Reheating Austenitizing Temperature of Spring Steel 60Si2MnA for Railway

The microsturctural transformation of austenite grain, pearlite interlamellar spacing, and lamellar cement ite thickness of spring steel 60Si2MnA for railway were studied in the hot-rolled and reheated states. Furthermore, the effect of microstructural characterization on its final mechanical properties was discussed. The results showed that as far as 60Si2MnA, the pearlite interlamellar spacing determined the hardness, whereas, the austenite grain determined the toughness. Compared with microstructure and mechanical properties in the hot rolled state, after reheating treatment at 950 ℃, its average grain sizes are apparently fine and the pearlite interlamellar spacing and lamellar cementite thickness coarsen to some extent, but both hardness and impact toughness increase to HRC 48 and 8.5 J, respectively. In the course of making spring, the optimum reheating austenitizing temperature for the 60Si2MnA steel is 950 ℃.     

Nb对V、N微合金化压力容器钢珠光体形态及低温韧性影响

为了在保证强度同时提升压力容器钢低温韧性，以铌(Nb)取代部分钒(V),研究Nb的添加对V、N微合金化正火压力容器钢板显微组织和力学性能的影响。结果表明，Nb+V试验钢相比于V试验钢，在强度保持630 MPa的同时可显著提升低温冲击韧性，-20、-40、-60℃冲击吸收功分别提升59、44、29 J。原因主要为Nb的添加促进了细小铁素体转变，其含量的增加使钢的塑韧性增强。此外V和Nb+V钢中碳原子扩散系数在平均转变温度下分别为2.64×10^-13、2.14×10^-13 cm²/s, Nb的添加降低了珠光体生长速度、增加了珠光体转变过程中的过冷度，从而细化了珠光体团簇和片层间距。EBSD分析可知以Nb取代部分V后试验钢有效晶粒尺寸由7.7μm减小至5.8μm,大角度晶界比例由83.1%增加至85.5%。微合金元素Nb的细晶作用及对大角度晶界比例提升的贡献也可以大幅提高钢的低温冲击韧性。     

锰对低碳耐候钢组织与强韧性的影响

在真空感应炉冶炼了2炉不同锰质量分数的低碳耐候钢,利用热模拟机和金相显微镜分析了其组织特征和相变规律,并通过室温拉伸、冲击实验且结合断口分析表征了实验钢的强韧性。热模拟实验表明,低碳高锰耐候钢组织在低冷速下（＜1 ℃/s)为铁素体＋少量珠光体,而在较大冷速内(1～10 ℃/s)为贝氏体＋铁素体复相特征,随冷却速度的增加则钢中贝氏体增多。分析轧态组织表明,2组实验耐候钢中主要组织均为等轴铁素体;增加钢中锰则其强度明显增大,虽塑性和冲击韧性有所降低,但仍可获得良好的强韧性组合。     

轧后热处理温度对热轧钢轨组织和性能的影响

 通过在Gleeble-1500热模拟试验机上对珠光体钢轨的轧后热处理模拟试验,研究了热轧后不同加热温度进行奥氏体化后,同一等温温度下得到的珠光体轨钢的显微组织和力学性能。试验结果表明：与热轧态相比,热处理后的钢轨钢在保持硬度稳定的基础上,冲击韧性随着奥氏体化温度降低得到明显改善。观察轧后热处理钢轨的组织,从原始奥氏体晶粒尺寸、相变后珠光体组织中珠光体域的尺寸和珠光体片层间距大小等方面,对轧后热处理温度对热轧钢轨性能的影响规律和原因进行了分析,阐明了轧后热处理温度对于控制珠光体钢轨的组织和性能的影响作用。     

锰对低碳耐候钢组织与强韧性的影响

在真空感应炉冶炼了2炉不同锰质量分数的低碳耐候钢,利用热模拟机和金相显微镜分析了其组织特征和相变规律,并通过室温拉伸、冲击实验且结合断口分析表征了实验钢的强韧性。热模拟实验表明,低碳高锰耐候钢组织在低冷速下（＜1 ℃/s)为铁素体＋少量珠光体,而在较大冷速内(1～10 ℃/s)为贝氏体＋铁素体复相特征,随冷却速度的增加则钢中贝氏体增多。分析轧态组织表明,2组实验耐候钢中主要组织均为等轴铁素体;增加钢中锰则其强度明显增大,虽塑性和冲击韧性有所降低,但仍可获得良好的强韧性组合。     

Low Cost High Performance Steel Plate With Superior HAZ Toughness for Large Heat Input Welding

In this paper, a laboratory study has been made to develop low cost high performance steel plates with superior HAZ toughness for large heat input welding. Simulated results show that the absorbed impact energy of heat-affected zone (HAZ) at -20℃reaches above 200J when large heat inputs of 100 to 400kJ/cm were applied, suggestive of superior HAZ toughness for large heat input welding of developed steel plate. The microstructures in HAZ are transformed from mainly fine ferrite and bainite at 100kJ/cm, through an intermediate stage of ferrite, bainite and pearlite at 200 and 300kJ/cm, to nearly fine ferrite and pearlite at 400kJ/cm. The prior austenite grain size and ferrite grain size in HAZ are controlled to ～50 and ～20μm, respectively. The high HAZ toughness is due to the inhibition of prior austenite grain size at high temperatures and the formation of beneficial microstructures to HAZ toughness during continuous cooling.     

铌对低温钢组织及性能的影响

通过金相组织观察、低温冲击试验和拉伸试验及拉伸断口形貌观察,研究了铌对正火+调质处理低温钢组织及性能的影响。结果表明:铸态下随着试样中铌含量的增加,组织中珠光体片间距逐渐减小,经过930℃正火+900℃淬火+630℃回火热处理后,铌质量分数为0.039%的试样组织及综合性能最佳,组织为回火索氏体,-20、-40℃夏比冲击功分别达到44.4和28.4J,抗拉强度和屈服强度分别为995和885MPa,断后伸长率达到17.0%。     

BVRE重轨钢奥氏体长大行为的动力学研究

以BVRE重轨钢为研究对象,通过真空冶炼、锻造和轧制工艺制备合格的重轨钢试样.在此基础上,系统研究稀土重轨钢奥氏体晶粒的长大动力学.实验结果表明,随着加热温度的提高,稀土重轨钢奥氏体晶粒呈指数关系长大;随着保温时间的延长,稀土重轨钢奥氏体晶粒长大呈抛物线规律.重轨钢中添加微量的稀土,可以明显降低不同加热条件下的奥氏体晶粒尺寸.模型计算结果表明,重轨钢的奥氏体晶粒长大公式分别为:d4.80=d4.800+ 2.82×1028texp(- 556450/RT)(不加稀土)和d5.34=d5.340 +4.52×1032texp(- 646890/RT)(稀土重轨钢).稀土主要通过晶界的偏聚机制使奥氏体晶粒长大激活能由556450J·mol-1增加到646890J·mol-1,从而抑制奥氏体晶粒尺寸的增加.     

稀土改善430铁素体不锈钢冲击韧性的作用机理

 采用金相、扫描电镜和能谱等分析手段,研究了微量稀土对430铁素体不锈钢在室温和低温下的横向冲击性能的影响。研究结果表明,稀土夹杂物减缓了裂纹的扩展。加稀土的试样断口为韧性撕裂,不加稀土的试样断口为解理断裂。加微量稀土的试样横向冲击性能比不加稀土的试样大幅度提高,最高提高了5倍。     

Mn2钢低温韧性变化规律研究

对Mn2钢在不同热处理工艺、不同试验温度和不同试样状态下的冲击韧性进行了详细的分析,结果表明:CM690钢在900℃保温90 min水冷淬火,600℃保温90 min水冷回火,在保证钢材的强度满足要求的情况下,可获得良好的韧性;淬火水温超过30℃时,因钢的淬透能力下降,会强烈地降低钢的强度和韧性;钢中加入0.015%~0.025%的Ti,提高冲击韧性值35~40 J;对于CM490钢,若轧后空冷或堆冷,由于冷却速度较低,会获得铁素体+珠光体+贝氏体的混合组织,不利于提高钢材的韧性,而正火后其组织为铁素体+贝氏体,其冲击值比前两种状态高3~5倍。     

轧制比和Nb对V-Ti微合金非调质钢组织及性能的影响

通过金相、扫描、透射电镜研究不同轧制比工艺下V-Ti、Nb-V-Ti两种微合金化非调质钢的微观组织及机械性能。结果显示:Nb-V-Ti非调质钢轧制比大于10时,冲击韧性值可以达到50 J,而V-Ti非调质钢的轧制比却需要大于15以上,才能达到类似的冲击韧性值。从相同轧制比对比也可以发现,Nb-V-Ti非调质钢的冲击性能明显优于V-Ti非调质钢,这是因为Nb能够显著提高非调质钢的奥氏体粗化温度,有效阻止奥氏体晶粒的快速长大,细化非调质钢晶粒,降低珠光体片层间距,使渗碳体呈粒状或球状分布;另外,Nb能促进V-Ti非调质钢中细小含铌碳化物的弥散析出,细化基体组织,同时提高非调质钢的强度。因此,Nb-V-Ti复合非调质钢经过未再结晶区变形后可获得均匀细小的铁素体-珠光体组织,且在900℃未再结晶区进行大轧制比变形能够有效改善Nb-V-Ti非调质钢的强韧性。     

Effect of Rare Earth on Microstructures and Properties of High Speed Steel With High Carbon Content

The effects of rare earth （RE） on the microstructures and properties of high carbon high speed steel （HCHSS） were investigated. The results show that when suitable RE is added to the HCHSS, the effect of RE on the austenite and eutectic carbides is obvious. The austenite grain and coarse eutectic structure are refined, and flake carbides in the eutectic structures become short and fine. After heat treatment, most of the eutectic carbides are spheroidized and distributed in a uniform manner. The hardness and red hardness of modified HCHSS are slightly increased; impact toughness is greatly increased by 37.81% and reaches 10.17 J/cm^2. The mechanism by which RE improves the structures and properties of HCHSS is also analyzed.     

高强度高韧性贝氏体钢轨研究

采用合金化方法生产的高强度高韧性贝氏体钢轨及道岔,其热轧态抗拉强度大于1 250 MPa,比U75V提高25%;轨腰冲击韧性大于30 J/cm2,比U75V提高3倍以上.介绍了热轧贝氏体钢轨的强化机理、生产工艺及各项检验结果.用贝氏体钢制作的铁路道岔在线路运行已一年半以上,货运量达2亿t,目前仍在使用.在北京铁路局铺设的全贝氏体组合道岔,其使用寿命进一步提高,高强度高韧性贝氏体钢在铁路使用将得到较大的社会和经济效益.     

回火温度对9Ni钢低温韧度的影响研究

为了研究不同回火温度对9Ni钢低温韧度的影响,利用OM、SEM、TEM对试验钢微观组织和断口形貌进行观察分析,研究表明:在550~600℃范围内回火,9Ni钢强度和韧度达到最佳匹配,且其他各项性能也达到最佳;回转奥氏体、碳化物及回转奥氏体诱发马氏体相变等均对低温韧度产生重要影响。     

Effect of Boron on CGHAZ Microstructure and Toughness of High Strength Low Alloy Steels

Effect of boron on the microstructure and impact toughness in the coarse-grained heat-affected zone(CGHAZ)of two high strength low alloy steels,boron-free and boron-containing,was investigated by means of weld thermal simulation test.The result shows that,for the boron-free steel,a microstructure consisting of grain boundary ferrite degenerates pearlite and granular bainite for longer t8/5(the cooling time from 800 to 500 ℃),while lath bainite for shorter t8/5.For the boron-containing steel,granular bainite is dominant for a wide range of t8/5.Continuous cooling transformation(CCT)study on the CGHAZ indicates that the transformation start temperature decreases by about 50-100℃under different t8/5,for the boron-containing steel compared with the boron-free steel.The presence of boron suppresses the nucleation of ferrite at prior austenite grain boundaries and hence enlarges the range of t8/5for granular bainite transformation.However,the addition of boron deteriorates the impact toughness of CGHAZ,which may be due to a markedly increased fraction of martensite-austenite(M-A)constituents and decreased fraction of high angle grain boundaries.     

15CrMoR钢的显微组织与时效冲击性能

 为探索原始组织形态对15CrMoR钢时效过程低温冲击性能的影响,明确15CrMoR钢具有高时效冲击性能稳定性的原始组织形态,通过控制奥氏体化后的冷却方式获得了15CrMoR钢的3种原始组织,使用OM、SEM、EPMA和EBSD等材料结构表征方法和低温冲击测试研究了15CrMoR钢的显微组织和时效态低温冲击性能。结果表明,15CrMoR钢奥氏体化后分别以炉冷、空冷和风冷的方式冷却至室温,分别获得了粗大铁素体+片状珠光体组织、铁素体+退化珠光体组织和粒状贝氏体组织。片状珠光体组织中碳化物主要呈层片状,退化珠光体中的碳化物主要呈断续短杆状和颗粒状,粒状贝氏体中的富碳M-A岛主要沿晶界分布。3种原始组织形态的15CrMoR钢在循环时效过程中均发生了晶界碳化物析出和长大,导致低温冲击性能不断恶化。当晶界碳化物呈链状分布时,15CrMoR钢的低温冲击性能较差。粗大的铁素体+片状珠光体组织晶界面积较少,导致晶界碳化物容易呈链状分布;粒状贝氏体中主要沿晶界分布的富碳M-A岛也容易导致晶界碳化物呈链状分布。因此,原始组织为铁素体+退化珠光体的15CrMoR钢在循环时效过程中具有较好的冲击性能稳定性,经历6次循环时效后,-10 ℃平均冲击吸收功仍高达196 J;而原始组织为铁素体+片状珠光体和原始组织为粒状珠光体的15CrMoR钢,经历4次循环时效后,晶界处已形成呈链状分布的碳化物,-10 ℃平均冲击吸收功均仅为18 J。     

Development of JG785E High Strength High Toughness Steel Plates

A high strength structure steel plate --brand JG785E, which with more than 690MPa yield strength ,more than 47 joules toughness at minus 40℃ has been developed by Jigang of Shandong Steel Group P. R. China. The steel plates can be easily welded in engineering structure due to its lower carbon equivalent value. The maximum thickness of heavy plate is 50.88mm (2 inch), the yield strength is 710-860MPa, the toughness of steel plate is 139~336J at the temperature of - 40℃ . The microstructure of steel plate is lower carbon Bainite. The main solid dissolve elements are silicon and manganese. All parameters of reheating, rolling and accelerating cooling are controlled strictly. This TMCP procedure can ensure to get better mechanical properties of steel plates, and to keep the market competitive power and lower cost of manufacture. The cleanness of steel is high by refined in ladle furnace (LF), the contents of P and S is lower. It is the low carbon Bainite microstructure that possesses the high strength, excellent lower temperature toughness and better weld-ability without preheat process. The JG785E is typical brand of the Jigang’s high strength steel brands as the S690QL conforms to EN10025-6 and as the ASTM A514M conforms to USA quenching and tempering steel specification.     

The effect of alloying elements and microstructure on the strength and fracture resistance of pearlitic steel

The processes of ductile and brittle fracture in fully pearlitic steel and their relation to both the scale of the microstructure and the presence of substitutional alloy elements have been investigated at room temperature using smooth tensile and over a range of temperatures using V-notched Charpy impact specimens. The results show that the early stages of cracking, revealed in both types of specimen, are largely the result of shear cracking of the pearlite lamellae. These cracks grow and can reach a size when they impinge upon the prior austenite boundary; afterward the character of fracture can be either microvoid coalescence or cleavage, depending on test conditions and metallurgical variables. Further, the carbide plates of the pearlite lamellae can act as barriers to the movement of dislocations as is the case normally with grain boundaries. For pearlite an optimum spacing of approximately 0.2 μm resulting from a balance between carbide plate thickness and interlamellar spacing was found to enhance toughness, although such changes are much smaller than corresponding changes due to varying alloy elements. Specific alloy elements used herein strengthened the lamellar ferrite in pearlite, inhibiting the movement of dislocations while also usually decreasing the lamellar cementite plate thickness for the same spacing. This dual behavior results in enhanced resistance to the initiation and propagation of microcracks leading to an improvement in strength, ductility, and toughness. The most effective alloy elements for the composition ranges studied in fully pearlitic steels are Si and Ni for strength improvement, and Ni and Mn for toughness.     

残留奥氏体对微纳贝氏体钢塑韧性的影响

采用高碳和中碳低温贝氏体转变工艺（095C钢为200℃等温10d，030C钢为320℃等温1d）研究了残留奥氏体对微纳结构钢塑韧性的影响，对不同试样的显微组织、各相体积分数、伸长率和冲击韧性进行观察、检测和分析。试验结果表明，中碳钢贝氏体转变的塑韧性明显高于高碳钢贝氏体转变，主要原因是中碳钢贝氏体转变中存在一定的亚微米级薄膜状残留奥氏体，在拉伸或冲击过程中引起的残留奥氏体的塑性变形，使断裂的能量增加，可以显著提高样品的塑韧性。     

80mm厚高韧性工程机械用Q460级TMCP钢的研制

采用低碳Cr-Mo系添加微量强碳化物形成元素的成分设计,通过TMCP工艺控制,获得均匀铁素体/贝氏体组织,充分发挥析出强化、细晶强化和贝氏体组织强化作用,研制80 mm厚高韧性工程机械用Q460钢。试制钢板力学性能均匀,不仅具有良好的拉伸力学性能,且低温冲击韧性优良,-60℃冲击功大于180 J,冲击断口呈明显塑性变形;SEM分析表明,断口微观形貌韧窝特征明显,面积约为55%,韧窝内圆形氧化物夹杂细小;钢板厚度方向铁素体/贝氏体组织均匀,晶粒尺寸约为8～10μm;TEM分析表明,晶内存在高密度位错,大量细小弥散的第二相粒子沿位错线析出。