EP1052296B1 - Use of a steel for the manufacture of amour plates - Google Patents

Abstract

A hot rolled armor plate is made of a low carbon, low alloy steel containing carbonitride-forming vanadium as precipitation hardening element. A novel hot rolled armor plate consists of a steel of composition (by wt.) 0.15-0.20% C, 0.10-0.50% Si, 0.70-1.70% Mn, less than 0.02% P, less than 0.005% S, less than 0.01% N, 0.009-0.10% Al, 0.50-1.00% Cr, 0.20-0.70% Mo, 1.00-2.50% Ni, 0.05-0.25% V, balan Fe and impurities. An Independent claim is also included for production of the above armor plate by hot rolling, double austenitizing at 880-980 degrees C, quenching and tempering at 150-550 degrees C.

Description

The invention relates to the use of a steel for Production of hot-rolled armored sheet.

For the production of armored sheets with a minimum hardness of 400 HB and a final thickness of over 50 mm from steel slabs by hot rolling, hardening and tempering DE 42 23 895 C1 a steel alloy known from 0.25 to 0.32% C, 0.05 to 0.75% Si, 0.10 to 1.50% Mn, 0.90 up to 2.00% Cr, 0.10 to 0.70% Mo, 1.20 to 4.50% Ni, 0.01 to 0.08% Al, max. 0.050% Nb, max. 0.10% V, Max. 0.015% P, max. 0.005% S, max. 0.012% N, balance Fe including common impurities and possibly 0.001 to 0.004% B.

After heating to a temperature of> 1150 ° C, the slabs, which are preferably produced in a continuous casting process, are hot-rolled into coarse strips or sheets. The armored sheet, which was rolled to its final thickness, is hardened after cooling to room temperature by reheating to above Ac ₃ and quenching at a rate of> 1 K / s in oil or water. The sheet can then be tempered in the temperature range of 180 to 250 ° C if necessary. As a result, a high hardness, which is as little as possible below the crack hardness, is set. These well-known armor plates are characterized by a homogeneous structure as well as high hardness and bullet resistance even with a large thickness. The penetration depth of projectiles can usually be reduced by 30%.

Furthermore, an armor plate made of steel is included 0.25 - 0.45% C, 0.08 - 0.50% Si, 0.30 - 1.50% Mn, ≤ 0.02% P, ≤ 0.02% S, 0.60 - 1.80% Cr, 0.20-0.60% Mo, ≤ 0.006% B, 0.02-0.15% Al and / or Ti and 0.005 - 0.03% Nb known from CA 1 266 760 C1, which austenitizes at 860 to 960 ° C, then quenched and tempered at 160-550 ° C.

In addition to the state of the art explained above, Dr.-Ing. B. Müsgen wrote article "High-strength water-tempered fine-grained structural steels with minimum yield strengths up to 90 kp / mm ² ", published in DECHEMA MONOGRAPHIEN, Verlag Chemie, Weinheim, Vol. 76, 1974, a high-strength water-tempered structural steel known from iron, inevitable impurities and contents Mo (in% by weight) 0.19% C, 0.30% Si, 0.65% Mn, 0.60% Cr, 2.00% Ni, 0.09% V. With a Mo content of at least 0.35% Mo and observing a suitable tempering temperature, the known steel achieves a tensile strength of at least 1,100 N / mm ² . However, the hardness of the known steel is lower than is usually required for armored sheets.

The invention has for its object one for Manufacture of steel sheet suitable for armor to propose, the one produced from this steel Armored sheet metal on the one hand with regard to bullet resistance properties at least as good as the armor plates of the on the other hand improved material properties, such as a higher one Yield strength, higher strength at the same time higher toughness and improved weldability having.

To achieve this object, the invention proposes the use of a (in mass%) 0.15 - 0.2% C 0.1 - 0.5% Si 0.7 - 1.7% Mn <0.02% P <0.005% S <0.01% N 0.009 - 0.1% al 0.5 - 1.0% Cr 0.2 - 0.7% Mo 1.0 - 2.5% Ni 0.05 - 0.25% V Rest of iron including unavoidable impurities,
steel for the production of armored sheet, which has a tempering structure and a yield strength> 1100 N / mm ² , a hardness> 400 HB and a notched impact strength A _v of at least 27 joules measured on an ISO-V cross-test at -40 ° C having.

A steel alloy of the following composition (in mass%) is preferred within the composition range used according to the invention: 0.16 - 0.18% C 0.2 - 0.4% Si 0.9 - 1.1% Mn <0.015% P <0.005% S <0.008% N 0.015 - 0.05% al 0.6 - 0.8% Cr 0.5 - 0.6% Mo 1.9 - 2.0% Ni 0.06 - 0.1% V Balance Fe including unavoidable impurities.

The steel alloy can additionally contain up to 0.005% boron contain. The nitrogen content of the steel alloy should preferably limited to 0.004 to 0.008%.

The steel alloy used according to the new use stands out compared to the above known steel alloy on the one hand by a lower carbon content and secondly through the Carbonitride former vanadium as a precipitation hardening agent Element off. Surprisingly, one reaches out of the Armor sheet produced according to the invention in the tempered condition despite the lower Carbon content compared to known armor plates a significantly higher yield strength and strength, however also a higher toughness and a higher elongation at break.

Due to the improved toughness in combination with the Improved elongation at break can be made according to the invention Armored sheet steel used the shock-like Exposure to mine explosions without the risk of Record breakage or cracking. Security too against the occurrence of jumps and against the Formation of cracks or flaking in direct Shelling is compared to steel according to the invention conventional steels of the generic type improved. Therefore, the performance characteristics of are according to the invention produced armor sheet compared to the prior art clearly improved.

The yield strength of the armor plate according to the invention is over 1100 N / mm ² compared to only 950 N / mm ^{2 of} the known armor plate. The minimum tensile strength is 1200 N / mm ² , in particular 1250 N / mm ² , and is consequently significantly higher than the minimum tensile strength of 1150 N / mm ^{2 achieved in} the prior art. The toughness of armor sheets according to the invention, measured on an ISO-V transverse sample at -40 ° C., is A _v ≥ 27 joules. Their elongation at break is more than 10%.

Armor sheet produced according to the invention preferably a predominantly martenistic structure a fine grain. Particularly good ones Material properties arise when the proportion of martensitic structure is at least 98%.

When the armored sheet is treated, a double austenitization in the temperature range of 880 up to 980 ° C with air cooling between the Austenitization processes, quenching after the second Austenitization to room temperature and on final tempering at 150 to 550 ° C preferred. By quenching to room temperature, i.e. to well below the martensite start temperature fine-grained martensitic structure. Whose Fine grain can be further improved in that the quench to room temperature after the second Austenitization in the temperature range of 800 - 500 ° C with one related to the sheet metal core Cooling rate of at least 5 K / s takes place, whereby preferred for the rapid cooling Pressurized water is used. By an invention composite, usually in heavy plate thickness executed sheet metal in the course of its remuneration up to cooled its core at such high speeds armor sheet is obtained, which has a share in very fine-grained martensite of more than 98%. Such an armor plate has, as already above mentions excellent properties and meets the requirements Sheets of the type in question reliable.

Example:

A melt of the composition shown in Table 1 was poured into a 260 mm thick slab. The slab was based on a furnace temperature of 1250 ° C, with a piercing temperature of about 1100 ° C at a final rolling temperature of 950 ° C to a final thickness of 10, 40 and 50 mm hot rolled. Then the Aging treatment. For sheets 1, 3 and 4 in Table 2 consisted of austenitizing (940 ° C / water) with subsequent tempering 320 ° C / air. Sheet 2 was austenitized twice, quenched and tempered. The samples of the like The properties of the armored sheet obtained are in Table 2 compiled.

The yield strength and tensile strength are clearly above the aforementioned minimum limits. The elongation values are approx. 11 to 12% is extraordinarily good, and the notched impact strength values are also significantly above the aforementioned minimum limit of 27 J. The hardness values are all above 400 HB. The double austenitized sheet 2 again achieved increased values of the mechanical properties. C Si Mn P S al Cr Mo Ni V 0.16 0.29 0.98 0,012 0,003 0,025 0.66 0.51 1.93 0.07 Sheet no. Thickness (mm) Re (N / mm ² ) Rm (N / mm ² ) A (%) ISO-V cross -40 ° C Hardness HB10 / 3000 1 10 1125 1339 10.9 35,32,28 415 2 10 1166 1386 12.0 39,39,39 420 3 40 1124 1345 11.0 28,35,29 412 4 50 1120 1317 11.7 42,38,34 408

Claims (5)

1. Use of a steel containing (in wt %) 0.15 to 0.20 % C 0.10 to 0.50 % Si 0.70 to 1.70 % Mn < 0.02 % P < 0.005 % S < 0.01 % N 0.009 to 0.10 % Al 0.50 to 1.00 % Cr 0.20 to 0.70 % Mo 1.00 to 2.50 % Ni 0.05 to 0.25 % V, up to 0.0050 % B, a balance iron including unavoidable impurities for the production of armour plate, which has a heat-treatable microstructure, yield point > 1100 N/mm², hardness > 400 HB and notched-bar impact-strength measured on an ISO V transverse test piece at -40 °C of at least 27 Joules.
2. Use according to Claim 1, characterised in that the steel alloy contains (in wt %) 0.16 to 0.18 % C 0.20 to 0.40 % Si 0.90 to 1.10 % Mn < 0.015 % P < 0.005 % S < 0.008 % N 0.015 to 0.050 % Al 0.60 to 0.80 % Cr 0.50 to 0.60 % Mo 1.90 to 2.00 % Ni 0.06 to 0.10 % V, a balance iron including unavoidable impurities.
3. Use according to any one of the above claims, characterised in that the nitrogen content of the steel alloy is limited to between 0.0040 and 0.0080 %.
4. Use according to any one of the above claims, characterised in that the armour plate possesses a predominantly martensitic microstructure.
5. Use according to Claim 4, characterised in that the martensitic percentage of the microstructure amounts to at least 98 %.