SURFACE SEGREGATION OF CHROMIUM CARBIDE IN … · modify surface chemistry ... In our project during this heat ... Surface segregation mainly refers to the enrichment of a free surface

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International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 7, July 2017, pp. 1732–1738, Article ID: IJMET_08_07_191

Available online at http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=7

ISSN Print: 0976-6340 and ISSN Online: 0976-6359

© IAEME Publication Scopus Indexed

SURFACE SEGREGATION OF CHROMIUM

CARBIDE IN STAINLESS STEEL AND ITS

THERMODYNAMIC STABILITY STUDY BY

CYCLIC HEAT TREATMENT

Baljeet Singh

Assistant Professor, School of Mechanical Engineering,

Lovely Professional University, India.

V.Midunkumar

School of Mechanical Engineering,


Dr. S.K. Kumara swamy

ICMCB, CNRS, Bordeaux, France.

Dr. Uday Krishna Ravella



Dr.Anil Midathda


Lovely Professional University, India

ABSTRACT

Steels are heat-treated to yield a great range of microstructures and properties.

Generally, heat treatment uses phase transformation during heating and cooling to

change a microstructure in a solid state. In heat treatment, the processing is most

often entirely thermal and modifies only structure. Thermomechanical treatments,

which change component shape and structure, and thermochemical treatments which

modify surface chemistry and structure, are also important processing approaches

which fall into the domain of heat treatment. Present work is the analysis of the

mechanical properties and microstructural changes that occur after the cyclic heat

treatment of 316L stainless steel. Here during heat treatment of stainless steels

chromium carbides will be formed, any type of stainless steels which are heated in the

temperature range of 400OC to 800OC will subject to formation of chromium carbides.

Surface Segregation of Chromium Carbide In Stainless Steel and its Thermodynamic Stability

Study by Cyclic Heat Treatment


Keywords: Heat Treatment, Thermomechanical Treatments, Mechanical Properties,

Microstructuralchange, Microstructural Change.

Cite this Article: Baljeet Singh, V.Midunkumar, Dr. S.K. Kumara swamy, Dr. Uday

Krishna Ravella and Dr.Anil Midathda Surface Segregation of Chromium Carbide In

Stainless Steel and its Thermodynamic Stability Study by Cyclic Heat Treatment.

International Journal of Mechanical Engineering and Technology, 8(7), 2017, pp.

1732–1738.

http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=7

1. INTRODUCTION

1.1. Heat Treatment in Stainless Steel

Heat treatment is one of the most exhilarating fields in the material science at present.

Prolonged existence of tools and equipment are significant factors in any industry in the

manufacturing process and the product itself. This heat treatment in case of advantages over

hardness will leads to give better resistance towards penetration, scratching, machining etc. In

our work we have done cyclic heat treatment that is something very rarely done on these types

of materials. Heat treating is a mixture of various engineering process along with metal

working procedures used to modify the materialistic and chemical property of a material. It

consists of the usage of heating system or distressing, typically to extreme temperatures, to

accomplish a preferred consequence such as toughening or become softer of a metal. The heat

treatment process comprises annealing, case hardening, normalizing, tempering and

quenching.

In our project during this heat treatment of stainless steels chromium carbides will be

formed, any type of stainless steels which are heated in the temperature range of 400OC to

800OC will subject to formation of chromium carbides.

1.2. Austenitic Stainless Steel

Austenitic stainless steel has austenite as its primary phase (face centered cubic

crystal).These are alloys containing chromium and nickel, and sometimes molybdenum and

nitrogen, structured around the Type 302 composition of iron, 18% chromium, and 8% nickel.

200 Series austenitic stainless steels replace the majority of their nickel content with

manganese to reduce cost. Austenitic steels are not hard enable by heat treatment. The most

familiar stainless steel is probably SAE 304 stainless steel, also called 18/8 or A2 stainless

steel. Type 304 surgical stainless steel is an austenitic steel containing 18-20% chromium and

8-10% nickel.

1.3. Stainless Steel 316l

This grade is mainly the second most in importance towards the 304 among these austenitic

stainless steels. This grade gives overall far better resistance in corrosion properties than other

grades such as 304. This 316L is mainly the low version of carbon in 316 and mainly

immunes from sensitization. In case of economical wise both 316 and 316L does not have

much difference. It gives as much as good level of toughness when compared to other

chromium nickels austenitic stainless steel. It mainly offers higher level of creep and at

elevated temperature it gives good tensile strength.

Baljeet Singh, V.Midunkumar, Dr. S.K. Kumara swamy, Dr. Uday Krishna Ravella and Dr.Anil

Midathda


Table 1 Composition range for 316L Stainless Steel

Grade C Mn Si P S Cr Mo Ni N

Min - - - - - 16.0 2.00 10.0 -

316L

Max 0.03 2.0 0.75 0.045 0.03 18.0 3.00 14.0 0.10

1.4. Surface Segregation

Surface segregation mainly refers to the enrichment of a free surface in a material constituent

or towards the internal interface of a material. The main site of this segregation can be in any

form such as dislocation, grain boundary, stacking fault etc.

1.5. Surface Segregation of Chromium Carbide

In a polycrystalline strong solid, an isolation spot on the site might be a disengaged, grain

Limit, stacking flaw, or an interface with an accelerate or auxiliary stage inside the solid

Normally segregation means enriching of a material element at a free surface or an internal

interface of a substance chromium carbide is compound which is ceramic that exists in quite a

few unlike chemical compositions:, Cr7C3, Cr23C6 and Cr3C2. At normal conditions it exist

like a gray solid. It is enormously hard in nature as well as corrosion resistant. In this the grain

boundary, stacking of chromium carbide is completed. This compound maintains its strength

at high temperatures which means that it is a refractory one. The corrosion and wear

resistance in the metal is produced due to integration of chromium carbide crystals into the

surface of a Metal and it helps in maintaining these properties at high temperatures. Cr3C2 is

the hardest as well as most usually used composition for this particular purpose. Chromium

carbide is of use in the case of surface treatment components of metal.

1.6. Sensitization

Sensitization is process of loss of alloy integrity. It leads to chromium depletion layer along

the grain boundaries by forming chromium carbides. Due to this steels under gone susceptible

to intergranular stress corrosion or intergranular corrosion. Chromium present in steels is

reacted with carbon and forms chromium carbides. If the chromium carbide forms along the

grain boundary then that steel is called “sensitized steel” and phenomenon is called

sensitization.

There are two main criteria’s which are to be satisfied in order to get the chromium

carbide precipitates along the grain boundaries. Carbides formation is along the grain

boundaries only because the grain boundaries provide heterogeneous nucleating sites.

Chromium carbide precipitates along the grain boundaries leads to chromium depletion layer

along grain boundaries it leads to intergranular corrosion. When carbides formation is

happens then chromium percentage along grain boundary is goes less than 2%, in the same

time except grain boundaries.




1.7. Cyclic Heat Treatment

The cyclic heat treatment process terminates its progress through a microstructure level of

spheroidized cementite in varying fine grained ferrite matrix that will provides an excellent

combination of both strength and ductility.

Depends upon the cyclic heat treatment and its properties of the specimen various levels

in case of microstructure are obtained with the good combination of ductility and strength

properties. Cyclic heat treatment was done in a muffle furnace in which that furnace can

withstand a maximum of 9000c.here we are going to heat in a cyclic manner of repeated

operation it consists of 8 cycles in which it has 8 samples these samples are kept in a muffle

furnace for 6900c. Here the first cycle will be done up to 4hrs after that the specimens are

allowed to cool inside the furnace and after an 22 hrs of Soaking period the first sample is

taken out of the furnace. And in next cyclic the same procedure is followed for the 7 specimen

likewise each specimen is taken out of the furnace when every cycles are completed similarly

these eight cycles were done.

Table 2 Temperature range and Duration of the Cyclic Heat Treatment

No. of

cycles

Temperature range

in degree Celsius

Time Duration

(hrs.)

Time taken to cool

down (hrs.)

1 690 4 12

2 690 8 12

3 690 12 12

4 690 16 12

5 690 20 12

6 690 24 12

7 690 28 12

8 690 32 12

2. METHODOLOGY

2.1. Rockwell Hardness Test

The hardness of heat treated specimens were measured using Rockwell Hardness Tester.

The procedure to be followed in Hardness test:

Initially the ball indenter ought to be inserted in the machine; then the load is to be

adjusted to100kg. The minor load of a 10 kg should be first applied to seat of the specimen.

Currently, the major load applied as well as the depth of indentation is recorded automatically

on a dial gage which in terms of arbitrary hardness numbers. The dial is containing hundred

divisions; where in each single division corresponds to 0.002mm of penetration. The dial is

reversed in order that a high hardness, which results in small penetration, gives in a high

hardness number. The hardness value thus obtained was converted into B scale by using the


Midathda


standard converter chart. The specified sample of both hardness and tensile testing of the

specimen with dimensions are shown in the fig below.

Figure 1 Hardness and Tensile Specimen

2.2. Microstructural Analysis

Microstructural evaluation ranges from simple determination of certain parameters such as

grain size or coating thickness through porosity and pore structure to full characterization of

multi-component systems or evaluation of degradation or failure mechanisms. Combinations

of techniques are used, including oSubita Bhagat and Pardeep Kumar Verma, Analysis of

Microstructure of Fumed Silica Reinforced Polyester Composites. International Journal of

Advanced Research in Engineering and Technology, 6(7), 2015, pp. 32-38. ptical and

Scanning Electron Microscopy (SEM), Energy Dispersive Analysis (EDA) and Micro

Diffraction (µ-XRD), all of which provide both physical and chemical information, with sub-

micron resolution.

Figure 2 S.E.M Images of Austenite Stainless Steel

The above SEM image shows the non-heat treated stainless steel specimen shows the

pearlite structures.

cyclic heat treatment at 6900c for 4 hrs cyclic heat treatment at 6900c for 8hrs

1m

1m

1m




cyclic heat treatment at 6900

c for 12hrscyclic heat treatment at 6900

c for 16hrs


c for 20hrs cyclic heat treatment at 6900

c for 24 hrs


c for 28hrs cyclic heat treatment at 6900

c for 32hrs

Figure 3 SEM images of cyclic heat treatment

• Microstructural analysis reveals the formation of fine carbide particles in the marten-site

matrix as a result of tempering.

• The increase in temperatures 690oC with respect to each cycle duration from Fig.3 shows that

the inter lamellar spacing of ferrite and cementite lamellae in pearlite becomes more

important as the amount of pearlite increases as the temperature increases.

• By comparing the SEM images of both the stainless steel of heat treated and normal steel

we tends to find some difference in their microstructure and there is a formation of

cavities and major structural changes

• Due to these structural changes there will be change in its grain properties and

microstructural changes that can be occurred in this process. From this the hardness level of

the specimen is increasing its effect.

• The solubility of carbon in ferrite, though insignificant in its absolute value, increases

gradually with rise of temperature.

3. CONCLUSION

• From the test carriedon the 316L Stainless Steel in case of its hardness, the result obtained

is that the hardness level of that particular specimen is constantly decreasing due the

carbon precipitation.

• The tensile properties of this material in concerned with the annealing of heat treatment

shows that the tensile strength of each samples is decreasing at a constant rate.

• From the hardness process it is inferred that the hardness decreases at a constant rate due

to the carbon precipitation where as resistance towards the scratch increases as this carbon

precipitated region leads to lack of penetration.


Midathda


• But by varying the temperature in different ranges and by using different type of cooling

process such as quenching process in heat treatment, there may be chances for improving

the hardness of these materials as compared to these techniques for both hardness and

tensile strength testing.

• Due to this varying heat treatment process there is a change in its microstructural and

grain boundaries, these excludes the level of formation of pores and cavity in its

microstructures.

• Due to the effect of cyclic heat treatment there is a increase in the conversion of

martensitic from the state of austenite. After each cyclic heat treatment the grain structure

gets more refined.

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SURFACE SEGREGATION OF CHROMIUM CARBIDE IN … · modify surface chemistry ... In our project during this heat ... Surface segregation mainly refers to the enrichment of a free surface