外场处理对低合金钢焊接接头组织和性能的影响

研究了电磁搅拌、氩弧表层处理、超声喷丸处理对低合金钢焊接接头组织和性能的影响。结果表明 :电磁搅拌促进奥氏体晶粒内针状铁素体生成和细化 ,使针状铁素体的含量由 85%提高到 92 % ,从而提高了焊缝金属的韧度。氩弧加热处理使焊缝表层发生熔化和重结晶 ,可消除焊缝表层的柱状晶 ,处理后的组织主要由针状和细晶铁素体组成。对接头焊趾部位进行氩弧快速重熔处理可消除焊趾部位的几何截面突变 ,使焊缝与母材圆滑过渡 ,有利于消除焊趾部位的应力集中 ,对抗应力腐蚀性能十分有益 ;焊趾部位热影响区中粗大的晶粒细化。表面高能喷丸处理使焊接接头表面层形成尺寸均匀的等轴状纳米晶 ,不仅提高了表层的硬度 ,而且可使焊接接头的疲劳强度提高 50 %。     

外场处理对低合金钢焊接接头组织的性能的影响

研究了电磁搅拌，氩弧表层处理，超声喷丸处理对低合金钢焊接接头组织和性能的影响，结果表明：电磁搅拌促进奥氏体晶粒内针状铁素体生成和细化，使针状铁素体的含量由85%提高到92%。从而提高了焊缝金属的韧度，氩弧加热处理使焊缝表层发生熔化和重结晶，可消除焊缝表层的柱状晶，处理后的组织主要由针状和细晶铁素体组成。对接头焊趾部位进行氩弧快速重熔处理可消除焊趾的部位的几何截面突变，使焊缝与母材圆滑过渡，有利于消除焊趾部位的应力集中，对抗应力腐蚀性能十分有益；焊趾部位热影响区中粗大的晶粒细化。表面高能喷丸处理使焊接接头表面形成尺寸均匀的等轴状纳米晶，不仅提高了表层的硬度，而且可使焊接接头的疲劳强度提高50%。     

电磁搅拌对管线钢埋弧焊熔敷金属低温韧性的影响

研究了电磁搅拌对管线钢埋弧焊熔敷金属低温韧性的影响。结果表明：电磁搅拌使０．２－０．６μｍ的夹杂物数量增加,促进了奥氏体晶粒内针状铁素体的生成和细化。使晶内铁素体含量由８５．１％提高到９１．７％,抑制了晶界铁素体和侧板条铁素体的形成,使熔敷金属的低温冲击性明显提高。     

低合金高强钢焊缝熔敷金属强韧化机理

向焊缝熔敷金属过渡微量的Ti-B和稀土元素,可以有效地抑制先共析铁素体的析出,使焊缝获得细小、均匀的针状铁素体组织.从而提高了焊缝的低温冲击韧性.通过透射电镜观察,发现焊缝中合金元素能形成细小、难溶的非金属夹杂物,成为针状铁素体的形核核心;Ti能形成细小、难溶而弥散分布的化合物(TiO)质点,对针状铁素体的形核更为有利.针状铁素体由许多亚结构组成,这相当于进一步细化了晶粒,是提高焊缝熔敷金属低温韧性微观原因.     

316L不锈钢搅拌摩擦焊与氩弧焊接接头组织性能比较

对316L不锈钢分别进行了搅拌摩擦焊接和钨极氩弧双面焊接,研究了不同焊接方法所得焊接接头组织性能的变化。结果表明:搅拌摩擦焊接过程中,由于焊缝金属受到了剧烈的机械搅拌和塑性变形促使母材粗大的晶粒破碎,组织晶粒明显细化;钨极氩弧焊接过程中,焊缝区域温度超过了焊件材料的熔点,整个焊接过程属于小熔池的凝固,焊缝呈现出典型的铸态组织。在焊接工艺参数选择合适的情况下,搅拌摩擦焊接接头的显微硬度与母材和钨极氩弧焊接接头相比显著提高。细晶强化作用对搅拌摩擦焊接接头显微硬度的提高起到了至关重要的作用。     

合金元素对高强管线钢埋弧焊缝组织性能的影响

通过对X80管线钢进行埋弧焊接试验,分析了合金元素Mn、Ni对高强度管线钢埋弧焊缝的显微组织和力学性能的影响.试验结果表明,当Mn元素含量过高时,焊缝金属的冷裂纹敏感指数提高,细化原奥氏体晶粒尺寸,对针状铁素体形核不利湘比较而言,Ni元素对焊缝的冷裂纹敏感指数影响较小,且使焊缝金属易于产生交滑移,更易保证焊缝针状铁素体含量,从而提高焊缝金属的韧性;另外,随着Mn、Ni元素含量的增加,焊缝金属中先共析铁素体受到抑制.     

低频磁场对轧辊埋弧堆焊组织及性能的影响

为提高堆焊层熔敷金属的力学性能,在轧辊埋弧堆焊过程中外加低频脉冲纵向磁场,通过对堆焊层硬度和显微组织的分析,研究了磁场参数对轧辊埋弧堆焊层金属组织及力学性能的影响规律。通过对不同磁场参数下堆焊表层试样的硬度及其组织的分析,发现低频脉冲纵向磁场的电磁搅拌作用能够影响晶粒的形核与长大过程,细化晶粒,提高堆焊层硬度,探讨了低频纵向磁场改善堆焊层金属的组织形态、细化晶粒和提高硬度的机理。结果表明:当磁场参数为Ip=300A,Ib=200A,f=5Hz时,焊缝组织细化最为明显,晶粒尺寸减小到30.1μm,硬度比不加磁场时提高了4.5HRC。外加低频纵向磁场通过电弧的旋转来搅拌熔池,改变晶粒的结晶过程,使焊缝晶粒得到细化,提高堆焊层硬度。     

低频磁场对轧辊埋弧堆焊组织及性能的影响

为提高堆焊层熔敷金属的力学性能,在轧辊埋弧堆焊过程中外加低频脉冲纵向磁场,通过对堆焊层硬度和显微组织的分析,研究了磁场参数对轧辊埋弧堆焊层金属组织及力学性能的影响规律。通过对不同磁场参数下堆焊表层试样的硬度及其组织的分析,发现低频脉冲纵向磁场的电磁搅拌作用能够影响晶粒的形核与长大过程,细化晶粒,提高堆焊层硬度,探讨了低频纵向磁场改善堆焊层金属的组织形态、细化晶粒、提高硬度的机理。试验结果表明：当磁场参数为I_p=300 A, I_b=200 A, f=5 Hz时,焊缝组织细化最为明显,晶粒尺寸减小到30.1 μm,硬度比不加磁场时提高了4.5 HRC。外加低频纵向磁场通过电弧的旋转来搅拌熔池,改变晶粒的结晶过程,使焊缝晶粒得到细化,从而提高堆焊层硬度。     

氩弧重熔对管线钢接头表层组织的影响

采用氩弧重熔单道和多道处理管线钢接头，不公使焊缝表层的柱状晶组织细化，而且使接头焊趾部位出现圆滑过渡，同时也细化了焊趾部位热影响区的粗大晶粒。接头表层组织的细化和焊趾部位的圆滑过渡都有利于提高管线钢接头的疲劳和腐蚀性能。     

低合金钢焊缝的针状铁素体微观组织

针对X70管线钢多道焊焊缝金属,利用Gleeble1500热模拟机进行了热模拟试验,对焊缝金属中初生针状铁素体组织及其与非金属夹杂物之间的关系以及经历二次热循环后感生形核的针状铁素体组织进行了SEM及TEM分析.结果表明,针状铁素体边界存在着一层富碳的薄膜,其长大既存在切变转变的特征,同时也伴随着C原子的扩散过程.共感生成的二次针状铁索体是在初生针状铁索体基体的高密度位错处形核并以一定的速度迅速长大到有限的尺寸.初生针状铁素体和共感形核针状铁素体都是在奥氏体晶内形核、长大,都具有细化奥氏体晶粒、提高多道焊焊缝金属和焊接热影响区韧性的作用.     

STUDY OF ELECTROMAGNETIC STIRRING REFINING MICRO-STRUCTURES OF PIPE-LINE STEEL SAW DEPOSITS

The effects of electromagnetic stirring on the microstructures of pipe-line steel SAW deposited metal were investigated. The results shouted that electromagnetic stirring increased the number density of inclusions with 0.2-0.6μm in diameter and promoted the formation and refining of acicular ferrite within austenite grains. The low tem-perature toughness of deposited metal was improved.     

Crystallographic analysis for acicular ferrite formation in low carbon steel weld metals

Inclusions contributing to acicular ferrite nucleation were investigated from a crystallographic point of view in low carbon low alloy steelweld metals. The samples from electro slag welding (ESW) and submerged arc welding (SAW) deposits with various cooling rates were prepared in this study. In those samples, intragranular acicular ferrite formation was observed from inclusions. The inclusions contributing to acicular ferrite formation were of multi-phase type consisting of amorphous phase, spinel type and MnS. They were surrounded by a Ti-enriched layer. It was confirmed by selected area diffraction patterns and energy-dispersive X-ray spectrometer analyses that the Ti-enriched layer was TiO. The acicular ferrite had a Baker–Nutting orientation relationship with the TiO layer on the inclusion surface. The misfit was 3.0% at the interface between the acicular ferrite and TiO. Therefore, it is considered that TiO on the inclusion surface contributes to the heterogeneous nucleation of acicular ferrite by small lattice misfit. However, themorphologies of ferrite growth which nucleated from inclusions were different in both samples. Whereas the growth of ferrites nucleated from TiO was enough in ESW, the size of nucleated ferrite in SAW was a few hundred millimetres in size. In the early stage of nucleation from TiO, ferrite had small deviation from Kurdjumov–Sachs orientation relationship (K–S relationship) in both ESW and SAW. However, there was a difference in the growth stage of ferrite. The ferrite orientations were gradually changed to fit to the K–S relationship in ESW. On the other hand, the nucleated ferrite in SAW stopped growing and the newly nucleated ferrite which had K–S relationship prior to austenite was formed adjacently because of large super cooling due to small heat input.     

In situ observation of the formation of intragranular acicular ferrite at non-metallic inclusions in C–Mn steel

Intragranular acicular ferrite is regarded as a most desirable microstructure feature, in view of its strength and toughness, both in weld metals and in the heat-affected zone. This paper systematically investigated the effect of Ti addition on the evolution of intragranular acicular ferrite in the heat-affected zone of C–Mn steel. We also systematically studied the effects of austenite grain size, alloy content and the characteristic of inclusions on the formation of intragranular acicular ferrite. The nucleation and growth of intragranular acicular ferrite was directly observed by laser scanning confocal microscopy. Subsequently, microscopy analysis was used to quantitatively determine and distinguish the potent and inactive inclusions with respect to the nucleation of intragranular acicular ferrite. Finally, some possible reasons are given to explain the formation of intragranular acicular ferrite in the C–Mn steel.     

Effect of Ti content and martensite–austenite constituents on microstructure and mechanical property

In this study, the relationship between impact toughness and microstructure in Cr–Mo–V multi-pass weld metals has been systematically investigated. The Charpy impact energy of two weld metals with various alloy elements increased remarkably. The primary cause of the change of impact toughness was attributed to the difference of acicular ferrite (AF) content and prior-austenite grain size, and the size and distribution of necklace martensite–austenite (M–A) constituents. With increasing Ti content, Ti-containing inclusions were increased, which resulted in an increased number of nucleation sites for AF, a change in the microstructure from allotriomorphic ferrite to AF, and refined ferrite grain size. In addition, smaller and more dispersive M–A constituents were observed in the weld metal with higher impact toughness.     

MICROSTRUCTURE AND INCLUSION CHARACTERIZATION IN THE SIMULATED COARSE-GRAIN HEAT AFFECTED ZONE WITH LARGE HEAT INPUT OF A Ti-Zr-MICROALLOYED HSLA STEEL

1. IntroductionA pplication oflargeheatinputw elding techniques, w hich have been developed forlarge engineer-ing structure, e.g., big oiland gas tanks, bridge, pipe-line and architecture constructions etc. usuallycausesdeterioration ofm echanicalproperti…     

MICROSTRUCTURE AND INCLUSION CHARACTERIZATION IN THE SIMULATED COARSE-GRAIN I-IEAT AFFECTED ZONE WITH LARGE HEAT INPUT OF A Ti-Zr-MICROALLOYED HSLA STEEL

The microstructure and the characteristics of the inclusions embedded in ferrite matrix in simulated coarse-grain heat affected zone (CGHAZ) of a Ti-Zr-treated high strength low alloy (HSLA) steel have been investigated. The microstructure of the simulated CGHAZ dominantly Consisted of intragranular acicular ferrite (IAF) combining with a small amount of polygonal ferrite (PF), widmanstiitten ferrite (WF), bainite ferrite (BF), pearlite and martensite-austenite (M-A) islands. The PF, WF and BF were generally observed at the prior austenite grain boundaries and the interlocking acicular ferrite was usually found intragranularly. It was found that the inclusions were composed of Ti2O3 ZrO2, Al2O3 locating at the center of the particles and MnS lying on the surface layer of the inclusions. The intragranular complex inclusions prorooted the acicular ferrite formation and the refinement of microstructure whilst those at prior austenite grain boundaries caused PF formation on the inclusions. The simulated CGHAZ consisting of such complicated microstructure exhibited desired mechanical properties.     

B元素对药芯焊丝焊缝金属针状铁素体形成的影响

利用金相组织观察、冲击试验和热膨胀试验,研究了B元素含量变化对高强钢药芯焊丝焊缝金属中针状铁素体形成的影响,得到了不同试验温度下焊缝金属冲击吸收功. 结合透射电镜分析和分级淬火试验从热力学和动力学的角度对B元素影响机理进行了分析. 结果表明,焊缝金属组织晶界中含有自由状态的B元素具有抑制晶界铁素体形核利于针状铁素体生成的作用;N元素含量增加会降低晶界B元素含量,并提高奥氏体向铁素体转变的温度,减少针状铁素体含量;针状铁素体是在以Ti元素和Mn元素的氧化物为核心,以Cu元素和Mn元素的硫化物为外层,以BN为过渡层的复杂结构上形核并长大的;针状铁素体含量的增加有利于提高焊缝金属冲击吸收功,–60 ℃冲击吸收功最大为70 J.     

Weldability of X100 linepipe

Abstract

Research has been carried out to identify weld metal compositions and microstructures capable of meeting high strength and toughness requirements for X100 seam welded linepipe. Single pass, multiwire submerged arc welds were made in experimental, high strength low alloy steel plates using consumables to give a wide range of weld metal alloying. Work has shown that the optimum strength and toughness are obtained in Mo–B–Ti alloyed weld metals with P _cm values between 0.218 and 0.250. Weld metal microstructures were almost fully acicular ferrite with an ultrafine grain size (1–2 µm). Dilatometric studies demonstrated that at typical weld cooling rates the optimised welds transformed at significantly lower temperatures than those reported for X65 plate deposits, which contain acicular ferrite in the form of idiomorphic primary ferrite and intragranular Widmanstätten ferrite. The maximum rate of transformation in the optimised welds occurred between 515 and 570°C, which indicates that the acicular ferrite in this case consisted of intragranular Widmanstätten ferrite and/or bainite. The ferrite would appear to have a fine plate morphology growing from large as well as small inclusions, but not very far before the onset of hard impingement, thereby ensuring an ultrafine grain size. Tensile strengths of 708–784 MPa were achieved with an 80 J Charpy impact transition temperature toughness between -68 and -115°C. More highly alloyed weld metals containing 2–3%Mn and 1.5%Si transformed at lower temperatures and showed increased strength, but there was a substantial loss of toughness, attributed to the relatively unimpeded growth of large ferrite plates from larger inclusions, and the replacement of ultrafine acicular ferrite between these plates by blocks of martensite–austenite. One pass per side, multiwire submerged arc welds manufactured to the optimum weld metal chemistry confirmed their applicability for thin section X100 linepipe.     

Acicular ferrite and bainite in C–Mn and low-alloy steel arc weld metals

Acicular ferrite is recognised as a desirable microstructural constituent in C–Mn and low-alloy steel weld metals. It is Widmanstätten ferrite that nucleates on the spheroidal non-metallic inclusions and grows by a reconstructive (diffusion-controlled) mechanism that proceeds substantially to completion. With increasing alloy content and/or cooling rate, the transformation to acicular ferrite may not be completed before the formation of bainite begins, the efficacy of inclusions in modern weld metal being such that colonies of bainite can nucleate on inclusions, forming by a displacive (shear) transformation mechanism, and producing colonies of similar size to acicular ferrite laths. Hence, in arc welds deposited with modern welding consumables, both acicular ferrite and intragranular bainite may form. As a consequence of the similarity in appearance of these two microstructural constituents in the optical microscope, some confusion in terminology has been introduced into the literature. This review seeks to eradicate this confusion.