CSP线高强度细晶热轧板的混晶和变形拉长晶粒的成因

对CSP线生产的高强度细晶热轧板的混晶和拉长晶粒的成因进行了分析,用有限元分析法模拟了热轧带钢的变形区的剪切应变场和温度场,用Gleeble实际模拟轧制工艺和组织变化。结果表明,CSP线高强度细晶热轧板的混晶和拉长晶粒的形成与钢板轧制过程中的钢板表层的变形场及温度场有关,也与先析出铁素体的形成后再进行轧制变形的过程有关;采用奥氏体深过冷轧制,既保证得到细晶粒又避免产生混晶和被变形拉长的晶粒。新的CSP轧制工艺,成功地生产了高强度高成形性细晶粒C-Mn热轧板。     

A Carbon-Stabilized Austenitic Steel with Lower Hydrogen Embrittlement Susceptibility

High-strength steels are susceptible to H-induced failure, which is typically caused by the presence of diffusible H in the microstructure. The diffusivity of H in austenitic steels with face-centered cubic (fcc) crystal structure is slow. The austenitic steels are hence preferred for applications in the hydrogen-containing atmospheres. However, the fcc structure of austenitic steels is often stabilized by the addition of Ni, Mn, or N, which are relatively expensive alloying elements to use. Austenite can kinetically also be stabilized using C. Herein, an approach is applied to a commercial cold work tool steel, where C is used to fully stabilize the fcc phase. This results in a microstructure consisting of only austenite and M₇C₃ carbide. An exposure to H by cathodic hydrogen charging exhibits no significant influence on the strength and ductility of the C-stabilized austenitic steel. While this material is only a prototype based on an existing alloy of different purposes, it shows the potential for low-cost H-resistant steels based on C-stabilized austenite.     

Investigation into Hydrogen Diffusion and Susceptibility of Hydrogen Embrittlement of High Strength 0Cr16Ni5Mo Steel

High strength bolt steel 0Cr16Ni5 Mo was charged with hydrogen by means of electrochemical technique to evaluate the hydrogen diffusion behavior.The bolt steels were investigated by a combination of electrochemical hydrogen permeation,thermal desorption spectroscopy(TDS),slow strain rate test(SSRT) and microstructure observation.The hydrogen concentration of both 10.9 grade(Rm=950—1 150 MPa) and 12.9 grade(Rm=1 150—1 250 MPa) bolt steels increases with increasing the hydrogen charging current densities and charging time.The 12.9 grade bolt steel has higher apparent diffusion coefficient than 10.9 grade steel,corresponding to the value of 4.7×10—7 mm2/s.By means of TDS tests,the activation energies of the two experimental steels are 17.74 k J/mol and 18.92 k J/mol,respectively.The hydrogen traps of both grade bolt steels are dislocations and crystal lattice.The notch tensile strength of the steels is reduced with the hydrogen concentration carried out by SSRT.The fracture morphologies of the steels after hydrogen charging present ductile dimple and quasi-cleavage characteristic.     

Effect of Morphology for Novel Bainite/Martensite Dual-Phase High Strength Steel on Its Hydrogen Embrittlement Susceptibility

It is very imperative to study the novel highstrength materials with high purity,high uniformityand refined grain,for improving the utilization rateand quality of materials.However,improving thestrength will reduce the resistance of materials tohydrogen embrittlement. For example,in lastcentury,some hydrogen embrittlements in thelanding gear of plane were reported[1] . When yieldstrength exceeds 1380 MPa,high strength steelsbeing used now exhibit strong susceptibility tohydrogen embrittlement…     

Cu-P-Cr-Ni-Nb系超细组织高强度耐大气腐蚀钢带开发

对传统345 MPa级Cu P Cr Ni系列09CuPCrNi钢采用Nb微合金化和低温控轧技术。研究结果表明,采用该项技术可使钢带获得超细晶组织,晶粒尺寸可细化至3 5~4 8μm,强度大幅度提高,钢带的屈服强度可达到500 MPa,同时,工业试验获得的超细晶高强度钢带仍具有良好的韧性、耐大气腐蚀性能和焊接性能。     

普通碳素钢超细晶微观组织的特征分析

 用Gleeble热模拟实验机对2种不同成分的普通碳素钢进行实验，实验的过程为：以10 ℃/s加热到950 ℃，保温2 min，再以10 ℃/s的冷速降到变形温度(900~600 ℃)，以10 s-1或30 s-1的变形速率进行了变形量为80%的变形，变形后立即水淬。通过光学显微镜和透射电镜观察分析，确定了普通碳素钢利用形变诱导铁素体相变获得的超细晶组织及两相区变形获得的超细晶组织的典型形貌特征。     

超细晶粒钢的制备原理及技术

 介绍了国内外超细晶粒钢的发展情况;阐述了晶粒细化对钢铁材料综合性能的影响,从微合金化、形变诱导相变、热处理和新型机械控制轧制技术及磁场或电场处理等方面介绍了获得细化晶粒钢的关键技术,最后从实际应用角度出发,提出了超细晶粒钢生产及应用中存在的问题。     

Hydrogen Embrittlement in a Plasma Tungsten Inert Gas-Welded Austenitic CrMnNi Stainless Steel

The study evaluates the effect of electrochemical hydrogen charging on the tensile properties and fracture behavior of the plasma tungsten inert gas weld of the high-alloy austenitic steel X3CrMnNiMoN17-8-4 in comparison to the pure base metal (BM). The weld metal exhibits a higher susceptibility to hydrogen embrittlement than the BM, which is mainly expressed by a loss in ductility. Based on the performed electron backscatter diffraction and X-ray diffraction examinations, this is attributed to the higher amount of δ-ferrite and the higher dislocation density in the weld zone. Furthermore, fractographic analyses reveal a change in the manner of fracture mode from ductile to brittle fracture starting from the edge in the hydrogen charged samples. The wider area of brittle fracture in the weld seam in relation to the BM indicates that hydrogen penetrates deeper into the material. Consequently, the diffusivity of hydrogen in the weld seam is determined to be significantly higher than in the BM.     

冷拔变形(F+M)型双相钢的氢脆

实验采用阴极电解预充氢试样拉伸的方法,研究了冷拔变形05Si2铁素体-马氏体型双相钢的氢脆敏感性及断裂行为。发现双相钢氢脆敏感性随着冷拔变形量的增大出现一峰值,以及氢致铁素体基体的脆化现象。     

The Effect of Second Tempering on Hydrogen Embrittlement of Ultra-High-Strength Steel

The objective of the present study is to enhance the resistance of hydrogen embrittlement (HE) via second tempering at 250 °C for 30, 60 and 120 minutes. Although second tempering results in a higher saturated hydrogen content for the second tempering specimens during a slow strain rate test (SSRT), it effectively reduces HE susceptibility. As the second tempering time increases, dislocation density decreases. In contrast, the size of the cementite and Mo_yC_x precipitates increase slightly. The density of Mo_yC_x precipitates increases, whereas the density of cementite remains approximately the same as the second tempering time increases. Regarding second tempering specimens, the volume fraction’s increase in Mo_yC_x precipitates, which acts as a hydrogen trap with high binding energy, plays an important role in reducing the HE susceptibility, and the decrease in dislocation density can also improve HE resistance. In addition, the growth of the interface of the cementite and matrix disperses more hydrogen, which could enhance HE resistance. The result also reveals that the cementite and matrix interface is a type of low-binding-energy hydrogen trap without plastic deformation, whereas the strain interface with interfacial dislocations is a type of high binding energy hydrogen trap under plastic deformation.

     

低温奥氏体钢的强度计算

研究了低温奥氏体钢的强度随温度及合金元素含量的变化规律。对大量试验结果用计算机处理得到了定量计算的系列表达式。经验证,计算结果是令人满意的,可用于低温奥氏体钢的设计和强度计算。     

Enhanced Mechanical Properties in a Low-Carbon Ultrafine Grain Steel by Niobium Addition

The microstructure and mechanical behavior of low-carbon ultrafine grain steel (UFG; 0.165 wt pct carbon) after niobium (Nb) addition were investigated. It was found that the addition of 0.028 wt pct of Nb resulted in the optimal tensile strength of 990.8 MPa with an adequate elongation of 15.5 pct. In comparison to the normal UFG steel (without Nb), the strength of Nb-UFG steel was substantially enhanced without any sacrifice of its elongation. The main increased strengthening mechanisms of Nb-UFG steel were precipitation and dislocation strengthening. The improved work hardening and adequate elongation of Nb-UFG steel could be ascribed to geometrically necessary dislocations and heterogeneous ferrite grains. Discontinuous static recrystallization occurred by a small rolling reduction on hardened martensite laths, resulting in the formation of heterogeneous ferrite grains. Ultrafine ferrite grains were surrounded by high-angle grain boundaries, and nanoscale Nb(C, N) carbonitrides providing precipitation strengthening were precipitated mainly in the α-phase.

     

Embrittlement of Intercritically Reheated Coarse Grain Heat-Affected Zone of ASTM4130 Steel

In this investigation, a thermal welding simulation technique was used to investigate the microstructures and mechanical properties of the intercritically reheated coarse grain heat-affected zone (IR CGHAZ) of ASTM4130 steel. The effect of post weld heat treatment (PWHT) on the toughness of IR CGHAZ was also analyzed. The toughness of IR CGHAZ was measured by means of Charpy impact, and it is found that IR CGHAZ has the lowest toughness which is much lower than that of the base metal regardless of whether PWHT is applied or not. The as-welded IR CGHAZ is mainly composed of ferrite, martensite, and many blocky M–A constituents distributing along grain boundaries and subgrain boundaries in a near-connected network. Also, the prior austenite grains are still as coarse as those in the coarse grain heat-affected zone (CGHAZ). The presence of the blocky M–A constituents and the coarsened austenite grains result in the toughness deterioration of the as-welded IR CGHAZ. Most of the blocky M–A constituents are decomposed to granular bainite due to the effect of the PWHT. However, PWHT cannot refine the prior austenite grains. Thus, the low toughness of IR CGHAZ after PWHT can be attributed to two factors, i.e., the coarsened austenite grains, and the presence of the remaining M–A constituents and granular bainite, which are located at grain boundaries and subgrain boundaries in a near-connected network. The absorbed energy of the IR CGHAZ was increased by about 3.75 times, which means that the PWHT can effectively improve the toughness but it cannot be recovered to the level of base metal.     

Potential of the High-Energy Hot Compaction in a Vacuum for Creating Materials with an Ultrafine Structure and High Strength

The typical form of specimens prepared by high-energy hot pressing in a vacuum using different deformation schemes and also the results of studying compaction, structure formation, and the physicomechanical properties of different materials in relation to billet heating temperature are presented. The structure and properties of specimens prepared by vacuum sintering are given for comparison. The efficiency of high-energy pressing of single-phase materials (nickel and molybdenum) and two-phase composites (dispersion-strengthened nickel Ni NiO and WC Co hard alloys) is demonstrated. The method makes it possible to prepare compact billets at quite low temperatures that provides retention of a fine-grained structure within them. As a result of this the materials have high mechanical properties that exceed those of specimens prepared by traditional methods.     

Effect of Grain Size and Grain Orientation on Dislocations Structure in Tensile Strained TWIP Steel During Initial Stages of Deformation

The effects of grain size and grain orientation on substructure in Fe–31Mn–3Al–3Si TWIP steel at a true strain of 0.06 were investigated. The results of the TEM observations indicated that where the grain size was 18.4 µm, the dislocations structure showed orientation dependence so that the mixture of both planar and tangled dislocations structure can be found in the deformed structure before the mechanical twinning initiation. Regardless of the grain orientation, however, the dislocation entanglements were mainly observed in the case of 2.1 µm grain size. Additionally, the reason for the suppression of the mechanical twinning as a result of the grain refinement at higher strains was described by the change of dislocations structure during initial stages of deformation.     

高强度建筑钢屈强比的研究

通过分析生产实际的数据和应用金相、扫描电子显微镜观察,对热轧态高层建筑钢板的屈强比的影响因素进行了分析,结果表明:随着钢板厚度的增加,屈服强度下降,抗拉强度有少许的上升,屈强比有明显的下降;随着C含量的增加,抗拉强度比屈服强度的上升快,钢板的屈强比减小,随着Mn、Si含量的增加,屈服强度、抗拉强度和屈强比增加;随着开轧温度、开冷温度的提高,屈服强度和屈强比均有明显的下降,而抗拉强度下降的幅度小;晶粒细化对屈服强度的提高比对抗拉强度的明显,并能显著的提高屈强比。     

Effect of Microstructure on Corrosion Fatigue Behavior of 1500 MPa Level Carbide-Free Bainite/Martensite Dual-Phase High Strength Steel

  Influence of microstructure of the experimental steels on the corrosion fatigue behavior in 35% of NaCl aqueous solution was studied. Experimental results show that compared with the full martensite (FM) steel, the carbide free bainite/martensite (CFB/M) steel has higher corrosion fatigue strength and corrosion fatigue crack threshold (ΔKthcf), and lower corrosion crack propagation rate [(da/dN)cf].