Influence of shallow and deep cryogenic treatment on the residual state of stress of 4140 steel

The present research work studies the effect of cryogenic treatment on the residual stress state in 4140 steel. Two kinds of cryogenic treatment, namely shallow (SCT, −80 °C × 5 h) and deep cryogenic treatment (DCT, −196 °C × 24 h) were carried out between quenching and tempering in conventional heat treatment process. The results evidenced an increase in the compressive residual stress in steel are subjected to cryogenic treatment before tempering. X-ray diffractometry revealed that residual stresses are relieved during tempering, according to the redistribution of carbon in martensite and the precipitation of transition carbides. While conventional heat treatment (CHT) and shallow cryogenic treatment (SCT) promote a tensile state of residual stress, DCT shows a compressive residual stress.     

深冷处理对M2Al高速钢高温耐磨性的影响

探究了不同深冷处理温度对M2Al高速钢高温耐磨性的影响。结果表明,经过深冷处理的M2Al高速钢试样微观组织发生了变化,残留奥氏体转变为马氏体,碳化物尺寸减小并且弥散分布在马氏体基体上。随着深冷温度的降低,碳化物的尺寸减小且分布均匀。M2Al高速钢经过深冷处理后高温摩擦因数比未深冷处理的减小,其中-160 ℃深冷处理试样的高温摩擦因数比未深冷处理的降低55.7%,经过深冷处理的M2Al高速钢磨损量比未深冷处理的减小,其中-160 ℃深冷处理后磨损量最小。未深冷处理的M2Al高速钢试样磨损形貌比较粗糙,发生严重的粘着磨损,经过-160 ℃深冷处理的试样,磨痕比较浅,磨损形式主要为磨粒磨损。当深冷处理温度为-160 ℃时,M2Al高速钢的高温耐磨性提升效果最好。     

Effect of deep cryogenic treatment on dilatometric curve and tribological properties of high speed steel

Abstract

Advantages of deep cryogenic treatment (DCT) over the standard heat treatment of high speed steels for the purpose of obtaining better properties are quoted in an increasing number of scientific papers to be found in literature. This paper deals with the improvements in high speed steel properties achieved by using DCT on test samples made of PM S390 MC high speed steel. The effect of DCT on the dilatometric curve during tempering and on the abrasive and the erosion wear resistance has been investigated and compared with results obtained from a set of test samples made of the same steel heat treated by the conventional method (hardened and three times high temperature tempered). Dilatometric tests confirmed the existence of common processes in tempering, which depend on the initial state of steel (only quenched, and quenched and deep cryogenically treated). These tests showed that the DCT had not completely eliminated the residual austenite, particularly in the case of the highest austenisation temperature. The tribological results obtained confirm that the application of DCT results in significantly improved erosive wear resistance, while the abrasive wear resistance depends on the temperature of austenisation used.     

镁合金钨极氩弧焊接头深冷强化机制

针对镁合金焊接接头软化问题,文中提出了AZ31镁合金TIG焊接接头深冷强化方法,进行了镁合金TIG焊接工艺试验和焊接接头的-160℃,8 h深冷处理试验;深冷处理使镁合金焊接接头抗拉强度从212.4 MPa提高到246.6 MPa;用X射线衍射仪(XRD)和透射电子显微镜(TEM)等观测了焊接接头深冷前后的微观组织与结构,分析了焊接接头深冷强化机理.结果表明,深冷处理使镁合金TIG焊接接头形成亚晶结构,第二相Mg17Al12颗粒弥散析出,提高了基体连续性,第二相颗粒数量增加,使接头组织细化并获强化,深冷处理使焊接接头的晶粒发生转动与位错转化为位错环,使接头组织产生孪晶,强化了焊接接头.     

深冷处理温度场和组织场的有限元模拟与实验验证(英文)

结合低温材料参数以及液氮浴沸腾换热系数,基于金属-热-力耦合理论建立深冷处理数值分析模型,再现新型冷作模具钢Cr8Mo2SiV(SDC99)的深冷处理过程。同时,通过设计深冷处理温度快速测量装置验证模拟结果的准确性。结果表明,深冷处理过程中试样心表温差和冷却速度的差异较大。这种温度和冷却速度的剧烈变化主要集中于从试件表面至心部的1/3厚度内。经过深冷处理后,试样内残余奥氏体将继续向马氏体转变,其最终体积分数减小为2.3%。模拟结果与实验结果非常吻合,这表明采用的数值分析方法能准确地捕捉试件在深冷处理过程中温度场和组织场的变化规律,能为深冷处理工艺的合理制定提供理论依据和借鉴。     

深冷处理对TC4钛合金表面性能的影响

研究了深冷处理对TC4钛合金滚磨光整加工和表面性能的影响。对TC4钛合金试样进行深冷处理,将不同深冷时间下的试样进行滚磨光整加工,根据表面粗糙度确定适合的深冷时间后,对比分析深冷处理前后合金试样的显微组织、显微硬度及残余应力的变化。利用扫描电镜探究了深冷处理和滚磨光整加工后合金试样表面形貌的变化。结果表明,深冷处理12 h后试样表面粗糙度最小,试样组织受到冷缩内应力的作用,α相的比例从未深冷处理的56.45%增加到85.42%,组织变得均匀且致密。试样的显微硬度在深冷处理12 h时最大,比未处理试样提高了3.47%。深冷处理12 h和滚磨光整加工后的试样相比未处理试样表面残余压应力增加26.26%。粗糙度测量和扫描电镜结果显示深冷处理使钛合金试样的可加工性增强,深冷处理12 h的试样经过离心式滚磨光整加工表面粗糙度可从约0.500 μm下降到约0.250 μm,表面质量明显变好。     

电站主管道用铸造奥氏体不锈钢断裂韧度尺寸效应试验研究

为了探究电站主管道用铸造奥氏体不锈钢韧性断裂的尺寸效应,对五种不同厚度的标准紧凑拉伸试样在室温下进行了断裂韧度试验,通过SEM观察并分析了断裂面的显微结构.结果表明:试样厚度在12～20 mm时,断裂韧度随着试样尺寸的增大呈上升趋势,在20～50mm厚度范围时断裂韧度随试样尺寸的增大而减小;撕裂模量随试样尺寸的减小而增加.断裂面上接近中截面的位置容易产生以大型韧窝为主的沿晶断裂,在接近外表面位置较易产生以大量微小韧窝为主的穿晶断裂.利用断裂韧度的定义进行理论分析,用约束水平和断裂影响区域体积的变化解释不同尺寸效应,通过有限元分析模拟得到断裂面上三向应力比的分布变化是影响断裂应变和断裂韧度的重要因素.     

深冷处理提高镀锌钢板点焊电极寿命的机理

为了提高镀锌钢板点焊电极寿命，作者提出了镀锌钢板点焊电极的深冷处理方法。采用不同深冷处理工艺参数处理了点焊镀锌钢板的Cr—Zr—Cu合金电极，用这些电极进行了镀锌钢板点焊电极寿命试验并与未深冷处理的电极寿命进行了比较。用扫描电子显微镜对深冷处理电极进行了背散射及面扫描分析，用X射线衍射法观测了深冷处理前后的电极晶粒度，测试了电极在深冷处理前后的电阻率。通过对深冷电极微观结构的观测及电极性能的测试，探讨了深冷处理提高镀锌钢板点焊电极寿命的机理。研究结果表明，深冷处理提高了镀锌钢板点焊电极基体的致密性，改变了合金元素的分布，细化了电极材料的晶粒，提高了镀锌钢板点焊电极的导电、导热能力及电极抗压渍变形的能力，从而提高了镀锌钢板点焊电极的寿命。     

化学成分对316L奥氏体不锈钢组织及变形行为的影响

利用万能试验机对不同镍当量(Nieq)的316L不锈钢热轧钢板进行常温单轴拉伸试验,借助扫描电镜(SEM)和透射电镜(TEM)对其拉伸变形前后的微观组织进行观察,探索镍当量对316L不锈钢微观组织及性能的影响规律。结果表明,固溶态试验钢的组织均为奥氏体组织及少量高温δ相,强度随Nieq的升高而降低,塑性和韧性随Nieq升高而增加;拉伸断口均呈韧性断裂特征,且随Nieq的提高,韧窝的数量减少,韧窝尺寸增加;TEM显示,变形后的试验钢均未发生马氏体相变,Nieq较低时,变形量大的地方位错密度高,发生位错交互作用,局部有形变孪晶生成,且随着Nieq的增加,形变孪晶密度增大,出现相互交叉、阻滞。     

Research about the Effect of Ultrasonic Impact on the Fatigue Properties of Cruciform Joints of 16MnR Steel

Surface impact treatment was carried out on the cruciform joint weldment of 16MnR steel by using the HJ-II-type ultrasonic impact machine.The ultrasonic impact current is 1.2 A,the impact amplitude is 30?m and ultrasonic impacting time is 30 and 60 min,respectively.Fatigue experiments were carried out for both treated specimen and un-treated specimen by using EHF-EM200K2-070-1A fatigue testing machine.The fatigue fractures were observed with the scanning electron microscope of 6360LA type and the microstructure of ultrasonic impact treating surface layer was analyzed by using high resolution transmission electron microscope of JEM-2100 type.The experimental results show that the microstructure of ultrasonic impact surface layer has been successfully nanocrystallized.The fatigue life of welded cruciform joints of 16MnR steel can be significantly improved through the ultrasonic impact treatment.The main reasons are that the ultrasonic impact treating can reduces the stress concentration in the weld toe,decrease the tensile stress,and even change to compressive stress in the weldment,the grain size in the welded joint can be refined.The longer the impact time,the greater increasing range of fatigue life will be.Compared to the sample without treatment,its fatigue life was increased 210.37%,362.48%,respectively,when the impact time was 30,60 min,respectively.     

深冷处理对35MnB合金钢残余应力的调控机理

以35MnB合金钢为研究对象,运用正交试验法,设计了以深冷温度、深冷时间和交变次数为自变量,残余应力为因变量的正交试验。通过X射线衍射仪测得试样表面的残余应力分布情况,运用极差法分析深冷工艺参数对试样残余应力的影响因素;通过扫描电镜观测试样在不同深冷处理工艺参数下的微观组织形貌,结合X射线衍射图谱定量分析了深冷处理后残留奥氏体体积分数的变化,从微观角度综合探索了残余应力的消减机理。结果表明:35MnB合金钢深冷工艺参数对试样残余应力的影响因素依次为:深冷温度＞交变次数＞深冷时间,最佳组合为:深冷温度-160 ℃,深冷时间12 h,交变次数1次。经深冷处理之后,残留奥氏体细化并转变为新生马氏体,分布在马氏体晶体边界处的残留奥氏体可以松弛马氏体界面上因位错堆积而造成的应力集中,从而减少了组织内部的残余应力。     

热处理对激光增材制造Ferrium M54钢微观组织及力学性能的影响

采用激光增材制造技术制备了Ferrium M54钢,研究了传统热处理对其组织和力学性能的影响。利用光学显微镜(OM)、扫描电镜(SEM)、X射线衍射仪(XRD)、拉伸试验机及维氏硬度计分析了沉积态和热处理后试验钢的微观组织和力学性能。结果表明,激光增材制造M54二次硬化钢是由沿沉积方向生长的柱状晶构成,沉积态试样纵向的抗拉强度和屈服强度分别为1832 MPa和997 MPa,断后伸长率和断面收缩率分别为9.5%和28%;经过传统热处理后,定向凝固形成的胞状结构消失,得到马氏体组织。经1075 ℃固溶+1060 ℃油淬+-73 ℃深冷+510 ℃时效处理后激光增材制造 Ferrium M54钢的性能最好,抗拉强度为1863 MPa,屈服强度为1594 MPa,断后伸长率为15%,断面收缩率为59%,硬度为603 HV。     

深冷处理对3Cr13组织和力学性能的影响

利用SLX-30程序控制深冷箱、金相显微镜、扫描电镜和洛氏硬度计,研究了刀剪材料3Cr13钢经普通热处理、深冷处理后的微观组织及力学性能变化。结果表明,与普通热处理相比.深冷处理后钢中析出的碳化物数量明显增加,分布更加均匀弥散;深冷处理后洛氏硬度值较普通热处理增加了5.3 HRC,冲击韧度增加了0.8 J。     

Mechanical properties of 32Mn-7Cr-0.6Mo-0.3N austenitic steel for cryogenic applications

The tensile, impact, and fracture toughness tests from ambient temperature to 77 K were carried out on 32Mn-7Cr-0.6Mo-0.3N austenitic steel. The fracture surfaces and the phase constitution were analyzed using scanning electron microscopy and x-ray diffraction. The results show that the relation between yield strength and temperature is σ_0.2 · 300 + 1392.4 exp (−0.0106T). The 77 K yield strength is 883 MPa · m^1/2 and the K _J0.05 value is about 236 MPa · m^1/2. The cryogenic intergranular fracture is fully suppressed. The 77 K fracture surfaces exhibit a tough character composed of many dimples and few small quasi-cleavage facets. The results of x-ray analysis show that the austenite phase of the steel is stable even under cryogenic deformation conditions.     

回火温度对高氮不锈轴承钢组织与力学性能的影响

对退火态高氮不锈轴承钢进行真空高压气淬并深冷后在不同温度下回火空冷处理,采用光学显微镜、X射线衍射仪、场发射环境扫描电镜、场发射透射电镜、洛氏硬度计和万能材料试验机,研究并分析了不同回火温度对高氮不锈轴承钢显微组织与力学性能的影响。结果表明:当回火温度由180 ℃升高到550 ℃时,硬度、抗拉强度及屈服强度呈现先下降后上升再迅速下降的变化趋势;试验钢降碳增氮,组织中没有粗大的共晶碳化物存在。当回火温度为500 ℃时,基体组织为回火索氏体,碳化物M₂₃C₆和氮化物Cr₂N细小弥散均匀分布于基体上;在500 ℃回火时出现了二次硬化,强度和硬度达到峰值,这与碳氮化物弥散强化有关。采用1050 ℃真空气淬60 min+深冷处理(-100 ℃×2 h)+500 ℃空冷2 h回火工艺可以获得良好的综合力学性能。     

Fatigue crack propagation of super duplex stainless steel with dispersed structure and time-frequency analysis of acoustic emission

The fatigue crack propagation of super duplex stainless steel was investigated for the effect of various volume fractions of the austenite phase by changing the heat treatment temperature. We also analyzed acoustic emission signals obtained during the fatigue crack propagation by the time-frequency analysis method. As the temperature of the heat treatment increased, the volume fraction of austenite decreased and coarse grain was obtained. The specimen treated at 1200 had a longer fatigue life and slower rate of crack growth. Results of time-frequency analysis of acoustic emission signals during the fatigue test showed the main frequency of 200-300 kHz to have no correlation with heat treatment and crack length, and the 500 kHz signal to be due to dimples and separation of inclusion.     

Artificial Neural Network Prediction of Fretting Wear Behavior of Structural Steel,En 24 Against Bearing Steel,En 31

In this study, artificial neural network (ANN) technique is used to predict the friction and wear behavior of various surface-treated structural steel (En 24) fretted against bearing steel (En 31). A three-layer neural network with a back propagation algorithm is used to train the network. Fretting wear volume and coefficient of friction obtained at different normal loads (ranging between 2.4 and 29.4 N) for various treated samples (hardened, thermo-chemically treated, MoS₂ coated) were used in the formation of training data of ANN. Results of the predictions of ANN are in good agreement with the experimental results. The degree of accuracy of predictions was 96.3 and 95.7% for fretting friction coefficient and wear, respectively.     

深冷处理对18Cr2Ni2MoNbA钢耐磨性的影响

使用正交试验对18Cr2Ni2MoNbA钢渗碳钢深冷处理工艺参数进行筛选优化,分析深冷处理时间、低温回火温度和时间对试样耐磨性的影响,并对试样磨痕形貌、显微组织、残留奥氏体以及显微硬度进行分析。研究表明,18Cr2Ni2MoNbA钢渗碳淬火后的-196 ℃深冷工艺参数对磨损量影响的显著性排序为:深冷处理时间＞低温回火时间＞低温回火温度。深冷处理能够有效增加试样的耐磨性,在深冷温度-196 ℃,深冷处理时间1 h,低温回火温度120 ℃,低温回火时间2 h的工艺下试样磨损量最小,与未深冷时相比减少46.67%,磨损机制变为磨粒磨损与氧化磨损。经过深冷处理后渗碳层的碳化物沿晶界析出,同时有小颗粒碳化物在基体上弥散析出。深冷处理能够降低钢的残留奥氏体含量,增加马氏体含量,使表层渗碳层的显微硬度增加,从而改善18Cr2Ni2MoNbA钢的耐磨性。     

30CrMo钢Q-P-T及深冷处理后的组织与性能

利用光学显微镜(OM),扫描电镜(SEM),X射线衍射仪(XRD)和力学性能测试等研究了不同深冷处理工艺对经Q-P-T工艺处理后30CrMo钢组织和力学性能的影响。结果表明,30CrMo钢最佳的Q-P-T+深冷工艺为:260℃淬火温度,400℃碳配分温度、60 s碳配分时间、-100℃深冷温度、1 h深冷保温时间和一次深冷。经最优的Q-P-T+深冷工艺处理后,30CrMo钢的碳化物的平均尺寸较小,残留奥氏体含量明显增加,残留奥氏体的体积分数约为7.9%,显微硬度约为482 HV,抗拉强度约为1629 MPa,强塑积约为20525 MPa·%,伸长率约为12.6%,其综合力学性能得到了较大幅度提高。     

13X15H4AM3-Ⅲ不锈钢热处理工艺研究

为了研究热处理工艺对13X15H4AM3-Ⅲ不锈钢硬度的影响,进行了多次冰冷处理、冰冷处理+深冷处理和时效工艺试验以及金相和硬度检验。结果表明,通过1070℃固溶处理+冰冷处理+液氮深冷,以及470℃×2 h时效处理后,材料硬度达到了≥46 HRC的较高值,热处理后轴向尺寸涨大0.4%,并用国产化材料进行了验证。