Alloy tool steel and manufacturing method thereof

Abstract

The present invention provides a tool steel containing, by mass percent, 0.55 to 0.85% of C, 0.20 to 2.50% of Si, 0.30 to 1.20% of Mn, 0.50% or less of Cu, 0.01 to 0.50% ofNi, 6.00 to 9.00% of Cr, 0.1 to 2.00% of Mo+0.5W, and 0.01 to 0.40% of V, with the balance of Fe and inevitable impurities, in which, when an area rate of a coarse carbide having a circle equivalent diameter of 2 [mu]m or more in a cross section parallel to a forging direction is represented by L(%) and an area rate of the coarse carbide in a cross section perpendicular to the forging direction is represented by T(%), the area rate L is 0.001 % or more, the area rate T is 0.001 % or more, and the ratio L/T is within a range from 0.90 to 3.00. The tool steel of the invention exhibits an isotropic size change in quenching and tempering.

Description

technical field [0001] The present invention relates to tool steels, and more particularly to tool steels which expand isotropically when quenched and tempered, and to a method for their preparation. Background technique [0002] Conventionally, tool steel is widely used to form dies (such as dies, press dies, or draw dies) and die parts connected to the dies, wherein the dies are used for cold forging, precision forging, continuous stamping, plastic forming, Warm forging, powder forming and magnet forming. [0003] Tool steel is a material that needs to have high hardness, so by quenching and tempering the tool steel, the structure of the tool steel is transformed into a martensitic structure, thereby imparting the required hardness, and this tool steel is used as Materials for the above-mentioned molds, etc. [0004] Tool steels expand in volume due to quenching and tempering. No problem arises when this expansion is isotropic, however, conventional cold work tool steel...

AI Technical Summary

Problems solved by technology

[0012] However, when the machining allowance for finishing becomes up to 0.09%, and at the same time tool steel is basically a material with high hardness, processing after heat treatment takes a considerable amount of time (assuming that at each 0.03% condition If the cutting is performed at the bottom, three cuttings are required)

[0013] Or, the following serious problem also arises: the load borne by the cutting tool increases excessively (when the machining allowance is 0.09% by one treatment), causing the cutting tool to break

However, since the factors controlling the uneven expansion caused by heat treatment have not been revealed, no countermeasures have been found so far

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