CN116855834A - 一种降低q345d中厚板带状组织等级的生产方法 - Google Patents
一种降低q345d中厚板带状组织等级的生产方法 Download PDFInfo
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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Abstract
一种降低Q345D中厚板带状组织等级的生产方法,钢的化学成分质量百分比为C=0.16~0.18,Si=0.10~0.20,Mn=1.10~1.30,P≤0.008,S≤0.0015,Alt=0.070~0.090,Nb=0.010~0.015,Ti=0.010~0.020,Ceq≤0.40%;其余为Fe和残留元素。本发明采用工艺路线为:转炉冶炼→LF精炼→RH真空精炼→连铸→板坯加热→控制轧制→控制冷却。中厚板经控轧控冷处理后,力学性能满足产品标准,带状组织≤2.0级。本发明的中厚板组织为细小的珠光体+铁素体,屈服强度≥345Mpa,抗拉强度:490~620Mpa,‑20℃低温横向冲击≥60J,产品表面及加工质量优良,NB/T47013.3标准TI级探伤合格率100%。
Description
技术领域
本发明属于钢铁冶炼轧制技术领域,涉及到一种降低Q345D中厚板带状组织等级的生产方法。
背景技术
随着钢铁材料专业技术的不断进步,中厚板不仅需要满足产品常规的机械性能,还需具有良好的内部质量、性能均匀性以及后期加工性能。根据应用实践证明,带状组织对中厚板的性能稳定性、焊接等加工性能具有显著影响,中国已推出GB/T 34474评级标准,带状组织等级作为衡量中厚板内部质量的一个重要指标正在逐步推广并不断被重视。因此,屈服强度≥345Mpa,抗拉强度:490~620Mpa,带状组织≤2.0级的中厚板在市场上具有广阔的应用前景。
中国专利CN 115652046 A公布了一种“一种消除钢中带状组织的热处理工艺”,该钢主要通过固溶淬火、循环淬火、回火等热处理工艺相变细化带状组织处的晶粒及碳化物,减轻钢中的带状组织,但该方法生产工序长、成本高,需进行多次热处理。中国专利CN115852137 A公布了“一种消除低合金高强度Q345E钢带状组织缺陷的方法”,但该方法主要通过热处理消除带状组织,未从成分设计以及轧制工艺方面对带状组织进行改善。中国专利CN 113999961 A公布了一种“改善带钢心部带状组织的生产方法”,但该方法是针对带钢,不适用于中厚板。
目前中厚板的带状组织通常需通过热处理进行改善或消除,但上述方法生产的钢板与GB/T 1591、GB/T 713等国家标准要求的TMCP交货状态不符且生产成本高。
发明内容
本发明的目的在于提供一种降低Q345D中厚板带状组织等级的生产方法,采用转炉冶炼+LF精炼+RH精炼+连铸+控轧控冷方法生产的钢板,其性能满足屈服强度≥345Mpa,抗拉强度490~620Mpa,断后伸长率A≥21%,-20冲击吸收能量≥60kV2J,带状组织≤2.0级。
本发明的技术方案:
一种降低Q345D中厚板带状组织等级的生产方法,钢的化学成分质量百分比为C=0.16~0.18,Si=0.10~0.20,Mn=1.10~1.30,P≤0.008,S≤0.0015,Alt=0.070~0.090,Nb=0.010~0.015,Ti=0.010~0.020,Ceq≤0.40%,其余为Fe和残留元素;包括以下工艺步骤:
(1)转炉炼钢:出钢C≥0.06%,P≤0.006%,出钢后进行炉后扒渣操作;
(2)LF精炼:钢水在LF炉总吹氩时间≥50分钟,白渣保持时间≥30分钟,钢水出LF前进行软吹氩操作,软吹氩时间≥12分钟;
(3)RH精炼:RH炉在站总吹氩时间≥30分钟,真空度在0.5tor以下,保持时间≥15分钟,钢水温度1590~1610℃,破空后氩气软吹时间≥15分钟;
(4)连铸:铸坯断面为220~350mm,实行全程保护浇铸,拉速0.6~0.9m/min,浇注温度按液相线温度+(6~13℃)控制,采用动态轻压下控制技术;
(5)板坯加热:板坯在步进炉中进行加热,限制炉膛温度≤1220℃,坯料出钢温度控制在1160~1180℃;
(6)控制轧制:一阶段开轧温度1000~1160℃,终轧温度>960℃,后三道次压下率>22%;二阶段开轧温度在870~890℃,终轧温度790~820℃;
(7)控制冷却:入水温度760~800℃,冷却速度控制在5~10℃/S,返红温度540~620℃,得到屈服强度≥345Mpa,抗拉强度490~620Mpa,断后伸长率A≥21%,-20冲击吸收能量≥60kV2J,带状组织≤2.0级的中厚钢板。
钢的化学成分组成设计原理:
C:碳元素在钢中常与其它合金元素形成碳化物,起固溶及析出强化作用。从保证钢板强度以及降低合金成本方面考虑,碳含量应保持在一定的水平上,但从改善钢板低温韧性的方面,又应降低碳含量。因此考虑到本钢的合金成分及性能要求,本发明钢的C含量控制在0.16~0.18。
Si:有固溶强化作用,能提高钢板屈服强度,但随着Si含量的增加低温韧性下降,同时未再结晶区温度下降,不利于轧制细化。本发明钢的Si控制在0.10~0.20%范围对综合性能有利。
Mn:是固溶强化元素,同时能细化晶粒,对提高钢板的强度和韧性均有利,但容易出现中心偏析以及形成MnS夹杂,加剧带状组织现象。本发明钢的Mn按照产品标准的下限进行控制。
P:冷脆性元素,在冷加工时容易产生“冷脆”,属于易偏析元素,容易导致中厚板内枝晶以及中心偏析的出现,不利于改善带状组织。因此应该严格控制钢中磷的含量,本发明钢中的P控制在0.008%以下。
S:属于易偏析元素,并与Mn结合形成MnS夹杂,不利于钢中带状组织控制。本发明钢中的S控制在0.0015%以内。
Nb:在钢中与氮、碳有极强的亲合力,可与之形成极稳定的Nb(C,N)化合物,细化铁素体晶粒,提高低温韧性和强度。但过高的Nb含量容易在中厚板心部聚集形成偏析带,因此本发明钢中的Nb控制在0.010~0.015%以内。
Al:促进AlN析出物的生成,充分发挥了细晶强化和沉淀强化两种强化方式,改善钢的强韧性配合。本发明钢将Al控制在0.070~0.090%。
本发明提供一种降低Q345D中厚板带状组织等级的生产方法,对该钢进行合理的化学成分设计,严格控制各工序生产工艺参数,通过LF精炼+RH真空处理+低过热度浇铸+连铸动态轻压下控制获得优良的铸坯。同时限制加热炉膛温度,避免铸坯原始晶粒的长大;设计合理的控轧温度区间,采用870~890℃的开轧温度,即可细化轧态晶粒破碎带状组织,又可以最大限制的减轻轧制带状组织的形成;采用合适的冷速及返红,可以有效细化晶粒并抑制碳元素的扩散以及聚集析出,从而改善中厚板的带状组织。钢板性能可以满足屈服强度≥345Mpa,抗拉强度490~620Mpa,断后伸长率A≥21%,-20℃冲击吸收能量≥60kV2J,带状组织≤2.0级。
本发明具有以下优点:
成分设计采用高C低Mn的成分体系,尽量降低Nb、V、Ti等微合金元素,主要通过Al元素进行晶粒细化,同时采用洁净钢冶炼技术,严格控制P、S等有害元素含量,从成分设计上充分考虑各元素的偏聚特性,改善中厚板偏析现象。
优良的铸坯内部质量,通过低过热度浇铸+连铸动态轻压下控制,铸坯低倍中心偏析≤C类1.0及。
合理的板坯加热工艺,通过限制加热炉膛温度,避免铸坯原始晶粒的长大,同时通过长时间的高温加热确保微合金元素的充分固溶。
合理的压下量设计,I阶段高温大压下慢速轧制,促进晶粒破碎再结晶。
合理的II阶段控轧温度区间,采用870~890℃的开轧温度,即可细化轧态晶粒破碎带状组织,又可以最大限制的减轻轧制带状组织的形成。
合适的冷却速度以及返红温度,冷却速度控制在5~10℃/s,返红温度区间540~620℃,可以有效细化晶粒并抑制碳元素的扩散以及聚集析出,改善中厚板的带状组织等级。
附图说明
图1为实施例1生产的20mm钢板金相组织图。
图2为实施例2生产的40mm钢板金相组织图。
具体实施方式
下面结合实施例对本发明做进一步说明。
一种降低Q345D中厚板带状组织等级的生产方法。工艺过程:转炉冶炼→LF精炼→RH真空精炼→连铸→板坯加热→控制轧制→控制冷却。
实施例1:20mm钢板的生产方法
炼钢工艺实施过程:转炉出钢C=0.09%,P=0.005%,出钢后进行扒渣操作。LF精炼白渣保持时间32min,出站S=0.0012%;RH真空度0.3tor,保真空时间16min,RH炉进站钢水温度1602℃,RH炉出站钢水温度1596℃。软吹氩时间15min,定氢1.0ppm。连铸浇注断面厚度为260mm,连铸拉速0.85m/min,动态轻压下量6mm,中间包钢水过热度7~11℃,熔炼成分如表1所示。
轧钢工艺实施过程:铸坯加热出钢温度1172℃,第一阶段开轧温度1065℃,最后三道次压下率分别为23%,23%,25%,终轧温度982℃,轧制中间坯厚度82mm。第二阶段开轧温度886℃,终轧温度812℃,入水温度774~796℃,返红温度540~580℃,轧制成品厚度20mm,其性能如表2所示,其金相组织如图1所示。
实施例2:40mm钢板的生产方法
炼钢工艺实施过程:转炉出钢C=0.07%,P=0.006%,出钢后进行扒渣操作。LF精炼白渣保持时间35min,出站S=0.0011%;RH真空度0.3tor,保真空时间15min,RH炉进站钢水温度1603℃,RH炉出站钢水温度1595℃。软吹氩时间18min,定氢1.1ppm。连铸浇注断面厚度为260mm,连铸拉速0.85m/min,动态轻压下量6.5mm,中间包钢水过热度6~13℃,熔炼成分如表2所示。
轧钢工艺实施过程:铸坯加热出钢温度1179℃,第一阶段开轧温度1042℃,最后三道次压下率分别为23%,24%,24%,终轧温度992℃,轧制中间坯厚度100mm。第二阶段开轧温度872℃,终轧温度797℃,入水温度762~783℃,返红温度580~620℃,轧制成品厚度40mm,其性能如表2所示,其金相组织如图2所示。
由表1可以看出,实施例成分符合设计成分要求。由表2可以看出,本发明中厚板经控轧+控冷处理后,钢板具有优良的强度以及低温韧性,完全满足表1的技术要求。由图1和图2可以看出,其组织为细小的珠光体+铁素体,带状组织评级≤2.0级。
表1 实施例1熔炼化学成分组成(wt.%)
。
表2 各实施例性能试验结果
。
Claims (1)
1.一种降低Q345D中厚板带状组织等级的生产方法,其特征在于:钢的化学成分质量百分比为:C=0.16~0.18,Si=0.10~0.20,Mn=1.10~1.30,P≤0.008,S≤0.0015,Alt=0.070~0.090,Nb=0.010~0.015,Ti=0.010~0.020,Ceq≤0.40%,其余为Fe和残留元素;包括以下工艺步骤:
(1)转炉炼钢:出钢C≥0.06%,P≤0.006%,出钢后进行炉后扒渣操作;
(2)LF精炼:钢水在LF炉总吹氩时间≥50分钟,白渣保持时间≥30分钟,钢水出LF前进行软吹氩操作,软吹氩时间≥12分钟;
(3)RH精炼:RH炉在站总吹氩时间≥30分钟,真空度在0.5tor以下,保持时间≥15分钟,钢水温度1590~1610℃,破空后氩气软吹时间≥15分钟;
(4)连铸:铸坯断面为220~350mm,实行全程保护浇铸,拉速0.6~0.9m/min,浇注温度按液相线温度+(6~13℃)控制,采用动态轻压下控制技术;
(5)板坯加热:板坯在步进炉中进行加热,限制炉膛温度≤1220℃,坯料出钢温度控制在1160~1180℃;
(6)控制轧制:一阶段开轧温度1000~1160℃,终轧温度>960℃,后三道次压下率>22%;二阶段开轧温度在870~890℃,终轧温度790~820℃;
(7)控制冷却:入水温度760~800℃,冷却速度控制在5~10℃/S,返红温度540~620℃,得到屈服强度≥345Mpa,抗拉强度490~620Mpa,断后伸长率A≥21%,-20冲击吸收能量≥60kV2J,带状组织≤2.0级的中厚钢板。
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