The Effect of Pre-Deformation at Elevated Temperatures on the Microstructure and Hardness of Boron Steel 22MnB5

To investigate the effects of the pre-deformation and deformation temperature on the microstructure and hardness of boron steel 22MnB5,isothermal tensile tests were carried out on the Gleeble 3800 system when the temperatures are 700℃,750℃,800℃,respectively.Three specimens were employed to obtain different deformation levels at each temperature.The cooling rate before and after deformation was 30℃/s.Then the microstructures of the specimens were observed and the harness of each specimen was measured.The results show the martensitic fraction decreases and the ferrite fraction increases with decreasing the deformation temperature or increasing the deformation level.The specimens deformed at higher temperature have greater hardness.The hot plastic deformation of austenite shortens the incubation period of ferrite transformation and accelerates the transformation rate.In addition,the isothermally holding time is longer in the case of a larger deformation amount,more austenite will transform to ferrite.Especially,the specimen deformed at 700℃ and with large deformation has almost full massive ferrite microstructure with larger size.     

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。     

含硼微合金钢奥氏体热变形行为

采用单道次压缩实验方法，通过Gleebe-1500热模拟试验机对成分(％)为：0．05C，1．57Mn，0。50Cu，0.05Nb，0．014H，0．0012B微合金化钢进行800～1100℃应力．应变曲线和再结晶组织演变的试验研究，建立了动态再结晶临界应变和晶粒尺寸模型。得出降低变形温度或提高变形速率可明显细化该微合金化钢的晶粒。     

Ti微合金钢热变形后连续冷却相变及第二相析出行为

采用热力模拟试验技术、金相显微镜(OM)、扫描电镜(SEM)及透射电镜(TEM),并结合宏观硬度测试,研究了钛微合金钢形变奥氏体的连续冷却相变和组织演变规律,建立了试验钢连续冷却转变曲线,探讨了不同冷速对第二相析出的影响。结果表明,不同冷速下,试验钢获得了不同的微观组织,随冷速增加,第二相析出量增多,尺寸更细小,但冷速过高,析出被抑制。     

Modeling of Microstructure Evolution in 22MnB5 Steel during Hot Stamping简

Automobile manufacturers have been inereasingl~r adopting hot-stamped parts for use in newly designed ve- hicles to improve crash worthiness and fuel efficiency. However, the simulation of hot stamping is rather complex and challenging, and further research still needs to be done on hot stamping hardening mechanism. The microstruc- ture evolution and hardening mechanisms during hot stamping of 22MnB5 steel were thoroughly investigated, using information provided in the literatures as well as experimental results. New models were developed to predict the grain growth during heating and the flow stress of a manganese boron steel （22MnB5） with high hardenability by the Gleeble simulation experimental results. The deformed austenite decomposition during stamping and quenching was emphatically quantified based on the transformation thermodynamic and kinetic theories, and the relationship of mi- crostructure to properties was analyzed. The results showed that the optimal process to obtain homogeneous and small lath martensite is heating at 900--950 ℃ for 5 min and then auenching at 50 ℃/s with a Dressing time about 8 s.     

Effect of Austenite Deformation on Continuous Cooling Transformation Microstructures for 22CrSH Gear Steel

 The effect of compressive deformation of austenite on continuous cooling transformation microstructures for 22CrSH gear steel has been investigated using a Gleeble 1500 thermal simulator. The experimental results show that the deformation of austenite promotes the formation of proeutectoid ferrite and pearlite, and leads to the increase of critical cooling rate of proeutectoid ferrite plus pearlite microstructure. The grain boundary allotriomorphic ferrite occupies the austenite grain surfaces when the prior deformation takes place or the cooling rate is decreased, which causes a transition from bainite to acicular ferrite. The deformation enhances the stability of transformation from austenite to acicular ferrite, which results in an increase of M/A constituent.     

贝氏体型非调质钢热变形奥氏体的连续冷却转变

研究了一种Ｍｎ－Ｂ系低碳贝氏体型非调质钢热变形奥氏体的连续冷却转变,得到了实验用钢热变形奥氏体的连续冷却转变曲线。结果表明,本实验用钢热变形奥氏体不发生先共析铁素体析出的临界冷却速度为１．５ ℃／ｓ;冷却速度在１．５～７ ℃／ｓ范围内可全部得到贝氏体组织;当冷却速度大于７ ℃／ｓ时,不再生成贝氏体,室温组织为马氏体和残余奥氏体。     

变形工艺对V、Ti微合金钢连续冷却相变的影响

采用Gleeble-1500热模拟实验机,结合显微硬度测试,建立了含V、Ti微合金钢的未变形和50%形变奥氏体的CCT曲线.利用光学显微镜、透射电镜分析研究了冷却速度、变形条件及微合金元素对显微组织的影响.结果表明,变形使铁素体 珠光体相变区左移,获得铁素体 珠光体组织的临界冷速增大.变形也使贝氏体相变温度有所提高,同时在较高的冷速下,变形可使显微组织变得更加细小.V、Ti的复合添加,提高了过冷奥氏体的稳定性,使相变温度降低,有利于得到细小的组织.     

Influence of Isothermal Deformation Conditions on The Mechanical Properties of 22MnB5 HPF Steel

In the present study, the aluminized 22MnB5 Hot Press Forming (HPF) steel was deformed isothermally in the temperature range of 600–800 °C. The specimens were deformed with 0%, 10% and 30% engineering strain at a strain rate of 0.5/s. Mechanical stabilization of austenite during phase transformation was observed. The influence of strain rate was also studied. It was found that the martensite transformation was affected by the combined effect of mechanical stabilization and dynamic recovery. The influence of high temperature deformation on the final microstructure, microhardness and mechanical properties were studied. Deformation applied below 750 °C resulted in a significant decrease of the strength and the hardness. The ferrite fraction and morphology had a clear effect on the room temperature tensile fracture morphology.     

热变形对86CrMoV7钢过冷奥氏体连续冷却转变的影响

用Ｆｏｒｍａｓｔｅｒ－Ｆ全自动膨胀信和ＴＨＥＲＭＥＣＭＡＳＴＯＲ－Ｚ热模拟试验装置测定了８６ＣｒＭｏＶ７钢未变形和奥氏体、一次变形奥氏全和二次变形奥氏体的ＣＣ一。结果表明，试验用钢只发生珠光体转变和马氏传转变；热变形明显地促进珠江体、马氏体转变；不发生珠光体转变的临界冷却速度由０．７６Ｃ／ｓ（未变形）提高到３．１Ｃ／ｓ（一次变形）和１．５Ｃ／ｓ（二次变形）；Ｍｓ点由１４３Ｃ（未变形）提高到１５０℃     

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The continuous cooling transformation process and the organization performance of transformation product was investigated by means of dilatation test during single pass deformation on Gleeble-3500. The result shows that bainite transition can be happened when the cooling speed about 3??/s on 460B steel with boron, and the grain size is coarse and hardness is higher when the cooling speed (0. 1, 0. 3, 0. 5??/s)is slowly, it is more tiny than without boron. Boron can make the CCT curves shift to right, the transition from austenite to ferrite and pearlite is restrained, the hardenability of the steel are obviously improved, the cooling speed from austenite to martensite is lower and Ac3, Ac1, Ar3, Ar1, Ms is dropped.     

一种含Nb、Ti微合金钢的连续冷却相变行为

利用MMS -200热模拟试验机对试验钢进行不同变形条件下的连续冷却转变试验.针对不同的冷却速度,采用热膨胀法结合金相法测定试验钢在连续冷却转变中的相变温度,利用光学显微镜及扫描电镜观察试样的显微组织,并测定珠光体的含量,进而绘制出试验钢在变形和未变形条件下的连续冷却转变(CCT)曲线,从而得出不同变形工艺对微合金钢连续冷却转变行为和显微组织的影响规律.     

硼对Q690D钢CCT曲线的影响

利用Formastor-F全自动相变仪测定了不同硼含量Q690D钢的临界点Ac1、Ac3,并绘制Q690D钢的连续冷却转变曲线。结果表明:硼的加入,使Q690D钢的Ac3、Ac1略有提高,使Ms点及Bs点有所降低,使Q690D钢的临界冷速降低,淬透性明显提高。硼对Q690D钢先共析铁素体转变及贝氏体转变均有不同程度的推迟作用,抑制了先共析铁素体的析出,在很宽的冷速范围可以得到完全的贝氏体组织。     

Effect of Pre-strain and High Stresses on the Bainitic Transformation of Manganese-boron Steel 22MnB5

During the last decade, the use of press-hardened components in the automotive industry has grown considerably. The so-called tailored tempering, also known as partial press hardening, employs locally heated tools seeking to obtain bainitic transformations. This leads to (seamless) zones within the formed parts with higher ductility. Due to the intrinsic nature of this process, phase transformations happen under the influence of high loads and in pre-deformed austenite. The austenite pre-strain state and applied stresses affect the kinetics of the bainitic transformation. Moreover, stresses have an additional relevant effect in this process, the so-called transformation plasticity. Linear transformation plasticity models have been successfully used to predict the behavior in the presence of low stresses. Nonetheless, because of the process’s severe conditions, these tend to fail. A strong nonlinearity of the transformation plasticity strain is observed for applied stresses above the austenite yield strength. Using thermomechanical tests on sheet specimens of a manganese-boron steel (22MnB5), widely utilized in the industry, the effect on the bainitic transformation of various degrees of deformation in the range of 0 to 18 pct, applied stresses in the range of 0 to 250 MPa and the transformation plasticity effect are investigated in this work.     

Hot Ductility of Ti-V Bearing Microalloyed Steel in Continuous Casting

Hot ductility of Ti-V bearing steel was studied by theoretical calculation and thermal simulation experiment.Meanwhile,microsegregation and precipitates were analyzed.The results showed that elements S,Ti and O were enriched at the grain boundaries,while the hot ductility was deteriorated by inclusions of(Fe,Mn,Si,Al)(S,O)in the interdendritic region.At the temperature of 1 100℃,large TiN particles had little effect on hot ductility.In the temperature range from 975 to 925℃,reduction of area(R.A)declined rapidly from 81.88% to 63.16% with the size of particles decreasing from 40 to 20nm and quantity increasing from 1.4 to 11.9μm-2,respectively.In the temperature range from 875 to 825℃,R.Areduced unobviously from 35.14% to 28.6% with ferric films thickening gradually.The critical stress,88.79 MPa,was equal to tensile strength at 825 ℃.Intergranular fracture was easy to occur with higher critical stress below 825℃.     

P510L钒微合金化钢连续冷却转变特征

采用膨胀法测定了攀枝花新钢钒热轧板厂的高强度P510L钒微合金化钢的CCT曲线,采用金相显微镜分析不同冷速下的显微组织.分析发现,冷却速度较慢(低于10℃/s)时,得到的显微组织为比较粗大的铁素体 珠光体组织;中速冷却时,组织为比较细小均匀的铁素体 珠光体组织;快冷时(高于35℃/s)主要为贝氏体和铁素体组织.进一步采用扫描电镜分析P510L显微组织,发现大量钒的析出物,V(CN)析出物的形态为从球形至长方形,其大小为10～30 nm.     

低碳微合金管线钢的连续冷却相变及组织研究

通过Gleeble 3800热模拟试验机测定了该低碳微合金管线钢的静态（无热变形）和动态连续冷却相变曲线,并通过光学显微镜和电子显微镜对连续冷却后的组织进行了详细观察和分析。发现随着冷却速度的提高,在连续冷却转变组织中依次出现多边形铁素体（PF）、珠光体（P）、针状铁素体（AF）、粒状贝氏体（GB）和下贝氏体（LB）。在未再结晶区的热变形使C曲线发生左移,扩大了试样的针状铁素体区,并使得相变后的组织得到细化。     

N含量对硼钢35MnB末端淬火性能的影响

35MnB钢由40 t EAF-LF-VD-180 mm×180 mm连铸的电弧炉流程和100 t BOF-LF-RH-200 mm×200mm连铸转炉流程冶炼。35MnB钢技术协议要求J19 HRC值为33～41。试验结果表明,电弧炉流程生产的35MnB钢J19HRC值为25～28,转炉流程生产的35MnB钢末端淬火试验J19HRC值为36～41。对比分析了电弧炉流程和转炉流程生产的35MnB钢的末端淬火性能。分析得出,电弧炉流程生产的35MnB钢中的平均N含量高达(80～90)×10^-6、转炉流程为(45～50)×10^-6,电炉钢中高N含量影响了B对提高钢材淬透性的作用,为了保证钢材末端淬火性能,应控制钢中N含量≤50×10^-6。     

ER70S-6热变形奥氏体连续冷却转变行为

采用Gleeble-1500热模拟机测定了ER70S-6合金焊线用钢在不同冷速下连续冷却转变的膨胀曲线,结合组织观察,获得了该钢的过冷奥氏体连续冷却转变动态CCT曲线;研究了其连续冷却转变产物的组织形态。试验结果表明,ER70S-6在0.1~20℃/s的冷却速度范围内组织主要由铁素体+珠光体、铁素体+珠光体+贝氏体、铁素体+珠光体+贝氏体+马氏体组成。