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.     

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.     

Influence of Mo on Growth and Coarsening of Nanometer-sized Carbides in Low-alloy Ferritic Steels Containing Ti

By optical microscopy, transmission electron microscopy and energy dispersive spectroscopy, the changes with aging time in size, composition and distribution of nanometer-sized （Ti, Mo）C precipitated in Ti-Mo low-alloy ferritc steel have been studied in comparison with that of nanometer-sized TiC precipitated in Ti low-alloy ferritc steel. It was found that the growth rate of （Ti,Mo）C in Ti-Mo steel was less than that of TiC in Ti steel. Nanometer- sized carbides formed at 650 ~C （or 550 ~C） for 55 h were at transitional stage from growth to coarsening. When aging time reaches 55 h, the coarsening rates of nanometer-sized carbides in Ti and Ti-Mo steel tend to be the same and in- variable. The influence of Mo on growth and coarsening of nanometer-sized carbides tends to decrease with increasing aging time, and Mo contents in nanometer-sized carbides with the same size at different aging time were different.     

Variation microstructure and properties of X80 pipeline steel in the rapid induction tempering process

A self-developed electromagnetic induction-heating device was used to investigate the variation in the microstructure and properties of X80 pipeline steel in the rapid induction tempering process at different process parameters. The effects of the tempering condition on toughness,microstructure,size and distribution of precipitates of X80 pipeline steel were observed using a metallographic microscopy and scanning electron microscopy.Compared with the samples prepared via traditional tempering techniques,results showthat the samples prepared via rapid induction tempering had improved performances. When the heating temperature is 590 ℃,at a holding time of90 s,it was found that acicular ferrite was refined,carbonite precipitation was small,and precipitates were evenly distributed in the matrix. The low-temperature impact energy,also known as the impact absorption energy,at- 40 ℃ was found to be 430. 5 J for the rapid induction tempering samples and 323. 2 J for the traditionally tempered sample. The low-temperature impact energy at- 60 ℃ was found to be 351. 3 J for the rapid induction tempered sample and 312. 1 J for the tradition tempering sample.     

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 ℃.     

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.     

Influence of Tempering Process on Mechanical Properties of 00Cr13Ni4Mo Supermartensitic Stainless Steel

To investigate the influence of tempering process on microstructural evolutions and mechanical properties of 00Cr13Ni4Mo supermartensitic stainless steel(SMSS),specimens were tempered in the temperature range of 520-720 ℃ for 3 h followed by air cooling and an optimized tempering temperature was chosen to prolong holding time from 3 to 12 h.After heat treatments,microstructure examination was conducted by scanning electron microscope,X-ray diffraction examinations,hardness measurements and tensile tests.The results revealed that the superior mechanical properties were achieved by quenching at 1040 ℃ for 1 h+water cooling and tempering at 600 ℃ for 3 h+air cooling.Increasing isothermal tempering time could improve the toughness notably.It was believed that the property was correlated with the microstructure of tempered lath martensite and retained austenite.More retained austenite content is beneficial to the higher toughness of the SMSS.     

Effect of the Ti/N ratio on the hardenability and mechanical properties of a quenched-and-tempered C-Mn-B steel

Ten experimental 0.18 pct C-1.2 pct Mn- 0.002 pct B steels with various Ti/N ratios were evaluated in this study. The hardenability of these steels was first determined using Jominy tests. Slab sections were then rolled to produce 12.5-mm-thick plates, and subsequently quenched and tempered for mechanical property evaluation. The volume fraction of coarse (greater than 1 μm) TiN particles was measured in all steels using quantitative metallographic techniques. Scanning transmission electron microscopy was used to investigate fine precipitates, and scanning electron microscopy was used to examine the fracture surface of Charpy specimens. The results show that a complete boron (B) hardenability effect is obtained with Ti/N ratios ≥2.9, a value slightly below the stoichiometric Ti/N ratio of 3.4. Any excess Ti, above that which combines with N, provides an additional increase in hardenability on quenching (effect of Ti in solution) and an increase in strength on tempering (Ti (C,N) precipitation). Steels with a higher (Ti)(N) product develop a higher volume fraction of coarse TiN particles during solidification. These coarse TiN particles result in reduced toughness levels of the heat-treated plates evaluated in the present study.     

A New Approach for Refining Carbide Dimensions in M42 Super Hard High-speed Steel

Obtaining small carbides is crucial but difficult for high-speed steels.A new approach for refining carbide dimensions in M42 super hard high-speed steel by increasing cooling rate and spheroidizing treatment was proposed. The morphologies and properties of eutectic carbides formed at different cooling rates were investigated by means of scanning electron microscopy (SEM),energy dispersive spectroscopy (EDS),X-ray diffraction (XRD),transmis-sion electron microscopy (TEM),electron back-scattered diffraction (EBSD)and differential scanning calorimeter (DSC).The results show that eutectic carbides change from a lamellar shape into a curved-rod shape as cooling rate increases.Despite different morphologies,the two carbides are both of M2 C type with a hexagonal close-packed structure and display a single crystal orientation in one eutectic colony.The morphology of M2 C mainly depends on the growing process of eutectic carbides,which is strongly influenced by cooling rate.Compared with lamellar car-bides,M2 C carbides with curved-rod shapes are less stable,and decompose into M6 C and MC at lower temperatures. They are more inclined to spheroidize during heating,which ultimately and distinguishably refines the carbide dimen-sions.As small carbides are much easier to dissolve into matrices during austenization,the process described herein improves the supersaturation of alloying elements in martensite,which leads to an increment of hardness in M42 steel.     

Thermal stability of retained austenite and mechanical properties of medium-Mn steel during tempering treatment

The thermal stability of retained austenite(RA)and the mechanical properties of the quenched and intercritical annealed 0.1C-5Mn steel with the starting ultrafine lamellar duplex structure of ferrite and retained austenite during tempering within the range from 200 to 500°C were studied by X-ray diffraction(XRD),transmission electron microscopy(TEM)and tensile testing.The results showed that there was a slight decrease in the RA volume fraction with increasing tempering temperature up to 400°C.This caused a slight increase in the ultimate tensile strength(UTS)and a slight decrease in the total elongation(TE);thus,the product of UTS to TE(UTS×TE)as high as 31GPa·% was obtained and remained nearly unchanged.However,aportion of the RA began to decompose when tempered at 500°C and thus caused a~35% decrease of the RA fraction and a~16%decrease of the value of UTS×TE.It is concluded that the ultrafine lamellar duplex structure is rather stable and the excellent combination of strength and ductility could be retained with tempering temperature up to 400°C.Thus,thermal processes such as galvanization are feasible for the tested steel provided that their temperatures are not higher than 400°C.     

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.      

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.     

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.      

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.     

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。