April_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 0 2 4 manufacturing components from HSCR steel and has the following advantages: minimized formation of oxide and ni- tride inclusions; low losses of alloying elements by oxidation; very close com- positional tolerance; precise tempera- ture control; removal of undesired trace elements with high vapor pressure; and removal of dissolved gasses, such as hy- drogen and nitrogen. Critical componentsmade of HSCR steel by casting + HIP can be a low-cost alternative to PM HIP or AM processes. It should be noted that the mechan- ical properties of components made by casting + HIP using HSCR steel are slightly lower than the properties of the same components made by the PM HIP or AM processes from HSCR steel pow- der. Projected cost reduction for criti- cal components made by casting + HIP from HSCR steel is 65% or more com- pared to the same weight components made by AM from Ti-6Al-4V. Table 1 shows a comparison of room-temperature mechanical proper- ties of HSCR steel samples and Ti-6Al-4V alloy samples made by the following processes: 1. HW + hardening: The forged HSCR steel is hardened by quenching, re- frigerating, and tempering (QRT) and the forged Ti-6Al-4V alloy is hardened by solution treating and aging (STA) [3] . 2. PM HIP + hardening: HSCR steel powder consolidated by PM HIP is hardened by QRT and Ti-6Al-4V al- loy powder consolidated by PM HIP is hardened by STA. 3. AM + annealing: Built by selec- tive laser melting (SLM) of HSCR steel powder is heat treated by an- nealing and built by SLM of Ti-6Al- 4V alloy powder is heat treated by annealing [4] . 4. Casting + HIP + hardening: Vacuum cast HSCR steel is subjected to HIP followed by hardening by QRT, and vacuum cast Ti-6Al-4V alloy is sub- jected to HIP followed by hardening by STA [5] . Figure 2 shows a comparison of mechanical properties of vacuum melted, forged, and hardened by QRT (HW + hardening) of HSCR steel and the vacuum melted, forged, and hard- ened by STA (HW + hardening) of Ti- 6Al-4V alloy. HSCR steel possesses slightly higher specific stiffness (E/ρ) and specific strength (UTS/ρ), high- er fatigue limits (S), slightly low frac- ture toughness (K 1C ), and higher impact toughness (CVN). Also, HSCR steel has higher elevated temperature strength, better workability and machinabili- ty, and better wear resistance. How- ever, Ti-6Al-4V alloy has better corro- sion resistance. Given the superior material prop- erties of HSCR steel over Ti-6Al-4V al- loy, the author concludes that critical components made by HW, PM HIP, and AM processes from Ti-6Al-4V alloy can be substituted with the same weight components made of HSCR steel by the same processes without sacrificing stiffness, durability, and lifetime. Cost of production plays a crucial role in the selection of materials for critical com- ponents. The lower cost of HSCR steel makes it a cost-effective alternative to high-strength titanium alloys. Figure 3 shows a comparison of the projected cost of components made by four different processes. Projected cost reductions for manufacturing com- ponents by HW, PM HIP, SLM, and Cast- ing + HIP from HSCR steel are 50% or more, 25% or more, 25% or more, and 50% or more, respectively compared to the same weight components made by the same process using Ti-6Al-4V alloy. Projected cost reduction of critical com- ponents made from HSCR steel by cast- ing + HIP is 65% or more compared to the same weight components made by AM from Ti-6Al-4V alloy. It should be noted that produc- tion of critical components made from HSCR steel reduces energy consump- tion by 25% or more compared to the same weight components made from Ti-6Al-4V alloy. HSCR steel is also well suited for defense applications such as missiles, artillery barrels, military land vehicles, and other applications where high-strength and fatigue limits, good toughness, and corrosion resistance at a reasonable cost are required. Fig. 2 — Summary comparison of key properties of the HW + hardening of HSCR steel and HW + hardening of Ti-6Al-4V alloy. Also see Table 1. Fig. 3 — Summary comparison of projected cost reduction of components made fromHSCR steel by HW, PM HIP, SLM, and casting + HIP.