RU2564502C1 - Low-alloyed structural steel with increased machinability - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: steel contains in wt %: carbon 0.14-0.20, manganese 1.3-1.5, silicon 0.05-0.45, phosphorus 0.02 maximum, sulphur from over 0.05 to 0.09, copper 0.25 maximum, vanadium 0.03-0.055, bismuth 0.005-0.02, nitrogen 0.004-0.015, molybdenum 0.05 maximum, and iron and impurities are the rest.

EFFECT: hot-rolled steel products have increased machinability by cutting upon keeping level of strength properties and impact toughness.

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Description

The invention relates to ferrous metallurgy, namely to the production of hot rolled steel from high strength for the manufacture of automotive components.

Known low alloy structural, with high strength steel, containing, by weight. %:

carbon 0.15-0.20;

Manganese - 1.3-1.5;

silicon - 0.05-0.45;

phosphorus - not more than 0.02;

sulfur - 0.02-0.05;

copper - not more than 0.25;

vanadium - 0.03-0.055;

nitrogen - 0.004-0.015;

iron and impurities - the rest [1].

This steel is the closest to the proposed mechanical properties, composition and purpose and is taken as a prototype.

A disadvantage of the known steel is insufficient for the consumer machinability by cutting hot rolled steel on metal cutting machines.

The main technical objective of the invention is to increase machinability by cutting over the entire cross section and volume of rolled products from structural steel while maintaining mechanical properties at the level of low alloy structural steel of increased strength.

The technical solution to the problem is achieved due to the fact that a modified low-carbon low-alloy structural, with increased machinability on metal-cutting machines, steel containing in wt. %:

carbon 0.14-0.20;

Manganese - 1.3-1.5;

silicon - 0.05-0.45;

phosphorus - not more than 0.02;

sulfur - 0.015-0.09;

copper - not more than 0.25;

molybdenum - not more than 0.05;

vanadium - 0.015-0.055;

bismuth - 0.005-0.02;

nitrogen - 0.004-0.015;

iron and impurities - the rest.

The introduction of bismuth in the specified interval and the increased sulfur content in the aggregate lead to an increase in the resistance of the tool used in the manufacture of parts of the declared steel by 1.2-1.4 times depending on the type of machining (milling, drilling, grinding, threading).

The minimum bismuth content in steel of 0.005% is due to the achievement of machinability that satisfies the consumer. The maximum content of 0.02% is experimentally selected for optimal casting conditions for continuous casting machines, compliance with the requirements for maximum permissible concentration (MAC) of bismuth in air (set at 0.5 mg / m ³ ).

Quantitative sulfur content below 0.015% leads to a decrease in the acceptable level of workability. A sulfur content above 0.09% leads to a decrease in impact strength (impact work value) of the declared steel.

Practical Example

Smelting of the declared steel grade is carried out at CJSC Omutninsky Metallurgical Plant in a steelmaking unit. In the SPA, steel of the main composition is smelted, containing carbon, manganese, silicon, iron and inevitable impurities; after heating to 1620-1640 ° C, it is released into the steel pouring ladle. Deoxidation of steel by aluminum is carried out at a drain from the steelmaking unit into the ladle, components for deoxidation are introduced into the bottom zone of the ladle at the optimal ratio [Mn] / [Si] ≤3. A sufficiently deep deoxidation of steel by secondary aluminum is carried out to obtain optimal conditions for the ascent of the formed large aluminum oxides. Additionally, oxygen is controlled (not more than 0.001% on the proposed steel grade).

After the release of the heat from the spa, furnace slag is removed from the steel pouring ladle. During out-of-furnace treatment with a metal purge with argon, lime-alumina slag is induced by additives of lime and aluminum-containing material. Get branded content of the basic elements (carbon, manganese, silicon) and deoxidated refining "white" slag.

Vanadium is introduced in the form of lumpy ferroalloy to achieve the target concentration. Then the metal is heated to a temperature guaranteeing a predetermined overheating of the metal above the liquidus temperature of the steel in the intermediate ladle during casting at the continuous casting machine, taking into account the existing heat losses and subsequent alloying with sulfur.

Sulfur is introduced into steel by flux-cored wire using a tribamer after thickening the slag with magnesite powder.

Bismuth is introduced into steel by cored wire with MnBi filler (20/80) after additional thickening with magnesite powder.

Casting in the continuous casting machine is carried out with the protection of the metal from secondary oxidation in a "under the level" way. Exposure of the metal surface in the bucket (sparking) is not allowed. During casting, the slag cover in the intermediate ladle is thickened with one-time additives of magnesite powder of 5-10 kg.

The obtained continuously cast billet is rolled on hot rolling mills according to technological instructions and rolling schemes of OMZ CJSC. Get a hot-rolled profile for the manufacture of hinges of car doors.

Made three heats with the proposed composition of the modified steel. The resulting chemical composition in comparison with the prototype are shown in table 1. The results of the study of the mechanical properties of the known and proposed steel are shown in table 2.

Pilot tests on the criterion of tool durability were carried out by EDSCHA, a manufacturer of door hinges for cars of various sizes. Table 3 shows the test results of the proposed steel. Products with the specified parameters satisfied the consumers of the company. There was a proposal to replace the steel grade S355JO mod of all supplied hot-rolled profiles with the one proposed as the most satisfying processing and operating conditions.

Thus, the proposed chemical composition makes it possible to obtain steel with a 1.2-1.4 times higher machinability by cutting on metal cutting machines over the entire cross section and volume of rolled metal while maintaining mechanical properties at the level of low alloy structural steel of increased strength in the manufacture of hot rolled automotive components.

Information sources

1. Patent for the invention No. 2505618. RU.

Claims (1)

Hot-rolled steel from low-carbon low-alloy structural steel with increased strength and machinability by cutting containing carbon, silicon, manganese, phosphorus, sulfur, nitrogen, copper, molybdenum, vanadium, iron and impurities, characterized in that the steel additionally contains bismuth in the following ratio of components, wt .%:
carbon 0.14-0.20 manganese 1.3-1.5 silicon 0.05-0.45 phosphorus no more than 0,02 sulfur from more than 0.05 to 0.09 copper no more than 0.25 molybdenum no more than 0,05 vanadium 0.015-0.055 bismuth 0.005-0.02 nitrogen 0.004-0.015 iron and impurities rest