EXP 3 - laboratory experiment report ferrous PDF

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laboratory experiment report ferrous...

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COURSE:

MATS-1021

COURSE NAME:

FERROUS METALLURGY

SECTION NUMBER:

05

EXPERIMENT NO:

03

TITLE:

HARDNESS TESTING METALLOGRAPHY

NAME:

1) KHUSHBU SINGH

AND

2) SIDDHARTH SANGHVI STUDENT NUMBER:

1) 0766813 2) 0799015

CLASS:

PEM 11 (H)

SUBMISSION DATE:

6TH OCTOBER 2016

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A. METALLOGRAPHY  Metallography and Phase Identification of AISI 4140 steel in hardened & tempered as well as annealed condition Tempered Martensite

Pearlite

Ferrite

Hardened and tempered AISI 4140 steel

Annealed AISI 4140 steel

[Fig No.1] Metallographic structure of hardened & tempered as well as annealed AISI 4140 grade steel

 

Magnification: Specimen:

400x AISI 4140 steel (etched with 2% nital)

Table: 1 Microstructural characteristics of annealed as well as hardened & tempered AISI 41410 steel Microstructural characteristics

Observations

Grain size Grain shape

Annealed steel ASTM grain size is 07-09 Almost equiaxed grains

Hardened & tempered steel It is not a grained structure -

Phase amount

70% ferrite + 30% pearlite

About 90% tempered martensite structure with 10% bainite/ferrite structure

Relatively uniform grained, ferrite and pearlite structure

Fine tempered martensite

Phase identification

B. TESTING I)

Brinell hardness testing

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Table: 2 Brinell hardness of AISI 4140 steel Sr. No.

1 2 3 Average

Rockwell B Rockwell C

II)

Brinell hardness readings at 3000 kg load (Indentor- 10 dia. Ball) Experimental hardness readings (BHN) Annealed 4140 steel Hardened and temped 4140 steel 228 782 241 782 228 744 232 769 Conversation from chart Rockwell hardness 99 HRb 22 HRc 68 HRC

Rockwell hardness testing

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Table: 3 Rockwell hardness of hardened and tempered AISI 4140 steel Sr. No. 1 2 3

Rockwell experimental hardness readings Annealed 4140 steel Hardened and temped 4140 steel Hardness readings (HRb) Hardness readings (HRc) 96.4 68.2 95.3 67.5 97.2 65.8

Average

96

67

Conversation from chart Brinell hardness (BHN) 223

744

BRINELL HARDNESS TESTING MACHINE: Hardened material: 769 BHN = 68 HRc Annealed material: 232 BHN = 99 HRb

ROCKWELL HARDNESS TESTING MACHINE:

Hardened material: 67 HRc Annealed material: 96 HRb

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C. ANSWERS



Mounted annealed specimen of AISI 4140 comprises of fine grained ferrite and pearlite microstructure. About 70% area of microstructure were covered with ferrite grains with remaining 30% of pearlite. This sample was given a heat treatment known as “Annealing”. In this heat treatment metal is heated above the AC1 (i.e. upper critical temperature), soaked for sufficient time at that temperature and finally slow cooled in furnace.



Hardened and tempered specimen showed microstructure of fine tempered martensite. Almost 90% area consist of martensite with remaining bainite/ ferrite structure. In this case sample was heated above AC1 and rapidly quench in water to obtain fully tempered martensitic structure



We obtained greater range of results on the annealed specimens are mainly because of two reasons which are as below: i)

ii)

Human error- mainly in case of Brinell hardness , size of the ball indenter should be measured manually which varies persons to person. Little inaccuracy in measurement of indenter size result noticeable variation in hardness readings. As 4140 grade steel in annealed condition shows dual phase structure which is ferrite and pearlite, it leads to variation in hardness during testing. Ferrite is a soft phase with maximum solubility of carbon upto 0.025% whereas pearlite is comparatively harder having 0.8% maximum carbon solubility. While hardness testing, location of indentation changes for different reading and it shows higher hardness on pearlite phase whereas lower hardness reading at ferrite region.



Hardness conversation: (A) Rockwell C 51 = 487 BHN (B) Rockwell B 8 = 165 BHN

Reference: ASTM E140 (Ref. 1)

D. CONCLUSION

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1)

Annealed Material Brinell Hardness Testing Machine 232 BHN= 99 HRb (After conversion)

Rockwell Hardness Testing Machine 96 HRb

Hardened Material Brinell Hardness Testing Machine 769 BHN = 68 HRc (After conversion)

Rockwell Hardness Testing Machine 67 HRc

As we see from the table, after conversion the hardness values of annealed material is 99 HRb which is near to measured hardness values of 96 HRb.

Similarly, hardness values of hardened sample is 68 HRc (after conversion). This hardness values is also almost equal to measured hardness values of hardened sample (i.e. 67 HRc). Both the values are almost equal.

2) If we look at the method of measuring hardness, it is very simple for both machines. But if we look at accuracy of measurement we can say that Rockwell Hardness testing machine is more accurate than Brinell Hardness testing machine. We arrived at such conclusion because in Brinell hardness, there are chances of human error while measuring indenter diameter. But Rockwell hardness gives the reading in digital form directly and there are no chances of Human error. Also if we look at the hardness testing on the basis of microstructure, than reproducibility of hardness in single phase material is higher than the dual phase structure. In other words, fully tempered martesitic structure show consistency in hardness values whereas dual phase structure (i.e. ferrite-pearlite) gives minor variation in hardness readings. Thus, we can say that reproducibility of both machines is good but it depends on some factors like the person testing the hardness and even on the microstructure of the material.

E. REFERENCES

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1. http://www.mdmstandard.ro/download/resurse/Tabele%20de%20conversie%20ASTM %20pentru%20duritati%20(in%20engleza).pdf 2. https://ocw.mit.edu/courses/mechanical-engineering/2-002-mechanics-and-materials-ii-spring2004/labs/lab5_s04_1045new.pdf

3. Metallurgy fundamentals, 5th edition, Daniel A. Brandt, the goodheart-willcox company, Inc, Pg no. 153-157.

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