CS201052B1 - Martensitic-austenitic steel - Google Patents

Description

The invention relates to martensitic-austenitic steel for the production of castings, forgings and rolled metal.

Steel containing 12 to 19 wt. % chromium, 3.5 to 7.5 wt. % nickel, 0.1 to 2.0 wt. % manganese, 0.1 to 2.0 wt. % silicon and optionally up to 2 wt. % molybdenum and longer than 0.08 wt. % carbon, 0.030 to 0.045 wt. % phosphorus and 0.015 to 0.030 wt. open. In these steels, the nitrogen content is usually not delimited and intentionally influenced during manufacture and therefore occurs within wide limits of from 0.005% to 0.050% by weight. even more depending on the raw materials used and the method of steel production. These steels have relatively good corrosion resistance and high enough strength. Their drawbacks are the unevenness in achieving the plastic values in the tensile test and the notch toughness and insufficient brittleness resistance, thereby limiting their applicability to the demanding load-bearing parts of highly stressed equipment.

These drawbacks of the prior art are overcome by martensitic-austenitic steel for castings, forgings and rolled steel according to the invention, which contains 12 to 19% by weight. % chromium, 3.5 to 7.5 wt. % nickel, 0.1 to 2.0 wt. Manganese, 0.01 to 0.01

201 0S2

1.5 wt. % silicon, traces up to 2.0 wt. % molybdenum and 0.001 to 0.03 wt. carbon. It is an object of the invention that, in addition to iron and the usual accompanying elements, they contain 0.001 to 0.030% by weight. % phosphorus, 0.001 to 0.015 wt. The present invention further provides that the steel further comprises 0.02 to 0.15% by weight of nitrogen and carbon in an amount corresponding to a nitrogen to carbon ratio of 0.2 to 2.0, but not more than 0.03%. % titanium and 0.05 to 0.50 wt. niobium, individually or in combination.

The advantage of the martensitic-austenitic steel according to the invention when used on castings, forgings and rolled steel is that it exhibits improved corrosion resistance, improved weldability, higher resistance to corrosion cracking mainly at higher temperatures and increased resistance to hardening cracks and premature and retarded of quarries. Another advantage is that it has a lower level of transition temperatures in the zero toughness test and a lower value of zero plasticity. This improvement in steel quality is due to the fact that the nitrogen content, to the carbon content, is in the ratio of 0.2 to 2.0 and most preferably in the ratio of 0.5 to 1, and if its concentration is not more than 0.03% by weight.

A further improvement of the steel property, in particular at a nitrogen content corresponding to the edge region of the above nitrogen to carbon ratio range, is achieved by adding stabilizers such as titanium in an amount of 0.02 to 0.15% by weight. % and niobium ranging from 0.05 to 0.50 wt.

For the production of castings of the gate valve body of the main shut-off valve of the primary circuit of the nuclear power plant, whose weight including the riser was 13 tonnes, steel containing 0.99% by weight was produced in an electric arc furnace. % manganese, 0.56 wt. % silicon, 0.018 wt. % phosphorus, 0.006 wt. % sulfur, 13.63 wt. % chromium, 6.14 wt. % nickel, 0.54 wt. % molybdenum and 0.032 wt. nitrogen. Due to the high nitrogen content, the melt was carburized with an electrode so that the tapping nitrogen content was 0.66% by weight. This Steel was tapped into a basement-laden basin, whereupon it stood in a vacuum caisson and, under vacuum, oxygen was blown from above by a water-cooled nozzle. At the same time, the steel was mixed with argon blown into the melt through a ceramic block located in the bottom of the ladle. After 40 minutes of oxygen blowing at a rate of 600 to 800 m ^ / h. at a gas pressure above 8 to 1 kPa, the melt was vacuum evacuated without oxygen oxidation for 15 minutes. The pressure of the gases in the vacuum chamber was gradually reduced to 60 Pa. The steel produced was deoxidized with aluminum and ferrosilicon and doped with ferrotitanium and contained 0.011% by weight. % of carbon, 0.77 wt. % manganese, 0.41 wt. % silicon, 0.018 wt. % phosphorus, 0.005 wt. % sulfur, 13.42 wt. % chromium, 6.10 wt. % nickel, 0.05 wt. % titanium and 0.0060 wt. nitrogen. A check calculation found that the ratio of nitrogen content to carbon content was 0.55, thus satisfactory. The steel was therefore cast into molds without further treatment. The castings produced after heat treatment showed high strength and trot limits both at normal temperature and at 350 ° C, at the same time a high level of elongation and tapering, as well as notch toughness values. From the same melting, ingots of square cross-section were cast, which were rolled into round bars of diameter

201 052 mm and octagonal ingot weighing 4 tons from which wedge plates were forged. Also these rolled and forged products showed a high level of basic mechanical properties and brittle fracture characteristics.

For the production of castings of gate lids and compressor parts of 1500 kg each and

800 kg was made in an electric arc furnace steel containing 0.57 95 wt. % of carbon, 0.89 wt. % manganese, 0.35 wt. % silicon, 0.016 wt. % phosphorus, 0.006 wt. % sulfur, 12.65 wt. % of chromium, 3.76 wt. % nickel and 0.0192 wt. nitrogen. After the steel has been vacuum dried by blowing oxygen to a steel level in a ladle, carried out in a manner similar to that of Example 1, a steel of 0.012 wt. % of carbon, 0.68 wt. % manganese, 0.18 wt. % silicon, 0.017 wt. % phosphorus, 0.005 wt. % sulfur, 12.50 wt. % chromium, 3.78 wt. % nickel and 0.0039 wt. Nitrogen was cast into a round die for the production of ingots weighing 1800 kg. After solidification, these ingots were charged into a 4-ton induction electric furnace with basic lining, where they melted under strongly alkaline slag. The steel was doped with nitrogen ferro-chromium to increase the nitrogen content by 0.003% by weight. and in order to reach a lower carbon to nitrogen ratio of 0.5, it was then deoxidized with ferro-silicon and aluminum. When tapped into the ladle, the melt was degassed, and then the desired castings were cast. According to the melting analysis, the steel produced had the following chemical composition: 0.013 wt. % of carbon, 0.67 wt. % manganese, 0.32 wt. % silicon, 0.018 wt. % phosphorus, 0.003 wt. % sulfur, 12.55 wt. % chromium, 3.75% wt. % nickel and 0.0085 wt. nitrogen. The mechanical values and the brittle fracture characteristics of the produced castings showed high parameters.

Claims (2)

SUBJECT OF THE INVENTION 1. Martensitic-austenitic steel for the production of castings, forgings and rolled products in composition by weight. 12 to 19 95 chromium, 3.5 to 7.5 95 nickel, 0.1 to 2.0% manganese, 0.01 to 1.50% of silicon, traces of up to 2% of molybdenum and 0.001 to 0.03% of carbon, characterized in that it contains 0.001 to 0.03% by weight of phosphorus, 0.001 to 0.015% by weight of sulfur and nitrogen relative to carbon 0.2 to 2.0, but not more than 0.0395, and the usual accompanying elements. 2. Martensitic austenitic steel according to claim 1, characterized in that it further contains, in 95% by weight, 0.02 to 0.15 95 titanium, 0.05 to 0.50% niobium, individually or in combination with each other.