Effect of Zr-Ti combined deoxidation on impact toughness of coarse-grained heat-affected zone with high heat input welding

In this study, the effects of Zr-Ti combined deoxidation and AI deoxidation on the impact toughness of coarse- grained heat-affected zone in high-strength low-alloy steels were investigated. More fine oxides were formed in the Zr-Ti-killed steel than in Al-killed steel. It was also found that more acicular ferrite grains were formed in the coarse-grained heat-affected zone in the Zr-Ti-killed steel than in Al-killed steel. The impact toughness of coarse-grained heat-affected zone of Zr-Ti-kiUed steel was higher than that of Al-killed steel. The good impact toughness was attributable to the pinning effect of fine oxides and the formation of acicular ferrite grains on fine oxides.

Probing microstructural evolution in weld metals subjected to varied CaF_(2)-TiO_(2) flux cored wires under high heat input electro-gas welding

Fused CaF_(2)-TiO_(2) fluxes have been designed,prepared,and applied in the flux cored wires to join EH36 shipbuilding steels under high heat input electro-gas welding.Ensuing microstructural evolution in the weld metals subjected to varied CaF_(2)-TiO_(2) flux cored wires has been fully documented.It has been demonstrated that as the content of TiO2 in the fused fluxes increases,columnar grain size increases,and major constituents in the weld metal change from lath bainite,to granular bainite,and then to acicular ferrite.Such phenomena are elucidated via salient chemical reactions involving oxygen pickup and concurrent titanium transfer.

Heterogeneous Microstructure-Induced Mechanical Responses in Various Sub-Zones of EH420 Shipbuilding Steel Welded Joint Under High Heat Input Electro-Gas Welding

Heterogeneous microstructure-induced mechanical responses in EH420 shipbuilding steel welded joint by electro-gas welding processed have been systematically studied by scanning electron microscopy,electron backscatter diffraction and mechanical testing.Comparing with the coarse-grained heat-affected zone(CGHAZ),the weld metal presents higher toughness(129.3 J vs.37.3 J)as it contains a large number of acicular ferrites with high-angle grain boundaries(frequency 79.2%)and special grain boundary∑3(frequency 55.3%).Moreover,coarse austenite grains in CGHAZ and slender martensite–austenite constituents between bainite laths may likely facilitate crack propagation.Polygonal ferrites and tempered pearlites formed at the junction of the fine-grained heat-affected zone and the intercritical heat-affected zone induced a softened zone with an average hardness of 185 HV0.5,which is the main reason for the occurrence of tensile fracture.

On the heterogeneous microstructure development in the welded joint of 12MnNiVR pressure vessel steel subjected to high heat input electrogas welding

Microstructure features of 12 MnNiVR pressure vessel steel welded joint deposited by the high heat input electrogas welding have been systematically investigated. It is revealed that the welded joint is featured by a heterogeneous juxtaposition. The coarse grained heat-affected zone(CGHAZ) primarily consists of lath bainites and minor granular bainites. The fine grained heat-affected zone(FGHAZ) is dominated by polygonal ferrites, pearlites, and fine cementite particles. Moreover, electron backscatter diffraction results further demonstrate that the CGHAZ is populated by coarse prior austenite grains(PAGs) with high frequency(61.3%) of low angle grain boundaries(LAGBs). On the other hand, the FGHAZ is filled with fine PAGs with a lower frequency(19.6%) of LAGBs. Such microstructural differences may likely contribute to differed mechanical properties for samples tested at designed positions.

工业试验Mg脱氧HSLA钢CGHAZ的夹杂物、组织及韧性的特征分析

Mg作为第三代氧化物冶金技术的关键脱氧剂有助于提升高强度低合金钢(HSLA)的组织韧性。利用夹杂物自动分析系统、金相显微镜、焊接热模拟试验机等研究了Mg脱氧对HSLA钢粗晶热影响区(CGHAZ)夹杂物、组织以及低温冲击韧性的影响。结果表明,在200 kJ/cm的大线能量焊接条件下,Mg脱氧钢CGHAZ中生成了大量Mg-Ti-Mn-S夹杂物,由于这种类型的夹杂物可以促进针状铁素体(IAF)组织的形成,所以在200 kJ/cm大线能量焊接后,Mg脱氧钢CGHAZ低温冲击韧性优异,-20℃冲击功为204 J,断裂方式为韧性断裂。本研究成果可为提高大线能量焊接厚板钢组织性能提供理论与试验依据。

热输入对超高强钢焊接接头组织与性能的影响

采用不同的热输入对1500 MPa级超高强钢进行熔化极气体保护焊,并通过硬度分布试验和DIC拉伸试验分析焊接接头硬化区,对比粗晶热影响区(CGHAZ)的冲击韧性,结合金相观察分析热输入对接头脆化行为的影响。结果表明:两种热输入的显微组织类型一致,焊缝区域主要为贝氏体、针状铁素体和准多边形铁素体,CGHAZ区域主要由板条马氏体构成,形成脆化区,硬度高达550HV_(10)。当焊接热输入由29 kJ/cm提高至47 kJ/cm后,焊缝和CGHAZ的组织发生显著粗化,CGHAZ的冲击韧性严重恶化,由47 J降至19 J。焊接接头的软化区位于熔合线焊缝侧,大小热输入焊接接头均在焊缝位置断裂,抗拉强度分别为704 MPa和628 MPa,区别在于大热输入下应变集中在根焊和第二层的交界,而小热输入应变集中在中层焊道的熔合线内侧。

线能量对焊接热影响区HAZ韧性的影响研究

设计了一种新型大线能量焊接用钢,对其实施了不同线能量的焊接热模拟实验,结果表明,在大线能量焊接条件下,焊接热影响区(HAZ)中形成了相互交叉互锁的AF组织,该组织可以阻碍裂纹的扩展,提高HAZ的低温冲击韧性。

高强钢焊接接头优化方法研究现状

高强钢以出色的力学性能在焊接结构的应用量急剧增加,其焊接接头性能已逐步成为研究焦点。为了解决高强钢焊接易出现冷裂纹、热影响区软化脆化、低温冲击韧度不高等问题,获得高强钢焊接接头优良强韧匹配。在使用熔化极气体保护焊接工艺的基础上采用不同的高强钢焊接接头优化方法,对严格控制热输入、焊前预热并控制热输入和研发并采用药芯焊丝这3种焊接接头优化方法进行分析总结,对3种优化方法下的焊接接头微观组织及力学性能进行分析,发现通过这3种接头优化方法可避免焊接接头产生裂纹、获得良好的韧性组织和力学性能优良的焊接接头。

Excellent heat affected zone toughness technology improved by strong deoxidizers

Excellent heat affected zone(HAZ)toughness technology improved by strong deoxidizers(ETISI)technology has been developed by Baosteel.In the deoxidation process of molten steel by adding strong deoxidizers,the formation of micrometer inclusions and nano-meter precipitates in steel plates can be effectively controlled by a precise control of oxygen concentration.In the welding process with a high-heat input,the formation of acicular ferrite can be selectively promoted with the aid of the micrometer inclusions;the growth of γ grains can also be selectively restrained by the pinning effect of the nano-meter precipitates.After welding with a high-heat input of 400 kJ/cm,excellent HAZ toughness can be obtained in the steel plates with both of the above microstructures,and the average absorbed energy is greater than 200 J for the V-notch Charpy impact test at-20℃.

460 MPa级高强韧海工钢板的焊接工艺研究

对460 MPa级高强韧海工钢板进行埋弧焊、垂直气电立焊试验。结果表明,460 MPa级高强韧海工钢在热输入为50、80和200 kJ/cm的条件下焊接,焊接接头的拉伸性能和冲击性能良好,满足船级社要求,说明该钢焊接性良好,适合大热输入焊接。

METAL INERT GAS WELDING OF 2519-T87 HIGH STRENGTH ALUMINUM ALLOY

20 mm thick plates of 2519-T87 high strength aluminum alloy have been welded.The effects of the compositions of filler wires,the heat input and the compositions of shielding gas on the mechanical properties and microstructure of the welded joint have been investigated.The results indicate that finer microstructure,better mechanical properties and higher value of hardness of HAZ can be obtained by using lower heat input.The use of Ar/He mixed shielding gas has several advantages over pure Ar shielding gas.With the increase of the proportion of He in the mixed shielding gas, the grain size of the weld metal as well as porosity susceptibility decreases.When the volume ratio of He to Ar reaches 7：3,the porosity and the grain size of weld metal reach the minimum,and the porosity can be further reduced by filling some CO2.

12MnNiVR钢板大热输入焊接接头组织与性能

采用12MnNiVR钢建造的10万m 3及以上原油储罐的纵缝焊接多采用气电立焊,大热输入对接头组织和性能有重要影响。对采用大热输入气电立焊的12MnNiVR钢板进行焊接试验,分析了焊接接头的微观组织和力学性能,重点研究了焊接接头的冲击韧性。研究结果表明:在大热输入焊接下,焊缝组织为大量针状铁素体,粗晶区为侧板条铁素体,粗晶区和细晶区之间有明显的过渡区域,细晶区为细小铁素体与珠光体,不完全重结晶区为粗大块状铁素体和珠光体。热影响区显微硬度由熔合线侧到母材侧表现出先增大、后减小、再增大的规律,最小值为177HV10。拉伸和弯曲性能优良;焊接接头在-20℃下的冲击吸收能量均大于80 J;由于熔合线处的侧板条铁素体晶粒粗大,熔合线冲击吸收能量较低为84 J,断口形貌为准解理形貌特征。

1000 MPa级高强钢埋弧焊熔敷金属组织及性能

针对水电用1000 MPa级高强钢设计了一种埋弧焊用焊丝、焊剂。借助JMat Pro软件对熔敷金属的组织和力学性能进行模拟,并通过拉伸试验、冲击试验、OM,SEM,EDS等手段对其进行评价。研究了熔敷金属成分和焊接热输入对熔敷金属组织及力学性能的影响。试验结果表明,研制的焊材焊接工艺性优良,通过控制合金元素含量使熔敷金属力学性能远高于标准值;重点分析了Cr含量对熔敷金属组织和力学性能的影响,熔敷金属中少量的Cr元素会提高针状铁素体含量,Cr元素含量较高时,会增加贝氏体含量,使熔敷金属强度不断提高,冲击韧性先提高后降低;随着焊接热输入的升高,熔敷金属中针状铁素体含量不断减少,先共析铁素体含量提高,组织粗化,熔敷金属强韧性不断降低。

大线能量钢焊接技术研究现状

大线能量用钢是一种微合金化钢,供货态多为正火或控轧控冷。目前390 MPa级别大线能量钢已在造船以及海洋工程中广泛应用。归纳了大线能量用钢在典型焊接热循环下的粗晶区分布特征,并对当前已有的应用于大线能量钢的焊接技术进行了总结。考察了常见的埋弧焊、气电立焊及窄间隙MAG焊条件下,大线能量钢焊接接头的力学性能。

MAG焊过程中热输入对DL510超高强钢焊接接头组织及力学性能的影响

采用熔化极活性气体保护电弧焊(MAG焊)焊接5 mm厚的DL510超高强钢(1 500 MPa级),研究了热输入量对焊接接头组织及力学性能的影响,并采用边焊边锤击的方式消除焊接接头残余应力。结果表明,热输入在43~70 kJ/cm范围内,均能获得成型良好的焊接接头;锤击时间低于20 min时,随着锤击时间延长,接头抗拉强度不断提升,但锤击时间超过20 min后,焊接接头抗拉强度变化不大;随着热输入增加,焊接接头晶粒明显长大;热输入为70 kJ/cm时,粗晶区出现少量细小粒状贝氏体组织,焊接接头韧性得到改善。

热输入对800 MPa级HSLA钢焊接接头组织及性能的影响

采用光学显微镜(OM)、扫描电子显微镜(SEM)、电子背散射衍射(EBSD)、拉伸和冲击等试验方法,研究不同热输入(14~20 kJ/cm)对18 mm厚800 MPa级低合金高强(HSLA)钢熔化极气体保护焊接接头组织和力学性能的影响。结果表明:不同热输入下的焊缝金属显微组织主要以贝氏体和马氏体的混合组织为主,粗晶热影响区组织主要由板条马氏体和联合贝氏体组成。随着热输入增大,粒状贝氏体占比增多,板条块亚结构由平行分布的细长条状向粗大块状转变,焊缝金属的冲击韧性先升后降。当热输入为17 kJ/cm时,焊缝金属显微组织中的短条状板条贝氏体、板条马氏体和细小的粒状贝氏体相互交织且分布均匀,使得焊缝金属韧性高,且分散度较小。在14~20 kJ/cm热输入条件下,焊缝金属、熔合线处、热影响区的-50℃冲击吸收功最低值分别为105、190、166 J;焊缝金属与母材的抗拉强度相差不大,焊材与母材匹配性良好,都能获得强韧性匹配良好的焊接接头。

Ti-Ca处理对DH36钢板焊接热影响区组织性能影响的研究

利用热力学计算软件和扫描电镜分析Ti-Ca处理DH36钢的夹杂物特征,运用Thermecmaster-100kN热力模拟实验机模拟热输入250—400 kJ·cm^(-1)的焊接热循环,利用光学显微镜、扫描电镜和激光共聚焦显微镜分析焊接热影响区的显微组织,利用冲击试验机测试了低温韧性。结果表明:DH36钢中的典型夹杂物为Al2O3,还存在Al-Ca-Ti-O-Mn-S复合夹杂物,该夹杂物可有效地抑制高温下的奥氏体晶界迁移,促进晶内针状铁素体形成;热输入为250—400 kJ·cm^(-1)时,热影响区的显微组织由针状铁素体、珠光体和铁素体组成,随着热输入的增大,珠光体和铁素体含量随之增多;在1/2厚度位置模拟250—400 kJ·cm^(-1)热输入时,在-20℃下热影响区的冲击韧性均能充分满足国家规定的行业使用标准要求。

1100 MPa级重型机械超高强吊臂钢焊接性能研究

通过Gleeble-3800试验机进行焊接过程热模拟,得出了Q1100D钢冷却过程中的CCT曲线。采用斜Y坡口焊接冷裂纹试验、金相分析和力学性能测试等方法,对不同热输入下焊接接头组织与性能进行了检测,结果表明包钢Q1100D重型机械超高强吊臂钢具有较好的抗冷裂性能。小热输入条件下可以实现室温下不预热焊接;较大热输入条件下,表面和断面未见冷裂纹,说明Q1100D钢板具有较好的抗冷裂性能。接头综合力学性能与组织性能评价结果表明,14 mm厚Q1100D钢板在1.05 kJ/mm的热输入下,焊接接头力学性能(拉伸、弯曲、冲击)处于最优状态。

线能量对超高强度海工钢热影响区组织演变与韧性的影响

研究了超高强度海工钢在不同线能量的模拟焊接条件下粗晶热影响区的组织演变和冲击韧性,并结合超高温激光扫描共聚焦显微镜原位观察模拟焊接热循环过程中奥氏体晶粒长大及贝氏体转变行为。结果表明:随着线能量的逐步增大,高温阶段停留时间变长使得粗晶热影响区原奥氏体晶粒粗大,中温阶段冷却速度下降促使粗晶热影响区贝氏体转变时变体选择减少,导致大角度晶界减少和对裂纹扩展的阻碍能力减弱,最终低温冲击韧性呈现下降趋势,断裂特征由韧性断裂转变为解理断裂。

Microstructure Characterization of High-heat-input Welding Joint of HSLA Steel Plate for Oil Storage Construction

In this paper, microstructure and mechanical properties of welding metals in 610 MPa high strength low alloy （HSLA） were studied after high-heat-input welding. Both the base material and the weld joint proved excellent strength and toughness by vibratory electrogas arc （VEGA） welding under 90 to 100 kJ/cm heatinput. The heat-affected zone （HAZ） was comprised of fine-grain zone （FGZ） and coarse-grain zone （CGZ）, which characterizes fine granular structure and lathing-bainite substructure, It has found that large quantity of dispersed TiN and M23E6 precipitates restrain structure growing in HAZ and strengthen the weldment together with dislocations in the welded joint.