Effects of Si on the stability of retained austenite and temper embrittlement of ultrahigh strength steels

Effects of silicon(Si)content on the stability of retained austenite and temper embrittlement of ultrahigh strength steels were investigated using X-ray diffraction(XRD),transmission electron microscopy(TEM),and other experimental methods.The results show that Si can suppress temper embrittlement,improve temper resistance,and hinder the decomposition of retained austenite.Reversed austenite appears gradually with the increase of Si content during tempering.Si has a significant effect on enhancing carbon(C)partitioning and improving the stability of retained austenite.Si and C atoms are mutually exclusive in lath bainite,while they attract each other in austenite.g-carbides are found in 1.8wt％ Si steel tempered at 250℃,and they get coarsened obviously when tempered at 400℃,leading to temper embrittlement.Not ε-carbides but acicular or lath carbides lead to temper embrittlement in 0.4wt％ Si steel,which can be inferred as cementites and composite compounds.Temper embrittlement is closely related to the decomposition of retained austenite and the formation of reversed austenite.     

Influences of copper on solidification structure and hardening behavior of high chromium cast irons

The influences of copper on microstructure and the hardening behavior of high chromium cast irons subjected to sub-critical treatment were investigated. The results show that the microstructure of the as-cast high chromium cast irons consists of retained austenite, martensite and M1C3 type eutectic carbide. When copper is added into high chromium cast irons, austenite and carbide contents are increased. The increased addition of copper content from 0% to 1.84% leads to the increase of austenite and carbide from 15.9% and 20. 0% to 61.0% and 35.5% , respectively. In the process of sub-critical treatment, the retained austenite in the matrix can be precipitated into secondary carbides and then transforms into martensite in cooling process, which causes the secondary hardening of the alloy under sub-critical treatment. High chromium cast irons containing copper in sub-critical treatment appear the second hardening curve peak due to the precipitation of copper from supersaturated matrix.     

贝氏体型白口铸铁组织结构及其抗磨料磨损特性的研究

本文应用光学显微镜、电子显微镜、扫透电子显微镜和X-射线衍射仪对贝氏体型白口铸铁的组织结构和形态进行了观察和测试,同时还对上、下贝氏体在不同试验条件下的抗磨性和残余奥氏体在磨损过程中的行为进行了研究。     

Characteristics of retained austenite in TRIP steels with bainitic ferrite matrix

Heat treatment process for producing cold rolled transformation induced plasticity-aided (TRIP-aided) steels with bainitic ferrite matrix was adopted. Characteristics of retained austenite (RA) in such TRIP steels were investigated. SEM and OM determination results showed that the stable austenite retained at room temperature were mainly located between laths and some of them inside the coarse ferrite. The grains were uniformly distributed in heat treated steel matrix and the regularly dispersed RA represented to be triangular morphology. XRD analysis indicated that RA content in matrix was not less than 10%, and TEM testified that RA inside the matrix were formed at the prior austenite boundaries and represented to be single or twin crystals. The ductile fracture originated from the boundaries of martensite islands from RA and ferrite. The cracks propagated along grain boundaries and some passed through the large ferrite grains and induced transgranular fracture.     

低碳低合金层片状双相钢的显微组织研究

0.18C-0.95Cr钢层片状双相组织中,马氏体板条间存在条形残余奥氏体,马氏体与奥氏体的位向关系同样服从K-S关系。铁素体区域中的微小奥氏体岛,淬火后可以得到多边体形单晶马氏体,铁素体与马氏体界面分布着微小粒状渗碳体。临界淬火加热速度较小(2℃/min)的层片状双相组织α＇中的Cr含量比与其相邻的铁素体的高。在马氏体与铁素体界面的EELS中出现明显的C,K峰和N,K峰。     

Relation of martensite-retained austenite and its effect on microstructure and mechanical properties of the quenched and partitioned steels

A two-step quenching and partitioning(QP) treatment was applied to low-carbon alloy steels. The relation of initial martensite- retained austenite- fresh martensite and its effect on microstructure and mechanical properties were investigated by experiments. The results reveal that the volume fraction of retained austenite can reach the peak value of 17%, and the corresponding volume fractions of initial martensite and fresh martensite are 40% and 43%, respectively, when the tested steel is treated by initial quenching at 330°C, partitioning at 500°C for 60 s and final quenching to room temperature. Moreover, the micromorphologies of austenite and martensite become finer with the increasing of initial martensite fraction. The elongation is the highest when the volume fractions of initial martensite and retained austenite are 70% and 11%, respectively, meanwhile, the yield strength increases and tensile strength decreases gradually with the increase of initial martensite fraction, which proves that the mechanical properties including elongation, yield strength and tensile strength are based on the comprehensive effect of the retained austenite fraction, the finer microstructure and austenite stability.     

GCr15钢中的残余奥氏体对干滑动磨损行为的影响

研究了残余奥氏体含量对ＧＣｒ１５钢干滑动磨损行为的影响，通过热处理获得ＧＣｒ１５钢不同的残余奥氏体含量，在室温下进行了磨损试验，试验结果表明，在低载荷下，残余奥氏体含量对耐磨性没有影响，一定载荷范围内，随着残余奥氏体含量增加，耐磨性下降；现款是一步增加载荷，随着残余奥氏体含量增加，耐磨性反而增强，硬度与耐磨性之间没有确定的比例关系。     

Microstructural evolution in 35CrMnSi steel during multi-cyclic quenching and partitioning heat treatment

A novel method,i.e.multi-cyclic quenching and partitioning(M-Q-P)heat treatment,is used to tailor the content of retained austenite(RA)in commercial steels.For 35CrMnSi steel,5 times of Q-P heat treatment can increase the content of RA from 8vol.%to 17 vol.%.As a result,the ultimate elongation of the steel is improved from 17.4%after the typical Q-P heat treatment to 27.1%after 5 times of Q-P treatment.Meanwhile,the improved combination of strength and ductility for steels by typical Q-P heat treatment is retained by the multi-cyclic Q-P heat treatment.It is shown that the content of RA in some specific steels,and furthermore their mechanical properties,can be regulated through the M-Q-P.     

渣浆泵用钢基表面耐磨复合材料的研究

以ZG45为基体，以多种合金粉末作为合金化原料，通过铸渗工艺制备出较为理想的渣浆泵用铁基表面耐磨材料．铸件合金层厚度均匀，基体组织为树枝状的奥氏体，增强相为二次碳化物(Cr，Fe)7C3和渗碳体型碳化物Fe3W3C，在合金化过程中，主要是铁液向合金层渗透，铬向母材的渗透也有，但量很少，合金层与母材的结合良好，属于冶金结合，其冲击磨损性能和硬度都有很大提高，耐磨性比ZG45提高了6．5倍，硬度从合金层到基体逐渐降低，合金层硬度比ZG45提高了3倍左右。     

Influence of secondary carbide precipitation and transformation on abrasion resistance of a 3Cr15Mo1V1.5 white iron

The relationship between the secondary carbide precipitation and transformation of the 3Cr15Mo1V1.5 white iron and abrasion resistance was investigated by using optical microscope （OM）, transmission electron microscopy （TEM） and X-ray diffrac- tion （XRD）. The results show that the properties of secondary carbides precipitated at holding stage play an important role in the abrasion resistance. After certain holding time at 833 K subcritical treatment, the grainy （Fe, Cr）23C6 carbide precipitated and the fresh martensite transformed at the holding stage for 3Cr15Mo1V1.5 white iron improve the bulk hardness and abrasion resistance of the alloy. Prolonging holding time, MoC and （Cr, V）2C precipitations cause the secondary hardening peak and the corresponding better abrasion resistance. Finally, granular （Fe, Cr）23C6 carbide in situ transforms into laminar M3C carbide and the matrix structure transforms into pearlitic matrix. These changes weaken hardness and abrasion resistance of the alloy sharply.     

残余奥氏体及其机械稳定性与钢强韧性关系的研究

钢中残余奥氏体发生应变诱发马氏体相变的百分量与拉伸应变量的对数呈线性关系,用直线斜率的倒数Ks值可表示残余奥氏体机械稳定性的大小。提高钢中残余奥氏体量及其机械稳定性是改善钢强韧性的有效途径之一。残余奥氏体发生应变诱发马氏体相变吸收能量是提高钢韧性的主要原因。在低碳贝氏体钢中,以M—A岛形式存在的残余奥氏体因受岛中马氏体的强化作用使屈服强度保持较高水平,而残余奥氏体在拉伸的均匀塑性变形阶段因应变诱发相变形成的马氏体使钢的抗拉强度提高。     

Influences of polypropylene fiber and SBR polymer latex on abrasion resistance of cement mortar

Influences of polypropylene (PP) fiber and styrene-butadiene rubber (SBR) polymer latex on the strength performance, abrasion resistance of cement mortar were studied. The experimental results show that the flexural strength, brittleness index (σ_F/σ_C) and abrasion resistance can be improved significantly by the addition of PP fiber and SBR polymer latex. The relationship between the flexural strength and abrasion resistance was analyzed, showing a good linear relationship between them. The reinforced mechanism of PP fiber and SBR polymer latex on cement mortar was analyzed by some microscopic tests. The test results show that the addition of SBR polymer latex has no significant influence on the cement hydration after 7 d curing. Adding SBR polymer latex into cement mortar can form a polymer transition layer in the interfaces of PP fiber and cement hydrates, which improves the bonding properties between the PP fiber and cement mortar matrix effectively.     

Influence of isothermal bainitic processing on the mechanical properties and microstructure characterization of TRIP steel

The mechanical properties of transformation induced plasticity (TRIP) steel are strongly affected by the conditions of iso-thermal bainitic processing. The multiphase microstructure of TRIP steel under different conditions of isothermal bainitic processing was investigated using OM, SEM, XRD and TEM. The volume fraction of retained anstenite and the carbon content in anstenite were determined quantitatively using X-ray diffraction patterns. The relationship between mechanical properties and isothermal bainitic processing parameters was investigated. The stability of retained anstenite was analyzed by the volume fraction of retained austenite and the carbon content in retained anstenite. The experimental results show that the multiphase microstructure consists of ferrite,bainite and metastable retained austenite. To obtain good mechanical properties, the optimal conditions of isothermal bainitic tem-perature and holding time are 410-430℃ and 180-240 s, respectively. After isothermal bainitic processing under the optimal condi-tions, the corresponding volume fraction of retained anstenite is 5vol%-15vol%, which can provide enough retained austenite and plastic stability for austenite with high carbon content.     

Electron theory study on the effect of Mn on as-cast structure of Fe-C-Cr-Mn cast irons

The valence electron structure of alloying austenite of 3C-15Cr high chromium white cast iron with different Mn contents from 1% to 6% is analyzed by BLD method and EET. Results show that the addition of Mn has major influence on the valence electron structure of the alloying austenite, especially on that of Fe-C, Fe-C-Cr and Fe-C-Cr-Mn unit cells of it. The effect becomes weak when Mn content is over 4%. Based on the effect of n~, F~~, the weighting of each unit cell and the degree of undercooling on phase transition of the aus- tenite, we can calculate the retained austenite content of as-cast structure of the high chromium white cast iron. The calculation results coincide well with those of the experiment. The phase transition characters of the austenite in high chromium white cast iron can be forecasted through valence electron structure analysis of alloying austenite by BLD method and EET on the basis of Fe-C-Cr equilibrium phase diagram.     

Cr12轧辊深冷处理工艺的实验研究

采用正交试验方法研究了Cr12轧辊深冷处理工艺.分析了不同工艺参数对轧辊硬度和耐磨性的影响.使用电子扫描显微镜(SEM)观察材料显微组织;使用X射线衍射仪(XRD)分析材料的晶格尺寸和残留奥氏体的含量.实验结果表明:深冷处理促使残留奥氏体向马氏体转变,并在马氏体的基体上析出碳化物颗粒,这是Cr12轧辊硬度和耐磨性提高的主要原因.     

奥氏体—贝氏体球铁的耐磨性

本文利用残余奥氏体的加工硬化特征,从抗磨材料角度出发,研究了合金元素铜、钼和热处理规范对奥-贝球铁的组职和性能、残余奥氏体量及其稳定性的影响。同时,对此高锰钢,研究了不同热处理规范的奥-贝球铁在小能量冲击载荷下的耐磨性,并首次将奥-贝球铁应用于颚式破碎机齿板上。实验室试验及生产现场运行结果表明,其耐磨性均优于高锰钢,约提高15～30％。     

高速重轨矫正圈用9Cr2MoRE钢的开发研究

通过添加不同含量的稀土元素,对比研究稀土含量对9Cr2Mo钢奥氏体晶粒度、相变点、抗拉强度及耐磨性的影响。研究结果表明,稀土元素可以有效细化9Cr2Mo钢的奥氏体晶粒,当稀土加入量为0.10%时,晶粒长大速率降低最明显。添加质量分数为0.1%的稀土后,9Cr2Mo钢的抗拉强度明显提高,塑性和延展性也有所改善。加入稀土元素后,9Cr2Mo钢在磨损过程中可以避免出现大块疲劳剥落现象,提高了耐磨性。     

淬火处理对激光选区熔化成形S136组织与性能的影响

为了改善激光选区熔化（SLM）成形S136模具钢的性能,对SLM成形的试样进行淬火处理. 采用X射线衍射(XRD)和扫描电子显微镜(SEM),研究淬火温度对SLM成形S136的微观组织、硬度和耐腐蚀性能的影响. 结果表明：SLM成形的S136试样组织由马氏体和少量残余奥氏体组成,经过980、1 020、1 050和1 100 °C的淬火处理之后,原晶界消溶,组织大部分转变为马氏体;淬火处理后试样的硬度得到改善,最高值达到54.24 HRC,比原始成形试样提高了近10%;淬火处理后试样原晶界消溶,耐腐蚀性元素分布均匀使得耐腐蚀性能得到了极大的提升,与原始成形试样相比,腐蚀失重量减少了近97%. 优化淬火处理工艺后表明：采用1 050 °C保温1 h并油淬的淬火处理条件,可以得到最佳的硬度/耐蚀性能匹配.     

铸铁激光表面改性的组织与性能特征的研究

论述了激光表面熔融处理后硬化层的显微组织与性能特征，讨论了组织对硬度分布的影响试验结果表明：经激光表面熔融处理后，球墨铸铁熔化层组织为先共晶奥氏体（快冷后转变为Ｍ＋ＡＲ）＋莱氏体，相变层组织为马氏体＋残余奥氏体＋球状石墨；灰口铸铁的熔化层组织为细小树枝（Ｍ＋ＡＲ）＋弥散分布的树枝间层片状变态莱氏体（Ｍ＋ＡＲ＋Ｆｅ３Ｃ）的变态亚共晶白口组织，相变层组织为马氏体＋残余奥氏体＋片状石墨在相变区，球状石墨周围的组织较复杂，靠近熔化层处的石墨球周围出现双壳层组织，由一层马氏体＋残余奥氏体包围，再围以莱氏体或先共晶奥氏体＋莱氏体组织     

钢中的低碳马氏体及条间奥氏体

低碳马氏体形成时可能存在碳的扩散,使条间奥氏体富碳,以及受协作形变强化的力学稳保持至室温,形成淬火钢中马氏体条间的奥氏体,它对低碳马氏体的韧化起重要的作用。低碳马氏体形成时,碳的扩散并非必需过程;马氏体与基体间为平直界面,而贝氏体界面却存在巨型台阶;低碳马氏体也并不按贝氏体形式长大;证明低碳马氏体形成机制和贝氏体的不同。低温回火时,由于渗碳体自马氏体脱溶的形核(长大)驱动力较大,先由马氏体析出渗碳体;长时间回火时,由于条间奥氏体分解驱动力较大,又受到马氏体脱溶呈收缩的拉应力促使分解;提出回火马氏体致脆的机制为马氏体脱溶和奥氏体分解的互为关连的过程。应用低碳马氏体时须注意避免回火马氏体致脆及加强条间奥氏体的稳定性。