CN103436663A - Technique for improving hot-rolling elongation of steel for bainite steel rail - Google Patents

Abstract

The invention relates to a technique for improving hot-rolling elongation of steel for a bainite steel rail. The technique is characterized in that a vacuum induction furnace with the weight of 25 kg is used for smelting microalloyed steel for the bainite steel rail, wherein the microalloyed steel comprises the chemical components in percentage by weight: 0.20-0.40 percent of C, 0.35-1.60 percent of Si, 0.60-2.0 percent of Mn, 0.70-1.80 percent of Cr, 0-0.6 percent of Ni, 0.20-0.50 percent of Mo, 0-0.02 percent of Cu, 0.03-0.80 percent of Al, 0.01-0.06 percent of Nb, 0.08-0.20 percent of V, 0-0.03 percent of RE, no more than 0.015 percent of S, no more than 0.025 percent of P and the balance of iron and unavoidable impurities; diffusion annealing is performed on a steel ingot before rolling, and the technology for heating processing comprises the steps as follows: heating the steel ingot with the speed of no more than 300 DEG C/h, and the temperature of 1200-1280 DEG C, performing heat preservation for 4-6 h and performing furnace cooling. The technique has the advantage that the hot-rolling elongation of steel for the bainite steel rail is improved under the conditions of smelting and rolling without changing the chemical components.

Description

A kind of processing method that improves bainite rail steel As rolled elongation

Technical field

The present invention relates to a kind of processing method that improves bainite rail steel As rolled elongation, belong to the ferrous metallurgy field.

Background technology

Plasticity is the important mechanical index of steel, and elongation and relative reduction in area during generally with quiet the stretching mean.In TB/T3276-2011 " rail for high-speed railway ", the mechanical performance index that elongation A must detect as rail together with tensile strength Rm, rail head end face medullary ray hardness HBW, it serves to show its importance.

The general approach that changes steel plasticity is: when improving even plasticity, avoid as far as possible or postpone the formation in micropore hole.Crystal grain thinning can weaken stress concentration, postpones the formation of hole, hole or tiny crack, improves elongation.In steel, second phase particles is usually by fracture itself, or with the Interface Cracking of matrix, form the position of bringing out the micropore hole, institute thinks and improves plasticity, distribution spherical, tiny, even, disperse that the second-phase in steel should be.

Steel ingot solute in process of setting distributes again, solidifies rear alloying elements distribution inhomogeneous, can produce dendritic segregation, through diffusion annealing commonly used, alleviates or eliminates dendritic segregation.

Diffusion annealing claims again homogenizing annealing, and it is that steel ingot, foundry goods or forging stock are heated to a little less than insulation for a long time at the temperature of solidus curve, and then Slow cooling is to eliminate the thermal treatment process of uneven chemical components phenomenon.Its objective is dendritic segregation and regional segregation that elimination ingot casting or foundry goods produce in process of setting, make composition and microstructure homogenization.

Have bibliographical information to carry out diffusion annealing to air-cooled bainitic steels 5Cr3Mo2VNb, can alleviate its intracrystalline component segregation, make homogeneous microstructure, strength and toughness obviously improves, but does not mention the impact on elongation.(impact [J] of diffusion annealing on casted air-colled bainite structure of steel and performance, metal heat treatmet, 1999,7:7-10)

Another bibliographical information forge before High temperature diffusion on the 2.25Cr-1Mo-0.25V forging after the vertically impact of mechanical property, the segregation degree of alloying elements cr, Mo reduces with the increase of High temperature diffusion soaking time before forging; Hour, vertically yield strength, impact of collision toughness increase with the increase of soaking time forging ratio simultaneously; After forging ratio reaches a certain numerical value, vertically yield strength, impact of collision toughness no longer change with soaking time is regular; Before forging the High temperature diffusion soaking time on endwise tensile strength substantially without affecting.The same document is not mentioned and is forged the impact of front High temperature diffusion on this steel elongation.(experimental study [J] of High temperature diffusion to the low alloy steel Effect on Mechanical Properties before forging, plastic engineering journal, 2007,14 (2): 64-68)

Summary of the invention

The objective of the invention is the limitation for above-mentioned research contents, a kind of processing method that improves bainite rail steel As rolled elongation is provided, its objective is in the situation that do not change chemical composition, smelting, rolling technology, the elongation of raising bainite rail steel As rolled.

For addressing the above problem, the technical solution used in the present invention is:

(1) by 25kg vacuum induction furnace smelting micro-alloyed bainitic steel rail steel, its chemical composition (wt%): C:0.20～0.40, Si:0.35～1.60, Mn:0.60～2.0, Cr:0.70～1.80, Ni:0～0.6, Mo:0.20～0.50, Cu:0～0.02, A1:0.03～0.80, Nb:0.01～0.06, V:0.08～0.20, RE:0～0.03, S :≤0.015, P :≤0.025, all the other are ferro element and inevitable impurity;

(2) steel ingot carries out diffusion annealing before rolling, and its thermal treatment process is: the rate of heating of steel ingot≤300 ℃/h, and Heating temperature is 1200～1280 ℃, is incubated 4～6h, stove is cold.

The invention has the beneficial effects as follows: in the situation that do not change chemical composition, smelting, rolling technology, improved the elongation of bainite rail steel As rolled.

Embodiment

Adopt micro-alloyed bainitic steel rail steel 6 stoves of 3 kinds of heterogeneities of 25kg vacuum induction furnace smelting, every kind of composition 2 stoves.Table 1 is the chemical composition of bainite rail steel in the present invention.

Select each 1 stove of steel ingot of 3 kinds of heterogeneities to carry out diffusion annealing, its thermal treatment process is: the 200 ℃/h of rate of heating of steel ingot, and Heating temperature is 1250 ℃, insulation 5h, stove is cold.

Adopt identical rolling technology steel rolling, rolling technology is: the 200 ℃/h of rate of heating of steel ingot, and Heating temperature is 1250 ℃, the original shaping temperature is 1200 ℃, 930 ℃ of final shaping unit temperature; Finish to gauge thickness is 21mm, rolls rear air cooling to room temperature.Its 6 stove steel to roll the state mechanical property as shown in table 2.

Table 1 is the chemical composition of bainite rail steel in the present invention

Table 2 is the As rolled mechanical property of embodiment in the present invention

Claims (1)

1. a processing method that improves bainite rail steel As rolled elongation is characterized in that:

(1) by 25kg vacuum induction furnace smelting micro-alloyed bainitic steel rail steel, its chemical composition (wt%): C:0.20～0.40, Si:0.35～1.60, Mn:0.60～2.0, Cr:0.70～1.80, Ni:0～0.6, Mo:0.20～0.50, Cu:0～0.02, A1:0.03～0.80, Nb:0.01～0.06, V:0.08～0.20, RE:0～0.03, S :≤0.015, P :≤0.025, all the other are ferro element and inevitable impurity;

(2) steel ingot carries out diffusion annealing before rolling, and its thermal treatment process is: the rate of heating of steel ingot≤300 ℃/h, and Heating temperature is 1200～1280 ℃, is incubated 4～6h, stove is cold.