Method for Producing Polishing Bar Made of Valve Steel 53Cr21Mn9Ni4N

Abstract

This invention provides a method for producing a polishing bar made of valve steel 53Cr21Mn9Ni4N. The process flow is as below: electric furnace smelting→outside-the-furnace refining→continuous casting→heating→high-speed wire rolling→heat treatment (off-line/online)→straightening→polishing→inspection→storage. The production method of the invention adopts a casting method of continuous casting to overcome the poor high-temperature plasticity and the great deformation resistance of 53Cr21Mn9Ni4N which leads to a difficulty in continuous casting. The continuous casting is directly carried out on casting billets for rolling, which greatly reduces the material loss and energy consumption of this step, and improves the yield of the billets. The high-speed wire precision rolling technology is directly used on the continuous casting billets to improve the production efficiency, and greatly improve the size precision control of rolled and finished wire rods.

What is claimed is: 
     
         1 . A method for producing a polishing bar made of valve steel 53Cr21Mn9Ni4N, comprising the following steps:
 S1. providing scrap steel and alloys including high carbon ferrochrome and ferronickel into an electric-arc furnace for melting and primary smelting, wherein a tapping temperature is higher than 1600° C. and P is less than 0.040%;   S2. AOD smelting, blowing nitrogen to smelt with oxygen in an oxidizing period, when a temperature reaches over 1660° C. and C is less than 0.60%, starting to add a predefined amount of ferrosilicon for a reduction operation, blowing nitrogen for alloying, adjusting alloy composition; tapping steel liquid when the ingredients meet a requirement of standard and the temperature is higher than 1490° C., and transferring the steel liquid to a ladle furnace for refining;   S3. ladle furnace refining, fine tuning a composition and the temperature of the steel liquid, maintaining a white slag operation, tapping the steel liquid when the temperature of liquid steel reaches a temperature of continuous casting and packaging;   S4. continuously casting through a billet continuous casting machine, wherein a continuous casting and packaging temperature is as below: first continuous casting packaging at 1490 ˜1510° C., continuous packaging at 1480 ˜1500; controlling superheat of the steel liquid between 25−35° C. during pouring, using a combination of crystallizer electromagnetic stirring and final electromagnetic stirring when pouring; marking continuous casting billets when ejecting the billets and air-cooled stacking;   S5. heating before rolling, heating in a pusher-type heating furnace or a walking beam type heating furnace;   S6. high-speed wire rolling at a rolling temperature of 1160˜1190° C., controlling a finish rolling and spinning temperature over 1050° C., force cooling by water spray after spinning; entering into a collection roll after cooling, packaging after a collection and transporting a wire rod into a heat treatment process;   S7. heat treating the wire rod;   S8. straightening, immersing the wire rod into a lime coating solution and maintaining for a while after a heat treatment of 53Cr21Mn9Ni4N wire rod, pulling out the wire rod, drying the wire rod naturally until a surface coating of the wire rod becomes dry and white; and straightening the wire rod using a seven-roll bar straightener at a straightness less than 1 mm/m; and   S9. polishing, rough grinding first and then fine grinding to meet design requirements using a centerless grinder for processing.   
     
     
         2 . The method for producing a polishing bar made of valve steel 53Cr21Mn9Ni4N of  claim 1 , wherein in the step 4, the temperature during pouring is 1415-1430° C., and a casting speed is 1.3-1.0m/min. 
     
     
         3 . The method for producing a polishing bar made of valve steel 53Cr21Mn9Ni4N of  claim 2 , wherein in the step 4, a cooling control mode of a secondary cooling area is provided with three-phase partitioning water distribution, when the casting speed is less than 1.0m/min, three phases of water in the secondary cooling area are all opened, a ratio of water distribution of the three phases is 50%:30%:20%; a water ratio automatically matches with the casting speed; when the casting speed is within a normal range of 1.0˜1.2 m/min, only first two phases of water in the secondary cooling area are opened and the ratio of water distribution is 55%:45%, a total water ratio is controlled to be 0.27˜0.32 L/Kg steel. 
     
     
         4 . The method for producing a polishing bar made of valve steel 53Cr21Mn9Ni4N of  claim 1 , wherein in the step 5, a heating temperature of the continuous casting billets is controlled as below: the heating temperature in a preheating section is lower than 1050° C.; the heating temperature in a heating section is 1030˜1080° C., the heating temperature in a soaking section is 1170˜1210° C. 
     
     
         5 . The method for producing a polishing bar made of valve steel 53Cr21Mn9Ni4N of  claim 1 , wherein in the step 6, a wire rolling speed is controlled as below: the wire rolling speed at an exit section of intermediate rolling is 1.10˜1.15 m/s, the wire rolling speed at an exit section of pre-finish rolling is 4.78˜5.64 m/s, the wire rolling speed at an exit section of finish rolling is 28˜33 m/s. 
     
     
         6 . The method for producing a polishing bar made of valve steel 53Cr21Mn9Ni4N of  claim 1 , wherein the heat treatment in the step 7 includes an off-line heat treatment and an online heat treatment,
 wherein the off-line heat treatment includes the following steps: solution treating a 53Cr21Mn9Ni4N hot rolling disk at a solution temperature of 1040-1150° C. for 30-60 min; wherein a cooling is performed in a water-cooled mode; a grain size is required to be finer than 6 grade and a face hardness of a sample is 32˜37 HRC;   wherein the online heat treatment includes the following steps: rolling 53Cr21Mn9Ni4N continuous casting billets through a high speed mill, wherein a heating temperature of rolling meets requirements described in the step 5, the wire rod is performed with the online heat treatment after spinning, and put into water for cooling, wherein the grain size is required to be finer than 8 grade, and the face hardness of the sample is 31˜36 HRC.