Influence of Initial Microstructure on Warm Deformation Processability and Microstructure of an Ultrahigh Carbon Steel

Various isothermal compression tests are carried out on an ultrahigh carbon steel(1.2% C in mass percent), initially quenched or spheroidized,using a Gleeble-3500system.The true stress is observed to decrease with increasing temperature and decreasing strain rate.The true stress of the initially quenched steel is lower than that of the initially spheroidized steel at high deformation temperature(700℃)and low deformation strain rate(0.001s-1).The value of the deformation activation energy(Q)of the initially quenched steel(331.56kJ/mol)is higher than that of the initially spheroidized steel(297.94kJ/mol).The initially quenched steel has lower efficiency of power dissipation and better processability than the initially spheroidized steel.The warm compression promotes the fragmentation and the spheroidization of lamellar cementites in the initially quenched steel.The fragmentation of lamellar cementites is the spheroidizing mechanism of the cementites in the initially quenched steel.Results of transmission electron microscope investigation showed that fine grains with high angle boundaries are obtained by deformation of the initially quenched steel.     

超高碳钢组织超细化的工艺

阐述了超高碳钢组织超细化工艺及其机理。这些工艺包括：二阶段热形变处理技术、热形变 离异共析转变处理技术、热形变 DET 形变处理技术、循环热处理技术及复合热处理技术。该超细化组织由极细的铁素体晶粒以及在其中均匀分布的渗碳体颗粒组成。此外，分析了硅、铝、铬等合金元素对相变温度的影响及其对网状碳化物和石墨化的抑制作用，讨论了合金化对超高碳钢的组织超细化的影响。     

细化剂和冷却速率对Al-Mg-Mn合金凝固组织的影响

细化剂含量和冷却速率对凝固过程具有重要影响.分别加入不同含量的Al-3Ti-B晶粒细化剂,研究其对一种Al-Mg-Mn合金晶粒组织的影响.结果表明,随着晶粒细化剂含量的增加,晶粒愈加细小,在本实验范围内当细化剂含量为0.1%Ti时,组织最为均匀细小.采用连续测温的方法,测定了使用不同铸模时,铸锭的冷却速率,并分析了冷却速率对凝固组织的影响.与使用耐火材料铸模相比,使用石墨铸模时,铸锭的冷却速率提高1～2个数量级,铸态组织得到显著细化,平均晶粒尺寸由138μm细化到35μm.     

控轧控冷工艺对低碳铌微合金钢组织和性能的影响

用Gleeble-1500热模拟实验机测定了低碳铌微合金钢变形后的连续冷却转变曲线(CCT曲线),并在实验室对该实验钢采用不同的工艺进行了控制轧制和控制冷却的实验.研究了工艺参数对实验钢力学性能和微观组织的影响,分析了低碳铌微合金钢的强韧化机制.热模拟实验结果表明,实验钢在较宽的冷却速度范围(0.5～30 ℃/s)内可以获得贝氏体组织.控轧控冷的实验结果表明,实验钢的组织主要为铁素体和贝氏体.随着终轧温度的降低,组织得到细化,强度提高,但屈强比也随之增加;降低卷取温度使组织中的贝氏体含量略有增加,强度有所提高.初步探讨了贝氏体对实验钢性能的影响,为制定合适的生产工艺制度提供了依据.     

Effect of Cooling Rate on Microstructure Evolution and Hardness of Steel Balls

Transactions of the Indian Institute of Metals - The objective of this study was to find the effect of cooling rate on microstructure and hardness of steel ball. Steel samples of...     

冷却速度对高强度低合金钢组织和性能的影响

采用热模拟试验机、拉伸试验机以及光学显微镜等设备,根据CCT曲线和拉伸实验的结果,研究了冷却速度对700MPa级超级钢组织和性能的影响。在实验室热轧实验的基础上,比较了500MPa和700MPa两个强度级别HSLA钢的组织和性能随冷却速度的变化情况。结果表明,冷却速度对两种钢的影响不同：冷却速度增大时,500MPa级钢的晶粒明显变细,而700MPa级钢的晶粒尺寸变化不大。     

Cooling Rate Dependence of Boron Distribution in Low Carbon Steel

The behavior of boron (B) segregation to austenite grain boundaries in low carbon steel was studied using particle tracking autoradiography (PTA) and secondary ion mass spectroscopy (SIMS). An effective time method was used to compare the cooling rate (CR) dependence of this segregation during continuous cooling and its time dependence during isothermal holding. Comparison of these segregation behaviors has confirmed that the CR dependence of B segregation agrees well with its time dependence and is mainly a result of the phenomenon of nonequilibrium segregation. Based on the CR dependence of B segregation, the continuous cooling transformation behavior of B-bearing steel as compared with B-free steel was also investigated using dilatometry and microstructural observations. The addition of a small amount of B to low carbon steel retarded significantly the austenite-to-ferrite transformation and finally expanded the range of cooling programs that result in the formation of bainitic microstructures. Analysis of the B distribution has confirmed that this retardation effect of B on ferrite transformation is attributed to the CR dependence of B segregation to austenite grain boundaries during cooling after austenitization.     

Effects of Rolling and Cooling Conditions on Microstructure and Mechanical Properties of Low Carbon Cold Heading Steel

 Effects of rolling and cooling conditions on microstructure and mechanical properties of low carbon cold heading steel were investigated on a laboratory hot rolling mill. The results have shown that the mechanical properties of low carbon steels exceed the standard requirements of ML30, ML35, ML40, and ML45 steel, respectively due to thermomechanical controlled processing (TMCP). This is attributed to a significant amount of pearlite and the ferrite-grain refinement. Under the condition of relatively low temperature rolling, the mechanical properties exceed standard requirements of ML45 and ML30 steel after water cooling and air cooling, respectively. Fast cooling which leads to more pearlite and finer ferrite grains is more critical than finish rolling temperatures for low carbon cold heading steel. The specimen at high finish rolling temperature exhibits very good mechanical properties due to fast cooling. This result has great significance not only for energy saving and emission reduction, but also for low-carbon economy, because the goals of the replacement of medium-carbon by low-carbon are achieved with TMCP.     

Effect of Cooling Patterns on Microstructure and Mechanical Properties of Hot-Rolled Nb Microalloyed Multiphase Steel Plates

 The effect of the run-out table cooling patterns on the microstructure and mechanical properties of Nb microalloyed steel plates was investigated by hot rolling experiment. The results showed that the mixed microstructure containing ferrite, bainite and significant amounts of retained austenite can be obtained through three kinds of cooling patterns on the run-out table under the same hot rolling condition. Three kinds of cooling patterns possess different austenite transformation kinetics, which leads to variations in microconstituent characteristics. The yield strength increases, the tensile strength decreases and the total elongation tends to increase as the cooling patterns Ⅰ, Ⅱ and Ⅲ were applied respectively. The yield strength, the total elongation and the product of tensile strength and ductility reach the maximum values (547 MPa, 37.2% and 28384 MPa·%, respectively) for the steel plate processed by cooling pattern Ⅲ.     

冷却速度对10Ni5CrMo钢组织和性能的影响

采用Gleeble-1500热模拟试验机,建立了10Ni5CrMo钢的连续冷却转变曲线。分析了10Ni5CrMo钢在不同冷却速度下的组织转变规律。结果表明:当冷却速度小于0.2℃/s时,钢中得到粒状贝氏体组织;当冷却速度为0.5℃/s时,组织为粒状贝氏体和下贝氏体;当冷却速度在1～2℃/s时,组织为板条状的马氏体和贝氏体的混合组织;当冷速进一步增大,达到5℃/s时,钢中得到了单一的马氏体组织。为了研究冷却速度对强度和低温韧性的影响,在实验室采用不同冷却方式模拟不同的冷却速度并进行冲击和拉伸试验,试验结果表明:不同冷却方式下钢的强度相差不大,低温冲击韧性有较大提高。对不同冷却方式下的精细结构进行深入分析,马贝混合细化了板条块及板条束。研究认为适当比例的马贝混合组织能提高10Ni5CrMo钢的低温韧性。     

热变形和加速冷却对低碳微合金钢组织的影响

利用Gleeble-1500热模拟实验机研究了热变形和加速冷却工艺对3种低碳微合金钢组织演变的影响,结果表明,在再结晶或未再结晶温区实施1道次变形的晶粒细化效果不如2道次形次的效果明显,在再结晶和再结晶温区实施4道次变形可以得到更细的组织,配合较高的冷却速度可以形成部分针状铁素体组织。随着冷却速度的提高,组织变得更细,并且针状铁素体的数量增加。在相近的变形和冷却条件下,碳、锰含量较高的试样具有更细的组织。     

正火冷速对10MnNiCr船体钢M-A岛和韧性的影响

采用Gleeble试验机模拟了10MnNiCr钢正火处理的连续冷却过程,观察了不同冷速下的显微组织,绘制了CCT曲线,测试了显微硬度和冲击功。结果表明:当该钢以0.167~15℃/s的速度冷却时,形成了M-A岛状组织;随着冷速提高,M-A岛附近的基体组织从粗大的多边形铁素体变为细化的贝氏体铁素体,岛的尺寸减小,与基体之间的硬度差值减小,冲击韧性改善。     

淬火钢件冷却速度、显微组织和硬度分布的计算预报

 利用ANSYS有限元软件计算了多种钢端淬试样和圆柱体零件指定部位的冷却速度。分析了合金元素对冷却速度的影响,表明对于一些热物理性能参数值未知的材料,可以用成分相近的钢的对应参数代替来计算其指定部位的冷却速度。进而结合梅尼尔模型预测了零件指定部位的组织和硬度,所得结果与文献中的数据一致,表明此类方法可用于对钢种化学成分和热处理工艺的并行设计优化。     

Correlation of Cooling Rate,Microstructure and Hardness of S34MnV Steel

Metallurgical and Materials Transactions B - A study of the hardenability, the microstructure and the phase transformations as a function of the cooling rate, of a marine crankshaft S34MnV steel...     

控轧控冷工艺参数对Nb微合金化高碳钢组织的影响

在Gleeble-1500热／力模拟机上模拟了加热温度、变形温度和冷却速度对含Nb和不含Nb高碳钢组织的影响。试验结果表明，0．71％c钢含0．031％Nb时，原始奥氏体平均晶粒尺寸减少30μm左右，再加热粗化温度由1050℃提高至1175℃以上，变形奥氏体再结晶温度由800℃提高到900℃以上。     

冷却速度对无缝钢管热处理组织及性能的影响

文章通过对出热处理炉后的钢管采用空冷和水冷的对比试验,研究了冷却速度对钢管组织结构及力学性能的影响。试验结果表明,加快钢管的冷却速度能够增加相变时的形核率、抑制析出相的聚集和长大,从而达到细化晶粒、改善组织、提高力学性能的目的。     

冷却速率对新型C61齿轮钢力学性能和微观组织的影响

借助光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)、X射线衍射仪(XRD)等设备,通过力学性能测试和显微组织观察,探究炉冷、水冷、石棉缓冷三种不同冷却方式对C61钢热轧态组织和性能的影响,对比不同状态下试验钢的性能。试验结果表明：冷却速度对试验钢的性能影响较大,由于冷却速率V_水冷>V_石棉缓冷>V_炉冷,导致试验钢在水冷条件下强度、硬度均高于炉冷和石棉缓冷处理时的性能;热轧后经水冷,试验钢的抗拉强度(R_m)和断面收缩率(Z%)分别为1450 MPa和62.7%,XRD分析得知,热轧后随冷却速率增加钢的残余奥氏体含量增多,面心立方的奥氏体有利于提升试验钢的韧性。可见,热轧水冷后的试验钢经过950℃加热1 h,水淬,经过-73℃冷处理1 h后,恢复到室温,最后在482℃回火16 h,空冷至室温是最佳工艺方案。     

控制冷却对CSP低碳锰钢组织和性能的影响

利用Gleeble 1500热模拟机测定了簿板坯连铸连轧EAF-CSP工艺生产的低碳含锰钢经奥氏体区二次变形后的CCT曲线.实验钢含有0.17%C,1.21%Mn和0.28%Si(质量分数).研究表明:提高热轧后的冷却速度使Ar_3温度降低,导致试验钢的晶粒进一步细化;冷速大于20℃/s时,出现贝氏体和铁素体的混合组织,可降低钢的屈强比;790℃终轧,550℃卷曲时出现铁素体/珠光体带状组织,提高冷速使溶质(如Mn和C)富集区在形成珠光体之前完成奥氏体—铁素体相变是避免生成铁素体/珠光体带状组织的有效方法.     

中碳钢形变及冷却过程中的组织演变

热模拟单向压缩下,中碳钢形变温度低于Ad3（786℃）点时,析出形变诱导铁素体（DIF）,DIF量随形变温度降低而提高;在低于750℃形变时,DIF量远高于平衡态铁素体含量54％。DIF析出时碳原子高度富集在铁素体晶界和铁素体／奥氏体界面。形变后在低于A1（719℃）温度等温或控冷过程中。过冷奥氏体将发生不同类型的转变：高于Ad3形变试样中,奥氏体转变为铁素体＋片层状珠光体;低于Ad3点但高于Ar3（645℃）点形变时,未转变奥氏体转变为铁素体＋片层状珠光体＋晶界渗碳体;稍高于Ar3点形变时,将获得铁素体＋弥散渗碳体的球化组织。