超低C贝氏体钢的进展

众所周知，具有低的C含量的贝氏体钢可以获得优良的强韧综合性能，主要原因是极低的C含量能降低或消除了贝氏铁素基体中的渗C体，因此钢的韧性能得到进一步的改善。为了保证贝氏体转变的淬透性良好，而马氏体转变的淬透性相对较低，应该适量添加其它合金元素。大量的研     

贝氏体钢的研究开发与应用

综述了国内外研究开发贝氏体钢的进展，评价了低，中碳贝氏体钢的性能及控制方法，以及新型高强高韧贝氏体钢的研究与应用前景。     

Creation of Air-Cooled Mn Series Bainitic Steels

The development and mechanical performances of new type air-cooled Mn series bainitic steels including granular bainitic steels, FGBA/BG duplex steels, CFB/M duplex steels, medium carbon bainite/martensite steels, cast bainitic steels invented by the authors are summarized. The novel series of bainitic steels are alloyed with Mn, and several series bainitic duplex microstructures can be easily obtained under the condition of air cooling through unique composition design. The invented idea, the principle of alloying design, the strengthening mechanism, and the evolution of the microstructure of new type air cooled Mn series bainitic steels are presented. Furthermore, the applications in different fields of these Mn series air cooled bainitic steels with different strength level are also introduced. It is suggested that the significance of the development of the air cooled Mn series bainitic steel can be summarized as follows： reducing costs of both raw materials and production; good combination of strength and toughness; self-hardening with high bainitic hardenahility by air cooling from hot working without additional quenching-tempering treatment or quenching procedure; large savings in energy resources; and reduced environmental pollution.     

Development of New High-Strength Carbide-Free Bainitic Steels

An attempt was made to optimize the mechanical properties by tailoring the process parameters for two newly developed high-strength carbide-free bainitic steels with the nominal compositions of 0.47 pct C, 1.22 pct Si, 1.07 pct Mn, 0.7 pct Cr (S1), and 0.30 pct C, 1.76 pct Si, 1.57 pct Mn, and 0.144 pct Cr (S2) (wt pct), respectively. Heat treatment was carried out via two different routes: (1) isothermal transformation and (2) quenching followed by isothermal tempering. The results for the two different processes were compared. The bainitic steels developed by isothermal heat treatment were found to show better mechanical properties than those of the quenched and subsequently tempered ones. The effect of the fraction of the phases, influence of the transformation temperatures, the holding time, and the stability of retained austenite on the mechanical properties of these two steels was critically analyzed with the help of X-ray diffraction, optical metallography, scanning electron microscopy, and atomic force microscopy. Finally, a remarkable combination of yield strength of the level of 1557 MPa with a total elongation of 15.5 pct was obtained.     

Hydrogen-Trapping Mechanisms in Nanostructured Steels

Nanoprecipitation-hardened martensitic bearing steels (100Cr6) and carbide-free nanobainitic steels (superbainite) are examined. The nature of the hydrogen traps present in both is determined via the melt extraction and thermal desorption analysis techniques. It is demonstrated that 100Cr6 can admit large amounts of hydrogen, which is loosely bound to dislocations around room temperature; however, with the precipitation of fine coherent vanadium carbide traps, hydrogen can be immobilized. In the case of carbide-free nanostructured bainite, retained austenite/bainite interfaces act as hydrogen traps, while concomitantly retained austenite limits hydrogen absorption. In nanostructured steels where active hydrogen traps are present, it is shown that the total hydrogen absorbed is proportional to the trapped hydrogen, indicating that melt extraction may be employed to quantify trapping capacity.     

Mechanical Behavior of Carbide-free Medium Carbon Bainitic Steels

The effect of bainitic transformation time on the microstructure and mechanical properties was investigated in a steel containing 0.4 pct C-2.8 pct Mn-1.8 pct Si. The microstructure was characterized using optical and transmission electron microscopy; it consisted of bainitic ferrite, martensite, and retained austenite. The volume fraction of bainite increased from 0.4 for the shortest bainitic transformation time (30 minutes) to 0.9 at the longest time (120 minutes). The above microstructures exhibited an extended elasto-plastic transition leading to very high initial work-hardening rates. The work-hardening behavior was investigated in detail using strain-path reversals to measure the back stresses. These measurements point to a substantial kinematic hardening due to the mechanical contrast between the microstructural constituents. The onset of necking coincided with the saturation of kinematic hardening. Examination of the fracture surfaces indicated that the prior austenite grain boundaries play an important role in the fracture process.     

Recent Development of Air-Cooled Bainitic Steels Containing Manganese

The superiorities of air-cooled bainitic steels were described. A series of air-cooled bainitic steels containing manganese were developed and presented, which include low carbon granular bainitic steels, low carbon grain-boundary allotriomorphic ferrite/granular bainite dual phase steels, medium and medium high carbon bainite/martensite dual phase steel, low carbon carbide free bainite/martensite dual phase steels and casting bainitic steels.The development of ultra-low carbon bainitic steels in China was also introduced.     

Notch-Fatigue Properties of Advanced TRIP-Aided Bainitic Ferrite Steels

To develop a transformation-induced plasticity (TRIP)-aided bainitic ferrite steel (TBF steel) with high hardenability for a common rail of the next generation diesel engine, 0.2?pct C-1.5?pct Si-1.5?pct Mn-0.05?pct Nb TBF steels with different contents of Cr, Mo, and Ni were produced. The notch-fatigue strength of the TBF steels was investigated and was related to the microstructural and retained austenite characteristics. If Cr, Mo, and/or Ni were added to the base steel, then the steels achieved extremely higher notch-fatigue limits and lower notch sensitivity than base TBF steel and the conventional structural steels. This was mainly associated with (1) carbide-free and fine bainitic ferrite lath structure matrix without proeutectoid ferrite, (2) a large amount of fine metastable retained austenite, and (3) blocky martensite phase including retained austenite, which may suppress a fatigue crack initiation and propagation.     

中低碳空冷贝氏体钢的冲击磨损性能

研究了4种碳含理分别为0.15%、0.18%、0.23%和0.30％的空冷贝氏体钢的冲击磨损性能,并用扫描电镜观察了磨损表面的貌特征。结果发现,随着碳含量的提高,冲击磨损速度降低,碳含量分别为0.18%,0.23%和0.30%的3种贝氏体钢的冲击磨损速率相近,前3种低碳空冷贝氏体钢的磨损表面除了有磨损犁沟外,还存在唇状裂纹,碳含量越低,磨损表面越粗糙,所研究的4种贝氏体钢中,当抗拉强度1550MPa,容易形成穿透性裂纹。     

Development of New Type Mn-Series Bainitic Steels in China

The alloying design idea,strengthening-toughening mechanism,microstructure,mechanical performances,development and application in China of new type Mn-series bainitic steels are introduced.Mn-series air-cooling bainitic steels including granular bainitic steels,FGBA /BG duplex steels,CFB/M duplex steels,medium carbon bainite/martensite steels,cast bainitic steels are presented.The invented idea mechanical performances,development and application of second generation of Mn-series bainitic steels,i.e.water quenching Mn-series bainitic steels invented by the authors newly are introduced.The water quenching Mn-series bainitic steels cover severe series steels containing ultra-low carbon,low-low carbon,medium-low carbon,and high-low carbon content etc,which can reduce the amount of alloying content,increase hardening capability and improve weldability.It should be pointed out that the application of both air cooling and water quenching Mn-series bainitic steels are complementary and mutually reinforcing,and the new type Mn-series bainitic steels can meet the performance requirements of most steels used in engineering structure.Some newest technologies of Mn-series bainitic steels in China are discussed in this paper.It is suggested that the significance of the development of the Mn-series bainitic steels can be summarized as:significantly reducing costs of both raw materials and production;good combination of strength and toughness;excellent weldability;simple procedure;large savings in energy resources and reduced environmental pollution.     

Reciprocating Sliding Wear Behavior of Newly Developed Bainitic Steels

The present work discusses the mechanical properties and wear behavior of newly developed bainitic rail steels with nominal composition of 0.71 pct C, 0.35 pct Si, 1.15 pct Mn, 0.59 pct Cr, 0.40 pct Cu, and 0.20 pct Ni (all in wt pct)). Isothermal transformation has been carried out at different time and temperatures for obtaining different bainitic morphologies. Linearly reciprocating sliding wear behavior of the steels has been studied and compared with that of the conventional pearlitic rail steel. Considerable improvement in mechanical properties of the bainitic steels has been noticed. The hardness of the bainitic steels increases with decrease in isothermal transformation temperature. It leads to enhancement of wear resistance of the bainitic steels compared to the conventional rail steel. Finally, it clearly draws correlation between mechanical properties, wear resistance, and microstructural variation of a series of bainitic rail steels.     

Study of TRIP-Aided Bainitic Ferritic Steels Produced by Hot Press Forming

A study is reported to produce high strength ductile steels by controlled cooling following hot press forming, instead of quenching, as is practiced in the traditional press hardened steels. Heat treatments of several specially designed low carbon steels were carried out by interrupting the fast cooling from the austenization temperature at temperatures between T ₀ and Ms and then cooling in controlled rates to room temperature. The effect of the interrupt temperature and the cooling rate afterward on the microstructures and tensile properties was studied. The microstructures were characterized using dilatometry, optical microscopy, X-ray diffraction, and TEM. A multi-phase microstructure including bainite, martensite, and retained austenite was obtained in the simulated hot press forming process. Volume fraction bainite was found to increase with an increase in interrupt temperature and a decrease in cooling rate. Structure–property correlations of the studied steels heat treated at different conditions were developed. Improved tensile properties were obtained by controlling the interrupt temperature and cooling rate which produced an optimum bainite content of 60 to 75 pct and retained austenite. Unfortunately, the bainite in the simulated samples was not completely carbide free even though the steels contained about 1.6 wt pct of Si.     

转向节用贝氏体型非调质钢的高周疲劳性能

 利用旋转弯曲疲劳试验方法对比研究了新开发的两种转向节用贝氏体型非调质钢的高周疲劳性能。结果表明, 两种不同碳含量的贝氏体型非调质钢具有细小均匀的贝氏体铁素体+M-A岛组成的粒状贝氏体组织;两者具有相当的强度水平和疲劳性能,但其疲劳性能低于同等强度水平的调质钢。与锻态相比,正火处理后,试验料的抗拉强度和疲劳强度均有一定程度的降低,但屈强比和疲劳极限比明显提高。对疲劳断口的分析表明,试验料的疲劳裂纹均起源于表面基体,疲劳裂纹以准解理机制扩展。裂纹扩展速率试验表明,含碳量较低的试验料的疲劳裂纹扩展速率da/dN明显低于含碳量较高的试验料。     

终轧温度对低碳Mn系贝氏体钢性能的影响

 Gleeble热模拟试验表明,低碳Mn系贝氏体钢随着变形温度降低,仿晶界铁素体和粒状贝氏体都发生了细化,冲击韧性显著提高。加Nb后的Mn系贝氏体钢在相同工艺下组织得到了进一步细化。实验室试轧数据表明,含Nb的Mn系贝氏体钢降低终轧温度后,韧性提高的幅度比不含Nb钢更大,工业化前景广阔。     

High-Strength Nanostructured Cold-Resistant Steels for Continental Shelf Development

The article describes principles of developing steels for maritime structures and main pipelines.The scientific approach lies in forming an ultra fine-grained and submicrocrystal structure through thermomechanical treatment of low-carbon low-alloyed steels,providing higher strength and resistance to brittle fracture.The article presents results of assessing the operability characteristics and introducing new steels.