DE1533298A1 - Martensite-hardenable nickel-molybdenum steel alloy - Google Patents

Description

"Martensite-age hardenable nickel-molybdenum steel alloy"

The invention relates to a martensite-hardenable nickel-molybdenum steel alloy, i.e. to a Steel alloy made without quenching or any substantial Deformation can be hardened in the martensitic state can.

Nickel-cobalt-molybdenum alloys in particular have proven themselves among the martensite-hardenable steel alloys according to the German patent application I 21 117 VIa / 40b with 10 to 259 * nickel, 1 to 10 * molybdenum and 2 to 50 * Cobalt proven, where the product of cobalt and molybdenum content is 10 to 100. These steel alloys possess an extremely advantageous combination of high strength and good toughness in the hardened state, because their tensile strength up to 210 kg / mm and the ratio the tensile strength in the notched and unnotched state (determined with a notch factor K ^ of at least 10) little-

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1.0, but generally much more.

In order to achieve such an advantageous combination of properties, the presence of both cobalt and molybdenum was, according to the previous view, indispensable. Adding only cobalt to nickel-iron alloys does not lead to an increase in hardness during aging. In the absence of cobalt, the molybdenum has a certain hardening effect in nickel-iron alloys with 18 to 20 $ nickel, but a molybdenum _{addition exceeding 6 # lowers the M e} temperature to such an extent that the alloy requires a very long low-temperature treatment, to completely convert to martensite.

The present invention is based on the surprising plague that is also found in cobalt-free Martensite age hardenable steel alloys result in a combination of high tensile strength and good toughness when the Contents of nickel, Moybdän, Hangan, silicon and carbon are coordinated in a certain way. About that In addition, the alloy only requires a one-step process after the usual hot deformation that follows casting Heat treatment in the form of hardening, i.e. it is neither a solution heat treatment nor a before hardening T ef t temperature treatment required.

The steel alloy according to the invention contains 009810/0690

For the letter of .13 · .Oct. 1 966 to "MartensltaUSMrtbare * ....« "Blatt & L

up to 16 $ nickel, 6 to 1 2? 6 molybdenum, with a total content of nickel and molybdenum of at most 2756 and at most 0.1 # carbon The contents of manganese and silicon should be as low as possible and can each be 0 to 0, 25 #. In addition, the steel can also be 0 to 1? 6 titanium, 0 to 1? 6 aluminum, 0 to 2 $ niobium, 0 to tf> tantalum, 0 to 0.1 «

Boron, 0 to 0.25 # zirconium, 0 to 2 <f » vanadium, 0 to 0.1? C calcium, 0 to 1 # beryllium and 0 to 4 # copper, ™ where the total content of the elements niobium, tantalum, Boron, zircon, vanadium, calcium, beryllium and copper does not exceed 10%. Molybdenum can be replaced by the same atomic percent of tungsten, ie by 2 parts by weight of tungsten for one part by weight of molybdenum up to 8% by weight of tungsten, whereby the total content of nickel, molybdenum and half the tungsten content must not exceed 27%. In addition, the steel alloy according to the invention can also contain 0 to 5 $ chromium. Although the good properties of the steel alloy according to the invention are achieved without cobalt, cobalt can be present up to a content of 196. The remainder, including impurities from the smelting process, consists of iron. The levels of common impurities such as sulfur, phosphorus, hydrogen, oxygen and nitrogen should be as low as possible.

The steel alloy is austenitic at high temperatures, but goes out during cooling Rolling heat into the martensitic state. In the marten

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In the sit-hardened state, the alloy generally has a 0.2 # yield strength of at least 105 kg / mm with an elongation of at least 5i> and a necking of at least 30 #, a high notch tensile strength and a tensile strength ratio in the notched and unnotched state of at least 1; it is therefore extremely well suited to withstand considerable impact stress.

In order to achieve the combination of properties mentioned above, the alloy components must lie within the content limits according to the invention. For example, nickel in contents of 10 to 16 # causes high toughness and ensures the desired martensitic structure, while higher nickel contents lead to the formation of residual austenite during cooling or to the regression of austenite during hardening. Although the risk of austenite formation during curing due to low curing temperatures, can be reduced, for example, under 37o C ^0, thereby impairing the strength of the alloy. At nickel contents below 10 ^, on the other hand, the alloy tends to form ferrite and other phases, which lead to a deterioration in the mechanical properties.

Molybdenum increases the strength of the alloy, makes it age-hardenable and, in addition, has a good bearing Forgeability and ductility. Molybdenum length too large

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However, hold impair the transformation of the structure into martensite when cooling from the rolling heat, so that the total content preferably not 265ε of nickel and molybdenum exceeds.

The steel alloy according to the invention inevitably contains traces of carbon, but its maximum content Is $ 0.1. However, for optimal mechanical properties, the carbon content should be $ 0.05, preferably not to exceed 0.03%.

Silicon and Hangan have a considerable amount Significance and must not exceed a certain minimum, otherwise the toughness is extremely impaired will. Since very small silicon and manganese contents of 0.5%, for example, reduce the notch toughness the total content of these elements should not exceed 0.30%. Preferably however, if the silicon and manganese content each exceed 0.1% not, although in practice it would be very difficult to maintain such a low content since these elements from the eon materials, the slag and the refractory Furnace lining to get into the melt.

Titanium and aluminum have a beneficial influence because they have a deoxidizing effect and are made of steel make it softer. For example, titanium binds the elements oxygen, nitrogen and carbon. Precautionary

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wise, the alloy contains at least 0.1% titanium and / or Aluminum, but the total content preferably does not exceed 1.5%.

The total content of other accompanying elements preferably does not exceed 6%, with niobium 1%, tantalum 2%, Boron 0.01%, Zirconium 0.1%, Vanadium 1%, Calcium 0.05%, Beryllium Preferably not to exceed 0.1% and copper 1%. If part of the molybdenum is replaced by tungsten, then the tungsten content preferably does not exceed 6%, more preferably not 4%. Since chromium deteriorates the properties of the alloy, it is only present as an impurity and does not exceed 1%.

A steel alloy with 11 to 15% nickel and 8 to 11% molybdenum has an optimal combination of properties with a total content of nickel and molybdenum of at most 25%, 0.1 to 1% titanium and / or aluminum with a total Content of titanium and aluminum of a maximum of 1.5% to 0.05% carbon, a maximum of 0.15% manganese, a maximum of 0.15% Silicon, the remainder including impurities caused by melting Sieen.

The alloy according to the invention can be melted both in air and under vacuum and is preferably remelted in an electric furnace. The ingots should be homogenized through, ^v *% r .spielsweise by a balancer annealing at 1200 to 1260 ⁰ C for about 25

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Minutes per cm of block thickness. Subsequently, the alloy can be hot worked to 760 ⁰ C and cold-formed, if appropriate, to the desired dimension at the 1260th The annealing and hot forming is very advantageous in that it achieves a thorough homogenization of the cast structure as a result of diffusion and dissolution of the cast structure.

The transformation of the austenitic structure into the martensitic state takes place during cooling from the temperature of the hot deformation. The cooling is preferably carried out in air, but can also be carried out in an oven or by quenching. After conversion, the alloy can be cured directly, for example through a 100 to 0.1-hour annealing at 400 to 595 ⁰ C, with the longer annealing times correspond to the lower Glühtemperatüren. Curing for one to four hours at 510 to 480 C gave good results. If a particularly hard surface is to be achieved, especially in combination with a softer core, the steel alloy can also be annealed at a higher temperature, provided that the structure is prevented from being converted back to austenite by choosing the appropriate annealing time. For example, the steel can be ^{annealed at 595 to 76O 0} C for a maximum of 30 minutes, with longer annealing times corresponding to lower annealing temperatures. An annealing time of a few seconds up to 5 minutes is sufficient at an annealing temperature from 675 to 735 ⁰ C.

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Although the advantageous properties of the steel alloy according to the invention are set during hardening following cooling from the rolling heat, the alloy can be subjected to an additional heat treatment, for example a solution heat treatment at 760 to 1200 ^° C. and a low temperature treatment.

The invention is explained in more detail below with the aid of some alloy examples, the composition of which is given in Table I. Alloys 1 to 10 correspond to the invention, while alloys A to J do not fall under the invention. GuQblÖcke of the alloys 1 to 10 and A were homogenized by soaking at 1200 to 126o ⁰ C, then hot worked and machined and then subjected to the heat treatments described below in detail without solution annealing:

Heat treatment I:

four-hour curing at 4-8O ⁰ C followed by cooling in air.

Heat treatment II;

eight hours curing at 48O ⁰ C followed by cooling in air.

Heat treatment III:

one hour curing at 540 ^° C. with subsequent cooling in air.

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Heat treatment IV;

for four hours annealing at 65O ⁰ C followed by cooling in air.

Small samples of the alloys B to J were annealed at 1150 ⁰ C and then cured at 48O ⁰ C (heat treatment V). The hardness of alloys 1 to 10 and A was determined both in the hot-rolled and in the hardened state and that of alloys B to J after solution heat treatment and after age hardening. The test results determined are summarized in Table I. In addition to the alloy constituents of Table I, the alloys contained up to 0.03 $ carbon and at most 0.15 ^ silicon or manganese and the remainder including impurities iron.

Ni
(*) Mon
(*) Ti
(*> Al T a b e 1 1 e I annealed I. II III IV V W. - ! Legie
tion 14th 10 0.2 0.2 51 56 45 - 1 10 10 0.2 0.2 _ 46 57 - 46 - 2 12th 10 0.2 0.2 "Ν. Hardness (re) heat treatment 50 - - - - 3 13th 9 0.2 0.2 / £? Whale state - 52 53 50 - - 4th 15th 9 0.2 0.2 37 - 49 51.5 48 - - 5 14th 8th 0.2 0.2 38 - 49 50 47 - 5 - 6th 10 12th 0.2 0.2 35 - 54 57 56 - - 7th 15th 7th 0.2 0.2 36 - 48 49 46 48, - 8th 16 6th 0.2 0.2 35 · _ 45 47 43 46 - 9 12th 10 0.2 0.2 36 - 50 - - - 15th 10 15th 15th 0.2 0.2 39 - 19th - - 21 18th A. 5 3 0.2 35 15th - - - - 22nd B. 10 3 0.2 .. 34 19th - - 29 G 15th 3 0.2 1 33 20th - - - - 20th D. 19th 3 0.2 _ 17th 20th - - - - 25th S. 5 5 0.2 - 21 - - - - 27 I. 9 5 0.2 .. _ 22nd - - - 0
0 & 4th 10 0.2 - .. _ 25th - - - - H 18th
22nd 10
10 0.2
0.2 Zo «Au aw O
0 - - - - I.
J - - - - - - 02) 8iä / 069G

For writing of .13 .'.... QlCt .. J 966 to "Martensitaushärtbare., ♦♦" Βία » IAtL

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The test results in Table I prove that the steel alloys according to the invention are an essential have greater hardness and strength after age hardening, while the other alloys show only a slight improvement learned. As the best of the alloys outside the invention, alloy E has a tensile strength which is considerably less than that of the alloys according to the invention. The extremely low hardness of the Alloys I and J result from the lack of conversion of the joint into martensite böia cooling.

Table II shows the compositions and mechanical properties of alloys 1 to 9 together with alloy 11, which is also part of the invention. In addition, Table II contains an alloy X which is similar in composition to alloy 1, but contains 0.5% each of silicon and manganese, while alloy 1 contains less than 0.155 ^ of these elements. All alloys of Table II were subjected to a Ausgleichsgltüien at 1200 to 126o ⁰ C, hot worked, then machined and annealed at 480 ⁰ C, namely alloy 1, eight hours and the other alloys for four hours.

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Table II

Alloy Ni Mo Ti Al Mn Si Zugfe- Stretch- Deh- Tensile Strength

tion (#) (#) (#) (^) (#) (#) stiffness limit speed

^{2 2} <*> ^hal

g g

(kg / nim ² ) (kg / mm ² ) <*> ffi * ^haltnia

H 10 0.2 0.2 0.05 0.05 190.0 179.7 11 55 1.29

16 6 0.2 0.2 <0.15 <0.15 154.3 147.1 11 57

11 * 14 10 - 0.2 0.05 0.05 183.1 200.1 12 37.5

K 14 10 0.2 0.2 0.5 0.5 213.7 191.9 8 31 0.68 ^f

tungsten

While alloys 1, 9 and 11, the good combination of properties characteristic of the invention
Alloy K proves the extremely harmful effect of low manganese and silicon contents.

The alloy according to the invention can be used as billets, wires, blanks or sheet metal, for casting and as pin wire and as a material for objects such as bolts and other fastening elements that have both a high
Require strength as well as high toughness.

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Claims (10)

To write from ... 1.3.ftflkt. «1.9.66 Qn" Martensite from mortars ..... ,,.,., ..?. Sheet * £ .., International Nickel Limited, Thames House, Millbänk, = s = ss == s == s = sasssBsss3snssszrssssssssssssass3Sss3 = aai London, S * W. 1, England Claims: 1. Martensite-hardenable nickel-molybdenum-steel alloy, consisting of 10 to 16 » nickel, 6 to 12 » molybdenum for a total content Nickel and molybdenum, a maximum of i "carbon, 0 to 1, i> titanium, 0 to 1, i" aluminum, 0 to 0.25% manganese, 0 to 0.25 * silicon, 0 to 2 to 0.1 i. Niobium, 0 to 4 » tantalum, 0 to 0.1 i» boron, 0 to 0.25 io zirconium, 0 to 2 i » vanadium, 0 to 0.1 £ calcium, 0 to 1.6 beryllium, 0 to 4 i » copper, the total salary being the Elements niobium, tantalum, boron, zirconium, Vanadium, calcium, beryllium and copper 10jt does not exceed 0 to 5 i »chromium and 0 to 1 i> cobalt, Remainder of iron including smelting conditional impurities. 009810/0690 For writing of _ ..!. 3.s .... Ofeii. * 1966 on "MarteniiMu.eMri.toare. * ..! .....? Sheet V -43- 2. Martens itauahärtbaren Stalillegierung according to claim 1, whose However, the total content of molybdenum and cobalt does not exceed 26 #. 3 · Martensite hardenable steel alloy according to claims 1 and 2, but their total manganese and silicon content Does not exceed 0.39 ^. 4β Martensite hardenable steel alloy according to claims 1 up to 3 »their total content of niobium, tantalum, boron, zirconium, Vanadium, calcium, beryllium and copper, however, do not exceed 69 *. 5 · Martensite hardenable steel alloy according to claims 1 up to 4, the chromium content of which does not, however, exceed 196. 6 · Martensite-hardenable steel alloy according to claims 1 to 5 »in which a part of the molybdenum is accounted for by equal atomic percentages Tungsten has been replaced up to a maximum level of 89 * Tungsten and the Maritime Office's nickel content is molybdenum and half the tungsten content does not exceed 279 *. 7 · Martensite age hardenable steel alloy according to claim 1, consisting from 11 to 1596 nickel, 8 to 11 fC molybdenum for one Total nickel and molybdenum content of at most 259 *, 0.1 to 1? 6 titanium and / or aluminum with a total content of Titanium and aluminum not exceeding 1.59 * »not exceeding 0.059 * Carbon, not more than 0.159 * manganese, not more than 0.159 * silicon, Best including smelting-related impurities Iron· 009810/06 * 0 For writing of 13 ⁰ ^ * ¹ .966 a ^ artensitaushärtbare ...... 'sheet 14 8. Martensite hardenable steel alloy according to claim 7 »their However, carbon content does not exceed $ 0.03. 9 · Martensite hardenable steel alloy according to claim 7 or 8, the manganese and silicon content of which does not exceed 0 _t 1 ^{c J>.} 10. A method for hardening a steel alloy according to claims 1 to 9 »characterized in that it is hardened ^{at 400 to 595 0 C after the hot forming and cooling.} 009810/0690