600 MPa级热镀锌双相钢再结晶和相变规律研究

在Gleeble-3800热模拟机上对600MPa级热镀锌双相钢进行了连续退火工艺模拟实验,利用光学显微镜与扫描电镜观察分析了600MPa级热镀锌双相钢在连续退火过程中的再结晶和相变规律。结果表明,600MPa级热镀锌双相钢在连续退火初期。650～700℃加热范围内再结晶剧烈进行。加热速度提高,冷变形组织的再结晶开始与结束温度也相应升高。两相区保温后快速冷却得到不同体积分数的铁素体和马氏体组织,随两相区保温温度升高,马氏体特征更加明显。     

热处理工艺对钒微合金化冷轧TRIP钢组织性能影响研究

采用盐浴热处理方法配合性能检测及显微组织分析方法研究了热处理工艺对含钒冷轧TRIP钢组织性能的影响,结果表明试验钢在所采用的热处理工艺下其抗拉强度均达到700 MPa,且在780℃×60 s+400℃×180 s工艺下获得最佳综合性能,屈服强度、抗拉强度、断后伸长率、强塑积分别为514 MPa、738 MPa、29%、21 402 MPa·%;随着两相区退火温度的升高,两相区奥氏体所占的体积分数也越高,使最终组织中贝氏体及马氏体等强化相含量增多,造成试验钢强度上升、塑性下降;钒在试验钢中对残余奥氏体的积极作用并未体现,可能与退火时间较短和贝氏体区等温时钒碳(氮)化物重新析出消耗残余奥氏体中碳原子造成其含量及稳定性下降有关。     

冷轧TRIP590钢带的成分优化

 化学成分和热处理工艺是影响TRIP钢力学性能的关键因素。通过热模拟试验方法研究了不同成分试验钢在临界区退火过程中的微观组织变化规律。结果表明：随着两相区退火温度的升高,铁素体平均晶粒尺寸逐渐减小,铁素体体积分数随着加热温度的升高而降低;残余奥氏体量和其中的C质量分数先随着退火温度的升高而降低,达到一个低谷以后,再随退火温度的升高而升高;在相同的退火温度下,随着Nb的加入,多边形铁素体晶粒尺寸细化,铁素体体积分数逐渐减少;既加Nb又高Si的试验钢钢中残奥数量最多,不加Nb的试验钢中残奥数量最少。TRIP钢试制结果表明,钢带组织类型为典型的TRIP钢组织,多边形铁素体平均晶粒尺寸约8μm,体积分数67%,残余奥氏体体积分数为5.58%,残余奥氏体中C质量分数为1.34%,同时,力学性能也完全满足TRIP590的性能要求。     

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1 150 MPa提高到1 340 MPa,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.     

工艺参数对800 MPa热镀锌双相钢组织性能的影响

 在实验室试制了低Si 的C Mn Cr Mo系的800 MPa级冷轧热镀锌双相钢,研究了卷取温度、退火温度、退火时间等工艺参数对双相钢微观组织和力学性能的影响。试验结果表明：试验用钢在820~850 ℃退火,保温100 s以上,抗拉强度可以达到800 MPa级以上。随着退火温度的升高,强度升高,但综合性能以退火温度为820 ℃时为最佳。在820 ℃退火时,随着保温时间的增加,双相钢的强度显著增加,当保温时间超过100 s以后,强度增加缓慢。690 ℃高温卷取有利于获得最终力学性能良好的双相钢组织。     

连续退火工艺对双相钢金相组织和力学性能的影响

利用河北钢铁技术研究总院连续退火热模拟机研究了退火工艺对双相钢金相组织与力学性能的影响。结果表明,两相区加热温度升高,试样中铁素体含量下降,晶粒细化,马氏体含量升高,屈服强度增加,抗拉强度变化不大,在820～840℃退火时伸长率达到最大值;两相区保温时间增加,组织中铁素体再结晶充分,晶粒长大,马氏体晶粒并无明显变化,室温时双相钢屈服强度与抗拉强度降低,伸长率明显增加;随着时效温度升高,屈服强度缓慢增加,抗拉强度缓慢减小,在时效温度230～270℃时,伸长率随时效温度升高而降低,并在290℃时取得最大值。     

贝氏体等温温度对超高强冷轧TRIP钢组织性能的影响

将C-Si-Mn钢加热至800℃保温120 s后,分别快速冷却至350～410℃保温600 s以模拟贝氏体等温转变工艺。通过扫描电镜(SEM)和拉伸测试的方法研究了贝氏体等温温度对超高强相变诱导塑性钢(TRIP钢)微观组织和力学性能的影响规律。结果表明,冷轧TRIP钢的微观组织由铁素体、贝氏体、马氏体和残余奥氏体组成;贝氏体和残余奥氏体形成于等温转变阶段,而马氏体形成于等温后的终冷阶段。随着贝氏体等温温度增加,固溶C原子扩散系数提高,促进残余奥氏体中碳化物的析出。因此,奥氏体中的平均固溶C含量降低,使得TRIP钢残余奥氏体分数降低,马氏体体积分数增加。贝氏体等温温度由350℃增加至410℃时,TRIP钢屈服强度由720 MPa降低至573 MPa,抗拉强度由1 195 MPa提高至1 312 MPa,伸长率A_(80)由17.8%降低至12.5%。贝氏体等温温度为350℃时,冷轧TRIP钢具有优良的综合力学性能,强塑积达到21 270 MPa·%。     

连续退火参数对980 MPa级冷轧双相钢组织和性能的影响

采用带钢连续退火模拟试验机,研究了连续退火过程中加热速率、两相区保温温度和过时效温度对冷轧双相钢DP980组织和性能的影响规律。研究结果表明,适当提高加热速率有利于马氏体晶粒的细化和带状组织的改善,当加热速率达到45℃/s时可获得较高的强度和塑性。退火温度直接决定了硬质第二相的体积分数、分布和形貌,在800℃左右进行退火保温可以获得良好的综合性能,保温温度过低或过高都会导致强塑性匹配较差。随着过时效温度的降低,强度升高,伸长率下降,试验钢退火后加工硬化系数明显增大。     

退火温度对冷轧中锰钢组织性能和断裂行为的影响

 为了系统研究临界区退火和全奥氏体区退火对中锰钢性能的影响,为中锰钢的实际应用提供理论基础,在650~900 ℃范围内系统研究了冷轧中锰钢的显微组织和力学性能,并通过断口形貌观察分析了试验钢的断裂特性。结果表明,试验钢在临界区退火的综合力学性能明显优于全奥氏体区退火。650~750 ℃退火时,抗拉强度在1 000 MPa左右,强塑积超过30 GPa·%,发生韧性断裂,宏观上可以观察到明显的层状裂纹,微观下为大量韧窝;在800~900 ℃退火时,抗拉强度在743~1 154 MPa范围内波动较大,强塑积不足10 GPa·%,断口平整,发生脆性沿晶断裂;退火温度为650 ℃时,组织为片层状和等轴状的奥氏体、铁素体双相及大量渗碳体;随着退火温度的升高,渗碳体逐渐溶解消失,等轴状组织所占体积分数明显增加,奥氏体体积分数也不断增加,在750 ℃时达到52.2%;退火温度为800 ℃时,有马氏体产生,奥氏体体积分数下降;退火温度为900 ℃时,组织基本为马氏体,残留奥氏体体积分数仅为14.6%。     

600 MPa级低合金高强钢的组织调控与工艺优化

为了开发并稳定600 MPa级低合金高强钢的生产工艺参数,利用连续退火模拟机对试验钢进行了连续退火试验,并通过扫描电镜和拉伸试验机研究了均热温度和过时效温度对试验钢显微组织和力学性能的影响。结果表明,随着均热温度的升高,试验钢的屈服强度和抗拉强度均逐渐减小,伸长率逐渐增大;随着过时效温度的升高,屈服强度逐渐增大,抗拉强度逐渐减小,伸长率则先增大后减小。试验钢在820 ℃均热、390 ℃过时效时,获得最优的力学性能,其中抗拉强度为627 MPa,屈服强度为493 MPa,总伸长率超过20%。此外,利用透射电镜观察到钢中存在大量的纳米尺度析出物,这些析出物对试验钢强度的提升有较大的贡献。     

低碳中锰热轧TRIP钢退火工艺及组织演变

研究了第三代高强度高塑性TRIP钢的退火工艺对性能的影响和组织演变规律.热轧后形成的原始马氏体与临界退火时形成的残余奥氏体使TRIP钢具有良好的强度和塑性.结果表明:实验用钢可获得1000MPa以上的抗拉强度和30%以上的断后延伸率,且强塑积>30 Gpa·%;退火温度和保温时间对钢的力学性能具有显著影响,热轧TRIP钢临界退火温度为630℃,保温时间18 h时,实验用钢能获得最佳的综合力学性能.      

Effects of Holding Temperature for Austempering on Mechanical Properties of Si-Mn TRIP Steel

A new type of high strength steel containing a significant amount of stable retained austenite was obtained by austempering immediately after intercritical annealing. This sort of low carbon steel only contains alloying elements of silicon and manganese rather than nickel and chromium. Its mechanical properties were enhanced considerably due to strain-induced martensite transformation and transformation-induced plasticity (TRIP) of retained austenite when it was strained at temperatures between Ms and Md, because retained austenite was moderately stabilized due to carbon enrichment by austempering. Austempering was carried out at different temperatures and 400℃ was found to be optimal. Tensile strength, total elongation and strength-ductility balance reached the maximum values and the product of tensile strength and total elongation exceeded 30 135 MPa % when the TRIP steel was held at 400℃ and strained at 350℃.     

热处理工艺对Fe-Mn-Al-C钢组织和性能的影响

利用SEM、XRD、EPMA等试验方法,对不同退火、固溶以及时效工艺下Fe-Mn-Al-C钢的组织演变规律和力学性能进行研究。结果表明,900～1050℃退火温度对试验钢的组织与性能影响较大,随着退火温度的升高晶粒尺寸增大、碳化物逐渐回溶,强度降低、塑韧性提高,在1050℃保温2 h空冷时抗拉强度为1036 MPa,断后伸长率为39%,冲击功41 J,强塑积40 GPa·%;经1050℃保温2 h水冷固溶后时效处理,试验钢组织为奥氏体+铁素体+κ碳化物,随着时效温度的增高,κ碳化物逐渐析出,使试验钢的强度增加、塑韧性降低。600℃时效时,抗拉强度1145 MPa、断后伸长率22%、冲击功28 J,综合力学性能全部满足设计要求。     

Influence of intercritical annealing temperature on microstructure and mechanical properties of medium Mn TRIP steel

The transformation, microstructure and mechanical properties of the 0. 2C- 5Mn TRIP steel after intercritical annealing were investigated using dilatometer, scanning electronic microscopy (SEM), transmission electron microscopy(TEM), X- ray diffraction (XRD), and tensile testing machine. The phase transformation thermodynamics of the investigated steel after intercritical annealing was calculated by Factsage software and the characteristics of the transformation were discussed. The results show that the reversed austenite content increases with the increasing of the intercritical annealing temperature, the carbon content in reversed austenite firstly increases and then decreases, manganese content in reversed austenite decreases, which results in the decreasing of the thermal stability of reversed austenite. When the intercritical annealing temperature is 700??, an obvious martensitic transformation occurs during the cooling process. With the increasing of intercritical annealing temperature, cementite is gradually dissolved, but it cannot be completely dissolved due to the short transformation time. When the intercritical annealing temperature is 600-675??, the microstructure after intercritical annealing consists of ferrite, cementite and retained austenite. When the intercritical annealing temperature is 700??, the microstructure after intercritical annealing consists of ferrite, retained austenite, martensite and a small amount of undissolved cementite. The engineering stress and strain curves of the investigated steel are significantly changed with increasing intercritical annealing temperature. At the same time, the optimal mechanical properties with tensile strength of 1138MPa and total elongation of 23% can be obtained after annealed at 675?? for 3min.     

Microstructures and mechanical properties of ferrite-based lightweight steel with different compositions

The microstructures and mechanical properties of ferrite-based lightweight steel with different compositions were investigated by tensile test,scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD)and thermodynamic calculation(TC).It was shown that the ferrite-based lightweight steels with 5wt.%or 8wt.%Al were basically composed of ferrite,austenite andκ-carbide.As the annealing temperature increased,the content of the austenite in the steel gradually increased,while theκ-carbide gradually decomposed and finally disappeared.The mechanical properties of the steel with 5wt.%Al and 2wt.%Cr,composed of ferrite and Cr7C3carbide at different annealing temperatures,were significantly inferior to those of others.The steel containing 5wt.%Al,annealed at 820°C for 50sthen rapidly cooled to 400°C and held for 180s,can obtain the best product of strength and elongation(PSE)of 31242MPa·%.The austenite stability of the steel is better,and its PSE is higher.In addition,the steel with higher PSE has a more stable instantaneous strain hardening exponent(n value),which is mainly caused by the effect of transformation induced plasticity(TRIP).When theκ-carbide or Cr7C3carbide existed in the microstructure of the steel,there was an obvious yield plateau in the tensile curve,while its PSE decreased significantly.     

两相区退火处理含铝中锰钢的组织和力学性能

 为了研究两相区退火处理对冷轧含铝中锰钢(0.2C-0.6Si-5Mn-1.2Al)(质量分数,%)微观组织和力学性能的影响规律,利用SEM、XRD及单轴拉伸等试验方法表征了不同工艺状态后的微观组织及测试了拉伸性能。结果表明,冷轧试验钢在退火过程中组织发生奥氏体逆转变,在退火温度为670 ℃、退火时间为10 min时可获得较佳的力学性能,即抗拉强度达到1 276 MPa,总伸长率达到51.8%,强塑积高达66.1 GPa·%。随着退火温度升高,残余奥氏体组织逐渐粗化且向马氏体组织转变,机械稳定性逐渐降低。残余奥氏体机械稳定性主要受残余奥氏体中碳质量分数及其晶粒尺寸的影响,而残余奥氏体中锰质量分数对其影响较小。     

Effects of heat treatment and alloying elements on the microstructures and mechanical properties of 0.15 wt pct C transformation-induced plasticity-aided cold-rolled steel sheets

The main emphasis of this study has been placed on understanding the effects of manganese and silicon additions and of heat-treatment (intercritical annealing and isothermal treatment) conditions on the microstructures and mechanical properties of 0.15 wt pct C transformation-induced plasticity (TRIP)-aided cold-rolled steel sheets. The steel sheets were intercritically annealed and isothermally treated at the bainitic region. Microstructural observation and tensile tests were conducted, and volume fractions of retained austenite were measured. Steels having a high manganese content had higher retained austenite fractions than the steels having a low manganese content, but showed characteristics of a dual-phase steel such as continuous yielding behavior, high tensile strength over 1000 MPa, and a low elongation of about 20 pct. The retained austenite fractions and mechanical properties varied with the heat-treatment conditions. In particular, the retained austenite fractions increased with decreasing intercritical annealing and isothermal treatment temperatures, thereby resulting in the improvement of the elongation and strength-ductility balance without a serious decrease in the yield or tensile strength. These findings suggested that the intercritical annealing and isothermal treatment conditions should be established in consideration of the stability of austenite and the solubility of alloying elements in the austenite formed during the intercritical annealing.     

不同热处理工艺对Nb-Mo中锰钢组织和力学性能的影响

摘要：探讨了不同热处理工艺对Fe-0.25C-3.98Mn-1.22Al-0.20Si-0.19Mo-0.03Nb中锰钢组织演变与力学性能的影响。研究发现,与临界退火和淬火配分（IA & QP）工艺相比,奥氏体逆转变（ART）工艺处理后的实验钢获得了更为优异的力学性能;采用ART工艺经过680℃临界退火5h后的实验钢展现出了最佳的力学性能,即抗拉强度为830MPa,伸长率为48.9%,强度与塑性的乘积达到40.6GPa·%;ART工艺实验钢因长时间退火而促进了Mn向奥氏体中富集,有利于奥氏体含量及稳定性增加,在应变中后期可展现更为广泛的TRIP效应,更有利于获得优异的力学性能。另外,微合金元素Nb和Mo在中锰钢主要起析出强化和细晶强化的作用。     

退火时间对冷轧中锰TRIP钢组织和力学性能的影响

采用CCT-AY-Ⅱ型钢板连续退火机模拟分析了退火时间对中锰TRIP钢0.1C-7Mn组织性能的影响规律.利用扫描电镜、透射电镜、电子背散射衍射和X射线能量色散谱等研究了不同工艺下制备的0.1C-7Mn钢的微观组织和成分,利用X射线衍射法测量了残留奥氏体量,利用拉伸试验测试了其力学性能.0.1C-7Mn钢在650℃保温3 min退火后获得最佳的综合力学性能,其强度为1329 MPa,总延伸率为21.3%,强塑积为28 GPa·%.分析认为,0.1C-7Mn钢的高塑性是由亚稳奥氏体的TRIP效应和超细晶铁素体共同提供的,而高强度是由退火冷却过程中奥氏体转变的马氏体和拉伸变形过程中TRIP效应转变的马氏体的强化作用造成的.