Effect of tempering temperature on the mechanical properties and microstructure of an copper-bearing low carbon bainitic steel

The effect of tempering temperature on the microstructure and mechanical properties of ultra-high strength, copperbearing, low-carbon bainitic steel has been investigated in the experiment. The results showed that the microstructure was mainly the laths of bainite in the as-quenched steel. The bainitic laths were restored and combined after the steel tempered at various tempera- tures. There were rnartensite/austenite （M/A） islands and numerous dislocations within and between the bainitic laths, while very t-me precipitates of ε-Cu were also observed within the laths. With increasing the tempered temperature from 400 to 600℃, the yield strength （YS） increased from 877 to 957 MPa, whereas the ultimate tensile strength （UTS） decreased from 1020 to 985 MPa. The Charpy V-notch （CVN） varied from 68.5 to 42 J, and the value was minimal for the steel tempered at 500℃. 2008 University of Science and Technology Beijing. All rights reserved.     

Effect of temper rolling on the bake-hardening behavior of low carbon steel

In a typical process, low carbon steel was annealed at two different temperatures (660°C and 750°C), and then was temper rolled to improve the mechanical properties. Pre-straining and baking treatments...     

Effect of hydrogen attack on acoustic emission behavior of low carbon steel

In order to investigate the effect of hydrogen attack degree on acoustic emission(AE) behavior of low carbon steel during tensiling,specimens made of low carbon steel was exposed to hydrogen gas of 18 MPa at 450 and 500℃ for 240,480 and 720h respectively,Experimental results show that with increase of the hydrogen attack degree,the totally AE activity decreases during tensiling.In addition,the count of AE signals with high amplitude for the specimens with hydrogen attack keeps a constant which is less than that without hydrogen attack.It is concluded that AE signals orginate in the specimens with hydrogen attack from intergranular fracture induced by methane blisterings or/and microcracks on grain boundaries.     

CSP工艺条件下低碳钢板带材力学性能研究

热轧板带材成品因其内在组织形态及成分不同而呈现较明显的力学性能差异.就包钢薄板坯连续连轧CSP工艺条件下,低碳典型钢种Q235B和SS400显微组织及轧制工艺对材料力学性能的影响进行了实验研究.用数理统计方法建立了工艺参数与产品性能回归数值模型,模型拟合效果较好.     

Nb对低碳微合金钢相变的影响

采用Gleeble-1500D型热模拟机测定了不同含铌量低碳微合金钢在不同冷却速度下,过冷奥氏体连续冷却相变点,分析观察了显微组织,测定了其显微硬度.得出:在同一冷却速度下,随着含铌量的提高,过冷奥氏体连续冷却相变点降低,容易出现条片状贝氏体铁素体,显微硬度提高;在相同成分下,随着冷却速度的增加,含铌钢中铁素体越来越细小,由等轴状大块铁素体组织向条片状贝氏体铁素体转变.     

低碳钢蚀刻工艺技术的研究

针对金属化学蚀刻的工艺技术进行了研究,选择氯化铁为金属蚀刻剂,通过初步试验和正交筛选,确定了蚀刻低碳钢的相对最佳工艺条件：蚀刻液浓度为22.0%,蚀刻温度为45℃,pH为1.0,转速为50r/min（蚀刻液相对流速为3.6m/min）.经化学蚀刻后的金属工件具有蚀刻厚度均一,蚀刻面光洁度良好,切面质地一致,精密度高等特点.     

Hot deformation behavior of a Cr-containing low carbon steel in the ferrite range

A low carbon steel with Cr addition of 0.46wt% combined with trace elements of Mn and Ti was studied.The apparent activation energy of deformation and the hot deformation equation of the steel in the ferritic range were determined by means of single hot compression tests.The hot-rolled strip of 3 mm in thickness rolled in the ferritic range was obtained using a laboratory hot rolling mill.The mechanical properties show that the values of yield strength and ultimate tensile strength are 230 and 330 MPa,respe...     

转炉-CSP工艺SS400热轧板带组织与力学性能分析

对包钢CSP工艺生产的SS400低碳热轧板卷进行了组织、力学性能测定分析.结果表明,成品薄板显微组织为大量的多边形铁素体和少量珠光体,晶粒细小、均匀,晶粒平均尺寸约为12 μm,中心区域比表面区域晶粒稍粗大,但差别不大.力学性能较国标的Q235B高,屈强比也较高.     

Precipitation and stability of reversed austenite in 9Ni steel

A new method was used to analyze the factors affecting the precipitation of reversed austenite during tempering. The samples were kept at various tempering temperatures for 10 min and their length changes were recorded. Then, the precipitation of reversed austenite which led to the length reduction was shown by thermal expansion curves. The results show that the effects of process parameters on the precipitation of reversed austenite can be determined more accurately by this method than by X-ray diffraction...     

Preparation and Properties of Anti-oxidation Inorganic Nano-coating for Low Carbon Steel at an Elevated Temperature

A new kind of anti-oxidation inorganic nano-coating for the common low carbon steel was prepared. It included magnesite mineral, metallurgic dust and silicate adhesive as the main raw materials. The nano-coating could be sprayed directly onto the low carbon steel slab even though with hot surface as far as under 1000 ℃ . And at the same time, a compact thin nano-film was formed, and the film would inhibit the oxygen into the interface of the steel body and decrease the loss of weight because of oxidation. The loss was decreased by about 60% or more. The properties and mechanism of oxidation resistance of the coating were discussed through XRD, TG-DTA and SEM. The experimental results show that many reactions would happen among the companents of the coating and then many microspheres with the size of 80- 100nm generated in the system. By using the heat of the steel body, the silicate adhesive would interact with the microspheres, and the other components of the coating would be soft and sintered so that when the coating was sprayed onto the suface of the steel slab , the intact and compact film could be formed and adhesive with the steel body. Besides the special properties of anti- oxidation, the coating could prevent the volatilization of microelement in the steel such as silicate and carbon at a high temperature. So it can improve the quality and output of steel with this new kind of nano-coating.     

低碳钢钢锭红送裂纹形成机理

研究了低碳钢钢锭红送裂纹的形成机理,分析并计算了钢锭红送及装炉再加热全过程的温度场和应力场的变化规律,测定钢锭的组织结构和高温强度、塑性,与内应力的变化相比较,分析其开裂的可能性和开裂的时机,得出了低碳钢钢锭红送裂纹的开成机理,为主产中防止红送裂纹提供了理论依据。     

回火工艺参数对DP600热轧双相钢组织和性能的影响

采用低温回火实验模拟热轧双相钢实际生产过程中卷取后的冷却过程,分析回火温度与保温时间对0．09C-0．1Si-1．3Mn-0．5Cr-0．05P热轧双相钢组织及力学性能的影响。结果表明,回火过程中主要是碳原子通过扩散影响铁素体与马氏体中的微结构,从而对其组织和力学性能产生影响;200℃回火后双相钢基本保持原有的组织与性能,230℃以上随回火温度升高和保温时间延长,马氏体分解逐渐明显,铁素体中碳原子钉扎可动位错造成屈服现象的发生;在230～250℃温度范围回火时,保温时间的延长较温升对回火程度的影响更加明显。     

空冷高硅中碳低合金钢的组织与性能

研究了高硅中碳低合金钢空冷态和空冷＋回火态的显微组织和力学性能.试验钢在860℃保温0.5 h奥氏体化后空冷处理,随后分别在250℃和400℃保温1 h回火.结果表明：试验钢空冷后组织为贝氏体/马氏体和残余奥氏体的混合组织,硬度约为41 HRC;而250℃回火后组织变化不大,硬度明显升高,约为49 HRC,韧性明显增加,由44 J/cm2增加到66 J/cm2,抗拉强度、屈服强度和延伸率明显下降.回火温度进一步增加对力学性能影响不大.     

Influence of isothermal bainitic processing on the mechanical properties and microstructure characterization of TRIP steel

The mechanical properties of transformation induced plasticity (TRIP) steel are strongly affected by the conditions of iso-thermal bainitic processing. The multiphase microstructure of TRIP steel under different conditions of isothermal bainitic processing was investigated using OM, SEM, XRD and TEM. The volume fraction of retained anstenite and the carbon content in anstenite were determined quantitatively using X-ray diffraction patterns. The relationship between mechanical properties and isothermal bainitic processing parameters was investigated. The stability of retained anstenite was analyzed by the volume fraction of retained austenite and the carbon content in retained anstenite. The experimental results show that the multiphase microstructure consists of ferrite,bainite and metastable retained austenite. To obtain good mechanical properties, the optimal conditions of isothermal bainitic tem-perature and holding time are 410-430℃ and 180-240 s, respectively. After isothermal bainitic processing under the optimal condi-tions, the corresponding volume fraction of retained anstenite is 5vol%-15vol%, which can provide enough retained austenite and plastic stability for austenite with high carbon content.     

锌液对低碳钢腐蚀机制的研究

分析了低碳钢在500 ℃下受不同时间的静态锌液腐蚀机制及含碳量对腐蚀过程的影响.实验表明，Fe与Zn通过反应扩散，依次形成了Г、δ₁、ζ相.且δ₁相的晶界强度低，在晶界应力和锌液腐蚀及锌液热对流冲击的共同作用下易于开裂而脱落到锌液中去.此外，含碳量越高，δ₁相层越厚，腐蚀越快.在反应过程中，Fe原子一方面通过化合物层溶解于锌液中，另一方面，δ₁相颗粒脱落到锌液中而消耗，腐蚀量为两者的总和.     

低碳钢厚壁球非定常热应力计算

基于变温粘弹性松弛型本构理论、热传导方程和有限元方法,对低碳钢厚壁球的非定常热应力进行了分析。在非定常热应力计算时只要确定物体内部各点的温度历史,及其终态温度等效拉伸松弛曲线、等效剪切松弛曲线,便可计算出物体内各点的瞬时热应力。这在工业生产上具有广泛的应用价值。     

Effect of Cu on the boron segregation at grain boundaries and vacancy-type defects in ultra-low carbon micro-alloy steels

By thermal neutron irradiation particle tracking autoradiography(PTA)technique,the development of boron segregation at grain boundaries in ultra-low carbon micro-alloy steels was investigated during cooling from 1150°C to 850°C,and the effect of Cu on boron segregation at grain boundaries was discussed.By positron annihilation lifetime(PAL)technique,the changes of vacancy-type defects with temperatures and the effect of Cu on vacancy-type defects in the cooling process were discussed.Results show that,the concentration of boron at grain boundaries increases rapidly at the beginning of the cooling;after that,it begins to decrease;and then,it increases gradually again.The addition of Cu not only increases the concentration of boron at grain boundaries but also speeds up the development process of boron segregation at grain boundaries.During the continuous cooling process,the addition of Cu significantly affects the change of vacancy-type defects with temperatures in ultra-low carbon micro-alloy steels.     

Effect of Nb on the transformation kinetics of low carbon （manganese） steel during deformation of undercooled austenite

The hot compression tests using Gleeble 1500 were performed by varying the true strain up to 1.6 （80% reduction） in Nbfree and Nb-microalloyed steels. The effect of Nb addition on the transformation kinetics during deformation of undercooled austenite was investigated. It was found that as compared with Nb-free steel, the transformation incubation period of Nb-bearing steel was prolonged and the transformation kinetics curves parallelly moved to higher strain because of the solute Nb drag effect. Studies on kinetics also showed that the deformation-enhanced ferrite transformation （DEFT） of the two steels were composed of three stages, which can be expressed by the J-M-A equations individually. However, the parameter n related to the mode of nucleation and growth is somewhat different in the first and second stages of the two steels, and the same in the third stage for both the steels corresponding to the nucleation Of retained austenite.     

Influence of Cu on microstructure and mechanical properties of high purity steel

研究了铜单一合金化高纯净钢在时效退火前后的组织与性能的关系 结果表明 ,铜具有明显的时效强化作用 ,在时效过程中铜的析出优先于钢板的再结晶 ,同时高纯净基体使钢材保持了良好的塑性 分析表明 ,铜单一合金化高纯净钢具有良好的发展前景