November 2020 Volume 2

AISI 4340 steel is a “ low-alloy steel ” containing chromium, nickel and molybdenum. Because of its high strength and toughness, this steel is commonly used in the forging industry for the manufacture of structural components for defense, aerospace, energy and automotive

coarsening behavior of Austenite and its decomposition during continuous cooling. The understanding gained will provide an in-depth knowledge of the response of the microstructures to processing and their subsequent performance. 2.0. Materials and Methods

FORGING RESEARCH AND TECHNOLOGY

1.0. Introduction AISI 4340 steel is a “low-alloy steel” containing chromium, nickel and molybdenum. Because of its high strength and toughness, this steel is commonly used in the forging industry for the manufacture of structural components for defense, aerospace, energy and automotive industries. This type of steel is also widely used in power transmission gears, shafts, aircraft landing gears and other structural parts. 4340 steels are also well-known for their excellent shock, impact, wear, and abrasion resistance in the as heat treated condition. In addition, this grade of steel can exhibit a good combination of fatigue strength with adequate atmospheric corrosion resistance. The vast majority of these components are made from Wrought 4340 steel, which represents a mature, well understood conventional processing technology. The development of alternative technologies such as selective laser melting provides both an opportunity and a challenge to study and compare the response of the as deposited microstructures to post processing-controlled laboratory experiments. The 4340 SLM steel used in this study was fabricated using Selective Laser Melting technology EOSINTM-270 3Dmetal printer. The goals of this study are to attain a comprehensive understanding industries. This type of steel is also widely used in power transmission gears, shafts, aircraft landing gears and other structural parts. 4340 steels are also well-known for their excellent shock, impact, wear, and abrasion resistance in the as-heat treated condition. In addition, this grade of steel can exhibit a good combination of fatigue strength with adequate atmospheric corrosion resistance. The vast majority of these components are made from Wrought 4340 steel, which represents a mature, well understood conventional proce sing t chnology. The d velopment of alternativ echnologi such as selective laser melting provides both an opportunity and a challenge to study and compare the response of the as deposited microstructures to post processing-controlled laboratory experiments. The 4340 SLM steel used in this study was fabricated using Selective Laser Melting technology EOSINT M-270 3D metal printer.

of the impact and response of the initial microstructure to heat treatments regarding the grain coarsening behavior of Austenite and its decomposition during continuous cooling. The understanding gained will provide an in-depth knowledge of the response of the microstructures to processing and their subsequent performance. 2.0. Materials andMethods The as-received steels were obtained from Ellwood Materials Technologies (Wrought 4340 steel) and from GKN Powder Metallurgy (SLM 4340 - Selective Laser Melted). Table 1 shows the chemical composition of the two steels studied in this research.The compositions are very similar, except for the higher Nitrogen and Oxygen content in the SLM 4340 steel compared to the Wrought 4340. The samples from the Wrought steel were produced from an ingot with approximated size of 40” (1016 mm) x 53” (1346 mm). The ingot was reheated at 2150F (1177C) and reduced to 18”x18” (457 X 457 mm) square round corners and air cooled to room temperature (ACRT). Subsequently heat treated at 1150F (621C) for 2 hours and ACRT. Sections from this forged piece were cut and provided for our study. The size of the samples received is shown in Table 2. The as-received steels were obtained from Ellwood Materials Technologies (Wrought 4340 steel) and from GKN Powder Metallurgy (SLM 4340 - Selective Laser Melted). Table 1 shows the chemical composition of the two steels studied in this research. The compo itions are very similar, except for the higher Nitrogen and Oxygen cont nt i the SLM 4340 steel compared to the Wrought 4340. The samples from the Wrought steel were produced from an ingot with approximated size of 40” (1016 m m) x 53” (1346 mm). The ingot was reheated at 2150F (1177C) and reduced to 18”x18” (457 X 457 mm) square round corners and air cooled to room temperature (ACRT). Subsequently heat treated at 1150F (621C) for 2 hours and ACRT. Sections from this forged piece were cut and provided for our study. The siz of the samples received is hown in Table 2. FORGING RESEARCH 2.1. Reheating Studies The Austenite grain coarsening studies were conducted on samples sectioned from the Wrought and SLM as-received conditions. The samples were reheated under Argon conditions to minimize oxidation. Samples from each steel starting condition were austenitized at 850C, 950C, 1050C, and 1150C for 1 hour, then water quenched (WQ). The WQ specimens we e pr pared using standard metallographic techniq es and etching to reveal and assess the Prior Austenitic Grain Size (PAGS). 2.2. Dilatometry soaking time of 15min prior to uniform cooling. Then the samples were cooled using different cooling rates: 0.25C/min (9), 0.5C/min (8), 1C/min (7), 5C/min (6), 10C/min (5), 20C/min (4), 50C/min (3), 100C/min (2) and 200C/min (1), as shown in Figure 1. The samples used for dilatometric studies were machined from the as-received conditions into cylinders approximately 3mm in diameter and 10mm in length. A total of 17 samples were studied, eight (8) from SLM 4340 and nine (9) from Wrought 4340. Each sample was reheated to 900C with a heating rate of 50C/min and a soaking time of 15min prior to uniform cooling. Then the samples were cooled using different cooling rates: 0.25C/min (9), 0.5C/min (8), 1C/min (7), 5C/min (6), 10C/min (5), 20C/min (4), 50C/min (3), 100C/min (2) and 200C/min (1), as shown in Figure 1. 4 Cr Mo V Cu Al N O 0.02 0.07

the dila subjecte 2.3. The sam have be plates. C with a h dimensi 12.4mm samples mid-eig In addit a smal geometr lubrican deforma compres each ste

The goals of this study are to attain a comprehensive understanding of the impact

Table 1: Chemical Composition of 4340 steels (wt%)

C

Mn

P

S

Si

Ni

Wrought 4340 0.42 0.75 0.013 0.008 0.31 1.75 0.85 0.27 0.006 0.22 0.021 SLM 4340 0.41 0.78 0.010 0.004 0.33 1.87 0.88 0.24

Table 2: Dimension of as-received materials (mm) Length Width Thickness Wrought 4340 235 235 50 SLM 4340 234 157 23

2.1 Reheating Studies The Austenite grain coarsening studies were conducted on samples sectioned from the Wrought and SLM as-received conditions. The samples were reheated under Argon conditions to minimize oxidation. Samples from each steel starting condition were austenitized at 850C, 950C, 1050C, and 1150C for 1 hour, then water quenched (WQ). The WQ specimens were prepared using standard metallographic techniques and etching to reveal and assess the Prior-Austenitic Grain Size (PAGS). 2.2 Dilatometry The samples used for dilatometric studies were machined from the as-received conditions into cylinders approximately 3mm in diameter and 10mm in length. A total of 17 samples were studied, eight (8) from SLM 4340 and nine (9) from Wrought 4340. Each sample was reheated to 900C with a heating rate of 50C/min and a

Figure Prior to were p process remova and 2) N containe 100mL HCl and immers Nickel

Figure 1: Schematic cycle for the dilatometry tests. Figure 1: Schematic cycle for the dilatometry tests. All the dilatometry tests were done using a LINSEIS L78 Machine coupled with an induction furnace. The temperature range of the system is between -150C to 1600C, with

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