400 MPa-grade Cr and Ti containing hot rolled ribbed steel bar and production technology thereof

Abstract

The invention discloses a 400 MPa-grade Cr and Ti containing hot rolled ribbed steel bar and a production technology thereof. The chemical components of the 400 MPa-grade Cr and Ti containing hot rolled ribbed steel bar comprise, 0.20%-0.25% of C, 0.55%-0.70% of Si, 1.15%-1.40% of Mn, smaller than or equal to 0.012% of N, smaller than or equal to 0.038% of P, smaller than or equal to 0.038% of S,0.20%-0.32% of Cr, 0.006%-0.012% of Ti, smaller than or equal to 30 ppm of O and the balance Fe and unavoidable impurities. A matrix structure is composed of ferrite and pearlite, the steel bar ReL islarger than or equal to 425 MPa, the Rm is larger than or equal to 590 MPa, the A is larger than or equal to 25.0%, the Agt is larger than or equal to 14.0%, the Rm<0> / ReL<0> is larger than or equalto 1.32, and the ReL<0> / ReL is smaller than or equal to 1.15. According to the 400 MPa-grade Cr and Ti containing hot rolled ribbed steel bar and the production technology thereof, the matrix is enhanced fully through cheap elements such as C, Si and Mn, the grain structure is refined through a micro Cr and Ti alternate weak cooling water penetrating rolling technology, the steel bar strength is further improved, the high-performance 400 MPa-grade Cr and Ti containing hot rolled ribbed steel bar meeting the stand requirements is obtained, and the manufacturing cost is low.

Description

technical field [0001] The invention relates to the technical field of threaded steel bar manufacturing, in particular to a 400MPa grade Cr and Ti-containing hot-rolled ribbed steel bar and a production process thereof. Background technique [0002] The national standard GB / T 1499.2-2018, which came into effect on November 1, 2018, has made different regulations on the macroscopic metallography, cross-sectional Vickers hardness, microstructure and inspection methods of hot-rolled ribbed steel bars. The new standard stipulates that the metallographic structure of hot-rolled ribbed steel bars is ferrite plus pearlite, and tempered martensite structure should not appear on the base circle, and the macroscopic metallographic structure does not allow the appearance of cross-sectional base circles that are obviously different from the inner area. The closed ring of contrast; for the non-closed ring that appears, the difference between the chilled layer at the edge of the base circ...

AI Technical Summary

Problems solved by technology

There are design defects in the technical solution of the invention: 1. The composition design is too wide, and the upper limit of C 0.30% and Si 1.00% exceeds the current national standard for construction steel bars GB / T 1499.1-2017 "Hot Rolled Plain Steel Bar" C 0.25% , Si 0.55%, GB / T 1499.2-2018 "Hot Rolled Ribbed Steel Bar" C 0.25%, Si 0.80% requirements, the 25mm diameter ribbed steel bar produced in Example 2 of the invention has C 0.29%, Si 0.95% components exceeding the standard , is a waste product; while the 12mm diameter ribbed steel bar C 0.16%, Mn0.65%, Si 0.33%, and Cr 0.11% in Example 1 are low in composition, resulting in the yield strength R of the steel bar eL 361MPa, tensile strength R m It is 461MPa, which cannot reach the yield strength R of HRB400 eL ≥400MPa, tensile strength R m ≥540MPa requirements, also for waste

2. In steel, if Ti exceeds 0.030% and does not go into LF refining, it will cause Ti oxide bonding at the continuous casting nozzle, and the nozzle will be seriously blocked in the 1st to 3rd furnace, and the steel cannot be poured smoothly, which increases the difficulty of production and the consumption of spare parts

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