Influence Of Grinding Operations On Surface Integrity And .
Influence of grinding operationson surface integrity and chlorideinduced stress corrosioncracking of stainless steelsNIAN ZHOULicentiate Thesis in ChemistryKTH Royal Institute of TechnologySchool of Chemical Science and EngineeringDepartment of ChemistrySE -100 44 Stockholm, Sweden
TRITA-CHE Report 2016:5ISSN 1654-1081ISBN 978-91-7595-838-5Akademisk avhandling som med tillstånd av KTH i Stockholm framlägges till offentliggranskning för avläggande av teknisk licentiatexamen tisdagen den 25 februari kl 13:00 i salQ34, KTH, Osquldasväg 6B (03 tr), 10044 Stockholm, Sweden.
AbstractStainless steels were developed in the early 20th century and are usedwhere both the mechanical properties of steels and corrosion resistanceare required. There is continuous research to allow stainless steelcomponents to be produced in a more economical way and be used inmore harsh environments. A necessary component in this effort is tocorrelate the service performance with the production processes.The central theme of this thesis is the mechanical grinding process. Thisis commonly used for producing stainless steel components, and resultsin varied surface properties that will strongly affect their service life. Theinfluence of grinding parameters including abrasive grit size, machinepower and grinding lubricant were studied for 304L austenitic stainlesssteel (Paper II) and 2304 duplex stainless steel (Paper I). Surfaceintegrity was proved to vary significantly with different grindingparameters. Abrasive grit size was found to have the largest influence.Surface defects (deep grooves, smearing, adhesive/cold welding chips andindentations), a highly deformed surface layer up to a few microns inthickness and the generation of high level tensile residual stresses in thesurface layer along the grinding direction were observed as the maintypes of damage when grinding stainless steels. A large degree of residualstress anisotropy is interpreted as being due to mechanical effectsdominating over thermal effects.The effect of grinding on stress corrosion cracking behaviour of 304Laustenitic stainless steel in a chloride environment was also investigated(Paper III). Depending on the surface conditions, the actual loading byfour-point bend was found to deviate from the calculated value using theformula according to ASTM G39 by different amounts. Grinding-inducedsurface tensile residual stress was suggested as the main factor to causemicro-cracks initiation on the ground surfaces. Grinding along theloading direction was proved to increase the susceptibility to chlorideinduced SCC, while grinding perpendicular to the loading directionimproved SCC resistance.
The knowledge obtained from this work can provide a reference forchoosing appropriate grinding parameters when fabricating stainlesssteel components; and can also be used to help understanding the failuremechanism of ground stainless steel components during service.Keywordsstainless steel, surface integrity, residual stress, stress corrosion cracking,grinding
SammanfattningRostfria stål utvecklades i början på 1900-talet och används där det finnskrav på en kombination av mekaniska egenskaperna hos stål och godkorrosionsresistens. Kontinuerlig forskning pågår för att möjliggöra merekonomisk produktion av rostfria komponenter och användning i merkrävande miljöer. En nödvändig del i detta arbete är att relaterakomponenternas livslängd till produktionsprocessen.Det centrala temat hos denna avhandling är den mekaniska slipprocessen.Slipning används ofta vid produktion av rostfria stålprodukter och gervarierande ytegenskaper som kraftigt påverkar komponentens livslängd.Inverkan av slipparametrar som kornstorlek, maskinkraft ochanvändning av skärvätska har studerats för 304L austenitiskt rostfritt stål(Paper II) och 2304 duplext rostfritt stål (Paper I). Ytintegritetenpåverkas i hög grad av slipparametrarna. Kornstorlek hos slipkornenvisade sig ha störst inverkan. Ytdefekter (djupa spår, utsmetning,vidhäftande/kallsvetsade flisor och hack), ett kraftigt deformerat skiktupp till några mikrometer i tjocklek samt alstring av högadragrestspänningar i ytan längs med slipriktningen observerades som dehuvudsakliga skadetyperna. En hög nivå av anisotropa restspänningarindikerar att mekaniska effekter vid slipning dominerat över termiskaeffekter.Slipningens inverkan på spänningskorrosionsbeteendet hos 304Laustenitiskt rostfritt stål i en kloridmiljö har undersökts (Paper III). Ytanstillstånd påverkade den faktiska belastningen vid fyrpunktsböjprovning,som därmed avvek från de beräknade värdena enligt formeln istandarden ASTM G39. Dragrestspänningar från slipningen föreslogsvara den huvudsakliga orsaken till initiering av mikrosprickor på deslipade ytorna. Slipning längs med belastningsriktningen ökadekänsligheten för kloridinducerad spänningskorrosion, medan spänningskorrosionsmotståndet.
Kunskapen från detta arbete kan utgöra en referens för att välja lämpligaslipparametrar vid tillverkning av rostfria stålkomponenter och kan ävenanvändas för att förstå skadefall hos slipade rostfria stålkomponenter vidanvändning.Nyckelordrostfritt stål, ytintegritet, restspänning, spänningskorrosion, slipning
List of papersThis thesis is based on the following papers, which are referred to in thetext by their Roman numerals.I.N. Zhou, R. Lin Peng, R. Pettersson, Surface integrity of 2304duplex stainless steel after different grinding operations,accepted by Journal of Materials Processing Technology.II.N. Zhou, R. Lin Peng, R. Pettersson, Surface characterization ofaustenitic stainless 304L after different grinding operations,submitted to Journal of Materials Processing Technology.III.N. Zhou, R. Pettersson, R. Lin Peng, M. Schönning, Effect ofsurface grinding on chloride induced SCC of 304L, submitted toMaterial Science and Engineering A.The author’s contribution to the papers:I.The author’s contributions to this article are the major part of theexperiments, evaluation and writing, apart from some of the XRDmeasurements.II.The author’s contributions to this article are the major part of theexperiments, evaluation and writing, apart from some of the XRDand thickness measurements.III.The author’s contributions to this article are the major part of theexperiments, evaluation and writing, apart from some of the XRDmeasurements.
AcknowledgementsFirst of all, I would like to express my sincere gratitude to my mainsupervisor Rachel Pettersson and co-supervisor Ru Lin Peng. Thank youfor the countless time that you have put into this project as well assupport and encouragement all the way. Also, many thanks to MikaelSchönning and Timo Pittulainen at Outokumpu Stainless AB for all thesupport and valuable advice.My colleagues at Högskolan Dalarna and Sandbacka Park, thank you allfor creating a fun and enjoyable working environment. The experimentalsupport from Ulf Modin is greatly appreciated.Friends and family, this would not be possible without you. My deepestgratitude is to my husband Erik Hedman for his love and support.This work was performed within the Swedish Steel Industry GraduateSchool with financial support from Outokumpu Stainless ResearchFoundation, Region Dalarna, Region Gävleborg, Länsstyrelsen Gävleborg,Jernkontoret, Sandviken kommun and Högskolan Dalarna. Specialacknowledgements are to Staffan Hertzman and Stefan Jonsson forproviding me the opportunity for the work.Nian ZhouSandviken, January 2015
List of abbreviationsσ Residual stress parallel to the rolling/grinding directionσ Residual stress perpendicular to the rolling/grindingdirectionσγResidual stress in austenitic phaseασResidual stress in ferritic phaseσMMacro residual stressm,γσMicro-residual stress in austeniteσm,αMicro-residual stress in ferriteADAs deliveredBCCBody centered cubic, ferrite phaseBCTBody centered tetragonalBSEBackscattered electronCl-SCCChloride induced stress corrosion crackingECCIElectron channeling contrast imagingFCCFace centered cubic, austenite phaseFEG-SEMField emission gun scanning electron microscopeFWHMFull Width at Half MaximumPREPitting resistance equivalentRaArithmetic average roughnessRDRolling directionRzAverage peak to valley heightSCCStress corrosion crackingSESecondary electronSEMScanning electron microscopyTDTransverse to rolling directionXRDX-ray diffraction
Contents1. Introduction 161.1. Background 161.2. Aim of this work 162. Stainless steels 182.1. Introduction 182.2. Categories 182.2.1. Austenitic stainless steels 182.2.2. Ferritic stainless steels 182.2.3. Martensitic stainless steels 192.2.4. Duplex stainless steels 192.3. Machinability of stainless steels 193. Grinding 213.1. Grinding process 213.2. Residual stresses in grinding 223.3. Published work on grinding 234. Surface integrity 244.1. Surface roughness 244.2. Surface defects 254.3. Microstructural alterations 254.4. Residual stresses 265. Corrosion of stainless steels 275.1. Pitting corrosion 275.2. Stress corrosion cracking 286. Experimental work 316.1. Materials 316.2. Grinding operations 326.3. Corrosion studies 346.4. Characterization techniques 356.4.1. 3D optical surface profilometry 356.4.2. Stereo microscope 366.4.3. Scanning electron microscopy 366.4.4. X-ray diffraction 387. Results and discussion 427.1. Summary of appended papers 427.1.1. Paper I 427.1.2. Paper II 427.1.3. Paper III 437.2. Influence of grinding on surface integrity 437.2.1. Surface roughness 43
7.2.2. Surface topography and surface defects 447.2.3. Cross-section microstructure 467.2.4. Residual stresses 487.3. Influence of grinding on chloride induced SCC 537.3.1. Corrosion behaviour without external loading 537.3.2. In-situ measurement of surface stress 547.3.3. Corrosion behaviour with four-point bend loading 557.3.4. Stress relaxation after exposure 608. Conclusions 639. Further work 6510. References 66
INTRODUCTION 161. Introduction1.1. BackgroundStainless steel is a very successful man-made material. A major advantageof stainless steels is the high corrosion resistance, either at low or hightemperatures, combined with good mechanical properties. Due to thediverse properties that can be achieved, stainless steels are extensivelyused in a variety of applications, such as general construction, chemicalengineering, petrochemical and nuclear industries, food and beverageproduction. Unfortunately, the chloride ion, which exists in commonenvironments like seawater, the kitchen or even in the human body, isfound to make stainless steel prone to stress corrosion cracking (SCC).One review in 1983 showed that almost 37% of one thousand failures ofaustenitic stainless steel 304 in chemical industry were attributed tostress corrosion cracking [1], so the problem should be taken seriously.Combating SCC of stainless steels not only means the reduction ofcatastrophic failures, but also long-term cost savings and reduction ofenvironmental impact.It is well recognized that the surface geometrical, physical and mechanicalproperties of machined components have significant effects on theirfunctional performance; service failures related to corrosion almostalways initiate from the surface or subsurface. Depending on theapplications, machining processes are nearly always needed for stainlesssteel components to obtain the required surface and dimensionalaccuracy. Grinding is an important and widely used surface finishingprocess, sometimes also used for bulk material removal. Grinding is acomplex process with geometrically unspecified cutting edges [2]. Theknowledge of the evolution of the surface and subsurface layers ofstainless steels during grinding is very limited, in spite of the fact that theprocess can be critical to service failure.1.2. Aim of this workThe current work is focused on surface integrity and stress corrosioncracking behaviour of stainless steel from the grinding operations. Theaim of the first part (Paper I and Paper II) was to learn about the
17 INTRODUCTIONinterrelation between surface integrity in terms of surface roughness,surface defects, surface and subsurface microstructures, residual stressesand different grinding parameters. Abrasive grit size, machine power andgrinding lubricant were identified as the most interesting parameters tobe studied. The aim of the second part (Paper III) was to correlate thecorrosion properties to the grinding operation, especially to determinethe role of induced residual stresses and applied stress on the stresscorrosion cracking behaviour. This study is relevant to industrialapplications and contributes to the scientific understanding of SCC. Theresults obtained can provide a reference for choosing appropriategrinding parameters when fabricating stainless steel components; also tohelp understand the failure mechanisms during service
STAINLESS STEELS 182. Stainless steels2.1. IntroductionStainless steels are iron-based alloys that contain a minimum of 10.5%chromium by mass [3]. Chromium reacts instantly with oxygen andmoisture in the environment, therefore a protective oxide layer, known asthe passive film, will be formed over the entire surface of the material [4].This oxide layer is very thin, only 1-3 nanometers in thickness [5]; growsslowly with time and has self-healing ability. Chromium is the mostsignificant alloying element affecting passivity, although other elementssuch as nickel, molybdenum and nitrogen can also be added to enhancethe corrosion resistance and structural properties of stainless steels [6] [7][8].2.2. CategoriesTraditionally, stainless steels are often categorized based on theirmicrostructure. The most common structures are austenitic, ferritic,martensitic and duplex stainless steels.2.2.1. Austenitic stainless steelsAustenitic stainless steels have a face centered cubic (FCC) crystalstructure. They contain a minimum of 16% chromium, a maximum of0.15% carbon and sufficient nickel and/or manganese to retain theaustenitic structure [9]. Additional elements, such as molybdenum,copper, titanium or nitrogen can be added to modify properties for morecritical applications. Austenitic stainless steels are non-magnetic and canonly be hardened by cold working. This group of steels has lower thermalconductivity than other stainless steels or low-alloyed structural steels.2.2.2. Ferritic stainless steelsFerritic stainless steels, which have a body centered cubic (BCC) crystalstructure, consist principally of iron and chromium. They contain verylittle carbon and no, or very little nickel. Compared with austenitic grades,they are ferromagnetic and generally have better engineering propertieswith higher thermal conductivity. Because of the reduced chromium andnickel content, they have lower corrosion resistance; however, the
19 STAINLESS STEELSresistance to stress corrosion cracking is higher than for some austeniticstainless steels [10].2.2.3. Martensitic stainless steelsMartensitic stainless steels have a body centered tetragonal (BCT) crystalstructure. They contain chromium and small additions of nickel,molybdenum and carbon [11]. They are usually hardened by quenchingand tempered. Martensitic stainless steels are magnetic. The corrosionresistance is generally lower than the other members in the stainless steelfamily; they are often used for high hardness requirement. Martensite canalso be formed as a result of deformation of metastable austeniticstainless steels.2.2.4. Duplex stainless steelsDuplex stainless steels, containing relative high levels of chromium and amoderate amount of nickel, have a microstructure balanced to containapproximately equal proportions of the austenitic and ferritic phases [11].Because of the duplex structure, they combine many of the beneficialaspects of both austenitic and ferritic stainless steels. They areferromagnetic due to the ferrite content and the thermal expansion liesbetween that of the austenitic and ferritic stainless steels. Compared withaustenitic grades, they provide excellent mechanical properties andimproved corrosion resistance, especially resistance to stress corrosioncracking.2.3. Machinability of stainless steelsThe term machinability refers to the ease with which a metal can bemachined to a desired shape with a satisfactory surface finishing at lowcost [12]. Two main problems may be generated when machiningcomponents with poor machinability: short tool life and damaged surface[13] [14] [15] [16]. Austenitic and duplex stainless steels are difficult tomachine compared to conventional steels or ferritic and martensiticstainless steels. Built-up edges formed on the cutting tool due to the highductility and there is a tendency to rapid work hardening [17]. Lowthermal conductivity leads to high machining temperature, which canburn the surface [18] or give high tensile residual stresses [19] in themachined surface. Transformation to martensitic can occur whenmachining austenitic stainless steels and significantly changes the
STAINLESS STEELS 20material properties [20]. Moreover, for duplex stainless steels, highductility in combination with high strength makes chip breaking difficult,which deteriorates the surface finishing [21]. The quality of the machinedsurfaces plays a significant role in the performance of the component,such as fatigue life and resistance to stress corrosion cracking. Thuscareful attention should be paid to surface properties when machiningstainless steels, especially the austenitic and duplex grades.
21 GRINDING3. Grinding3.1. Grinding processThe grinding process employs abrasives that contain grains of hardmineral bonded in a matrix [2]. Grinding is a type of cutting, in which thecutting edges are randomly spaced and irregularly shaped. Figure 1 showsa sketch of how abrasive grains in a grinding wheel remove material froma workpiece. During grinding, each grain acts as a microscopic singlepoint cutting edge and shears a short chip with gradually increasingthickness. Because of the irregular shape of the grains, sometimesploughing occurs between the grain and the workpiece instead of cutting[22].Figure 1 Schematic drawing of a grinding wheel, showing abrasive grains remove materialfrom a workpiece.Grinding is often categorized as a separate process from the conventionalcutting processes (turning, milling, drilling, etc.). There are severalaspects make it different from the other metal removal processes, thesedifferences are m
influence of grinding parameters including abrasive grit size, machine power and grinding lubricant were studied for 304L austenitic stainless steel (Paper II) and 2304 duplex stainless steel (Paper I). Surface integrity was proved to vary significantly with different grinding parameters. Abrasive gri
different operations like turning, threading, tapper grinding, end drilling etc. The plant has the capacity to do most of operation except taper grinding. Presently the plant has to outsource the shaft to outside plant for the taper grinding. presently the plant have a grinding machine of G 17-22U, which means it is a universal grinding machine that can machine a job up to 220mm diameter shaft .
GRINDING MACHINE OPERATIONS (SEIP-LIG-MSP-6- O) Carry out cylindrical Carry out surface grinding machine Perform Universal tools and cutter grinding machine operations. Prepare for the precession grinding machine operations. Perform thread cutting operations Perform off-hand grinding operation Clean, care maintain and store tools and equipment.
Grinding wheel selection, Qw, Vw Wheel dressing parameters Limitations of on-board inspection Grinding Wheel 101 Grinding wheel definitions and descriptions Dressable and Non-dressable grinding wheels Tool wear Hands on Lab or Gear Grinding Simul
29. Grinding Machines Grinding Machines are also regarded as machine tools. A distinguishing feature of grinding machines is the rotating abrasive tool. Grinding machine is employed to obtain high accuracy along with very high class of surface finish on the workpiece. However, advent of new generation of grinding wheels and grinding machines,
difficult to grind than conventional structural steel. In order to achieve successful results when grinding tool steel, it is necessary to choose the grinding wheel with care. In turn, choosing the right grinding wheel and grinding data requires an understanding of how a grinding wheel works
A grinding wheel's surface texture has a strong influence upon its grinding performance. This is clearly evidenced by the increase in grinding forces, power consumption, and cutting zone temperatures as a wheel wears [Butler and Blunt, 2002]. If the surface texture of a grinding wheel could be measured and quantified, then it could be
-Surface speeds involving grinding are very fast. 3 types of action Cutting, rubbing and plowing actions occur (a) (b) Grinding Process. Grinding Forces A knowledge of grinding forces is essential for: -Estimating power requirements. -Designing grinding machines and work-holding fixtures and devices. -Determining the deflections .
The Adventures of Tom Sawyer ADVANCED PLACEMENT TEACHING UNIT OBJECTIVES The Adventures of Tom Sawyer Objectives By the end of this Unit, the student will be able to: 1. identify the conventions of satire. 2. examine theories of humor. 3. analyze the narrative arc including character development, setting, plot, conflict, exposition, narrative persona, and point of view. 4. identify and analyze .
