热轧条件下产生的15MnV 钢混晶

本文用定量金相的方法研究了钢坯加热温度和热轧工艺参数是如何影响奥氏体和铁素体混晶,以及奥氏体混晶在热轧期间的变化趋势,目的在于为制定控制轧制工艺提供参考依据。     

微合金化热轧低硅多相钢的组织与性能

为了开发微合金化热轧低硅多相钢,在不含替代硅的合金元素的化学成分设计基础上,通过热轧实验研究了终冷温度对显微组织和力学性能的影响。结果表明,终冷温度从420℃升高到500℃,均可得到多相组织,其中残余奥氏体量增加了6.5%,马氏体消失,组织中出现大量的贝氏体。当实验钢的轧制工艺参数和开冷温度相近时,组织中的铁素体量、铁素体平均晶粒尺寸大致相同,终冷温度对其硬相特性以及残余奥氏体的分布有很大影响。终冷温度为470℃时,硬相特性及残余奥氏体的分布匹配良好,其屈服强度、延伸率、强塑积分别达到460 MPa、31.3%和21 754 MPa·%。     

轧制工艺对钒铌微合金化钢显微组织的影响

应用Gleeble—1500热模拟试验机对V、Nb复合微合金化钢进行了模拟轧制,测定了形变奥氏体的动态再结晶曲线,研究了轧制工艺对铁素体晶粒大小和亚结构的影响,从而确定了能够获得细小铁素体—珠光体组织的V、Nb含量及与之相应的轧制工艺。     

控制轧制工艺参数对15MnV钢奥氏体状态和铁素体组织的影响

本文研究了热轧工艺参数对15MnV钢奥氏体再结晶行为,奥氏体状态和铁素体组织的影响。实验结果表明,由于奥氏体的形变和再结晶细化,铜坯的加热温度对轧后奥氏体晶粒大小影响不大。在奥氏体的完全再结晶温度范围内,形变量对再结晶百分数有显著的影响。低于完全再结晶温度范围,则热轧温度的影响将会变得更为重要。随着形变温度的下降或形变量增大,奥氏体晶粒内的形变带密度将增大,铁素体晶粒将细化。     

热穿-热轧法生产的新型贝氏体中空渗碳钢的组织和性能

用热穿-热轧法制备了新型贝氏体中空钢．研究了热处理对新型贝氏体钢和渗碳处理对中空钢组织和性能的影响．结果表明：新型贝氏体钢正火＋低温回火热处理后的组织为贝氏体铁素体和奥氏体,淬火＋低温回火后的组织由马氏体、贝氏体和奥氏体组成;正火或淬火＋低温回火后,新型贝氏体中空钢具有良好的强韧性．正火＋低温回火后,中空钢的组织为贝氏体铁素体和残余奥氏体组织．新型贝氏体中空钢渗碳后空冷,渗层的组织为高碳马氏体和残余奥氏体组织,非渗层为贝氏体铁素体和残余奥氏体组织,实体中空钢具有较好的强韧性和渗碳效果．     

304/Q235B热轧复合板界面的显微组织特征

采用金相显微镜、扫描电镜和透射电镜等手段研究304/Q235B热轧复合板复合界面处的显微组织特征、元素分布以及过渡层的微观组织。结果表明:304/Q235B热轧复合板复合界面附近的组织由不锈钢基体的奥氏体、5μm厚的过渡层、50μm厚脱碳层的铁素体和碳钢基体的铁素体+珠光体等4个部分组成;界面存在Cr、Ni、C等合金元素的扩散区,并形成明显的元素分布曲线;过渡层的微观组织含高密度位错的板条马氏体,且马氏体板条中存在大量细小的针状M3C型碳化物。     

基于神经网络的微合金钢热轧奥氏体晶粒尺寸预报模型

基于神经网络原理，对微合金钢热轧控制参数的选取进行了研究。制订了一套获取样本数据的实验方案。该方案利用Gleeble-1500热力模拟机提取了轧制温度、应变量、应变速率和相应的应力应变曲线，并通过显微观察获取了实验后样品断面的奥氏体晶粒尺寸。通过归一化把实验所得数据进行必要的处理。采用改进BP算法训练网络，对热轧控制参数（轧制温度、应变量、应变速率）和描述微合金钢组织性能的参数（奥氏体晶粒尺寸）之间的映射关系进行了函数逼近，建立了奥氏体晶粒尺寸流变应力神经网络模型，实践证明，将该神经网络模型运用于热轧控制预报，提高了预测精度并取得较好的效果。     

用低碳钢制备表层铁素体金相显微试样

提出了一种用常规低碳钢代替工业纯铁制备铁素体金相显微试样的方法.阐述了铁素体、渗碳体、珠光体的组织特征.利用碳钢在无保护加热时表层易产生脱碳这一特点,使低碳钢脱碳后表层变为单相铁素体,从而获得了表面与工业纯铁效果相同的金相显微组织.     

冷变形共析钢的显微组织与织构探讨

为了探讨共析钢冷变形显微组织和织构,对严重塑性变形的共析钢进行一定的热处理获得了一定形状与亚微米尺寸的渗碳体样品,然后对上述样品进行不同形变量轧制,获得了显微组织与织构的分析样品,采用场发射扫描电镜(FE-SEM)和织构衍射仪(XRD)对轧制样品进行显微组织和形变织构的分析.研究结果表明:对冷轧高碳钢的退火,可以发现层片状渗碳体数量减少,粒状渗碳体数量增多,形成了两种形状的渗碳体与铁素体共存的复相显微组织样品.冷轧过程中,铁素体晶粒被拉长并逐渐发展为纤维状;渗碳体晶粒大小与形状变化不大,分布较均匀.随着形变量的增加,共析钢中主要织构逐渐形成了由<110>//RD(轧向)的α-纤维织构和<111>//ND(轧面法向)的γ-纤维织构组成,晶粒取向逐渐聚集到{558}<110>以及{001}<110>等主要织构组分类型.     

淬火温度对X80管线钢组织影响分析

采用双相区加速冷却法(DPAC),X80管线钢经奥氏体化及缓冷后分别在760、740、720、700、680℃淬火。淬火组织分别经4%硝酸酒精与LePera试剂进行金相腐蚀,分别进行组织定性/定量分析及整体/组织硬度测试。结果表明,不同淬火温度下组织为多边形铁素体+针状铁素体+贝氏体/马氏体复相组织。与硝酸酒精腐蚀的微观结构相比,LePera试剂可清晰显示马氏体/奥氏体组织,但铁素体晶界模糊。随淬火温度下降,铁素体晶粒尺寸与含量增加;针状铁素体逐渐向贝氏体/马氏体复相组织转化;马氏体/奥氏体岛状组织分布上由铁素体/贝氏体两相晶界间向铁素体同相晶界间转变,组织形态上由薄膜状向颗粒状转变。     

热轧TRIP钢的组织与力学性能研究

采用热轧后控制冷却的工艺制备了TRIP钢，拉伸试验表明，试验钢的性能为：σb=605 MPa，σs=440 MPa，δ=28．4％；对试验钢的组织进行了研究，定量金相检测结果表明，试验钢中残余奥氏体含量为5．6％．     

Grain refinement of low carbon steel produced by CSP process

In comparison with conventional production for hot strips, compact strip production (CSP) brings about some new micro-structural phenomena. Investigations were carried out to clarify the grain refinement mechanism of low carbon steel strips produced by the EAF-CSP process. Samples, obtained from the same rolling stock during continuous rolling, were examined through SEM,TEM and XEDS. Thin slabs have a dominant columnar structure and the spacing of the secondary dendrite arms ranges from 90 to ～125 μm. The average grain sizes for the central area of the samples from the 1st to 6th pass are 41.6, 25.2, 21.4, 20.2, 13.1, 6.7 μm,respectively. Large number of nanometer oxide and sulfide have been found in the low carbon steel produced by the CSP process.The grain refinement mechanism can be summarized as follows: finer solidification structure of the thin slab; austenite recrystalliza-tion at higher temperature and stain accumulation at lower temperature caused by the great reduction of single rolling pass during continuous rolling; nano-scaled precipitates of sulfide and oxide which drag grain boundaries of austenite or ferrite to prevent the grain coarsening.     

Precipitation characteristic of high strength steels microalloyed with titanium produced by compact strip production

Transmission electron microscopy (TEM) and physics-chemical phase analysis were employed to investigate the precipitates in high strength steels microalloyed with Ti produced by compact strip production (CSP). It was seen that precipitates in Ti microalloyed steels mainly included TiN, Ti4C2S2, and TiC. The size of TiN particles varied from 50 to 500 nm, and they could precipitate during or before soaking. The Ti4C2S2 with the size of 40-100 nm might precipitate before rolling, and the TiC particles with the size of 5-50 nm precipitated heterogeneously. High Ti content would lead to the presence of bigger TiC particles that precipitated in austenite, and by contrast, TiC particles that precipitated in ferrite and the transformation of austenite to ferrite was smaller. They were less than 30 nm and mainly responsible for precipitate strengthening. It should be noted that the TiC particles in higher Ti content were generally smaller than those in the steel with a lower Ti content.     

Microstructure and strengthening parameters of ultra—thin hot strip of low carbon steel

The microstructure and precipitation mechanism of ultra-thin hot strip produced by CSP technology were analyzed by electron back scattered diffraction(EBSD),H-800 transmission electron microscope(TEM) and thermodynamics theory.The EBSD results show that the finishing hot rolling microstructures are mixture of recrystallized and deformed austenite.After phase transformation,ferrite grains embody subastructures and dislocations that led ultra-thin hot strip high strength and relatively low elongation rate.TEM observations show that there are a lot of fine and dispersive precipitates in microstructures.Most of aluminium nitrides are in grains.While coexisted precipitates of MnS along grain boundaries,Coexisted precipitates compose cation-vacancy type oxides such as Al2O3 in the core,while MnS at the fringe of surface.At the same time,reasons for microstructure refinement and strengthening effect were invstigated.     

Influence of hot rolling conditions on the mechanical properties of hot rolled TRIP steel

Influence of hot rolling conditions on the mechanical properties of hot rolled TRIP steel was investigated. Thermomechanical control processing （TMCP） was conducted by using a laboratory hot rolling mill, in which three different kinds of finish rolling temperatures were applied. The results show that polygonal ferrite, granular bainite and larger amount of stabilized retained austenite can be obtained by controlled rolling processes. The finer ferrite grain size is produced through the deformation induced transformation during deformation rather than after deformation, which affects the mechanical properties of hot rolled TRIP steel. Mechanical properties increase with decreasing finish rolling temperature due to the stabilization of retained austenite. Ultimate tensile strength （UTS）, total elongation （TEL） and the product of ultimate tensile strength and total elongation （UTS×TEL） reaches optimal values （791 MPa, 36% and 28 476 MPa%, respectively） when the specimen was hot rolled for 50% reduction at finish rolling temperature of 700 ℃.     

薄板坯连铸连轧工艺生产的低碳钢冷轧基板力学特性

以采用薄板坯连铸连轧工艺生产的低碳钢作为冷轧基板,在实验室二辊可逆轧机上进行不同程度的冷变形,对不同变形后的冷轧板进行室温拉伸试验和显微硬度值测定,分析了其加工硬化情况,并对不同冷变形后试验钢的显微组织进行分析。结果表明:低碳钢经冷变形后,屈服强度和抗拉强度增大,加工硬化显著;试验钢的显微组织为铁素体和少量的珠光体,晶粒随着变形量的增大而拉长细化。     

Effect of deformation and cooling rate on the transformation behavior and microstructure of X70 steels

The effects of the deformation in the non-recrystallization region of austenite and the cooling rate on the transformation behavior and microstructure of low-carbon low-alloy steel for pipeline application were studied on the thermal-mechanical simulator Gleeble-1500. It was shown that an increase in deformation amount can greatly increase the nucleation site of ferrite when deformed in the non-recrystallization region of austenite, and an increase in nucleation ratio can greatly refine grains. When the cooling rate is accelerated, the driving force of nucleation is increased and the nucleation rate also improves. Ultra-refine grains can be obtained by controlled rolling. The high density of ferrite nucleus, which forms along the austenite grain boundary, twin interface, and deforma- tion band are introduced in the matrix of austenite by the control of hot rolling, after which the microstructure can be refined. It was found that the acicular ferrite has a very fine sub-structure, high dislocation density, and a thin slab with ultra-fine grains. Small M/A islands and cementite are precipitated on the matrix of the slabs by the analysis technique of TEM and SEM.     

Microstructures and properties of 550 MPa grade high strength thin-walled H-beam steel

The microstructures and mechanical properties of 550 MPa grade lightweight high strength thin-walled H-beam steel were experimentally studied. The experimental results show that the microstructure of the air-cooled H-beam steel sample is consisted of ferrite, pearlite and a small amount of granular bainites as well as fine and dispersive V（C,N） precipitates. The microstructure of the water-cooled steel sample is consisted of ferrite and bainite as well as a small amount of fine pearlites. The microstructure of the water-cooled sample is finer than that of the air-cooled sample with the average intercept size of the surface grains reaching to 3.5 gna. The finish rolling temperature of the thin-walled high strength H-beam steel is in the range of 750 ~C-850 ~C. The lower the finish rolling temperature and the faster the cooling rate, the finer the ferrite grains, the volume fraction of bainite is increased through water cooling process. Grain refinement strengthening and precipitation strengthening are used as major strengthening means to develop 550 MPa grade lightweight high strength thin- walled H-beam steel. Vanadium partially soluted in the matrix and contributes to the solution strengthening. The 550 MPa grade high-strength thin-walled H-beam steel could be developed by direct air cooling after hot rolling to fully meet the requirements of the target properties.     

7．9Mn－1．4Si－0．07C钢高强韧机理研究

通过热轧、温轧、奥氏体化、两相区退火处理得到7．9Mn－1．4Si－0．07C钢板,该材料的拉伸强度及塑性随奥氏体化温度不同而具有显著差异．奥氏体化温度降低,室温下奥氏体含量升高,综合力学性能提高．当奥氏体化温度由900℃降低为800℃时,所得到钢板的奥氏体体积分数由15％增加到28％,拉伸强度由1150MPa提高到1340MPa,塑性由21％提高至27％．实验钢优异的力学性能源于其中大量的超细铁素体及奥氏体,细晶强化使其具有超高强度,铁素体基体及变形过程中奥氏体向马氏体相变提供了良好的塑性．基体组织中的位错强化,形变诱导马氏体转变的TRIP效应等是增强该钢板加工硬化能力的主要因素．