通过OM、SEM、XRD、TEM、EPMA、拉伸试验及维氏硬度测试等手段对不同冷却速度和加热温度下Fe-18Mn-0.8C-0.3Si-xAl(x=3,6,9)轻质钢中含铝碳化物—K相析出的规律以及其对性能的影响进行了研究.研究发现,影响K相析出的因素有Al含量、冷却速率和加热温度等.在炉冷的情况下,冷却速率约为0.020℃/s时,Al含量达到9％以上的轻质钢中K相可以在奥氏体边界上析出;在900℃以下K相可以存在,高于900℃时,K相就不再析出.析出的K相会对轻质钢的力学性能产生影响,会急剧降低轻质钢的塑性.因此在生产中应避免粗大的K相在钢中析出,采用较快的冷却方式以及较高的加热温度(>900℃)可避免K相的析出.

通过热轧厂热轧和冷轧厂盐酸酸洗,试制了含钛和不含钛的两种热轧酸洗钢板.采用金相显微镜、透射电子显微镜和拉伸试验机研究了两种试制钢板的显微组织和性能.结果表明:两种钢板的显微组织均由铁素体和珠光体组成,其屈服强度达到400 MPa以上,抗拉强度高于500 MPa,断后伸长率大于30％.与不含钛的钢相比,含钛钢的晶粒细小,屈服强度和抗拉强度高,断后伸长率低,屈强比高.

通过在工业生产的热轧卷不同位置取样进行力学性能和显微组织分析,研究卷取过程中冷却速度的差异对低碳微合金钢组织性能的影响.结果表明:不同部位试样的显微组织均为形态各异的铁素体和M/A岛;随着取样部位由钢卷外部向内部变化,等轴铁素体比例增加,并且晶粒尺寸增大,M/A岛减少;钢卷外部试样的(Nb,Ti)C析出物尺寸小,数量较少,其力学性能较差.温度场模拟分析表明,沿热轧卷长度方向冷却速度变化较大,导致钢卷内部第二相粒子析出数量增加,因此随着取样位置由钢卷外部向内部变化,试验钢屈服强度和拉伸强度显著增加,伸长率变化不大.

研究了不同铜含量下超低碳钢在不同热处理条件下的阻尼性能及其精细结构.结果 表明:固溶状态的铜对超低碳钢阻尼性能影响较小,铜以沉淀相形式存在显著提高了超低碳钢的阻尼性能.在实验范围内,含铜量升高,超低碳钢的阻尼性能提高.

Taking SAPH440 steel as the research object,hot rolling trial production was carried out on 1780mm hot continuous rolling line.The microstrueture and mechanical properties of hot rolled steel sheet were studied.Cracking causes of SAPH440 hot rolled steel plate during stamping were analyzed by using macrographic examination and metallographic examination.The results show that:the mechanical properties of SAPH440 steel plate accord with the JIS G3113-2006 standard.The main cause of cracking is that the stress concentration of the steel plate results in the crack defect during stamping.

通过1780 mm热连轧机热轧和1700 mm酸洗机组酸洗,试制了含铌和不含铌两种成分的钢板.并采用金相显微镜、投射电镜、拉伸试验机和扩孔试验机研究了添加铌对热轧酸洗钢板的组织和性能的影响.结果表明,两种成分试制钢板的显微组织均由铁素体和珠光体组成,其抗拉强度均高于460 MPa,断后伸长率大于34％.与不含铌钢板相比,加铌钢板的屈服强度和扩孔率明显提高,但抗拉强度和断后伸长率变化不大.

采用1 780 mm热连轧机和1 700 mm酸洗机组等设备,试制了一种碳的质量分数为0.030％、厚度1.8 mm的钢板,即热轧酸洗低碳薄钢板.检测了钢板的显微组织、力学性能和成形性能.试验结果表明,该热轧酸洗薄钢板的显微组织由铁素体和珠光体组成,铁素体晶粒度为9级,钢板的抗拉强度大于310MPa,屈服强度达200 MPa以上,断后伸长率大于42％,塑性应变比r值为0.5～0.6,应变硬化指数n值为0.19～0.21,钢板的成形性能符合要求.

Four hot rolled high-Mn light-weight steels of Fe-19Mn-xAl-0. 3Si-0. 8C(x =3. 5, 6, 8, 11) with different Al contents were investigated. The effect of Al element on mechanical properties, microstructure, strain hardening behavior and fracture behavior was analyzed by means of room temperature tensile test, XRD, metallography observation and fracture scanning, etc. The results show that with the increase of Al content, ferrite content increases, grain size of austenite decreases, yield strength and tensile strength increase, ductility and strain hardening capacity decrease, and the steels exhibit three-stage strain hardening characteristics. The 3. 5Al, 6Al, 8Al steels exhibit ductile fractures and the 11Al steel exhibits a mixed fracture of ductility and quasi-cleavage.

The relationship between the texture and grain boundary character distributions in fine-grain and high-strength IF steel was investigated by means of the electron backscatter diffraction ( EBSD ) . The results show that the γ texture enhances by devouring other texture, and the corresponding texture reduces accordingly with the increase of annealing time. The test plate contains a large amount ofΣ3,Σ9,Σ11 and Σ13 low-energy grain boundaries. The ΣCSL category and proportion vary gradually according to the increase of annealing time, and the variation leads to the corresponding changing of recrystallization texture component. The formation of recrystallization texture has close relationship with the distribution of ΣCSL boundaries.

In order to satisfy the light weighting of car body, the 590 MPa grade high yield strength steel for automobile structure was developed through fine-grain strengthening and Nb and Ti microalloying precipitation strengthening and the control of process parameters.The results show that the microstructure of this steel is fine grain ferrite, tempered martensite, a small amount of bainite and fine microalloy carbonitride particles precipitated in ferrite.The results of property tests, spot welding and form experiments indicate that this steel has a good mechanical property formability and weldability.

以含硼和铌细晶高强IF钢为研究对象,通过改变不同的冷轧压下率对试验钢进行连续退火实验.采用光学显微镜和透射电镜进行显微组织观察,并用拉伸试验机进行力学性能测试,得到了不同冷轧压下率下细晶高强IF钢的显微组织和力学性能的变化规律.试验结果表明,随着冷轧压下率的升高,试验钢的晶粒尺寸变小且分布不均,屈服强度和抗拉强度有所升高,r值升高,n值降低.

The effect of metastable austenite and microalloying elements (Nb and V) on prop-erties of such cold rolled high strength automobile steels as TRIP, TWIP and Q&P steels are intro-duced, which includes these influencing factors such as adjusting and controlling the composition system of the metastable austenite microstructure in cold rolled high strength automobile steels, continuous annealing process, the characteristics of the metastable austenite microstructure and the method for measuring these characteristics as well as the effect of metastable austenite on the product of strength and ductility and shapes of the tensile curves of high strength automobile steels. And also the effect of microalloying elements (Nb, V) on these Individual properties such as formability, strength grade and delayed fracture of cold rolled high strength automobile steels is intrduced.

Multi-axis deformation (MAD) tests were performed on a low carbon microalloyed steel with different process parameters. The effect of temperature and strain on the microstructure evolution were analyzed. The strain reversal effect was observed from the comparison between the microstructure resulting from the MAD process and the one from a uniaxial deformation process. However, with 0.3 strain per pass and the alternating compression time equal to 10 or more during the MAD process, ultra fine structures were obtained at deformation temperature below 800 °C. Due to the microalloyed elements in the tested steel, nanometer sized precipitates were introduced under MAD conditions, which also contributed to the microstructure refinement.

The developments of advanced high strength steels for automobile in Angang are introduced.These steels include hot rolled steel products,cold rolled steel products and hot dip galvanized steel products such typical steel grades as 980 MPa grade DP steel,TRIP steel,TWIP steel as well as QP steel.The hot dip galvanizing technology for producing advanced high strength steel products developed by Angang is also discussed and the trend for developing the advanced high strength steels in Angang is forecasted.

The ultra-fine grained cold-rolled IF steel sheets with high strength for Automobile is developed in Angang based on micro-precipitation of Nb(C or N) and grain refinement mechanism.The tensile strength of the new developed steel sheet is more than 390 MPa,in which there exists the tendency for forming the zone without precipitation the grain boundary.However the yield strength of the new steel grade is lower while it shows high plastic strain ratio and work hardening index and better formability and so the new developed steel sheet can meet the requirement required by vehicle weight reduction.

Dynamic CCT curves and microstructure evolution of 42CrMo steel were detected by dilatometry and metallography and hardness test.The results show that at low cooling rate,the microstructure of 42CrMo steel mainly consists of ferrite,pearlite and bainite.With increasing of cooling rate(in the range of 0.2-1 ℃/s),the ferrite and pearlite reduce gradually until the microstructure mainly composed of bainite at the cooling rate of 1 ℃/s.As the cooling rate ≥3 ℃/s,martensite starts to form and until the martensite completely formed at the cooling rate ≥10 ℃/s.The high cooling rate and deformation is proposed to be responsible for the formation of martensite.

S355 steel plates are welded by using the active gas shielded arc welding method and then the effects of post-welded heat-treatment on the crystal structures of inclusions in weld metal of the steel are analyzed.The results show that the structures of the inclusions in the as-welded weld metal are amorphous structures.After normalizing at 900 ℃ for 2 hours,the structures of amorphous inclusions in the weld metal are transformed into the crystalline structures.These crystalline inclusions contain Fe1.1Mn3.9C2,MnS and Mn2.5Fe2.5SiC phases.When the normalizing temperature is raised to 1 000 ℃,the Mn2.5Fe2.5SiC phase is disappeared while the amorphous phase is appeared again.When the normalizing temperature is raised to 1 100 ℃,only MnS and amorphous phases are observed in the inclusions.

S355 steel plates are welded by using the Nb-bearing welding wire.The effects of heat treatments process on the microstructure and mechanical properties of the Nb-bearing weld metal after being welded are analyzed.The results show that the strength of the Nb-bearing weld metal after annealing treatment improves,but the elongation and impact toughness reduce.With the normalizing temperature going up,the strength of the weld metal increases sharply and the elongation and impact toughness go down remarkably.However,with adding the times for normalizing,all properties such as the strength,elongation and impact energy increase first and then decrease.After normalizing for three times,the optimal values for its microstructure and properties can be obtained.

High strength IF steel sheets with sufficient formability had been extensively used in automotive industry.In this paper,a new type of high strength cold-rolled IF steel with higher carbon and niobium contents was studied.Thermal plastic and continuous annealing were performed on thermo-mechanical simulator.The transformation points were tested by thermal expansion apparatus.Optical microscopy and transmission election microscope （TEM） were used to analyze the microstructure and the secondary precipitates of the steel.The results showed,the ductibility temperature range was from 950℃ to 1250℃ and the transformation points were 887℃ and 913℃ respectively.The grain size of this steel was smaller than that of conventional high strength IF steel.At the mean time,there were many fine Nb（C,N） precipitates distributed in the intra-granular regions and the PFZ （precipitate free zone） were formed in the neighborhood of grain boundaries.Due to the unique micro-structural feature,the yield strength and the yield ratio of the steel were decreased while the tensile strength was increased.With the increasing of the annealing temperature,the strength decreased,the total elongation A50,r-value at 15% strain and n-value were all increased.In order to obtain the favorable mechanical properties,the skin-pass rolling rate should be chosen at 0.6-0.8%.