Theory
Heating and cooling steel results in modified physical characteristics. Heating steel to the austenitizing temperature (the temperature at which astenite is present) and then cooling by different means will induce varying hardness and different phases in the same type of steel. For example, if steel is heated to austenitizing temperature and then water quenched, martinsite will form and the steel will become harder. Testing the hardness can be done by using a hard stylus that is pressed into the surface of interest. Hardness relates to the depth and diameter of the indent. Different phases are depicted using a microscope.
Part A-End Quenching For The Jominy Test
Procedure
The wrought specimens were made from rolled 1045 and 4140 steel stock 1 in diameter by 4 long. (Ref. ASTM A255-85-4.1) To ensure a constant temperature the furnace ran for 3 hours at 1700°F before the test specimens were inserted. For the specimens to thoroughly reach austenitizing temperature they remained in the furnace for 30 minutes. (Ref. ASTM A255-85-5.2) The water temperature and flow-rate of the water-quenching device were regulated to follow the ASTM A255-85-5.3 standard. The Jominy test specimen was then quenched. Following, the quenching 2 flats were milled on the Jominy bar to ensure proper contact during the hardness testing. (Ref. ASTM A255-85-5.4) For data collection one of the flats,on the Jominy bar, was stained and marked off with a scale every 1/16. The hardness test machine was set to the Rockwell C scale and the data was collected at the scribed marks.
Results
For actual results click here. RESULTS
Figure 1
Figure 2
Figure 3
Interpretation of Results
Following the ASTM A-255-85 standard the hardenability for 1045 steel ranges from 20 to 57 Rockwell C shown in figure 1 and 2. Hardenability for 4140 steel ranges from 31 to 55 Rockwell C shown in figure 3 This holds true to the theory in that the faster you cool some thing the harder it will become.
Part B Microstructure
Procedure
The wrought specimens were made from 1045 and 4140 steel stock 1 in diameter by 1 long. To ensure a constant temperature the furnace ran for 3 hours at 1700°F before the test specimens were inserted. For the specimens to thoroughly reach austenitizing temperature they remained in the furnace for 30 minutes. To obtain different phases the buttons were air quenched, water quenched, untreated and annealed. Button preparation was critical for meaning full results with the microscope. Preparation started with a hand water sanding process that gradually polished the surface using a increasing grit sand paper. When the surfaces were relatively polished a finial polish was obtained using a diamond then Alumina finishing technique. The surface was etched using a drop of nitric acid to expose the different microstructure, which were viewed using a microscope.
Results
Interpretation of Results
There were definate similarities between the 1045 and 4140 steel that were cooled in the same manor. The two specimens that were water cooled had martinsite and pearlite present. The two specimens that were air cooled had pearlite present. The annealed specimens had mostly pearlite present witch relates to a slower cooling process. Untreated specimens consisted mostly of pearlite similar to the annealed buttons. By understanding the phase and isothermal transformation diagrams along with the material background you can also obtain similar results.
Chemical Composition:
| C | Mn | P | S | Si | |
| 1045 Steel
Heat Number-B 52510 |
.450 | .730 | .020 | .022 | .250 |
| 4140 Steel
Heat Number-H 44099 |
.392 | .890 | .017 | .023 | .260 |
Table 1 (chemical composition refers to the weight percent)
