Monthly Engineering Horizons

 ECONOMICAL ALLOY DEVELOPMENT FOR IMPROVED WEAR RESISTANCE STEEL PLATES FOR STONE CRUSHERS AND CEMENT INDUSTRY

 ECONOMICAL ALLOY DEVELOPMENT FOR IMPROVED WEAR RESISTANCE STEEL PLATES FOR STONE CRUSHERS AND CEMENT INDUSTRY

September 21
16:52 2020

 Supervisor:                           Dr. Mohammad Mujahid*

Co-supervisor:                      Dr. Mohammad Iqbal Qureshi**

Group Members:                 Umair Riaz*, Tayyab Hussain*

 

*School of Chemical and Materials Engineering (SCME) National University of Sciences and Technology (NUST) Islamabad, Pakistan

**Steel Castings and Engineering Works (SCEW), Gujranwala – 52250, Pakistan

 

 

ABSTRACT

In this research paper the focus has been on ways to improve the wear resistance and simultaneously optimize the cost factor of manufacturing the steel plates used in stone crushers. Hadfield steel is one of the toughest and hard steel used in stone crushers and for wear purposes. This paper presents an extensive study on methods used to improve the properties of this steel.

Several ways are there to improve the wear and hardness properties of steel. Modifying the heat treatment cycle or by addition of alloying elements are the two major one. The later one was selected in which micro alloying of element Niobium (Nb) was done at the same time Mn content was lowered significantly. Heat treatment cycle stays the same as it is carried out.       

INTRODUCTION

High manganese steels are widely used in the jaw crusher plates, cement industry and railroads. Austenitic manganese steel or high manganese steel which is also commonly known as Hadfield steels, contain around 11 – 14 % manganese and 0.8-1.2 % carbon. (All compositions in this paper are given in weight %, unless otherwise stated.) Austenitic manganese steels combine a good ductility with a high gouging abrasion resistance and resistance to metal wear. [1] Wear steels are used in components such as crusher plates and railway tracks. Components are cast to final shape, and then austenitized and water quenched to dissolve carbides formed at solidification, so that a completely austenitic structure is obtained [2].

The high manganese and carbon content in their plates result in a structure that solidifies with an austenitic microstructure and lack a solid state phase transformation that could refine the grain structure during subsequent cooling and heat treatment.[3] To obtain a finer grain structure during casting is therefore important to improve the properties of these alloys[4]. These plates are usually relatively large and are cast in sand moulds

Increasing the quantity of manganese will escalate the cost of the final product.  Similarly, increase in carbon content will decrease the toughness of manganese steel. So a solution is adopted which will not only reduce the price but also enhance the properties of Hadfield steel.

EXPERIMENTAL DESIGN

Niobium was used as micro alloying agent and the amount of manganese was lowered to enhance the properties as well as reduce the price. It is used as grain refiner and stable carbide former.

The basis for the experiments

Ferro niobium with typically (66.5% Nb) corresponds to the equivalent intermetallic phase. Hence it is brittle and can be crushed easily to the required lump size. Various lump size distributions around the standard size of 1-50 mm are common, dependent on the vessel to which the Ferro niobium is added and the alloying technique employed.

 Pure niobium was used in casting process. Ferro niobium can be used instead. Heat treatment is done in gas fired furnace 2 hours at 1000 degree Celsius followed by water quenching.

The composition of our sample is 6-7 % Mn with 0.05%, Niobium. The sample was in main contemplation with the reference sample with 10-11% Mn (industrial manufactured).

        I.            CASTING PROCEDURE:

Casting of high manganese steel was done in 1 ton induction furnace, limestone was continuously charged to form slag and reduce heat loss. Samples of dimensions 3cm x 10cm x 30cm were cast in sand moulds.

      II.            HARDNESS TEST 

Harness test is performed on a Rockwell hardness testing machine. C scale was used for hardness measurement with 150 kg major load, and a dwell time of 10s is used.

    III.            OPTICAL MICROSCOPY

Optical microscopy is done to reveal the grain structure and grain refinement of metals. Metallography has been done in accordance to the ASTM standard E3-01. Microstructure has been observed through optical microscope/ 

   IV.            CHARPY IMPACT TEST

This test is used to measure the toughness of material. ASTM A370 standard is followed. A hammer is struck to the material with standard dimension of 550mm*100mm*100mm with a notch. This is a simple test used to compare toughness. Toughness values are same for these two alloys 12 MJ/cm3.

     V.            WEAR TESTING

 Abrasion resistance test was performed using dry sand rubber wheel abrasive wear (DSRW) tester with a load of 130N and fixed sliding speed of 6000 rpm. ASTM standard G65 is followed in this experiment. 

   VI.            SEM

SEM images of these samples were taken at 1500x. Samples were electroplated using gold then at different magnification images were taken. Line analysis is also done at different regions to evaluate the phase and compositional differences at different points.   

 VII.            TENSILE TESTING

Tensile test is performed using standard E8. Tensile properties provide stress strain analysis UTS, Yield Strength, Elastic region and Plastic region analysis.

VIII.            COST ANALYSIS 

Cost analysis is done between samples to validate the economic aspects of alloys. Market rates per ton were taken for the calculations. Ferro niobium price is considered instead of pure niobium price. This comparison shows a vital economic aspect of manufacturing new alloy.

RESULTS AND DISCUSSIONS

I.            HARDNESS TEST

 There was a significant difference in the harness of the samples before and after the heat treatment of both samples.

 

Before Heat Treatment

After Heat Treatment

Unmodified Sample

12 HRC

28 HRC

Modified Sample

16 HRC

42 HRC

                                                                              Hardness Test Result Comparison

The results showed that the hardness of the sample which was micro alloyed with niobium was significantly higher than unmodified sample. Niobium carbide particles were distributed in the austenitic phase uniformly which increase the hardness by decreasing the dislocation movement.

II.            OPTICAL MICROSCOPE AND SEM IMAGES OF MODIFIED AND UNMODIFIED SAMPLES

Optical microscopy images and scanning electron microscopy results showed that grain size has been reduced after micro alloying of niobium. Line analysis showed that manganese concentration was high around the grain boundaries in unmodified sample. Manganese should be the modified sample.

 

 

 

 

 

 

 


Manganese steel contains fully austenitic region confirmed by XRD analysis

A simple grain boundary structure is revealed in previous fig (a) where carbide precipitation can be clearly seen on grain boundaries. Fig (b) shows significant precipitation in a single region, carbides are dissolved homogenously. XRD of new alloy conforms the fully austenitic region

DRY SAND/RUBBER WHEEL ABRASION TEST

Wear resistance tests were performed according to the ASTM G65.We can see from table that average adjusted volume loss of modified alloy is far less than reference alloy.

Specimen

Reference Alloy

Modified Alloy

Test Load

130 N

130 N

Wheel Revolutions

6000

6000

Initial Mass (mi), gm

164.40

165.54

Final Mass (mf), gm

162.00

163.48

Mass Loss (mi-mf), gm

2.40

2.06

Density, g/cm3

7.82

7.82

Volume Loss, mm3, (mass loss/density)*1000

302

263

Adjusted Volume Loss, mm3 (*)

302

263

 

TENSILE TESTING

Tensile strength of both the alloys was less than the normal strength of austenitic manganese steel in the literature. But tensile strength of modified alloy was still higher than reference alloy. There was a segregation of manganese around the grain boundaries in the reference alloy due to which its strength was reduced.

Modified alloy contained four percent less manganese than the reference alloy but still it showed better results than reference alloy. Yield strength of reference alloy is 310Mpa whereas modified alloy was 350Mpa (offset method).

        

 

 

COST ANALYSIS

Cost analysis was performed to compare our product with the market products.. Following were the prices of different materials used at that time. Current prices may vary. Calculations were done for one ton because one heat of one ton capacity was cast at a time.

PRICE PER KG

Mn Steel Scrap (10 – 11 % Mn)                                            =                                                Rs. 60/- per Kg

Mild Steel Scrap                                                                   =                                                Rs. 46/- per Kg

Ferro Manganese (60 % Mn)                                                               =                                                Rs. 160/- per Kg

 

 

 

Ferro Niobium (60 % Nb)                                                     =                                                Rs. 3,550/- per Kg

For Reference Alloy

Mn Steel Scrap (10-11% Mn)                                             =                                              974 Kg

Mild Steel Scrap                                                                   =                                              0 Kg

Ferro-Manganese                                                                              =                                                26 Kg

Ferro-Niobium                                                                    =                                                0 Kg

For Modified Alloy

High Mn Steel Scrap                                                            =                                              760 Kg

Mild Steel                                                                              =                                              240 Kg

Ferromanganese                                                                  =                                             0 Kg

Ferro Niobium                                                                      =                                              0.835 Kg

Cost in Pakistani Rupees

Reference Alloy

 

 

Modified Alloy

Scrap (High Mn steel)

58,440

45,600

MS Scrap

0

11,040

FeMn

4,160

0

 

FeNb

0

2,965

 

Total

Rs. 62,600/-

Rs.59,605/-

                     

  CONCLUSION

This report presented a comparison between two austenitic manganese steel alloy compositions. 10-11% manganese steel was taken as a reference alloy while 6-7% manganese alloy with 0.05% niobium as micro alloying agent was taken as modified alloy. Different tests were performed on these two alloys to study the variation in properties. Cost analysis was also done as part of the project. Analysis showed that the casting of modified alloy is economical. There are other avenues of this project to be explored. The mechanical properties of newly developed alloy surpasses the properties of industrial alloy. Hardness, tensile and wear properties are enhanced while toughness remains almost same. 

REFERENCES

 

  1. Agunsoye J.O, Balogun S.A, Esezobor D.A, M Nganbe2,University of Lagos, Yaba, Nigeria;University of Ottawa, Ottawa, Canada
  2. Haakonsen F, Optimization of Stormhard Steel, Norwegian University of Science and Technology; 2007
  3. Huang, Z. Metallkde. 8 (1990), No 6, p. 397-404
  4. Hai-lun,Y., Jing-pei, X., Ai-qin, X., and Cheng, W. (2007). Plastic deformation wears in modified medium manganese steel. China foundry, Vol. 4, No 3. Mendez, M. Ghoreshy, W.B.F. Mackay, T.J.N. Smith, R.W. Smith(2004), Weld ability of austenitic manganese steel. Materials Processing Technology.
  5. HE Zheng-ming, JIANG Qi-chuan, FU Shao-bo, (1987) Improved workhardening ability and a wear resistance of austenitic steel under non-severe impact loading condition. Wear,
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Engineering Horizons

Engineering Horizons

“Engineering Horizons” is the first & leading technical magazine of Pakistan covering Process, Mechanical, Metallurgical, Mining, Electrical & Electronics field under a single cover. We also feel pleasure in saying that this is the only magazine of its own kind & style, which is widely circulated in all Engineering Sectors of Pakistan.

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As you know, monthly “Engineering Horizons” is the first & Leading Technical Magazine of Pakistan covering Process, Mechanical, Metallurgical, Mining, Electrical & Electronics fields under a single cover. We also feel pleasure in saying that this is the only magazine of its own kind & style, which is widely circulated in all Engineering Sectors of Pakistan.
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