氮在非调质钢中的作用

介绍了氮在非调质钢中的有益作用。非调质钢中增氮,改变了钒在相间的分布,促进Ｖ（Ｃ,Ｎ）析出,使析出相的颗粒尺寸明显减小,从而增强了钒的沉淀强化作用、大幅度提高钢的强度。氮通过促进Ｖ（Ｃ〉Ｎ）析出,有效地钉扎奥氏体－－铁素体昌细化了铁素体晶粒。增氮还可促进晶内铁素体的形成,进一步细化了铁素体组织。对微钛处理非调质钢,增氮提高了ＴｉＮ颗粒的稳定性,更有效地阻止奥氏体晶粒长大,充分利用廉价的氮元素,在保     

增氮对钒微合金钢组织和性能的影响

 通过对不同钒、氮质量分数的试验钢进行热模拟压缩试验和实验室轧制试验,用OM、SEM和TEM分析试验钢的显微组织,研究增氮对钒微合金钢组织和性能的影响。结果表明,普通钒微合金钢为板条贝氏体＋粒状贝氏体组织,增加氮质量分数,可促进晶内铁素体相变,得到针状铁素体组织,使M/A组织细化且弥散分布,改善韧性;而增加钒质量分数,可以增加析出强化作用,提高强度,但组织形态无明显变化,不能提高韧性。增氮钢中的钒在奥氏体内以VN析出,低氮钢内的钒在铁素体内以VC的形式析出,奥氏体-铁素体、VC-铁素体和VN-铁素体的平面点阵错配度分别为6.72%、3.89% 和 1.55%,在奥氏体内析出的VN可以作为铁素体的优先形核位置,促进晶内铁素体相变。     

钒微合金化钢的技术进展与应用

介绍了钒微合金化技术的最新进展以及钒钢的开发与应用情况。氮是含钒钢中有效的合金元素,含钒钢中增氮,优化了钒在钢中的析出,显著提高沉淀强化效果。采用钒氮微合金化设计,配合适当的轧制工艺,促进V(C,N)在奥氏体中析出,起到了晶内铁素体形核核心作用,实现了含钒钢的晶粒细化。最新的研究成果表明钒微合金化可以提高双相钢、贝氏体钢、相变诱导塑性钢、孪晶诱导塑性钢、热成型马氏体钢等汽车用先进高强度钢的强度并改善使用性能,显示出良好的应用前景。钒氮微合金化技术在中国高强度钢筋、高强度型钢、非调质钢、薄板坯连铸连轧高强度带钢等产品中获得广泛应用,大大促进了中国钒微合金化钢的发展。     

Production of ultra-high strength wire rod steels by vanadium microalloying

Ultra-high strength high-carbon wire rod steels have been produced using vanadium-microalloying technique instead of the conventional expensive and environment polluting lead patenting treatment. The strength increment attained in the hot rolled steels due to vanadium additions is maintained in the cold drawn wire. By using this technique, high tensile strength levels of 1550-1600 N/mm² were attained either by cold drawing of 0.17% V microalloyed high-carbon steel to 45-47% reduction or by cold drawing of 0.20% V microalloyed high-carbon steel to 25-30% reduction. An equation has been developed to predict the tensile strength from the chemical composition, cooling rate and reduction of area due to cold drawing. A combination of vanadium microalloying and accelerated cooling resulted in additional strength increment due to refining of microstructure and increasing the precipitation strengthening component. Inspite of the decrease in the amount of vanadium precipitates due to the increase in cooling rate, it is suggested that an increase in precipitation strengthening due to refining of these precipitates by accelerated cooling more than offsets the loss of precipitation strengthening due to decreasing the precipitates fraction.     

氮在非调质钢中的作用

了氮在非调质钢中所起的有益作用。在Ｎｂ,Ｖ,Ｔｉ三咱微合金化元素中,钒有较高的溶解度,钒有较高的溶解度,是非调质钢最常用也是最有效的强化元素。钒在钢中通过形成细小析出相起细化晶粒和沉淀强化作用。与碳相比,氮与钒有更强的亲和力,且氮化物更稳定,因此,氮对控制钒的析出起更重要的作用。大量研究结果表明,非调质钢中增氮改变了钒在相间的分布,促进Ｖ（Ｃ,Ｎ）析出,使析出相的颗粒尺寸明显减小。因而氮增强了非调     

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The beneficial effects of the elements Nb, V, Ti and N in microalloyed forging steels was reviewed. Among these elements, the vanadium is the most effective and commonly used strengthening element for non-quenched and tempered steels due to its high solubility in the steels. The effects of grain refinement and precipitation strengthening can be achieved in non-quenched and tempered steels through micro-alloying elements Nb, V and Ti inhibiting the recrystallization of deformed austenites and grain growth, and enchancing strain induction precipitation during hot processing. Although the Nb, V and Ti are all strengthening elements, their strengthening effect and strengthening mechanism vary with the C and N content of these steels. Therefore, it would be the most effective way to improve strength and toughness of the ferrite-pearlite non-quenched and tempered steels through making use of the microalloying characteristics of the elements Nb, V, Ti and N and meanwhile applying the proper forging process.     

微钛固氮降低含铌钢皮下裂纹敏感性的机理

 降低含铌低合金钢铸坯的裂纹敏感性,是实现热装热送工艺的必要条件,采用超高温激光共聚焦显微镜(HT-CLSM)、透射电镜(TEM)等手段研究了钛含量不同的含铌低合金钢(Q390、Q390GJD)高温铸坯的晶粒度及析出物特征,旨在揭示微钛固氮降低含铌钢皮下裂纹敏感性的机理。热力学计算与TEM检测结果表明,增加钢中钛质量分数(由0.010%上升到0.023%)提高了氮化钛粒子的析出温度(大于1 400 ℃),高温析出细小弥散的氮化钛粒子可钉扎奥氏体晶界,细化高温铸坯的晶粒度(由4级变成6.5级),晶粒尺寸降低了约44%,使高温铸坯的裂纹敏感性明显降低;氮化钛粒子优先析出固氮降低了铌碳氮化物、氮化铝的开始析出温度,并作为异质形核核心,抑制了铌、铝析出物在晶界析出概率,降低了析出物脆化晶界的危害。通过微钛固氮调控氮化物的析出温度、析出位置及细化晶粒的作用,有效降低了含铌钢第三脆性温度槽的宽度和深度,同时,高温抗拉强度提高了21.3%~27.5%,铸坯皮下裂纹发生率降低了80%以上。为了避免析出物的晶界链状析出导致含铌钢铸坯热装轧制裂纹,应将其钛质量分数控制在0.015%~0.020%的合理范围。     

钒钢的技术进展

 介绍了V在钢中的应用及V微合金化技术最新进展。通过含V钢中增N,利用廉价的N元素,优化了V的析出,显著提高沉淀强化效果,达到节约V用量及降低成本的目的。V-N钢中V（C,N）在奥氏体中析出,起到晶内铁素体核心作用,明显细化铁素体晶粒。V在贝氏体中的析出起到明显强化作用,提高了贝氏体的强度。V-N微合金化技术在高强度钢筋、高强度型钢、非调质钢、薄板坯连铸连轧高强度带钢等产品中获得广泛应用。     

Influence of base composition on the strength of vanadium-microalloyed steel bars

In this work, the effect of base composition on the strength of hot-rolled V-microalloyed steel bars was studied. Industrial heats with a wide range of carbon contents from 0.15 to 0.3% and manganese contents from 0.65 to 1.3% in combination with V-microalloying up to 0.1%, were carried out. The grain size of the produced hot rolled steel bars was measured and the different strengthening mechanisms were analysed. Carbon and manganese were found to have pronounced effect on refining the microstructure. Vanadium-micraolloying up to 0.1% has a slight grain refinement. This slight grain refinement effect of vanadium decreases with increasing the carbon content. The strengthening potential of vanadium seems to be due to precipitation strengthening rather than grain refinement effect. Both carbon and manganese in combination with vanadium showed a significant effect on increasing the precipitation strengthening. The vanadiumprecipitation strengthening is correlated with carbon and manganese contents. Two modified equations are derived to predict the yield strength of hot-rolled steel bars, in terms of chemical composition and grain size or only chemical composition.     

Recent Development and Applications of V Microalloying Technology in China

This paper reviews recent developments of V microalloying technology and its applications in HSLA steels.Enhanced-nitrogen in V-containing steel promotes precipitation of fine V(C,N) particles,and improves markedly precipitation strengthening effectiveness of vanadium,therefore,there is a significant saving of V addition in the same strength requirement.Vanadium can be used effectively for ferrite grain refinement by the nucleation of intragranular ferrite promoted by VN precipitates in Austenite.The combination of intragranular ferrite (IGF) on VN particles and the recrystallization controlled rolling (RCR) technology realize the grain refinement in V-containing steel.V-N process is a cost-effective way for high strength rebars,forging steels and thin slab direct rolling strips.     

Influence of microalloying on the mechanical properties of medium carbon forging steels after a newly designed post forging treatment

For more than twenty years the classical quench and tempering of medium carbon Cr-alloyed steels has been substituted in the production of drop-forged parts for the automotive industry by a direct continuous cooling of less expensive V-microalloyed steels with lower carbon content. However, this simplified treatment has serious limitations concerning the yield strength and ductility if compared with the properties after quench and tempering. On a group of such V-bearing steels additionally microalloyed with Ti and Nb and with different N contents, an alternative two-step-cooling (TSC) strategy after forging, combined with an additional annealing (AN), has been applied. This new post forging treatment results in a significant improvement of the final mechanical properties. The paper is focused on the particular contributions of a different microalloying in the optimized deformation schedules to improve mechanical properties after TSC + AN. The aim of this additional microalloying is to achieve a more homogeneous distribution of ferrite in the final multi-phase microstructure due to a proper austenite conditioning as well as to make a full use of the strengthening potential of vanadium in these forging steel grades.     

The prediction of precipitation strengthening in microalloyed steels

The effectiveness of interphase precipitation strengthening in microalloyed steels depends on the temperature dependence of the solubility of the precipitation phase in austenite and on the temperature utilized in soaking. Using an approximate method of calculating the solubility of microalloying elements in the presence of both carbon and nitrogen, a precipitation strengthening potential parameter was developed. On relating this parameter to the chemical compositions and thermal histories of microalloyed steels, it was determined that the interphase precipitation strengthening determined in this and other studies increases linearly with the strengthening potential parameter. On the basis of the linear dependence of precipitation strengthening on the precipitation potential and other observations, it appears that interphase precipitation strengthening is not due to the Orowan looping mechanism but rather to interactions of gliding dislocations with the strain fields of coherent precipitates.     

Precipitation and fine structure in medium-carbon vanadium and vanadium/niobium microalloyed steels

Hot-rolled and continuously cooled, medium-carbon microalloyed steels containing 0.2 or 0.4 pct C with vanadium (0.15 pct) or vanadium (0.15 pct) plus niobium (0.04 pct) additions were investigated with light and transmission electron microscopy. Energy dispersive spectroscopy in a scanning transmission electron microscope was conducted on precipitates of the 0.4 pct C steel with vanadium and niobium additions. The vanadium steels contained fine interphase precipitates within ferrite, pearlite nodules devoid of interphase precipitates, and fine ferritic transformation twins. The vanadium plus niobium steels contained large Nb-rich precipitates, precipitates which formed in cellular arrays on deformed austenite substructure and contained about equal amounts of niobium and vanadium, and V-rich interphase precipitates. Transformation twins in the ferrite and interphase precipitates in the pearlitic ferrite were not observed in either of the steels containing both microalloying elements. Consistent with the effect of higher C concentrations on driving the microalloying precipitation reactions, substructure precipitation was much more frequently observed in the 0.4C-V-Nb steel than in the 0.2C-V-Nb steel, both in the ferritic and pearlitic regions of the microstructure. Also, superposition of interphase and substructure precipitation was more frequently observed in the high-C-V-Nb steel than in the similar low-C steel.     

Microalloying of manufacturing steel with vanadium and nitrogen

The influence of microalloying with nitrogen and also vanadium and other nitride-forming elements on the properties of manufacturing steels is systematically analyzed. In rolling specialized components, thanks to decrease in austenite grain size, dispersional hardening by nitride nanoparticles, and the formation of improved substructure, the steel has distinctive properties: 30–50% increase in strength with excellent plasticity and resistance to fatigue and brittle failure. Principles are outlined for controlling the properties of steel in different components without quenching, with a view to replacing traditional nickel steels. Examples of the applications of microalloyed steels are presented.     

Different Roles for Vanadium as a Microalloying Element in Structural Steels

Vanadium is the most versatile of the microalloying elements used in steels.The present paper describes three separate ways in which vanadium is used to optimize mechanical properties in different products.Firstly,precipitation of V(C,N) during the γ→α transformation or in ferrite during cooling provides strengthening that is especially useful in long products and forgings.Additionally,VN particles which precipitate in austenite act as efficient intra-granular nucleants for ferrite,contributing improved strength and toughness in suitable process routes such as seamless pipe production.Thirdly,vanadium is supremely effective in preventing recovery in martensite and bainite.In this way it can be applied to maintain strength and reduces variability of properties in hot rolled strip steels.     

Nb微合金化对齿轮钢高温渗碳奥氏体晶粒度的影响

摘要：通过Nb微合金化提高渗碳温度是当前发展高端齿轮钢的重要思路。以20Cr钢为基准成分,通过实验室熔炼、锻造以及977~1134℃范围内高温伪渗碳实验,研究了0.02%、0.04%、0.06%、0.08%等不同Nb质量分数下渗碳后的奥氏体晶粒结构。在此基础上,依据热力学计算及析出颗粒熟化模型,对AlN、Nb(C,N)颗粒的钉扎强度进行估算并与晶粒尺寸建立联系,得到了适用于含Al、Nb齿轮钢的奥氏体晶粒度控制预测模型。最后,依据此模型分析了Nb含量对20Cr钢渗碳温度的影响,并基于高温渗碳目标提出了Nb微合金化的成分建议。     

V-N微合金化钢筋中钒的析出行为

研究了氮对含钒微合金化钢筋中钒的析出行为的影响。实验结果表明：低氮钒钢中,大部分钒固溶于铁素体基体,比例高达565,只有35．5％钒形成V（C,N）;高氮钒钢中,70％的钒析出形成V（C,N）,只有20％的钒因溶于基体,钢氮还减小了V（C,N）颗粒尺寸,明显增加细小V（C,N）析出相的体积分数。     

Precipitation and Recrystallization in Some Vanadium and Vanadium-Niobium Microalloyed Steels

Static precipitation and recrystallization following hot compression of austenite and the interactions between the two processes have been studied in a set of aluminum-killed HSLA steels containing 0.1 pct carbon, [0.016 - 0.026] pct nitrogen and 0.1 or 0.2 pct vanadium. Two steels containing both vanadium (0.1 and 0.2 pct) and niobium (0.03 pct) were included for purposes of comparison. The compression and the static tests were all carried out isothermally at temperatures between 800 and 900 °C. The course of recrystallization was followed by measurements of the rate of softening and by optical metallography of specimens quenched from the test temperature after different times. Precipitation was studied by measurements of the rate of hardening, by transmission electron microscopy of thin foils, carbon and aluminum extraction replicas, and by X-ray dispersion and energy-loss spectroscopy from individual precipitates. The temperature of the nose of theC-curve for precipitation in vanadium steels is much lower than that in niobium steels, as is the temperature, T_R, below which no recrystallization occurs in short times. Precipitation occurs both at austenite grain boundaries and in the grains (matrix precipitation). The former starts early and the precipitates grow rapidly to an approximately constant size; the matrix precipitates grow more slowly and are responsible for the observed hardening of the austenite. The relevance of various models proposed for the retardation and arrest of recrystallization of austenite are discussed. In the steels containing vanadium and niobium the precipitates contain both heavy elements: (V,Nb) (C,N). The Nb/V ratio in the matrix precipitates is different than in the parent austenite. The grain-boundary precipitates, however, contain the same Nb/V ratio as the parent austenite. The rate of hardening exhibits a reverseC-curve behavior, being more rapid than in the corresponding vanadium steels at higher temperatures and about the same at lower temperatures. Formerly Research Associate at MIT     

Influence of nitrogen on hot ductility of steels and its relationship to problem of transverse cracking

Abstract

The present review examines the influence of nitrogen on the hot ductility of steels, with particular relevance to the problem of transverse cracking during continuous casting. Nitrogen itself is not detrimental to hot ductility, but when it is present with aluminium or microalloying additions, ductility can be adversely affected through the formation of nitrides or carbonitrides. The addition of aluminium to low nitrogen C–Mn steels (0·005%N)impairs ductility during casting at an acid soluble level as low as 0·02%Al. This arises because segregation of aluminium to the grain boundaries occurs on solidification, and the temperature cycling that takes place when the strand is cooled encourages AlN precipitation. However, for low nitrogen, high strength low alloy (HSLA) steels with carbon levels in the peritectic range 0·08–0·17%C, transverse cracking is not generally encountered until the aluminium level is >0·04%. Higher nitrogen levels are likely to cause problems even at very low aluminium levels, as precipitation of AlN is controlled by the product of the aluminium and nitrogen contents. The microalloying additions vanadium and niobium are detrimental to ductility but, of the two elements, niobium is more damaging, as it gives finer precipitation. Increasing the nitrogen level has a more pronounced influence on ductility in vanadium containing steels, since vanadium forms a nitride while niobium forms Nb (CN), which is mainly carbon based. Nevertheless, the product of vanadium and nitrogen contents has to approach 1·2 × 10^-3, for example 0·1%V and 0·012%N, before ductility deteriorates to that normally given by a niobium containing steel with 0·03%Nb and 0·005%N. When small titanium additions are made to low nitrogen C–Mn–Al steels (0·005%N), the best ductility is likely to be given by a high Ti/N ratio of 4–5 : 1; the excess titanium in solution encourages growth of the TiN particles. For high nitrogen steels (0·01%N), a low titanium level (0·01%)is recommended to limit the volume fraction of TiN particles. A low soluble aluminium level is also needed to prevent the excess nitrogen from combining to form AlN. For C–Mn–Nb–Al steels, similar recommendations can be made with regard to adding titanium. However, the presence of niobium and aluminium appears to have little influence on ductility, since these elements coarsen the titanium containing precipitates.     

钒氮微合金化技术在HSLA钢中的应用

含钒钢中增氮，促进了碳氧化钒的析出，增强了钒的沉淀强化作用，大幅度提高钢的强度。因此，氮是含钒钢一种经济有效的合金化元素。通过充分利用廉价的氮元素，钒氮微合金化钢在保证相同的强度水平下，可节约钒的用量，降低钢的成本。V－N微合金化技术在高强度钢筋、结构钢板带及型钢、无缝钢管、非调质钢、高碳钢钱棒材以及高速工具钢等产品中获得了广泛应用。