Tool steel is usually made up of around 75% scrap – a mix of mill scrap and purchased scrap. it’s extremely important to avoid contamination of the scrap, especially from metals which can’t be oxidized like nickel, cobalt and copper. the bulk of alloy steel production is completed through discharge Furnace (EAF) melting.
Primary Melting
Tool steel is usually made up of around 75% scrap – a mix of mill scrap and purchased scrap. It’s vital to avoid contamination of the scrap, especially from metals which can’t be oxidized like nickel, cobalt and copper.
The majority of alloy steel production is completed through discharge Furnace (EAF) melting.
There are two stages:
The scrap is melted rapidly within the furnace.
The hot metal is transferred to a separate ladle or converter vessel to be refined. This process is understood as secondary refining, and it allows for nice efficiency and therefore the processing of huge volumes.
The refined metal is then transferred into the casting station and poured into ingots. The resulting ingots are usually annealed (heated and cooled slowly) to stop cracking.
Electroslag Melting
Electroslag remelting or refining (ESR) may be a progressive melting process wont to produce ingots with smooth surfaces and no pipe (holes) or porosity (imperfections). ESR ingots give improved hot workability, better processing yields, increased cleanliness, better transverse tensile ductility and fatigue properties.
ESR is an upscale process, and therefore the costs saved through the rise in yield aren’t always sufficient to offset the prices of ESR processing. However for a few specialized alloy steel applications ESR is worthwhile .
Vacuum arc remelting (VAR) may be a process sometimes used alongside ESR. However its use in tool steels is restricted to specialized applications with specific bearing requirements. within the VAR process, heat is supplied via an arc during a high-vacuum environment. The resulting steel features a refined macrostructure and microstructure and excellent chemical uniformity.
Primary Breakdown
The breakdown method used for tool steels employs either an open-die press or rotary forging machine. These processes are extremely versatile and may produce lengths of 6 to 13 m (20 to 43 ft) in squares, rectangles, hollows or stepped cross sections. the ultimate product is extremely top quality , having few cracks, laps or seams, and a high degree of straightness are often achieved.
Rolling
In modern steel manufacture, up to 26 rolling mills are utilized in a row. The metal is heated via a gas-fired pusher, walking-beam furnace, or high powered induction furnace. Rapid heating is employed to stop decarburization (loss of carbon content). the method is automated by computers and measuring devices are wont to monitor the diameter tolerance and surface quality of the metal. Through this process, a coil of steel sheet are often produced in but 12 minutes.
Hot and Cold Drawing
Drawing operations are usually used on tool steels to supply better tolerances, smaller sizes, or special shapes. As tool steels are of high strength and limited ductility, cold drawings are limited to one light pass so as to stop breakage. Warm drawing at temperatures up to 540 °C (1000 °F) is employed in multiple passes to strengthen the metal.
Continuous Casting
Continuous casting of alloy steel is usually finished economic reasons. Following casting, the billets are annealed and sometimes ground, then forged by hammer or rotary, after which they will be rolled. Electroslag rapid remelting (ESRR) may be a modern process which runs at higher temperatures than ESR.
Powder Metallurgy
Powder metallurgy (P/M) is employed to supply highly alloyed steels like high-carbon, high-chromium and high-speed. This process has become increasingly popular in recent years. Using traditional methods, the assembly of high-carbon, high-alloy tool steels are particularly challenging. The relatively slow cooling times for these methods leads to the formation of undesirable coarse structures of eutectic carbide, which ends up in non-uniform heat-treat response, poor transverse qualities and low toughness.
In P/M, the issues of traditional methods are overcome. A fine, uniform distribution of carbides are often produced using P/M which ends up in improved machinability within the annealed condition, a faster response to hardening heat treatment, and improved grindability. However, there’s a downside — a discount in wear resistance.
Osprey process
The Osprey Process remains a really specialized activity limited to sites in Japan and therefore the UK, However, it’s tremendous technical and commercial potential. The molten alloy is poured from an induction furnace through a nozzle and blasted with high-pressure gas atomization jets, causing the formation of small droplets. The droplets are collected and wont to form billets, hollows and sheets.
The advantages of the Osprey process are almost like P/M. alloy steel produced from Osprey material have a consistent distribution of fine carbides. However, the Osprey process is currently not as economically competitive as P/M.
