jomini hardenability lab report

8/10/2019 Jomini Hardenability Lab Report

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Lab 1

Jomini Hardenability Test

MAS 406

Ronny Landsverk

October 12, 2014

Date Performed: Sept 23, 2014Partners: Alexander SjoebergInstructor: Dr. Cecilie Oedegaard

1 Objective

To determine the hardenability of two different steel qualities, by aid of theJomini Test.

Further analysis of the grain structure along the specimen should be carriedthrough, but there was no time left to do the necessary steps in the laboratorybefore the end of working hours so this part is intentionally left out.

2 Theory

2.1 Hardness and Micro-structure

Hardness is a measure of the ability of a material to resist plastic deformation.From measurements of hardness we can obtain the flow curve, i.e. the truestress-strain curve. Hardness is dependant of the microstructure which canchange when the material is subjected to heat.(This section has not been given great consideration since the microstructureanalysis were dropped).

2.2 The Jomini Test

The purpose of the Jomini test, is to determine the ability of a steel to be hard-ened in bulk depth by method of preheating and quenching.

A specimen of the alloy of interest, with standard measurements, is preheated ina furnace with a temperature of 900 C, for a period of 30 min. This specimen

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is then fixed in space as a jet of water is cooling the rod. This jet of water iscontrolled such that only one end of the rod is subjected to water during the

period of cooling. Thus, a cooling gradient in the rod axial direction will beobtained.

The rod is then carefully grinded to remove inpurities, preparing for measure-ments of hardness either by Vickers or Rockwell method, Marrow (2001). Thehardness testing is carried through by testing linearly spaced points from oneend to another, simulating the surface and bulk-depth of a quenched body.

2.3 Vickers Hardness

This method of testing involves indenting the surface of a specimen by applyinga load on a square-based diamond pyramid. The occurring hardness is thenobtained by measuring the diagonal of the indentation left from the pyramid.These measurements are made by using an optical microscope. The average di-agonal length measured is converted to a corresponding Vickers hardness num-ber by means of table or formula.

3 Method

The attending class was divided into two groups, each given a test specimenquenched as defined in 2.2. These specimen were of different material composi-tion. Our group was given the ST60 specimen.

The groups were then sent into another part of the lab to grind a smooth planeenabling for the Vickers testing along the bar.

The test specimen was fastened in a screw drive in such an orientation thatthe smooth grinded plane was horizontally facing upwards. This was done byeyesight. The fastened specimen on the Vickers testing machine can be adjustedin all directions in a plane perpendicular to the indenting pyramids axis of mo-tion/load. Normally there are relatively small adjustments in position needed,but for our case, we had to move 10 cm along the specimen relative to the mi-croscope and the machine could only be moved 20 mm by turning the nob onthe positioning screw. So we had to relocate the specimen and as we did so ina cumbersome way, this lead to a decrease in measuring quality as the bar wasnot supported properly.

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4 Results and Conclusions

The following figure displays the data from both groups, as listed in table 1.

Figure 1: Results

As expected, the measurements taken near the quenched end of the specimenhave the greatest Vickers hardness values. The data from the ST60 specimenimplies that bulk depth over 30 mm have limited quench hardening abilities.For the Rigor specimen, there is a tendency in the data to drop more slowly asthe distance increases, but there are large discrepancies from one data-point tothe next.

The measuring quality could have been greater if we had supported the speci-men sufficiently during the Vickers hardness test. However the benefit for doingsuch mistakes, are valuable as lessons for being better prepared for practice tocome.

Reading the obtained data, one can conclude that the quench hardening processwill have a greater effect near the surface for the ST60 composition comparedto the Rigor composition. However, for the Rigor case, the effect seems to godeeper into the material.

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Dist [mm] St60 [HV10] Rigor [HV10]0 304 613

5 299 62010 236 58515 193 59920 169 60625 126,4 61331 187 61335 102,7 59240 108,2 60645 104,6 59950 115,3 55455 100,3 37660 157 579

65 123,8 54870 118,9 54275 166 59280 123,2 60685 151,4 55490 225 53695 176 503

Table 1: Acquired Data from Experiment

References

Marrow, J. (2001). Understanding the jomini end quench test.

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jomini hardenability lab report

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