Q&P热处理工艺对含Cu TRIP钢组织和性能的影响

随着能源的短缺和环境污染的日益严重,汽车轻量化需求日益迫切,如何通过工艺及成分设计革新、获得兼具高强度和高塑性的钢板尤为重要.尝试将Cu作为合金元素加入TRIP钢中,采用淬火配分(QP)工艺对含Cu TRIP钢进行一步法和两步法热处理,通过拉伸试验、X射线衍射分析、扫描电镜、透射电镜等实验手段,对热处理后的组织及性能进行测试和观察,探究了不同热处理工艺对组织和性能的影响.研究结果表明:一步法处理后的显微组织为铁素体、马氏体和残余奥氏体,两步法处理后不仅包含上述3种组织,还含有贝氏体.一步法处理后,抗拉强度达2 200 MPa,拉伸延展率为15%,强塑积为33 GPa·%;两步法处理后综合力学性能优于一步法,在400℃等温5 min后,抗拉强度为1 300 MPa,拉伸延展率为43%,强塑积超过55 GPa·%.实验钢良好的综合力学性能得益于铁素体、马氏体/贝氏体和残余奥氏体的合理配比,变形过程中残余奥氏体的相变诱导塑性效应,以及马氏体位错与Cu粒子的交互作用.     

分级固溶处理对8Cr4Mo4V钢的微观组织和硬度的影响

对8Cr4Mo4V航空轴承钢进行分级固溶处理,即在1000~1060℃的初级固溶处理和在1080~1100℃的二级固溶处理,并观察和测试其组织和硬度,研究了分级固溶温度的影响。结果表明,随着初级固溶温度的提高(二级固溶处理为1080℃×10 min),钢中未溶碳化物的体积分数从4.37%逐渐降低到3.43%,但是晶粒没有明显长大。随着二级固溶温度的提高(初级固溶处理为1060℃×30 min),未溶碳化物的体积分数从3.51%逐渐降低到2.84%,平均晶粒尺寸显著增大。当初级固溶温度较低或二级固溶温度较高时,8Cr4Mo4V钢的回火硬度较高。为了使8Cr4Mo4V钢具有高硬度同时避免晶粒粗化,初级固溶温度宜为1020~1050℃,二级固溶温度宜为1080~1090℃。对这种钢进行1020℃×20 min+1090℃×10 min固溶处理后,其平均晶粒尺寸为12.1 μm,回火硬度为63.8 HRC,冲击吸收功为15.28 J,室温抗拉强度为2664.3 MPa。     

新型Ti-650合金电子束焊接头组织及性能研究

采用电子束对新型耐650 ℃使用的高温钛合金板材进行焊接,并进行1 000 ℃/1 h/AC+700 ℃/4 h/AC的退火处理,研究了接头的组织、硬度分布,母材和接头的拉伸性能和持久性能.结果表明,接头组织由α相、少量β相、以及大量细小的再结晶α相构成.接头中母材、热影响区和焊缝的显微硬度值比较均匀,介于440~490HV之间.室温条件下,母材和接头的抗拉强度均高于1 000 MPa,延伸率均介于7%~10%;650 ℃拉伸,母材抗拉强度达到了750 MPa,延伸率最高达20%;接头的抗拉强度在700 MPa以下,延伸率在10%~14%之间.接头与母材的持久断裂均是由孔洞聚集形成微裂纹,在力的作用下不断扩展,直至最终断裂.而接头中柱状晶的晶界促进了裂纹的扩展,所以母材的持久寿命和应变优于接头.根据结果分别得出了650 ℃下接头和母材应力与寿命的关系式.     

固溶后时效成形对7075铝合金FSW构件性能的影响

为评价搅拌摩擦焊(FSW)构件的可时效成形性,对7075铝合金FSW构件固溶处理后进行时效成形工艺,试验研究了固溶处理影响下FSW构件时效成形后构件性能的变化规律.试验结果表明,固溶处理后时效成形工艺有助于提高FSW构件的抗拉强度、延伸率和电导率.固溶处理后180℃时效成形时,FSW试样抗拉强度峰值显著提高,达到449.4 MPa,是仅时效成形工件抗拉强度的139.5%,为原始焊接试样抗拉强度的1.4倍,此时焊件延伸率达到峰值4.2%,固溶处理对试样延伸率有一定的提升作用.微观结构观察结果表明,固溶处理的引入对FSW构件时效成形过程焊缝区特征组织产生显著影响,有助于消除焊缝的不均匀组织特征的影响,从而有利于成形试样的性能均匀化和提高.     

真空分级淬火对8Cr4Mo4V钢组织和性能的影响

在真空条件下对航空轴承用8Cr4Mo4V钢进行不同温度的分级淬火并采用扫描电镜观察其微观组织、用XRD谱进行相分析并测试洛氏硬度、冲击性能和旋转弯曲疲劳性能,研究了真空分级淬火对其微观组织和力学性能的影响。结果表明,真空分级淬火后的8Cr4Mo4V钢其微观组织由下贝氏体、马氏体/残余奥氏体和碳化物组成;随着分级淬火温度的提高,淬火和回火态钢中析出碳化物的数量增加,残余奥氏体的含量降低。分级淬火温度为580℃时淬火态钢中贝氏体的含量最高(达到13.87%),残余奥氏体的含量为28.59%。回火后析出碳化物的含量和洛氏硬度均为所有分级温度中的最大值,分别为4.37%和62.38HRC。真空分级淬火能提高8Cr4Mo4V钢的综合力学性能。与未分级真空淬火相比,进行580℃×10 min真空分级淬火的8Cr4Mo4V钢的冲击韧性提高了23.3%,旋转弯曲疲劳极限提高了110 MPa。     

一种新型高强塑积异质冷轧中锰钢的力学性能

使用原位电子背散射衍射(EBSD)和球差透射电镜(ACTEM)等手段,研究了新型异质结构中锰TRIP钢在拉伸过程中微观组织的演变机制和力学性能。结果表明,在680℃退火后的实验钢中生成了多形貌、多尺度的异质奥氏体结构(颗粒状、块状、片层状奥氏体)和铁素体组织,其抗拉强度为1272 MPa,总延伸率为54.5%,强塑积高达69.3 GPa·%。在拉伸过程中C/Mn含量较低的颗粒状奥氏体先发生相变,而C/Mn含量较高的块状和片层状奥氏体在较大的应变范围内逐渐发生相变,从而导致高强度与高塑性的良好匹配。结果还表明,马氏体相变优先在奥氏体晶界/相界附近的区域形核。与晶粒尺寸相比,C/Mn元素对奥氏体稳定性的作用更重要。     

热处理对激光选区熔化成型316L合金综合性能的影响

为获得力学性能优良的316L合金,研究了激光选区熔化(SLM)成型316L合金试样在400℃/2 h、900℃/2 h、1050℃/2 h热处理后的微观组织与力学性能.使用拉伸试验机和冲击试验机分别对试样进行拉伸和冲击实验;用数显硬度计测试316L合金在不同热处理工艺下的硬度差别,通过光学显微镜和SEM观察试样的断裂表面组织形貌,分析断裂机理.采用电子背散射衍射仪观察热处理前后晶面的相位变化.结果表明:SLM成型试样在900℃/2 h水冷条件下,抗拉强度最高达到680 MPa;在1050℃/2 h水冷条件下,试样具有最大(18％)的延伸率;试样的硬度随着热处理温度的升高呈现出先升高后降低的趋势.未处理的SLM成型试样沿沉积方向形成柱状晶粒,但经处理的试样随着热处理温度的升高,合金元素固溶重组,晶面位向差减小,得到较均匀的各向同性配置.     

锆、铜及均匀化处理对高导耐热铝合金电工圆杆性能的影响

通过扫描电镜、X射线物相分析等方法,研究了Zr、Cu元素及均匀化工艺对高导耐热铝合金电工圆杆组织及性能的影响。结果表明,通过"添加Zr(0.10%)Cu(0.08%)+300℃×16h均匀化+83%轧制"处理后,试样综合性能较优,试样导电率为59.5%IACS,抗拉强度达到149 MPa,230℃保温1h,强度残存率为94.3%。     

深冷处理对GCr15组织和力学性能的影响

对经不同深冷处理后的GCr15钢进行了组织观察、力学性能检测和摩擦磨损试验。试验结果表明:深冷处理可提高GCr15钢的硬度;淬火后进行深冷处理+180℃×8h回火处理后,GCr15钢的冲击韧性有所降低;深冷处理可明显提高GCr15钢耐磨性并降低钢中残留奥氏体含量,其中深冷处理6h后效果最为显著,其相对磨损率下降了30%、残留奥氏体含量降幅高达81%。     

激光选区熔化AlSi7Mg合金的微观组织和力学性能

利用激光选区熔化(Selective laser melting, SLM)成形技术对AlSi7Mg合金成形工艺进行研究,并对最佳工艺参数成形沉积态和热处理试样微观组织和力学性能进行分析。结果发现:沉积态试样抗拉强度、屈服强度和延伸率均明显高于铸态性能,横向试样分别达到435.78 MPa、299.23 MPa和14.36%。热处理对SLM试样的微观组织和力学性能影响很大,350℃、3 h退火工艺下,试样延伸率增加到30.83%,抗拉强度和屈服强度分别下降到210.35 MPa和152.01 MPa。本工作表明,可以通过改变工艺参数和热处理控制晶粒尺寸和形状,以获得所需微观组织和力学性能的合金。     

Microstructures and Mechanical Properties of Si-Al-Mn TRIP Steel with Niobium

Microstructure consisting of ferrite, bainite and retained austenite can be obtained through intercritical annealing and isothermal treatment in bainite transformation region for low silicon TRIP (transformation induced plasticity) steel containing niobium. Effects of strain rate, Nb content and soaking temperature in bainite region on microstructure and mechanical properties of test steels were investigated. It is shown that as strain rate ranges from 10-2 to 10-4 s-1, the volume fraction of transformed martensite from retained austenite,as well as tensile strength, elongation rate and strength-ductility product, increases. When Nb is added, the volume fraction of retained austenite decreases, but tensile strength and yield strength increase. While Nb content reaches 0.014%, the steel exhibits high elongation and combination of strength and ductility. Higher retained austenite volume fraction and good mechanical properties are obtained in the test steels when the soaking temperature in bainite region is 400℃. The maximum values of tensile strength, total elongation rate and strength-ductility product can reach 739 MPa, 38% and 28082 MPa%, respectively.     

Low carbon high manganese bainitic steel

Abstract

The present study concerns the mechanical properties of low carbon (0·05 wt-%) high Mn bainitic steel. The continuous cooling transformation diagram exhibited bainitic transformation without any prior diffusive transformation of austenite even for a cooling rate as low as 0·5°C/s. The bainitic steels have shown continuous elongation behaviour with attractive combination of strength (>1200 MPa) and elongation (>14%). The bainitic microstructure obtained after annealing treatment has yielded excellent combination of strength, uniform elongation, yield ratio and static toughness value.     

时效态Fe-Mn-Al-C钢的性能和变形机制

采用OM、SEM、XRD、EBSD以及TEM等手段分析时效温度对Fe-30Mn-9Al-0.9C-0.45Mo钢中奥氏体的晶粒尺寸和力学性能的影响.结果 表明:时效处理对Fe-30Mn-9Al-0.9C-0.45Mo钢的组织和性能有较大的影响.在450℃时效的实验钢其抗拉强度为863 MPa、断后伸长率为56.1％、强...     

Microstructure Features with Ultrafined and Purified Grains for Si-Mn Hot-rolling TRIP Steel

1. IntroductionThe material with ultra fine grain size less than5 μm has comprehensive mechanical properties of highstrength, high toughness and high ductility, while con-ventional common steel usually has grain size around10 μm[1~8]. Besides, the transformation induced plas-ticity (TRIP) steels with appropriate retained austen-ite have been well known for the high plasticity but lessstrength loss and considered as one of prospective highstrength low alloy steels in decades[9~16]. However,…     

Effect of inter-critical annealing parameters on ferrite recrystallization and austenite formation in DP 590 steel

This research investigates the effect of inter-critical annealing parameters on ferrite recrystallization and austenite formation during processing of a dual phase microstructure from a cold rolled low carbon steel. The main effort was to determine optimum annealing parameters for producing a desired ferrite-martensite dual phase microstructure in the steel for improved strength–ductility combination. A 57% cold rolled steel sheet was subjected to inter-critical annealing under different temperature–time conditions. Annealing temperatures were determined using Thermo-Calc. After annealing experiments, the resulting microstructures and corresponding hardness values were evaluated to determine ferrite recrystallization and austenite fraction under different conditions. The activation energy for ferrite recrystallization was 235.6?kJ/mol using standard Johnson–Mehl–Avrami–Kolmogorov analysis. Experiments showed that inter-critical annealing parameters affect the phenomenon of ferrite recrystallization and austenite formation. It was observed that both the rate of ferrite recrystallization and austenite formation increase with an increase in annealing temperature. Finally, steel was annealed under conditions similar to industrial processing in an annealing simulator with the selected annealing parameters to obtain improved strength–percentage elongation combinations. The steel under these conditions showed significant improvements in strength–ductility combination (610?MPa–26%; 680?MPa–15%) with an ideal yield strength to an ultimate tensile strength ratio of 0.5.     

Microstructures and Mechanical Properties of Si-AI-Mn TRIP Steel with Niobium

Microstructure consisting of ferrite, bainite and retained austenite can be obtained through intercritical annealing and isothermal treatment in bainite transformation region for low silicon TRIP （transformation induced plasticity） steel containing niobium. Effects of strain rate, Nb content and soaking temperature in bainite region on microstructure and mechanical properties of test steels were investigated. It is shown that as strain rate ranges from 10^-2 to 10^-4 s^-1, the volume fraction of transformed martensite from retained austenite, as well as tensile strength, elongation rate and strength-ductility product, increases. When Nb is added, the volume fraction of retained austenite decreases, but tensile strength and yield strength increase. While Nb content reaches 0.014%, the steel exhibits high elongation and combination of strength and ductility. Higher retained austenite volume fraction and good mechanical properties are obtained in the test steels when the soaking temperature in bainite region is 400℃. The maximum values of tensile strength, total elongation rate and strength-ductility product can reach 739 MPa, 38% and 28082 MPa%, respectively.     

Intercritical annealing pre-treatment used in a hot-dip galvanised TRIP steel

An intercritical annealing pre-treatment was added before the conventional two-step heat treatment process, and the effect of the isothermal bainitic transformation (IBT) time on the steel's microstructure and mechanical properties were investigated. The microstructure was investigated using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, while the mechanical properties were evaluated using tensile testing. The microstructure of the three-step hot-dip galvanised transformation induced plasticity (TRIP) steel consists of ferrite, bainite, retained austenite, and martensite. The mechanical properties of the steel after the three-step heat treatment process are excellent, with a tensile strength above 770?MPa and elongation above 29%. The effect of IBT time on the mechanical properties was insignificant because the intercritical annealing pre-treatment increases the bainitic transformation rate.     

初始组织对低碳钢IQ&P工艺残留奥氏体及力学性能的影响

采用双相区再加热-淬火-碳配分(IQP)工艺,研究初始组织为铁素体+珠光体的IQP-Ⅰ多相钢和初始组织为马氏体的IQP-Ⅱ多相钢的组织形貌、残留奥氏体及力学性能。结果表明:初始组织为铁素体+珠光体的IQP-Ⅰ多相钢室温组织中,铁素体和马氏体基本呈块状分布,块状残留奥氏体存在于铁素体与马氏体界面处,薄膜状只存在于马氏体内的板条之间,且残留奥氏体含量较少,TRIP效应不明显,其抗拉强度为957 MPa,伸长率只有20%,强塑积为19905.6MPa·%。初始组织为马氏体的IQP-Ⅱ多相钢中铁素体和马氏体大多呈灰黑色的板条状或针状,且细小的针状马氏体均匀地分布在铁素体基体上,残留奥氏体只以薄膜状平行分布在铁素体基体上,体积分数达到了13.2%,且具有较高的稳定性,TRIP效应较明显,强塑积达到21560MPa·%,可以获得强度和塑性的良好结合。