EP0264528B1 - Non-ledeburitic high speed steels - Google Patents

Abstract

This invention relates to non-ledeburitic high-speed steels containing tungsten and/or molybdenum as main alloying components, especially containing by weight 6.0 to 7.0 % of tungsten, or 5.0 to 6.0 % of molybdenum, or totally 1.0 to 6.0 % of tungsten and molybdenum and, moreover, 1.2 to 2.3 % of carbon, 4.0 to 7.0 % of chromium, 1.0 to 1.3 % of vanadium, up to 1.5 % of manganese, up to 4.0 % of nickel, 0.2 up to 0.5 % of zirconium, 0.4 up to 1.5 % of silicon, up to 0.03 % of sulphur, up to 0.03 per cent of phosphorus and having a total content of titanium and niobium from 1.5 up to 6.0 % and properly a balanced carbon content according to the following formula: 0.5 + 0.2 [% Ti + % Nb + % Zr + (% V - 1)] <% C <0.65 + 0.26 [% Ti + % Nb + % Zr + (% V - 1)].

Description

• This invention relates to non-ledeburitic, economical, high-speed steels containing tungsten and/or molybdenum, chromium, vanadium and titanium and/or niobium as carbide­forming elements.
• According to SU-A-823 450 high-speed steels comprising 0.8-1.15 wt.% C, 3.8-4.2 wt.% Cr, 0.6-1.2 wt.% V, 4.5­5.5 wt.% Mo, 0.2-0.4 wt.% Si, 0.2-0.4 wt.% Mn, 4.5­10.5 wt.% Co, 0.6-1.2 wt.% Ti and the balance being iron are known which show improved hardness and heat resistance.
• In EP-0 105 861 Al high-speed steels are disclosed which include 0.84-1.05 wt.% C, up to 1.0 wt.% Si, up to 1.0 wt.% Mn, 3.6-4.5 wt.% Cr, 4.6-6.5 wt.% Mo, 2.0­4.0 wt.% W, 0.5-1.6 wt.% V, 0.5-1.5 wt.% Nb, the balance being iron and unavoidable impurities.
• After having been cast, these steels exhibit ledeburitic structure, and after plastic working they exhibit a con­siderable macrosegregation and microsegregation of car­bides, which is the main cause of the deformation and cracking of tools during heat treatment, and strongly varying usefulness.
• These undesirable phenomena encountered in the above­mentioned steels are caused by improperly chosen contents of alloying elements. Thus, if the content of tungsten, molybdenum and vanadium is insufficient and does not cor­respond to the limiting solubility of these elements in martensite, no secondary hardness is observed during the tempering process and the required hardness greater than 62 HRC cannot be obtained. On the other hand, the required chromium content is essential for ensuring the desired considerable hardening capacity. An improper amount of niobium and titanium in the aforementioned steels leads in effect to the appearance of a pseudo-binary eutectic in the structure. If the carbon content is not good, then the required hardening capacity cannot be obtained.
• According to the invention, a steel is provided containing by weight 1.2 to 2.3% carbon, 6.0 to 7.0% tungsten, 4.0 to 7.0% chromium, 1.0 to 1.3% vanadium, up to 1.5% manganese, 0.2 to 0.5% zirconium, 0.4 to 1.5% silicon, up to 0.4% nickel, up to 0.03% sulphur, up to 0.03% phosphorus, totally 1.5 to 6.0% titanium and/or niobium, the balance being iron and unavoidable impurities.
• In another embodiment of the present invention, the 6.0 to 7.0% tungsten in the above steel is replaced by 5.0 to 6.0% molybdenum.
• Finally, the invention comprises a steel of the above first-indicated art, wherein the 6.0 to 7.0% tungsten is substituted by 1.0 to 6.0% tungsten and molybdenum.
• In a preferred embodiment the above steels have a proper carbon content of the following inequality:
  $$\text{0.5 + 0.2 [\% Ti + \% Nb + \% Zr + (\% V \_ 1)] < \% C < 0.65 + 0.26 [\% Ti + \% Nb + \% Zr + \% V \_ 1)]}$$

  

  
  
• The inventive steels are used for the manufacture of tools.
• Steels according to the invention contained in the casting form no carbon eutectics. Moreover, these steels do not exhibit, after having been both cast or plastic worked, any macrosegregation or microsegregation of carbides. After final heat treatment, the structure of these steels exhibits a uniform distribution of primary carbides of titanium, niobium and zirconium, as well as secondary car­bides containing mainly tungsten, molybdenum and vanadium in tempered martensite matrix and a small amount of re­tained austenite.
• If an alloy with a carbon content smaller than that given on the left-hand side of the presented inequality is pro­duced, then the matrix of that alloy will contain a stable ferrite. Such an alloy cannot attain high-enough hardness exceeding 62 HRC and cannot be treated as high-speed steel.
• If an alloy with a carbon content greater than that on the right-hand side of the presented inequality has been pro­duced, then its structure will contain a considerable amount of carbon eutectics with molybdenum and tungsten carbides. It will exhibit both macrosegregation as well as microsegregation of carbides.

  

Claims (5)

1. Non-ledeburitic high-speed tungsten steel consisting by weight of 1.2 to 2.3% carbon, 4.0 to 7.0% chromium, 6.0 to 7.0% tungsten, 1.0 to 1.3% vanadium, up to 1.5% man­ganese, 0.2 to 0.5% zirconium, 0.4 to 1.5% silicon, up to 0.4% nickel, up to 0.03% sulphur, up to 0.03% phosphorus, totally 1.5 to 6.0% titanium and/or niobium, the balance being iron and unavoidable impurities.

2. Non-ledeburitic molybdenum high-speed steel consisting by weight of 1.2 to 2.3% carbon, 4.0 to 7.0% chromium, 5.0 to 6.0% molybdenum, 1.0 to 1.3% vanadium, up to 1.5% man­ganese, 0.2 to 0.5% zirconium, 0.4 to 1.5% silicon, up to 0.4% nickel, up to 0.03% sulphur, up to 0.03% phosphorus, totally 1.5 to 6.0% titanium and/or niobium, the balance being iron and unavoidable impurities.

3. Non-ledeburitic tungsten-molybdenum high-speed steel consisting by weight of 1.2 to 2.3% carbon, 4.0 to 7.0% chromium, 1.0 to 6.0% tungsten and molybdenum, 1.0 to 1.3% vanadium, up to 1.5% manganese, 0.2 to 0.5%. zirconium, 0.4 to 1.5% silicon, up to 0.4% nickel, up to 0.03% sulphur, up to 0.03% phosphorus, totally by weight 1.5 to 6.0% titanium and/or niobium, the balance being iron and un­avoidable impurities.

4. Non-ledeburitic high-speed steel according to any of the claims 1 to 3, characterised in that it has a proper carbon content according to the following inequality:
$$\text{0.5 + 0.2 [\% Ti + \% Nb + \% Zr + (\% V \_ 1)] < \% C < 0.65 + 0.26 [\% Ti + \% Nb + \% Zr + \% V \_ 1)}$$

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5. The use of the steel according to claims 1 to 4 for the manufacture of tools.