CS238031B1 - High-strength structural steel micro-alloyed with titanium and boron additive and a heat treatment process - Google Patents

Abstract

The purpose of the invention is a steel whose chemical composition creates good conditions for cold forming in the natural rolled state without the need for annealing, a high-strength structural steel microalloyed with titanium and boron, especially for high-strength chains and connecting parts, containing in an amount by weight of carbon 0.18 to 0.26 S, manganese 0.80 to 1.40%, silicon 0.15 to 0.55%, nickel traces up to 0.50%, aluminum 0.020 to 0.070%, chromium 0.02 to 0.15%, lead 0.03 to 0.12%, phosphorus traces up to 0.03 S, sulfur traces up to 0.030% is characterized by containing titanium from 0.01 to 0.10%, boron 0.0015 to 0.006%, while the sum of the contents of phosphorus, tin and antimony must not exceed 0.045%. The steel is heat treated by quenching from a heating temperature of 870 to 900 °C and tempered in the temperature range of 340 to 440 °C.

Description

BACKGROUND OF THE INVENTION The present invention relates to high-strength structural steels microalloyed with titanium and boron additive suitable for the production of high-strength chains and fasteners and to a method of heat treatment thereof.

For this purpose, chromium, nickel, molybdenum and vanadium alloyed steels have been used on a large scale in combination with these alloying elements. Steel with a carbon content of 0.17 to 0.25%, containing manganese from 0.60 to 1.70%, chromium from 0.20 to 0.60%, molybdenum from 0.15 to 0. 55% and nickel from 0.40 to 1.10% (DIN 17 115).

This type of steel is used to produce ISO-C grade chains. More recently, in order to save molybdenum deficiency, vanadium steel has been introduced: carbon 0.19 to 0.26%, manganese 0.60 to 1.00%, silicon 0.35 to 0.60%, chromium 0.30 up to 1.00%, nickel 0.40 to 0.80%, vanadium 0.05 to 0.015%.

After heat treatment, these steels are characterized by a microstructure in the form of tempered martensite. The chains of these steels are treated to a strength of 1000 to 1200 MPa. The chemical composition of these steels is selected so as to guarantee good weldability by all known methods. '«.

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These steels, due to their chemical composition and their tendency to form a metastable structure _t when rolling on high-speed rails with more intense cooling, often exhibit deterioration in their natural state of plasticity, which tends to be a defect in forming cold chain components.

When molybdenum steel is alloyed, tin and antimony accompanying elements also enter the steel, which impaired weldability. The combination of alloying elements based on chromium, nickel, molybdenum or chromium, nickel, vanadium increases the cost of manufacturing these types of steels.

The above-mentioned disadvantages are overcome by the high-strength structural steel according to the invention, containing in an amount by weight carbon from 0.18 to 0.26%, manganese 0.80 to 1.40%, silicon 0.15 to 0.55%, nickel trace to 0, 50%, aluminum 0.020 to 0.070%, chromium 0.02 to 0.15%, copper 3 0.03 to 0.12%, phosphorus max 0.030%, sulfur max. 0.030%, where the essence of the invention is that it contains titanium 0.01 to 0.10%, and boron 0.0015 to 0.006%, and the sum of phosphorus, tin and antimony contents does not exceed 0.045%.

It is further an object of the invention that the steel is heat treated by quenching from a heating temperature of 870 to 900 ° C into water and subsequently tempered within a temperature range of 340 to 440 ° C.

The advantage of the steel according to the invention is that, due to the presence of free boron, it has a guaranteed hardenability characterized by a 100% martensitic structure over the entire cross-section.

The steel has uniform mechanical values.

The presence of titanium and nickel, respectively, guarantees the fineness of the structure after heat treatment, which is characterized by a high notch toughness value. Due to its chemical composition and limited content of harmful elements, the steel has good weldability.

The chosen chemical composition of the steel creates good conditions for cold forming in the natural rolled state without the need for annealing. The chemical composition steel according to the invention brings about a significant reduction in production costs and a reduction in alloying.

According to one embodiment of the invention, a steel containing 0.19% carbon was produced,

1.10% manganese, 0.26% silicon, 0.49% nickel, 0.04% titanium, 0.005% boron, 0.040% aluminum,

0.07% chromium, 0.09% copper, 0.018% phosphorus and 0.016% sulfur, with a total phosphorus, tin and antimony content of 0.045%.

The steel was produced in an electric arc furnace using conventional technology. Ingots were fed into the billets and these into bar steel φ 18.5 mm. Mechanical properties in the natural state: yield strength 420-440 MPa, yield strength 600-622 MPa, elongation 25%, contraction 67%.

In tempered state after quenching from 870 ° C to νοφ and subsequent tempering

A yield strength of 1 013 to 1045 MPa, a yield strength of 1054 to 1076 MPa, an elongation of 14%, a contraction of 62%, a notch toughness of KCU2 of 120 J.cm were reached at 380 ° C. The hardenability of the steel was satisfactory.

Bar steel was processed into high-strength chains of the ISO-C class. The cold workability on the automatic bending machines was very good;

The chains were heat treated by quenching from 900 ° C to water followed by tempering to 400 ° C. The breaking load was 415 to 442 kN / min. 410 kN /, elongation 12,2 to 14,1% / requirement min. 10%.

According to a second exemplary embodiment, one was produced containing 0.23% carbon, 1.27% manganese, 0.47% silicon, 0.06% titanium, 0.0041% boron, 0.043% aluminum, 0.03 ΐ nickel, 0.07 ΐ chromium and 0.10% copper.

Mechanical values in the natural state: yield strength 538 to 560 MPa, me2 strength 720 to 755 MPa, elongation 19.8%, contraction 57%. In the quenched state after quenching from a temperature of 880 ° C into water and subsequent tempering to 380 ° C, a yield strength of 1 178 MPa, a yield strength of 2 256 MPa, an elongation of 14%, a contraction of 59%, a notched toughness of KCU2 of 125 J were achieved. cm.

The hardenability of the steel was satisfactory. Bar steel has been processed into ISO-C grade high-strength chains. Following the heat treatment of the chains, the prescribed values were also achieved as in the first embodiment:

Claims (2)

The first high strength structural steel micro-alloyed with titanium and boron, in particular for high-strength chains and linking component containing carbon in an amount of from 0.18 to 0.26% manganese 0.80 to ^{R <} 40%, silicon 0.15 to 0, 55 t, nickel trace up to 0.50 *, aluminum 0.020 to 0.070%, chromium 0.02 to 0.15 i, copper 0.03 to 0.12%, phosphorus trace to 0.030%, trace sulfur to 0.030%, marked further comprising titanium from 0.01 to 0.10%, boron 0.0015 to 0.0060%, the remainder iron, wherein the sum of phosphorus + tin + antimony contents does not exceed Q.045%. 2. The method of heat treatment of high strength structural steel according to claim 1, characterized in that the steel is heat treated by hardening from a heating temperature of 870 to 900 [deg.] C. into water and tempered within a temperature range of 340 to 440 [deg.] C.