硼对高强度弹簧钢脱碳敏感性的影响

弹簧表面形成脱碳层将恶化其疲劳性能,因此要求弹簧钢具有低的脱碳敏感性。研究了不同硼含量(0．0006％～0．0027％)对中碳高强度弹簧钢脱碳敏感性的影响。采用等温处理和等时处理研究了含硼中碳弹簧钢和作为对比的60Si2Mn钢的脱碳层深度和氧化失重量的变化情况。结果表明：实验钢的脱碳层深度和氧化失重量均随硼含量的增加而减少。这表明,钢中添加微量硼能够抑制弹簧钢的氧化和脱碳。硼的这种良好作用主要与其在原奥氏体晶界的偏聚有关。含硼中碳弹簧钢的氧化和脱碳敏感性明显低于所对比的60Si2Mn钢,这除了与硼抑制钢的氧化和脱碳的作用有关外,前者较低的碳含量也是一个主要原因。     

60Si2Mn弹簧钢加热温度对表面脱碳的影响

表面脱碳是高速线材生产的重要问题之一.在考虑碳扩散和氧化因素后,理论计算了加热温度对60Si2Mn弹簧钢表面脱碳影响的规律,表明在900～1000℃加热温度下60Si2Mn弹簧钢脱碳层厚度存在最小值,此结果与60Si2Mn弹簧钢氧化脱碳试验结果一致.结合钢的相变进一步分析了不同加热温度下表面脱碳层形貌变化的规律,并简要介绍了脱碳控制的主要途径.     

碳含量和晶粒尺寸对高碳钢表面脱碳类型和深度的影响

摘要：硬线在加热、轧制等过程中会发生表面脱碳，严重影响工件的性能。通过等温加热实验，研究了加热温度和碳含量对硬线60、70和82B钢表面脱碳层类型和深度的影响，及原始奥氏体晶粒尺寸对弹簧钢60Si2MnA表面脱碳类型和深度的影响。结果表明：保温90min后，60钢在700~750℃时仅存在完全脱碳层，在850~900℃时仅存在部分脱碳层，其完全脱碳层深度随温度增加而逐渐减小，部分脱碳层则相反。70钢仅在850~900℃时存在部分脱碳层。82B钢的脱碳层深度随着温度增加先增加后减少至消失，然后又逐渐增加。硬线在碳含量处于γ单相区时主要发生部分脱碳，且深度随碳含量的升高而增大；碳含量处于α+γ两相区时主要发生完全脱碳，且深度随着碳含量增加先减小后增大。弹簧钢60Si2MnA的完全脱碳层深度随着原始奥氏体晶粒尺寸的增大逐渐减小。     

Si对中碳弹簧钢氧化脱碳行为的影响

试验研究了成分(%)为0.49C-0.29Si-1.65Mn、n53C-0.78Si-1.56Mn和0.54C-1.74Si-0.71Mn(60Si2MnA)3种中碳弹簧钢850℃5～120 min水冷和780～1000℃60 min水冷热处理后的脱碳敏感性和氧化失重行为。结果表明,随钢中硅含量增加,钢的脱碳层深度增加,氧化失重量减少,说明Si能增加钢中碳的扩散系数,促进钢的脱碳。     

汽车悬架系统弹簧钢60Si2MnA的断裂失效分析

用箱式电阻炉研究了不同加热温度和保温时间对弹簧钢60Si2Mn A脱碳层深度的影响。结果表明:随着加热温度和保温时间的增加,脱碳层深度增加,加热温度1 000℃时,脱碳层最大,而随保温时间的增加脱碳层增加速率变缓。调质处理后试样的疲劳试验结果表明,复合夹杂物和脱碳层的存在导致了试样断裂失效。     

加热期间弹簧钢55SiCr表面脱碳的影响因素研究

在实验室研究了加热温度、保温时间和加热炉内气氛对弹簧钢55S iCr表面脱碳的影响,并对脱碳反应进行了热力学分析。结果表明：在950℃-1250℃范围随温度升高,弹簧钢完全脱碳层厚度先增加后减小,1200℃时完全脱碳层厚度达到最大值,1250℃时由于氧化速度大于脱碳速度,完全脱碳层消失。弹簧钢完全脱碳层厚度分别随加热时间延长、气氛中CO2含量升高、O2含量升高和H2O（g）含量增加而明显增加。当温度为950℃、气氛中O2含量为1%、加热时间为35 min的条件下,可避免完全脱碳层的形成。     

钒氮微合金化对Si-Mn系弹簧钢热处理特性的影响

分别采用VN、Fe—V合金在实验室冶炼了不同钒含量的Si—Mn系弹簧钢，并系统研究了其淬透性、抗回火稳定性、表面脱碳敏感性和力学性能的变化情况。结果表明，本试验条件下，采用钒氮微合金化的Si—Mn系弹簧钢(0．50％C，0．06％-0．10％V，0．01％N)具有较好的淬透性和抗回火稳定性。钒含量增加，强度显著增加。钒氮微合金化对表面脱碳敏感性没有明显影响。     

42CrMo钢表面脱碳行为研究

利用S60/58507型高温热重分析仪研究了加热温度对42CrMo钢脱碳的影响，分析了脱碳组织形貌规律，对传统脱碳模型进行了修正。结果表明，总脱碳深度随加热温度的升高而增加。当加热温度为900℃时，42CrMo钢表面出现完全脱碳层和部分脱碳层，当温度为950℃及以上温度时，42CrMo钢表面只出现部分脱碳层。部分脱碳层中铁素体沿晶界分布，形成网状铁素体组织。由于合金元素的作用，传统的脱碳模型不能适用于42CrMo，修正之后的模型能够较为准确地预测42CrMo钢的总脱碳深度。     

60Si2MnA弹簧钢盘条脱碳层控制工艺的优化

60Si2MnA弹簧钢ø9ø12 mm盘条的生产流程为100 t BOF-LF-VD-150 mm×150 mm坯连铸-高速线材轧制工艺。讨论了脱碳机理和分析了脱碳的影响因素。通过适当降低二加热段温度,提高均热段温度,铸坯总加热时间由2.7 h降至1.5 h,控制加热炉内氧含量3%5%,开轧和吐丝温度分别从（1000±20）℃和（850±15）℃降至（950±20）℃和（820±20）℃,减少727℃以上温度的风冷时间等工艺措施,使60Si2MnA弹簧钢盘条的全脱碳层由0.072 mm降至0,总脱碳层由0.142 mm降至0.063 mm,弹簧的疲劳寿命由17.7万次提高到23.2万次。     

新型高强韧性弹簧钢40T 和44T 脱碳倾向的研究

新型高强韧性弹簧钢40T(%:0.41C-2. 12Si- 1.03Cr- 1.98Ni-0.31Mo-0.25V),44T(%:0.44C-2.28Si- 1.42Cr-0.25V)和弹簧钢60Si2CrVA(%:0.59C-1.65Si-1.11Cr-0.18V)的φ18 mm 和φ26 mm 试验钢材由北满特钢 20t电弧炉冶炼,经轧制、冷拔而成。各钢材经860～1000℃加热脱碳试验的结果表明,40T钢碳含量较低,并 有～2%Ni,其脱碳倾向明显低于44T钢和60Si2CrVA钢;880 ℃加热1 h时,40T钢没有脱碳,44T钢脱碳层深 0.05mm,60Si2CrVA钢脱碳层深0.15 mm;1000 ℃加热20 min,40T钢脱碳层深0.1 mm,44T 钢0.2 mm, 60Si2CrVA钢0.4 mm。40T钢脱碳倾向小,有利于提高弹簧的疲劳寿命。     

Secondary Hardening, Austenite Grain Coarsening and Surface Decarburization Phenomenon in Nb-Bearing Spring Steel

 The secondary hardening, the austenite grain coarsening and the surface decarburization phenomenon of Nb-bearing spring steel were investigated, and the effects of niobium on tempered microstructure was studied using scanning electron microscope. The results show that the micro-addition of niobium increases the tempering resistance and produces secondary hardening. The effect of niobium on the size and distribution of cementite particles is one of the primary reasons to increase the hardness after tempering. The grain-coarsening temperature of the spring steel is raised 150 ℃ due to Nb-addition. Furthermore, both the secondary hardening and the austenite grain coarsening phenomenon congruously demonstrate niobium begins observably dissolving above 1100 ℃ in the spring steel. Besides, niobium microalloying is an effective and economy means to decrease the decarburization sensitivity of the spring steels.     

Effect of carbon content and grain size on structure and depth of surface decarburization of high carbon steel

The surface decarburization of hard wire will occur in the process of heating and rolling, which will seriously affect the performance of workpiece. The effects of holding temperature and carbon content on the type and depth of decarburized layer on hard wire 60, 70 and 82B steel were studied by isothermal heating experiment. The effects of crystallite dimensions of original austenite on decarburization depth of spring steel 60Si2MnA were analyzed. The results show that there is only a complete decarburization layer of 60 steel at 700-750℃ after heating at different temperatures for 90min. There is only a partial decarburization layer at 750-850℃. The depth of decarburized layer decreases gradually with the increase of temperature, and there is only a partial decarburization layer at 850-900℃. The depth of complete decarburization layer decreases gradually with the increase of temperature, and the depth of partial decarburization layer increases gradually with the increase of temperature. The partial decarburization layer of 70 steel only exists at 850-900℃. The depth of complete decarburization layer of 82B steel increases gradually with the increase of temperature, then gradually decreases to zero, at least gradually increases. Only a complete decarburization layer exists at 700℃. There is partial decarburization when the hard wires carbon content is in the γ single phase region, and the depth increases with the increase of carbon content. There is complete decarburization when the carbon content is mainly in the α+γ two phase region, and the depth decreases first and then increases with the increase of carbon content. The depth of the complete decarburization layer of the spring steel 60Si2MnA decreases with the increase of crystallite dimensions of original austenite.     

1000MPa级高延伸率Q&P钢的实验室研究

以C-Si-Mn系TRIP钢成分为基础,设计了四种不同Si和Mn含量的合金成分,并采用不同两相区奥氏体化温度的淬火—配分(QP)工艺进行处理,得到了兼具高强度和高塑性的QP钢。其中,当奥氏体化温度为820℃时,0.18C-1.8Si-2.2Mn(质量分数,%)钢和0.18C-1.8Si-2.5Mn钢在抗拉强度达到1 000 MPa以上的同时断后延伸率仍不低于20%,显示了极佳的强塑性结合。利用SEM和XRD等对热处理材料的显微组织进行了表征,结果显示,其显微组织为铁素体、板条马氏体和一定量的残余奥氏体,残余奥氏体多呈块状且被铁素体所包围,且奥氏体化温度为820℃时,材料中的残余奥氏体含量和平均碳浓度均较高。更多且稳定的残余奥氏体在变形过程中发生TRIP效应,可以在不显著降低材料强度的情况下更有效地改善材料的塑性,这也是四种试验用钢经820℃的QP工艺处理后显示出更佳强塑性结合的主要原因。     

Mechanical properties and retained austenite in intercritically heat-treated bainite-transformed steel and their variation with Si and Mn additions

Processing peculiarities and functions of alloying elements, such as Si and Mn, were studied for improving formability of steel sheets with mixed microstructures. Annealing a sheet steel with 0.2 pct C in the intercritical range produced very fine particles of retained austenite which were moderately stabilized due to C enrichment by subsequent holding in the bainite transformation range. Its strength-ductility balance is greatly superior to that of other dual-phase steels due to transformation-induced plasticity (TRIP). The holding time in the bainite transformation range varies with temperature, depending on the activation energy of C diffusion in austenite, and shifts to longer times with an increase of Si or Mn additions. The optimum cooling rate from the intercritical region is reduced with an increase of Mn content but is not influenced by Si content. Additional Mn makes the retained austenite content larger, although uniform elongation remains the same. In this case, the product of tensile strength and total elongation is increased due to an increase in the tensile strength. Contrary to Mn, Si does not affect retained austenite content but improves the uniform elongation by increasing its stability.     

热轧相变诱发塑性钢的热模拟实验

 利用Gleeble 1500热应力 应变模拟机研究了铌含量、热变形参数(终轧温度和卷取温度)对相变诱发塑性(TRIP)钢组织和性能的影响。实验结果表明：不含铌实验钢的残余奥氏体量、残余奥氏体相中的碳含量、宏观维氏硬度和抗拉强度与常规低碳硅锰系TRIP钢的水平相当;增加铌含量,残余奥氏体量和残余奥氏体相中的碳含量有所下降,而宏观维氏硬度和抗拉强度提高;铌含量为0014%、终轧温度为780 ℃、卷取温度为400 ℃时,残余奥氏体量、残余奥氏体相中的碳含量与宏观维氏硬度和抗拉强度具有最佳组合。     

Effects of Niobium and Vanadium on Hydrogen-Induced Delayed Fracture in High Strength Spring Steel

 Influence of vanadium and/or niobium additions on delayed fracture behavior in high strength spring steel was studied by hydrogen permeation method and slow strain rate technique (SSRT), and its mechanism was analyzed. The results show that apparent diffusion coefficient of hydrogen in microalloyed spring steels Nb V steel and Nb steel is lower than that in non microalloyed steel 60Si2MnA. Percentage of strength reduction in SSRT in air after precharged hydrogen of the microalloyed steels is smaller than that of 60Si2MnA. Addition of the microalloys changes the fracture characteristics. Thence, vanadium and/or niobium additions are a very effective and economy means to improve the hydrogen induced delayed fracture resistance of high strength spring steel.     

Decarburization kinetics of low alloy ferritic steels in sodium

The rates of decarburization of low alloy and plain carbon steels in static, isothermal sodium have been measured over the temperature range 1000° to 1300°F. Low alloy steels studies in these tests were 2-1/4 Cr-1 Mo (T22), 2-1/4 Cr-1Mo-1Nb,and 2-1/4 Cr-1Mo-low carbon (0.015 C). Plain carbon steels studied were 1020, 1040, and 1095. Periodic measurements of the specific carbon loss (mass of carbon lost per unit surface area of specimen) revealed that the decarburization of normal 2-1/4 Cr-1 Mo steel is controlled by diffusivity and solubility of carbon in the matrix. Decarburization rate constants measured in this study for the normal 2-1/4 Cr-1 Mo steel were found to be in good agreement with rate constants calculated from data reported in previous studies. Tests of modified 2-1/4 Cr-1 Mo steels showed that: a) the carbon content of the niobium-stabilized steelwill either remain unchanged or will increase and b) the low carbon steel will decarburize slightly during exposures in the same sodium systems which produce rapid decarburization of the steel with normal amounts of carbon. Decarburization tests on plain carbon steels revealed that both the depths of the decarburized layer and the specific carbon losses were controlled by diffusivity and solubility in the matrix. Comparison of the measured decarburization rate constants with theoreticalvalues (based on a moving-boundary diffusion process) were in good agreement. These data were used to calculate the carbon content at the surfaces of the steels during decarburization in the liquid and vapor phases of a sodium system. It was demonstrated that plain carbon steels can serve as carbon monitors for sodium systems.