Microstructure and fracture toughness of electron beam welded joints of 30CrMnSiNi2A steel

Two post-weld heat-treatments ( PWHT) , 900℃ oil quenched and low temperature tempered (PWHTA) and high temperature tempered and then 900~C oil quenched and low temperature tempered ( PWHTB ) , are employed to treat the weldment. Then the effect of two post-weld heat-treatment processes on the microstructure, mechanical properties and fiacture toughness of electron beam welded joints of 30CrMnSiNt‘2A steel have been discussed. The results show that, after two kinds of PWHT the microstructure and hardness at every zones of EBW joints are nearly same. Although the welds have good mechanical properties, fiacture toughness of both weld and heat-affected zone (HAZ) is low, the CTOD values of welds are comparatively higher than that of HAZ. Microstructure and fiacture toughness of two EBW joints have no evident differences.     

Effect of interpass temperature on microstructure,impact toughness and fatigue crack propagation in joints welded using the GTAW process on steel ASTM A743-CA6NM

Mainly due to their great toughness, martensitic stainless steels are used for manufacturing hydraulic turbines. However, these steels have some restrictions regarding regions recovered by welding, mainly due to the formation of non-quenched martensite, which causes a reduction in toughness. Considering repair of hydraulic turbines, there is a great interest in developing welding procedures that increase impact toughness and avoid post-welding heat treatment (TTPS). This study aims to analyse the influence of interpass temperature on microstructure, impact toughness and fatigue crack propagation in multipass welded joints on martensitic stainless steel CA6NM, using AWS410NiMo filler metal and the gas tungsten arc welding (GTAW) process. In the sample with interpass temperature of 80°C, influence of the interpass temperature on the formation of ferrite δ, with intragranular formation in the two-phase δ field, was observed, while in the sample welded at 150°C, the formation of ferrite δδ occurred mainly in the single-phase field. The change in the formation of ferrite δ, with the low interpass temperature, promoted an increase in impact toughness and a decrease in the fatigue crack propagation when compared with the sample welded with a higher interpass temperature. The results obtained indicate that the TIG process is an excellent alternative for the repair of CA6NM steel, with a significant influence from the interpass temperature.     

Microstructures and Mechanical Properties of 12Cr1MoVG Tube Welded Joints With/Without Post-weld Heat Treatment

Small-caliber, thick-wall 12Cr1MoVG seamless steel tube welded joints were fabricated in this study by gas tungsten arc welding and shielded metal arc welding techniques, then the microstructures, mechanical properties, and residual stress distributions of the joints with or without post-weld heat treatment (PWHT) were compared. The welded joints are mainly composed of bcc ferrite (F), Fe₃C, and M₇C₃ carbides. PWHT did not cause an apparent microstructure evolution in the joints, but promoted granular pearlite decomposition and growth of F grains and carbides, therefore decreasing the yield, tensile strength, and hardness while increasing the impact toughness and elongation of the welded joints. PWHT also released the circumferential residual stress and altered the stress state in the joint from tensile to compressive. Although the mechanical properties and bending performance of the small-caliber, thick-wall 12Cr1MoVG seamless welded joints without PWHT are acceptable, our results show that the joints with PWHT are more reliable.     

Dynamic fracture toughness (JId) behavior of armor-grade Q&T steel weldments: Effect of weld metal composition and microstructure

Austenitic stainless steel, low hydrogen ferritic steel and high nickel steel consumables are used for the welding of armor-grade quenched and tempered (Q&T) steels. The use of such consumables in the welding of armorgrade Q&T steel leads to the formation of distinct microstructures in the respective welds and has a major influence on the dynamic fracture toughness. Hence, this paper examines how shielded metal arc welding consumables affect the dynamic fracture toughness (J_1d) of armor-grade Q&T steel joints. The J_1d values of joints fabricated with high nickel steel joints are superior than all other joints.     

Mathematical modelling of mechanical properties of quenched and tempered steel

Abstract

New mathematical expressions for the prediction of hardness, yield strength and Charpy-V notch toughness of quenched and tempered steel were established. Quenched and tempered steel’s hardness is predicted based on as quenched hardness of steel. In the relation to hardness between quenched and tempered steel and as quenched steel, the hardenability of steel is taken in account. The mathematical model of hardness of steel is similar to the relationship established by Just. Yield strength and Charpy-V notch toughness of steel are predicted using the hardness of the quenched and tempered steel. Charpy-V notch toughness of cast steel is predicted using the Charpy-V notch toughness of steel with a same chemical composition. The mathematical expressions established were applied in computer simulation of mechanical properties of shafts made of quenched and tempered steel which the very well known relationship between hardness of as quenched steel and characteristic cooling time from 800 to 500°C (t_8/5) during the quenching is used.     

聚变堆用CLAM钢激光焊接接头显微组织及性能

对聚变堆用CLAM钢进行了激光焊接试验,并对接头进行740℃/1 h焊后回火处理,分别对热处理前、后接头的显微组织及性能进行了研究.结果表明,获得了成形良好、无缺陷的焊接接头;焊态下,焊缝由淬硬的板条马氏体和大量的δ铁素体组织组成.完全淬火区由板条马氏体和极少量的δ铁素体组成,其硬度高达545 HV;焊后热处理使焊缝及完全淬火区的板条马氏体分别转变为碳化物弥散分布的回火马氏体和回火索氏体组织.显著降低了接头的淬硬程度,最大硬度仅比母材高约15%;焊后回火热处理前、后接头的抗拉强度均高于基体母材,虽然焊后热处理使接头强度有所降低,但仍达到原始母材的98%以上.     

Effect of tempering on the toughness of a Cr- Mo bainitic steel

The effect of tempering on impact and fracture toughness properties of a Cr-Mo bainitic steel was studied in the quenched and stress relieved (Q & SR) condition. The lowest tempering parameter used resulted in considerable improvement in impact properties. Further tempering increased the upper shelf energy, had a minor effect on the transition temperature, and increased both the initiation fracture toughness (J_IC) and the tearing modulus(T). However, the effect on J_IC andT was much greater than the effect on the impact upper shelf energy. The results were discussed in light of the changes in microstructure and flow properties due to tempering.     

焊后热处理对31CrMoV9钢电子束焊接接头组织及性能的影响

研究了31CrMoV9钢电子束焊接接头在焊后去应力退火、焊后调质两种不同焊后热处理状态下的焊缝组织与性能,并与同等强度等级下的母材组织与性能进行了对比研究。结果表明,接头焊后组织为板条马氏体及少量残留奥氏体;焊缝经调质处理后,组织为相对均匀的回火索氏体,接头力学性能与母材相当,相比于焊后去应力退火处理,焊缝冲击性能大幅提高。两种类型的焊后热处理均未消除焊缝柱状枝晶等凝固组织形态,但焊后调质工艺可减轻焊缝柱状枝晶组织偏析,并使之细化,使得焊缝与母材的组织与硬度更加均匀;焊后经多次重复淬火,焊缝经检测均未见裂纹,说明焊后采用调质工艺可行,这为提高焊缝冲击性能提供了可行工艺路线。     

Influence of post-weld heat treatment (PWHT) on the structure and properties of welded joints of chromium–nickel stainless steel with soft martensite

This paper reviews the results of investigations on how post-weld heat treatment (PWHT) influences the hardness and microstructures of welded joints in stainless steel X3Cr-NiMo 13-4. It is known that welding leads to high segregation of components in the solidification process, which has an influence on phase transitions in PWHT. The investigated steel has a very narrow PWHT range, about 600–620°C, which provides optimum levels of hardness and toughness. Excessive annealing temperature leads to decreased toughness, which in turn causes exceeding of the A_c1 temperature in the segregation range, which then leads to increased ‘fresh’ martensite content.     

Fatigue crack propagation in structural steel after flash welding

The study was carried out to evaluate the effect of the tempered martensite fraction in the fatigue behaviour of type R4 structural steel as used, quenched and tempered, in the manufacture of chains for offshore mooring systems. As the manufacturing process for these uses flash welding, the study also includes welded joints of the same steel. Different fractions of martensite were achieved by means of variations in the austenitization temperature of the material and the fatigue resistance of the tempered test pieces was evaluated by means of the kinetics of crack growth of crack under cyclic loading at a constant amplitude. The results indicated that an increase in the amount of ferrite was associated with an increase in the number of cycles to material failure, and for the same microstructural condition, the fatigue life of the welded joint was always lower than that of the base material. Finally, the fatigue behaviour of the test pieces is presented and discussed on the basis of the mechanical properties and toughness of the material.     

热处理工艺对0Cr13Ni5Mo钢焊接接头组织和性能的影响

对马氏体不锈钢0Cr13Ni5Mo焊接接头经过1000℃油淬后,分别进行了600℃,620℃+600℃,400℃回火。通过显微组织分析、拉伸试验、冲击试验和硬度检测对3种焊接接头的组织和力学性能进行了研究。结果表明,3种焊接接头中焊缝组织粗大,硬度最高;焊接接头的韧性低于相应热处理状态下母材的韧性;随着回火温度的降低,韧性下降,强度提高。二次回火比一次回火组织更加细小,强度和韧性更好;620℃+600℃二次回火后焊接接头具有比较理想的综合力学性能。     

焊后热处理对DQTHT80钢热影响区断裂韧性的影响

研究了直接淬火回火调质钢ＤＱＴＨＴ８０多层焊热影响我的ＣＴＯＤ断裂韧性。焊态和焊后热处理状态下的试验结果表明：焊态下热影响区断裂韧性高于焊后热处理态。焊后热处理降低了该钢热影响区的断裂韧性。焊态下断口韧窝状,而焊后热处理断口叶解理状。模拟焊接热影响区粗晶区试验结果进一步证实了焊后热处理对韧性的不利影响。     

低碳调质铸钢焊接接头焊后消应力处理研究

介绍了G10MnMoV6-3和S355J2的焊接接头分别进行焊后消应力处理和不进行焊后消应力处理的各项力学性能对比.经比较分析,焊后消应力处理后各项力学性能数值变化均在4％以内.从经济性角度考虑,得出低碳调质铸钢焊接接头可不进行焊后消应力退火处理.     

Fracture toughness properties of high-strength martensitic steel within a wide hardness range

Fracture toughness tests were carried out on six grades of high-strength martensitic steel within the hardness range from 270 to 475 HB. Four types of tests were performed: (a) Charpy V-notch (CVN) impact over the temperature range −120 to 60 °C, (b) plane strain fracture toughness, K _IC , near the onset of crack growth, (c) fracture toughness, J _IC , near the initiation of slow crack growth, and (d) fracture toughness, J _iC , and crack tip opening displacement (CTOD _iC ) at the onset of slow crack growth using direct current potential drop (DCPD) technique. Further, true plane strain fracture toughness, K _o , at the onset of crack initiation was determined. Fracture toughness behavior including the measured and determined values of CVN, K _IC , K _o , J _IC , K _iC , and CTOD _iC have been interrelated over the entire hardness range using the various analytical and empirical correlations reported in the literature. The results indicate that the steel acquires the optimum fracture toughness properties at a hardness of 305 HB, corresponding to a tempering temperature of 630 °C. Further, the steel exhibits a slight 300 °C temper embrittlement phenomenon.     

Toughness evaluation of a shielded metal arc carbon-manganese steel welded joint subjected to multiple post weld heat treatment

This study was part of a program to investigate the influence of multiple post weld heat treatment (PWHT) on the fracture toughness and defect tolerance of a welded joint. The present work reports base metal data obtained for a quenched and tempered BS7191 Grade 450EM steel (0.10wt%C–1.08wt%Mn), weld metal data for a ferritic multipass weld obtained by shielded metal arc welding using an AWS E9018M type electrode, and heat affected zone (HAZ) data obtained using a modified bead on groove technique for different PWHT conditions. The effect of the repeated heat treatment cycles on the mechanical properties was evaluated by hardness tests and toughness testing assessed by Charpy V-notch and crack tip opening displacement (CTOD) techniques. The characterization of the microstructure was undertaken utilizing optical and electron microscopy. As fabrication codes for new equipment do not allow more than three PWHT cycles, the application of more cycles is only justifiable for old equipment when a fitness for purpose criterion is applied and these restrictions are not applicable. The results obtained are currently applied in repair work and revamps of pressure vessels and gas storage tanks.     

Slurry Erosive Wear Evaluation of HVOF-Spray Cr2O3 Coating on Some Turbine Steels

In this study, Cr₂O₃ coatings were deposited on CF8M and CA6NM turbine steels by high-velocity oxy-fuel (HVOF)-spray process and analyzed with regard to their performance under slurry erosion conditions. High Speed Erosion Test Rig was used for slurry erosion tests, and the effects of three parameters, namely, average particle size, speed (rpm), and slurry concentration on slurry erosion of these materials were investigated. SEM micrographs on the surface of samples, before and after slurry erosion tests, were taken to study the erosion mechanism. For the uncoated steels, CA6NM steel showed better erosion resistance in comparison with CF8M steel. The HVOF-sprayed Cr₂O₃-coated CF8M and CA6NM steels showed better slurry erosion resistance in comparison with their uncoated counterparts. It may be due to the higher hardness as a result of HVOF-sprayed Cr₂O₃ coating in comparison with the uncoated CF8M and CA6NM steels.     

Characterization of microstructure of HAZs in as-welded and service condition of P91 pipe weldments

Steels 9-12% Cr, having the high creep rupture strength are advocated for the modern low polluting thermal power plants. In the present investigation, the P91 pipe weldments have been characterized for microstructural responses in as-welded, post-weld heat treatment (PWHT) and ageing conditions. The PWHT of welded samples were carried out at 760 °C for time of 2 h and ageing at 760 °C for 720 h and 1440 h, respectively. The effect of time has been studied on precipitates size, distribution of precipitates and grain sizes present in various zones of P91 steel weldments. The impact toughness and hardness variation of heat affected zone (HAZ) have also been studied in as-welded condition as well as at different heat treatment condition. A significant change was observed in grain size and precipitates size after each heat treatment condition. The maximum impact toughness of HAZ was obtained after PWHT at 760 °C for 2 h. The main phase observed in weld fusion zone in as-welded, PWHT and ageing conditions were M₂₃C₆, MX, M₇C₃, Fe-rich M₃C and M₂C. The unwanted Z-phase (NbCrN) was also noticed in weld fusion zone after ageing of 1440 h.     

D406A钢焊接接头断裂韧度测试

根据英国标准BS7448断裂韧度试验标准,采用多试样法,测试了D406A超高强度钢焊接接头的J-R曲线.取尺寸为B(板厚)×2B、缺口方向为板厚方向、带预制疲劳裂纹的标准试样进行三点弯曲试验.测试试件焊缝和热影响区的载荷-施力点位移曲线,从而得到J积分.然后对数据点进行拟合得到J-R曲线,计算出J积分临界值,从而解决了由于板厚不足而无法直接测试焊接接头临界应力强度因子的问题,为固体火箭发动机壳体设计提供依据.     

用微型剪切试验研究WDL610焊接接头性能

采用微型剪切的试验方法对WDL610钢焊接接头进行了研究,绘制出强度梯度曲线和塑性梯度曲线,直观地显示出接头各个狭窄区域的性能和变化规律.尤其是调质钢焊接接头的软化区,其性能值和宽度严重影响接头的承载能力.     

Effect of groove shapes on mechanical properties of welded joints of ASTM4130 steel

The 30 mm thick ASTM4130 steel pipe was fabricated by gas tungsten arc welding and shielded metal arc welding under quenched and tempered conditions.Whereafier,the mechanical properties of welded joints of both V groove and combination double V groove were measured,while the microstructure feature and fracture morphology of both welded joints were investigated.Moreover,the effect of groove shapes on the properties of welded joints was explored.The results show that the welding efficiency of the combination double V groove joint is as two times as that of the V groove joint.But the hardness and toughness of the heat-affected zone (HAZ) with combination double V groove can not satisfy the requirements.Also,the coarse grain heat-affected zone (CGHAZ) of the cap layer is mainly composed of granular bainite,tempered manensite and a small amount of carbon-free bainite,and the fractured surface of the fusion line is entirely dominated by the quasi-cleavage mode.That the mechanical properties of the combination double V groove are lower than that of the V groove lie in the penetration ratio,welding heat input,and the areas and distribution feature of brittle zones.The combination double V groove is not suitable for the fabricating of ASTM4130 steel.