阅读说明：本技术 一种冷硬制管用钢的生产方法 (Production method of steel for cold-hardening pipe ) 是由 王鹏 刘磊 康华伟 王兴 杨贵玲 王栋 郝亮 何召东 金光宇 曹光明 于 2019-10-18 设计创作，主要内容包括：本发明涉及一种冷硬制管用钢的生产方法,钢水在经脱硫、转炉冶炼和精炼后经连铸产出连铸板坯,板坯进行热轧,热轧卷冷却后经酸洗、切边、冷轧,冷轧采用5机架六辊连轧机组,冷轧压下率为30％～45％,卷取得到厚度为1.2mm～2.5mm的冷硬成品钢卷。显微组织为铁素体+珠光体,未经退火处理,抗拉强度为550MPa～650MPa,纵向延伸率为5％以上。通过优化成分设计和生产工艺,提高了冷硬带钢的机械加工性能,使冷硬带钢可以直接作为圆形、方形钢管制造等一些成型工艺较复杂的原料,拓宽了冷硬带钢的用途。冷硬带钢表面质量优于热轧带钢,同时硬度远高于热轧和冷轧带钢,对应制造的钢管产品表面硬度更高,耐磨性更好。(The invention relates to a method for producing steel for cold-hardening pipe, which comprises the steps of continuously casting molten steel after desulfurization, converter smelting and refining to produce a continuous casting plate blank, carrying out hot rolling on the plate blank, carrying out acid cleaning, trimming and cold rolling on a hot-rolled coil after cooling, wherein the cold rolling adopts a 5-frame six-roller continuous rolling mill set, the cold rolling reduction rate is 30-45%, and coiling to obtain a cold-hardening finished steel coil with the thickness of 1.2-2.5 mm. The microstructure is ferrite plus pearlite, and the tensile strength is 550 MPa-650 MPa without annealing treatment, and the longitudinal elongation is more than 5%. By optimizing the component design and the production process, the machining performance of the cold and hard strip steel is improved, so that the cold and hard strip steel can be directly used as a raw material with complex forming processes for manufacturing round steel pipes, square steel pipes and the like, and the application of the cold and hard strip steel is widened. The surface quality of the cold-hard strip steel is superior to that of the hot-rolled strip steel, the hardness of the cold-hard strip steel is far higher than that of the hot-rolled strip steel and the cold-rolled strip steel, and correspondingly manufactured steel pipe products have higher surface hardness and better wear resistance.)

1. A production method of steel for a cold-hardened pipe is characterized by comprising the following steps:

1) The molten steel is subjected to desulfurization, converter smelting and refining and then is subjected to continuous casting to produce a continuous casting plate blank, and the continuous casting plate blank is subjected to crack inspection due to the fact that the content of C in the molten steel is in a peritectic region;

2) Heating the plate blank to 1180-1230 ℃ in a heating furnace, and then carrying out hot rolling, wherein the furnace time is 140-220 min, the hot rolling is a 1+5+7 three-stage rolling process, wherein the rough rolling R1 is 1-pass rolling, the rough rolling R2 is 5-pass reversible rolling, the finish rolling is 7-frame continuous rolling, and the finish rolling temperature is 850-890 ℃; the thickness of the finish rolled strip steel is 2.0 mm-4.0 mm, the laminar cooling adopts a front section cooling mode, the coiling temperature is 620 ℃ -660 ℃, and the hot rolled coil is naturally cooled after coiling;

3) And cooling the hot rolled coil, pickling, trimming, cold rolling and coiling to obtain a cold and hard finished steel coil with the thickness of 1.2-2.5 mm.

2. The method for producing a steel for a cold-hardened pipe according to claim 1, wherein the molten steel in the step 1) comprises the following components in percentage by weight: c: 0.08-0.14%, Si: less than or equal to 0.030 percent, Mn: 0.30% -0.40%, P: less than or equal to 0.040%, S: less than or equal to 0.030 percent, Als: 0.015 to 0.060 percent, and the balance of Fe and inevitable impurities.

3. The method for producing a steel for a cold-hardened pipe as claimed in claim 1, wherein the cold rolling in the step 3) employs a 5-stand six-roll continuous rolling mill train, and the cold rolling reduction is 30% to 45%.

Technical Field

the invention belongs to the technical field of steel rolling, and particularly relates to a production method of steel for a chilled pipe.

Background

The hot-rolled coil is used as a raw material at normal temperature, the iron scale of the hot-rolled coil is removed by acid cleaning, then the cold continuous rolling and coiling are carried out, or the hot-rolled and acid-cleaned coil is continuously rolled and coiled, and the finished product is called a cold hard coil. The strength and hardness of the chilled coil are rapidly increased due to work hardening caused by continuous deformation, the toughness and plasticity index are greatly reduced, and the internal crystal grains are deformed and elongated without annealing treatment, the structure is uneven, the cold-hardened coil has poor mechanical processing performance, only simple and directional processing can be carried out, and the cold-hardened coil cannot be directly used as a forming processing raw material for manufacturing pipes and the like.

Although the cold hard coil is far inferior to the hot rolled coil and the cold rolled coil in the aspect of mechanical property, the cold hard strip steel is superior to the hot rolled strip steel in surface quality, appearance and size precision and superior to the cold rolled strip steel in the aspects of cost, energy consumption and the like, so the cold hard product has wide application in a certain range. With the increasing market competition, the willingness of cold rolling product users to reduce the cost is stronger and the widening of the application of the cold-hard strip steel is a great development trend of the whole cold rolling industry.

At present, hot rolled and cold rolled carbon steel or alloy steel is basically adopted as the raw material of the tube-making steel strip on the market, and the hot rolled and cold rolled carbon steel or alloy steel has certain defects. The hot-rolled strip steel has low cost, but the surface quality of the product is poor due to the existence of iron scales and the like, and meanwhile, the thickness of the product is greatly limited, so that some steel for manufacturing pipes with thinner thickness can not be produced; the surface quality of the cold-rolled strip steel is superior to that of the hot-rolled strip steel, but the product cost is greatly increased and the profit margin of users is greatly reduced through the procedures of acid washing, cold rolling, annealing and the like. The cold-hard strip steel has poor mechanical processing performance, particularly has too low elongation, and is very easy to crack in the processing and bending process, so that corresponding cold-hard products for manufacturing pipes are basically not available, and the traditional production process and products of the cold-hard strip steel can not meet diversified user requirements more and more.

Disclosure of Invention

The invention aims to provide a production method of steel for a cold-hard pipe, which improves the machining performance of the traditional cold-hard strip steel by designing chemical components and steel-making, hot rolling and cold rolling production processes, so that the designed cold-hard product can directly meet the forming use requirements of some users, thereby solving the technical problem that the existing cold-hard strip steel cannot be directly used for manufacturing steel pipes.

The technical scheme adopted by the invention for solving the technical problems is as follows: a production method of steel for a cold-hardened pipe comprises the following steps:

1) the molten steel is subjected to desulfurization, converter smelting and refining and then is subjected to continuous casting to produce a continuous casting plate blank, and the continuous casting plate blank is subjected to crack inspection due to the fact that the content of C in the molten steel is in a peritectic region;

2) Heating the plate blank to 1180-1230 ℃ in a heating furnace, and then carrying out hot rolling, wherein the furnace time is 140-220 min, the hot rolling is a 1+5+7 three-stage rolling process, wherein the rough rolling R1 is 1-pass rolling, the rough rolling R2 is 5-pass reversible rolling, the finish rolling is 7-frame continuous rolling, and the finish rolling temperature is 850-890 ℃; the thickness of the finish rolled strip steel is 2.0 mm-4.0 mm, the laminar cooling adopts a front section cooling mode, the coiling temperature is 620 ℃ -660 ℃, and the hot rolled coil is naturally cooled after coiling;

3) and cooling the hot rolled coil, pickling, trimming and cold rolling, wherein the cold rolling adopts a 5-frame six-roller continuous rolling mill set, the cold rolling reduction rate is 30-45%, and the cold and hard finished steel coil with the thickness of 1.2-2.5 mm is obtained by coiling.

specifically, the molten steel in the step 1) comprises the following components in percentage by weight: c: 0.08-0.14%, Si: less than or equal to 0.030 percent, Mn: 0.30% -0.40%, P: less than or equal to 0.040%, S: less than or equal to 0.030 percent, Als: 0.015 to 0.060 percent, and the balance of Fe and inevitable impurities.

the chemical composition of the steel for a cold-hardened pipe according to the present invention is set within the above range for the following reasons:

Carbon: c exists in the form of interstitial atoms and cementite in the steel, has a strong strengthening effect in the steel, needs to retain a certain amount of C in the material to improve the strength, and simultaneously, the C content is increased to reduce the Ar3 phase transition temperature of the material, so that the hot rolling is not easy to generate mixed crystal structure in the two-phase region. The client has corresponding strength requirements for the cold-rolled finished product, so the content range of C in the invention is set to be 0.08-0.14%;

silicon: si can obviously improve the elastic limit, yield point and tensile strength of steel, but the high Si content is easy to generate iron scale to influence the surface of strip steel, and the increase of the Si content can reduce the welding performance of the steel. The Si content is set to be less than or equal to 0.030 percent;

Manganese: mn is a strengthening element like C, proper Mn is added to be beneficial to improving the strength of steel, meanwhile Mn can be combined with S to generate MnS, the surface hot brittleness is reduced, the surface quality problem is avoided, but too much Mn is added to improve the deformation resistance of the material, weaken the corrosion resistance of the steel and reduce the welding performance. The Mn content is set to be 0.30-0.40 percent;

Phosphorus: in general, P is a harmful element in steel, increases cold brittleness of steel, deteriorates weldability, decreases plasticity, and deteriorates cold bending properties. The content of P is set to be less than or equal to 0.040%;

sulfur: s is also a harmful element in normal cases. Hot shortness of steel occurs, ductility and toughness of steel are reduced, cracks are formed during rolling, and S is also disadvantageous in welding performance. The technical scheme of the invention sets the S to be less than or equal to 0.030 percent;

Aluminum: al is a commonly used deoxidizer in steel, a small amount of aluminum is added into the steel, crystal grains can be refined, and impact toughness is improved. The content range of Als in the present invention is set to 0.015% to 0.060%.

1. setting of heating temperature of slab

The heating uniformity of the plate blank is ensured, generally, when the carbon steel is controlled to be rolled, the heating temperature of the plate blank is 1200-1300 ℃, the heating temperature is increased to obtain enough plasticity to reduce the load of a rolling mill and ensure the production stability, but the problems of serious oxidation burning loss, poor removal of iron oxide scales and the like can be caused by overhigh heating temperature. Because the invention is a cold-hardened product without annealing treatment, AlN does not need to be completely dissolved into austenite in the slab heating process. According to the capacity of the heating furnace, the heating temperature of the plate blank set by the invention is 1180-1230 ℃, and the in-furnace time is 140-220 min.

2. setting of finishing temperature in hot rolling and finish rolling

The low outlet temperature of the hot rolling and finish rolling can cause the phenomenon of mixed crystals caused by the fact that the hot rolling enters a two-phase region for rolling in advance, so that the finishing rolling temperature is higher than the Ar3 phase transformation point, and a thermal deformation texture can not be formed, and the maximum static phase transformation point temperature of the steel grade is about 852 ℃, and the dynamic temperature is reduced by 10-15 ℃ through research. Comprehensively considering, the finishing temperature of the finish rolling is set to be 850-890 ℃.

3. Setting of coiling temperature in Hot Rolling

Under the condition of not considering the plate shape control difficulty, the laminar cooling after finish rolling adopts front-section cooling to refine grains, thereby improving the strength, reducing the air cooling time of a high-temperature section and reducing the thickness of generated iron scales. Meanwhile, the hot rolling coiling temperature cannot be too high, and scale can be generated when the hot rolling coiling temperature is too high, so that the surface quality of the hot rolled substrate is influenced. Comprehensively, the laminar cooling of the invention adopts front-stage cooling, and the coiling temperature is 620-660 ℃.

4. Setting of Cold Rolling reduction

The invention adopts a 5-frame six-roller cold continuous rolling mill to carry out cold rolling production, and the cold hard coil is different from a common cold rolled product and can be directly used without a subsequent annealing process, so that higher reduction rate cannot be used. In order to ensure that the cold hard coil greatly retains the excellent performance of the hot rolling base material, particularly, the cold hard coil still retains larger elongation percentage after cold rolling, avoids excessive deformation of crystal grains, is beneficial to direct forming processing and use, and comprehensively considers that the reduction rate of the cold rolling is set to be 30-45 percent.

The microstructure of the steel for the cold-hardened pipe is ferrite plus pearlite, the steel is not annealed, the tensile strength is 550 MPa-650 MPa, and the longitudinal elongation is more than 5%.

The invention has the following beneficial effects:

1. By optimizing the component design and the production process, the machining performance of the cold and hard strip steel is improved, so that the cold and hard strip steel can be directly used as a raw material with complex forming processes for manufacturing round steel pipes, square steel pipes and the like, and the application of the cold and hard strip steel is widened.

2. the cold-hard strip steel is directly used without annealing treatment, thereby saving the annealing treatment cost, replacing the traditional use of partial cold-rolled strip steel, reducing the user cost and increasing the additional value of the cold-hard strip steel.

3. The surface quality of the cold-hard strip steel is superior to that of the hot-rolled strip steel, the hardness of the cold-hard strip steel is far higher than that of the hot-rolled strip steel and the cold-rolled strip steel, the surface hardness of a correspondingly manufactured steel pipe product is higher, the wear resistance of the steel pipe product is better, and the performance of a final user product is optimized within a certain range.

Drawings

FIG. 1 is a photograph of a transverse metallographic structure of a steel for cold hardening tube at a magnification of 200 in example 1 of the present invention;

Fig. 2 is a transverse metallographic structure photograph of a steel for cold hardening tube of example 2 of the present invention at a magnification of 200.

Detailed Description

The following are specific examples of the present invention and further describe the technical solutions of the present invention, but the scope of the present invention is not limited to these examples. All changes, modifications and equivalents that do not depart from the spirit of the invention are intended to be included within the scope thereof.