辨骨识踪——从陕北靖边庙梁遗址中出土的奥氏马骨谈起

奥氏马Equus(Sussemionus)ovodovi是一种已经灭绝的马科动物。庙梁遗址的奥氏马骨骼大都出土于房址和灰坑中,长骨几乎都从中间断裂,且观察到切割痕、刻划痕、砍斫痕等人为痕迹,这些骨骼表面痕迹表明奥氏马在遗址中是一种肉食来源。年龄和性别都无法体现出奥氏马被人为饲养或驯化的特征。综合来看,龙山时代早期晚段奥氏马已成为该遗址先民主要的狩猎对象。中国出土奥氏马的全新世晚期遗址共有四个,都分布在北方农牧交错带范围内,当时人口大量增长和气候干凉化导致的人地关系矛盾波及到了未被驯化的奥氏马,使奥氏马最终走向灭绝。

Influence of cooling rate on phase transformation and microstructure of Ti-50.9%Ni shape memory alloy

Heat treatment of Ti-50.9%Ni （mole fraction） alloy was studied by differential scanning calorimetry, X-ray diffraction, scanning electron microscopey and energy dispersive X-ray analysis to investigate the influence of cooling rate on transformation behavior and microstructures of NiTi shape memory alloy. The experimental results show that three-stage phase transformation can be induced at a very low cooling rate such as cooling in furnace. The cooling rate also has a great influence on the phase transformation temperatures. Both martensitic start transformation temperature （Ms） and martensitic finish transformation temperature （Mf） decrease with the decrease of the cooling rate, and decreasing the cooling rate contributes to enhancing the M→A austenite transformation temperature. The phase transformation hysteresis （Af-Mf） increases with the decrease of the cooling rate. Heat treatment is unable to eliminate the textures formed in hot working of NiTi sample, but can weaken the intensity of them. The cooling rate has little influence on the grain size.

Influence of Fe addition on phase transformation behavior of Ni Ti shape memory alloy

Three different NiTi-based alloys,whose nominal compositions were Ni50Ti50,Ni49Ti49Fe2,Ni45Ti51.8Fe3.2(molefraction,%),respectively,were used in the current research to understand the influence of Fe addition on phase transformationbehavior in NiTi shape memory alloy(SMA).The microstructure and phase transformation behavior of the alloys were investigatedby optical microscopy(OM),transmission electron microscopy(TEM),X-ray diffraction(XRD)and differential scanningcalorimetry(DSC)analysis.The results show that the matrix of the Ni50Ti50alloy consists of both B19′(martensite)phase and B2(austenite)phase.Moreover,the substructures of twins could be observed in the B19′phase.However,the ternary alloys of NiTiFeexhibit B2phase in the microstructures.Such microstructures were also characterized by large presence of Ti2Ni precipitatesdispersed homogenously in the matrix of the two kinds of alloys.The addition of Fe to the NiTi SMA results in the decrease in phasetransformation temperatures in the ternary alloys.Based on mechanism analysis,it can be concluded that this phenomenon isprimarily attributed to atom relaxation of the distorted lattice induced by Ni-antisite defects and Fe substitutions during phasetransformation,which enables stabilization of B2phase during phase transformation.

Influence of austenitizing temperature on apparent morphologies of as-quenched microstructures of steels

The effects of austenitizing temperature on the morphologies and substructures of as-quenched microstructure were investigated by using 13 medium and high carbon steels. The formation reasons of various morphologies of martensite quenched at different austenitizing temperatures were also studied. The results show that the packet martensite in medium and high carbon steels quenched at higher austenitizing temperature is entirely different from that in as-quenched low carbon steels, which is still plate martensite, and not lath martensite. All the change laws of as-quenched microstructures in medium and high carbon steels are identical with an increase in austenitizing temperature, and the austenitizing temperature can merely change the combined morphology of martensitic platelets, but cannot alter the type of product of martensitic transformation in commercial steels.

陕北靖边庙梁遗址动物遗存研究兼论中国牧业的形成

对庙梁遗址龙山早期出土的动物骨骼按照发掘单位逐一进行系统分类、测量、鉴定,总共鉴定出8种哺乳动物,分别为蒙古兔(Lepus tolai)、奥氏马(Equus ovodovi)、家猪(Sus domesticus)、梅花鹿(Cervus nippon)、马鹿(Cervus elaphus)、狍(Capreolus capreolus)、绵羊(Ovis aries)和普通牛(Bos taurus)。庙梁先民的肉食来源以狩猎奥氏马和饲养家猪、普通牛和绵羊为主。庙梁遗址中3件绵羊骨骼F20:D22、H49:D31和F19:D34经过^(14)C-AMS测年分别为4406~4186 cal.a B.P.、4401~4155 cal.a B.P.和4342~4151 cal.a B.P.;离庙梁遗址仅24 km的同时期的龙山时代早期横山红梁遗址,2件普通牛骨骼IF4③:D2、IIH26②:D23经过^(14)C-AMS测年分别为4406~4186 cal.a B.P.、4405~4158 cal.a B.P.,1件绵羊骨骼IF4③:D4的^(14)C-AMS测年为4407~4237 cal.a B.P.。这是目前我国发现时代最早、数量较多和具有直接测年数据的一批绵羊和普通牛的遗址,代表牧业经济活动的一批绵羊和普通牛开始出现,预示着龙山时代早期晚段庙梁遗址和红梁遗址极有可能是牧业形成的萌芽时期。另外,使用古DNA检测手段,确认了目前陕北地区数量较大的一批奥氏马标本,同时对保存较好的奥氏马下颌骨标本的形态学特征进行了对比和总结,为今后奥氏马标本的鉴定提供了参考依据。奥氏马的发现不仅扩大了该物种的地理分布范围,还增加了马科成员的种类,纠正了以往全新世中国野马全部是普氏野马的传统认知。

Technology for high performance TRIP steel

Thermodynamics of martensite transformation in low alloy TRIP steel was evaluated.It follows from the calculation that ε phase might be formed at above room temperature in the low Mn steel.Tested steel was therefore prepared according to the estimation result.High volume fraction of retained austenite(above 20%) containing 1.37%C was obtained in the steel after continuous annealing treatment.Tensile test showed that the ultimate strength of the steel was 1248 MPa,elongation rate 25%,the product of strength and elongation rate 31200 MPa%,reaching the grade of the third generation automobile steel.XRD detection indicated that after tensile test there existed ' martensite while TEM revealed that ε martensite also existed in the steel.Strengthening-toughening of the steel was thus raised due to the effect of transformation induced plasticity of two kinds of martensite.In addition,the phase stability of carbonitrates containing V was estimated and the complex micro-alloying effect was applied to the steel to control the size of austenite(about 1 μm) and enhance the stability of austenite.

Third generation high strength low alloy steels with improved toughness

On-line thermo mechanical controlled processing(TMCP) was conducted to develop the third generation high strength low alloy(HSLA) steel with high toughness economically.The ultra-low carbon content ensured a high level of upper shelf energy while ultrafine lath martensitic structure transformed from super-thin pancaked austenite during controlled rolling and cooling.The reduction of martensite block size decreased ductile-to-brittle transition temperature(DBTT) and compensated the strength loss due to carbon reduction.Consequently,the excellent balance of strength and toughness values was obtained as 950-1060 MPa for yield strength,180 J for Charpy V-notch impact absorbed energy at 30℃,which is much superior to that of traditional martensitic steel.Two mechanisms for the refinement of lath martensite block were proposed:One is the austenite grain refinement in the direction of thickness,and the other is the reduction in the fraction of sub-block boundaries with small misorientation and the increase in the fraction of block boundaries with large misorientation,possibly due to austenite hardening.

Relation of martensite-retained austenite and its effect on microstructure and mechanical properties of the quenched and partitioned steels

A two-step quenching and partitioning （Q＆P） treatment was applied to low-carbon alloy steels. The relation of initial martensite - retained austenite - fresh martensite and its effect on microstructure and mechanical properties were investigated by experiments. The results reveal that the volume fraction of retained austenite can reach the peak value of 17%, and the corre- sponding volume fractions of initial martensite and fresh martensite are 40% and 43%, respectively, when the tested steel is treated by initial quenching at 330℃, partitioning at 500℃ for 60s and final quenching to room temperature. Moreover, the micromorphologies of austenite and martensite become finer with the increasing of initial martensite fraction. The elongation is the highest when the volume fractions of initial martensite and retained austenite are 70% and 11%, respectively, meanwhile, the yield strength increases and tensile strength decreases gradually with the increase of initial martensite fraction, which proves that the mechanical properties including elongation, yield strength and tensile strength are based on the comprehensive effect of the retained austenite fraction, the finer microstructure and austenite stability.

Austenite/martensite structure and corresponding ultrahigh strength and high ductility of steels processed by Q&P techniques

The microstructure of steels treated by Q&P(quenching and partitioning) process was characterized,a method of controlling retained austenite fraction based on inhomogeneous martensitic transformation was proposed,and the mechanical properties of steels treated by Q&P process were measured.The results show that the microstructure of the studied steels is mainly composed of initial martensite,fresh martensite and retained austenite.The initial marteniste formed at the first quenching step is easily etched;the fresh martensite formed at the final quenching step looks like 'blocky' type phase,and the retained austenite is mainly located on the packet boundary and initial austenite grain boundary.The inhomogeneous microstructure causes the experimental optimum quenching temperature corresponding to maximum retained austenite fraction to be higher than the calculation based on CPE(constrained paraequilibrium) model.The product of tensile strength and total tensile elongation is 47.5 GPa%,and tensile strength of 1760 MPa was obtained for the steel with carbon content of 0.51 wt%.The TRIP(transformation induced plasticity) effects of the large fractioned metastable austenite make a main contribution to the high ductility improvement,and the martensitic matrix provides high strength.