Tempering Behavior of 45Cr-2W-0.25V Steel

 In this research the tempering behavior of a Cr-W-V steel was investigated. This new alloy with the composition of Fe-4.5Cr-2W-0.25V-0.1C was austenitized at 1000°C for 30 min and tempered at 500°C to 700°C for different times up to 100h. An OM analysis of the microstructure of air cooled and water quenched specimens before tempering showed that although in both conditions fully martensitic matrix formed, finer structure had formed in the water quenched specimens. The XRD and TEM results showed that the most stable carbides formed during tempering of the steel were M23C6 and M7C3, respectively. Other carbides such as M3C and M2C, formed in the first stages of tempering, and stable MC were also observed. The results showed that when the tempering time, temperature and cooling rate were increased, weight percent of extracted precipitates was increased. In addition, the formation rate of the stable carbides such as M23C6 and dissolution rate of the metastable carbides such as M3C and M2C were increased. The hardness results was revealed that tempering at 600°C and 700°C result in gradual decrease in hardness, but didn't observed significant changes in hardness at 500°C even for long tempering times.     

Evolution and Coarsening of Carbides in 2.25Cr-1Mo Steel Weld Metal During High Temperature Tempering

Transformation and coarsening of carbides in 2.25Cr-1Mo steel weld metal during tempering at 700 ℃ for different time intervals ranging from 1 to 150 h were examined by transmission electron microscopy and scanning electron microscopy. M3C carbides were observed in the as-welded specimens and when tempered, the precipitates were mainly composed of M3C, M7C3, and M23C6 carbides. A sequence for corresponding carbide transformation during tempering with initial precipitation of M3C and the subsequent precipitation of M7C3 and M23C6 was proposed. The precipitation of M7C3 with higher chromium content was the main factor contributing to the decrease in coarsening rate of precipitates after prolonged tempering. The decrease in hardness of the tempered specimens agreed well with the prediction of the weakening of precipitation strengthening owing to the coarsening of carbides.     

Phase Transformation of a Cold Work Tool Steel during Tempering

The hardness and microstructure evolution of a 8% Cr cold work tool steel during tempering for 40 h were investigated. Transmission electron microscope examinations showed that M_3C carbides precipitated from supersaturated martensite after tempering at 350 ℃. When the tempering temperature was higher than 520 ℃,the M_(23)C_6 carbides precipitated to substitute for M_3C carbides. After ageing at the temperature of 520 ℃ for 40 h,it was observed that very fine and dense secondary Mo_2C precipitates were precipitated. Thus,it can be concluded that the early stage of Mo_2C-carbide precipitation is like to be Gunier-Preston( G-P) zone formed by [Mo-C] segregation group which is responsible for the secondary hardening peak at 520 ℃. Overageing at 700 ℃ resulted in recovery of martensitic microstructure and precipitation of M_(23)C_6 carbides.When ageing at 700 ℃ for more than 20 h,recrystallization occurred,which resulted in a change of the matrix morphology from martensitic plates to equiaxed ferrite. It was noticed that the size of recrystallized grain / subgrain was very fine,which was attributed to the pinning effect of M_(23)C_6 precipitates.     

Tempering process of high strength and high toughness Cr- Mo- V bulb- flat steel

Aim at the problems that the heat treatment process of high strength and high toughness Cr- Mo- V bulb- flat steel was difficulty and the granular bainite was not fully decomposed, the influence of different tempering temperatures and tempering holding times on the microstructure and mechanical properties of high strength and high toughness Cr- Mo- V bulb- flat steel were studied by optical microscopy, SEM, TEM and mechanical property tests. The results show that the metastable granular bainite in the steel can be recovered and transformed to quasi- polygonal ferrite by tempering at temperatures above 600?? and holding for more than 2h. The large- sized and long- shaped M- A islands in the original microstructure are decomposed and transformed into granular M- A islands. With the increase of the tempering temperature, the granular bainite in the steel can be further decomposed to make the particles finer and more dispersed, which significantly improves the low- temperature toughness of the steel and obtains a good comprehensive performance. For this steel, the best heat treatment process to get good match of strength and toughness is tempering at 660-680?? and holding for 3. 0-3. 5h.     

无莱氏体高速钢2W－3Mo－4Cr－6V

在本文作者研制的有别于基体钢，低碳高速钢和普通渗碳高速钢的新型无莱氏体高速钢的基础上，又成功地研制成一种高Ｖ无莱氏体高速钢２Ｗ－３Ｍｏ－４Ｃｒ－６Ｖ。该钢经热处理后硬度高于７０ＨＲＣ，６００℃红硬性为６７．５ＨＲＣ。用其制成Ｍ３３挤压丝锥的使用寿命较１８Ｗ－４Ｃｒ－Ｖ丝锥高２倍。     

In-situ TEM Observation of Cementite Coarsening Behavior of 5Mn Steel during Tempering

The cementite formation and coarsening behaviors of 0. 2 mass% C-5 mass% Mn steel during tempering at 500℃ were investigated by in-situ transmission electron microscope( TEM). In-situ TEM observation showed uniform distribution of cementite particles at the early stage of tempering in the rapidly heated( 500 ℃ / s) sample. Elemental analysis confirmed that the cementite growth was dominated by Mn diffusion. During the cementite growth,the coarsening behavior of intragranular cementite was significantly controlled by the matrix diffusion,while that of the intergranular cementite was mainly governed by the boundary diffusion. The in-situ TEM observation revealed that the dislocation pipe diffusion of Mn took place during tempering,which accelerated the Mn diffusion between cementite particles. The coarsening rates of individual cementite particles were calculated based on the in-situ TEM observation.     

回火温度对高锰钢ZGMn13Cr2性能的影响

通过系列回火工艺及拉伸试验 ,研究了回火温度对ZGMn13Cr2性能的影响。结果表明 :ZGMn13Cr2经水韧处理后 ,再经过 2 5 0℃× 6h回火 ,在韧性不降低的情况下 ,强度提高 10 % ,达到国外牌号GX12 0Mn12性能要求。     

M_2C Precipitate in Isothermal Tempering of High Co-Ni Alloy Steel

Secondary hardening alloy has been studied fordecades and emphases are focused on the mechanismof secondary hardening and carbides precipitationduring second hardening reaction.It has got to awide common view that alloy carbides replace ce-mentite during the aging time reaction in secondaryhardening alloy steel[1] .Many studies were conduct-ed on the alloy carbide precipitation mechanism[2 ,3]and it is well established that the secondary harden-ing is accomplished by the precipitation of fine …     

一种新型高性能非调质钢

采用合适的合金化设计方案、优化冶炼和轧制工艺,研制了一种组织为粒状贝氏体的非调质钢。该钢晶粒细小、组织均匀、力学性能优异,并且具有较好的热稳定性,能满足超高强度抽油杆对强韧性、疲劳寿命及热加工工艺性能的要求,可以替代传统的优质合金结构钢,也可以用于其它需调质处理的性能要求高的结构件。     

热处理工艺对2.25Cr-1Mo-0.25V钢低温韧性的影响

模拟实际大型锻件热处理工艺条件,研究了不同预备热处理和最终性能热处理工艺规范对2.25Cr-1Mo-0.25V钢-30℃冲击韧性的影响,结果表明经调质预处理后的低温韧性随再奥氏体化温度的升高而降低,而经1 200℃正火预处理后进行1 040℃奥氏体化,不仅有利于碳氮化物充分溶解与合金元素的均匀化,同时有利用奥氏体的自发再结晶细化晶粒并获得较高的低温韧性.     

回火温度对9Ni钢低温韧度的影响研究

为了研究不同回火温度对9Ni钢低温韧度的影响,利用OM、SEM、TEM对试验钢微观组织和断口形貌进行观察分析,研究表明:在550~600℃范围内回火,9Ni钢强度和韧度达到最佳匹配,且其他各项性能也达到最佳;回转奥氏体、碳化物及回转奥氏体诱发马氏体相变等均对低温韧度产生重要影响。     

Tempering Process to Improve Hardness Uniformity of Plastic Mould Steel

 A new design of copper-bearing non-quenched plastic mold steel is presented and explained. Two kinds of microstructure can be obtained from this new type copper-bearing steel via cooling with different cooling rates, bainite and a mixed microstructure consisting of ferrite and bainite. It is found that, after proper tempering process, the hardness will be increased. Moreover, the hardness difference between different microstructures will be reduced. For further investigation, the samples tempered at different temperatures were examined by XRD and 3DAP (three dimensional atom probe) analysis. Results show that the improvement is contributed mainly by the precipitation of Cu phase and transformation of residual austenite.     

回火温度对Mo-V-Ti钢组织与性能的影响

为了研究回火温度、析出相对含Mo-V-Ti钢组织与性能的影响,试验采用550 mm轧机对含Mo-V-Ti钢轧制后进行完全淬火,然后在630~710℃不同的温度下进行回火。结果表明,高温回火后,钢的组织由回火索氏体和少量贝氏体组成,组织中发生回复和再结晶,钢的强韧性匹配发生变化。在670℃以下回火时产生的析出相主要为Ti、V和Mo复合的碳氮化合物和V、Mo复合的碳氮化合物,随着回火温度的提高,产生了新的析出相Fe、Mn和Mo及V合金渗碳体,析出相对钢的强韧性有重要影响。     

Co—Ni钢长期回火脆性的研究

用透射电镜、扫描电镜及俄歇能谱研究了１６ＮｉＣｏ钢和２３ＮｉＣｏ钢长时间回火后韧性降低及冲击韧性断口出现沿晶断裂的原因。产生脆性的原因主要是由于杂质元素Ｐ、Ｓ及合金元素Ｎｉ在晶界偏析所致。已经变脆的试样，经６００℃保温处理可消除脆性及沿晶脆断。     

淬火硼钢回火时硼碳化物的形成及其动力学

用透射电子显微分析，金相分析及扫描俄歇微探针研究了５０Ｂ钢淬火后回火是硼碳化物的形成及其动力学，确认硼碳化物Ｆｅ２３（Ｂ，Ｃ）６和Ｆｅ３（Ｃ，Ｂ）。Ｆｅ２３（Ｂ，Ｃ）６在马氏体分解时析出于Ｆｅ３Ｃ之后，析出温度在４９０℃或更高，析出的动力学曲线为“Ｃ”形的下半部，Ｆｅ３（Ｃ，Ｂ）则在较长时间回火时由Ｆｅ３Ｃ转变而成，其形成的学曲线是以７００℃和５５０℃为鼻尖“ε”形。     

回火温度对Q960级高强结构钢组织及力学性能的影响

 以屈服强度960MPa级高强调质结构钢板开发为目标,研究了在相同轧制及淬火条件下,回火温度对试验钢显微结构及力学性能的影响。结果表明：随回火温度的升高,试验钢强度下降,韧塑性总体上呈现升高趋势,其中在300~450℃范围内出现一个韧塑性能的恶化区。当回火温度为600℃时,试验钢呈回火索氏体组织,屈服强度为1030MPa,抗拉强度为1080MPa,伸长率为15.9%,-40℃冲击功达144J,各项指标均满足国标GB/T 16270—2009要求。并对试验钢的拉伸力学性能进行了探讨。     

低碳高强钢中纳米析出相回火过程中的透射分析

 研究了一种800MPa级低碳高强钢中纳米析出相在回火过程中的演变规律。通过透射、高分辨电镜,并结合能谱仪系统分析了不同回火温度下析出相的形貌特征及其与基体的位相关系。研究表明,低碳高强钢中的纳米析出相主要为Nb、Ti、V、Mo等元素的碳氮化物,低温回火时主要为Nb、Ti的二元析出,高温回火后则为含Mo、V、Ti、Nb等多种元素的复合碳化物析出;钢中纳米析出相按大小分为两类,大尺寸颗粒是钢在轧制过程中形变诱导析出的,小尺寸颗粒是钢在回火过程中相变诱导析出的;同时,随回火温度的升高,钢中的析出相均慢慢长大并粗化,长大方式为典型的Oswald熟化机制;析出相与母相基体之间存在特定的取向关系,在析出的开始阶段,析出与基体的界面基本保持共格关系,析出相形状主要为球形或者类球形,随着回火温度的升高,析出逐渐长大并粗化,形状渐渐变为方形或者椭圆形,同时与基体脱离共格界面,保持的界面关系为：{100}MC∥{100}α-Fe,<100>MC∥<110>α-Fe。     

The Investigation for Development on Precipitation Phases in 25Co15Ni11Cr2MoE Steel during Tempering

The evolution law of precipitated alloy carbides and reverted austenite in a high Co-Ni secondary hardening ultra-high strength 25Co15Ni11Cr2MoE steel tempered at 300??~ 660?? after quenched has been studied by means of transmission electron microscopy (TEM) and X ray diffraction (XRD) in this paper. The results show that the precipitate order of alloy carbides with the increasing of tempering temperature from 300?? to 600?? in experimental steel is: dispersed ??-carbides?? lamellar alloy cementites?? dispersed M2C carbides?? coarse M23C6 carbides. When the experimental steel tempering at 495??, fine M2C carbides precipitated on the lath martensite matrix. Meanwhile, coarse lamellar alloy cementites that precipitated during the early tempering stage has all dissolved, and reverted austenite precipitated at the boundaries of lath martensite and grows up into thin-film sharp along the lath boundaries. When the tempering temperature rose to 530??, the content of reverted austenite continues to increase, but the morphology of reverted austenite changed from thin-film to strip or block. When the tempering temperature rose to 530??, the content of reverted austenite in the steel reaches maximum value.     

Effect of Tempering Temperature on Strength and Toughness of Novel Carbide-Free Bainite/Martensite Duplex Phase Steel

Ｔｈｅｍｉｃｒｏｓｔｒｕｃｔｕｒｅｏｆｓｏｍｅｈｉｇｈｓｔｒｅｎｇｔｈｌｏｗａｌｌｏｙｓｔｅｅｌｓａｎｄｕｌｔｒａｈｉｇｈｓｔｒｅｎｇｔｈｌｏｗａｌｌｏｙｓｔｅｅｌｓｉｎｃｏｍｍｅｒｃｉａｌｕｓｅｉｓｕｓｕａｌｌｙｔｅｍｐｅｒｅｄｍａｒｔｅｎｓｉｔｅ .Ｈｏｗｅｖｅｒ ,ｓｌａｃｋ ｑｕｅｎｃｈｅｄｍｉｘｅｄｍｉｃｒｏｓｔｒｕｃｔｕｒｅｃｏｍｐｒｉｓｉｎｇｍａｒｔｅｎｓｉｔｅａｎｄｂａｉｎｉｔｅｉｓｇｅｎｅｒａｌｌｙｅｎ ｃｏｕｎｔｅｒｅｄｉｎｃｏｍｍｅｒｃｉａｌｐｒａｃｔｉｃｅｗｈｅｎｔｈｅｓｅｌｏ…     

Effect of M3C on the Precipitation Behavior of M23C6 Phase during Early Stage of Tempering in T91 Ferritic Steel

Tempered martensitic structure is the service condition of T91 ferritic steel after adopting the austenitizing followed by tempering. Needle‐like M₃C particles are precipitated during air cooling after austenization, while the precipitation of M₃C is suppressed during the water cooling. The effect of existence of M₃C on the precipitation behaviors of M₂₃C₆ during the early stage of tempering, as nucleation site, number density and size distribution, was investigated by means of TEM observation. The TEM results indicate that, upon the same tempering time, the size of M₂₃C₆ is smaller and its number density is higher in the sample pre‐existing M₃C than in the sample without M₃C. This can be explained that existence of M₃C results in more M₂₃C₆ precipitates forming inside of grain, where a relatively low self‐diffusion coefficient of alloy element leads to M₂₃C₆ hardly coarsening. However, with the prolongation of tempering time, this effect becomes weaken. Microhardness results indicate that the existence of M₃C phase results in the increase of hardness after tempering due to the precipitation of finer and denser M₂₃C₆ particles.