Microstructure Laboratory#2

Group # 4

José A. Rojas Cordero

Course ??

Date the experiment was performed

Date the experiment was due

Professor Julio Noriegas, Phd

Introduction

• The objective of this investigation is to train the student on the techniques for metallographic sample preparation.

• The use of optical microscopes to examine the structure of metals.

• Brass and steel specimens will be mounted, ground, polished, etched, and microscopically examined.

• The history and properties of the metal. • The ASTM specifications.

ME LABORATORY 2

Comparision Laboratories

3

Modern physical metallurgy 8th ed., R.E. SMALLMAN, A.H.W. NGAN. Fundamentals of physical metallurgy, and basic techniques of microstructure. (How can we applicant metals properties).

Ancient Metals: Microstructure and Metallurgy Vol.1; David A. Scott. 2011. Introduction of metallographic and ancient metals.

Steel metallurgy: Properties, specifications, and applications. S.K. Mandal. 2015. (Microstructure origin, grains sizes, and properties, metals types,heat tratements, weldings).

Your take away goes hereME LABORATORY

Theory

4

• Using the Jeffries Planimetric Method, for counting the grains. The number of grains per mm2 is computed using the equation:

Equation 1

Where the variables are:• M is the magnification of the photographic image.• n1 is the number of grains completely in the inscribed area.

• n2 is the number of grains intersecting the perimeter of the test area.

Equation 1.Your take away goes here

ME LABORATORY

NA M2

5000n1

n 22

• The Heyn-Intercept Method, estimating the average grain size by counting (On a photomicrograph of a representative field of the specimen) the number of grains intercepted by one or more straight lines.

ME LABORATORY 5

LЗ = LC / (M ∙ P)Equation 2.

• And the number of intercepts per unit length of test line is computed using the equation:

NL = 1 / LЗ

Equation 3.Where:LЗ is the the mean intercept distance.LC is the circumference length.M is the magnification of the photographic

image.P is the number of grains intersecting the

perimeter of the test area.

EQUATIONS :

• Euler Triple Point Method as with the Jeffries method, a circle is drawn on the figure with a diameter of 79.79 mm. This defines an inscribed area of 5000 mm2.

The value of NA is computed using the equation:

(substitution of P for PY)

Where:• PY is the count of the number of grain boundary triple points.

• AT is the area of the inscribed area at 1X magnification.ME LABORATORY

6

,12/

TA A

PN

EQUATIONS :

EquipmentFor the Microstructure Experiment, the following will be used.

• Three different specimens will be analyzed, which included Brass SAE 660, Steel 1018 and Steel 4140.

• The specimens were grinded using sand paper of 240, 320, 400 and 600.

• Polishing was performed using a bench polisher with three microns Alumina (Al2O3) grid size, and using a polishing velvet cloth.

• The samples were analyzed using a light reflective microscope.• Samples were pictured using a metallographic computer interface. • Etched reagents Nital.

ME LABORATORY 7

EXPERIMENTAL PROCEDURES

ME LABORATORY 8

Specimen Preparation

• A specimen for metallographic examination is prepared to reveal its metal structure. So its surface must be flat and free from scratches resembling a mirror before etched.

Sampling • Specimen should be carefully selected for examination. Rolled shapes should be

examined on the longitudinal and transversal direction.• Sectioning is performed to remove a suitably sized sample for subsequent mounting

and polishing. Abrasive cutting should be used whenever possible. Enough cooling should be provided during the cutting process to avoid changing the structure of the specimen.

• When samples must be removed from large parts by destructive methods such as torches or hacksaws, the cuts should be made at a reasonable distance from the area of interest. Subsequent cutting to remove the damage areas should be performed with an abrasive cutter.

ME LABORATORY 9

EXPERIMENTAL PROCEDURES

9

Your take away goes hereME LABORATORY

5. After sectioning, samples must be mounted using compression molding. Compression molding resins are dry powders which cure at 3,000 to 4,200 psi pressure and 150°C temperature.6. To mount a specimen using the Specimen Mount Press, place sample face down upon polished surface of Mold Base. Carefully lower Mold Cylinder upon Mold Base (do not force). Pour approximately six to eight grams of Molding Powder into Mold Cylinder.7. Carefully lower Mold Ram, polished side down, into Mold Cylinder. Transfer entire assembly to Insulating Plate and apply the initial hydraulic pressure (100psi approximately).8. Active Heater at Cord Switch for about 20 minutes. After that increase pressure to 4200psi. Switch off current and lift Heater onto Heater Hook. Allow Mold Assembly to cool to 100°F before ejecting mounting.

EXPERIMENTAL PROCEDURES

Grinding • Any burrs on the edges of the specimen should be removed before mounting

by means of a coarse grinding paper or a file. After mounting, rough grinding is carried out mechanically using 240 and 320 grit grinding papers.

• The sample should be maintained cool, so open the grinder water valve such that the specimen surface is dipped in water during grinding.

• The grinding operation should be done by a forward motion until only scratches due to the particular paper can be seen to cover the surface. When the coarser scratches appear uniform, the next grinding paper should be used (specimens and hands should be washed with soap and water before using the next paper).

• When using the next paper, the specimen is rotated 90 degrees to grind at right angles to the scratches formed by previous paper. After rough grinding operation is finished, fine grinding is carried out similarly using 400 and 600 grit grinding papers.

ME LABORATORY 10

Polishing

• After grinding operation is finished, the specimen is polished by holding it against a horizontal wheel covered with a velvet cloth containing Alumina (Al2O3) 3 microns grid size as polishing media. During polishing the velvet cloth is supplied with these particles as an aqueous suspension at regular intervals.

• During this process the surface must attain, such good polish, as to resemble a mirror.

ME LABORATORY 11

Etching• Among the methods of metallographic etching, we have the optical, chemical, and physical etching.

The purpose of this type of etching is to chemically attack the metal surface to bring out its structure. This results from the different rate of attack of the chemical reagent on grains that have different orientation, and on constituents present in multiphase materials.

• Ferrous samples can be etched with Nital which is a solution of 2-5% nitric acid in alcohol. Austenitic and stainless steel samples can be etched with ferric chloride solution containing 5g of FeCl in ml of hydrochloric acid and 100ml of water. Cooper and many of its alloys can be etched with an ammonium solution containing 5 parts of ammonium hydroxide, 5 parts of water, and 2-5 parts of hydrogen peroxide.

• Before etching, the specimen should be thoroughly washed with water and dries with alcohol.• The specimen, with its polished surface upwards, should be immersed in the etching solution,

contained in a small porcelain dish.• The specimen surface should be examined from time to time, and the specimen is removed from the

etchant when the grain structure is just visible to the unaided eye. The etching time could range from a few seconds to one minute.

• After etching, the specimen is thoroughly washed with water and then dried with alcohol.

ME LABORATORY 12

Microscopic Examination

• Fix the specimen on a plane sheet using mounting clay.

• Level the etched surface with the aid of a leveling device.

• Place the specimen on the microscope, and select the most appropriate magnification to examine the sample.

ME LABORATORY 13

Results

• Draw the structure of the samples as watched in the microscope, use Table 1.1 for this purpose. You could also take photomicrographs using the Metallograph and 669 Polaroid film.

• Describe the shape and distribution of the grains and constituent phases, i.e. indicate the presence of ferrite, fine pearlite, coarse pearlite, spheroidite, martensite, etc.

• Measure the grain size and the area fraction of constituent phases in each specimen as standardized by the American Society for Testing and Materials (ASTM).

• Based on the microstructure of the specimens, predict their properties and relate to their history.

ME LABORATORY 14

RESULTS

ME LABORATORY 15

ME LABORATORY 16

ME LABORATORY 17

B. Specimen No: 2

• Designation: Steel 1018• Condition: Polished and etched sample• Etchant: Nital• Magnification: 40x ( red = shared grains, green =internal grains)

ME LABORATORY 18

ME LABORATORY 19

ME LABORATORY 20

ME LABORATORY 21

Figure 3. Steel 4041 Microstruture at 40X of

magnification.

ME LABORATORY 22

Using the Jeffries Planimetric Method:

ME LABORATORY 23

Discussion

• Three samples of different materials were analyzed to find their microstructure. The specimens consist in Brass SAE660 alloy, Steel 1018 and Steel 4140. These samples passed through the preparation process that included sample preparation, polishing, and etching.

• The Brass SAE 660 alloy sample was etched using Ammonium Hydroxide. The sample was then analyzed under the microscope and the grains revealed. The magnification used was of 40x. The sample was analyzed to obtain the micro grain size using Planimetric (or Jeffries) Method. The ATSM micro grain size obtained by this method was 1.07. With the number of grains per square millimeter are of .

ME LABORATORY 24

• The second specimen analyzed was the Steel 1018. After the specimen was carefully polished and etched with Nital, it was analyzed under the microscope using a 40x magnification. For this sample the Jeffries Planimetric Method was used to obtain the micro grain size. The number of grains per square millimeter was of , with an ASTM micro grain size of 9.77.

• The last specimen analyzed was the Steel 4041. The micro grain sized was obtained after the sample was carefully polished and etched with Nital at a magnification of 40x. For this sample the Jeffries Planimetric Method was used to obtain the micro grain size. The ASTM micro grain sized obtained was 6.66, with a number of grains per square millimeter area of .

• The dark spots on the steels samples reflect the presence of impurities. The most common type of impurity found was the ferrite which is also known as iron; or a solid solution with iron as the main component, with a body centered cubic crystal structure. It is the component which gives steel and cast iron their magnetic properties.

ME LABORATORY 25

Conclusion• The experiment performed analyzed three different samples of alloys that

included Brass 360, Steel 1018, and Steel 4041. The samples were analyzed under the microscope using a magnification of 80x and after the proper etching material was used. The objectives established were accomplished as the techniques for metallographic sample preparation were performed and the microstructure for each specimen analyzed was obtained and grain sized found and compare againg the ASTM E-112 Standards.

• By using the Jeffries Planimetric Method the ATSM micro grain size obtain 1.4, 1.2 and 1.5 for Brass360, Steel 1018, Steel 4041 respectively. For the Brass specimen the error between the Jeffries Planimetric Method vs. Heyn-Intercept Method was of 4.8368 %, the error between Jeffries Planimetric Method vs. Euler Triple Point Method was 12.1021 %, and the error between Heyn-Intercept Method vs. Euler Triple Point Method was 10.818 %.

ME LABORATORY 26

Recommendation

• Our recommendation would be to have an electric grinder with a steady slow speed so the grinding process would be better. The polishing procedure needs to be a clean one, would recommend using clean velvet cloth and pure materials.

• The etching part has to be one without touching the specimen, I would recommend using gloves.

ME LABORATORY 27

Figure 7: Prof. Noriegas Analizing Specimen

ME LABORATORY 28

Figure 8. 40X Zoom Microscope Microstructure

ME LABORATORY 29

Figure 6: Specimen setup in the Microscope

ME LABORATORY 30

Figure 5: Drying the specimen after applying the etching and cleaning with

alcohol.

ME LABORATORY 31

Figure 3: Polishing of the specimen after grinding with lower viscosity

liquid.

ME LABORATORY 32

Figure 4: Polished Finish of the specimen

ME LABORATORY 33

Abstract

ME LABORATORY 34

Figure 1: Grinding of the specimen.

Figure 2: First Polish after grinding with higher viscosity liquid.

ME LABORATORY 35

References

• Callister, W. D. & Rethwisch, D.W. (2007). Materials Sciences and engineering: An introduction, 7 Ed. New York, USA; John Wiley & Sons, Inc.

• ASTM E112-06 ,E407-06• Polytechnic University of Puerto Rico,

Department of Mechanical Physical Metallurgy Laboratory Manual, pp. 1-13, 2009.

ME LABORATORY 36