Under supervision of: J.P.M. Hoefnagels T. Nulens V.G. Kouznetsova M.P.F.H.L. van Maris Eindhoven, September 2008

Martensite Transformation In Sandvik Nanoflex

Influence of heat treatments on strain induced transformation

T.A.J.M. van de Ven MT 08.38

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Abstract In this report the metastable austenitic steel Sandvik Nanoflex is investigated. This material is interesting because it possesses the capability of combining good deformability with high strength. The final microstructure and associated mechanical properties strongly depend on the thermal and mechanical loading history of the sample. The chemical composition of Sandvik Nanoflex is 12Cr-9Ni-4Mo-2Cu %wt. The microstructure changes from austenite to martensite during straining or isothermal cooling. The martensite transformation is a irreversible plastic deformation. This is why it is called a TRIP steel (TRansformation Induced Plasticity) During the research on the transformation austenite to martensite a remarkable material property was discovered, i.e. an unexpected increase of the yield and tensile strength of the material was observed after a heat treatment. Therefore the goal of this project is to study if there is a relation between the development of the martensite fraction and the development of the stress-strain curve. This is done by determining the martensite fraction at different strains. It was found that the evolution of the stress-strain curve of the samples heat treated at 1000°C and 1100°C can be explained with the evolution of the martensite fraction during the tensile test. For the 1000°C samples the martensite fraction develops linearly which explains the nearly constant stress in the measured area. The relaxation effect observed in the 1100°C samples can be explained by the observed increase transformation rate during the tensile test. Also the 1100°C samples were expected to show the most martensite because they are stronger but this is not the case. The samples heat treated at 1000°C are showing the most martensite. In all the samples heat treated at 1000°C a martensite band is formed. Martensite band are bands with a very high density of martensite. These bands explain why the samples heat treated at 1000°C have the most martensite in it.

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Table of contents

Abstract.................................................................................................................1 Table of contents ..................................................................................................2 Table of contents ..................................................................................................2 1 Introduction....................................................................................................3

1.1 Philips .....................................................................................................3 1.2 Sandvik Nanoflex....................................................................................3 1.3 Motivation and Goal of this project .........................................................3 1.4 Structure of the report.............................................................................4

2 Heat treatment ...............................................................................................5 3 Experimental procedure for the initial tensile tests.........................................6

3.1 Introduction.............................................................................................6 3.2 Cutting out the samples..........................................................................6 3.3 Tensile tests ...........................................................................................7

4 Results of the initial tensile test......................................................................8 4.1 Introduction.............................................................................................8 4.2 Results....................................................................................................8 4.3 Hypothesis..............................................................................................9

5 Experimental procedure for determining the martensite fraction..................10 5.1 Introduction...........................................................................................10 5.2 Precipitation treatment..........................................................................11 5.3 Embedding in a resin............................................................................11 5.4 Grinding and polishing..........................................................................11 5.5 Etching..................................................................................................11 5.6 Images..................................................................................................12 5.7 Image analyses ....................................................................................12

6 Experimental results ....................................................................................14 6.1 Graphs and images ..............................................................................14 6.2 Results of the as-received samples......................................................19 6.3 Resuls of the 1000°C samples .............................................................19 6.4 1100°C samples ...................................................................................19 6.5 Standard deviation................................................................................20

7 Conclusion and recommendations...............................................................21 7.1 Conclusions ..........................................................................................21 7.2 Recommendations................................................................................21

8 References ..................................................................................................23 9 Appendices..................................................................................................24

9.1 Martensite fractions ..............................................................................24 9.2 As-received sample images..................................................................25 9.3 1000°C sample images ........................................................................26 9.4 1100°C sample images ........................................................................27

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1 Introduction

1.1 Philips

Philips uses the stainless steel Sandvik Nanoflex for the production of razorblades and caps for their electrical shavers. The material properties are very well suited for this application. In the austenitic phase the material is reasonably soft and easy to form into a razorblade. After deformation the razorblade becomes much harder and less deformable due to the martensite transformation induced by the deformation during forming. The use of Sandvik Nanoflex comes with some problems because there is no accurate micro scale model for this material. For each batch of this material Philips is receiving they have to determine the material properties. A change in the material properties of that batch Philips may require the alteration of the production process parameters.

1.2 Sandvik Nanoflex

Sandvik Nanoflex is a TRIP steel. TRIP stands for TRansformation Induced Plasticity. In the as-received state the material has an austenite phase. During thermal or mechanical loading the austenite will transform to martensite. This transformation comes with a volume change. The volume will increase with approximately 3 to 6 percent. Due to the transformation the material will deform inelastically [2]. The transformation is not reversible with removal of the mechanical load. To turn the martensite back into austenite is has to be heat treated. In the austenite phase this material has a FCC (Face Centered Cubic) microstructure. In this state the material is soft and ductile. During the transformation martensite is formed. Martensite has a BCT (Body Centered Tetragonal) microstructure and has a higher yield strength and hardness than austenite The chemical composition of the material is given in Table 1.1. The large amounts of chrome, nickel and molybdenum are making this material corrosion resistant. Element Cr Ni Mo Cu Ti Al Mn Si C+N

Wt-% 12,0 9,0 4,0 2,0 0,9 0,4 0,3 <0,5 <0,05 Table 1.1 Composition of Sandvik Nanoflex [2]

1.3 Motivation and Goal of this project

Already quite some research was done on Sandvik Nanoflex. Due to the considerable inhomogenity even at macroscopic length scales it is hard to make an accurate micro scale model of the material properties. The inhomogenity

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becomes more clear when different material behavior occurs even when the samples where cut out of the same plate. During the study on this material more and more material properties that are hard to explain where discovered. One of those material properties was discovered by Tom Nulens [3]. During his study he discovered that the material becomes stronger during a heat treatment. A heat treatment in general enlarges the grain size. A material with larger grains normally becomes weaker because dislocations have to travel through fewer grains boundaries. It is observed, however, that a sample of Sandvik Nanoflex that is heat treated becomes stronger. The apparent yield point becomes higher and the heat treatment also changes the shape of the stress-strain curve. The aim of this project is to study if there is a link between the increase in strength after a heat treatment and the martensite fraction in the material. To research this, heat treatments and tensile tests were performed. To make the martensite visible the sample is precipitation hardened. The precipitates form around the martensite and these precipitates become visible when the material is etched with Kalling No1. After etching the martensite fraction is determined using images taken of the material. The images of the samples are analyzed with the image processing toolbox in matlab, to dertemine the martensite fraction in the material.

1.4 Structure of the report

In Chapter 2 the heat treatments are explained, why they were chosen and at which temperatures they were done. In Chapter 3 the experimental procedure for the initial tensile tests are explained. In Chapter 4 the results of these tensile tests are discussed an a hypothesis is made for further investigation. The experimental procedure for determining the martensite fraction is explained in chapter 5. In Chapter 6 the results of the measured martensite fraction are presented and discussed. In Chapter 7 the conclusions and some recommendations are formulated.

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2 Heat treatment Tom Nulens [3] performed heat treatments, discussed below, to reduce a certain texture in the as-received material. During the research to martensite bands in this material only one orientation was wanted. This was to rule out the effect of the grain orientation on the development of martensite bands. Figure 2.1 shows a graphic representation of the temperature development during the heat treatments. The timescale is only indicative because it is slightly different for each heat treatment. The heat treatment chosen was to heat the sample to a certain temperature (T) and keep it at that temperature for one minute and then let it cool down slowly. First the grains will recover. At this stage the grains are very small and will start to grow. During the cooling stage of the heat treatment the grains will grow further. They were expected to all grow at the same rate so that at the end of the cooling stage all the grains are approximately the same size and larger than before the heat treatment. Tom Nulens [3] tested heat treatments at different temperatures T, (950°C, 1000°C, 1050°C, and 1100°C). The heat treatment at 1100°C showed the most remarkable change in material properties. The other three tests didn’t differ that much from each other. That is why 1100°C and 1000°C heat treatments were chosen to test during this research.

Figure 2.1 Temperature development during heat treatment. The heating and cooling time is different for each temperature T (1100°C and 1000°C)

of the different heat treatments. The time scale and the pictures of the grains are indicative

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3 Experimental procedure for the initial tensile tests

3.1 Introduction

The initial goal is to reproduce the results that were obtained earlier in the research of Tom Nulens [3]. Therefore the same tests as Tom Nulens [3] did were performed. Before the tensile test, described below, the samples were heat treated as described in the heat treatment section.

3.2 Cutting out the samples

In Figure 3.1 the sample dimensions are presented. The test samples are cut out of a sheet of Nanoflex using Electrical Discharge Machining (EDM). This is to minimize the possible martensite transformation during the production of the samples. Other methods like punching the samples out of a sheet will form martensite at the edges of the sample due to the deformation that comes with this process. Rolling of the material causes a particular grain orientation which affects the material properties in the three principal directions. Therefore during earlier studies the samples were persistently cut out in the rolling direction. The samples used during this research were also cut out in the rolling direction.

Figure 3.1 dimensions of the sample

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3.3 Tensile tests

The tensile tests are performed with the Kammrath & Weiss tensile stage. During the tensile test the elongation speed is set at 0,1 µm/s. This speed is chosen so low because higher speeds may locally increase the temperature and this can influence the martensite transformation [5]. Later on, the martensite fraction will be investigated that is why the martensite is given an excess amount of time to transform. The displacement limit for the tensile test is located at 2000µm because in this region everything interesting is happening like the observed relaxation. After this limit other material properties can be studied like fracture mechanics. To determine the evolution of the martensite transformation during a tensile test, several tensile tests were done with the same kind of sample. All the tensile tests will be aborted at a different elongation, such that at that point the martensite fraction can be determined post-mortem.

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4 Results of the initial tensile test

4.1 Introduction

In this chapter the results of the initial tensile test will be discussed. Also a hypothesis for what is causing this material behavior will be given.

4.2 Results

Figure 4.1 shows the stress-strain curves of the tensile tests performed by Tom Nulens [3] and the newly performed tensile tests (referred to as ‘second’). The results are presented with the engineering strain along the x-axis and the engineering stress along the y-axis. Figure 4.1 shows that the heat treatment is making the material stiffer than without heat treatment. The slope of the elastic region of the stress-strain curve is getting steeper with an increasing temperature T of the heat treatment. The sample heat treated at 1100°C shows a kind of relaxation effect at a strain of ~ 0.02 which is probably caused by a fast increase of the martensite transformation. Martensite transformation comes with a volume increase. This increase in volume is relaxing the material. Because the increasing volume is relaxing at small strains some strain and at lower strains the stress is lower. Figure 4.1 also shows that the material is getting stiffer when it is heat treated. The sample heat treated at 1100°C is even stiffer than the one heat treated at 1000°C.

Figure 4.1 Stress-strain curves of the tensile test done by Tom Nulens [3]

and the stress-strain curves of the new tensile tests (referred to as second)

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It is clear that the new tests correspond well to the results that were obtained by Tom Nulens [3] (Figure 4.1). The second stress-strain curves and the ones from the test done by Tom Nulens [3] do not lie exactly on top of each other but they have the same evolution. The first reason for why they are not exactly on top of each other is that the second samples didn’t come out of the same plate as the samples used by Tom. A second reason could be that when the heat treatment was performed the sample didn’t transform exactly the same because of a little difference in temperature and vacuum conditions.

4.3 Hypothesis

There are several explanations that may explain the change of material properties after a heat treatment. Differences in grain size can cause other material properties. Also during the heat treatment precipitates can be formed. An example of such a precipitate is the chi-phase [4]. The chi-phase is a precipitate that will form on the grain boundary. The concentration of chi-phase on the grain boundary makes the movement of dislocations through the grain boundaries harder. When dislocation cannot move easily the material will become stronger. A difference in martensite fraction can also explain differences in material properties. In this report the effect of the martensite fraction is studied.

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5 Experimental procedure for determining the martensite fraction

5.1 Introduction

To determine the martensite fraction at different stages of the tensile tests, several samples will be stretched to different strains. In all these samples, with different strains, the martensite fraction will be determined. Figure 5.1 shows at which stage of the stress-strain curves the measuring points are located. The green dotted lines indicate the measuring points. The first sample will be stretched to a strain of +0,4% which is still in the elastic region, it is not expected to show any martensite. The second point is just after the apparent yield point. At this point (ε = +1%) it should start to show martensite due to the strain applied to the sample. The third point (ε = +1,5%) is at the local peak of the 1100°C stress strain curve. At this point the sample is expected to show a massive increase of martensite to cause the relaxation effect. The fourth point at a strain of +3% where all the samples start to show the same material behavior. After that point there are no significant differences between the different heat treated samples. Martensite will gradually form to a maximum level and the sample will break.

Figure 5.1 Stress-strain curves of the second tensile tests. The green

lines represent the point at which the martensite fraction will be measured

The martensite transformation is determined using the following etching method. After the tensile tests the samples are precipitation hardened. Precipitates will form around the martensite. Etching makes the precipitates around the martensite visible. After etching images of the sample can be analyzed with

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image processing toolbox in Matlab. In this section all the steps of this method will be explained. The following steps are described in detail in the report of H.M. Slootbeek [5].

5.2 Precipitation treatment

There are no good etching methods to make the martensite in this material visible. Therefore a heat treatment is needed to make the martensite visible. This is a precipitation hardening heat treatment at 550 °C during 30 minutes [5]. During this treatment precipitates are forming around the martensite. These precipitates become visible after etching and because they are forming around the martensite this can be used to investigate the martensite fraction. This treatment is altering the material properties of the sample but it has no effect on the martensite fraction. Only the martensite fraction is studied so the change in other material properties does not matter.

5.3 Embedding in a resin

After the precipitation treatment the samples have to be embedded in a resin for better handling during etching, grinding and polishing. Already some research was done about which resin is the best for this application. In this study [5] durofast was determined as the best material for this application because it is resistant to the etchant and it is nearby black so it has good contrast to the sample [5]. The embedding is done with the Struers Labopress-3. The sample clamped in a sample holder has to be inserted in the machine. Then 1,5 spoons durofast is added. The machine has too heat the resin and sample for 180s at 180°C with a compressing force of 20kN and let it cool down for four minutes.

5.4 Grinding and polishing

Polishing is needed because when the surface is rough height differences can cause darker areas on the sample which can be identified as martensite during the analysis. Polishing and grinding is done in four steps with the Tegrapol-21. The first one is with the MD-Piano120 grinding disk with a force of 40N at 300rpm during 120s with water as lubricant. The second step uses the MD-Allegro with a force of 35N at 150rpm during 240s with Diapro 9um as abrasive lubricant. The third step is using the MD-Largo grinding disk with Diapro 3um as abrasive lubricant with a force of 35N at 150rpm for 120s. The last step is using the MD-DAC polishing disk at 150rpm with 20N for 120s. After each step the sample holders were rinsed with water and alcohol and examined for scratches. When there are scratches left on the sample the last step has to be repeated.

5.5 Etching

The etching is done with Kalling No1 (distilled water, CuCl2, HCl and C2H5OH). The samples have to be etched for two seconds. This gave the best contrast between the precipitates surrounding the martensite and austenite.

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5.6 Images

After etching, images have to be made of all the etched surfaces of the samples. This is done with an optical light microscope and a Zeiss Axiocam optical camera. On each sample three series of pictures were taken at number 1, 2 and 3 in Figure 5.2. Each series of pictures consists of 4 pictures taken over the full thickness of the sample. The pictures have approximately 50 percent overlap. This overlap is needed to accurately stitch the pictures together using Autostitch [6]. The results of this stitching can be seen in appendices 9.2, 9.3 and 9.4

Figure 5.2 A: Resin, B: Clamp, C: Sample. Numbers 1, 2 and 3 indicate the locations

of analysis on the sample, as listed in appendix 9.2, 9.3 and 9.4

5.7 Image analyses

The image analysis is done with the image processing toolbox in Matlab. First a region is defined (Figure 5.3) which is going to be analyzed. Matlab converts this color-picture into a black and white picture and determines the average gray level of this region. Counting the pixels with a gray level higher than the average grey level will result in a martensite fraction. Every pixel with a larger gray level is described to martensite. The picture in Figure 5.4 is the output picture: the white is martensite and the black is austenite. This picture has to be compared by eye with the first picture. When the estimated martensite level is too high or low the gray level can be altered and the martensite fraction can be computed again. This has to be done until the calculated martensite fraction looks satisfactory.

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Figure 5.3 Matlab analysis region

Figure 5.4 Matlab output picture

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6 Experimental results

6.1 Graphs and images

In Figure 6.1 the martensite fractions of the tree different heat treated samples are plotted against the strain. The blue line indicates the as-received samples, the green line the 1000°C samples and the red the 1100°C samples. Figure 6.2, Figure 6.3 and Figure 6.4 show the engineering stress-engineering strain curves of, as-received, 1000°C and 1100°C samples respectively. Figure 6.5, Figure 6.6 and Figure 6.7 show the images taken from the samples at location number two, from the as-received, 1000°C and 1100°C samples respectively with the lowest engineering strain at image (a) increasing to the highest strain level at image (d).

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Figure 6.1 Martensite fraction and standard deviation

Figure 6.2 Stress-strain curves of the as-received samples

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Figure 6.3 Stress-strain curves of the 1000 degrees samples

Figure 6.4 Stress-strain curves of the 1100 degrees samples

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a b c d

Figure 6.5 Images from location two of the as-received samples at different strains a) ε = 0,0039 b) ε = 0,0097 c) ε = 0,0159 d) ε = 0,0290

a b c d

Figure 6.6 Images from location two of the 1000°C samples at different strains a) ε = 0,0039 b) ε = 0,0097 c) ε = 0,0159 d) ε = 0,0290

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a b c d

Figure 6.7 Images from location two of the 1100°C samples at different strains a) ε = 0,0039 b) ε = 0,0097 c) ε = 0,0159 d) ε = 0,0290

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6.2 Results of the as-received samples

The development of the martensite fraction in the as-received samples (Figure 6.1) is hard to clarify. It was expected that the martensite fraction of the as-received sample is ascending linearly. Because the stress is nearly constant between ε = +1% and ε = +3%. This constant stress can be explained with a constant transformation rate. Though the martensite fraction is constant, within the standard deviation at the first three strain levels that were tested. It is increasing massively at the last strain level. The constant martensite fraction can be caused by the use of three different samples. Normally it is desirable that the martensite fraction at different strain stages is determined in one sample. To determine the martensite fraction the sample is embedded in a resin so it is impossible to stretch it further after determining the martensite fraction. This explanation for the constant martensite fraction is not likely because Figure 6.2 shows no significant differences in the stress-strain curves of the as-received samples. There is no other way to prove this because the development of the martensite fraction isn’t monitored during the tensile tests. There is likely something else what is causing this development of the martensite fraction, but this cannot be explained with the results obtained during this study.

6.3 Resuls of the 1000°C samples

The most remarkable change in these samples can be seen in Figure 6.6 and Appendix 9.3. All the samples have a martensite band. In the as-received samples and the 1100°C samples martensite bands only develop at ε = +3% .A 1000°C heat treatment is somehow triggering the development of martensite bands. A sudden development of a martensite band may explain the sharp kink at the yield point on the curve of the 1000°C sample that was terminated at a strain of ε = +3% (Figure 6.3). Possibly a martensite band is developing quickly at this point, as a result of that the stress is stabilizing. The martensite fraction (Figure 6.1) increases roughly linearly with an increasing strain within the standard deviations of the measuring points. This is exactly what was expected because after the kink in the curve the stress-strain curve is nearly constant. A constant stress with an ascending strain points to a constant martensite transformation rate. A constant martensite transformation rate produces a linear martensite fraction.

6.4 1100°C samples

The development of the martensite fraction (Figure 6.1) is exactly as expected for the 1100°C samples. The curve of the martensite fraction was expected to have an increasing slope when the tensile test progresses. This was expected because the increasing slope of the martensite fraction can explain the relaxation observed in the stress- strain curves of the 1100°C samples. Remarkable is that the curve of the martensite fraction lies lower than the other two curves. It was expected to be higher than the as-received and 1000°C stress-strain curves because this sample is the strongest.

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The martensite fraction is growing with an increasing rate (Figure 6.1). This behavior is also observed in the stress-strain curves (Figure 6.4) of these samples. When the material is plastically deformed the stress is still increasing. At some point (approximately at ε = 0,0159) the stress is decreasing. The martensite transformation rate is ascending at that point. The martensite transformation rate is causing a relaxation effect due to the increasing volume of the sample. The volume is increasing because the austenite to martensite transformation is attended with a volume change. When looking at the images of the samples in Figure 6.7 the first sample (a) is clearly showing martensite. When it is compared to the other samples that were only elastically deformed (Figure 6.5 (a), Figure 6.6 (a)) the martensite fraction is approximately the same. In the graph of the martensite fraction (Figure 6.1) this sample shows a lower martensite fraction. This is due to the method used to analyze the images. It is clear that the sample of Figure 6.7 (a) is much darker. This is caused by some dirt. Matlab has more trouble determining the martensite fraction of this darker image, because it is harder to make the distinction between the precipitates surrounding the martensite and the dirt.

6.5 Standard deviation

The standard deviations of the measurements are pretty large at some points (Figure 6.1, Appendix 9.1). Also the variations in between the stress strain curve between different samples of the same heat treatment are clearly visible (Figure 6.3, Figure 6.4). This can be caused by two different reasons, the differences in stress-strain curves are caused by the inhomogeneous material behavior of the Sandvik Nanoflex and the large standard deviations are caused by the inhomogeneous material behavior and the measuring inaccuracy. The Matlab results have to be judged by eye because Matlab only determines the martensite fraction bases on an average gray level of the image. Sometimes the gray value used by Matlab is wrong and it has to be altered. It has to be judges by eye when the gray level is ok. This judgment is causing inaccuracies.

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7 Conclusion and recommendations

7.1 Conclusions

It is not possible to make a hard conclusion about the material behavior with the information gathered during this study. More information of the sample is needed, such as a detailed view of the microstructure. But there are some things that can be concluded from this study using the stress strain plots and the pictures. The behavior of the 1100°C sample is probably caused by the way the martensite transformation rate develops during a tensile test. The continuously ascending martensite transformation rate seems to be causing the relaxation affects observed in the stress strain curve. Something is triggering the development of martensite bands when the sample is heat treated at 1000°C, however it is impossible to say what exactly is the reason. Therefore more research is needed. Probably it has something to do with the microstructure of this material so that has to be studied. In these samples the martensite transformation rate is constant because the martensite fraction ascends linearly. This seems to be causing the horizontal part of the stress strain curve. The as-received samples are hard to judge because of the strange results. During the first part of the tensile tests the martensite fraction stays constant. This cannot be explained with the stress strain curve. The martensite fraction was expected to increase linearly because of the plateau in the stress–strain curve. The results obtained during this research cannot be explained with the stress-strain curve. Therefore some more measurements have to be done with the as-received samples to rule out statistics and effects caused by the location the samples were taken out of the plate. A remarkable thing is that the martensite fraction curve (Figure 6.1) of the 1100°C is located lower than the as-received and 1000°C curves as it was expected to be located above those two other curves of the martensite fraction. According to the stress strain curves this is the strongest sample, so it was expected to show the most martensite. In this case where the 1100°C sample is not showing the most martensite, there must be some thing else in the macrostructure what makes the material stronger.

7.2 Recommendations

It is useful to measure the martensite fraction at much more strains such that there are more measuring points and a clearer view of the martensite fraction during the tensile test is obtained. To get a more accurate result more measurements of the martensite fraction at the same strain have to be done. This is to rule out the large statistical variations.

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A more consistent method of analyzing the images has to be found and employed. Now the obtained martensite fraction is heavily depending on the judgment of the person who is analyzing the images. It was found out that if someone else is doing the same analysis the result will be different. To get better knowledge of this material it is useful to investigate the microstructure of the material. Grain size and orientation can also cause different material behavior. Also the chi-phase mentioned earlier can cause these kind of difference in material behavior. It is expected that the chi-phase is making the movement of dislocations harder because of its higher hardness.

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8 References [1] William, D., Callister, Jr. (2003). Materials science and engineering an

introduction, sixth edition. Hoboken: Wiley. [2] Louws, L.C.N. (2007). Martensitic phase transformation in Sandvik Nanoflex,

Experimental research on isothermal and strain induced transformation behavior. Internal report, Eindhoven University of Techologie, The Nederlands, MT 07.11

[3] T. Nulens (2008). Experimental Characterization of Martensitic Phase Transformation in Sandvik NanoflexTM. Internal report, Eindhoven University of Techologie, The Nederlands, MT 08.37

[4] Xu, W., San Martin, D., Rivera Diaz del Catillo, P.E.J., van der Zwaag, S. (2007). Modelling and characterization of chi-phase grain boundary precipitation during aging of Fe-Cr-Ni-Mo stainless steel. Materials science and engineering A 467. Page 24-32

[5] Slootbeek, H.W. (2007). Experimental study and phenomenological modeling of transformation behavior of Nanoflex. Internal report, Eindhoven University of Techologie, The Nederlands, MT 07.36

[6] Brown, M., Lowe, D. (2008). Autostitch, University of British Columbia. http://www.cs.ubc.ca/~mbrown/autostitch/autostitch.html

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9 Appendices

9.1 Martensite fractions

Elongation 80 micron 200 micron

Engineering strain 0,0039 0,0097

Heat treatment

Place on sample

sample No.

martensite fraction average

standard deviation

sample No.

martensite fraction average

standard deviation

as-received 1 3.6 3,2685 4,1677 0,9984 5.3 1,0740 3,3304 0,1573

2 3,7338 3,2192

3 5,5007 3,4416

1000 degrees 1 3.2 4,2474 4,1414 0,5191 5.4 8,5451 8,1120 1,8894

2 4,5994 9,7472

3 3,5775 6,0436

1100 degrees 1 4.1 1,2505 1,3364 0,1214 1.4 2,5545 2,3151 0,6695

2 1,4222 2,8320

3 3,6731 1,5589

Elongation 330 micron 600 micron

Engineering strain 0,0159 0,0290

Heat treatment

Place on sample

sample No.

martensite fraction average

standard deviation

sample No.

martensite fraction average

standard deviation

as-received 1 2.1 4,6408 3,8179 2,3226 4.8 25,9742 23,5490 2,1740

2 5,6170 21,7750

3 1,1959 22,8977

1000 degrees 1 1.8 12,5306 10,6741 1,7726 2.6 20,0028 20,6746 0,9908

2 10,4923 20,2084

3 8,9995 21,8125

1100 degrees 1 5.5 11,9666 5,3382 2,0659 5.7 19,3515 21,6135 5,4967

2 6,7990 27,8803

3 3,8774 17,6088

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9.2 As-received sample images

These images are rotated 90° with respect to Figure 6.5, Figure 6.6 and Figure 6.7

Location Location

1

1

2

2

3

3

ε = + 0,4% ε = + 1%

1

1

2

2

3

3

ε = + 1,5% ε = + 3%

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9.3 1000°C sample images

These images are rotated 90° with respect to Figure 6.5, Figure 6.6 and Figure 6.7

Location Location

1

1

2

2

3

3

ε = + 0,4% ε = + 1%

1

1

2

2

3

3

ε = + 1,5% ε = + 3%

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9.4 1100°C sample images

These images are rotated 90° with respect to Figure 6.5, Figure 6.6 and Figure 6.7

Location Location

1

1

2

2

3

3

ε = + 0,4% ε = + 1%

1

1

2

2

3

3

ε = + 1,5% ε = + 3%