Soft annealing is an annealing technique that softens materials in order to make them easier to process and shape. This includes working with a lathe, milling, and other machining.
It is usually quite difficult to process unalloyed steel with a high carbon content and most non-air-hardened, high-alloyed types of steel after forging or rolling. If you want to use these materials to manufacture high-grade products, you’ll need to apply soft annealing. This heat treatment process decreases the steel’s tensile strength and hardness by 10-25%, while simultaneously bolstering its elongation. This makes the materials easier to process.
The soft annealing process creates a material structure with so-called globular carbides, causing the chips to break off more easily during machining and making the metal surface smoother compared to non-annealed materials. Soft annealing furthermore decreases the risk of cracking during subsequent hardening. A final advantage is that soft annealing will increase the service life of your machines and tools, since softer materials cause less wear and tear
Soft annealing is a type of heat treatment for steel and for copper and brass alloys. Soft annealing of steel generally involves heating the material to 680-710 °C, whereas soft annealing of copper and brass alloy requires lower temperatures: 300-650 °C.
Soft annealing is mostly used for types of steel that have a carbon content of 0.9% or more; these are mostly tool steels. Types of steel with a carbon content of 0.5% or less will not benefit from soft annealing: the material will become too soft to properly cut it. Such materials are easiest to machine after normalising.
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