10.9-grade niobium-containing non-quenched and tempered cold-heading steel and rolling method of hot finished rod thereof

Abstract

The invention provides a 10.9-grade niobium-containing non-quenched and tempered cold-heading steel. The cold-heading steel comprises the following components in percentage (%) by weight: C accounts for 0.08-0.14, Si accounts for 0.03-0.35, Mn accounts for 1.80-2.30, P accounts for less than or equal to 0.025, S accounts for less than or equal to 0.015, B accounts for 0.0005-0.003,Ti accounts for0.01-0.03, Als accounts for 0.010-0.050, Nb accounts for 0.02-0.04 and the balance is iron and micro-impurity. The rolling method of the hot finished rod comprises the following steps: the heating temperature is ranged from 1050 to 1,250 DEG C, the rough and intermediate rolling temperature is ranged from 1000 to 1050 DEG C, the precision rolling temperature is ranged from 750 to 830 DEG C, the amount of deformation is 50-60 percent, the rate of deformation is 20 / s, the spinning temperature is ranged from 750 to 830 DEG C, the cooling is carried out in two sections after spinning, the rapid cooling is carried out at a low speed being higher than or equal to 5 DEG C / s at the temperature above 550 DEG C, and the slow cooling is carried out at a cooling rate of 0.1-3 DEG C / s at the temperature below 550 DEG C.

Description

technical field [0001] The invention belongs to the field of cold heading steel for fasteners, in particular to a non-quenched and tempered cold heading steel for grade 10.9 fasteners and a production method for hot-rolled wire rods thereof. Background technique [0002] The strength levels of high-strength fasteners such as high-strength bolts are generally divided into four grades: 8.8, 9.8, 10.9 and 12.9. They are usually quenched and tempered medium carbon steel or medium carbon alloy steel, and there are also non-quenched and tempered steels. Compared with the production process of quenched and tempered fasteners, the production process of non-quenched and tempered fasteners can save the spheroidizing annealing before cold heading, reduce the number of drawing times and save the adjustment after cold heading. Mass heat treatment, etc., which greatly simplifies the production process, shortens the production cycle, reduces energy consumption, and also avoids surface oxid...

AI Technical Summary

Problems solved by technology

The microalloying element design of the steel has the following defects: (1) Ti content is 0.04-0.08%, Ti element is easy to oxidize, when adding > 0.04-0.10% Ti, it will increase the TiO in the steel 2 The number of inclusions and the source of fatigue cracks, thereby reducing the service life of the fastener; (2) B content is 0.001-0.005%, when the boron content exceeds 0.004%, the boron compound brittle phase is prone to appear; (3) V The content is 0.08-0.12%, the addition of vanadium element can improve the strength and toughness of steel, but when the addition amount is more than 0.03%, the addition of vanadium element will reduce the impact toughness and reduce the cold heading performance

And limited by the level of production technology, the cold deformation ability of the wire rod is poor, and the strength fluctuates greatly, so it has not been able to be industrialized and mass-produced and applied.