Influence of Rotational Speed on Microstructure and Mechanical Properties of Dissimilar Metal AISI 304-AISI 4140 Continuous Drive Friction Welds

 Fundamental investigation of continuous drive friction welding of austenitic stainless steel (AISI 304) and low alloy steel (AISI 4140) is described. The emphasis is made on the influence of rotational speed on the microstructure and mechanical properties such as hardness, tensile strength, notch tensile strength and impact toughness of the dissimilar joints. Hardness profiles across the weld show the interface is harder than the respective parent metals. In general, maximum peak hardness is observed on the stainless steel side, while other peak hardness is on the low alloy steel side. A trough in hardness distribution in between the peaks is located on the low alloy steel side. Peak hardness on the stainless steel and low alloy steel side close to the interface increases with a decrease in rotational speed. All transverse tensile joints fractured on stainless steel side near the interface. Notch tensile strength and impact toughness increase with increase in rotational speed up to 1500 r/min and decrease thereafter. The mechanism of influence of rotational speed for the observed trends is discussed in the torque, displacement characteristics, heat generation, microstructure, fractography and mechanical properties.     

Crack Arrest Toughness of Two High Strength Steels (AISI 4140 and AISI 4340)

The crack initiation toughness (K _c ) and crack arrest toughness (K _a ) of AISI 4140 and AISI 4340 steel were measured over a range of yield strengths from 965 to 1240 MPa, and a range of test temperatures from -53 to +74°C. Emphasis was placed onK _a testing since these values are thought to represent the minimum toughness of the steel as a function of loading rate. At the same yield strengths and test temperatures,K _a for the AISI 4340 was about twice as high as it was for the AISI 4140. In addition, theK _a values showed a more pronounced transition temperature than theK _c values, when the data were plotted as a function of test temperature. The transition appeared to be associated with a change in fracture mechanism from cleavage to dimpled rupture as the test temperature was increased. The occurrence of a “pop-in” behavior at supertransition temperatures has not been found in lower strength steels, and its evaluation in these high strength steels was possible only because they are not especially tough at their supertransition temperatures. There is an upper toughness limit at which pop-in will not occur, and this was found for the AISI 4340 steel when it was tempered to its lowest yield strength (965 MPa). All the crack arrest data were identified as plane strain values, while only about one-half of the initiation values could be classified this way.     

Effect of heat input on microstructure and mechanical properties of dissimilar joints of AISI 316L steel and API X70 high-strength low-alloy steel

The microstructure and mechanical properties of dissimilar joints of AISI 316L austenitic stainless steel and API X70 high-strength low-alloy steel were investigated.For this purpose,gas tungsten arc welding(GTAW)was used in three different heat inputs,including 0.73,0.84,and 0.97 kJ/mm.The microstructural investigations of different zones including base metals,weld metal,heat-affected zones and interfaces were performed by optical microscopy and scanning electron microscopy.The mechanical properties were measured by microhardness,tensile and impact tests.It was found that with increasing heat input,the dendrite size and inter-dendritic spacing in the weld metal increased.Also,the amount of delta ferrite in the weld metal was reduced.Therefore,tensile strength and hardness were reduced and impact test energy was increased.The investigation of the interface between AISI 316L base metal and ER316L filler metal showed that increasing the heat input increases the size of austenite grains in the fusion boundary.A transition region was formed at the interface between API X70 steel and filler metals.     

Hydrogen Uptake Enhancement and Accelerated Hydrogen Re-embrittlement of Cd-plated AISI 4340 Steel Bolts Coupled with IN718 Nuts

Hydrogen re-embrittlement on anodically coated high strength steels could be of great concern because the uptake of hydrogen from the corrosion process can cause component failure. A scratched Cd-coated AISI 4340 steel membrane has been coupled with different materials reproducing crevice conditions, and the hydrogen uptake has been measured using a modified Devanathan?CStachurski permeation apparatus. Experimental tests proved that, in presence of a crevice, metals nobler than cadmium strongly enhance local hydrogen reduction on exposed steel areas, thus possibly favoring brittle failure of high strength steel components during service. Therefore, the coupling of uncoated nuts made of noble passive alloys (like Inconel) to Cd-plated AISI 4340 steel bolts should be avoided.     

An investigation of the plastic fracture of AISI 4340 and 18 Nickel-200 grade maraging steels

The mechanisms of plastic fracture (dimpled rupture) in high-purity and commercial 18 Ni, 200 grade maraging steels and quenched and tempered AISI 4340 steels have been studied. Plastic fracture takes place in the maraging alloys through void initiation by fracture of titanium carbo-nitride inclusions and the growth of these voids until impingement results in coalescence and final fracture. The fracture of AISI 4340 steel at a yield strength of 200 ksi (1378 MN/mm²) occurs by nucleation and subsequent growth of voids formed by fracture of the interface between manganese sulfide inclusions and the matrix. The growth of these inclusion-nucleated voids is interrupted long before coalescence by impingement, by the formation of void sheets which connect neighboring sulfide-nucleated voids. These sheets are composed of small voids nucleated by the cementite precipitates in the quenched and tempered structures. The sizes of non-metallic inclusions are an important aspect of the fracture resistance of these alloys since the investigation demonstrates that void nuclea-tion occurs more readily at the larger inclusions and that void growth also proceeds more rapidly from the larger inclusions. Using both notched and smooth round tensile specimens, it was demonstrated that the level of tensile stress triaxiality does not effect the void nu-cleation process in these alloys but that increased levels of triaxial tension do result in greatly increased rates of void growth and a concomitant reduction in the resistance to plastic fracture.     

Dissimilar Spot Welds of AISI 304/AISI 1008: Metallurgical and Mechanical Characterization

This paper aims at investigating structure‐properties relationships in dissimilar resistance spot welding of AISI 304 austenitic stainless steel (SS) and AISI 1008 low carbon steel (CS). Microstructural characterization, microhardness test and the tensile‐ shear test were conducted. It was shown that the shape of the SS/CS fusion zone (FZ) is unsymmetrical and the final fusion line shifts from sheet/sheet interface into the higher resistivity side (i.e. AISI 304). FZ microstructure was ranged from ferrite‐austenite to full martensite depending on the dilution ratio of the base metals. The variation of SS/CS dissimilar welds failure mode was explained in terms of hardness/microstructure characteristics. It was concluded that to ensure pullout failure mode, welding parameters needed to adjust so that the FZ size is sufficiently large and dilution is sufficiently high to produce a martensite FZ. Fusion zone size at CS side proved to be the most important controlling factor of SS/CS peak load and energy absorption. Finally, the mechanical properties of SS/CS dissimilar welds were compared with SS/SS and CS/CS similar welds.     

High Power Laser Powder Deposition Repair of AISI 4340 Steel in Aircraft Applications

High power laser powder deposition (LPD) has been used to investigate the potential of repairing damaged aero-grade high strength steel.Metallurgical analysis was performed to analyze the integrity of the clad layer.A 4kW fiber laser was used to deposit two separate alloys (AISI 4340 and AISI 420 stainless steel) on an AISI 4340 steel substrate and metallurgical analysis was performed to analyze the integrity of the clad layer.No microcracks was observed on the clads,but porosity and high dilution was observed on most clads.However,microstructural analysis showed a crack and porosity free clad layer with low dilution can be achieved for some laser conditions.     

高强度焊丝WER80的应用研究

介绍了以高强度、高韧性气保护焊丝WER80为材料,对焊丝熔敷金属及武钢HG785钢、HG980钢对接进行气保护焊接试验研究。采用富氩气体保护熔敷金属抗拉强度达到了810 MPa,-30℃冲击功达到106 J;匹配HG785钢气保护焊焊接接头抗拉强度达到815 MPa,-30℃冲击功大于90 J;匹配HG980钢气保护焊...     

Optimization of Welding Parameters,Influence of Activating Flux and Investigation on the Mechanical and Metallurgical Properties of Activated TIG Weldments of AISI 316 L Stainless Steel

This research investigation articulates the joining of AISI 316 L austenitic stainless steel plates of thickness 5 mm by activated tungsten inert gas (A-TIG) welding. Prior to the welding, the optimization of process parameters and the selection of suitable flux have been carried out to join the plates in a single pass welding. The experimental results show that the complete weld penetration can be achieved by using activating flux. The microscopic study divulges the presence of delta ferrite, sigma phase and various forms of austenite in the weld zone. Fischer Feritscope result indicates that the delta ferrite content in the weld is higher (7.8 FN) than the base metal (1.3 FN) which results in superior mechanical properties of the weld. Field Emission-Scanning Electron Microscope (FE-SEM) fractography reveals that the failure of weldments occurs in ductile mode. 180° bend test study reveals the good ductility of the joint.     

Experimental investigation into microstructure,metallurgy and mechanical properties of AISI 422 stainless steel weldments produced using fibre laser welding direct forming

In this study, the Taguchi design method was used to determine the optimal parameters for the fibre laser welding direct forming (FLWDF) of AISI 422 stainless steel (SS) weldments for use in the repair of the tenons in steam turbine blades. Experiments were then conducted to investigate the microstructural characteristics and mechanical properties of the weldments. Our results show that the fusion zone of the AISI 422 SS weldments possesses a grain structure of significantly higher refinement than does the original AISI 422 SS. Moreover, tempering at 700°C for 2?h was found to enhance the hardness as well as the impact toughness of the weldments. Finally, mock-up trials of tenon repair were performed using the optimal FLWDF parameters. Our results reveal that the repaired tenons are able to withstand a tensile load of 30?kN in as-welded condition and up to 55?kN following tempering at 700°C for 2?h.     

Evaluation of toughness in AISI 4340 alloy steel austenitized at low and high temperatures

It has been reported for as-quenched AISI 4340 steel that high temperature austenitizing treatments at 1200°C, instead of conventional heat-treatment at 870°C, result in a two-foldincrease in fracture toughness,K _Ic, but adecrease in Charpy impact energy. This paper seeks to find an explanation for this discrepancy in Charpy and fracture toughness data in terms of the difference betweenK _Ic and impact tests. It is shown that the observed behavior is independent of shear lip energy and strain rate effects, but can be rationalized in terms of the differing response of the structure produced by each austenitizing treatment to the influence of notch root radius on toughness. The microstructural factors which affect this behavior are discussed. Based on these and other observations, it is considered that the use of high temperature austenitizing be questioned as a practical heat-treatment procedure for ultrahigh strength, low alloy steels. Finally, it is suggested that evaluation of material toughness should not be based solely onK _Ic or Charpy impact energy values alone; both sharp crack fracture toughness and rounded notch impact energy tests are required.     

Effect of Heat Treatment on Microstructure of Modified Cast AISI D3 Cold Work Tool Steel

 High chromium high carbon AISI D3 steel is used as cold-work tools and dies in industry. Microstructure of this wrought steel usually consists of chromium carbides homogenously dispersed in a ferritic or martensitic matrix. On the other hand, a eutectic network consisting of chromium carbide and austenite forms in a cast D3 steel, at the end of solidification due to the segregation of carbon and chromium. This heterogeneous microstructure gives rise to the reduced mechanical properties such as toughness, impact strength, and tensile strength. In this research, modified AISI D3 steel was developed by replacing part of Cr with Nb and Ti, in which chromium carbide was partially replaced with MC carbides. The cast samples produced by investment casting were heat treated at different conditions. The microstructures of the samples were studied by light and scanning electron microscope attached with EDS analyzer. To determine the optimized homogenizing process, the effects of homogenizing treatment on the microstructure and the morphology of carbides were also studied.     

Effect of vanadium on the microstructure and properties of metastable austenitic stainless steel AISI 301LN

In this study,the effect of vanadium on the microstructure and properties of the metastable austenitic stainless steel AISI 301LN w as investigated. Results of the study show that the addition of vanadium can refine grains and increase the strength of AISI 301LN by solution treatment. After 60%cold-rolling reduction,the microstructure of the steel w as composed of w ork-hardened austenite bands and deformation-inducedɑ'martensite.Considerable w ork-hardening and phase transformation strengthening occurred. After cold rolling and subsequent annealing,the deformation-inducedɑ'martensite w as reversed into fine-grained austenite. The w orkhardened austenite bands underw ent recrystallization; how ever,the structure of the recrystallized austenite grains w as coarser than that of the reversed ones.Simultaneously,the strength of the experimental steels decreased w ith the increase in annealing temperature. The pinning effect of precipitates of vanadium inhibited the grow th of austenite grains.Thus,the desirable combination of strength and ductility w as obtained by grain refinement.     

Optimization of Friction Welding Process Parameters for Joining Carbon Steel and Stainless Steel

 Friction welding is a solid state joining process used extensively currently owing to its advantages such as low heat input, high production efficiency, ease of manufacture, and environment friendliness. Materials difficult to be welded by fusion welding processes can be successfully welded by friction welding. An attempt was made to develop an empirical relationship to predict the tensile strength of friction welded AISI 1040 grade medium carbon steel and AISI 304 austenitic stainless steel, incorporating the process parameters such as friction pressure, forging pressure, friction time and forging time, which have great influence on strength of the joints. Response surface methodology was applied to optimize the friction welding process parameters to attain maximum tensile strength of the joint. The maximum tensile strength of 543 MPa could be obtained for the joints fabricated under the welding conditions of friction pressure of 90 MPa, forging pressure of 90 MPa, friction time of 6 s and forging time of 6 s.     

Evaluation of toughness in AISI 4340 alloy steel austenitized at low and high temperatures

It has been reported for as-quenched AISI 4340 steel that high temperature austenitizing treatments at 1200°C, instead of conventional heat-treatment at 870°C, result in a two-foldincrease in fracture toughness,K _Ic, but adecrease in Charpy impact energy. This paper seeks to find an explanation for this discrepancy in Charpy and fracture toughness data in terms of the difference betweenK _Ic and impact tests. It is shown that the observed behavior is independent of shear lip energy and strain rate effects, but can be rationalized in terms of the differing response of the structure produced by each austenitizing treatment to the influence of notch root radius on toughness. The microstructural factors which affect this behavior are discussed. Based on these and other observations, it is considered that the use of high temperature austenitizing be questioned as a practical heat-treatment procedure for ultrahigh strength, low alloy steels. Finally, it is suggested that evaluation of material toughness should not be based solely onK _Ic or Charpy impact energy values alone; both sharp crack fracture toughness and rounded notch impact energy tests are required. formerly with Effects Technology, Inc., Santa Barbara, CA     

Fracture toughness of AISI M2 and AISI M7 high-speed steels

A study has been made of the fracture toughness of AISI M2 and M7 high-speed steels. Fracture toughness of these steels was found to depend principally on austenitizing temperature and hardness level. The results are highly reproducible. At usual working hardness levels the fracture toughness of M7 and M2 were approximately equal. Instrumented unnotched Charpy tests showed M2 to have higher impact strength than M7. A model for fracture that assumed preexisting flaws was tested with the data obtained. The model is consistent with the results obtained for M7 but not for M2. The assumption of preexisting flaws in M2 high-speed steel does not seem warranted. Possible mechanisms for crack initiation in M2 are discussed briefly.     

Evaluation of Microstructure and Mechanical Properties of Laser Beam Welded AISI 409M Grade Ferritic Stainless Steel

 The microstructure analysis and mechanical properties evaluation of laser beam welded AISI 409M ferritic stainless steel joints are investigated. Single pass autogeneous welds free of volumetric defects were produced at a welding speed of 3000 mm/min. The joints were subjected to optical microscope, scanning electron fractographe, microhardness, transverse and longitudinal tensile, bend and charpy impact toughness testing. The coarse ferrite grains in the base metal were changed into dendritic grains as a result of rapid solidification of laser beam welds. Tensile testing indicates overmatching of the weld metal is relative to the base metal. The joints also exhibited acceptable impact toughness and bend strength properties.     

Characterization Method of Mechanical Properties of Dissimilar Steel Resistance Plug Welding Joints

A novel resistance plug welding process has wide prospects for dissimilar steel. However, until present, there is no effective method to characterize the mechanical properties of resistance plug welding joints. In this paper, the influence factors such as diameter of filler, diameter of surface plastic ring, and diameter of nugget were first used for analysis. Slug ratio and indentation depth (height) ratio were designed to characterize the mechanical properties of the resistance plug welding joints. The results show that smaller the slug ratio, better the mechanical properties of the joint. The tensile shear load of the joint is higher when the indentation depth (height) ratio is 92–102%, and the joint has the best tensile shear load when the indentation depth (height) ratio is 96% or 97% in this study. Slug ratio and indentation depth (height) ratio are suitable for characterizing mechanical properties of dissimilar steel resistance plug welding joints.     

Heat Treatment Optimization and Properties Correlation for H11-Type Hot-Work Tool Steel

The aim of this research was to determine the effect of vacuum-heat-treatment process parameters on the material properties and their correlations for low-Si-content AISI H11-type hot-work tool steel using a single Circumferentially Notched and fatigue Pre-cracked Tensile Bar (CNPTB) test specimen. The work was also focused on the potential of the proposed approach for designing advanced tempering diagrams and optimizing the vacuum heat treatment and design of forming tools. The results show that the CNPTB specimen allows a simultaneous determination and correlation of multiple properties for hot-work tool steels, with the compression and bending strength both increasing with hardness, and the strain-hardening exponent and bending strain increasing with the fracture toughness. On the other hand, the best machinability and surface quality of the hardened hot-work tool steel are obtained for hardness values between 46 and 50 HRC and a fracture toughness below 60 MPa√m.     

Effects of Ti and Nb on the Grain Refinement and Mechanical Properties of AISI 4145 Steel

In this study, we investigated the effects of Ti and Nb additions on the grain size of prior austenite and mechanical properties such as yield strength, yield ratio, and impact toughness in quenched and tempered AISI 4145 steel. It was found that the grain size of prior austenite directly influenced the mechanical properties. Thermodynamic calculations were carried out to find the characteristics of the precipitates such as dissolution temperature of precipitates, the average size of precipitate particles, precipitate fraction, and mean distance among precipitate particles, quantitatively. A specimen with low Ti content had a smaller Ti/N ratio than the stoichiometric ratio of 3.42 and showed an effective inhibition of grain growth of prior austenite, whereas a specimen with high Ti content showed a little effect to prevent the austenite grain growth compared with a Ti-free sample. Based on the thermodynamic simulation, the (Nb, Ti) (C, N) complex was precipitated and contributed to the inhibition of austenite grain growth, resulting in not only higher yield strength and yield strength/tensile strength ratio but also improved toughness.