Correct Answer - Option 1 :
Hot hardness
Explanation:
Tool steels refer to a variety of alloy steels that are particularly useful for making tools. The four major alloying elements that form carbides in tool steel are tungsten, chromium, vanadium, and molybdenum.
The most essential requirement for all the types of cutting tool materials are:
Hot hardness or red hardness: It is the ability of the cutting tool to withstand high temperatures without losing its cutting edge. The red hardness of the tool materials can be increased by adding tungsten.
Abrasion resistance: It is the ability to resist wear. Abrasion resistance not only depends on hardness but also on the extent of hard, undissolved carbides present. This abrasion resistance increases as the carbon and alloy content increase.
Toughness: Toughness is the ability to resist shock and/ or impact forces and also to resist a high unit pressure against the cutting edge.
Friction coefficient: In order to have low wear and better surface finish, the coefficient of friction between the chip and tool should be as low as possible in the operating range of speed and feed.
Thermal Conductivity and specific heat: It is very much desired that the tool material should possess high thermal conductivity and specific heat, so that the materials may conduct away the heat generated at the cutting edge.
Machinability: This is the property of the material that defines the ease with which material would machine. The tool material should be comparatively easier to the machine.
There are different types of tool materials like plain carbon steels, low alloy steels, high-speed steels, Cemented carbides, Ceramics, etc.
The carbon content of tool steels varies from 0.8 to 1.5%.