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1.
In an attempt to understand the role of retained austenite on the cryogenic toughness of a ferritic Fe-Mn-AI steel, the mechanical
stability of austenite during cold rolling at room temperature and tensile deformation at ambient and liquid nitrogen temperature
was investigated, and the microstructure of strain-induced transformation products was observed by transmission electron microscopy
(TEM). The volume fraction of austenite increased with increasing tempering time and reached 54 pct after 650 °C, 1-hour tempering
and 36 pct after 550 °C, 16-hour tempering. Saturation Charpy impact values at liquid nitrogen temperature were increased
with decreasing tempering temperature, from 105 J after 650 °C tempering to 220 J after 550 °C tempering. The room-temperature
stability of austenite varied significantly according to the(α + γ) region tempering temperature;i.e., in 650 °C tempered specimens, 80 to 90 pct of austenite were transformed to lath martensite, while in 550 °C tempered specimens,
austenite remained untransformed after 50 pct cold reductions. After tensile fracture (35 pct tensile strain) at -196 °C,
no retained austenite was observed in 650 °C tempered specimens, while 16 pct of austenite and 6 pct of e-martensite were
observed in 550 °C tempered specimens. Considering the high volume fractions and high mechanical stability of austenite, the
crack blunting model seems highly applicable for improved cryogenic toughness in 550 °C tempered steel. Other possible toughening
mechanisms were also discussed.
Formerly Graduate Student, Seoul National University. 相似文献
2.
Influence of tempering on the microstructure and mechanical properties of HSLA-100 steel plates 总被引:5,自引:0,他引:5
The influence of tempering on the microstructure and mechanical properties of HSLA-100 steel (with C-0.04, Mn-0.87, Cu-1.77,
Cr-0.58, Mo-0.57, Ni-3.54, and Nb-.038 pct) has been studied. The plate samples were tempered from 300 °C to 700 °C for 1
hour after austenitizing and water quenching. The transmission electron microscopy (TEM) studies of the as-quenched steel
revealed a predominantly lath martensite structure along with fine precipitates of Cu and Nb(C, N). A very small amount of
retained austenite could be seen in the lath boundaries in the quenched condition. Profuse precipitation of Cu could be noticed
on tempering at 450 °C, which enhanced the strength of the steel significantly (yield strength (YS)—1168 MPa, and ultimate
tensile strength (UTS)—1219 MPa), though at the cost of its notch toughness, which dropped to 37 and 14 J at 25 °C and −85
°C, respectively. The precipitates became considerably coarsened and elongated on tempering at 650 °C, resulting in a phenomenal
rise in impact toughness (Charpy V-notch (CVN) of 196 and 149 J, respectively, at 25 °C and −85 °C) at the expense of YS and
UTS. The best combination of strength and toughness has been obtained on tempering at 600 °C for 1 hour (YS-1015 MPa and UTS-1068
MPa, with 88 J at −85 °C). 相似文献
3.
研究了一种屈服强度大于785 MPa的船板钢,测试了其动态连续冷却相变曲线(CCT),研究了试验钢经控制轧制+直接淬火+回火(DQ- T)工艺处理后的组织性能。结果表明,直接淬火(DQ)钢板组织为板条马氏体(LM),回火后铜、铌元素呈弥散析出。经500 ℃回火钢板的强度最高,冲击韧性(KV2)最低。钢板经710 ℃回火,其组织为二次马氏体(SLM)+铁素体,屈服强度(Re)为810 MPa,抗拉强度(Rm)为 1 066 MPa,伸长率(A)为17%,在-80 ℃下KV2为97 J,达到最佳强韧性匹配。 相似文献
4.
5.
Effect of Heat Treatment Process on Properties of 1000 MPa Ultra-High Strength Steel 总被引:1,自引:0,他引:1
Two types of steel, C-Mn-Cr-Mo-B microalloyed steel and C-Mn-Mo-Nb-Cu-B microalloyed steel, are designed to develop 1000 MPa ultra-high strength steel. Two kinds of processes, thermomechanical controlled process (TMCP) combined with traditional off-line quenching and tempering (QT) process versus controlled rolling process (CR) combined with direct quenching and tempering (DQ+T) process, are applied. The effect of heat treatment processing mode on the microstructure and mechanical properties is studied. The relationship between microstructure and mechanical properties is investigated by SEM and TEM. After tempering at 450 to 550 ℃ for 1 h, the steel produced by TMCP+QT process shows combination of excellent strength and low temperature toughness. The yield strength is above 1000 MPa, elongation above 15% and impact energy at -40 ℃ more than 30 J. After tempering at 450 ℃, a large number of ε-Cu particles precipitated in C-Mn-Mo-Nb-Cu-B steel produced by CR+DQ+T process lead to a significant increase in yield strength. And after tempering at 500 to 600 ℃, the yield strength of the steel is further improved to 1030 MPa because of precipitates, such as nitride or carbide of niobium, carbide of molybedenum and vanadium. When the tempering temperature is increased above 620 ℃, the yield strength is still higher than 1000 MPa and elongation is above 20% and impact energy at -40 ℃ is more than 35 J. After tempering at above 500 ℃, the toughness of the steel treated by TMCP+QT process is superior to that of steel by CR+DQ+T process. 相似文献
6.
A study of the structure and mechanical properties of Fe-Cr-Mo-C martensitic steels with and without boron addition has been
carried out. Nonconventional heat treatments have subsequently been designed to improve the mechanical properties of these
steels. Boron has been known to be a very potent element in increasing the hardenability of steel, but its effect on structure
and mechanical properties of quenched and tempered martensitic steels has not been clear. The present results show that the
as-quenched structures of both steels consist mainly of dislocated martensite. In the boron-free steel, there are more lath
boundary retained austenite films. The boron-treated steel shows higher strengths at all tempering temperatures but with lower
Charpy V-notch impact energies. Both steels show tempered martensite embrittlement when tempered at 350 °C for 1 h. The properties
above 500 °C tempering are significantly different in the two steels. While the boron-free steel shows a continuous increase
in toughness when tempered above 500 °C, the boron-treated steel suffers a second drop in toughness at 600 °C tempering. Transmission
electron microscopy studies show that in the 600 °C tempered boron-treated steel large, more or less continuous cementite
films are present at the lath boundaries, which are probably responsible for the embrittlement. The differences in mechanical
properties at tempering temperatures above 500 °C are rationalized in terms of the effect of boron-vacancy interactions on
the recovery and recrystallization behavior of these steels. Although boron seems to impair room temperature impact toughness
at low strength levels, it does not affect this property at high strength levels. By simple nonconventinal heat treatments
of the present alloys, martensitic steels may be produced with quite good strength-toughness properties which are much superior
to those of existing commercial ultra-high strength steels. It is also shown that very good combinations of strength and toughness
can be obtained with as-quenched martensitic steels. 相似文献
7.
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. 相似文献
8.
The variation of heat treatments including directed quenching and tempering off-line after controlled rolling (DQT) and quenching off-line and tempering off-line after controlled rolling (RQT) with microstructure and mechanical properties of a low-carbon microalloyed steel was compared and analyzed. For DQT, the quenched steel was obviously banded microstructure, with increasing tempering temperature, lath martensite coarsened, the cusp carbide precipitated at grain boundaries, the yield strength fluctuated slightly, and the fracture-separation was obvious. The impact toughness was better in the steel tempered at 500 ℃ for 1 h. In RQT, with increasing tempering temperature, lath martensite degenerated, intragranular and intergranular finer precipitations with smaller than 30 nm precipitated and grew up and were distributed dispersedly, the stripe-like carbides were distributed at grain boundaries, and the yield strength and tensile strengthen decreased obviously. The impact toughness of RQT process was much better than that of DQT process, and the comprehensive mechanical properties were better for the steel tempered at 500 ℃ for 1 h of RQT process. 相似文献
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10.
Vijaya L. Manugula Koteswararao V. Rajulapati G. Madhusudhan Reddy R. Mythili K. Bhanu Sankara Rao 《Metallurgical and Materials Transactions A》2017,48(8):3702-3720
The effects of tool rotational speed (200 and 700 rpm) on evolving microstructure during friction stir welding (FSW) of a reduced activation ferritic-martensitic steel (RAFMS) in the stir zone (SZ), thermo-mechanically affected zone (TMAZ), and heat-affected zone (HAZ) have been explored in detail. The influence of post-weld direct tempering (PWDT: 1033 K (760 °C)/ 90 minutes + air cooling) and post-weld normalizing and tempering (PWNT: 1253 K (980 °C)/30 minutes + air cooling + tempering 1033 K (760 °C)/90 minutes + air cooling) treatments on microstructure and mechanical properties has also been assessed. The base metal (BM) microstructure was tempered martensite comprising Cr-rich M23C6 on prior austenite grain and lath boundaries with intra-lath precipitation of V- and Ta-rich MC precipitates. The tool rotational speed exerted profound influence on evolving microstructure in SZ, TMAZ, and HAZ in the as-welded and post-weld heat-treated states. Very high proportion of prior austenitic grains and martensite lath boundaries in SZ and TMAZ in the as-welded state showed lack of strengthening precipitates, though very high hardness was recorded in SZ irrespective of the tool speed. Very fine-needle-like Fe3C precipitates were found at both the rotational speeds in SZ. The Fe3C was dissolved and fresh precipitation of strengthening precipitates occurred on both prior austenite grain and sub-grain boundaries in SZ during PWNT and PWDT. The post-weld direct tempering caused coarsening and coalescence of strengthening precipitates, in both matrix and grain boundary regions of TMAZ and HAZ, which led to inhomogeneous distribution of hardness across the weld joint. The PWNT heat treatment has shown fresh precipitation of M23C6 on lath and grain boundaries and very fine V-rich MC precipitates in the intragranular regions, which is very much similar to that prevailed in BM prior to FSW. Both the PWDT and PWNT treatments caused considerable reduction in the hardness of SZ. In the as-welded state, the 200 rpm joints have shown room temperature impact toughness close to that of BM, whereas 700 rpm joints exhibited very poor impact toughness. The best combination of microstructure and mechanical properties could be obtained by employing low rotational speed of 200 rpm followed by PWNT cycle. The type and size of various precipitates, grain size, and evolving dislocation substructure have been presented and comprehensively discussed. 相似文献
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13.
《钢铁研究学报(英文版)》2011,(Z1):637-640
High strength abrasion resistant steel plates are widely used in mining,construction and agricultural machineries.The plates are,however,usually poor in impact toughness.An attempt is made to improve the impact toughness of HB400 grade abrasion resistant steel by controlling quenching and tempering of the plates.Optimized combination of the strength and the toughness has been achieved by choosing best fit set of quenching and tempering condition.Mechanism underlying the achievement has been investigated in terms of the microstructure consisting of tempered lath martensite,retained austenite and precipitated carbides. 相似文献
14.
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 608 to HRC 616 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 592 to HRC 616 and the Charpy U-notch impact toughness will retain about 173 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. 相似文献
15.
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。 相似文献
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17.
Peravudh Lowhaphandu John J. Lewandowski 《Metallurgical and Materials Transactions A》1999,30(2):325-334
The effects of Cu infiltration on the monotonic fracture resistance and fatigue crack growth behavior of a powder metallurgy
(P/M) processed, porous plain carbon steel were examined after systematically changing the matrix strength via heat treatment. After austenitization and quenching, three tempering temperatures were chosen (177 °C, 428 °C, and 704 °C)
to vary the strength level and steel microstructure. The reductions in strength which occurred after tempering at the highest
temperature were accompanied by the coarsening of carbides in the tempered martensitic steel matrix, as confirmed by optical
microscopy and by microhardness measurements of the steel. Each steel-Cu composite, containing approximately 10 vol pct infiltrated
Cu, had superior fracture toughness and fatigue properties compared to the porous matrix material given the same heat treatment.
Although the heat treatments given did not significantly change the fatigue behavior of the porous steel specimens, the fatigue
curves (da/dN vs ΔK) and fracture properties were distinctly different for the steel-Cu composites given the same three heat treatments. The
fracture toughness (K
IC
and J
IC
), tearing modulus, and ΔK
TH
values for the composites were highest after tempering at 704 °C and lowest after tempering at 177 °C. In addition, the fracture
morphology of both the fracture and fatigue specimens was affected by changes in strength level, toughness, and ΔK. These fractographic features in fatigue and overload are rationalized by comparing the size of the plastic zone to the microstructural
scale in the composite.
This article is based on a presentation made in the symposium “Fatigue and Creep of Composite Materials” presented at the
TMS Fall Meeting in Indianapolis, Indiana, September 14–18, 1997, under the auspices of the TMS/ASM Composite Materials Committee. 相似文献
18.
Studies have been made of the microstructure of steel 18KhGNMFR after the quenching and tempering and “ normalizing rolling”
of plates 12 and 22 mm thick. Raising the quenching temperature to 950°C leads to growth of the austenite grains, which reduces
impact toughness. Thus, the quenching temperature for steel 18KhGNMFR should be no greater than 920°C. On the whole, the structure
of the steel in 9–14-mm-thick plates subjected to normalizing rolling is uniform and is free of grain-boundary precipitates
of carbide particles. This ensures that the steel will have satisfactory toughness properties.
__________
Translated from Metallurg, No. 6, pp. 55–58, June, 2005. 相似文献
19.
ZHAO Xi qing PAN Tao WANG Qing feng SU Hang YANG Cai fu YANG Qing xiang 《钢铁研究学报(英文版)》2011,18(5):47-51
Mechanical properties of quenching, intercritical quenching and tempering (QLT) treated steel containing Ni of 9% were evaluated from specimens subject to various tempering temperatures. The detailed microstructures of steel containing Ni of 9% at different tempering temperatures were observed by optical microscope (OM) and transmission electron microscope (TEM). The volume fraction of austenite was estimated by XRD. The results show that high strength and cryogenic toughness of steel containing Ni of 9% are obtained when the tempering temperature are between 540 and 580 ℃. The microstructure keeps the dual phase lamellar structure after the intercritical quenching and there is cementite created in the Ni rich constituents when tempering temperature is 540 ℃. When tempering temperatures are between 560 and 580 ℃, the reversed austenites (γ′) grow up and the dual phase lamellar structure is not clear. The γ′ becomes instable at 600 ℃. When tempered at temperature ranging from 500 to 520 ℃, the increase of dislocation density in the lamellar matrix makes both tensile strength and yield strength decrease. When tempered at 540 ℃ and higher temperature, the yield strength decreases continuously because the C and alloying elements in the matrix are absorbed by the cementite and the γ′, so the yield ratio is decreased by the γ′. There are two toughness mechanisms at different tempering temperatures. One is that the precipitation of cementite absorbs the carbon in the steel which plays a major role in improving cryogenic toughness at lower temperature. Another is that the γ′ and the purified matrix become major role at higher tempering temperature. When the tempering temperature is 600 ℃, the stability of γ′ is decreased quickly, even the transformation takes place at room temperature, which results in a sharp decrease of Charpy V impact energy at 77 K. The tempering temperature range is enlarged by the special distribution of cementite and the lamellar structure. 相似文献
20.
为了揭示1 000 MPa级低碳加铌钒钛微合金钢的高强韧机制,研究了S1(w(C)=0.09%)与S2(w(C)=0.17%)两种合金成分的油井管钢成分-工艺-组织-性能关系。试验表明,两种成分试验钢经水淬后的组织分别为板条贝氏体加少量马氏体和马氏体加少量贝氏体的复相组织。两种成分钢经过450~600 ℃、30 min的中温回火后,组织中均出现碳化物析出,且S1试验钢回火后的屈服强度基本不变,抗拉强度下降了约70 MPa,S2试验钢回火后的屈服强度与抗拉强度迅速升高170 MPa左右。溶度积公式的计算结果表明,两种钢的水淬组织中铌、钛元素析出彻底且析出物的体积分数都很小,因此回火铁素体基体中的VC析出强化对S1试验钢回火后屈服强度保持不变以及S2试验钢回火后屈服、抗拉强度提高起到重要作用。 相似文献