KR20110075611A - Wear resistant steel - Google Patents

Abstract

PURPOSE: Wear-resistant steel is provided to reduce the content of high-priced alloy components and carbon and secure a uniform martensite structure at a relatively low cooling speed. CONSTITUTION: Wear-resistant steel comprises carbon(C) 0.06-0.1wt%, manganese(Mn) 6.0-10.0wt%, silicon(Si) 0.05-1.0wt%, niobium(Nb) 0.1wt% or less, titanium(Ti) 0.05wt% or less, boron(B) 0.01wt% or less, and iron(Fe) and other inevitable impurities of the remaining amount. The wear-resistant steel has a micro-structure including martensite 90% or greater and a Brinell hardness of 300 or greater.

Description

Wear Resistant Steel {WEAR RESISTANT STEEL}

The present invention relates to steel applied to construction, machinery, and the like, which requires a Brinell hardness of 300 Hv or more, and more particularly, to wear-resistant steel having excellent strength, hardness, and toughness.

Recently, with high performance and large-scale construction, machinery, and transportation machinery, not only the high strength of the material but also the wear resistance has emerged. Abrasion resistant steel is largely divided into austenitic hardened steel and martensitic hardened steel.

A representative example of the austenitic wear resistant steel is the hardfield steel used for the last 100 years. Headfield steel contains about 12% of manganese (Mn) and about 1% of carbon (C), and its microstructure has austenite and is used in various fields such as mining industry, railroad, and munition. However, the initial yield strength is very low around 400MPa, there is a problem that the application is limited as a general wear-resistant steel or structural steel.

On the contrary, martensitic high hardness steels have high yield strength and tensile strength and are widely used in structural materials and transportation / construction machinery. In general, high hardness steels include high carbon and high alloying elements, and a quenching process is essential to obtain martensite structure that can obtain sufficient strength. A typical martensitic wear resistant steel is the HARDOX series of SSAB, which has a relatively low carbon equivalent (Ceq) and is excellent in strength and hardness.

However, the conventional martensitic wear-resistant steel can be produced by increasing the content of carbon and alloying elements in order to secure high hardness and high strength, and through a separate heat treatment process such as quenching, but if it contains a lot of carbon and alloying elements In addition to adversely affecting weldability and low temperature brittleness, there is a problem in that manufacturing cost is high because an expensive alloying element must be added. In addition, there is a separate heat treatment to obtain a martensite structure, at this time there is a problem that the high residual stress remains in the material may worsen the shape of the product.

The present invention relatively reduces the content of carbon and expensive alloying components, and has high mechanical properties such as high strength, high hardness, and high toughness resulting in a component system capable of obtaining a uniform martensite structure even at a relatively low cooling rate. It's about the river.

In one embodiment, the present invention provides, by weight, carbon (C): 0.06 to 0.1%, manganese (Mn): 6.0 to 10.0%, silicon (Si): 0.05 to 1.0%, residual iron (Fe) and other unavoidable impurities. It provides a wear-resistant steel comprising a.

The microstructure of the wear-resistant steel preferably contains at least 90% martensite.

The wear resistant steel may further include niobium (Nb): 0.1% or less, titanium (Ti): 0.05% or less, and boron (B): 0.01% or less by weight.

The Brinell hardness value of the wear resistant steel is preferably 300 HBW or more.

The tensile strength of the wear resistant steel is preferably 1250MPa or more.

The average packet size of the martensite is preferably 20 μm or less.

The present invention can provide a wear resistant steel excellent in mechanical properties such as yield strength, tensile strength, hardness, toughness.

The present invention relates to a high manganese wear-resistant steel which improves mechanical properties such as hardness, strength and toughness by optimizing the component system and controlling martensite to the columnar phase.

High manganese steel generally refers to a steel having a manganese content of 6.0% or more, and can be composed of various physical property combinations using the microstructural characteristics of the high manganese steel, and the aforementioned high carbon high alloy martensitic wear resistant steel described above. This can solve the technical problem.

When the manganese content is 6.0% or more, the bainite or ferrite generation curve is rapidly moved backwards on the Continuous Cooling Transformation Diagram, so that after hot rolling or solution treatment, compared with the conventional high carbon abrasion resistant steel Martensite is produced stably even at low cooling rates. In addition, when the manganese content is high, there is an advantage that a high hardness can be obtained even with a relatively low carbon content compared to general high carbon martensitic steel.

However, the hardness rises sharply with the addition of a relatively small amount of carbon, whereas the impact toughness is significantly reduced when excessively added. Therefore, in order to have the required physical properties of high hardness wear-resistant steel, high manganese steel needs to optimize not only manganese but also carbon content. In addition, alloying elements such as niobium, titanium, and boron may be further added, and the content thereof may be controlled to provide a steel having improved hardness, strength, and toughness.

Hereinafter, the component system (weight%) of the steel of the present invention will be described.

Carbon (C): 0.06 ~ 0.1%

Carbon is an element included in steel to improve the yield strength and tensile strength of the steel. Thus, as the content increases, the strength of the steel increases, but the toughness decreases. The content of carbon proposed in the present invention is preferably included in the manganese composition range of 0.06% or more in order to ensure the mechanical properties required by the present invention. However, when it adds too much, elongation and toughness will fall remarkably, It is preferable to limit the upper limit to 0.1%.

Manganese (Mn): 6.0-10.0%

Manganese is one of the most important elements added in the present invention. It may also serve to stabilize martensite within an appropriate range. In order to stabilize the martensite within the range of the carbon content, manganese is preferably included 6.0% or more. If less than 6.0%, ferrite or bainite may be formed as the main tissue. If it exceeds 10.0%, the quasi-stable epsilon martensite may be formed, which may deteriorate the mechanical properties of the final product. Therefore, the present invention includes 6.0 to 10.0% manganese as described above, it is possible to easily secure a stable martensite structure without performing quenching in the cooling step after hot rolling or solution treatment.

Silicon (Si): 0.05-1.0%

Silicon is an element that acts as a deoxidizer and improves the strength due to solid solution strengthening, but the lower limit is 0.05% in the manufacturing process, and when the content is high, the toughness of the welded part and the base material is lowered, so the upper limit of the silicon content is 1.0%. It is preferable to limit.

The remaining component of the present invention is iron (Fe). However, in the usual steel manufacturing process, impurities which are not intended from raw materials or the surrounding environment may be inevitably mixed, and thus cannot be excluded. Since these impurities are known to those skilled in the art of ordinary steel manufacturing, not all of them are specifically mentioned herein.

In addition, the steel of the present invention can further improve the effects of the present invention when additionally adding niobium (Nb), titanium (Ti) and boron (B) described below.

Niobium (Nb): 0.1% or less

Niobium is an element that increases strength through solid solution and precipitation strengthening effect, and refines grains at low temperature rolling to improve impact toughness, but when its content exceeds 0.1%, coarse precipitates are formed, and thus hardness and impact toughness are increased. It is preferable to limit the content to 0.1% or less because it deteriorates.

Titanium (Ti): 0.05% or less

Titanium is an element that maximizes the effect of B, which is an important element to improve the hardenability. Titanium increases the content of solid solution B by inhibiting BN formation by TiN formation, and improves the hardenability. Precipitated TiN fixes austenite grains (Pinning) exhibits the effect of suppressing grain coarsening, but when excessively added, problems such as reduced toughness are caused by coarsening of titanium precipitates.

Boron (B): 0.01% or less

Boron is an element that effectively increases the hardenability of materials even with a small amount of addition, and has an effect of suppressing grain boundary fracture through strengthening of grain boundaries, but it reduces the toughness and weldability due to the formation of coarse precipitates when excessively added. It is preferable to limit to.

The steel of the present invention that satisfies the above-described component system is manufactured through a series of hot rolling and cooling processes, and the main phase of the microstructure is martensite, and preferably 90% or more of the martensite is contained. If the fraction of martensite is less than 90%, the hardness intended by the present invention cannot be secured.

In addition, the average packet size of the martensite is more preferably 20 μm or less. When the packet size is 20 μm or less, the martensite structure is refined to further improve impact toughness.

It is preferable that the martensitic steel material which concerns on this invention is 300 or more of Brinell hardness. In addition, the tensile strength of 1250MPa or more, yield strength 900MPa or more, elongation 10% or more and Charpy impact energy (-20 ℃) 25J or more can be secured.

(Example)

Yield strength, tensile strength, elongation, hardness, of the inventive steels 1 to 11 and comparative steels 1 to 5 manufactured by a series of processes, such as hot rolling (final thickness 13mm) of the slab satisfying the component system shown in Table 1 The impact toughness, microstructure, and martensite packet sizes were observed and shown in Table 2 below. In addition, the microstructure of the inventive steel 1 was observed with an optical microscope, and a photograph thereof is shown in FIG. 1.

division C (% by weight) Mn (% by weight) Si (% by weight) Nb (% by weight) Ti (% by weight) B (% by weight) Inventive Steel 1 0.06 7.2 0.15 - - - Inventive Steel 2 0.07 8.4 0.2 - - - Invention Steel 3 0.08 9.2 0.1 - - - Inventive Steel 4 0.09 6.8 0.01 - - - Inventive Steel 5 0.08 7.1 0.04 - - - Inventive Steel 6 0.06 6.74 0.2 - - - Inventive Steel 7 0.074 7.12 0.18 - - - Inventive Steel 8 0.06 6.02 0.09 - - - Inventive Steel 9 0.08 9.8 0.17 0.04 0.015 0.0020 Inventive Steel 10 0.06 6.25 0.21 0.043 0.020 0.0038 Takmyeonggang 11 0.07 7.42 0.24 - - - Comparative Steel 1 0.15 8.45 0.1 - - - Comparative Steel 2 0.03 7.97 0.2 - - - Comparative Steel 3 0.08 4.4 0.3 - - - Comparative Steel 4 0.07 13.4 0.7 - - - Comparative Steel 5 0.065 7.5 1.5 - - -

Comparative steel 1 is a steel grade whose carbon content exceeds the carbon content range defined by the present invention, and Comparative steel 2 is a steel grade whose carbon content is less than the carbon content range defined by the present invention. In addition, Comparative steel 3 is a steel grade whose manganese content is less than the manganese content range defined in the present invention and Comparative Steel 4 is a steel grade whose manganese content exceeds the manganese content range defined in the present invention. In addition, Comparative Steel 5 is a steel grade in which manganese and carbon content satisfy the range defined in the present invention but the silicon content exceeds the silicon content range defined in the present invention.

division Yield strength
(MPa) The tensile strength
(MPa) Elongation
(%) Hardness
(HBW) Impact toughness
(-20 degrees Celsius) (J) Microstructure
(%) Martensite
Packet size (㎛) Inventive Steel 1 901 1311 14.1 395 25 M (100) 35 Inventive Steel 2 977 1390 14.8 397 28 M (100) 38 Invention Steel 3 995 1410 13.9 374 29 M (100) 37 Inventive Steel 4 1056 1420 13.7 371 24 M (100) 31 Inventive Steel 5 942 1412 14.8 379 35 M (100) 39 Inventive Steel 6 976 1462 14.5 381 28 M (100) 34 Inventive Steel 7 911 1411 13.8 391 25 M (100) 33 Inventive Steel 8 934 1424 14.4 401 31 M (100) 38 Inventive Steel 9 1075 1370 13.8 409 65 M (100) 24 Inventive Steel 10 1005 1342 13.5 399 74 M (100) 22 Inventive Steel 11 1054 1374 14.2 395 95 M (100) 13 Comparative Steel 1 1124 1211 7.7 427 7 M (100) 34 Comparative Steel 2 752 980 14.7 278 41 M (100) 36 Comparative Steel 3 812 952 13.5 284 35 B + F + M (82) 41 Comparative Steel 4 521 1250 11.2 282 98 ε + γ - Comparative Steel 5 921 1210 10.2 377 8 M (100) 38

(However, M: martensite, ε: epsilon martensite, γ: austenite, B: bainite, F: ferrite)

Comparative steel 1 has a carbon content of 0.15%, the content is high, the strength is excellent, but it can be confirmed that the elongation is poor. Comparative steel 2 has a low carbon content and excellent elongation, but reduced strength and hardness. Comparative steel 3 has a low content of manganese, which does not delay the transformation of bainite and ferrite, resulting in the formation of bainite and ferrite structures, resulting in reduced strength and hardness. Comparative steel 4 had high content of manganese, resulting in epsilon martensite and austenite structures, resulting in reduced hardness. In comparison steel 5, the manganese and carbon ranges satisfy the component ranges of the present invention, but the silicon content is high, so the elongation and impact toughness are greatly reduced.

On the contrary, the inventive steels 1 to 11 satisfied all the component systems of the present invention, and thus martensite structure was obtained, and excellent yield strength, tensile strength, elongation, hardness, impact toughness, and the like were obtained. In particular, the invention steels 9 and 10 further include niobium, titanium, boron, etc., it was confirmed that the impact toughness is greatly improved. In addition, it can be seen that the inventive steel 11 has a very fine packet size of martensite of 13 µm, which significantly improves impact toughness. In addition, it can be confirmed that the microstructure of the inventive steel 1 shown in FIG. 1 is martensite.

1 is a microstructure photograph of Inventive Steel 1;

Claims (6)

Abrasion resistant steel containing weight%, carbon (C): 0.06 to 0.1%, manganese (Mn): 6.0 to 10.0%, silicon (Si): 0.05 to 1.0%, residual iron (Fe) and other unavoidable impurities. The method of claim 1, Abrasion resistant steel, characterized in that the microstructure of the wear-resistant steel contains more than 90% martensite. The method of claim 1, The wear-resistant steel is a weight-%, wear resistance steel further comprises niobium (Nb): 0.1% or less, titanium (Ti): 0.05% or less and boron (B): 0.01% or less. The method of claim 1, Brinell hardness value of the wear-resistant steel is wear-resistant steel, characterized in that more than 300. The method of claim 1, The tensile strength of the wear resistant steel is a wear resistant steel, characterized in that 1250MPa or more. The method of claim 2, Wear-resistant steel, characterized in that the average packet size of the martensite is 20㎛ or less.

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