钢的铁素体区热轧,研究了摩擦对IF钢铁素体区热轧、退火织构的影响。结果表明：无润滑轧制时,钢板表层形成强高斯织构组分{110}〈001〉,弱γ纤维织构,导致再结晶织构中高斯组分强度高,γ纤维织构强度低;润滑轧制时,钢板表层高斯织构组分强度降低,{100}〈011〉、γ纤维织构强度提高,退火后γ纤维织构强度提高。钢板中心受摩擦作用影响较小,轧制过程中发展为较强的α和γ纤维织构,退火后γ纤维织构成为主要织构组分。     

非调质型15万m~3石油储备罐体用610MPa高强度钢板轧制和热处理工艺研究与实践

主要采用热模拟技术研究了不同终轧工艺和不同回火温度对石油储备罐体用高强度钢板JGR610E显微组织的影响,并利用金相和萃取复型等分析方法对不同工艺下的显微结构和碳化物进行了分析。结果表明,JGR610E钢在860℃左右终轧温度、20℃/s冷却速度下可以获得板条状低碳贝氏体组织,经过620℃回火后得到具有良好强韧性能的板条贝氏体和针状铁素体混合组织,其析出相主要有两类,尺寸在300 nm左右的为含有Fe和Mn的MxCy型碳化物,尺寸范围在50～100 nm的为含有Ti和Nb的MC型碳化物,且在该回火温度下,有大量的尺寸范围在几个纳米至十几个纳米尺寸的Ti(CN)析出。     

Microstructure and Properties of Ti and Ti+Nb Ultra-Low Carbon Bake Hardening Steels

 Hot rolling, cold rolling and continuous annealing processes of Ti bearing and Ti+Nb stabilized ultra low carbon bake hardening(ULC-BH) steels were experimentally studied. The microstructure and texture evolution, as well as the morphology, size and distribution of the second phase precipitates during the hot rolling, cold rolling and continuous annealing were also analyzed. The results showed that the size of NbC precipitates in Ti+Nb stabilized ULC-BH steel was smaller than that of TiC precipitates in Ti bearing ULC-BH steel, this caused the average grain size of Ti+Nb stabilized ULC-BH steel to be finer than that of Ti bearing ULC-BH steel, for the yield strength, the former was higher than the latter, but for the r value which reflecting the deep drawing performance, the former was lower than the latter.     

铬、锰及退火温度对无取向硅钢组织性能影响

 为探究铬、锰元素及退火温度对高强无取向硅钢性能的影响规律,借助OM、SEM、EBSD与万能拉伸试验机等分析不同制造工艺下3组不同含量铬、锰元素的无取向硅钢热轧、常化及退火处理后组织与性能。结果表明,试验钢热轧后组织不均匀,心部为沿轧向分布纤维状组织,边部为少量再结晶晶粒,常化处理能显著改善热轧板组织均匀性,消除热轧板中心部位的纤维状组织。经冷轧及退火后得到多边形铁素体晶粒,其中960 ℃退火,晶粒尺寸偏大,有利织构{100}组分体积分数减少,不利织构{111}组分体积分数增加,成分为0.2Mn-1Cr的1号试验钢960 ℃退火后铁损最大,磁感强度偏小;成分为0.5Mn-1Cr的2号试验钢930 ℃退火后,磁性能与强度等综合性能最佳,工频铁损P1.5/50为2.41 W/kg,高频铁损P1.0/400为17.36 W/kg,磁感应强度B5 000为1.638 T,抗拉强度为685 MPa。     

初始组织对一种Nb-Mo微合金化中锰TRIP钢组织演变与力学性能的影响

研究了热轧后冷却方式和冷轧压下量对一种Nb-Mo微合金化中锰TRIP钢临界退火过程中组织演变与力学性能的综合影响规律.结果表明:当热轧后冷却方式由油淬变为炉冷时,在冷轧压下量一定的条件下,退火组织中长条状铁素体的体积分数增加,且长轴/短轴比增大,而等轴铁素体的晶粒尺寸变化不明显;对于热轧后油淬试样,当冷轧压下量由50%增至75%时,退火组织中长条状铁素体的体积分数减少,铁素体的平均晶粒尺寸由400~500 nm减至300~400 nm.综合分析,增加热轧后的冷却速率,可在较小的冷轧压下量条件下获得一种综合性能良好的超细晶中锰TRIP钢,其性能指标为:屈服强度为976 MPa,抗拉强度为1 165 MPa,延伸率可达34.1%,强塑积接近40 GP·%.     

退火温度对非调质960 MPa高强钢组织和性能的影响

为了稳定热轧高强钢的组织和性能,需进行退火处理。了解不同的温度对组织的影响规律至关重要,为此对相同终轧温度条件下退火温度对非调质960 MPa高强钢组织和性能的影响进行研究。结果表明,试验钢在不同退火温度下处理后,均得到回火马氏体组织,并出现明显的纤维组织,使得马氏体板带具有明显的方向性,且随着退火温度的升高马氏体组织粗化。经不同退火温度处理后,试验钢的强度在RD方向(轧制方向)的下降趋势低于TD方向(轧件宽度方向),说明TD方向的强度对温度变化较敏感;同时随着退火温度的升高,伸长率和冲击韧性在RD方向为先升后降,在TD方向伸长率持续升高,冲击韧性几乎不变。综合考虑,确定退火温度为500 ℃时为最佳退火工艺方案。     

薄板坯连铸连轧工艺下Hi-B钢的组织及织构

采用金相显微镜和扫描电镜研究实验室模拟薄板坯连铸连轧（TSCR）工艺试制的高磁感取向硅钢（Hi-B钢）组织、织构的演变特征.研究发现实验室模拟薄板坯连铸连轧工艺试制的Hi-B钢热轧板显微组织及织构在厚度方向上存在不均匀性.常化板表面脱碳层铁素体晶粒明显粗化,常化板织构基本继承了热轧板相应的织构类型,仅织构强度不同.一次大压下率冷轧后,晶粒及其晶界沿轧向被拉长形成鲜明的纤维组织,织构主要为α纤维织构和γ纤维织构,脱碳退火后试样发生回复和再结晶现象并形成初次晶粒组织,脱碳退火后织构分布较为集中.温度升高至1000℃时二次再结晶开始,1010℃时钢中晶粒发生异常长大,高斯织构强度达到61.779.成品磁感为1.915 T,铁损为1.067 W·kg-1.      

Numerical Simulation of Austenite Recrystallization in CSP Hot Rolled C-Mn Steel Strip

An integrated mathematical model is developed to predict the microstructure evolution of C-Mn steel during multipass hot rolling on the CSP production line,and the thermal evolution,the temperature distribution,the deformation,and the austenite recrystallization are simulated.The characteristics of austenite recrystallization of hot rolled C-Mn steel in the CSP process are also discussed.The simulation of the microstructure evolution of C-Mn steel ZJ510L during CSP multipass hot rolling indicates that dynamic recrystallization and metadynamic recrystallization may easily occur in the first few passes,where nonuniform recrystallization and inhomogeneous grain size microstructure may readily occur;during the last few passes,static recrystallization may occur dominantly,and the microstructure will become more homogeneous and partial recrystallization may occur at relatively low temperature.     

Recrystallization kinetics of an austenitic high-manganese steel subjected to severe plastic deformation

The evolution of the microstructure and the properties of an austenitic high-manganese steel subjected to severe deformation by cold rolling and subsequent recrystallization annealing is investigated. Cold rolling is accompanied by mechanical structural twinning and shear banding. The microhardness and microstructural analysis of annealed samples are used to study the recrystallization kinetics of the high-manganese steel. It is shown that large plastic deformation and subsequent annealing result in rapid development of recrystallization processes and the formation of an ultrafine-grained structure. A completely recrystallized structure with an average grain size of 0.64 μm forms after 30-min annealing at a temperature of 550°C. No significant structural changes are observed when the annealing time increases to 18 h, which indicates stability of the recrystallized microstructure. The steel cold rolled to 90% and annealed at 550°C for 30 min demonstrates very high strength properties: the yield strength and the tensile strength achieve 650 and 850MPa, respectively. The dependence of the strength properties of the steel on the grain size formed after rolling and recrystallization annealing is described by the Hall–Petch relation.     

钇元素对6.5 % Si无取向硅钢组织、高温拉伸及断裂机制的影响

通过微观组织表征、高温拉伸和断口形貌分析,研究了钇（Y）元素对 6.5 % Si无取向硅钢组织、高温拉伸及断裂机制的影响。研究结果表明,添加Y元素可以在钢液中形成YS和YP的复合析出。YS和YP可以充当异质形核基底,提高形核率,细化凝固组织。热轧组织不均匀,由表层至芯部分别形成等轴晶、等轴晶/拉长晶和拉长晶的混合组织。退火后,热轧变形组织转变为等轴晶,含Y实验钢的退火组织得到明显细化。500 ℃时效处理后,含Y实验钢具备较低的有序度,300 ℃的拉伸断口呈现韧性断裂特征,断后伸长率达到20.2 %。相反,无Y实验钢发生脆性断裂,断后伸长率仅为2.1 %。研究结果证实,Y元素可以通过组织细化和降低有序度提高6.5 % Si无取向硅钢的中温塑性。     

控轧控冷TRIP钢的微观相组成及其与力学性能的关系

采用电子背散射衍射技术等实验方法,研究了控轧控冷工艺制备的铌钒微合金化C-Mn-Si系热轧TRIP钢的显微组织及相组成,并分析了与其对应的力学性能.奥氏体轧制过程中的热变形及随后的冷却工艺对最终各相组织的形貌、大小和分布都有直接影响,并决定TRIP钢最终的力学性能.对TRIP钢卷取温度的模拟结果显示,与450和350℃模拟卷取温度相比,400℃模拟卷取温度能使该钢获得更好的综合力学性能.      

退火温度和平整对冷轧热镀锌双相钢组织和性能的影响

本文在实验室试制了高强度冷轧热镀锌用双相钢,探讨了不同的退火温度和平整工艺对双相钢力学性能和组织的影响规律.研究表明:退火温度在800℃以上时,试制的低硅C-Mn-Cr系双相钢才能得到由铁素体和马氏体组成的性能优良的双相钢.平整工艺显著提高双相钢的屈服强度和屈强比,降低双相钢的延伸率,平整率小于1%时,有利于工业上得到综合性能良好的双相钢.