1Cr18Ni9Ti Austenitic Stainless Steel Research Articles

Effect of Laser Shock Peening on High-Cycle Fatigue Performance of 1Cr18Ni9Ti/GH1140 Weld

The welded joints of 1Cr18Ni9Ti austenitic stainless steel and GH1140 nickel-based superalloy dissimilar materials used in certain types of aero-engine combustion liner components are prone to crack initiation during service, seriously affecting the service life of the combustion liner. In this study, laser shock peening (LSP) was applied to the dissimilar metal weld of 1Cr18Ni9Ti and GH1140, which are used in the combustion liner parts of aero engines. The effects of LSP on the residual stress, microhardness, microstructure and high-cycle fatigue performance of the weld were analyzed. The results show that the residual stress in the weld and heat-affected zones was converted from tensile residual stress to high amplitude compressive residual stress via LSP. Furthermore, the surface hardness of every region of the combustion liner weld was increased, especially in the weld zone, where an increase of 41.4% from 162 HV to 229 HV was observed. Simultaneously, with the introduction of grain refinement, gradient plastic deformation in the depth direction and the dislocation structure of the surface material, the high-cycle fatigue limit of the weld specimen was significantly increased and the fatigue limit of the 1Cr18Ni9Ti/GH1140 welded joint was improved by 65.39%, from 289 to 478 MPa.

Effect of the grain boundary character distribution on the self-organization of adiabatic shear bands in 1Cr18Ni9Ti austenitic stainless steel

The self-organization of adiabatic shear bands (ASBs) in the steel with a different grain boundary character distribution (GBCD) was investigated using the radial collapse of thick-walled cylinders. GBCD of 1Cr18Ni9Ti austenitic stainless steel was optimized by thermo-mechanical treatment. The results showed that the proportion of special grain boundaries, especially the Σ3 grain boundaries, were increased from 27.8, 18.9 to 72.5, 55.8%, respectively. And the high-angle grain boundaries were replaced or interrupted by the low-angle grain boundaries and special grain boundary clusters. The results of optical microscopic examination showed that the shear bands mainly propagated along the clockwise direction, and the multiple shear bands influenced each other along with bifurcation and merging. Also, the number and spacing of the shear bands of the solution treatment specimen (ST specimen) and thermo-mechanical treatment specimen (TMT specimen) were the same, which meant that GBCD optimization had no obvious effect on the nucleation of shear bands. However, the lengths of ASBs in TMT specimen were much shorter than those of the ST specimen under the same deformation conditions. The slower propagation rate of ASBs in TMT specimen suggested that by introducing a large number of special grain boundaries, the GBCD optimization hindered the propagation of ASBs and improved the damage resistance under high-strain-rate loading. Also, voids were nucleated preferentially in the ASBs and coalesced along ASBs, and cracks formed finally.

Experimental study of chemical mechanical polishing of the final surfaces of cemented carbide inserts for effective cutting austenitic stainless steel

Defects of the final surfaces of cemented carbide inserts by means of conventional grinding method include grinding burn, crack, and thermal deformation, causing low cutting efficiency. To address the problems of the conventional way in grinding the insert surfaces, the chemical mechanical polishing (CMP) process is adopted in finish machining rake faces. First, the CMP process parameters are optimized with orthogonal experiments and Taguchi’s method, and the cemented carbide insert surfaces are made with 14.399 nm Ra of its rake face. Second, the inserts made with the conventional grinding and the CMP methods are used to lathe 1Cr18Ni9Ti austenitic stainless steel. Under the same cutting conditions, the cutting forces of the polished insert is less than those of the grinding insert, the cutting time of the polished insert is longer than that of the grinding insert, and the average life of the polished insert is 32.3% longer than that of the grinding insert. Finally, the scanning electron microscopy (SEM) and the energy dispersive spectroscopy (EDS) analysis have shown that the polished insert rake face has less adhesive wear , abrasive wear, and minor oxidation wear compared to the wear of the grinding insert rake face. This study demonstrates that the CMP is a potential way of processing the insert surfaces in the tooling industry.

The Microstructural Evolution of Vacuum Brazed 1Cr18Ni9Ti Using Various Filler Metals.

The microstructures and weldability of a brazed joint of 1Cr18Ni9Ti austenitic stainless steel with BNi-2, BNi82CrSiBFe and BMn50NiCuCrCo filler metals in vacuum were investigated. It can be observed that an interdiffusion region existed between the filler metal and the base metal for the brazed joint of Ni-based filler metals. The width of the interdiffusion region was about 10 μm, and the microstructure of the brazed joint of BNi-2 filler metal was dense and free of obvious defects. In the case of the brazed joint of BMn50NiCuCrCo filler metal, there were pits, pores and crack defects in the brazing joint due to insufficient wettability of the filler metal. Crack defects can also be observed in the brazed joint of BNi82CrSiBFe filler metal. Compared with BMn50NiCuCrCo and BNi82CrSiBFe filler metals, BNi-2 filler metal is the best material for 1Cr18Ni9Ti austenitic stainless steel vacuum brazing because of its distinct weldability.

Grinding process of helical micro-drill using a six-axis CNC grinding machine and its fundamental drilling performance

Helical drill point is characterized by a continuous helical flank surface and an S-shape chisel edge, and its special geometry contributes to a superior drilling performance and a better grinding efficiency. However, the existing grinding processes are complicated and hard to be reproduced in practice, and it is difficult to meet the accuracy requirements as the drill diameter becomes smaller. Thus, it is crucial to research further grinding method of helical micro-drill and its drilling performance. In this paper, a grinding method of helical drill flank using a six-axis CNC grinding machine is proposed based on the mathematical model of generatrix of the helical surface. Then, this grinding process is simulated using the 3D CAD software and is validated by experimentally fabricating the helical micro-drill. The results show that this method is feasible for obtaining the micro-drill with high dimensional accuracy. For the comparison with helical micro-drill, the planar and conical micro-drills with the same geometry parameters are produced as well. The drilling experiments on 1Cr18Ni9Ti austenitic stainless steel with the planar, conical, and helical micro-drills are conducted, and the drilling force, tool wear, and hole quality are measured and analyzed. The experiment results show that the increasing rate of the radial force of helical micro-drills at the beginning of the drilling process is smaller than those of planar and conical micro-drills, the thrust force and wear of helical drill point are also smaller, and the quality of micro-holes by helical drill point is better as well. It is confirmed that the proposed grinding process is effective to fabricate the helical micro-drill with good drilling performance.

Influence of Drill Geometry Parameters on Helical Point Micro Drilling Performance

Helical point micro-drill is characterized by a continuous helical flank instead of the piecewise planar flank, and its improved drilling performance is validated compared with planar drill point by some researchers. In this study, to analyze the effect of geometry parameters of helical point drill on the drilling performance, the micro-drills with different point angles, web thicknesses and helix angles of the flute are fabricated on a 6-axis CNC tool grinder, and a serial of micro-drilling experiments involving these drills on 1Cr18Ni9Ti austenitic stainless steel are carried out. In experiments, the drilling forces are measured and exit burrs are observed. Within a certain range of geometry parameters, thrust force increases with the increase of point angle and web thickness, and the decrease of the helix angle of the flute. The point angle is the main contributory factor for the thrust force followed by web thickness, while helix angle has a moderate effect on the force. Furthermore, poisson burr and rollover burr are generated with different point angles. Based on the results, a good selection of the helical point drill geometry parameters with small point angle, big helix angle and small web thickness are proposed to improve the micro-drilling performance.

Preparation and Micro-analysis of the 1Cr18Ni9Ti with Different Magnetic and Same Component

In some studies, the metal materials with different magnetic permeability and same chemical composition need to be prepared to avoid the interference caused by different compositions and make the parameter of magnetic permeability become the key variable directly. In order to prepare the metal materials with different magnetic and same component, the paper has considered other two commonly schemes, such as the casting method by adding some ferromagnetic elements and the heat-treatment process to increase its phase content of martensite or ferrite. Finally, it has been found that the cold working process was preferable if the austenitic stainless steel 1Cr18Ni9Ti with paramagnetic was selected as a raw material, because it got better control in forging ratio. The method of magnetic balance has been used to measure the relative magnetic permeability of every specimen with different hardness HB 165 (A), HRC 20 (B), HRC 25 (C) and HRC 30 (D). The metallurgical microscope, XRD, TEM and SEM has been put to use to analyse their microstructure before and after forging. The results show, the cold working process improved magnetic properties of 1Cr18Ni9Ti continuously and largely within limits by controlling different forging rate, as well as the process was not complicated. The relative rate of magnetic permeability for 1Cr18Ni9Ti and W18Cr4V (high-speed steel) could be up to 1:2.435 at 0.03 T. The 20.1 % maximum reduction of the austenite phase should be a main reason to improving magnetic permeability of 1Cr18Ni9Ti. The real magneto-crystalline anisotropy should be due to martensite or ferrite phases with strong magnetic property. The 1Cr18Ni9Ti after cold working still maintained high corrosion resistance. Furthermore, this process method was also applicable to other austenitic steels with paramagnetic and strong cold work hardening characteristics. DOI: http://dx.doi.org/10.5755/j01.ms.21.4.9696

Experimental Study on the Cutting Performance of In Situ Fabricated TiB2 Toughened TiN-Based Composite Ceramic Tool in Turning Stainless Steel

A new developed TiN-TiB2 ceramic cutting tool material (marked as TBN5) with high comprehensive mechanical properties was fabricated by the in-situ integration synthesis process. The cutting performance of TBN5 tool in continuously turning the austenitic stainless steel 1Cr18Ni9Ti was experimentally investigated; the failure modes and failure mechanisms of the cutting tool TBN5 were analyzed combined with its mechanical properties. Aiming at the materials removal amount, the optimal cutting parameters of TBN5 tool in turning 1Cr18Ni9Ti were firstly obtained by the orthogonal tests; and then with this cutting parameters, the cutting performance of TBN5 compared to the commercial tools LT55 and SG4 was studied. The results showed that the advanced tool TBN5 could get longer tool life than LT55 and SG4; the main failure modes of TBN5 were flank wear, breakage and the flaking of main cutting edge. The scope of its flaking was smaller and diffusion wear was not obvious, which was related to the higher fracture toughness and the higher thermal conductivity of TBN5.

Experimental Study on Face Milling Austenitic Stainless Steel

Based on the characteristics of austenitic stainless steel 1Cr18Ni9Ti, aiming to decrease surface roughness and milling force orthogonal face milling experiment with four factors and four levels was designed to optimize machining parameters with consideration of material removal rate. Three relatively excellent machining parameters were taken to further figure out the influences of cutting speed on tool life, and the tool wear mechanism was also analyzed. The results indicated that both surface roughness and milling force were greatly influenced by cutting speed and feed. The best machining parameters obtained in the experiments were v: 200m/min, fz: 0.1mm/z, ap: 0.9mm, ae: 35mm. The main tool failure mode under this circumstance was tool chipping at the flank between main cutting edge and surface to be processed, besides, the wear of rake face was relatively slight.

Experimental Investigation on Chip Deformation in Drilling 1Cr18Ni9Ti

It is difficult to study the chip deformation due to the complexity of the chip formation process in drilling. The chip deformation has a direct effect on the drilling forces, drilling temperature and surface quality. The austenitic stainless steel 1Cr18Ni9Ti belongs to the hard-to-cut material, so it is necessary to investigate the chip deformation of 1Cr18Ni9Ti in drilling. An experimental investigation of the chip transformation process on the cutting edges using quick-stop of the drilling processes is carried out. Results indicate that the chip deformation increases with the increment of drilling velocity and decreases with the increment of the distance to chisel edge on cutting edge and the feed rate in drilling 1Cr18Ni9Ti; the chip deformation decreases with the increment of drilling velocity, and decreases with the increment of the distance to chisel edge on cutting edge and the feed rate in drilling AISI 1045; the chip deformation in drilling 1Cr18Ni9Ti is larger than that in drilling AISI 1045.

The Influence of Alloying Additives on the Machinability of Austenitic Stainless Steel

In this study, non-lead machinable austenitic stainless steel was investigated through performing the machinability tests using a CA6164 lathe. The metallurgical properties, machinability and mechanical properties of the developed alloy were compared with those of the conventional austenitic stainless steel 1Cr18Ni9Ti. The results have shown that the inclusions were composed of MnS, Bi, CuO and Ti4C2S2 in the developed non-lead machinable austenitic stainless steel. Bismuth is an important factor to improve the machinability of austenitic stainless steel, and it has a distinct advantage over lead. The presence of alloying additives contributes to the improvement of the machinability of the developed austenitic stainless steel. The mechanical properties of non-lead machinable austenitic stainless steel exhibit a good combination of tensile strength and total elongation, despite the inclusion had a minor detrimental effect on them.

Modeling of stress induced nitrogen diffusion in nitrided stainless steel

The nitrogen transport mechanism in plasma nitrided austenitic stainless steel at moderate temperatures is explained by influence of internal stresses gradient. The model considers the diffusion of nitrogen in the presence of internal stresses gradient induced by penetrating nitrogen as the next driving force of diffusion after concentration gradient. For mathematical description of stress induced diffusion process the equation of barodiffusion is used which involves concentration dependant barodiffusion coefficient. For calculation of stress gradient it is assumed that stress depth profile linearly relates with nitrogen concentration depth profile. Calculated nitrogen depth profiles in an austenitic stainless steel are in good agreement with experimental nitrogen profiles. The diffusion coefficient D=1.68·10−12cm2/s for nitrogen in plasma source ion nitrided 1Cr18Ni9Ti (18-8 type) austenitic stainless steel at 380°C was found from fitting of experimental data. It is shown that nitrogen penetration depth and nitrogen surface concentration increases with nitriding time and with incoming nitrogen flux nonlinearly.

A Study on Chip Breakage in Mini-Pore Vibration Drilling for Hard-to-Cut Material of Austenitic Stainless Steel

This research aims to improve the method of Mini-pore Drilling superimposed an axis vibration for hard-to-cut material of Austenitic Stainless Steel 1Cr18Ni9Ti, as well as to make it easier for the chips to be discharged. A mathematical model of vibration drilling is presented, and the relationship between the vibration parameters and cutting parameters to generate little and short broken-chips in vibration drilling is investigated, analyzed and verified by experiments. The results show that when the processing parameters meet the conditions given in this article, stable and reliable chip-breaking can be achieved. The results provide a theoretical guidance to achieve chip-breaking in mini-pore vibration drilling for hard-to-cut material.

Corrosion behaviour of electroless Ni–P coatings in simulated acid rain

The corrosion behaviour of electroless Ni–P coatings deposited on A3 steel in simulated acid rain at pH=3·5, 4·0, 4·5, 5·0, 5·5 and 6·0 were investigated by weight loss test and electrochemical test. The protection of A3 steel by Ni–P coating was discussed, and 1Cr18Ni9Ti austenitic stainless steel was used for comparison. The results indicate that the weight loss of the three materials increased, and the corrosion resistance of Ni–P coating decreased, with decreasing pH value of the acid rain solution. The corrosion resistance of A3 steel can be significantly improved with the protection of Ni–P coating, which showed better corrosion resistance than 1Cr18Ni9Ti stainless steel.

X-ray diffraction of high nitrogen face centred cubic phase formed on nitrogen modified austenitic stainless steel

High nitrogen face centred cubic phase formed on the nitrogen modified Fe–Cr–Ni austenitic stainless steel, which is named by γN phase, has a combined wear and corrosion resistance. X-ray diffraction (XRD) patterns of the γN phase on the stainless steel depict a set of broad and asymmetry diffraction peaks with a peak shift to low Bragg angles and a decrease in intensity, even disappearing of some peaks of high index planes, from each austenite peak for the γ matrix. The peak shift of the XRD patterns was first explained by Warren's XRD theory by Blawert et al. (Surf. Coat. Technol., 2001, 136, 181). In this paper, a systematic study of XRD on the peak shift, peak asymmetry, peak broadening and peak intensity of the γN phase has been carried out, based on a fault induced scattering geometry in diffraction to imperfect crystals by Warren's theory and Wagner's method. Both the higher deformation faults density α in a range of 0·02–0·25 and the lower twin faults density β of 0·01–0·1 were successfully used to describe the line profiles in the XRD patterns of the γN phase formed on plasma source ion nitrided 1Cr18Ni9Ti (18-8 type) austenitic stainless steel. A novel stacking faults factor Sαβ dependent on α and β described, in good agreement, the peak intensity of the γN phase. The calculated XRD patterns of the γN phase using the imperfect crystals model of a face centred cubic phase with a higher deformation faults density and a lower twin faults density were associated with the experimentally structural characteristics.

Effect of Free-cutting Additives on Machining Characteristics of Austenitic Stainless Steels

The machinability tests were conducted by using a YD-21 dynamometer on a CA6161A lathe. The experiments were conducted to determine the effect of free-cutting additives on machining characteristics of austenitic stainless steels. The conventional austenitic stainless steel 1Cr18Ni9Ti (steel A) and the free cutting austenitic stainless steel (steel B) were prepared. The results have shown that machinable inclusions were composed of MnS and CuO, and they might be also Ti4C2S2. The presence of Bi in the inclusion was detected by the atom map and electro-probe microanalysis (EPMA), which might be one of the most important factors to improve the machinability of austenitic stainless steels. The cutting forces for steel B were lower than those of steel A at various cutting speeds; the abrasion depth of the flank of the tool for steel B was less than that of the steel A under the same cutting conditions. The machinability of austenitic stainless steel was visibly improved by adding free-cutting additives, such as S, Cu and Bi. Ultimate tensile, yield strength, and total elongation values of the free cutting austenitic stainless steel were improved due to the addition of these free-cutting additives.

Tribological Behavior of Plasma Nitrided 1Cr18Ni9Ti Austenitic Stainless Steel Under the Effect of Lubricant Additives

To expand the engineering application of stainless steel as tribological material, it is important to study the tribological interaction of the nitrided layer with lubricating additives. The friction and wear properties of plasma nitrided 1Cr18Ni9Ti stainless steel were investigated under lubricated conditions on an Optimol Schwinyung Reibung Versch oscillating friction and wear tester. The lubrication oil was 1,1,1-trihydroxymethylpropyl trioctoate containing zinc dibutyl dithiophosphate, bismuth dibutyl dithiophosphate, and bismuth N, N-dibutyldithiocarbamate as the antiwear and extreme pressure additives. The variations in the nitrided stainless steel and the unnitrided one under the tribological action of the additives were contrasted and the tribological chemical interaction between the nitrided layer and the additives was revealed. The results showed that the selected additives had good synergetic effect with the nitrided layer on tribological performance and the bismuth containing additive had better friction-reducing and antiwear abilities than the zinc containing additive. Meanwhile, under the effect of these additives, the N/(Fe+Cr) ratio rose and the Fe/Cr ratio decreased in the nitrided layer, while the Fe/Cr ratio in the unnitrided stainless steel varied little. Three main elements, N, Cr, and Fe, in nitrided layer had different actions with the additives and contributed to tribological performance by different methods.

Study on Minipore Drilling to Stainless Steel 1Cr18Ni9Ti

Based on reviewing the applications and machining of the stainless steels, the cutting performance of the austenitic stainless steel 1Cr18Ni9Ti is analyzed through the contrastive experiments. This paper studies drilling minipore mechanics of hard-to-cut material—Austenitic Stainless Steel 1Cr18Ni9Ti by simulation and experiment, analogy results displays the trend that drill thrust, torque and temperature changed with amount of feed, it matches with test result in the same cutting condition well. The research results would be of great benefit for the selection of proper tools and cutting parameters in drilling austenitic stainless steels.

Finite Element Simulation on Face Milling of Austenitic Stainless Steel with Chamfered Tools

Due to the high strength of austenitic stainless steels, it is essential for cutting tool to keep with appropriate chamfered edges during the face milling process. In this paper, face milling mechanics with chamfered edge based on cutting force and chip formation were analyzed through finite element analysis (FEA). Three kinds of tools with different chamfered edges were studied on face milling of 1Cr18Ni9Ti austenitic stainless steel. The primary research results indicated that FEA results showed good consistency with experimental results. This can provide references for development and application of tools during face milling process.

Stacking Faults in a High Nitrogen Face-Centered-Cubic Phase Formed on Nitrogen-Modified Austenitic Stainless Steel

Effects of stacking faults in a high nitrogen face-centered-cubic phase (γΝ) formed on plasma source ion nitrided 1Cr18Ni9Ti (18-8 type) austenitic stainless steel on peak shift and peak asymmetry of x-ray diffraction were investigated based on Warren’s theory and Wagner’s method, respectively. The peak shift from peak position of the γΝ phase is ascribed to the deformation faults density α, while the peak asymmetry of the γΝ phase is characterized by deviation of the center of gravity of a peak from the peak maximum (Δ C.G.) due to the twin faults density β. The calculated peak positions of x-ray diffraction patterns are consistent with that measured for plasma source ion nitrided 1Cr18Ni9Ti stainless steel.