分段冷却工艺对低碳钢中板力学性能的影响

轧机轧制能力不足时无法完成真正意义上的控轧控冷,设计适当的生产工艺以最大限度地提高产品力学性能十分必要。研究了控制冷却工艺对低碳钢力学性能和微观组织的影响。与空冷相比,采用控制冷却工艺进行冷却,可以提高试验钢的力学性能,减轻试验钢的带状组织。在控制冷却过程中,除开始冷却温度对试验钢的性能影响较大外,分段冷却工艺参数对试验钢性能的提高也起很大作用。结果表明:采用前段冷却为主的工艺生产的试验钢较采用后段冷却为主的工艺生产的试验钢的屈服强度提高50 MPa以上,抗拉强度提高约30 MPa,同时拥有良好的塑性和低温韧性。     

层冷工艺和卷取温度对700 MPa大梁钢组织性能的影响

对700 MPa级汽车大梁钢进行了热轧试验,采用光学显微镜、扫描电镜和能谱仪等设备研究了不同的层冷工艺和不同的卷取温度对试验钢组织和力学性能的影响.结果表明,在轧后不同的冷却工艺中,前段集中冷却模式所得到产品强度高于后段集中冷却模式所得到的产品强度,两段冷却模式所得到产品强度最优;在相同的冷却模式条件下,降低卷取温度,...     

不同冷却制度下X100管线钢组织特征及力学性能

采用热模拟试验机和试验轧机研究了X100管线钢连续冷却相变规律及不同冷却制度下显微组织特征及力学性能变化规律.研究结果表明:随冷却速度升高及终冷温度降低,试验钢显微组织由针状铁素体过渡至板条贝氏体及马氏体,非淬火条件试验钢中马氏体岛或M-A岛为微孪晶马氏体;轧制后直接以30℃/s冷却至450℃左右时,试验钢具有良好强韧...     

热轧条件下Nb-Mo及Nb微合金化X100管线钢的组织特征及力学行为

采用实验室热轧、显微分析及力学性能检测手段,对Nb-Mo及Nb微合金化X100管线钢在不同工艺条件下的组织特征及力学行为的变化规律进行了研究.分析结果表明:工艺参数对Nb-Mo复合成分试验钢影响较大,控轧控冷工艺条件下Nb-Mo及Nb微合金化X100管线钢力学性能均能达到API 5L中X100管线钢要求,但Nb-Mo复合成分力学性能富余量较大,性能较优.随冷却速度的增加及终冷温度的降低,试验钢强度增加,韧性及塑性恶化.板条马氏体与贝氏体复相组织较板条马氏体可大大提高试验钢的塑性及低温冲击韧性.     

抗震耐火钢Q420FRE动态CCT曲线及组织研究

为研究抗震耐火钢Q420FRE的生产工艺,采用膨胀法测定了临界转变温度Ac1、Ac3;使用Gleeble-3800型热模拟试验机测定了不同冷却速度下连续冷却转变过程,记录温度体积变化曲线,并结合试验钢金相组织和硬度变化分析在不同冷却速度下的组织转变区间和组织转变类型,绘制出该钢的动态CCT曲线,为该钢的控轧控冷生产提供科学指导。     

轧后冷却条件对低碳贝氏体钢组织性能的影响

 为了研究轧后不同冷却条件对高强低碳贝氏体钢组织和性能的影响,采用热模拟试验、扫描电镜、透射电镜和拉伸试验等手段,阐明不同冷却条件下高强低碳贝氏体钢的组织和性能变化规律。结果表明,在终冷温度为510 ℃时,组织以粒状贝氏体为主,终冷温度为450 ℃时以板条状贝氏体为主,前者组织中具有更多岛状马氏体;随着冷却速率提高,粒状贝氏体和板条状贝氏体尺寸细化,岛状马氏体减少。此外,不同冷却速率下,较低的终冷温度均具有更高的相变速率,冷却速率为50 ℃/s时,贝氏体相变速率最大。另外,终冷温度较高时,试验钢呈现出更好的塑性,强度随冷速变化较小;终冷温度较低时,试验钢呈现出更高的强度,但塑性较低,冷却速率对强度有较大的影响。     

宝钢1880mm热轧试生产DP600双相钢的组织性能

采用Si-Mn系简单成分设计,充分发挥宝钢1 880 mm热连轧机组的密集冷却能力和卷取能力,通过密集水冷—空冷—水冷的三段式冷却模式和低温卷取,成功实现在1 880 mm机组工业试生产600 MPa级热轧双相钢。结果表明,通过合理的冷却速度、中间待温温度和待温时间配合,试验钢可获得铁素体和马氏体比例适合的双相组织,力学性能满足600 MPa级双相钢设计要求;同时试验发现,冷却和卷取工艺显著影响双相钢的微观组织和性能,因轧速变化造成钢卷头尾冷却条件不一致,导致钢卷不同位置力学性能波动较大。     

TMCP工艺对微合金高强度钢组织性能的影响

  在实验室条件下,对一种微合金高强度钢进行热膨胀试验和热轧试验,测定了该试验钢的连续冷却转变动力学(CCT)曲线,并研究了不同温度转变的组织和第二相的体积分数、尺寸对其力学性能的影响。试验结果表明：变形温度的降低,贝氏体转变开始温度与转变结束温度均升高,硬度值也出现不同程度的提高;变形温度的降低,使得不同冷却速度下组织细化程度存在明显差异。利用合理控轧控冷工艺,使得屈服强度均达到690MPa以上,-30℃冲击功均达到230J以上。其中,第二相粒子在整个基体内呈细小弥散分布,起到有效的强化作用并改善钢的冲击韧性。     

组织状态对X120管线钢力学性能的影响

在实验室条件下对热轧X120管线钢进行两种不同工艺淬火,研究了回火温度对不同淬火态试验钢组织力学性能的影响。试验结果表明:直接快冷工艺下,显微组织以板条铁素体+马氏体为主;缓冷+直接快冷工艺下以粒状贝氏体+板条铁素体+马氏体为主。随回火温度升高,两种试验钢强度均出现起伏,在400~500℃范围内回火后,冲击功和伸长率均得到改善;采用直接快冷工艺在350℃和600℃回火后出现断口分离现象,从而导致力学性能波动,而缓冷+快冷工艺在回火过程中力学性能稳定性较好。因此,采用缓冷+快冷工艺+(450~500℃)回火,其力学性能达到X120级管线钢性能要求。     

核岛用P280GH钢的冷却相变过程及数值模拟

 为了研究核岛用P280GH钢管热轧成形后的冷却过程组织演变,采用物理模拟方法建立了CCT和TTT相变动力学曲线。结果表明,低冷速会形成粗大铁素体和珠光体,增大冷速可细化低温相组织,当冷速超过10 ℃/s时即开始出现贝氏体组织。运用叠加原理,基于有限元法,建立了试验钢冷却过程数值模型,分析了[?]219.1 mm×18.26 mm规格P280GH钢管在空冷和水冷两种冷却过程沿壁厚方向温度场、组织演变规律。结果显示,空冷条件相变组织为均匀的珠光体、无贝氏体和残余奥氏体;水冷条件获得相变组织为马氏体组织,管内外表面体积分数相差3.6%,计算结果与实际热处理工况基本一致。研究结果可为热轧P280GH钢管生产的控冷工艺提供指导。     

Comprehensive Control on Microstructures and Properties of Medium Carbon V-N Microalloyed Steel Seamless Oil-Well Tubes of Hot-Rolling Non-Quenched/Tempered

The relationship between microstructures and mechanical properties of a medium carbon V-N microalloyed steel used for N80 seamless oil-well tubes of hot rolling non-quenched/tempered (non-Q and T) was investigated.The results have shown that volume percentages of upper bainite,modified bainite and ferrite have a decisive influence on impact energies of steel tubes.When the total volume percentage of bainite is larger than 5%,the impact energy of tubes can not satisfy with the industrial criteria.Moreover,if the total volume percentage of bainite is smaller than 5%,then the impact energy of steel tubes enhances with volume percentage of ferrite increasing.The final microstructures have closely relation with tube billet quality,controlled cooling temperature after tube rolling and cooling method after stretch-reduction-diameter.High quality of medium carbon V-N microalloyed steel for non-Q and T oil-well tubes can be produced through comprehensive control of microstructures and mechanical properties in sub-procedures,especially for tube billet quality and controlled cooling parameters.     

Influence of Heat Treatment on Hydroformability of TRIP Seamless Steel Tube

A low-carbon TRIP seamless steel tube, which is expected to be used in the hydroforming process, was successfully fabricated using piercing, cold-drawing and two-stage heat treatment process. The two-stage heat treatment is one crucial step because it significantly affects the microstructure and mechanical properties of TRIP seam less steel tube. In order to obtain the TRIP seamless steel tube with high hydroformability, several different heat treatment processes were conducted. The effects of heat treatment conditions （intercritical annealing （IA） and isothermal bainite treatment （IBT）） on the TRIP seamless steel tube hydroformability which was determined by free hydraulic bulge test were analyzed. Two different internal pressure boosting velocities of 0.2 and 0.5 MPa/s of free hydraulic bulge tests were adopted to determine the effective stress vs. effective strain curve of TRIP seamless steel tube. The results showed that for the predetermined IA condition, the maximum bulge height increased, but the maximum burst internal pressure decreased, with the increase of IBT holding time from 4 to 6 rain. For the predetermined IBT condition, the maximum bulge height decreased, but the maximum burst internal pressure increased, with the increase of IA holding time from 5 to 10 rain. By analyzing the free hydraulic bulge test results, it was found that the maximum bulge heights of TRIP seamless steel tubes with the internal pressure boosting velocity of 0.5 MPa/s were higher than those when the internal pressure boosting velocity was 0.2 MPa/s. This means that an appropriate deformation rate should be chosen to obtain the optimal hydroformability of TRIP seamless steel tube. In addition, the effective stress vs. effective strain curves of TRIP seamless steel tubes were ohtained with free hydraulic bulge test.     

Comparison of Austenite Decomposition Models During Finite Element Simulation of Water Quenching and Air Cooling of AISI 4140 Steel

An indigenous, non-linear, and coupled finite element (FE) program has been developed to predict the temperature field and phase evolution during heat treatment of steels. The diffusional transformations during continuous cooling of steels were modeled using Johnson–Mehl–Avrami–Komogorov equation, and the non-diffusion transformation was modeled using Koistinen–Marburger equation. Cylindrical quench probes made of AISI 4140 steel of 20-mm diameter and 50-mm long were heated to 1123 K (850 °C), quenched in water, and cooled in air. The temperature history during continuous cooling was recorded at the selected interior locations of the quench probes. The probes were then sectioned at the mid plane and resultant microstructures were observed. The process of water quenching and air cooling of AISI 4140 steel probes was simulated with the heat flux boundary condition in the FE program. The heat flux for air cooling process was calculated through the inverse heat conduction method using the cooling curve measured during air cooling of a stainless steel 304L probe as an input. The heat flux for the water quenching process was calculated from a surface heat flux model proposed for quenching simulations. The isothermal transformation start and finish times of different phases were taken from the published TTT data and were also calculated using Kirkaldy model and Li model and used in the FE program. The simulated cooling curves and phases using the published TTT data had a good agreement with the experimentally measured values. The computation results revealed that the use of published TTT data was more reliable in predicting the phase transformation during heat treatment of low alloy steels than the use of the Kirkaldy or Li model.     

H65黄铜管冷轧变形模拟分析与实验研究(续)

图3-b可以看出,孔型脊部区域的管坯内表面温度明显高于外表面,这主要是由于外表面摩擦较小,而内表面的摩擦相对较大,产生的摩擦热远远大于外表面。由此可知,对于减壁量不大的皮尔格冷轧管,引起金属温度变化的主要因素不是塑性功的转化而是由于摩擦所引起的,因此实际生产中应加强对管坯表面的润滑,以免产生过高的温升。H65黄铜在200℃～700℃会发生脆性转变,如果实际冷轧管生产中,管坯变形区的温度出现如图3所示的情况,即使工作应力较小,也可能超过材料此时的强度极限,从而产生如图4所示的周期性横向裂纹。     

相变潜热对ф160mm GCr15轴承钢棒材控冷工艺的影响

利用MSC.Marc软件,对直径ф160mm GCr15轴承钢喷水冷却过程的温度场进行模拟分析。利用编写的ufilm和flux子程序,将相变潜热以内热源的方式添加到温度场。通过分析棒材在不同相变潜热取值下沿径向的温度变化情况,理论探讨了相变潜热对控冷工艺的影响。结果表明:相变潜热显著减缓了棒材的冷却速度,且越接近棒材芯部相变潜热引起的温升越大。考虑相变潜热时,原来的控冷方案不满足工艺要求。因此,在模拟研究控冷时,就本文理论探讨的GCr15轴承钢棒材的控冷工艺来看,相变潜热不应忽略。     

层流冷却工艺对NM300TP热轧耐磨钢组织性能的影响

为探究NM300TP热轧耐磨板最佳冷却工艺,采用两段式冷却工艺,通过控制中冷温度和空冷时间,得到不同冷却工艺下的轧板.轧板具有贝氏体+铁素体+残余奥氏体的三相组织,无需轧后热处理便可获得良好的综合力学性能.研究结果表明,耐磨钢中各相含量与其力学性能有明显的对应关系,贝氏体越多,布氏硬度越大,抗拉强度越高,磨损失重越小,...     

CT20钛合金管材的冷轧工艺及组织性能的研究

研究了CT20低温钛合金管材的加工工艺及冷轧变形量、退火温度对管材力学性能的影响。结果表明：CT20合金对加工硬化不敏感,冷轧最大变形量应控制在45％以内;CT20合金管材通过不同温度热处理所获得的等轴、双态和片状组织的室温力学性能差别不大;20K低温下由于孪生变形的发生,片状组织的塑性最好,双态组织则介于片状和等轴组织之间;管材为等轴和双态组织时,冷成型性能优异;对管材进行αt＋β两相区910℃×1h,FC的热处理,可获得综合性能优良的双态组织。     

热处理对N06230合金无缝管组织及抗拉强度的影响

 为了探索合金无缝管的热处理工艺,采用光学显微镜(OM)、扫描电镜(SEM)、室温拉伸试验等方法,研究了热处理工艺对N06230高温合金冷轧无缝管的组织和抗拉强度的影响。通过OM、SEM表征方法,分析了温度为1 200～1 300 ℃、保温0.5～5.0 h时M₆C型碳化物面积百分比及晶粒尺寸变化规律,并建立了晶粒尺寸长大动力学模型。结果表明,该合金中有很多富钨的M₆C型碳化物,横向呈现颗粒状弥散分布,沿轧制方向呈链状分布,部分M₆C型碳化物呈椭圆状特征,面积百分比约为1.97%。随着热处理温度的升高及保温时间的延长,无缝管的抗拉强度逐渐降低。     

Effect of Isothermal Bainite Treatment on Microstructure and Mechanical Properties of Low‐Carbon TRIP Seamless Steel Tube

In this work, a low‐carbon transformation‐induced‐plasticity (TRIP) seamless steel tube (Fe–0.15C–1.34Si–1.45Mn–0.029Nb–0.024Ti, in wt%), having potential in application of hydroforming process, has been successfully manufactured by using piercing, cold‐drawing, and two‐stage heat‐treatment process. The optimal heat‐treatment conditions, inter‐critical annealing (IA), and isothermal bainite treatment (IBT) were firstly obtained to maximize the volume fraction and stability of the retained austenite (RA). The effects of temperature and holding time IBT on the microstructures of the TRIP steel tube were studied via optical microscopy (OM), scanning microscopy (SEM), transmission electron microscopy (TEM), and X‐ray diffractometer (XRD). The mechanical properties in the axial direction and hydroformability were also evaluated by conventional tensile test and flaring test, respectively. Two‐stage heat‐treatment was finally performed to achieve the required mechanical properties for the hydroformed tube. The results shows that the RA volume fraction increased at first and then decreased with the increase of IBT holding time and IBT temperature for a particular set of IA temperature and IA holding time. It was also demonstrated that high tensile strength of 618 MPa, total elongation of 35.5%, n‐value of 0.23, and better hydroformability could be successfully produced in this TRIP steel tube at IA temperature of 800°C, holding for 10 min, and IBT of 410°C for 4 min holding time.