回火温度对两相区退火海工钢组织和性能的影响

对690 MPa级海工钢进行“淬火+两相区退火+回火”三步热处理,研究了回火温度对其组织和性能的影响、分析了力学性能变化与组织演变和残余奥氏体体积分数之间的关系。结果表明：回火后实验钢的显微组织为回火贝氏体/马氏体、临界铁素体和残余奥氏体的混合组织。随着回火温度的提高贝氏体/马氏体和临界铁素体逐渐分解成小尺寸晶粒,而残余奥氏体的体积分数逐渐增加;屈服强度由787 MPa降低到716 MPa,塑性和低温韧性明显增强,断后伸长率由20.30%增至29.24%,-40℃下的冲击功由77 J提升至150 J。残余奥氏体体积分数的增加引起裂纹扩展功增大,是低温韧性提高的主要原因。贝氏体/马氏体的分解和残余奥氏体的生成,引起组织细化、晶粒内低KAM值位错的比例逐渐提高和小角度晶界峰值的频率增大,使材料的塑性和韧性显著提高。     

热处理工艺对压裂泵阀体用钢4330MOD组织及性能的影响

为提高压裂泵阀体的强度和韧性,研究了不同热处理工艺对改进型4330钢组织及力学性能的影响。结果表明:4330MOD钢通过添加微合金元素及调质工艺优化能够提高强度和韧性。微合金元素Nb、V,正火+调质工艺能够降低晶粒尺寸,提高强韧性。4330MOD钢在550℃～700℃回火时,组织为回火索氏体组织,随回火温度的升高强度降低,韧性先升高后降低,在600℃～650℃回火强韧性匹配较好。4330MOD钢通过微合金元素添加及热处理工艺优化使晶粒尺寸及板条块宽度细小,大角度晶界比例高,从而提高了钢的强韧性。      

循环淬火工艺对连铸10CrNi3MoV钢组织与性能的影响

针对高温热成型及正常调质处理后结构件用连铸10CrNi3MoV钢性能恶化这一问题,采用循环淬火热处理工艺研究了力学性能、显微组织及晶粒度。结果表明,采用860℃三次循环淬火+高温回火(630℃×3 h)热处理工艺,能够有效细化连铸10CrNi3MoV钢的晶粒,改善其低温韧性,使其力学性能满足使用要求。     

两相区热处理对ZG14Ni3CrMoV铸钢低温韧性的影响

对比了淬火+回火(QT),淬火+两相区淬火+回火(QLT)两种热处理工艺对ZG14Ni3CrMoV铸钢组织和性能的影响。结果表明,QLT工艺在保证铸钢板厚四分之一处强度满足指标要求、塑性良好的情况下,大幅度提高了ZG14Ni3CrMoV铸钢的低温韧性,-80℃冲击吸收功提高到171J,NDT温度降低至-95℃;晶粒细化和双相组织是两相区二次淬火提高低温韧性的主要原因。     

两相区热处理对ZG14Ni3CrMoV铸钢低温韧性的影响

对比了淬火+回火(QT),淬火+两相区淬火+回火(QLT)两种热处理工艺对ZG14Ni3CrMoV铸钢组织和性能的影响.结果表明,QLT工艺在保证铸钢板厚四分之一强度满足指标要求、塑性良好的情况下,大幅度提高了ZG14Ni3CrMoV铸钢的低温韧性,-80℃冲击吸收功提高到171 J,NDT温度降低至-95℃;晶粒细化和双相组织是两相区二次淬火提高低温韧性的主要原因.     

基于组织和结构调控9CrV钢大尺寸活塞性能的优化EI北大核心CSCD

研究了热处理和结构调控对直径为190 mm的9CrV钢仿形活塞不同部位显微组织和力学性能的影响及其机理。结果表明,经850℃×5 h-230℃×4 h等温淬火、230℃×4 h回火后,9CrV钢活塞的表层至心部依次为下贝氏体、贝氏体+索氏体+M/A岛、珠光体类组织;表层的抗拉强度和冲击吸收功均高于心部。淬火温度降至800℃、回火温度升至400℃,使表层的抗拉强度提高到1610 MPa、冲击吸收功降低到7.4 J,心部的冲击韧性有所提高但是强度降低。经800℃×5 h-230℃×4 h等温淬火、230℃×4 h+400℃×4 h二次回火后,表层的抗拉强度达到1672 MPa、冲击吸收功达到9.8 J,且改善了心部的冲击韧性,使活塞整体的强度与韧性趋于平衡。淬火加热温度的降低保留了适量的未溶碳化物颗粒,阻碍了奥氏体的长大和细化了晶粒,从而提高了钢的强度。在230℃回火使残余奥氏体转化为下贝氏体、防止在400℃回火(提高心部韧性)时生成薄壳碳化物和平衡了整体韧性。综合热处理和活塞结构的调控,实现了大尺寸活塞的整体强韧性平衡。     

热处理工艺对连铸10CrNi3MoV钢性能的影响

针对高温热成型及正常调质处理后连铸10CrNi3MoV钢性能恶化这一问题,研究了循环/亚温淬火热处理工艺,进行了力学性能测试、显微组织观察及晶粒度评定.结果表明,采用亚温淬火( 835℃×2h+ 820℃×2h)+高温回火(630℃×3h)热处理工艺,可有效细化连铸10CrNi3MoV钢的晶粒,显著改善其低温韧性,使其...     

改善09MnNi容器钢低温冲击韧性的机理

用热膨胀法测量了典型容器用09MnNiDR钢的Ac1和Ac3温度,并用在此基础上设计的淬火工艺对其进行热处理。使用扫描电镜、EBSD和夏比冲击试验机等手段研究了09MnNiDR钢在其厚度方向1/2处的组织、织构和低温冲击性能。结果表明：实验钢的Ac1=692.9℃,Ac3=883.1℃。与“准亚温淬火+回火”或“准亚温淬火+亚温淬火+回火”热处理工艺相比,采用“预淬火+准亚温淬火+回火”热处理,能使09MnNiDR钢板1/2厚度处的低温冲击性能有较大的提高。其原因,一是晶粒的细化,二是织构的漫散分布。     

回火工艺对65Mn钢疲劳裂纹扩展行为的影响

采用中温回火和高温回火对65Mn钢进行热处理,测试其拉伸性能,并对其疲劳裂纹扩展行为进行研究,探索其疲劳断裂机制．结果表明,两种回火方案对应的裂纹扩展速率的m值相差不大,而C值差异较大,反映出在稳定扩展区的疲劳裂纹扩展对其微观组织不敏感,塑性变形消耗了裂纹扩展的能量,使裂纹扩展速率下降;随着回火温度的升高,实验钢的疲劳断裂特征由脆性逐渐变为韧性,高温回火提高了其裂纹扩展的门槛值,降低了疲劳裂纹扩展速率,65Mn钢经高温回火后有较优的综合力学性能和疲劳性能．     

新型贝氏体钢的组织和冲击疲劳性能研究

通过显微组织观察和冲击疲劳实验,研究了不同热处理新型贝氏体钢的组织和冲击疲劳性能.结果表明:新型贝氏体钢正火低温回火的组织由贝氏体铁素体和奥氏体组成,淬火低温回火组织为回火马氏体和残余奥氏体,正火低温回火热处理的冲击疲劳寿命高于淬火低温回火热处理的冲击疲劳寿命.分析了多冲疲劳裂纹扩展的行为,讨论了正火低温回火提高冲击疲劳的原因.     

The effect of single and double quenching and tempering heat treatments on the microstructure and mechanical properties of AISI 4140 steel

This investigation is concerned to evaluate the effect of double quenching and tempering (DQT) with conventional quenching and tempering (CQT) heat treatment processes on microstructure and mechanical behavior of a commercially developed hot rolled AISI 4140 type steel. Comparison of microstructure and mechanical properties of DQT and CQT heat treated specimens have been established in details. Optical and scanning electron microscopies have been used to follow impurity concentration and microstructural changes, and their relation to the associated mechanical properties. The results indicate that the improvement of mechanical properties particularly impact toughness of DQT heat treated specimens is much higher than that of the CQT condition, and this observation is rationalized in terms of finer austenite grain size developed in the DQT condition providing much finer martensitic packets within the grains and a lower level of impurity concentration of sulfur (S) and phosphorus (P) near the prior austenite grain boundaries as well.     

Experimental investigation on heat treatment of a high‐speed steel for hot rolling roll mill

The authors describe the researching results to optimise the hardening and tempering of the high carbon high‐speed steel for rolls containing 2.38%C, 5.07%V, 6.34%Mo, 5.09%Cr, 1.20%Ni, 1.17%Nb, 0.09%Ti and 0.05%RE by means of light optical microscope (LOM), scanning electron microscope (SEM), backscattered electron image (BSE), X‐ray diffraction (XRD), and hardness, tensile strength, impact toughness and wear testers. The results show that the microstructure of above casting high‐speed steel is given by a tempered martensitic matrix surrounded by eutectic carbides. Casting high‐speed steel has higher hardness quenching at 1280 K–1340 K, and it has higher hardness, tensile strength, impact toughness, and abrasive wear resistance tempering at 793 K–833 K. The comprehensive properties of casting high‐speed steel is the best while air‐cooling quenching about 1340 K and tempering about 813 K.     

Studies on influence of reheating temperature and cooling rate on structure–property behaviour of lean chemistry HSLA-100 steel

Abstract

Simulation studies on the influence of reheating temperature on austenite grain coarsening in lean chemistry high strength low alloy (HSLA)-100 steel were carried out to establish optimum soaking temperature before hot rolling. Experiments carried out in ‘Gleeble-3500’ dynamic thermomechanical simulator revealed that prior austenite grain sizes varied between 26 and 98 and 34 and 126 μm after soaking at 1150, 1200 and 1250°C for 1 and 5 min respectively; a soaking temperature of 1200°C was found to be optimum. Simulation experiments on the influence of cooling rate on microstructural changes and dilatometric studies indicated lowering of transformation temperature with faster cooling. Microstructural examination of dilatometric samples confirmed martensitic transformation at faster cooling rate. The martensite structure is desirable to achieve better strength and toughness. The findings of simulation studies were subsequently used for standardising thermomechanical treatments of Nb–Cu bearing lean chemistry HSLA-100 steels. One laboratory heat of Cu bearing HSLA steel containing 0·028%Nb was made. This heat was hot rolled into 12·5 mm thick plate by varying finish rolling temperature in the range of 800–1000°C. The soaking temperature was maintained at 1200°C. The rolled plates were heat treated by both conventional reheat quenching and tempering (RQT) as well as direct quenching and tempering (DQT) techniques. Evaluation of mechanical properties revealed that plates processed through DQT route were superior to those processed through RQT route. Transmission electron microscopy revealed that martensite structure and finer interlath spacing in DQT plates resulted in superior strength and impact toughness properties as compared to RQT steels.     

Effect of direct quenching on the microstructure and mechanical properties of the lean-chemistry HSLA-100 steel plates

The influence of direct quenching on structure-property behavior of lean chemistry HSLA-100 steels was studied. Two laboratory heats, one containing Cu and Nb (C:0.052, Mn:0.99, Cu:1.08, Nb:0.043, Cr:0.57, Ni:1.76, Mo:0.55 pct) and the other containing Cu, Nb and B (C:0.04, Mn:1.02, Cu:1.06, Nb:0.036, Cr:0.87, Ni:1.32, Mo:0.41, B:0.002 percent) were hot-rolled into 25 and 12.5 mm thick plates by varying finish-rolling temperatures. The plates were heat-treated by conventional reheat quenching and tempering (RQT), as well as by direct quenching and tempering (DQT) techniques. In general, direct-quench and tempered plates of Nb-Cu heat exhibited good strength (yield strength ∼ 900 MPa) and low-temperature impact toughness (average: 74 J at −85 °C); the Charpy V-notch impact energies were marginally lower than conventional HSLA-100 steel. In Nb-Cu-B heat, impact toughness at low-temperature was inferior owing to boron segregation at grain boundaries. Transmission electron microscopy (TEM) and scanning auger microprobe (SAM) analysis confirmed existence of borocarbides at grain boundaries in this steel. In general, for both the steels, the mechanical properties of the direct-quench and tempered plates were found to be superior to reheat quench and tempered plates. A detailed transmission electron microscopy study revealed presence of fine Cu and Nb (C, N) precipitates in these steels. It was also observed that smaller martensite inter-lath spacing, finer grains and precipitates in direct-quench and tempered plates compared to the reheat quench and tempered plates resulted in their superior strength and good impact toughness.     

回火方式对调质高强度钢组织和性能的影响

为改善高强度钢的塑性和韧性,对同一种低合金高强度钢进行两种不同回火方式的调质处理,淬火+缓慢加热回火的传统调质与淬火+感应加热回火的新调质工艺,分析该工艺对钢的组织与性能的影响.利用扫描电镜和透射电镜观察组织及析出物的变化,采用X射线衍射仪分析了钢中残余奥氏体体积分数.结果表明:两种工艺下,钢的组织均为板条宽300～500 nm左右的马氏体组织,感应加热回火调质工艺处理后,板条组织明显,析出物大多约为20 nm,比传统调质处理后的细小;两种不同热处理工艺均能提高钢的屈服强度.感应加热至500℃回火后试验钢具有16%以上的延伸率,-40℃冲击功达到32 J,优于传统调质工艺处理钢板的综合性能.感应加热回火能获得更多小尺寸析出物和更多的残余奥氏体,有利于改善钢的塑性和韧性.     

抗大变形管线钢热影响区软化问题的研究

为了研究抗大变形管线钢热影响区出现软化区的具体原因,本文采用焊接热模拟实验研究了X80级抗大变形管线钢的焊接热循环过程,结合金相显微镜、扫描电镜、EBSD、透射电镜和冲击实验,分析了热影响区软化区的组织变化、晶体学特征和冲击韧性.结果表明:当母材组织为多边形铁素体+贝氏体时,焊接热影响区的软化区出现在峰值温度600~700℃的高温回火区,此时组织转变成硬度较低的粗大铁素体+回火贝氏体,并且回复过程加快,组织中亚结构的大幅度减少和位错密度的显著降低是产生软化区的主要原因;软化区的韧性较好,但是在800℃的临界区,M/A组元发生了聚集和粗化,并且大角度晶界比例降低,导致了韧性低谷的出现.