Development of NbVTi HotRolled High Strength Steel With Fine Ferrite and Precipitation Strengthening

A hotrolled steel with high yield strength of 700 MPa, good elongation of about 20% and low ductilebrittle transition temperature (DBTT) lower than -70 ℃ has been developed in laboratory. The results show that adopting finishing rolling temperature of around 800 ℃ is rational, and coiling temperature is between 400 and 500 ℃. The strength of developed 700 MPa hotrolled high strength steel is derived from the cumulative contribution of fine grain size, dislocation hardening and precipitation hardening. The fine grain strengthening and precipitation hardening are the dominant factors responsible for such high strength, and good elongation and toughness are predominantly due to fine grain ferrite.     

Textures and Properties of Hot Rolled High Strength TiIF Steels

The texture evolution in a high strength TiIF steel during the processing of hot rolling, cold rolling, and annealing is studied. For comparison, both ferrite rolling and austenite rolling are employed. It is found that the texture type is the same after ferrite rolling and austenite rolling, but the texture intensity is much higher in the ferrite rolled sample. Furthermore, texture characteristics at the surface are absolutely different from those at the midsection in both ferrite rolled and austenite rolled samples, as well as under the cold rolled and annealed conditions. The shear texture {110}<001> disappears and orientation rotates along {110}<001>→{554}<225>→{111}<112>→{111}<110>→{223}<110> during cold rolling. Compared to the austenite rolled sample, the properties of the cold rolled and annealed sheet which is subjected to ferrite rolling are higher.     

SelfLearning and Its Application to Laminar Cooling Model of Hot Rolled Strip

The mathematical model for online controlling hot rolled steel cooling on runout table (ROT for abbreviation) was analyzed, and water cooling is found to be the main cooling mode for hot rolled steel. The calculation of the drop in strip temperature by both water cooling and air cooling is summed up to obtain the change of heat transfer coefficient. It is found that the learning coefficient of heat transfer coefficient is the kernel coefficient of coiler temperature control (CTC) model tuning. To decrease the deviation between the calculated steel temperature and the measured one at coiler entrance, a laminar cooling control selflearning strategy is used. Using the data acquired in the field, the results of the selflearning model used in the field were analyzed. The analyzed results show that the selflearning function is effective.     

Effect of Boron on Delayed Fracture Resistance of MediumCarbon High Strength Spring Steel

The delayed fracture behavior of mediumcarbon high strength spring steel containing different amounts of boron (0000 5%, 0001 6%) was studied using sustained load delayed fracture test. The results show that delayed fracture resistance of boron containing steels is higher than that of conventional steel 60Si2MnA at the same strength level and it increases with the increase of boron content from 0000 5% to 0001 6%. The delayed fracture mode is mainly intergranular in the boron containing steels tempered at 350 ℃, which indicates that the addition of boron does not change the fracture character. However, the increase of boron content enlarges the size of the crack initiation area. Further study of phase analysis indicates that most boron is in solid solution, and only a very small quantity of boron is in the M3(C, B) phase.     

Research, Development, and Production of VN Microalloyed High Strength Rebars for Building in China

The research, production, and application of VN microalloyed high strength rebars in China were reviewed. Enhanced nitrogen in vanadiumcontaining rebars promotes the precipitation of fine V(C, N) particles, and markedly improves the precipitation strengthening effectiveness of vanadium. Therefore, vanadium added to VN microalloyed rebars can be reduced by 40% compared to the same strength level of vanadiumcontaining rebars.     

Effect of Solid Solution Treatment on Microstructure of FeNi Based High Strength Low Thermal Expansion Alloy

The influence of solid solution treatments on the dissolution of carbides precipitates, the grain size, and the hardness of high strength low expansion alloy were investigated through XRD analysis, microstructure observations, and theoretical computation. It was seen that most primary Mo2C type carbide band dissolved in a temperature range of 1 100-1 150 ℃. When the temperature was over 1 200 ℃, the grain size increased remarkably, which led to the reduction of hardness.     

Hot Deformation Behavior and Processing Map of Spray Formed M3∶ 2 High Speed Steel

Hot deformation behavior of a new type of M3∶ 2 high speed steel with niobium addition made by spray forming was investigated based on compression tests in the temperature range of 950-1 150 ℃ and strain rate of 0. 001-10 s~(-1). A comprehensive constitutive equation was obtained,which could be used to predict the flow stress at different strains. Processing map was developed on the basis of the flow stress data using the principles of dynamic material model. The results showed that the flow curves were in fair agreement with the dynamic recrystallization model. The flow stresses,which were calculated by the comprehensive constitutive equation,agreed well with the test data at low strain rates( ≤1 s~(-1)). The material constant( α),stress exponent( n) and the hot deformation activation energy( Q_(HW)) of the new steel were 0. 006 15 MPa~(-1),4. 81 and 546 kJ·mol~(-1),respectively. Analysis of the processing map with an observation of microstructures revealed that hot working processes of the steel could be carried out safely in the domain( T = 1 050-1 150 ℃,ε = 0. 01- 0. 1 s~(-1))with about 33% peak efficiency of power dissipation( η). Cracks was expected in two domains at either lower temperatures( 1 000 ℃) or low strain rates( 0. 001 s~(-1)) with different cracking mechanisms. Flow localization occurred when the strain rates exceeded 1 s~(-1) at all testing temperatures.     

Mechanism of Austenite Evolution During Deformation of UltraHigh Carbon Steel

The mechanism of transformation of austenite to cementite and pearlite during the deformation of ultrahigh carbon steel was discussed. The results indicate that the pearlite and cementite can be induced by deformation between Acm to Arcm. The transformation during deformation is still considered as a diffusioncontrolled process. With the increase of time and reduction, the pearlite fraction increased. At the beginning of the transformation, the pearlite was lamelliform. When the rate of reduction was increased to 70%, some of the induced lamellar pearlite was broken up under deformation.     

Uniaxial TimeDependent Ratcheting of SS304 Stainless Steel at High Temperatures

The uniaxial timedependent strain cyclic behaviors and ratcheting of SS304 stainless steel were studied at high temperatures (350 ℃ and 700 ℃). The effects of straining and stressing rates, holding time at the peak and/or valley of each cycle in addition to ambient temperature on the cyclic softening/hardening behavior and ratcheting of the material were discussed. It can be seen from experimental results that the material presents remarkable time dependence at 700 ℃, and the ratcheting strain depends greatly on the stressing rate, holding time and ambient temperature. Some significant conclusions are obtained, which are useful to build a constitutive model describing the timedependent cyclic deformation of the material.     

Effects of TMCP Schedule on Precipitation,Microstructure and Properties of Ti-microalloyed High Strength Steel

Using the similar compositions of the Ti-microalloyed high-strength steels produced by the thin-slab casting process of compact strip production(CSP),four thermo-mechanical control processes(TMCP)after the simulated thickslab casting,i.e.the two hot rolling routes and the two cooling processes,were designed,aiming at achieving the same mechanical properties as the thin strip products.The final microstructures after the four TMCP processes were examined by optical microscope(OM),scanning electron microscope(SEM)and transmission electron microscope(TEM).The tensile properties and Charpy impact energy were measured correspondingly.Strain-induced TiC precipitation was found in the two-stage rolling route with the finish rolling temperature at low levels,leading to grain refinement due to the pinning effect during austenite recrystallization.Precipitation hardening in ferrite was observed when a period of isothermal holding was applied after hot rolling.It could be concluded that both finish rolling temperature and the subsequent isothermal holding temperature were crucial for the achieved strength level due to the combined effect of grain refinement and precipitation hardening.At the same time,it was found that the isothermal holding led to poor impact toughness because of remarkable precipitation hardening.Therefore,it was suggested that the precipitation kinetics of titanium carbides in both austenite and ferrite should be investigated in future.     

Development of Ti-Microalloyed 600 MPa Hot Rolled High Strength Steel

A high strength steel with yield strength on the order of 600 MPa was developed successfully with only addition of titanium alloying element based on a low-carbon steel.The results showed that the hot deformation accelerated ferrite and pearlite transformation and retarded bainite transformation under continuous cooling condition.The microstructure of this steel was mainly composed of fine grained ferrite and carbides distributing along the ferrite grain boundaries.The yield and tensile strengths of steels ...     

600MPa级C-Si-Mn-Cr热轧双相钢的研制

根据鞍钢中薄板坯连铸连轧线的实际条件,通过采用合理的微合金化成分设计以及控轧控冷技术,开发出了600 MPa级C-Si-Mn-Cr热轧双相钢。钢板组织主要由大量铁素体和少量马氏体组成,其力学性能良好,抗拉强度达到600 MPa以上,屈强比低于0.70,延伸率A80大于19.0%,n值高于0.15,满足国家标准要求。     

静电搪瓷用高强度热轧薄钢板的性能

 简述了工业生产高强度热轧薄钢板的成分和生产工艺，其室温组织由极细的铁素体晶粒和极少量的珠光体组成。模拟高温搪烧时，随着温度的提高和保温时间的延长，屈服强度和抗拉强度下降，伸长率提高。经857 ℃保温10 min后，钢板的屈服强度满足了不小于310 MPa的要求。预变形时的变形量对模拟高温搪烧后钢板的力学性能也会产生影响。所研究的钢板在制作热水器内胆时能满足耐压不小于12 MPa和2万次的压力循环试验要求。     

低成本超高强度热轧锚杆钢筋的开发

利用新建100万t棒材车间具备完善的控制空冷的条件优势,通过制定合理的工艺方案和可控轧控冷参数,采用微合金化+控轧控冷工艺路线,成功开发出低成本、超高强度的热轧锚杆钢筋。经检测,该产品屈服强度达到690 MPa,抗拉强度达到860 MPa,冲击功达到36 J,具有良好的综合性能。     

汽车结构用550MPa级热连轧钢板的研制开发

介绍了汽车结构用热连轧钢板QStE550TM的试制情况,包括化学成分、冶炼工艺及热连轧工艺设计思路,同时针对产品组织、力学性能和工艺性能等进行了检测分析。试验结果表明,采用低碳、复合添加钛铌微合金化和控轧控冷技术,能够成功开发出厚度为3.0~16.0 mm的低成本高强度汽车结构钢。该钢具有较高的强度、良好的低温冲击韧性和宽冷弯性能等,可以广泛地用于重载汽车的横、纵梁和底盘零件的制造。     

轴承钢热轧钢带的开发

介绍了南钢利用自炼的优良坯料资源进行轴承钢带钢的开发,以替代棒材轴承钢,简化了下游的制造工艺,降低了加工成本。通过对加热工艺、轧制工艺、冷却工艺的摸索,使产品的碳化物控制水平达到并超过了棒材的水平,实现对棒材成功替代。     

含铌微合金化热轧多相钢的控轧控冷工艺

通过热轧试验研究了两阶段轧制+层流冷却、空冷、超快冷的TMCP工艺对高硅铌钢、高硅Nb-Ti钢、低硅Nb-Ti钢显微组织和力学性能的影响。结果表明,控轧控冷后的试验钢含有铁素体、贝氏体、马氏体以及少量残余奥氏体的混合组织。在控轧控冷工艺参数相近的情况下,高硅铌钢、高硅Nb-Ti钢、低硅Nb-Ti钢的抗拉强度依次减小,其伸长率和强塑积依次增大。低硅Nb-Ti钢的伸长率和强塑积分别达到了41%、25 256 MPa.%的最大值。     

鞍钢热轧镀锌板HD340LAD+Z开发

阐述了鞍钢开发的热轧镀锌板HD340LAD+Z其基板成分、组织及工艺设计,归纳出该热轧镀锌板开发过程中的控制要点,对钢板的金相组织、显微组织及表面形貌进行了检测。结果表明,热轧镀锌板HD340LAD+Z力学性能、表面质量等指标完全满足标准及用户要求。     

新钢600MPa级汽车车厢用热轧钢卷试制

通过成分设计、冶炼、热轧、工艺的控制,开发出厚度为2.3 mm的600 MPa级含铌钛微合金化高强度汽车板,并分析了此钢种的力学性能、金相组织、析出粒子特征及变化规律和厚度等质量特性。     

Strengthening Mechanism of a New 700 MPa Hot Rolled High Strength Steel

The microstructural evolution in a 700 MPa hot rolled high strength steel was analyzed in terms of strengthening mechanisms.The results show that the hot rolled sheet steel has yield strength of 710 MPa with good elongation and toughness.The strength of the developed 700 MPa hot rolled high strength steel is derived from the cumulative contribution of fine grain size,dislocation hardening and precipitation hardening.The fine grain strengthening and precipitation hardening are the dominant factors responsible for such high strength,and the amount of precipitation hardening is two or four times higher than that of conventional microalloyed hot rolled sheet steels reported in the past.Good toughness is due to refinement of ferrite grain size.