Tempering Behavior of 4.5Cr-2W-0.25V Steel

The tempering behavior of a Cr-W-V steel was investigated in this research.This new alloy with the composition of Fe-4.5Cr-2W-0.25V-0.1C was austenitized at 1000 ℃ for 30 min and tempered at 600 and 700 ℃ for different time up to 100 h.An OM analysis of the microstructure of air cooled and water quenched specimens before tempering showed that although under 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,mass 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.     

V、Ta微合金化12Cr低活性F/M钢的优化设计

采用Thermo-Calc热力学模拟计算与实验相结合的方法,优化设计了一种V、Ta微合金化的低活性F/M钢12Cr3WVTa,经1 050℃水淬及780℃回火后对其显微组织及析出相进行光学显微镜、扫描电镜和透射电镜观察以及能谱分析.实验钢淬火回火后显微组织由回火马氏体和少量δ铁素体相组成,析出相主要为M₂₃C₆和MX相(M=V,Ta;X=C,N),其中M₂₃C₆主要分布于回火马氏体板条界和相界,而MX弥散析出于回火马氏体板条内以及δ铁素体内.实验钢室温和高温(600℃)拉伸力学性能良好,600℃下材料抗拉强度为507 MPa,屈服强度为402 MPa,满足超临界水冷堆用包壳管的拉伸性能要求.      

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.     

Precipitation of nanoscale carbides in Ti- Mo microalloyed steel during tempering process

The distribution, morphology and size of the carbide precipitates in as- rolled and as- tempered Ti- Mo microalloyed steels were elucidated by optical microscopy and transmission electron microscopy. The change in nanoscale precipitate during tempering and its effect on strength of test steel were analyzed by tensile test. The results revealed that substantial improvement in yield strength occurred on tempering at 600?? for 2 h because of the supersaturated precipitation and homogeneous distribution of profuse (Ti, Mo)C carbide in the matrix in average size from 5-6nm except interphase precipitation, and the precipitation volume fraction of the sample tempered at 600?? exhibited an approximate 3%-5% increase compared to the samples tempered at 650 and 700??. With increase in tempering temperature and holding time, the interphase- precipitated carbides were observed to have slightly coarsened to a maximum size of less than 8nm, but did not coarsen as much as the supersaturated carbides formed during tempering. The interphase precipitation exhibits more excellent behavior of thermal stability than supersaturated precipitation during tempering process.     

Coarsening of M23C6 Precipitates in an Fe-Cr-C Ternary Alloy

 Coarsening of M23C6 precipitates in an Fe-12.4Cr-0.13C ternary alloy has been investigated ageing at 780 ℃ up to 200 h. Evolution of M23C6 carbides at different ageing times was determined experimentally using transmission electron microscopy. Particle size distribution was obtained with different measuring methods. Simulations of coarsening of M23C6 precipitates were carried out using computational thermodynamics and kinetics. Results showed low coarsening rates for M23C6 precipitates in the Fe-Cr-C ternary alloy. Interfacial energy of M23C6/ferrite interface is between 0.1 and 0.3 J·m-2 for the coarsening of M23C6 ageing at 780 ℃.     

Microstructure and Mechanical Properties of Martensitic Stainless Steel 6Crl5MoV

 Martensitic stainless steel containing Cr of 12% to 18% (mass percent) are common utilized in quenching and tempering processes for knife and cutlery steel. The properties obtained in these materials are significantly influenced by matrix composition after heat treatment, especially as Cr and C content. Comprehensive considered the hardness and corrosion resistance, a new type martensitic stainless steel 6Cr15MoV has been developed. The effect of heat treatment processes on microstructure and mechanical properties of 6Cr15MoV martensitic stainless steel is emphatically researched. Thermo-Calc software has been carried out to thermodynamic calculation; OM, SEM and TEM have been carried out to microstructure observation; hardness and impact toughness test have been carried out to evaluate the mechanical properties. Results show that the equilibrium carbide in 6Cr15MoV steel is M23C6 carbide, and the M23C6 carbides finely distributed in annealed microstructure. 6Cr15MoV martensitic stainless steel has a wider quenching temperature range, the hardness value of steel 6Cr15MoV can reach to HRC 608 to HRC 616 when quenched at 1060 to 1100 ℃. Finely distributed carbides will exist in quenched microstructure, and effectively inhabit the growth of austenite grain. With the increasing of quenching temperature, the volume fraction of undissolved carbides will decrease. The excellent comprehensive mechanical properties can be obtained by quenched at 1060 to 1100 ℃ with tempered at 100 to 150 ℃, and it is mainly due to the high carbon martensite and fine grain size. At these temperature ranges, the hardness will retain about HRC 592 to HRC 616 and the Charpy U-notch impact toughness will retain about 173 to 20 J. A lot of M23C6 carbides precipitated from martensite matrix, at the same time along the boundaries of martensite lathes which leading to the decrease of impact toughness when tempered at 500 to 540 ℃. The M3C precipitants also existed in the martensite matrix of test steel after tempered at 500 ℃, and the mean size of M3C precipitates is bigger than that of M23C6 precipitates.     

Al对淬回火H11钢力学性能和碳化物的影响

研究了Al质量分数为0.77%及不含Al的H11钢在不同淬回火处理工艺下的硬度和冲击功的变化规律,并对两种钢原始退火态、1060℃淬火、1060℃淬火+510℃回火、1060℃淬火+560℃回火和1060℃淬火+600℃回火处理后的试样进行碳化物萃取,同时借助扫描电子显微镜（SEM）和X射线衍射仪（XRD）分析了Al对H11钢中碳化物形态及类型的影响.结果表明:（1）Al能提高H11钢的冲击韧性和回火硬度,但会使淬火硬度有所降低.（2）Al可以促进H11钢淬火过程中碳化物的溶解和元素的均匀分布.（3）Al会阻碍H11钢回火过程中碳化物的析出和聚集,这种作用在560℃以下回火时更加显著.（4）Al可以使H11钢回火时的（Fe,Cr）₂C、MoC、Cr₇C₃类碳化物更加稳定,抑制（Fe,Cr）₃C、Mo₂C和Cr₂₃C₆类碳化物的析出,这是因为Al可以阻碍H11钢中碳及合金元素在回火过程中的聚集.      

M2C precipitates in isothermal tempering of high Co-Ni secondary hardening steel

The effects of isothermal tempering on the coarsening behavior of hexagonal M₂C precipitates and the secondary hardening reaction in ultrahigh-strength AerMet 100 steel were investigated. The tempering temperatures were 468 °C, 482 °C, and 510 °C, and the tempering time spanned the range from 1 to 400 hours. Experimental studies of the coarsening behavior of the carbides were made by utilizing transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffractometry (XRD). The hardness at the secondary hardening peak was about HRc 55. The average length and diameter of M₂C carbides were 4 to 8 nm and 1.5 to 2.5 nm, respectively, at all three tempering temperatures; hence, the aspect ratio was almost 3, an equilibrium value in this case. The size of the M₂C carbides increased monotonically with time, but the growth kinetics did not exactly follow the classical coarsening behavior. The amount of precipitated austenite increased with tempering time and temperature. M₂C precipitates were still relatively fine even after 200 hours of tempering. This feature seemed to be closely related to the high hardness maintained after prolonged tempering.     

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.     

回火时间对0．16C－10Ni－14Co－1Cr－1Mo钢和0．23C－12Ni－14Co－3Cr－1Mo钢组织与性能的影响

研究了０．１６Ｃ－１０Ｎｉ－１４Ｃｏ－１Ｃｒ－１Ｍｏ（１６ＮｉＣｏ）钢在５１０℃和０．２３℃－１２Ｎｉ－１４Ｃｏ－３Ｃｒ－１Ｍｏ（２３ＮｉＣｏ）钢在４８２℃回火的组织与性能。随回火时间的延长，强度、硬度的降低主要是由于Ｍ_２Ｃ的粗化及与基体共格性降低所致。Ｍ_２Ｃ的粗化速度２３ＮｉＣｏ钢要小于１６ＮｉＣｏ钢。     

Coarsening resistance of M2C carbides in secondary hardening steels: Part III. Comparison of theory and experiment

A model for the coarsening resistance of multicomponent carbides was used to study the effect of Mo and Cr on the coarsening kinetics of M₂C carbides in commercial AF1410 and experimental alloy steels. Experimental studies of coarsening behavior of the carbides in these steels have been made by using transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The measured coarsening rate constant agrees with model predictions within a factor of 2 to 3. The coarsening kinetics of M₂C carbides in these alloys is found to be controlled by the volume diffusion of alloying element M. A Cr-Mo alloy steel with the predicted optimum composition showed the slowest coarsening kinetics and highest hardness at long tempering times.     

Microstructural changes during overtempering of high-speed steels

To elucidate the mechanisms determining the creep resistance of high-speed steels during tool service, overtempering at 600°C has been investigated for two alloys modeling the matrix compositions of AISI M2 and T1. Composition changes and coarsening of the secondary hardening precipitates were studied by transmission electron microscopy and field-ion microscopy with atom probe analysis. Strengthening in the peak-hardened state is due to coherent precipitates of types M₂C and MC. During overtempering, M₂C coarsens too rapidly to be of importance for the sustained strength of the material. The MC precipitates, on the other hand, are fairly stable. Some coarsening does occur, but the MC population is replenished by a second wave of precipitation which makes use of the roughly 50 pct of carbide-forming elements, carbon, and nitrogen, which remained in solid solution after tempering to the peak-hardened state. This precipitation reaction continues for times of the order of the tool life.     

Influence of tempering temperature on stability of carbide phases in 2.6cr-0.7mo-0.3v steel with various carbon content

The present work evaluates the influence of the bulk carbon content (0.1, 0.006, and 0.005 wt pct) and tempering temperature (823, 853, and 913 K) on stability, chemical composition, and size of carbide particles in 540 ks tempered states of 2.6Cr-0.7Mo-0.3V steel. The scanning transmission electron microscopy/energy-dispersive X-ray spectroscopy (STEM/EDXS) and electron diffraction methods were used to analyze the carbide particles. A characteristic energy-dispersive X-ray (EDX) spectrum can be attributed to each of the identified carbides. The MC carbide is stable in all experimental states. The phase stability of Fe-Cr-rich carbides increased in the order ε, Fe₃C → M₃C → M₇C₃, with tempering temperature increasing. In steels with higher carbon content tempered at low temperature, M₂₃C₆ carbide was also noted. The Mo₂C and M₆C carbides were not observed. It was shown that the decrease of the bulk carbon content has the same influence on the carbide phases stability as the increase of the bulk vanadium content at the unchanged Cr, Mo, C bulk contents and tempering temperature. Similarly, the decrease of tempering temperature has the same influence on the carbide phases stability as the decrease of the bulk Cr content at the unchanged V, Mo, and C bulk contents.     

Carbide Precipitation in 2.25 Cr-1 Mo Bainitic Steel: Effect of Heating and Isothermal Tempering Conditions

The effect of the tempering heat treatment, including heating prior to the isothermal step, on carbide precipitation has been determined in a 2.25 Cr-1 Mo bainitic steel for thick-walled applications. The carbides were identified using their amount of metallic elements, morphology, nucleation sites, and diffraction patterns. The evolution of carbide phase fraction, morphology, and composition was investigated using transmission electron microscopy, X-ray diffraction, as well as thermodynamic calculations. Upon heating, retained austenite into the as-quenched material decomposes into ferrite and cementite. M₇C₃ carbides then nucleate at the interface between the cementite and the matrix, triggering the dissolution of cementite. M₂C carbides precipitate separately within the bainitic laths during slow heating. M₂₃C₆ carbides precipitate at the interfaces (lath boundaries or prior austenite grain boundaries) and grow by attracting nearby chromium atoms, which results in the dissolution of M₇C₃ and, depending on the temperature, coarsening, or dissolution of M₂C carbides, respectively.     

Evaluation of Microstructural and Mechanical Behaviours of Tempered 2.25Cr–1Mo Steel Through Electromagnetic Characterization

The effect of tempering treatment has been investigated on water quenched P22 steel with the chemical composition of 0.13C, 0.24Si, 0.47Mn, 0.012P, 0.005S, 2.19Cr, 0.93Mo and balance Fe (all in wt%) within the temperature ranges of 650–900 °C. The microstructural, mechanical and magnetic properties of as-quenched and tempered steels have been investigated through optical and scanning electron microscopy, hardness and universal tensile testing, electromagnetic sensor (Magstar), respectively. The water quenched sample consists of fine martensitic structure with a hardness of 381 HV. With the progress of tempering, the martensite becomes coarse till 800 °C, decreasing the hardness of steel samples. The tempering at 700 °C results in martensite coarsening and precipitation of rod and globular shaped carbides; while a fraction of globular carbide is observed to increase in the matrix after 750 °C of tempering. Beyond 800 °C, the ferrite and bainite phases gradually form by replacing martensite, and the ferrite structure is prevalent after 900 °C. Due to microstructural changes, the magnetic properties are also affected as a function of tempering temperature. The coarsening of martensite causes the decrease in coercivity with increasing tempering temperature, leading to magnetic softening.     

Ripening behavior of M23C6 carbides in P92 steel during aging at 800℃

The rapid coarsening of the M23 C6 carbides has been held responsible for the creep fracture in 9-12Cr mar-tensitic heat resistant steels.A commercial P92 steel was subjected to thermal aging at a high temperature of 800℃ to investigate the ripening behavior of the M23 C6 carbides.Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to characterize the microstructure evolution, especially the ripening process of the M23 C6 carbides.The new concept of the effective mean size, depend-ent on the critical radius, was introduced to correct the measured mean size and then the Ostwald theory was applied to describe the ripening behavior of the M23 C6 carbides.The ripening of the M23 C6 carbides was revealed to be grain boundary diffusion controlled.     

Precipitation Reactions during the Heat Treatment of Ferritic Steels

The precipitation reactions in two ferritic steels, 9Cr-1Mo-V-Nb and 12Cr-1Mo-V-W, were studied. Analytical electron microscopy, optical microscopy, electrolytic extractions, and hardness measurements were used to determine the types, amounts, and effects of precipitates formed as a function of the heat treatment. The effect of variations in the austenitizing treatment was ascertained. In addition to variations in the austenitizing time and temperature, different cooling rates after austenitization were also used. Air cooling after austenitization (normalization) resulted in little precipitation in both alloys. Precipitation in the 12Cr-1Mo-V-W alloy after furnace cooling was found in all cases examined. Under certain conditions precipitation was also found after furnace cooling the 9Cr-1Mo-V-Nb alloy. However, when compared to the amount of precipitate in the fully tempered state, the 9Cr-1Mo-V-Nb showed a much greater variation in the degree of precipitation following furnace cooling. In addition, the matrix microstructure of the 9Cr-1Mo-V-Nb alloy was very sensitive to cooling rate. The precipitation reactions during tempering after a normalizing treatment were followed as a function of tempering treatment. Tempering temperatures were varied from 400 to 780 °C. The carbide precipitation was essentially complete after one hour at 650 °C for both alloys. Analytical microscopy was used to identify the precipitates. In the 9Cr-1Mo-V-Nb alloy, a combination of chromium-rich M₂₃C₆ and vanadium-niobium-rich MC carbides was found. The carbides in the 12Cr-1Mo-V-W alloy were identified as chromium-rich M₂₃C₆ and vanadium-rich MC. The results give an indication of the sensitivity of these alloys to heat treatment variations. This paper is based on a presentation made at the “Peter G. Winchell Symposium on Tempering of Steel” held at the Louisville Meeting of The Metallurgical Society of AIME, October 12-13, 1981, under the sponsorship of the TMS-AIME Ferrous Metallurgy and Heat Treatment Committees.     

Influence of long-term aging and superimposed creep stress on the microstructure of 2.25cr-1Mo steel

To understand the influence of high-temperature aging and superimposed creep stress on the microstructural variations in a 2.25Cr-1Mo steel, the shoulder and gage portions of the specimens subjected to stress-rupture tests at 540 °C and 580 °C have been studied by transmission electron microscopy. In the normalized and tempered condition, the steel exhibited a tempered bainitic structure and the carbides were present as M₃C globules, M₂C platelets, and M₂₃C₆ rectangular parallelepipeds. Aging the steel at 540 °C for 7022 hours or 17,946 hours resulted in considerable coarsening of M₂C and caused precipitation of M₆C carbides. The superimposed creep stress enhanced the M₂C precipitation. The ferrite matrix exhibited some recovery in the specimens exposed for 17,946 hours. While M₂C platelets were observed in a few areas after 14,836 hours of aging at 580 °C, this carbide was virtually nonexistent when a stress of 78 MPa was superimposed. Amounts of M₂₃C₆ persisted throughout the tests at both 540 °C and 580 °C. The M₆C carbide became more predominant after long exposure at 580 °C. The ferrite matrix recovered considerably in specimens subjected to creep stress at 580 °C for 14,836 hours.     

超高强度钢15Cr2Ni10MoCo14回火组织的研究

利用透射电子显微镜（ＴＥＭ）系统研究了１５Ｃｒ２Ｎｉ１０ＭｏＣｏ１４的超高强度钢回火后的微观组织结构。从低温到高温回火，钢的回火马氏体组织中顺次析出Ｆｅ３Ｃ，Ｍ２Ｃ，Ｍ２３Ｃ６和Ｍ６Ｃ，并在６５０℃过时效回火时发现一种在钢的回火组织中未见报道过的正交结构相，点阵常数为ａ＝０．４４８ｎｍ，ｂ＝１．４０ｎｍ，ｃ＝１．２１ｎｍ。     

含氮Cr-W-Mo-V半高速钢回火过程中的沉淀析出行为

进行了Cr-W-Mo-V(%:46Cr-24W-24Mo-1.52.0V)系和Cr-W-Mo-V+N(0.05%0.10%)系半高速钢(Semi-HSS)1050℃淬火后分别在100~600℃两次回火沉淀析出行为的研究。采用透射电镜、扫描电镜及能谱仪和能量损失谱对碳化物形貌和成分进行分析,用X射线衍射法测定残余奥氏体的体积分数。结果表明,氮有增强钢的二次硬化的效果,氮促进碳氮化物在425~475℃回火析出,在550℃回火碳化物依附在氮化物表面而沉淀形成复合碳氮化物。Semi-HSS+N在淬火及400℃以下回火,残余奥氏体为15%~17%;随回火温度增加,残余奥氏体量急剧降低,在525℃回火残余奥氏体小于3%。