CS272825B1 - Tough secondary hardenable steel - Google Patents

Abstract

Steel intended for cold volume forming and cutting has a composition by weight of 0.5 to 0.8 % carbon, 3.8 to 5.2 % chromium, 1.0 to 3.0 % molybdenum, 1.0 to 3.0 % wolfram, 0.5 to 0.9 % vanadium, traces up to 0.01 % cerium, traces up to 0.01 % calcium, traces up to 0.01 % magnesium and 0.02 to 0.07 nitrogen.

Description

(57) Steel intended for bulk forming and cold cutting has a composition of 0,5 to 0,8% by weight. % carbon, 3.8 to 5.2 wt. % chromium, 1.0 to 3.0 wt. % molybdenum, 1.0 to 3.0 wt. 0.5 to 0.9% by weight of vanadium, traces up to 0.01% by weight of tungsten; eeru, traces up to 0.01 wt. calcium, traces up to 0.01 wt. % magnesium and 0.02-0.07 wt. nitrogen.

272 825 (ID, (13) Bl (51) Int. CI. ⁵

OJ C 22 C 38/22, C 22 C 38/24

CS 272 825 BI

BACKGROUND OF THE INVENTION The present invention relates to tough, secondary hardenable cold-working steels suitable for tools operating under high pressure, cyclic impact and combinations of abrasive and adhesive wear.

In the group of cold-hardened steels with good strength and wear resistance, tungsten-chromium, chromium-molybdenum-vanadium, nickel-chromium, etc. steels are currently produced. However, the combination of properties, resistance to wear and compressive strength on the one hand and impact strength and fatigue characteristics on the other are not at the desired level. With increasing tempering temperature, plastic properties increase, however, the strength parameters and abrasion resistance significantly decrease. Therefore, these steels are tempered to temperatures up to 300-350 ° C. The disadvantage of these relatively low tempering temperatures is that they prevent the use of modern functional surface treatments by chemical heat treatment and physical coating processes that require higher temperatures. Also, the quenching stresses are still considerable after this low temperature tempering and prevent the wider application of progressive methods of EDM.

Recently, for the above reasons, they have been established in the group of cold ledeburitic steel forming and shearing tools, which are tempered to temperatures above 500 ° C. The steels have high wear resistance and high compressive strength. However, the level of toughness, resistance to chipping of functional edges and fatigue properties is insufficient. Due to the high content of alloying additives, their production is uneconomical, the semi-finished products have considerable heterogeneity and carbide rows, which lead to a significant anisotropy of properties. Also, the use of a greater amount of steel reinforcing additives is low due to their bonding in eutectic carbides and thus not participating in the structural changes in tempering in the region of secondary hardness. In heat treatment under plant operating conditions, steels often have an increased content of stabilized austenite, which worsens the used properties of the steel due to lower strength values and plastic deformations of the functional edges.

The abovementioned drawbacks are eliminated by the tough secondary secondary hardenable steel intended for bulk forming and cold shearing, containing 1 to 3 wt. % molybdenum, 1 to 3 wt. % tungsten, 3.8 to 5.5 wt. chromium, traces up to 0.01 wt. cerium, traces up to 0.01 wt. calcium, traces up to 0.01 wt. % magnesium and 0.02-0.07 wt. nitrogen. The principle of the solution is that the steel further contains a lower carbon content of 0.5 to 0.8% by weight. and 0.5 to 0.9 96 wt. vanadium.

A suitable combination of properties - high toughness and fatigue failure resistance with very good wear, machinability and abrasion resistance is achieved by heat treatment. The technology of heat treatment comprises hardening from a temperature in the range of Ac _{1 2} + 100 to Ac _{1 2} + 300 ° C in oil, in air, in a salt bath at 220 to 500 ^s C or in an inert gas stream and tempering at least twice at lying 0 to 100 ° C beyond the maximum secondary hardness. Alternatively, the steel is quenched from Ac. ₀ + 20 ° C to Ac, + 100 ° C to oil, air, in a salt bath at a temperature of 220 to 500 ° C or in a stream of inert gas and tempered at a temperature of 150 to 300 ° C.

The steel according to the invention is suitable for subsequent surface treatment by modern physical processes, TiN and TiC coating and for laser heat treatment, as well as for classical chemical-heat treatment processes by nitriding and carbonitriding. Due to the tempering temperatures above 500 ° C, the structure obtained is free of hardening stresses, therefore, progressive technology of tool shape production by electro-spark machining can be advantageously applied.

The steel is suitable for cold bulk forming and shearing tools, especially for modern precision cutting and gradual cutting, punching and machining tools. Further improvement in performance and performance is ·>

CS 272 825 B1 coating of functional parts of tools with TiN and TiC or nitriding and carbonitriding of the surface is recommended.

The steel according to the invention is described in more detail in the following examples:

Example 1 Steel with a chemical composition of 0.62 wt. % carbon, 3.9 wt. % chromium, 2.2 wt. % tungsten, 1.4 wt. % molybdenum, 0.7 wt. vanadium, 0.007 wt. % cerium, 0.062 wt. % nitrogen, 0.001 wt. % calcium and 0.005 wt. Magnesium was used for the production of cold stamping punches for M 16 screw heads. Compared to high-alloy steel, 9,830, the service life has doubled. The steel was heat treated under the following conditions:

quenching temperature: 1080 ° C cooling environment: nitrogen tempering temperature: 540 ° C final hardness: 59 to 60 HRC

Example 2

The screw head punch of Example 1 was coated with a 3 µm TiN layer. Compared to the uncoated tool, the service life has doubled.

Example 3

The chemical composition steel as in Example 1 was used to produce a cold stamping die. Compared to steel 19733, the service life has tripled: The heat treatment conditions were as follows:

quenching temperature: 1100 ° C cooling environment: salt bath at 450 ° C tempering temperature: 530 ° C final hardness: 58 to 59 HRC

Claims (1)

SUBJECT OF THE INVENTION Tough secondary hardenable steel for bulk forming and cold cutting, containing 1 to 3 wt. % molybdenum, 1 to 3 wt. % tungsten, 3.8 to 5.5 wt. chromium, traces up to 0.01 wt.% cerium, traces up to 0.01 wt. calcium, traces up to 0.01 wt. % magnesium and 0.02-0.07 wt. % of nitrogen, characterized by a lower carbon content of 0.5 to 0.8 wt. and 0.5 to 0.9 wt. vanadium.