Method for rolling high-toughness high-strength low-alloy steel

Abstract

The method for rolling a high-toughness high-strength low-alloy steel, sequentially comprising the following steps: heating, descaling, rough rolling, continuous rolling, first water cooling, finish rolling, second water cooling, and cold hearth cooling; and using a converter continuous casting billet as a raw material, the continuous casting billet comprising the following chemical components in percentage by mass: C≤0.20, Si≤0.60, Mn: 1.00-1.70, Cr≤0.30, P≤0.020, S≤0.020, V: 0.05-0.10, Al≤0.03, and N≤0.025, with the balance being Fe and inevitable impurities. By using the rolling method, the actual grain size of the high-strength low-alloy steel can be refined; the comprehensive performance of the high-strength low-alloy steel is excellent; the metallographic structure is fine ferrite and pearlite; the grain size reaches 9.0 or above; the impact energy at −20° C. is greater than 100 J, and the impact energy at −40° C. is greater than 80 J.

1 . A rolling method for a high-toughness high-strength low-alloy steel, its characteristic is that, the rolling method sequentially comprises the following steps:
 Heating, descaling, rough rolling, continuous rolling, first water cooling, finish rolling, second water cooling, and cold hearth cooling;   Using a converter continuous casting billet as a raw material, the continuous casting billet comprises the following chemical components and contents in percentage by mass: C≤0.20; Si≤0.60; Mn:1.37˜1.70; Cr≤0.30; P≤0.020; S≤0.020; V:0.07˜0.10; Al≤0.03; N:0.008˜0.025; with the balance being Fe and inevitable impurities;   After the first water cooling, the temperature is 765˜800° C.;   In the step of the finish rolling, entry temperature of initial rolling during the finish rolling is 832˜850° C.;   During the second water cooling, the temperature under which the steel performs the second water cooling after the step of the finish rolling is 600° C.˜700° C., wherein, water cooling rate is 25˜100° C./s, hydraulic pressure is 0.2˜0.6 MPa;   The cold hearth cooling means the steel after the second water cooling is cooled on the cold hearth.   
     
     
         2 . According to the rolling method for a high-toughness high-strength low-alloy steel in  claim 1 , its characteristic is that, the step of the heating is divided into four zones, which are sequentially as follows: pre-heating zone, heating first zone, heating second zone, and soaking zone,
 The temperature of the pre-heating zone is less than or equal to 750° C.;   The temperature of the heating first zone is 900˜1050° C.;   The temperature of the heating second zone is 1050˜1150° C.;   The temperature of the soaking zone is 1150˜1210° C.   
     
     
         3 . According to the rolling method for a high-toughness high-strength low-alloy steel in  claim 2 , its characteristic is that, the total heating time of the step of the heating is 3˜5 h; the soaking time of the soaking zone is 30˜80 min. 
     
     
         4 . According to the rolling method for a high-toughness high-strength low-alloy steel in  claim 2 , its characteristic is that, the step of the heating is performed in a four-section stepwise heating furnace. 
     
     
         5 . According to the rolling method for a high-toughness high-strength low-alloy steel in  claim 1 , its characteristic is that, the entry temperature of the rough rolling is 950˜1050° C., the pass of the rough rolling is 5˜7. 
     
     
         6 . According to the rolling method for a high-toughness high-strength low-alloy steel in  claim 5 , its characteristic is that, the number of rough-rolling mills provided in the step of the rough rolling is 6; the pass of the rough rolling is 6. 
     
     
         7 . According to the rolling method for a high-toughness high-strength low-alloy steel in  claim 6 , its characteristic is that, the step of the continuous rolling includes intermediate rolling and pre-finish rolling,
 The entry temperature of the intermediate rolling is 900˜1000° C., the pass of the intermediate rolling is 5˜7;   Outlet temperature of the pre-finish rolling is 850˜950° C., the pass of the pre-finish rolling is 3˜5.   
     
     
         8 . According to the rolling method for a high-toughness high-strength low-alloy steel in  claim 7 , its characteristic is that, the number of intermediate-rolling mills provided in the step of the intermediate rolling is 6; the pass of the intermediate rolling is 6. 
     
     
         9 . According to the rolling method for a high-toughness high-strength low-alloy steel in  claim 7 , its characteristic is that, the number of pre-finish-rolling mills provided in the step of the pre-finish rolling is 4; the pass of the pre-finish rolling is 4. 
     
     
         10 . According to the rolling method for a high-toughness high-strength low-alloy steel in  claim 5 , its characteristic is that, during the first water cooling, the first water cooling is performed with incoming materials after the step of the continuous rolling, wherein, the water cooling rate is 25˜50° C./s, the hydraulic pressure is 0.2˜0.6 MPa. 
     
     
         11 . According to the rolling method for a high-toughness high-strength low-alloy steel in  claim 5 , its characteristic is that, a reducing and sizing mill set is used for the finish rolling. 
     
     
         12 . According to the rolling method for a high-toughness high-strength low-alloy steel in  claim 11 , its characteristic is that, the reducing and sizing mill set is a three-roller reducing and sizing mill set. 
     
     
         13 . According to the rolling method for a high-toughness high-strength low-alloy steel in  claim 5 , its characteristic is that, in the step of the descaling, high-pressure water descaling is used with the aim to descale an iron sheet, the hydraulic pressure of the high-pressure water is 15˜20 MPa. 
     
     
         14 . According to the rolling method for a high-toughness high-strength low-alloy steel in  claim 13 , its characteristic is that, the hydraulic pressure of the high-pressure water is 17˜20 MPa. 
     
     
         15 . According to the rolling method for a high-toughness high-strength low-alloy steel in  claim 1 , its characteristic is that, a high-toughness high-strength low-alloy steel bar is obtained after the rolling method. 
     
     
         16 . According to the rolling method for a high-toughness high-strength low-alloy steel in  claim 15 , its characteristic is that, the specification of the steel bar is Ø60˜120 mm.