Effects of Silicon Content and Intercritical Annealing on Manganese Partitioning in Dual Phase Steels

Steels of constant manganese and carbon contents with silicon content of 0.34%-2.26% were cast.The as-cast steels were then hot rolled at 1100 ℃ in five passes to reduce the cast ingot thickness from 80 to 4 mm, air cooled to room temperature and cold rolled to 2 mm in thickness. Dual phase microstructures with different volume fraction of martensite were obtained through the intercritical annealing of the steels at different temperatures for 15 min followed by water quenching. In addition to intercritical annealing temperature, silicon content also altered the volume fraction of martensite in dual phase steels. The partitioning of manganese in dual phase silicon steels was investigated using energy-dispersive spectrometer (EDS). The partitioning coefficient, defined as the ratio of the amounts of alloying element in the austenite to that in the adjacent ferrite, for manganese increased with increasing intercritical annealing temperature and silicon content of steels. It was also found that the solubility of manganese in ferrite and austenite decreased with increasing intercritical temperature. The results were discussed by the diffusivity and the solubility of manganese in ferrite and austenite existed in dual phase silicon steels.     

中碳钢球化退火行为和力学性能的研究

采用常规双相区球化退火和亚温球化退火工艺研究了常规轧制（CR）和控轧控冷（CRC）的中碳钢SWRCH35K的球化退火行为和力学性能。结果表明,与传统的双相区球化退火相比,亚温球化退火时碳化物球化进程明显加快,球化率高,且碳化物比较细小,具有良好的塑性和冷成形性,采用亚温球化退火处理可明显地缩短球化退火时间。控轧控冷的中碳钢线材尽管具有比较粗大的珠光体组织,但因有相当部分的珠光体发生退化,其球化退火进程要明显快于细珠光体组织。     

连续退火过时效温度对热处理双相钢组织性能的影响

 采用光亮连续退火模拟实验机研究了0.08C 1.7Mn 0.03Si钢在不同连续退火过时效温度下组织和性能的变化规律,并构造了各相在连续退火工艺期间的反应关系式。试验结果表明：过时效温度在450 ℃时,组织中的第二相主要为粒状贝氏体＋马氏体,350 ℃时为板条状贝氏体＋马氏体,250 ℃时为马氏体或M A岛;过时效温度降低,试验钢抗拉强度明显升高,屈服强度明显降低,而n值、值和杯突值变化不大;350 ℃过时效时,试验钢的伸长率有增高的趋势,因此调整第二相组分比例可能是提高试验钢塑性的有效手段。     

鞍钢2130连退生产线产品碳含量的控制

因连续退火与罩式退火工艺的差别,鞍钢冷轧厂在新投产的2130连退生产线实施了产品碳含量的控制。按钢中碳的不同含量制定不同的退火工艺,提高了产品性能,达到了与罩式炉产品相近的性能水平,满足了不同用户的个性化需求。     

两相区保温时间对冷轧双相钢组织性能的影响

对Q345冷轧钢板两相区退火进行了研究,通过对不同保温时间试验钢板的金相组织以及拉伸试验结果对比,得出如下结论：保温时间对试验钢微观组织和力学性能有影响,790℃下60～120 s退火,可以有效消除冷轧过程中产生的带状组织,并能避免因过长保温造成的组织粗化。     

Microstructure and Properties of Mo Microalloyed Cold Rolled DP1000 Steels

  Two kinds of ultra high strength cold rolled dual phase steels have been developed by designing C Si Mn Cr and C Si Mn Cr Mo alloy systems. Tensile strength and elongation of both steels exceed 1100 MPa and 10%, respectively. The microstructures of both steels consist of massive martensite and ferrite. And the massive martensite of Mo free steel disperses in the ferrite with volume fraction of 64%. However, the massive martensite of Mo containing steel is connected or closed by small martensite islands each other, and martensite volume fraction is 69%. As to Mo free steel, the yield strength, yield ratio, and work hardening exponent n are 548 MPa, 049, and 026, respectively. As for Mo containing one, the yield strength, yield ratio, and n value are 746 MPa, 066, and 033, respectively. Besides, the ferrite of Mo free steel is deformed at the initial stage of plastic deformation. However, for Mo containing one, Mo solution strengthened ferrite and small overaged martensite islands are deformed preferentially at small strain, which causes the yield strength to reach approximately 200 MPa higher than that of Mo free steel.     

Microstructure and Properties of Mo Microalloyed Cold Rolled DP1O00 Steels

Two kinds of ultra-high strength cold rolled dual phase steels have been developed by designing C-Si-Mn-Cr and C-Si-Mn-Cr-Mo alloy systems. Tensile strength and elongation of both steels exceed 1 100 MPa and 10%, respectively. The microstructures of both steels consist of massive martensite and ferrite. And the massive martensite of Mo-free steel disperses in the ferrite with volume fraction of 64%. However, the massive martensite of Mo-containing steel is connected or closed by small martensite islands each other, and martensite volume fraction is 69%.As to Mo-free steel, the yield strength, yield ratio, and work hardening exponent n are 548 MPa, 0.49, and 0.26,respectively. As for Mo-containing one, the yield strength, yield ratio, and n value are 746 MPa, 0. 66, and 0.33,respectively. Besides, the ferrite of Mo-free steel is deformed at the initial stage of plastic deformation. However,for Mo-containing one, Mo solution strengthened ferrite and small overaged martensite islands are deformed preferentially at small strain, which causes the yield strength to reach approximately 200 MPa higher than that of Mo-free steel.     

冷轧双相钢连续退火组织的转变

采用光学显微镜与扫描电镜观察分析了实验钢冷轧组织在连续退火过程中的再结晶与相变规律,研究了过时效回火对双相钢显微组织的影响.实验表明,在连续退火初期的加热过程中,在600～720℃大量进行再结晶.加热速度对再结晶行为有较大影响,以10℃/s加热,再结晶将持续到双相区.珠光体在低于720℃的加热过程中变化不明显,而铁素体晶界与晶内出现球状碳化物颗粒.双相区退火过程中,奥氏体首先在珠光体处形成,原铁素体晶界与晶内的碳化物颗粒也形成奥氏体岛.800℃保温后缓慢冷却至630～680℃可以得到合理比例的双相钢组织.当过时效温度大于300℃,马氏体分解,碳化物颗粒析出,将对双相钢性能产生不良影响.     

碳含量对Fe-Ni-Mn-Si-C系TWIP钢应变硬化行为的影响

采用单向拉伸、金相组织观察、TEM等方法,研究了3种不同碳含量Fe-Ni-Mn-Si-C系TWIP钢的拉伸应变硬化行为。研究结果表明,随着碳含量的增加,合金的强度和伸长率均提高,当碳质量分数为1.0%时,该TWIP钢具有较好的综合力学性能,强塑积达到83 160 MPa.%。3种TWIP钢的真应力-真应变曲线均不完全遵...     

Effect of Ti on Austenite Grain Growth Behavior in High Carbon Steels

Austenite grain growth behavior of two high carbon steels was observed using Confocal l.aser Scanning Mi croscope （CLSM）. Apparent austenite grain sizes for different holding time under a series of temperatures were measured by employing linear intercept method. Experimental results showed that Ti bearing steel exhibited a much sluggish growth rate compared with Ti free counterpart, which was attributed to the pinning effect of Ti（C,N） nan oparticles with the size of 20 to 40 nm on austenite grain boundaries. Based on the research conducted by using Transmission Electron Microscope （TEM） observation and Thermo Calc calculation, Ti（C, N） was confirmed to be the dominant phase at elevated temperature. Some models were introduced to predict the grain sizes of both steels. By comparison, the results predicted by the modified Gladman equation are found to be closest to the experimental resuits, which could be employed to predict accurately the austenite grain growth of high carbon steels.     

碳含量和组织类型对低合金钢耐蚀性的影响

 研究了碳含量不同和显微组织不同的低合金钢的耐腐蚀性能和腐蚀行为,并和商业耐候钢09CuPCrNi做了相应的比较。在碳含量比较低的情况下,组织类型对试验钢的耐蚀性影响不大;碳含量比较高时,单相贝氏体钢的耐蚀性优于由铁素体、渗碳体(珠光体)等构成的复相组织钢。轧后水冷时,不同碳含量的钢耐蚀性差别不大;轧后空冷时,碳含量低的钢的耐蚀性优于碳含量较高的钢。用扫描电镜对锈层进行观察,可以看出耐蚀性较好的试样在腐蚀后期形成了较致密的内锈层。碳的质量分数分别为0.03%和0.1%的钢水冷后的平均腐蚀速率相差很小,但从微观角度看其点蚀发展趋势不同。加速腐蚀5个周期后,w(C)为003%的水冷钢中蚀坑尺寸不再增加,而w(C)为01%的钢中蚀坑尺寸仍有增加趋势。     

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Effects of intercritical quenching temperature on microstructural evolution and mechanical properties of a new type of cryogenic steel with Ni replaced by Mn were investigated by XRD, EBSD and TEM. The results show that the volume fraction of metastable austenite at room temperature decreases with the increase of intercritical quenching temperature. When interctritical quenching temperature is at 700 or 740??, metastable austenite mainly precipitates in the shape of thin film along the lath boundaries of tempered martensite, paralleling to the surrounding martensitic laths. This ??film-type?? metastable austenite is uniformly distributed and stable, with a thickness of about 100nm. When intercritical quenching temperature is 780??, the volume faction of ??film-type?? metastable austenite decreases, and large ??blocky-type?? metastable austenite appears at the junction of interface of tempered martensite. Analysis indicates that the differences on ??effective grain size?? of matrix, volume fraction of metastable austenite and its stability caused by different heat treatment process lead to the difference on low temperature toughness of the tested steel at different intercritical quenching temperature.     

红外吸收法测定超低碳钢中的碳硫

文章介绍了利用红外碳硫分析仪对超低碳钢中的碳、硫进行分析的实验过程。实验数据表明：采用红外吸收法可对超低碳、硫进行分析测定,分析方法的精度和准确度满足ASTME1019—2000的要求,在实际操作中切实可行。     

Effect of Cyclic Annealing on Microstructure and Mechanical Properties of Medium Carbon Steel

The microstructure and mechanical properties of medium carbon steel after cyclic heat treatment were in-vestigated.The effects of cyclic numbers and long time annealing on the microstructure and mechanical properties of the experimental steel were compared.A short-duration (5 min)holding at 1 023 K (above A1 temperature)and a short-duration (3 min)holding at 893 K are adopted in each cyclic heat treatment.The spheroidization is accelerated during cyclic heat treatment,and the spheroidizing ratio grows with cyclic numbers.After 1 2-cycle heat treatments, there are few incompletely spheroidized regions in the specimens,and cementite lamellae mostly change into cement-ite particles.The morphological character of cementite for 12 cycles is similar to that undergoing annealing for 10 h at 973 K.The strength of the experimental steel after 5-cycle heat treatment is the lowest in the following cyclic heat treatment,but it is still higher than that of specimens with subcritical annealing over a long period (10 h).After 12-cycle heat treatment,the strength of the experimental steel is close to that of the normalized steel,and the plasticity is the best in all heat-treated specimens.     

Influences of Austenization Temperature and Annealing Time on Duplex Ultrafine Microstructure and Mechanical Properties of Medium Mn Steel

A duplex ultrafine microstructure in a medium manganese steel(0.2C-5Mn)was produced by austenite reverted transformation annealing(ART-annealing).The microstructural evolution during annealing was examined by scanning electron microscopy(SEM),transmission electron microscopy(TEM)and X-ray diffraction(XRD).Based on the microstructure examination,it was found that some M3 C type carbides appeared in the martensitic matrix at the beginning of the ART-annealing.But with further increasing annealing time,these carbides would be dissolved and finally disappeared.Meanwhile,the austenite lath was developed in the ART-annealing process and the volume fraction of austenite increased with the increase of the annealing time,which resulted in a duplex microstructure consisting of ultrafine-grained ferrite and large fraction of reverted austenite after long time annealing.The mechanical property examinations by uniaxial tensile tests showed that ART-annealing(6h,650 ℃)resulted in a superhigh product of strength to elongation up to 42GPa·%.     

Improvement of Hole-Expansion Property for Medium Carbo Steels by Ultra Fast Cooling After Hot Strip Rolling

 The improvement of hole-expansion properties for medium carbon steels by ultra fast cooling (UFC) after hot strip rolling was investigated. It was found that finely dispersed spherical cementite could be formed after ultra fast cooling, coiling and annealing treatment. Tensile strength of the steel after annealing was measured to be about 440 MPa. During hole-expansion test, cracks were observed in the edge region around the punched hole because necking or cracking took place when tangential elongation exceeded the forming limit. Cracks were mainly formed by the coalescence of micro-voids. Fine and homogeneous microstructure comprised of ferrite and spheroidized cementite could increase elongation values of the tested sheets by suppressing the combination of the adjacent micro-voids, resulting in the improved hole-expansion property.