Method for producing molten steel having high wear resistance and steel having said characteristics

Abstract

The invention refers to a method for producing a molten steel having high wear resistance having a mainly bainitic microstructure and a suitable balance of tensile strength and hardness for pieces of large size in mining operations such as milling and grinding, the chemical composition of which, expressed in weight percentage, comprises: 0.30-0.40% of C, 0.50-1.30% of Si, 0.60-1.40% of Mn, 2.30-3.20% of Cr, 0.0-1.00% of Ni, 0.25-0.70% of Mo, 0.0-0.50% of Cu, 0.0-0.10% of A, 0.0-0.10% of Ti, 0.0-0.10% of Zr, less than 0.050% of P, less than 0.050% of S, less than 0.030% of N, optionally less than 0.050% of Nb, optionally 0.0005-0.005% of B, optionally 0.015-0.080% of rare earth metals, and residual contents of W, V, Sn, Sb, Pb and Zn of less than 0.020%, and the balance in iron. The method for producing the molten steel includes smelting and heat treatment. The smelting can be carried out in an electric arc furnace having basic or acid refractory or an electric induction furnace. Smelting in an electric arc furnace as a normal operation includes melting, oxygen insufflation, blocking, refining and deoxidation. Smelting in an electric induction furnace includes melting, refining, control of nitrogen in solution and deoxidation. Heat treatment comprises settling and tempering. The molten steel described in the invention exhibits a suitable balance of the chemical composition, tensile strength and hardenability to assure complete hardening in cast pieces of large size, typically up to 17 inches in thickness, with Brinell hardness preferably in the range of 385-495 BHN throughout the section of the piece and excellent resistance to wear by abrasion impact.

Description

FIELD OF APPLICATION[0001]The present invention relates to the field of wear-resistant metallic materials, especially cast steels resistant to wear by abrasion and impact for mining applications. More particularly, the present invention relates to a method for producing cast steel, by which a wear-resistant steel is obtained, with predominantly bainite microstructure and a suitable balance of toughness and hardness for use thereof in mining applications, such as grinding, crushing and all those applications that require large components with high resistance to wear by abrasion and impact. Even more particularly, the present invention relates to a cast steel of predominantly bainite structure, with a suitable balance of toughness and hardness and resistant to wear, to be used in the applications mentioned above.The Technical Problem[0002]Various methods for producing steels for mining applications are known in the prior art. However, the useful life of the components obtained by thes...

AI Technical Summary

Benefits of technology

The present invention relates to a method for making a cast steel with increased hardness through the cross section of a component of large thickness. The cast steel has a suitable balance of chemical composition, toughness, and hardenability to ensure complete hardening in castings of large size, typically up to 17 inches in thickness, with brinell hardness preferably in the range 385-495 BHN throughout the cross section of the component and excellent resistance to wear by abrasion and impact. The method involves melting and casting the steel using a specific method that ensures the increased hardness is constant throughout the component. The cast steel obtained using this method has a chemical composition, toughness, and hardenability that make it suitable for use in coatings for SAG mills and other applications. The method can be performed using specific chemical compositions and heat treatment conditions that ensure complete hardening and excellent resistance to wear and abrasion. The resulting cast steel has superior properties, including increased hardness, toughness, and wear resistance.

Problems solved by technology

However, the useful life of the components obtained by these methods is unable to meet production requirements.

In particular, the known methods do not provide steels whose hardenability is sufficient to ensure high hardness over the entire cross section of components of large thickness made with this steel.

However, when the mechanical stress is not sufficient to produce high hardening by cold working, austenitic manganese steels inevitably display low abrasive wear resistance, greatly reducing the useful life of components made with said steels.

Despite the foregoing, owing to the global trend in the mining industry to use ore processing equipment of larger size, added to the ever-increasing mechanical stress to which the components are subjected, the “acceptable results” currently obtained with Cr—Mo steels are inadequate.

In view of this, the use of low-alloy Cr—Mo steels with predominantly pearlitic microstructure is limited, since it is not possible to increase their wear resistance by increasing the hardness, without having an adverse effect on toughness.

Consequently, the use of these alloys under the current conditions inevitably increases the probability of failure.

However, since these steels do not possess sufficient hardenability, it is not possible to guarantee constant high hardness through the cross section of the component, from the surface to the center, for components with thicknesses above 6 inches (15.2 cm).

However, it has been found that this route causes a considerable decrease in toughness.

This not only gives rise to higher costs of manufacture, but also hampers the production of large components or those with complex geometry with large changes of section.

Moreover, said document teaches that a chromium content below 3.0% w / w adversely affects the hardenability of the steel.

Although the bainitic steel of high strength and toughness described in JP 09 170017 uses microalloying elements to obtain a fine bainite microstructure, it has a lower content of silicon and manganese to ensure high toughness, and accordingly it does not develop sufficient hardness, hardenability and wear resistance for use in conditions of abrasion and severe impact in mining operations.

Although both documents disclose steels with increased toughness, the high silicon concentration in these steels (1.40-2.05% w / w) has an adverse effect on the manufacture of components with large thickness, since it promotes the occurrence of phenomena of hot cracking during solidification of the components.

These steels differ from the steels of the present invention in that, although they possess high toughness, they do not have a suitable balance of chemical composition that allows them to obtain a high hardness that is practically constant through the cross section in components with large thickness, despite the fact that high contents of manganese, silicon and / or nickel are specified.

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