Heat-treatment-free grade 8.8 fastener-use cold forging steel and manufacturing method thereof

Abstract

The invention relates to heat-treatment-free grade 8.8 fastener-use cold forging steel and a manufacturing method thereof. The heat-treatment-free grade 8.8 fastener-use cold forging steel is preparedfrom the following chemical ingredients in percentage by weight: 0.13 to 0.20 percent of C, 0.10 to 0.35 percent of Si, 1.40 to 1.80 percent of Mn, 0.03 to 0.10 percent of V, 0.01 to 0.03 percent ofTi, 0.008 to 0.02 percent of N, at most 0.02 percent of P, at most 0.015 percent of S and the balance of Fe and impurities, wherein the Ti and N meets the requirement that N-0.15Ti-0 .1V is greater than or equal to 0 .003 percent; the ratio of V to N is smaller than or equal to 10. In the rolling steps, the low-temperature heating is performed; the low-temperature rolling does not need to be executed; the equipment requirement and the production cost are reduced; the obtained grade 8.8 fastener-use cold forging steel has good cold deformation capability; after the drawing, cold forging and aging treatment, the high-intensity grade of a 8.8 fastener can be reached; the use requirement of the fastener can be met.

Description

technical field [0001] The invention belongs to the field of cold heading steel manufacturing, and in particular relates to a heat-free cold heading steel for grade 8.8 fasteners and a manufacturing method thereof. Background technique [0002] Cold heading steel is a material that is formed by one or more impact loadings at room temperature, and is widely used in the production of standard parts (fasteners) such as bolts, screws, pins, and nuts. Cold heading steel products are mainly used in industries such as automobiles, shipbuilding, equipment manufacturing, electronics, home appliances, bicycles, tools, light steel structures, and construction. [0003] The commonly used fastener production process is: cold heading steel wire rod annealing + pickling, phosphating + drawing + (annealing, high strength) + cold heading + quenching and tempering heat treatment + surface treatment + packaging. The fastener processing process shows that the production of high-strength fasten...

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Problems solved by technology

[0013] It can be seen that in the prior art, high-strength non-quenched and tempered steels are obtained by adding carbide-forming elements such as Cr, Mo, Nb, V, B, Ti, etc. alone or in combination on the basis of medium and low-carbon Mn-containing steels, The carbides formed by these elements form particles that hinder dislocation slippage and annihilation, thereby avoiding the reduction of dislocation density and improving strength; the hot rolling process adopts low-temperature rolling (750-950°C) for refining grains, and The post-rolling cooling process promotes the precipitation of carbides, thereby improving the strength of the material, while low-temperature rolling greatly increases equipment requirements and increases production costs

[0014] However, the strength of this type of material itself has reached a relatively high level, such as MFT8, whose tensile strength is ≥625MPa. During the cold deformation process such as drawing and cold heading, the loss (damage) of the processing mold is relatively large, which increases the The cost of the secondary processing of the wire rod affects the surface quality of the steel wire, and the probability of cold heading cracking is also relatively high

[0015] Moreover, due to the precipitation strengthening and grain refinement of the rolling process, the cold deformation ability of the wire rod is poor and the strength fluctuation is large, which seriously affects the consumption of tools and molds of downstream enterprises and the deterioration of the working environment in the subsequent drawing and cold heading processes. , so although these materials have been developed for a long time, they have not been industrialized

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