热处理对铸造高速钢组织与性能的影响

研究了热处理工艺对铸态和变质处理铸造高速钢组织与性能的影响.结果表明：变质处理可以使高速钢组织得到细化,同时改变钢中网状共晶碳化物的形貌,使高速钢的硬度和耐磨性得到提高;铸态高温加热、退火、淬火和回火等热处理工艺对铸造高速钢中碳化物的形貌影响不大.铸态和变质处理高速钢退火时,随着加热温度的升高,硬度逐渐升高;淬火＋回火和铸态直接回火的高速钢随着回火温度的升高,硬度和耐磨性逐渐升高,在560℃三次回火时获得最高的硬度及室温耐磨性,且与锻造高速钢相当.     

热处理对低合金高速钢碳化物的影响

利用XRD对低合金高速钢及通用型高速钢M2各热处理状态下碳化物的数量及类型变化特点进行研究,同时对力学性能进行了测试。结果表明:由于采用较高的碳饱和度,低合金高速钢退火态的碳化物数量接近通用型高速钢M2,淬火过程中溶入基体及回火时析出的碳化物数量与M2钢相当,增加了固溶强化效果及二次硬化能力;使低合金高速钢经1170℃淬火+540℃×3 h三次回火后,其硬度和600℃红硬性可达M2钢的水平,获得了良好的综合性能。     

热处理对铸造高速钢组织与性能的影响

研究了热处理工艺对铸态和变质处理铸造高速钢组织与性能的影响。结果表明:变质处理可以使高速钢组织得到细化,同时改变钢中网状共晶碳化物的形貌,使高速钢的硬度和耐磨性得到提高;铸态高温加热、退火、淬火和回火等热处理工艺对铸造高速钢中碳化物的形貌影响不大。铸态和变质处理高速钢退火时,随着加热温度的升高,硬度逐渐升高;淬火+回火和铸态直接回火的高速钢随着回火温度的升高,硬度和耐磨性逐渐升高,在560℃三次回火时获得最高的硬度及室温耐磨性,且与锻造高速钢相当。     

热处理工艺对高速钢组织性能的影响

对含钒、铌的高速钢进行了淬火与回火热处理试验,研究了淬火温度、回火温度对高速钢硬度的影响,并通过显微观察和能谱分析,最终确定了获得高硬度颗粒状弥散分布碳化物的热处理工艺.     

喷射成形含铌M3:2型高速钢的热处理工艺

为探索适合喷射成形高速钢的热处理工艺,利用XRD、SEM等分析手段和硬度测试,研究了淬火温度和回火温度对喷射成形含铌M3:2型高速钢显微组织和硬度的影响。结果表明,试验钢淬火组织由马氏体、残留奥氏体和碳化物组成,随淬火温度升高,试验钢中碳化物数量减少。淬火硬度随淬火温度先增加后减小,低温淬火后回火未发现二次硬化现象。沉积态试样经过1220℃淬火,560℃回火后,硬度最高值为66.7 HRC。     

含稀土轧辊用高速钢淬回火过程微观组织转变

利用金相(OM)、扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)及能损谱(EELS)等手段,研究了含稀土轧辊用高速钢在1100℃淬火和550℃两次回火热处理过程的微观组织变化特征,重点探讨了碳化物行为。结果表明,淬火加热过程中热稳定性较高的MC和M6C型一次共晶碳化物难以溶解,亚稳态的M2C型一次共晶碳化物则发生分解反应得到MC和M6C两种碳化物,分解形成的M6C较MC量多且尺寸较大,小颗粒MC包含在M6C之中;淬火基体组织由马氏体和残留奥氏体组成,淬火马氏体既有板条马氏体也有孪晶型马氏体。经两次回火后,残留奥氏体得以有效消除,大量细小富V的MC型二次碳化物弥散析出产生二次硬化现象。     

淬火处理对轧辊用高硼高速钢组织和性能的影响

利用光学显微镜、扫描电镜、X射线衍射、硬度计及MM-200磨损试验机,研究了淬火温度对轧辊用高硼高速钢显微组织和性能的影响。结果表明,高硼高速钢的铸态组织由马氏体、铁素体、珠光体和沿晶界呈连续网状分布的共晶硼碳化物组成,共晶硼碳化物主要是M2B和M7(C,B)3;随着淬火温度的升高,基体全部转变成为马氏体,并有二次硼碳化物M23(C,B)6析出;高硼高速钢的硬度和耐磨性随着淬火温度的升高而明显增加,在1150℃淬火时硬度最高、耐磨性最好。     

高碳高钒高速钢的高温硬度及热处理的研究

研究了高碳高钒高速钢的淬火、回火热处理及高温硬度。结果表明,其峰值硬度温度较常规高速钢低１５０～２５０℃左右,随碳量增加,峰值硬度温度降低,相同碳量、钡量增加,峰值硬温度升高。回火后的硬度变化和常规高速钢呈相同的趋势,次硬化温度约在５５０℃,但二次硬化的峰值硬度峰较小,在二次硬化温度二次回火,二次硬化作用消失。随碳量、钒量增加,高温硬度增加。根据轧辊辊面硬度要求,高碳高钒高速钢的淬火温度为９５０～     

热处理对高速钢W6Mo5Cr4V3Co8组织和性能的影响

采用OM,SEM,EDS,TEM以及力学性能试验,研究了热处理工艺对不同尺寸规格的粉末冶金高速钢W6Mo5Cr4V3Co8微观组织和力学性能的影响。结果表明,区别于普通高速钢,粉末冶金高速钢微观组织中没有大颗粒尺寸共晶碳化物,退火组织中碳化物均匀、细小,颗粒尺寸小于3μm。因此,不同尺寸规格钢材以及不同截面方向的组织都保持着高度的一致性;试验钢在1080～1180℃较宽的温度范围内淬火都能够获得67 HRC以上的硬度。淬火后的组织为马氏体+残留奥氏体+未溶碳化物,淬火奥氏体晶粒尺寸非常细小;经过高温回火后,试验钢存在明显的二次硬化效应,二次硬化峰出现在520℃。二次硬化现象是由残留奥氏体转变和合金碳化物析出共同作用的结果,TEM分析显示,试验钢经高温回火析出的二次硬化碳化物包含VC;冲击韧性试验结果表明,不同截面尺寸粉末高速钢的冲击韧性基本相当,同一钢材其横向和纵向的冲击韧性相差不大。     

M42热处理中淬火温度对碳化物转变机制的影响

以精锻M42喷射成形高速钢为原料,通过热处理正交试验,优化了材料热处理工艺,并分析了不同热处理制度下材料显微组织、硬度、抗弯强度及碳化物的演变规律。结果显示,最佳热处理工艺为:淬火保温温度1180℃,回火温度540℃,回火3次,每次1 h。该工艺下,M42洛氏硬度达到67.2 HRC,抗弯强度达到3115 MPa。淬火保温温度通过控制M_6C型碳化物的溶解量,影响最终碳化物的尺寸。淬火温度为1190℃时,M_6C型碳化物充分溶解,回火过程碳化物均匀弥散析出。     

热处理工艺参数对Cr8冷作模具钢组织和性能的影响

针对Cr8冷作模具钢的二次硬化问题,采用金相显微镜、SEM、EDS和洛氏硬度计,研究了低温回火和高温回火对Cr8冷作模具钢材料组织和性能的影响。结果表明,原材料组织为珠光体和少量长为9~41μm、宽为2~11μm大颗粒共晶碳化物;不同回火温度下,材料的组织为马氏体和少量长为4~25μm、宽为1~8μm的大颗粒共晶碳化物及细小二次析出碳化物;经1030℃淬火、高温520℃回火之后材料出现二次硬化现象,硬度为58. 4 HRC,比低温200℃回火下的硬度高出1. 4 HRC。Cr8钢的二次硬化是由于高温520℃回火之后,二次纳米级小颗粒碳化物析出较多,且颗粒均匀弥散分布于基体中造成的。     

The Kinetics of Phase Transformations During Tempering in Laser Melted High Chromium Cast Steel

The precipitation of secondary carbides in the laser melted high chromium cast steels during tempering at 300-650?°C for 2?h in air furnace was characterized and the present phases was identified, by using transmission electron microscopy. Laser melted high chromium cast steel consists of austenitic dendrites and interdendritic M₂₃C₆ carbides. The austenite has such a strong tempering stability that it remains unchanged at temperature below 400?°C and the secondary hardening phenomenon starts from 450?°C to the maximum value of 672 HV at 560?°C. After tempering at 450?°C fine M₂₃C₆ carbides precipitate from the supersaturated austenite preferentially. In addition, the dislocation lines and slip bands still exist inside the austenite. While tempering at temperature below 560?°C, the secondary hardening simultaneously results from the martensite phase transformation and the precipitation of carbides as well as dislocation strengthening within a refined microstructure. Moreover, the formation of the ferrite matrix and large quality of coarse lamellar M₃C carbides when the samples were tempered at 650?°C contributes to the decrease of hardness.     

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。     

淬火回火工艺对Cr26过共晶高铬铸铁组织及性能的影响

采用X射线衍射仪、光学显微镜、扫描电镜、硬度测试、冲击试验和磨损试验等手段,研究了淬火和回火工艺对Cr26型过共晶高铬铸铁组织、硬度、冲击吸收能量和耐磨性的影响。结果表明,经980~1100 ℃淬火和250~600 ℃回火后的Cr26过共晶高铬铸铁的组织主要是马氏体基体,M₇C₃碳化物和少量奥氏体。初生碳化物为六边形,共晶碳化物和回火生成的二次碳化物呈短棒状。总体碳化物含量随淬火温度升高略有上升。随回火温度的升高,硬度先降低后增加,超过500 ℃回火时再次降低,而冲击吸收能量先增加后降低,超过350 ℃回火时再次上升。不同温度淬火时,对应最大耐磨性的回火温度不同。980、1050 ℃淬火时,再经250 ℃回火获得最高的耐磨性,而1100 ℃淬火时,再经350 ℃回火获得最大耐磨性。     

Relative Dimensional Change Evaluation of Vacuum Heat-Treated JIS SKD61 Hot-Work Tool Steels

JIS SKD61 hot-work steel is usually used as precision mold material for die casting; hence, it demands a higher level of dimensional stability during the hardening process, especially for fairly large sections. This study investigates the microstructural evolution and measures the relative dimensional changes in various tempering states. The results show that the retained austenitic contents of all quenched and tempered SKD61 steel specimens were less than 2%. When the tempering temperature reached 500 °C, the retained austenitic content decreased from 1.35 to 0.45%. TEM investigations revealed that a large number of secondary carbides, molybdenum-rich M₂C and vanadium-rich MC carbides, precipitated near the dislocations when the tempering temperature reached 525 °C. A secondary hardening phenomenon and evident expansion phenomenon occurred as the tempering temperature exceeded 500 °C. These phenomena were mainly contributed by the precipitation of secondary carbides in hot-work steels. The reason is that only 0.9% of the retained austenite transformed into martensite as the tempering temperature reached 500 °C, allowing the hardness and dimensional change to be neglected.     

回火温度对二次硬化马氏体不锈钢组织和性能的影响

二次硬化对回火温度非常敏感,研究了某含Mo二次硬化马氏体不锈钢在250~650 ℃回火时组织和性能的演变过程,并利用XRD、SEM、TEM以及冲击测试等手段分析了显微组织与力学性能之间的关系,着重讨论了试验钢二次硬化与残留奥氏体增韧机理。结果表明: 480~500 ℃回火时,试验钢同时出现了二次硬化和回火脆性现象,宏观硬度达到了56 HRC以上,冲击性能为14 J·cm^-2左右,显微组织主要由纳米级合金碳化物、板条马氏体以及残留奥氏体构成,其中纳米级合金碳化物弥散强化引起了二次硬化,体积分数约为10%的残留奥氏体有利于提高钢的冲击性能。而在上述温度区之外低温和高温回火时,试验钢均具有较高的冲击性能,但宏观硬度相对较低。     

Semisolid structure for M2 high speed steel prepared by cooling slope

Effects of cooling slope angle and the temperature of molten metal on the globular structure of M2 high speed steel after holding at the semisolid state have been investigated. The globular structure was achieved by pouring the molten metal at 1595 °C on the ceramic cooling slope with the length of 200 mm and the angle of 25°. The globular structure of M2 high speed steel in the form of rolled–annealed and as cast condition after holding at semisolid state has been achieved. The size of globular grains of cooling slope sample was smaller than that of the rolled–annealed and as cast samples. Solid particles of rolled–annealed sample after holding at semisolid state had better roundness compared with cooling slope sample. Dissolution of carbides in the austenite phase at grain boundaries leads to formation of globular particles in the semisolid state. MC-type and M₆C-type eutectic carbides reprecipitate during cooling cycle along grain boundaries.     

PHASE AND STRUCTURE TRANSFORMATION OF BAINITE IN 3Cr3Mo3VNb STEEL DURING TEMPERING

本文研究了3Cr3Mo3VNb钢等温淬火后贝氏体回火时的相及组织转变规律。实验结果表明,贝氏体的二次硬化机制和马氏体一样,主要是由Mo_2C,V_4C_3,NbC等细小弥散的合金碳化物析出造成的。回火时,贝氏体中粗大的渗碳体溶解较慢,减慢了合金碳化物的析出速率。贝氏体中的残余奥氏体分解和转变的行为与马氏体中的不同。贝氏体中位错密度较低,不利于合金碳化物的聚集粗化。以上诸因素的共同作用,使贝氏体具有比直接淬火所获得的马氏体更高的二次硬化效应、热强性和组织稳定性。     

EFFECT OF TEMPERING IN PULSE MAGNETIC FIELD ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF HIGH SPEED STEEL

Using a self-made pulse magnetic field heat treatment equipment with low or medium intensi-ty,the tempering process of high speed steel W6Mo5Cr4V2 was investigated.It was foundthat the secondary hardening process and the transformation of retained austenite for the steelwere accelerated by the pulse magnetic field,and the tempering period could be reduced tohalf of the original.It was shown by the analyses of X-ray and eletron microscopy that theprecipitation of carbides becomes more homogeneous and dispersive,and the tetragonality ofmartensite increases obviousely,which causes the improvement of hardness and red-hardnessfor the steel.It was confirmed that the service life of tools as centre bits,screw taps andpunches for nuts could be increased by 0.4 to 1.4 times by the tempering in magnetic field.