Low-carbon microalloyed free-cutting steel

Abstract

The invention discloses low-carbon microalloyed free-cutting steel. The low-carbon microalloyed free-cutting steel comprises the following constituents in percentage by weight: 0.05-0.15% of C, 0.40-0.60% of Si, 1.2-1.5% of Mn, lower than or equal to 0.015%, S lower than or equal to 0.015% of S, 0.03-0.05% of N, 0.01-0.02% of B, 0.01-0.03% of Al, 0.02-0.05% of Nb, 0.01-0.02% of Mo, and the balance of Fe and unavoidable impurities. On the premise that the low-carbon microalloyed free-cutting steel can ensure that the yield strength Rel is larger than or equal to 600 Mpa, the tensile strength Rm is larger than or equal to 850 Mpa, the ductility A is larger than or equal to 20%, the percentage of reduction of area Z is larger than or equal to 55%, the cutting performance is excellent, and the steel is free of harmful elements for the environment, the cutting performance is equal to that of the Pd series free-cutting steel, and better than that of the sulfur series free-cutting steel with simple constituents; the low-carbon microalloyed free-cutting steel can be processed with a conventional process to completely meet the steel requirements on parts for a small but non-critical or a significant component.

Description

technical field [0001] The present invention relates to a kind of free-cutting steel, specifically belongs to a kind of low-carbon micro-alloyed free-cutting steel, and is exactly a kind of steel for high-end small parts of automobiles which not only requires high strength but also is easy to cut. kind. Background technique [0002] Compared with the emerging additive manufacturing (3D printing), traditional mechanical manufacturing requires multiple cutting processes. The data shows that the cost of cutting parts accounts for more than 40% of its manufacturing cost. Therefore, choosing materials that meet the conditions and are easy to cut can significantly Improve production efficiency and reduce production costs. Modern manufacturing industries, such as the automobile industry, mostly use CNC machine tool machining centers. The automation, precision and high efficiency of machine tools require higher and higher cutting performance of materials, but at the same time some ...

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Problems solved by technology

However, because lead is extremely harmful to the environment and human body, developed countries such as the European Union and the United States impose strict restrictions on the production, use and recycling of free-cutting steels containing Pd. It is foreseeable that Pd-free is the development direction of free-cutting steels

Free-cutting steels such as sulfur-based and bismuth-based free-cutting steels are common Pd-free free-cutting steels, but their production or application faces various problems: the high sulfur and oxygen content in sulfur-based free-cutting steels will reduce the purity of steel, Seriously deteriorate the mechanical properties of steel and the inclusion of MnS in steel will lead to an increase in the anisotropy of mechanical properties, which limits its application range; rare elements such as Se (selenium), Te (hoof), Bi (bismuth) and other rare elements help to improve the cutting of steel performance without significantly deteriorating the mechanical properties of steel, but cannot be applied on a large scale due to high cost

Its shortcomings: this document is a sulfur-based free-cutting steel, and its mechanical properties are anisotropic, which limits its application range; although this document uses Ti microalloying, its mechanical properties are not good, that is, the yield strength Rel≥450MPa, Tensile strength Rm≥650MPa, elongation A≥20%, and reduction of area Z≥55%, which are difficult to meet the requirements of high-end automobiles and machinery, and the control process of titanium microalloys is complicated, and large particles of TiN inclusions are prone to appear in steel, which affects Anterograde production and steel properties

Its shortcomings: the mechanical properties of the steel in this document are low, that is, the yield strength Rel ≥ 400Mpa, the tensile strength Rm ≥ 600Mpa, the elongation A ≥ 16%, and the aluminum content in the steel is high, which affects the purity of the steel. Unfavorable, affecting the performance of steel

[0006] With the development of automobile lightweight and increasingly stringent requirements for automobile safety, higher requirements are put forward for material performance under the condition of reducing the amount of steel. In the existing technology, small and non-critical or important automobile parts Low-carbon steel is mostly used, but its mechanical properties and cutting performance are difficult to meet the requirements; and if high-strength medium-carbon or even high-carbon steel is used in the existing processing technology, it is difficult to cut, not only the processing accuracy is difficult to guarantee, but also the efficiency is low , which also consumes a lot of processing equipment

Another related patent report uses Nb-V composite microalloying technology to produce non-quenched and tempered free-cutting steel, but it is a medium carbon steel with a large amount of alloy added, and strict requirements on inclusion control, so the cost is high, and It is mostly used for stress-bearing and large-sized parts, such as automotive connecting rods, crankshafts, etc., and is not suitable for the processing and manufacturing of small-sized parts

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