先进高强钢的显微组织与力学性能

为满足汽车轻量化发展的需求,开发了大量的先进高强度钢,如DP钢、TRIP钢、CP钢、M钢、TWIP钢等.与普通高强钢相比,先进高强钢具有高强度,高能量吸收性、高加工硬化率及优良的烘烤硬化和成形性能等一系列优点,在理论研究和实际应用上引起了人们极大的关注.近年来,世界各国纷纷致力于先进高强钢的研究开发.文章简要介绍了先进高强钢的显微组织与力学性能.     

不同热处理工艺下TC4-DT钛合金的显微组织及力学性能

研究了几种热处理制度对TC4-DT钛合金板材显微组织和力学性能的影响。结果表明:等轴或双态组织具有好的拉伸性能,片层组织能够有效提高材料的断裂韧性;控制单相区固溶的冷却速度以及第二重热处理的温度和冷却速度,可以获得不同尺寸的片层组织;单相区固溶后空冷,再经两相区第二重热处理,空冷的组织中含有粗的初生α片层和细小的次生α片层,炉冷的组织中α片层变厚,单相区固溶后水冷得到马氏体组织,在两相区热处理保温时,马氏体组织直接分解成粗的α片层。采用1 015℃/1 h/AC+955℃/1.5 h/AC+550℃/6 h/AC多重热处理,可以获得粗细相间的片层组织,具有更好的强度-塑性-断裂韧性的综合匹配。     

标准热处理状态下高强耐蚀C-22HS合金的显微组织和力学性能

采用热力学计算、SEM与TEM观察、力学性能测试等手段研究了一种新型高强耐蚀合金C-22HS在标准热处理状态下的显微组织及力学性能.结果表明:标准热处理状态下C-22HS合金由大小不均匀的等轴晶组成,合金中析出相主要有聚集分布的颗粒相(Mo,Cr)₆C和弥散分布的强化相Ni₂(Mo,Cr).合金经标准热处理后不仅具有较高的强度,而且具有良好的塑性与冲击韧性;无论是在室温还是高温,它的屈服强度都大大高于C-22合金.     

氮含量对3Ⅱ479钢显微组织和力学性能的影响

用实验方法研究了氮含量对3Ⅱ1479钢显微组织和力学性能的影响，结果表明：为满足550-590℃回火后的技术条件要求，氮含量应控制在上限，淬火温度、回火温度均应控制在中下限；为满足640-680℃回火后的技术条件要求，氮含量应控制在中下限。     

热处理工艺对GH4706合金显微组织与力学性能的影响

为掌握热处理工艺对GH4706合金组织性能的影响规律,研究了A、B、MST三种热处理工艺与合金组织性能的相关关系.结果表明,GH4706合金的主要强化相为γ＇相与γ＇/γ″共析出相,η相附近易形成γ＇、γ″相贫化区.A工艺在中间时效阶段析出的大尺寸γ＇相与时效阶段析出的小尺寸γ＇/γ″共析出相能够起到错配强化的效果,增大合金的室温拉伸强度.室温下η相为脆性相,不利于室温拉伸塑性与冲击韧性,因而B工艺的室温塑性与冲击韧性最佳.高温下η相能够起到协调晶内与晶界变形的作用,提高合金的650℃/690 MPa持久寿命与塑性,但过量η相析出不利于合金的持久寿命.     

热处理对TC18钛合金丝显微组织与力学性能的影响

研究了热处理对TC18钛合金丝材显微组织与力学性能的影响。研究结果表明,对于多道次热拉2.0 mm丝材,随着退火温度由760℃升高至820℃,显微组织明显发生了再结晶和晶粒长大过程,并且α相含量显著减少,β相含量显著增多。随着温度的升高,抗拉强度呈明显下降趋势,由760℃时的1 110 MPa下降到820℃时的970MPa。在760℃退火时,保温时间由0.5 h延长到1.5 h,丝材的显微组织晶粒略有长大,力学性能略有降低。     

Ce对IF钢显微组织和力学性能的影响

采用向IF钢中添加微量Ce元素的方法,研究不同Ce含量对IF钢组织和性能的影响。借助于金相显微镜、扫描电镜、能谱仪和万能拉伸试验机等检测手段,对添加Ce的IF钢的显微组织、夹杂物和力学性能进行了表征和分析。结果表明,IF钢中加入微量Ce可明显改善钢的显微组织,晶粒得到细化,且随着Ce含量的增加,分布更加均匀;同时钢中夹杂物得到变性,由原来多边形的Al2O3和TiN复合夹杂转变为椭球状或球状的含Al、Ti的稀土复合夹杂。钢中Ce含量达到0.0042%时,其抗拉强度、屈服强度、延伸率及洛氏硬度比未加Ce的IF钢分别提高了44%、37%、13%和59%。     

氮含量对ЗП479钢显微组织和力学性能的影响

用实验方法研究了氮含量对ЗП479钢显微组织和力学性能的影响,结果表明:为满足550～590 ℃回火后的技术条件要求,氮含量应控制在上限,淬火温度、回火温度均应控制在中下限;为满足640～680 ℃回火后的技术条件要求,氮含量应控制在中下限.     

Mn和Si对中锰热轧高强钢组织和性能的影响

为了研究Mn和Si元素对中锰热轧高强钢显微组织和力学性能的影响,设计了不同Mn、Si含量C-Si-Mn系试验用钢.利用热膨胀仪、扫描电镜、透射电镜、X射线衍射和单向拉伸等实验方法对试验用钢的相变点、显微组织、残余奥氏体含量和力学性能进行了测定与分析.结果表明：Mn和Si对中锰热轧高强钢的显微组织影响较大,对于低Si高Mn的试验钢,其显微组织主要由粒状贝氏体组成;对于高Si高Mn的试验钢,主要由贝氏体铁素体、马氏体和残余奥氏体组成;对于高Si低Mn的试验钢,则由块状铁素体、贝氏体、马氏体和残余奥氏体组成.高Si高Mn试验钢获得最高的综合力学性能,抗拉强度达1200 MPa以上,总伸长率为16%,强塑积接近20 GPa·%.分析认为,试验钢这种高强度和较高的塑性是由超细晶组织和TRIP效应共同决定的.     

Effect of heat input on microstructure and mechanical properties of dissimilar joints of AISI 316L steel and API X70 high-strength low-alloy steel

The microstructure and mechanical properties of dissimilar joints of AISI 316L austenitic stainless steel and API X70 high-strength low-alloy steel were investigated.For this purpose,gas tungsten arc welding(GTAW)was used in three different heat inputs,including 0.73,0.84,and 0.97 kJ/mm.The microstructural investigations of different zones including base metals,weld metal,heat-affected zones and interfaces were performed by optical microscopy and scanning electron microscopy.The mechanical properties were measured by microhardness,tensile and impact tests.It was found that with increasing heat input,the dendrite size and inter-dendritic spacing in the weld metal increased.Also,the amount of delta ferrite in the weld metal was reduced.Therefore,tensile strength and hardness were reduced and impact test energy was increased.The investigation of the interface between AISI 316L base metal and ER316L filler metal showed that increasing the heat input increases the size of austenite grains in the fusion boundary.A transition region was formed at the interface between API X70 steel and filler metals.     

Clarifying effect of welding conditions on microstructure and mechanical properties of friction stir spot-welded DH590 automotive high-strength steel plates

Friction stir spot welding was successfully applied to the 1.2-mm-thick DH590 dual-phase steel plates by using a polycrystalline cubic boron nitride rotating tool.During welding,the rotation speed ranged from 600 to 1000 r/min and the penetration depth ranged from 0.1 to 0.3 mm.In the spot joints,the size of the stir zone increased with the increase in rotation speed as well as the penetration depth of the tool.Comparing with the banded ferrite and martensite structure of the base metal,a mixed microstructure of ferrite and tempered martensite,refined bainite structure and coarse martensite structure were found in the heat-affected zone,thermomechanically affected zone and stir zone of the joints,respectively.Two kinds of interfacial shapes were formed between the upper and lower steel plates,and the formation of the bonded interface was dominated mainly by the penetration depth of the rotating tool rather than the rotation speed.It was revealed that the joints with straight interfaces showed higher shear tensile loads comparing with those with hook-like interfaces.Shear tensile tests showed that the maximum shear tensile load reached about 15.56 kN when the rotation speed and penetration depth were set as 800 r/min and 0.3 mm,respectively.The specimen was fractured through plug failure mode with a total elongation of about 5.6 mm.     

Influence of coiling temperature on microstructure and mechanical properties of a hot-rolled high-strength steel microalloyed with Ti,Mo and V

Influence of coiling temperature(CT)on the microstructure and mechanical properties of a hot-rolled high-strength steel microalloyed with Ti,Mo and V was elucid...     

Effect of cool deformation on mechanical properties of a high-strength pipeline steel

One of the requirements to successfully produce high-strength pipeline steel is the optimization of precipitation strengthening. Some high-strength pipeline grades rely on increased levels of niobium (Nb); in these grades, it is important to ensure that all of the Nb is effectively employed. It is generally accepted that the choice of coiling temperature (i.e., the temperature of steel strip just before coiling) is critical in maximizing Nb carbonitrides in ferrite. Additional control of this precipitation may be attained by deformation at these coiling temperatures, an approach termed “cool deformation.” In this work, steel specimens were heated to a temperature of 1200 °C and held for 20 minutes to ensure significant dissolution of the Nb precipitates. Some specimens were aged at 400 °C for times ranging from 10 minutes to 10 hours followed by air cooling. Others were subjected to deformation at 400 °C (cool deformation) prior to aging. It was found that cool deformation improves the mechanical properties (both yield and tensile strengths are significantly higher than those of the aged only specimens). A field emission gun—scanning electron microscope (FE-SEM) was applied successfully in the characterization of Nb precipitates using carbon extraction replicas. The FE-SEM observation of the replicas confirmed the presence of Nb precipitates in ferrite. The FE-SEM could analyze small particles (below 50 nm) embedded in the steel, but the analysis had to be carried out at low voltages to maximize spatial resolution, resulting in a poor signal. However, it is possible to analyze carbon extraction replicas in the FE-SEM using high voltages, because the interaction volume effect is no longer a problem.     

Correlation of microstructure with mechanical properties of 300m steel

300M steel was subjected to a wide range of quenched and tempered heat treatments. The plane-strain fracture toughness and the tensile ultimate and yield strengths were evaluated. Results indicate that substantial improvement in toughness with no loss in strength can be accomplished in quenched and tempered steel by austenitizing at 1255 K (1800°F) or higher. Low fracture toughness in conventionally austenitized 300M steel (1144 K (1600°F)) appears to be caused by undissolved precipitates seen both in the submicrostructure and on the fracture surface which promote failure by quasi-cleavage. These precipitates appeared to dissolve in the range 1200 to 1255 K (1700 to 1800°F). Formerly Research Metallurgist at NASA-Johnson Space Center, Houston, TX. Formerly NRC Postdoctoral Research Associate at NASA-Johnson Space Center.     

轧制复合厚钢板的界面组织及力学性能

摘要：以Q345钢为原料，采用组坯抽真空热轧复合的方法制备了55mm的厚板，利用OM和SEM观察界面微观组织，结果表明，基体和复合界面组织均为珠光体+铁素体，再结晶细化晶粒效果显著。随累计压下率的增加，界面缺陷减少，界面结合强度提高，当累计压下率达到66.0%时，界面剪切强度达到321MPa，Z向抗拉强度达到520MPa，断后伸长率最高达到39.5%，满足GB/T 1591—2008《低合金高强度钢》的要求。但复合界面经强酸深度腐蚀后，即使经多道次轧制变形，其仍然存在被强酸腐蚀的痕迹；同时，冲击试验结果表明，复合界面的冲击功低于母材的冲击功。     

The microstructure and mechanical properties of a modified 2.25Cr-lMo steel

Tensile and creep properties were determined on a V-Ti-B-modified 2.25Cr-lMo steel. The modified 2.25Cr-lMo steel had about 0.2 pct V added for improved elevated-temperature strength. Boron was added to improve the hardenability, thus allowing thicker sections to be quenched or normalized to completely bainitic microstructures. Lower carbon and silicon concentrations were used (~0.1 pct C and 0.02 pct Si) than in standard 2.25Cr-lMo steel. The modified steel had substantially better stress-rupture properties than did a standard 2.25Cr-lMo steel (both with bainitic microstructures) with equivalent tensile properties — especially at the lowest stresses and highest temperatures. Comparative transmission electron microscopy studies of the standard and modified 2.25Cr- lMo steels indicated that the differences involved the carbide precipitates and the dislocation substructures present in the steels.     

Influence of phase transformations on the mechanical properties of high-strength austenitic Fe-Mn-Cr steel

The influence of Cr and N additions on the mechanical properties of a Fe-Mn-C steel was investigated. The chemical composition was found to have a pronounced effect on the strain-hardening behavior, due to the strain-induced sequence of the γ → ▓ → α′ martensitic transformations. It was found that Cr and N suppress this transformation sequence. At Cr levels higher than 7.5 mass pct, no α′ martensite was formed, which led to a pronounced improvement of the ductility. The differences in transformation behavior can be attributed to the change in the intrinsic stacking-facult energy (ISFE): in the compositional range studied, Cr and N additions cause an increase of the ISFE.