Simulation of dissimilar weld joints of steel P91

Abstract

Results of computer simulations of long term service exposure for weldments of the CSN 15 128/P91 and SK3STC/P91 steels are presented and compared with corresponding results of phase and composition experiments. The welded material P91 (EU designation: X10CrMoVNb 9–1) represents progressive chromium steel alloyed with molybdenum, vanadium, carbon, and nitrogen. The CSN 15 128 (13CrMoV 2–5) material is low alloy Cr–Mo–V steel. The SK3STC alloy (12CrMo 10–10) represents the consumable electrode material. The stability of the weldment microstructure is investigated at elevated temperatures (500–700° C). The simulation method is based on the Calphad approach complemented with the theory of multicomponent bulk diffusion, local conditions of phase equilibrium, and the assumption that diffusion is the process that controls the rate of phase transformation. Significant phase profiles, concentration profiles, and phase transformation processes in the diffusion affected zone are simulated, investigated, and compared with experimental results. The potentially deleterious carbon depleted region inside each weld joint is discussed. The method described can be used to predict microstructure instability in weld joints.     

Solidification cracking in low alloy steel welds

Abstract

The high solidification cracking susceptibility of low C steel weld metals was investigated using pure Fe model alloys containing 0–0·23%C, 0–5%Ni and 0–0·0144%B. In addition, a few Fe–C–Ni ternary alloys were also tested. Solidification cracking susceptibility was tested using longitudinal varestraint and transvarestraint tests. Cracking was evaluated using crack length and brittleness temperature range criteria. The Fe–C alloys showed high cracking tendency in two regimes, the first in the ultralow carbon range of 0·03–0·05%C and the second in a narrow band close to 0·1%C. The cracking was much more than that attributable to solute segregation. In Fe–Ni and Fe–B alloys, cracking was a function of alloy content. Solidification cracking due to C and Ni was higher in the ferritic mode of solidification compared to the austenitic, unlike in stainless steels, where the ferritic mode provides high resistance to cracking. In Fe-C-Ni ternary alloys, cracking could be better related to composition in terms of a variable coefficient for C in the Ni equivalent. In the vicinity of 0·1%C, cracking was attributable to shrinkage due to solid state transformation from δ to γ in the brittle temperature range, and is similar to that occurring during continuous casting of steel. However, this factor did not appear to play a role in cracking in the ultralow C range of 0·03–0·05%C.     

Laser pressure welding of Al alloy and low C steel

Abstract

This study was performed to obtain fundamental knowledge concerning the development of laser pressure welding technology for the joining of dissimilar metals. Laser pressure welding of Al alloy A6061 and low C steel SPCC sheets was carried out to investigate the effects of the roller pressure, laser beam scanning speed and irradiation position on the tensile shear and peel strength of welded joints. The interfaces of the joints were observed and analysed by SEM and EDX, and the formation phases on the peeled surfaces were identified with XRD. It was revealed that prevention and suppression of oxidation during welding was extremely important to the production of a sound joint with good mechanical properties. The highest tensile strength and the highest peel strength of joints were obtained at a laser power of 1·8 kW, laser scanning speed of 30 Hz, laser irradiation position at the centreline, roller pressure of more than 245 MPa and welding speed of 0·5 m min^?1 in an Ar atmosphere. The fracture occurred not in the welded zone but in the A6061 base alloy specimen.     

Effect of solidification velocity on weld solidification process of alloy tool steel

Abstract

In order to clarify the effect of solidification velocity on the weld solidification process of alloy tool steel during the welding, the information about microstructure evolution was obtained by the concurrent experiments of liquid tin quenching and time resolved X-ray diffraction technique using intense synchrotron radiation. It was found from the experiments that the solidification mode was transferred from an FA to an A mode at the high solidification velocity. The effect of solidification velocity on the phase selection during solidification between the primary δ-ferrite and γ-austenite was theoretically proved by the Kurz, Giovanola and Trivedi (KGT) model. It is thus explained that the solidification cracking susceptibility of the weld metal of alloy tool steel was enhanced due to the δ to γ transition of the primary phase.     

Influences of post-weld heat treatment on fatigue crack growth behaviour of strength mismatched HSLA steel welds

Abstract

Welding of high strength low alloy steels (HSLA) involves usage of low, even and high strength filler materials (electrodes) compared with the parent material depending on the application of the welded structures and the availability of the filler material. In the present investigation, the influences of post-weld heat treatment (PWHT) on fatigue crack growth behaviour of under matched (UM), equal matched (EM) and over matched (OM) weld metals has been studied. The base material used in this investigation is HSLA-80 steel of weldable grade. The Shielded Metal Arc Welding (SMAW) process has been used to fabricate the single 'V' butt joints. Centre Cracked Tension (CCT) specimens have been used to evaluate the fatigue crack growth behaviour of the welded joints. Fatigue crack growth experiments have been conducted using servo hydraulic controlled fatigue testing machine at constant amplitude loading (R = 0). From this investigation, it has been found that the fatigue performance of over matched joints is superior compared to under matched and equal matched joints. Moreover, PWHT reduced the magnitude of the tensile residual stress field in the weld region and subsequently enhanced the fatigue performance of the joints irrespective of weld metal strength mismatch.     

Tom Bell Young Author Award Winner 2008 Influence of silicon on nitriding behaviour of hot work tool steels

Abstract

Hot work tool steels are widely used for pressure die casting moulds, die inserts, extrusion tools for aluminium processing and for steel forging. Nitriding increases the lifetime of such tools in many cases, yet delivers disappointing results in others. To optimise performance and for knowledge based surface design, it is indispensable to understand the mechanisms which occur in the near surface zone during nitriding. Nitrogen and carbon profiles obtained for X38CrMoV51 (AISI H13) steels with two silicon levels (1·1 and 0·3%), together with high resolution microscopy and electron energy loss spectroscopy, revealed that the secondary carbides are gradually transformed into nitrides during nitriding. Thermodynamic calculations confirmed the experimental observations. The near surface zone can be divided into three subzones: (1) a nitrogen enriched, almost carbon free zone with high nitride precipitation density and high hardness; (2) a nitrogen enriched and carbon depleted zone where the carbide–nitride transformation occurs; (3) a carbon enriched zone where the displaced carbon from zones 1 and 2 reprecipitates. A correlation between microstructure and microhardness and residual stress profiles was observed for all three zones. It was found that silicon, although not directly participating in the formation of nitrides, has a strong impact on the properties of the near surface zone by stabilising the secondary carbides and retarding the carbide–nitride transformation. This results in homogeneous precipitation in the transformation zone, thus avoiding micrometre sized precipitates which can act as defects and promote crack propagation. The conclusions of the present work are in accordance with literature studies on the effect of silicon on the tempering behaviour and the secondary carbide structure of 5%Cr martensitic steels.     

Interfacial structure and mechanical properties of hot roll bonded joints between titanium alloy and stainless steel using copper interlayer

Abstract

The hot roll bonding was carried out in vacuum condition between titanium alloy and stainless steel using copper interlayer. The stainless steel/Cu can not be bonded if the bonding temperature is lower than or equal to 730°C, and the Cu–Ti alloy can not be bonded if the bonding temperature is higher than or equal to 880°C. The testing results show that the total thickness of intermetallic layers at the interface between copper and titanium alloy increases with the bonding temperature, and the tensile strength of bonded joints decreases with increasing bonding temperature. The maximum strength of 343 MPa was obtained at the bonding temperature of 780°C, the reduction of 20% and the rolling speed of 38 mm s^–1.     

Effect of zinc plating of low carbon steel on corrosion resistance in cassava fluid environment

Abstract

This research work investigated the corrosion resistance of zinc plated low carbon steel in cassava fluid (i.e. containing hydrogen cyanide). It simulated the effect of continuous use of the material in a cyanide environment where corrosion products are left in place. Low carbon steel samples were zinc electroplated at voltages between 0˙5 and 0˙9 V for 5 to 20 min. The plated samples were then subjected to a cassava fluid environment for 30 days. The electrode potentials, in mV (SCE), were measured every day. Weight loss was determined at intervals of 5 days for duration of the exposure period. The result showed corrosion attack on the zinc plated steel, the severity increasing with increasing weight of zinc coating on substrate. The result showed that thinly plated low carbon steel did not have any advantage over unplated steel and were quickly stripped of their zinc plating with resultant corrosion of the underlying steel substrate. Heavily zinc plating steel was observed to offer some protection for the steel but not for a long time. The pH of the cassava solution which initially was acidic because of the cyanide content in the cassava was observed to progress to neutrality after 5 days and then became slightly alkaline at the end of the 30 days test (because of corrosion product contamination of the cyanide), contributing to the reduced corrosion rate. Unplated steel was found to be unsuitable for the fabrication of cassava processing machinery without some form of surface treatment, but unfortunately, zinc is not suitable as a protective coating in this environment.     

Friction welding of TiNi alloy to stainless steel using Ni interlayer

Abstract

Friction welding was carried out between TiNi alloy and austenitic stainless steel with and without a Ni interlayer. When TiNi alloy was welded to stainless steel without the Ni interlayer, a large amount of brittle Fe₂Ti intermetallic compound was formed at the weld interface. The formation of this brittle compound led to degradation of the joint strength. The Ni interlayer changed the microstructures at the weld interface and improved the joint strength. A fracture occurred at the interface between Ni and TiNi. The interface between Ni and TiNi was free from Fe₂Ti and consisted of mainly TiNi₃ and TiNi. After TiNi₃ was formed as the reaction layer, a eutectic reaction occurred between the TiNi₃ and TiNi base alloy. A reaction layer with a eutectic structure tends to form at the periphery, where the temperature would be higher than that of the central region.     

Induction welding and heat treatment of steel pipes: evolution of crystallographic texture detrimental to toughness

Abstract

Steel welding using induction heating to produce pipelines is found to have lower toughness at the weld junction than the base material, even after a heat treatment which reaustenitises the weld zone. Detailed crystallographic characterisation indicates that the poor toughness is due to the crystallographically coarse grains present after welding; the coarse scale is not visible using just optical microscopy. The post-weld heat treatment does not improve the situation at the weld junction, because the detrimental crystallographic characteristics are reproduced on cooling.     

Classic contributions: cryogenic treatment Effects of cryogenic treatments on mechanical properties and wear behaviour of high-speed steel M2

Abstract

In this contribution, originally published in 2000, the levels of hardness, impact toughness and wear resistance of M2 high-speed steel after conventional heat treatment are compared with those imparted by additional subzero and deep cryogenic processing.     

Prediction of burn-on and mould penetration in steel casting using simulation

Abstract

Burn-on and penetration defects in steel casting are principally caused by localised overheating of the sand mould or cores. Such overheating can cause liquid metal to compromise the mould surface and entrain onto the surface of the mould. A method has been developed to predict likely burn-on and penetration defect locations as part of a standard casting simulation. The method relies on determining, from simulation results, the locations where the mould is above a certain critical temperature. The critical temperature is generally above the temperature at which the steel is fully solidified. By measuring the time periods during which these locations in the mould are above the critical temperature, burn-on and penetration defects can be predicted. The method is validated through comparison with previous experimental data. Several parametric studies are conducted to investigate the sensitivity of the predictions to the choice of the critical temperature, the interfacial heat transfer coefficient between the steel and the mould, the pouring temperature, and the mould material. The results of one case study are presented where burn-on or penetration defects observed on a production steel casting are successfully predicted.     

Effect of post-weld heat treatment on joint properties of friction welded joint between brass and low carbon steel

Abstract

This paper describes the effect of post-weld heat treatment (PWHT) on joint properties of copper–zinc alloy (brass) and low carbon steel friction welded joints. The as-welded joint obtained 100% joint efficiency and the brass base metal fracture without cracking at the weld interface, and had no intermetallic compound layer. The joint efficiency with PWHT decreased with increasing heating temperature and its holding time, and its scatter increased with those increasing parameters. When the joint was heat treated at 823 K for 360 ks, it did not achieve 100% joint efficiency and fractured between the weld interface and the brass base metal although it had no intermetallic compound. The cracking at the peripheral portion of the weld interface was generated through PWHT. The cracking was due to the dezincification and the embrittlement of the brass side during PWHT.     

Joining phenomena and joint strength of friction welded joint between pure aluminium and low carbon steel

Abstract

This paper describes the joining phenomena and joint strength of friction welded joints between pure aluminium (P-Al) and low carbon steel friction welds. When the joint was made at a friction pressure of 30 MPa with a friction speed of 27·5 s^?1, the upsetting (deformation) occurred at the P-Al base metal. P-Al transferred to the half radius region of the weld interface on the low carbon steel side, and then it transferred toward the entire weld interface. When the joint was made at a friction time of 0·9 s, i.e. just after the initial peak of the friction torque, it had ～93% joint efficiency and fractured on the P-Al side. This joint had no intermetallic compound at the weld interface. Then, the joint efficiency slightly decreased with increasing friction time. The joint had a small amount of intermetallic compound at the peripheral region of the weld interface when it was made at a friction time of 2·0 s. When the joint was made at a friction time of 0·9 s, the joint efficiency decreased with increasing forge pressure, and all joints were fractured at the P-Al side. Although the joint by forge pressure of 90 MPa had hardly softened region, it had ～83% joint efficiency. To clarify the fact of decreasing joint efficiency, the tensile strength of the P-Al base metal at room temperature was investigated, and the tensile test was carried out after various compression stresses and temperatures. The tensile strength of the P-Al base metal has decreased with increasing compression stress at any temperature. Hence, the fact that the joint did not achieve 100% joint efficiency was due to the decrease in the tensile strength of the P-Al base metal by the Bauschinger effect. To obtain higher joint efficiency and fracture on the P-Al side, the joint should be made without higher forge pressure, and with the friction time at which the friction torque reaches the initial peak.     

Corrosion of reinforcing steel and low cycle fatigue behaviour

Chloride induced corrosion of reinforcing steel can be highly detrimental and of great influence on the low cycle fatigue (LCF) characteristics. An experimental study conducted on BSt500_s reinforcing steel, showed that the LCF and life expectancy were reduced considerably according to the level of corrosion. Low cycle strain controlled fatigue testing under ± 1 and ± 2.5% constant amplitude strain indicated that the corroded steel bars exhibit gradual reduction in available energy, number of cycles to failure and the load bearing ability. Formation of irregularities such as pits, notches and cavities occurred on the corroded steel surface and stress concentration points were developed which are highly localized at imperfections and especially at the rib bases. The experimental investigation of the corroded specimens subjected to LCF showed that the life expectancy, the remaining energy density and the strength properties were reduced considerably as a result of these irregularities combined with the mass loss and reduction of the exterior hard layer of martensite. Structural design capable of resisting seismic activity that does not account for the reduction of the load bearing ability and life expectancy as well as the cumulative plastic deformation of the steel reinforcement due to corrosion and loading history that a structure will be subjected in harsh climatic environments and ground oscillating motion could lead to serious and unpredictable performance.     

全自动石油钢管调质生产线

简要介绍了西安重型机械研究所与胜利石油管理局总机械厂开发研制的油井管淬火和回火处理生产线的工艺流程、设备组成及其特点 ,为进一步研制生产调质钢油井管的设备和工艺提供了宝贵的经验     

Effect of friction welding condition on joining phenomena and joint strength of friction welded joint between brass and low carbon steel

Abstract

This paper describes the effect of friction welding condition on joining phenomena and joint strength of friction welded joints between copper–zinc alloy (brass) and low carbon steel (LCS). When the joint was made at a friction pressure of 30 MPa with a friction speed of 27·5 s^?1, brass transferred to the half radius region of the weld interface on the LCS side. Then, transferred brass extended towards the almost whole weld interface with increasing friction time. The joint efficiency increased with increasing friction time, and then the joint obtained 100% and the brass base metal fracture when the joint was made with a friction time of 4·2 s or longer. However, the fact that all joints had some cracks at the periphery portion of the weld interface was due to a deficiency of transferred brass at the periphery portion on the weld interface of the LCS side. On the other hand, brass transferred to the peripheral region of the weld interface on the LCS side, and then transferred towards the entire weld interface when the joint was made at a friction pressure of 90 MPa with a friction speed of 27·5 s^?1. The joint efficiency increased with increasing friction time, and it reached 100% at a friction time of 1·5 s or longer. In addition, all joints fractured from the brass base metal with no cracking at the weld interface. To obtain 100% joint efficiency and the brass base metal fracture with no cracking at the weld interface, the joint should be made with opportune high friction pressure and friction time at which the entire weld interface had the transferred brass.     

回火温度对低合金双相钢的组织和力学性能的影响

通过对低合金双相钢Fe-0.14C-0.9Mn-0.025Nb不同温度的回火处理,通过控制组织的碳化物的析出和位错变化,研究回火温度对双相钢组织和性能的影响.试验表明:随着回火温度的增加,MA岛逐渐分解,逐渐析出颗粒状碳化物;显微硬度和抗拉强度降低,屈服强度先增后降,断后伸长率、均匀伸长率和加工硬化指数先降后增,冲击吸收能量逐步增加.     

Influence of case hardening on wear resistance of a sintered low alloy steel

PM technique has been applied for some products in the autoindustries due to unique functions and cost saving. The wear resistance of PM steel parts is one of the most significant surface properties. Nitriding and carburizing processes consist of exposing metallic materials to nitrogen and carbon to improve their surface hardness and wear resistance. In this research, the partially diffusion prealloyed powders, Ultrapac LE, containing Fe-4Ni-1.5Cu-0.5Mo with 0.2% graphite and two different densities were sintered at 1120 °C for 30 min. Depending on the applied pressures during cold pressing, two different porosities of 14.11 and 10.26 vol.% were obtained. Some specimens were carburized and some others were nitrided in cyanate liquid salt bath. The pin-on-disc wear test and hardness test were used to evaluate the surface behavior of specimens. The results showed that the wear resistance increased by nitriding and carburizing processes and the effect of nitriding is more than carburizing on wear resistance. In the case of materials studied, except for 4 h nitrided specimens, other specimens with higher porosity level showed better wear resistance. In these specimens, large pores entrapped the wear debris and created a densified layer. It prevented the formation of large abrasive agglomerates. For the carburized specimens, wear mechanisms were affected by the brittle fracture caused by abrasive wear. So, wear resistance did not increase significantly. In this investigation, abrasive, plastic deformation and oxidation wear were observed as wear mechanisms.     

Properties and improvement of super fine grained steel friction welded joint

Abstract

This paper describes friction welded joint properties of super fine grained steel (SFGS) and discusses improvements in these joint properties. The average grain size diameter of the SFGS base metal is ～0·6 μm, and its ultimate tensile strength is 660 MPa. The joint, made by a continuous drive friction welding machine (conventional method), fractured at the welded interface even though it possessed 100% joint efficiency. This was due to both the coarsening of the grain size and the softening of the welded interface with its adjacent region caused by heat input during braking times. The authors developed a joining method using a continuous drive friction welding machine that has an electromagnetic clutch to eliminate heat input during braking time, which was called the 'low heat input friction welding method' (LHI method). The joint obtained by the LHI method had the same tensile strength as the base metal at the friction time when the friction torque reached the initial peak. That is, the joint obtained 100% joint efficiency and fractured at the base metal, although the adjacent region of the welded interface softened only slightly. The grain size of this joint was smaller than that obtained by the conventional method. It was clarified that the optimum friction welded joint of the SFGS could be obtained by the LHI method in comparison with the conventional method.