High Carbon Alloy Steels with Multiple Types of Ultra-fine Carbides and Their Characteristics

Under normal forging and annealing conditions, there are different ultra fine carbides (M3C, M23C6, M7Cj, M6C and MC) in high carbon alloy steels when alloy composition design is carried out properly. On the basis of carbides transformation orderliness, the alloy composition design of the high carbon alloy steels is conducted by phase-equilibrium thermodynamic calculation for Fe-Cr-W-Mo-V-C system. The nucleation and growth of new carbides, dissolution of previous partial carbides in these steels during annealing process, all these lead to ultra-fine distribution of carbides. Due to different crystal structures of carbides and different thermodynamics as well dynamics parameters of the carbides dissolution and precipitation, the range of quenching temperature of these steels is widened, and the good temper-resistance is obtained. The characteristics of heat treatment process and microstructure variance, and the carbides transformation for different temperature are explained by the phase-equilibrium component satisfactorily. Their bend and yield strength, flexibility and toughness all are advanced markedly comparing with that of kindred steels. Results of the applications have proved that the microstructure of ultra-fine carbides in these steels played importance roles in the enhancement of edginess and fatigue crack resistance of the die and knives.

Influence of soaking time in deep cryogenic treatment on the microstructure and mechanical properties of low-alloy medium-carbon HY-TUF steel

The influence of soaking time in deep cryogenic treatment on the tensile and impact properties of low-alloy medium-carbon HY-TUF steel was investigated in this study. Microstructural studies based on phase distribution mapping by electron backscatter diffraction show that the deep cryogenic process causes a decrease in the content of retained austenite and an increase in the volume fraction of η-carbide with increasing soaking time up to 48 h. The decrease in the content of retained austenite from ~1.23vol% to 0.48vol% suggests an isothermal martensitic transformation at 77 K. The η-type precipitates formed in deep cryogenic-treated martensite over 48 h have the Hirotsu and Nagakura orientation relation with the martensitic matrix. Furthermore, a high coherency between η-carbide and the martensitic matrix is observed by high-resolution transmission electron microscopy. The variations in macrohardness, yield strength, ultimate tensile strength, and ductility with soaking time in the deep cryogenic process show a peak/plateau trend.

Effect of Boron on Delayed Fracture Resistance of Medium-Carbon High Strength Spring Steel

The delayed fracture behavior of medium carbon high strength spring steel containing different amounts of boron （0. 000 5%, 0. 001 6 %） was studied using sustained load delayed fracture test. The results show that delayed fracture resistance of boron containing steels is higher than that of conventional steel 60Si2MnA at the same strength level and it increases with the increase of boron eontent from 0. 000 5% to 0. 001 6%. The delayed fracture mode is mainly intergranular in the boron containing steels tempered at 350℃, which indicates that the addition of boron does not change the fracture character. However, the increase of boron content enlarges the size of the crack initia tion area. Further study of phase analysis indicates that most boron is in solid solution, and only a very small quantity of boron is in the M3 （C, B） phase.

Effect of RE-Modifier on Microstructure and Mechanical Property of High-Carbon Medium-Manganese Steel

The effect of RE-modifier on the microstructure and mechanical properties of high carbon-medium manganese steel has been investigated in present work.The results showed that the RE-modifier can refine the crystalline grain of high-carbon medium-manganese steel.The shape and distribution of carbides are improved and the columnar grains and phosphide in grain boundary are eliminated.Consequently,the impact toughness of the steel is increased by more than one time,compared with no addition of RE-modifier.

PHASE TRANSFORMATION UNIT OF BAINITIC FERRITE AND ITS SURFACE RELIEF IN LOW AND MEDIUM CARBON ALLOY STEELS

The lath-or plate-shaped bainitic ferrite of low and medium carbon alloy steels consists of packets of ferrite sublaths which are composed of many finer and regular ferrite blocks.They are uniform shear growth units of bainitic phase transformation.No carbide is precipitated from them.The bainitic O-carbides are precipitated from γ-α interface or carbon-rich austenite.The mode of arrangement of the units in ferrite sublath packet is in uni-or bi-di- rection.Single surface relief is produced by the accumulation of uniform shear strains with all the ferrite units arranged unidirectionally in a sublath packet,while tent-shaped surface relief is formed by the integration of the uniform shear strains of two groups with ferrite units piling up in two directions and growing face to face;whereas if they grow back to back,the integra- tion will be responsible for invert-tent-shaped surface relief.The interface trace between two groups of ferrite units in a sublath packet is shown as“midrib”.

The micro structure of high carbon low alloy steel for easy drawing

For better processing performance of high carbon low alloy steel wire rod,an investigation about the influence of cementite lamellar spacing on wire 'easy drawing' performance is completed.It is pointed out that too thin cementite lamellar spacing(<80 um) reduces the strain hardening level of wire drawing, and reduce the torsion performance of drawn wire at same time.For the wire or wire rod from industrial production,compared with the micro-structure with troostite,the micro-structure with sorbite or sorbite mixed with pearlite is more suitable to the drawing process with high reduction ratio.

High-temperature mechanical properties of near-eutectoid steel

The high-temperature mechanical properties of near-eutectoid steel were studied with a Cleeble-1500 simu- lation machine. Zero strength temperature （ZST）, zero ductility temperature （ZDT）, hot ductility curves, and strength curves were measured. Two brittle zones and one plastic zone were found in the temperature range from the melting point to 600℃. Embrittlement in zone I is caused by the existence of liquid film along dendritic interfaces. Ductility loss in zone Ⅲ mainly results from precipitates and inclusions as well as S segregation along grain boundaries. Pearlite transformation also accounts for ductility deterioration in the temperature range of 700-600℃. Moreover, the straightening temperature of the test steel should be higher than 925℃ for avoiding the initiation and propagation of surface cracks in billets.

Microstructure evolution of an ultra-high strength metal alloy with tempering temperature

Optical microscopy (OM) and transmission electron microscopy (TEM) were used to investigate the effect of tempering temperature on the experimental extra-high carbon steels. It is found that tempering reaction can reduce austenite content and influence the stability of the austenite. As-normalized microstructure is a mixture of twinned martensite and retained austenite. Tempered at 250 °C for 2 h, lath martensite can occasionally be found nearby the diffusionally decomposed austenite area. It also is found that tempering at 650 °C for 2 h, nanoparticles of carbides precipitate in the martensite and decomposed austenite. © The Nonferrous Metals Society of China and Springer-Verlag Berlin Heidelberg 2012.

Cr-W-Mo-V高碳中合金钢在αγ相变过程的碳化物转变及形貌

研究表明,Cr-W-Mo-V高碳中合金钢加热至αγ温度区附近,M23C6和M3C会逐渐溶解于基体中,缓冷过程逐渐析出M23C6、M3C,并在αγ温度区发生M23C6M6C转变,而球状VC则变化不大,其碳化物超细化主要南溶解、形核的转变过程所引起的。碳化物细化及不均匀程度依赖于碳化物类型及其比例,因此,合理的成分设计是常规锻轧和热处理工艺下获得超细碳化物高碳中合金钢的关键。

Cr-W-Mo-V高碳中合金钢的抗回火性及其硬度

研究了4种不同成分Cr-W-Mo-V高碳中合金钢的回火硬度曲线和相关的组织结构,分析讨论了抗回火温度区间及高回火硬度的机理。结果表明:Cr-W-Mo-V高碳中合金钢在抗回火温度区间,较高的回火硬度是碳化物沉淀强化与回火马氏体固溶强化和残留奥氏体转变及分解共同作用。随着含C量和合金含量尤其含Cr量增加,抗回火性增强。抗回火时新析出相不与平衡相完全对应,其中沉淀析出主要是(Fe,Cr)3C。

精炼钢水造渣分级管控的研究与应用

结合不同钢种精炼造渣特点和钢水进精炼期间不同的生产条件,以普碳低合金钢HRB400E系列、优质碳素高碳钢65#系列以及板坯普碳钢Q235B系列为例进行研究,在原先精炼造渣的基础上进一步实施精炼钢水顶渣造渣分级管控,通过对不同钢种、不同硫含量等条件下精炼造渣分级管控措施的落实,实现精炼造渣效率有效提升、钢材质量稳步提高、精炼系统成本有效降低,进一步推动炼钢系统精细化管理向好、向深发展。

二次碳化物特征调控及其对高碳高合金马氏体钢耐磨性的影响

二次碳化物的尺寸、含量对高碳高合金马氏体钢的力学性能及耐磨性有着重要影响.本文采用扫描电子显微镜、透射电子显微镜和磨粒磨损实验等手段,研究了高碳高合金马氏体钢锻造及球化退火过程中二次碳化物的演变行为及其对高碳高合金马氏体钢力学性能及耐磨性的影响.结果表明:球化退火显著增加了锻造空冷态实验钢中二次碳化物的含量及尺寸;在奥氏体化过程中,二次碳化物通过钉扎晶界显著细化了奥氏体晶粒,同时二次碳化物的存在降低了马氏体中合金元素固溶量,进而有效提升了实验钢的冲击韧性.高硬度的微米级二次碳化物配合高韧性马氏体基体可有效阻碍磨粒切削并减轻磨损表面的微观断裂,进而提升实验钢的耐磨性.

汽车用不锈钢表面激光熔覆CoCrNi中熵合金熔覆层微观组织及耐蚀性研究

为提升车用304不锈钢的表面硬度及耐蚀性,采用激光熔覆技术在304不锈钢表面制备了CoCrNi中熵合金熔覆层,并研究了熔覆层的相组成、元素分布及耐蚀性能。结果表明,CoCrNi中熵合金熔覆层与基体形成了良好的冶金结合,无裂纹、气孔等缺陷;熔覆层由单一FCC相组成,组织为枝晶、枝晶间结构,各元素在熔覆层中均匀分布,无明显偏析现象,Cr元素的均匀分布对提升涂层耐蚀性具有积极作用;CoCrNi中熵合金熔覆层的极化电阻(101.65 kΩ)高于304基体的极化电阻(90.56 kΩ),耐蚀性明显高于304基体。

中高碳钢碳含量稳定性控制生产实践

结合中高碳钢生产特点,通过对炼钢冶炼过程全流程分析,找出影响碳含量波动的影响因素,识别出关键工艺控制点,制定了控制转炉终点氧含量、降低出钢温度、减少连铸增碳、稳定班组操作差异等措施,实现中高碳钢碳含量的稳定控制,为炼钢厂生产高质量产品奠定了基础,也为炼钢生产成本降低作出了积极贡献。

中碳CrMo钢中Ti、Nb液析形貌及生成机理分析

通过观察微合金Ti、Nb、V在42CrMo钢连铸坯中的液析形貌,以及液析经加热轧制后的变化,同时,采用热力学计算的方式推导液析生成机理。结果表明,在含w[Ti]0.012%、w[Nb]0.030%、w[V]0.030%、w[N]0.003 5%的42CrMo钢410 mm×530 mm连铸坯中,可观察到Ti、Nb以复合碳氮化物的形式析出,形成微米级液析,w[Ti]较高(70%~83%)的多呈多边形块状,w[Nb]较高(70%~85%)的多呈薄膜状或不规则块状,液析中基本不含V元素;Ti和Nb的碳氮化物液析可互溶并共同生长,Nb含量较高的液析以Ti含量较高的液析为核心长大为块状,部分液析以含硫夹杂物为核心形核并长大;连铸坯心部的碳氮化物液析较多,并且尺寸较大(最长达35μm),连铸坯表面的数量较少,尺寸较小(10μm以下);连铸坯经1 200℃加热并轧制后,液析可部分回溶,数量减少,尺寸减小,并且在轧制过程中破碎。

Cr-W-Mo-V高合金高碳钢的二次硬化特性及回火硬度计算

Cr-W-Mo-V高合金高碳钢高温回火时的二次硬化有两种形式，其一是最高回火硬度对应着一定的淬火温度和回火温度，且回火温度随淬火温度升高而升高；其二是最高回火硬度随淬火温度升高而升高，但回火温度基本不变。二次硬化的回火温度和最高回火硬度既与各类型碳化物沉淀的热力学和动力学有关，亦与残余奥氏体转变的进程有关，归根结底由淬火加热时的奥氏体基体成分决定的。依据奥氏体化温度下基体成分，提出基体成分配比碳公式为Cp=0、011W＋0．02Mo＋0．057Cr＋0．19V，二次硬化的回火硬度的计算公式为Hc=a（1＋b）／（0．0127a＋0．00267），其中a为基体碳饱和度，b为碳化物沉淀量的修正因子。

转炉终渣低全铁控制研究和应用

借鉴国内外学者对降转炉终渣全铁和炉渣脱磷的研究,结合120 t转炉生产实际,对40Cr钢进行了终渣低全铁控制实验。实验本着“前期渣早化,提高冶炼前期渣脱磷率,过程渣化透不返干”的原则,枪位由三段式优化为五段式,通过终点低枪位搅拌,在促进金—渣界面反应和促进脱磷反应的同时,加速降低渣中FeO的含量,在满足终点磷钢种要求的同时,达到降低渣中全铁的目的。实验结果表明:渣中w(TFe)平均为13.59%,较实际生产降低了2.50%。脱磷率平均为92.4%,较实际生产提高了2.8%。通过炉渣矿相分析,验证了降低渣中FeO,可以促进渣中磷的富集、固磷相C_(2)S的生成、长大。工业推广应用后,转炉终渣全铁控制在14.6%,实现了中高碳钢转炉终渣高拉碳低磷低全铁控制,取得了良好的效果。

降低中高碳钢脱碳层工艺技术研究

针对中高碳钢表面脱碳层产生原因、对产品质量影响、工艺影响因素进行了系统性分析,识别了加热温度、保温时间和炉内气氛等重点因素,并在生产中对不同工艺参数条件下脱碳层深度变化规律进行了研究,提出了有效的工艺改进措施,实现中高碳钢脱碳层深度的稳定控制,满足高质量产品要求,解决了行业共性技术难题,为同类型钢铁企业技术革新具有很好的借鉴推广意义。