Problem: A tube heat treater was making heavily distorted tubes with “hooked” ends on their induction heat treating line. The first and last meter of every tube was more than 1cm out of straightness. Hypothesis: Non-uniform phase transformation can occur from asymmetric heating and cooling, and the observed distortion is due to asymmetric heating and cooling during heat treatment of the tube

Frame, Lesley D.

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Induction Heat Treating for Tube and PipeIn-line induction heat treating of tube and pipe involves a high temperature stage (austenitizing), followed by rapid cooling (quench), and lower temperature heating (tempering). Careful positioning of the tubes within the induction coil and spray quench as well as rotation of the tubes asthey are heat treated helps to ensure uniform forces and temperatures in the tubes.Distortion in Heat Treated Tube: A Materials Engineering ApproachLesley D. Frame, PhDDepartment of Technology ManagementUniversity of Bridgeport, Bridgeport, CT Objectives BackgroundMethods ResultsConclusionsAcknowledgements References[1] H. Pollack. Materials Science and Metallurgy, 4th ed., Englewood Cliffs, NJ: Prentice-Hall, 1988.[2] J.M. Moyer and G.S. Ansell, The Volume Expansion Accompanying the Martensite Transformation in Iron-Carbon Alloys, Metallurgical Transactions A, Vol. 6A, 1975, pp. 1785-1791.[3] C.L. Magee and R.G. Davies, On the Volume Expansion Accompanying the F.C.C. to B.C.C. Transformation in Ferrous Alloys, Acta Metallurgica, Vol. 20, 1972, pp. 1031-1043.[4] S.-J. Lee, M.T. Lusk and Y.-K. Lee, Conversional Model of Transformation Strain to Phase Fraction in Low Alloy Steels, Acta Materialia, Vol. 55, 2007, pp. 875-882.[5] H.K. Yeddu, Martensitic Transformations in Steel – A 3D Phase-field Study, PhD Thesis, Stockholm, Sweden, 2012.[6] K. Arimoto, D. Lambert, G. Li, A. Arvind and W.T. Wu, Development of Heat Treatment Simulation System “DeformTM-HT”, Heat Treating: Proceedings of the 18th Conference, R. Wallis and H. Walton (eds.), ASM International, 1999, pp. 639-644.[7] Total Materia Database. Retrieved Feb. 20, 2017 from www.totalmateria.com[8] L. Frame, Distortion in Tube and Pipe Products:  Microstructural and Computational Evidence, Quenching Control and Distortion 2012: Proceedings of the 6th International Quenching and Control of Distortion Conference Including the 4th International Distortion Engineering Conference (September 9-13, 2012, Chicago, Illinois), pp. 876-888. TheoreticalCalculation of volume changes due to phase transformation based on published materials data.rg density of austenite (kg/m3)T temperature (oC)Cm wt% Cra density of ferrite (kg/m3)rFe3C density of cementite (kg/m3)rM density of martensite at room temperature (kg/m3)aM linear CTE, martensite (oC-1)Ca at% CA      B C D E𝜌𝛾 𝑇, 𝐶𝑚 = 8099.79 − 0.506𝑇 ∗ (1 − 1.46 × 10−2𝐶𝑚)𝜌𝛼 𝑇 = 7875.96 − 0.297𝑇 − 5.62 × 10−5𝑇2𝜌𝐹𝑒3𝐶 𝑇 = 7686.45 − 6.63 × 10−2𝑇 − 3.12 × 10−4𝑇21𝜌𝛼+𝐹𝑒3𝐶(𝑇)=1 −𝐶𝑚6.689427𝜌𝛼+𝐶𝑚6.689427 ∗ 𝜌𝐹𝑒3𝐶(𝑇)𝜌𝑀 𝐶𝑚 = 7870.98 − 168.2𝐶 + 7.92𝐶𝑚2 𝛼𝑀 = (14.9 − 1.9 ∗ 𝐶𝑎) × 10−6SimulationSolidWorks Simulation Express to model non-uniform volume expansion in the rotating tube.A tube was modeled as two helices to represent the rotation of the tube on a heat treat line.  The helix angle was changed to represent different rotation-to-linear motion ratios.  A uniform volumetric expansion was applied to one of the two helices to determine the distortion in a tube as a function of rotation angle.  One end was constrained (representing its attachment to a longer length of tube) while the other was allowed to deform freely. TheoreticalBy plotting multiple cooling paths on a continuous cooling transformation (CCT) diagram, and calculating the percent volume change based on the phases formed, it is possible to determine the relative volume for a fully martensitic steel (blue), 50% martensite and 50% ferrite + pearlite steel (red, pink), and fully ferritic and pearlitic steel (green).  The fully martensitic steel has a slightly larger volume than the others.-35-30-25-20-15-10-50510150100200300400500600700800900% Volume change (1/1000)Temperature (oC)Volumetric changes during cooling of Carbon SteelA (100% M)B (50% M)C (50% M)D (0% M)E (0% M)ProblemA tube heat treater was making heavily distorted tubes with “hooked” ends on their induction heat treating line.  The first and last meter of every tube was more than 1cm out of straightness.HypothesisNon-uniform phase transformation can occur from asymmetric heating and cooling, and the observed distortion is due to asymmetric heating and cooling during heat treatment of the tube.  Causes of Distortion in Tubular ProductsUneven heating / coolingPhase changeResidual StressesApplied macro-stressesNon-uniform grainsizeMicrosegregation of alloysIntricate part designPoor process designTemperTimeVolume change due to phases present in steelNo rotation in tube over sample length0.5 rotation1.75 rotationsSimulationFive scenarios were modeled:No rotation 0.5 rotation over sample length1.0 rotation1.5 rotations1.75 rotations1 full rotationL: 750 mmOD: 25 mmWall: 1.55 mmDistortion in tube provided by customer matches simulated results of 1 full rotationMaterials AnalysisMetallurgical evaluation of distorted tube. The distorted tube was sectioned using a Leco wet abrasive saw as indicated (dotted lines).  Sample orientations were carefully marked before polishing to 1 mm finish and etching with 2% Nital solution for 20 sec to enable the examination of the microstructure.  Quantitative image analysis was performed using Adobe Photoshop.Materials AnalysisNital preferentially attacks the carbon-rich martensite phase, making it appear dark (M).  The carbon-poor ferrite phase appears light (F).  In this tube there is a high amount of retained ferrite (ferrite that was never converted to austenite during austenitizing, arrows).  The microstructures at several positions around the tube cross section are shown (tube surface is on the left of each micrograph).  The location ofthe maximum amount of retained ferrite for each cross-section is shown with blue shading below the micrographs. The highest ferrite position spirals around the tube.C B A90o180o270o0oLooking at 270o face180o90o0o20mmMF0o45o90o135o180o225o270o315oDownward deflection is greatest with the volumetric expansion on right of end face.Orientation where location C has greatest downward deflection.1. Non-uniform martensite-ferrite ratio around the tube cross-section can cause a localized volumetric expansion.2. Localized volumetric expansion can result in distortion (hooked ends) at lower rotation-to-linear movement ratios for in-line heat treated tube.3. A helical volumetric expansion with one full rotation over the length of the tube (75 cm) will result in a downward hook to the tube end (purple arrow) when the expanded volume is positioned at the right face of the end (red shading).4. The tube sample provided by the customer contained significantly higher retained ferrite (smaller volume) in the 315o position of sample C, corresponding to the left face of the tube end when positioned in the greatest downward deflection orientation, thus matching the simulation results.Recommendations to Heat Treater1. Retained ferrite is due to inadequate heating during austenitizing.  Temperature should be increased or soak time at maximum temperature should be extended.2. Simulation results suggest that a high rate of rotation for tube may result in less deformation (even without changing heating parameters).High Ferrite (smaller volume) High Martensite(larger volume)A B CThank you to Thermatool Corp., Mike DiDonato, Yoni Adonyi, and (confidential) Heat Treat Customer for providing resources and feedback for this research.0510150 45 90 135 180 225 270 315 0% FerritePosition (degrees)Area Percent of Retained FerriteABC90o0o270o180o90o0o270o180o90o0o270o180oExpansionRef. [1]Ref. [2-6]Ref. [7]Ref. [8]

Distortion in Heat Treated Tube: A Materials Engineering Approach

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Distortion in Heat Treated Tube: A Materials Engineering Approach

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