DE1217076B - Martensite-hardenable steel alloy - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Ο .:

C22c

German class: 40 b -39/40

Number: 1217 076

File number: J 28295 VI a / 40 b

Filing date: June 5, 1965

Opening day: May 18, 1966

Soft steels are commonly used for construction purposes and it is known that their yield strength is much lower than that of alloy steels. There are a number of low-alloy carbon steels which have a yield strength of 105 to 140 kg / mm ² or more, but they generally lack adequate toughness. In addition, the high yield strength of these steels is usually achieved by tempering and quenching, the quenching treatment being associated with the risk of warping and dimensional change. There is therefore a real need for structural steels with a yield strength of 105 kg / mm ² and more, with adequate toughness and which do not require a quenching treatment for their strength. This requirement is met by the steels according to the invention.

The steel alloys according to the invention are martensitic after quenching from the temperature of the solution annealing and can be hardened in the martensitic state. Besides iron, they contain 10 to 20 per _cent. Nickel, 1.75 to 4% silicon, 0 to 5% chromium, the sum of the nickel, silicon and chromium content being 12 to 23%, less than 0.03% carbon, 0 to 1% titanium, 0 to 1 % Aluminum, the total content of titanium and aluminum not exceeding 1%, and 0 to 0.75% manganese.

The steel alloys according to the invention are essentially silicon-containing nickel steels. Silicon is an element that is contained in almost all carbon and low-alloy steels. Occasionally, in amounts up to 1% i ⁿ structural steels before, when a high strength is not required. The "Metals Handbook" (8th edition, 1961, on p. 228) states that silicon contents above 0.3% have a detrimental effect on the ability of steel to absorb impact energy. Despite its frequent occurrence in steel, silicon was never used to achieve high yield strengths with at the same time satisfactory toughness, including notch toughness.

The silicon content of the steels according to the invention is therefore of particular importance; if it is less than 1.75%, the yield strength is adversely affected, and when the silicon content exceeds 4.0%, the toughness deteriorates. With regard to optimal properties the silicon content should be between 2.5 and 3.5%.

The nickel content is advantageously 16 to 20 ° / _0th Lower nickel contents lead to lower strengths, and higher nickel contents promote the resistance of the austenite during the

Martensitic hardenable steel alloy

Applicant:

International Nickel Limited, London

Representative:

Dr.-Ing. G. Eichenberg

and Dipl.-Ing. H. Sauerland, patent attorneys,

Düsseldorf, Cecilienallee 76

Named as inventor:
Stephen Floreen, Westfield, NJ;
Raymond Frank Decker, Fanwood, NJ
(V. St. A.)

Claimed priority:

V. St. v. America June 9, 1964 (373 872)

Quenching from the solution heat treatment temperature to room temperature. It will be understood that on quenching from the solution heat treatment temperature, a conversion of the austenite to martensite takes place, which normally occurs on cooling through the M _s -M / conversion range to room temperature. In order for this transformation to take place completely, it may sometimes be necessary to quench the steels below room temperature, for example down to -75 ° C. Cold deformation can also be used to completely transform the structure.

Although chromium can be present in the steel alloys, the chromium content preferably does not exceed 1% or the alloy is advantageously free of chromium. If the total content of nickel, silicon and chromium 23 ° / ₀ exceeds remains in quenching austenite; If the total content of the elements exceeds 22%, quenching to below room temperature is necessary. On the other hand, for achieving optimum properties should be the total content of nickel, silicon and chromium 18.5 ° / _0th

Carbon is always present, but the carbon content of the steel alloys according to the invention is allowed Do not exceed 0.03%, otherwise both the yield strength and the toughness will be impaired will. .

It is desirable to have at least one, but preferably both, of titanium and aluminum are, the contents of each of these elements

609 559/374

between 0.05 and 0.15 ° / ₀ . In these content limits, titanium and aluminum contribute to achieving optimum toughness.

Also manganese is present in most steels, but the manganese content of the alloy 0.1 ° / ₀ according to the invention should not exceed.

If necessary, other elements may be present, particularly cobalt, molybdenum, vanadium, tungsten, niobium, tantalum, and copper, up to 2 ° / ₀ and beryllium up to 0.2 ° / _0, but the total content of these elements should in each case 2 Do not exceed ° / _0.

The level of impurities like sulfur, phosphorus, oxygen, nitrogen and lead should be like this be as low as possible with conventional steelmaking processes. There may also be deoxidation residues such as boron, zircon, calcium, lithium and magnesium may be present, however, the impurities are attributable.

In addition to the impurities and the elements mentioned in detail above, there are alloys according to the invention made of iron. They can be subjected to a conventional heat treatment.

For the purpose of achieving optimal properties, the blocks should be diffusion annealed at temperatures Homogenized from 1200 to 1315 ° C and then hot-formed and optionally cold-rolled will.

The solution annealing is then preferably carried out at a temperature of 760 to 870 ° C. It can can also be annealed at higher temperatures, but these cause a loss of tensile strength.

The aging takes place preferably at temperatures of 370 to 480 ° C., the duration of the annealing treatment fluctuates greatly. The alloys according to the invention can be used for 3 to 24 hours, for example 425 ° C. If the aging takes place below 370 ° C, one is undesirable for hardening long time required.

The preferred alloys of the invention have the following nominal composition: 18 ° / ₀ nickel, 3% silicon, less than 0.02 ° / ₀ carbon and very low levels of manganese, aluminum and titanium, the balance, apart from impurities, iron. An actual composition of these preferred alloys is from 17.5 to 18.5 ° / ₀ nickel, 2.75 to 3.3 ° / ₀ of silicon, from 0.006 to 0.025 ° / ₀ carbon, 0.02 to 0.08 ° / ₀ manganese, 0.07 to 0.12 ° / ₀ titanium and 0.07 to 0.12 ° / ₀ aluminum.

Five examples of inventive alloys 1 to 5 are presented below along with two Alloys A and B with insufficient silicon content

ίο as well as two alloys C and D with too high Described silicon content. The compositions of these test alloys are shown in Table I below reproduced.

Table I.

alloy Ni
° / o Si
% C.
° / o Al
• ° / o Ti
° / o Mn
% A. 18.1 0.55 0.006 <0.05 0.08 <0.05 B. 18.4 0.96 0.015 - - 0.09 1 16.7 1.87 0.010 <0.05 0.08 0.04 2 18.4 2.02 0.018 - ' - 0.1 3 17.8 2.58 0.008 <0.05 0.07 0.06 4th 18.3 3.18 0.016 - - 0.11 5 18.5 3.30 0.006 <0.05 0.11 0.10 C. 18.1 4.27 0.018 0.07 0.09 0.10 D. 18.5 4.75 0.35 - - 0.07

In each of the examples listed in Table I, the remainder, apart from impurities, consisted of made of iron.

Samples of these alloys were solution annealed for 1 hour at 815 ° C and then held at -75 ° C for 16 hours to ensure complete conversion to martensite. They were then stored at 425 ° C, various samples were stored for different lengths of time. Then the yield point (0.2 ° / ₀ permanent elongation), the elongation at break, constriction and notch tensile strength of the samples were measured. The test results are given in Table II together with the ratio of the notched tensile strength to the tensile strength, which should be as high as possible.

Table II

alloy Outsourcing
hours 0.2% stretch
border
kg / mm ² tensile strenght
kg / mm ² fracture
strain
° / o A
lacing
° / o Notch pull
strength
kg / mm ² Notched tensile strength A. 3 92 96 23 76 156 tensile strenght B. 3 94 94 18th 65 156 1.62 1 3
24 117
126 121
129 19th
17th 70
69 194
198 1.66 2 3
24 116
149 121
153 14th
16 64
56 191
189 1.60
1.53 3 3
24 129
138 136
144 17th
15th 64
60 216
226 1.57
1.59 4th 3
24 141
149 149
153 12th
16 57
56 176
189 1.59
1.57 5 3
24 146
155 153
160 13th
14th 58
58 229
187 1.17
1.24 C. 3
24 177
191 188
203 4th
A. 8th
* 70
79 1.49
1.17 D. 3
24 ■ 153
103 186
212 2 3
* 108
94 0.37
0.39 0.58
0.45

* Broken into pieces.

The high yield strength of the steel alloys according to the invention associated with adequate toughness is clearly evident, d. i.e., the yield strength is much greater than that of steel alloys A and B, which had a low silicon content. The high silicon alloy D had a good one However, its toughness was remarkably low, as evidenced by both elongation and yield strength from the constriction and in particular from the notch toughness. Alloy D contained 4.75% Silicon still 0.35% carbon, which also contributed to the remarkably poor properties.

In order to show the influence of hardening, further samples of alloy 3 were aged for different times at 370 and 425 and 480 ^° C. and the hardness of these samples was measured. The relevant test results are shown in Table III.

Table III

1 3 Rockwell hardness hours 72 250 temperature 38 35 Time in i 24 ⁰ C 41 42 8th 32 45 - 480 38 41 33 43 46 48 425 42 45 370 42

The data in Table III show that at 480 ^° C. there is a risk of overaging and that the hardness increases at low temperatures.

The steel alloys according to the invention can be easily machined or deformed before hardening will. In the hardened state, they can advantageously be in the form of fine or heavy plate, wire, Bars, etc. are used for construction purposes.

Claims (5)

Patent claims: 1. Martensitic hardenable steel alloy consisting of 40 not more than 0.03% carbon,
10 to 20% nickel,
1.75 to 4% silicon,
up to 5% chromium, 45 where the total content of nickel, silicon and chromium is 12 to 23%, 0 to 1% titanium and / or aluminum, 0 to 0.75% manganese, 0 to 2% cobalt, 0 to 2% molybdenum, 0 to 2% vanadium, 0 to 2% tungsten, 0 to 0.2% beryllium, 0 to 2% niobium, 0 to 2% tantalum, 0 to 2% copper, where the total content of cobalt, molybdenum, vanadium, tungsten, beryllium, niobium, tantalum and Copper does not exceed 2%, the remainder is iron and impurities from the melting process. 2. Steel alloy according to claim 1, wherein the manganese content is at most 0.1%. 3. Steel alloy according to claim 1, consisting of not more than 0.03% carbon, up to 20% nickel, 2.5 to 3.5% silicon, 0 to 1% chromium, where the total content of nickel, silicon and chromium is 18.5 to 23%, 0.05 to 0.15% titanium,
0.05 to 0.15% aluminum, 0 to 0.1% manganese, The remainder is iron and impurities from the melting process. 4. Steel alloy according to claim 1, wherein the titanium and aluminum contents are each 0.07 to 0.12% be. 5. Steel alloy according to claim 1, consisting of 0.006 to 0.025% carbon, 17.5 to 18.5% nickel,
2.75 to 3.3% silicon,
0.02 to 0.08% manganese,
0.07 to 0.12% titanium,
0.07 to 0.12% aluminum, The remainder is iron and impurities from the melting process. 609 569/374 5. 66