高强度低合金钢中纳米析出相对腐蚀行为影响的研究进展

高强度低合金钢中Nb、V和Ti等微合金化元素的纳米析出相对于调控钢的组织和性能具有重要作用,它可以确保钢基体同时拥有较高的力学性能和较强的耐蚀性能。本文基于国内外最新研究现状,系统阐述了纳米析出相在高强度低合金钢中的存在形态以及其对钢中氢扩散、均匀腐蚀、应力腐蚀开裂以及各类氢损伤等腐蚀行为的影响规律和机制。研究表明,纳米析出相对钢基体腐蚀行为的影响受其尺寸、数量和分布状态的控制。细小且与基体共格或半共格的纳米析出相不仅可以通过改善钢的微观组织（包括亚结构）提高耐蚀性能,其导致的不可逆氢陷阱及对氢扩散的强烈抑制作用还可以极大提高抗应力腐蚀和各类氢损伤的能力。而大尺寸的非共格析出相则可能恶化钢基体的耐蚀性能和促进氢损伤。最后展望了目前关注较少的纳米析出相对腐蚀疲劳影响的相关研究。明确纳米析出相对高强度低合金钢腐蚀行为的影响规律与机制将有助于更高品质耐蚀钢的开发和应用。      

Study of the Effect of Microstructure Characteristics on Corrosion Resistance of Cold-Rolled Micro-Alloyed Sheet Steels (Hsla) of Strength Classes 340–420 for Automobile Building

Metallurgist - The effect of microstructure characteristics and also production regimes on corrosion resistance of cold rolled high-strength low-alloy steels (HSLA) grades 340 and 420 is studied....     

Features of the Effect of Microstructure Characteristics on Corrosion Resistance of Cold-Rolled High-Strength Low-Alloy Steels (HSLA) Grade 260–300 for Automobile Building

Metallurgist - An experimental study is conducted on the effect of production parameters on the corrosion resistance of cold-rolled high-strength low-alloy steels (HSLA) grade 260–300,...     

低合金高强度调质钢控轧控冷工艺优化

研究了低合金高强度调质钢的轧制方式及轧后冷速对调质后微观组织及力学性能的影响。结果表明:在试验条件下,试验钢采用不同轧制方式及冷速获得不同淬火加热前的初始组织及力学性能,但调质后却具有相同的微观组织和力学性能。建议低合金高强度调质钢采用一阶段的轧制方式,终轧温度应高于奥氏体部分再结晶区的上限温度,轧后采用适宜的冷速(4~15℃/s)进行加速冷却。以此工艺调质后的试验钢具有较高的均匀性,与现行TMCP工艺相比,强塑性和强韧性更为优异。     

微合金钢等温沉淀析出动力学模型

采用形核长大模型对高强度低合金钢中的微合金元素铌、钛和钒的等温析出行为进行了定量计算,把计算结果与等温应力松弛实验结果相比较,分析产生计算误差的原因,为连续冷却的析出计算提供依据.     

铌对高强度低合金钢的组织和强化机制的影响

研究了铌的质量分数分别为0.021%、0.081%和0.17%的高强低合金钢热轧态的组织和力学性能,并通过计算分析了3种钢的强化机制.研究结果表明,铌含量的提高抑制了珠光体的形成,促进了针状铁素体的形成,细小的碳氮化铌析出相增多;随铌含量的增加,细晶强化作用差别不大,沉淀强化效果明显增大.     

Microstructure in low-carbon low-alloy high-strength pipe steel

The microstructure of a broad range of low-carbon low-alloy high-strength pipe steels produced by thermomechanical treatment is studied by transmission electron microscopy. Such steels consist of a mixture of various types of ferrite matrix with high-carbon phases and structural components. The classification of the structures is refined, with separate consideration of the components forming the low-carbon ferrite matrix and the high-carbon components that appear as isolated regions and also as layers and inclusions in bainitic ferrite. A deformational dilatometer is used to determine the temperatures ranges in which the various phases and structural components are formed.     

罩式退火铌微合金化汽车钢的强化机理

 通过比较相同冷轧与罩式退火工艺下Mn-Si系和铌微合金化2种汽车用低合金高强钢的显微组织与力学性能,研究微量铌在冷轧罩式退火低合金高强钢中的强化机理。利用OM、SEM、TEM和拉伸试验机分别对2种钢的显微组织与力学性能进行了表征。对比分析表明：相对热轧板来说,2种钢冷轧退火板的铁素体晶粒和第二相析出物的尺寸都有所长大,导致了强度降低。相对Mn-Si钢而言,铌微合金化钢热轧板和冷轧退火板中的铁素体晶粒和第二相析出物尺寸更细小,细小第二相析出物的数量也更多,在相同的伸长率水平下明显提高了强度。冷轧罩式退火板的强化机理分析表明,铌微合金化低合金高强钢的主要强化方式是细晶强化和NbC的沉淀强化;研究认为添加质量分数为0.025%的铌时细晶强化更强烈。     

Effect of heat treatment on mechanical properties and structure of high-strength pipe steels with a ferrite-bainite structure*

The effect of heat treatment on mechanical properties and microstructure of high-strength low-alloy ferrite-bainite pipe steels is studied. Specimens are heated in a laboratory furnace up to a temperature in the range 100?C850°C. Dependences for the change in mechanical properties on heating temperature and the main features of steel structure are determined. TEM is used to study excess phase precipitation, including Nb and V carbonitrides, during heating. Unfavorable temperature ranges are determined for heating pipe steels with a ferrite-bainite structure. The results obtained may be used in industrial production and during development of new technology for thermomechanical treatment.     

Strain-aging of vanadium, niobium or titanium-strengthened high-strength low-alloy steels

Four commercially available high-strength low-alloy (HSLA) steels were evaluated in this study. It was determined that all four steels were susceptible to strain-aging by interstitial solutes. The increase in strength due to strain-aging was similar to that observed in a low carbon steel studied for comparison. At high levels of prestrain, the percent loss in ductility in the HSLA steels was comparable to that observed in the low-carbon steel in specimens prestrained to the same fraction of the total elongation of the as-received metal. However, when considered on an absolute basis, the residual ductility in the HSLA steels was 25 to 50 pct of that observed in the low-carbon steel. The kinetics of strain-aging were briefly examined. Indications are that the kinetics are slower in the HSLA steels than they are in the low-carbon steel.     

Strain-aging of vanadium,niobium or titanium-strengthened high-strength low-alloy steels

Four commercially available high-strength low-alloy (HSLA) steels were evaluated in this study. It was determined that all four steels were susceptible to strain-aging by interstitial solutes. The increase in strength due to strain-aging was similar to that observed in a low carbon steel studied for comparison. At high levels of prestrain, the percent loss in ductility in the HSLA steels was comparable to that observed in the low-carbon steel in specimens prestrained to the same fraction of the total elongation of the as-received metal. However, when considered on an absolute basis, the residual ductility in the HSLA steels was 25 to 50 pct of that observed in the low-carbon steel. The kinetics of strain-aging were briefly examined. Indications are that the kinetics are slower in the HSLA steels than they are in the low-carbon steel.     

Ladle deoxidation,desulphurisation and inclusions in steel –Part 2: Observations in practice

Practical observations on the application of oxygen sensors, argon stirring, mould additions for rimstabilized steel. Discussion of ladle desulphurisation. Deformability of oxide inclusions, control of blowhole formation. Suppression of the precipitation of MnS by absorbing the dissolved sulphur with minute calcium aluminate particles entrained in liquid steel containing less than 0.002% S, and by rare earth treatments before casting steel containing 0.002 to 0.006% S. Aspects of steelmaking and casting clean steel, particularly high-strength, low-alloy steels.     

Studies on kinetics of strain ageing in Nb,Ti, V-bearing HSLA steels and a dual-phase steel

Strain-ageing behaviour of different high-strength low-alloy (HSLA) and dual-phase steels was investigated. Single factor experiments were carried out to decide on the range of variation of variables for construction of the matrix of experimental design. Quantitative relationships between time and temperature of ageing (within a narrow range) at constant pre-strain, with increase of yield strength after strain ageing was developed in the form of regression equations by applying statistical design of experiments. Validity of these equations was checked by statistical method as well as by random experiments. Activation energies for strain ageing of these steels were determined by using the developed regression equations. These values were in close agreement with the values reported by other investigators.     

On the Role of Ni in Cu Precipitation in Multicomponent Steels

The nature of Cu precipitation in quench-tempered multicomponent high-strength low-alloy steels is characterized by atom probe tomography. The detected nanometer sized Ni-rich clusters act as preferential nucleation sites for Cu-rich clusters, and Ni segregation at the Cu-rich precipitate/matrix heterophase interface contribute to fast growth of Cu precipitates. Molecular dynamics simulation indicates that local Ni clustering at atomic scale significantly quickens the solute diffusion. The initial Ni composition has a profound effect on the nature of Cu precipitation.     

低合金高强度钢的强化机理及生产工艺的探讨

针对国内低合金高强度钢发展中存在的问题，探讨了该钢种微合金元素的强化机理，简要介绍了低合金高强度钢的成分的优化设计及生产工艺。     

Microstructural model for hot strip rolling of high-strength low-alloy steels

The microstructural evolution during hot-strip rolling has been investigated in four commercial high-strength low-alloy (HSLA) steels and compared to that of a plain, low-carbon steel. The recrystallization rates decrease as the Nb microalloying content increases, leading to an increased potential to accumulate retained strain during the final rolling passes. The final microstructure and properties of the hot band primarily depend on the austenite decomposition and precipitation during run-out table cooling and coiling. A combined transformation-ferrite-grain-size model, which was developed for plain, low-carbon steels, can be applied to HSLA steels with some minor modifications. The effect of rolling under no-recrystallization conditions (controlled rolling) on the transformation kinetics and ferrite grain refinement has been evaluated for the Nb-containing steels. Precipitation of carbides, nitrides, and/or carbonitrides takes place primarily during coiling, and particle coarsening controls the associated strengthening effect. The microstructural model has been verified by comparison to structures produced in industrial coil samples.     

Bauschinger Effect in Microalloyed Steels: Part II. Influence of Work Softening on Strength Development During UOE Line-Pipe Forming

The Bauschinger effect (a reduced yield stress at the start of reverse deformation following forward prestrain) is an important factor of strength development for cold metal forming technology. In steels, the magnitude of the Bauschinger effect depends on composition, through the presence of microalloy precipitates, and prior processing, through the size and distribution of the microalloy precipitates and the presence of retained work hardening. In this article, the parameters of the Bauschinger effect and work hardening (coefficient and exponent) in forward and reverse deformations were quantitatively related to the particle number density and dislocation density for two high-strength low-alloy (HSLA) steels. An example of the application of the obtained dependences is discussed with respect to the strength development during UOE forming of large diameter line pipes.     

Effect of prestrain on stretch-zone formation during ductile fracture of Cu-strengthened high-strength low-alloy steels

The effects of prestrain on the ductile fracture behavior of two varieties of Cu-strengthened high-strength low-alloy (HSLA) steels have been investigated through stretch-zone geometry measurements. It is noted that the ductile fracture-initiation toughness of both the steels remained unaltered up to prestrains of ∼2 pct, beyond which the toughness decreased sharply. A methodology for estimating the stretch-zone dimensions is proposed. Fracture-toughness estimations through stretch-zone width (SZW) and stretch-zone depth (SZD) measurements revealed that the nature of the variation of ductile fracture toughness with prestrain can be better predicted through SZD rather than the SZW measurements. However, for the specimen geometries and prestrain levels that were investigated, none of these methods were found suitable for quantifying the initiation fracture toughness.     

The significant impact of Ti content on microstructure–toughness relationship in the simulated coarse-grained heated-affected zone of high-strength low-alloy steels

This study aims to investigate the influence of Ti addition on microstructure and toughness in the simulated coarse-grained heated-affected zone (CGHAZ) of high-strength low-alloy steels. The steels with low and high Ti content respectively were subjected to 100?kJ/cm heat input welding thermal cycle. The results indicated that the second-phase particles were mainly oxide covered with MnS and fine (Ti,Nb)N precipitate in low-Ti steel, which were modified to the oxide surrounded by TiN and coarse (Ti,Nb)N precipitate in high-Ti steel. Compared with low-Ti steels, the coarser precipitates induced larger austenite grain in CGHAZ of high-Ti steel. Moreover, the wrapping of TiN decreases the ability of inclusion to promote the nucleation of acicular ferrite, resulting in lower fraction of acicular ferrite in CGHAZ of high-Ti steel. Content of martensite-austenite constituent increased in CGHAZ of high-Ti steel. They were all responsible for the degeneration in toughness in CGHAZ of high-Ti steel.