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CN118814075A - 一种抗拉强度1370MPa以上的冷轧塑性增强复相钢及制备方法 - Google Patents

一种抗拉强度1370MPa以上的冷轧塑性增强复相钢及制备方法 Download PDF

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CN118814075A
CN118814075A CN202411313119.4A CN202411313119A CN118814075A CN 118814075 A CN118814075 A CN 118814075A CN 202411313119 A CN202411313119 A CN 202411313119A CN 118814075 A CN118814075 A CN 118814075A
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CN118814075B (zh
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蒋睿婷
胡智评
刘仁东
徐鑫
郭金宇
林春青
钟莉莉
李侠
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Angang Steel Co Ltd
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Abstract

本发明涉及一种抗拉强度1370MPa以上的冷轧塑性增强复相钢及制备方法,钢中化学成分为C:0.21%~0.24%,Si:1.2%~1.6%,Mn:2.3%~2.7%,P≤0.01%,S≤0.08%,Al:0.1%~0.12%,Cr:0.3%~0.6%,Mo:0.22%~0.50%,Ti:0.03%~0.06%,Nb:0.03%~0.06%,B:0.0003%~0.0005%,且Cr+Mo:0.60%~0.95%,Ti+Nb:0.07%~0.11%,其余为Fe和杂质。制备过程包括连铸、热轧、卷曲、酸洗、冷轧、连续退火及平整工序。通过成分与工艺的匹配,实现了复相钢有较高的拉延性能与扩孔性能。

Description

一种抗拉强度1370MPa以上的冷轧塑性增强复相钢及制备 方法
技术领域
本发明涉及汽车用钢制造技术领域,尤其涉及一种汽车用抗拉强度1370MPa以上的冷轧塑性增强复相钢及其制备方法。
背景技术
对于汽车产业来说,降低汽车车身重量是实现二氧化碳减排的重要手段,而采用高强钢制造车身结构件可有效降低车身重量,如双相(DP)钢,复相(CP)钢等。相比于相同强度级别的双相钢,复相钢是在铁素体或贝氏体基体上分布马氏体、残余奥氏体、珠光体组织,因而有更好的翻边扩孔性能和弯曲性能,能够极大地降低板材成形开裂风险。冷轧CP钢主要用于生产对翻边性能要求高的零件,如保险杠、门槛、座椅滑轨等。目前,对高塑性复相钢的研究主要集中在抗拉强度1200MPa以下级别,对更高强度级别的高塑性复相钢研究较少。制造更高强度的钢板有助于零件厚度减薄,因此,迫切需要开发高强度、成形性增强的复相钢,以满足汽车制造行业轻量化的需求,同时完成产品的升级迭代。
授权公告号为CN113528946B的中国发明专利公开了“一种1200MPa级增强成形复相钢及其制备方法”,复相钢主要化学成分为:C:0.21~0.24%,Si:1.0~1.4%,Mn:2.1~2.6%,P≤0.01%,S≤0.005%,Cr:0.4~0.7%,Nb:0.02~0.04%,强化元素,其余为Fe及不可避免杂质。钢板性能可达屈服强度:951~1148MPa,抗拉强度:1201~1344MPa,断后伸长率:A80为8~13%,扩孔率:40~59%。该复相钢虽然有较高的扩孔率及延伸性能,但对于有更高抗拉强度要求的结构件来说仍无法满足要求。
公开号为CN114574760A的中国专利申请公开了“一种1500MPa级高成形性合金化热镀锌双相钢板及其制备方法”,钢板主要化学成分为:C:0.21%~0.24%,Si:0.71%~0.8%,Mn:2.66%~2.85%,Alt:0.91%~1.1%,Cr:0.71%~1.1%,Mo:0.21%~0.35%,Nb:0.041%~0.085%,Ti:0.051%~0.095%,B:0.003~0.005%,P:0.035~0.07%,S≤0.004%,N≤0.0025%,且Si+Al:1.62%~1.9%,Cr+Mo:0.92%~1.45%,其余为Fe和不可避免杂质。其产品性能为:抗拉强度≥1510MPa,屈服强度≥805MPa,断后伸长率≥8%,其通过组织调控形成大量细小弥散分布的纳米尺度第二相粒子使强度达到1500MPa级,但其未提及翻边扩孔性能。
发明内容
本发明提供了一种抗拉强度1370MPa以上的冷轧塑性增强复相钢及制备方法,通过巧妙的成分设计与工艺设计的匹配,实现了复相钢有较高的拉延性能与扩孔性能,完成钢铁企业对于产品的升级迭代,满足汽车行业制造形状复杂零部件对钢板性能提出的更高要求。
为了达到上述目的,本发明采用以下技术方案实现:
一种抗拉强度1370MPa以上的冷轧塑性增强复相钢,钢中化学成分按质量百分比计为C:0.21%~0.24%,Si:1.2%~1.6%,Mn:2.3%~2.7%,P≤0.01%,S≤0.08%,Al:0.1%~0.12%,Cr:0.3%~0.6%,Mo:0.22%~0.50%,Ti:0.03%~0.06%,Nb:0.03%~0.06%,B:0.0003%~0.0005%,且Cr+Mo:0.60%~0.95%,Ti+Nb:0.07%~0.11%,其余为Fe和不可避免的杂质元素。
进一步的,成品钢板的金相组织包括临界区铁素体、外延铁素体、贝氏体铁素体、马氏体及残余奥氏体;且按体积百分比计,临界区铁素体:3%~6%,外延铁素体:4%~9%,贝氏体铁素体:50%~65%,马氏体:22%~40%,其余为残余奥氏体;其中:贝氏体铁素体板条宽度小于5μm,马氏体板条宽度小于5μm;基体中还弥散分布有包括碳化物、氮化物及碳氮化物在内的细小析出物,细小析出物的直径为40~60nm。
进一步的,成品钢板的屈服强度为1020~1250MPa,抗拉强度≥1370MPa,延伸率≥8%,扩孔率≥35%。
一种抗拉强度1370MPa以上的冷轧塑性增强复相钢的制备方法,包括连铸、热轧、卷曲、酸洗、冷轧、连续退火及平整工序;其中控制如下工序:
1)热轧;板坯加热温度为1230℃~1250℃,保温1~2h;开轧温度为1050℃~1130℃,终轧温度在890℃~930℃;轧后钢板经层流冷却至600℃~650℃;卷曲温度为550℃~650℃,保温2h以上,随后空冷至室温;
2)冷轧;冷轧压下率为50%~65%;
3)连续退火;包括加热、保温、缓冷、第一阶段快冷、过时效保温及第二阶段冷却过程;带钢以5~10℃/s的速度加热到820℃~870℃,保温150s~220s,缓冷到770℃~800℃,缓冷冷速为1.5~4℃/s,第一阶段快冷冷却至350℃~380℃,快冷冷速>25℃/s,过时效保温350s~600s,最后第二阶段冷却以20~25℃/s冷却到室温;
4)平整;平整时的延伸率为0.2%~0.4%。
进一步的,热轧钢板的厚度为2.5~3.2mm,成品钢板的厚度为0.8~2.0mm。
与现有技术相比,本发明的有益效果是:
1)通过合金元素选择与配比,尤其是控制“Si+Al”和“Cr+Mo”含量,提高钢的淬透性,降低钢的临界冷却速率,获得一定量的贝氏体与马氏体组织;同时引入一定量的取向附生铁素体协调组织变形,引入一定量的残余奥氏体提高钢材塑性;
2)通过合理控制热轧终轧温度及冷硬板退火温度、退火时间及冷却速率,控制钢的组织构成与相比例,通过固溶强化、析出强化、细晶强化、相变强化等手段提高钢板强度;
3)本发明所述生产方法,利用钢厂现有的高强钢生产产线即可满足生产要求,减少了生产投入,降低了生产成本。
附图说明
图1是本发明实施例1中成品钢板的金相组织图。
具体实施方式
本发明涉及一种1370MPa塑性增强复相钢及其制备方法;钢中化学成分(以质量百分比计)为C:0.21%~0.24%,Si:1.2%~1.6%,Mn:2.3%~2.7%,P≤0.01%,S≤0.08%,Al:0.1%~0.12%,Cr:0.3%~0.6%,Mo:0.22%~0.50%,Ti:0.03%~0.06%,Nb:0.03%~0.06%,B:0.0003%~0.0005%,且Cr+Mo:0.60%~0.95%,Ti+Nb:0.07%~0.11%,其余为Fe和不可避免的杂质元素。
本发明所述一种1370MPa级塑性增强复相钢,成品钢板的性能为:屈服强度1020~1250MPa,抗拉强度≥1370MPa, 延伸率≥8%,扩孔率≥35%。
本发明所制备成品钢板的金相组织包括临界区铁素体(3%~6%)、外延铁素体(4%~9%)、贝氏体铁素体(50%~65%)、马氏体(22%~40%)及残余奥氏体(余量)。其中:贝氏体铁素体板条宽度小于5μm,马氏体板条宽度小于5μm,在钢板的基体中弥散分布着包括碳化物、氮化物及碳氮化物在内的细小析出物,细小析出物的直径在40~60nm。
本发明所述一种1370MPa塑性增强复相钢中,各元素的作用及含量选择理由如下:
C:碳原子是钢中一种间隙原子,通过固溶强化保证钢的强度。碳含量增加可提高钢的淬透性,并可促进贝氏体与马氏体等硬相组织的形成。奥氏体中碳含量增加,可使过冷奥氏体在冷却过程中不发生相变,保证钢在常温时有4%~7%的残余奥氏体,进而提高钢的塑性。但过高的含碳量会影响钢的焊接性能,因此本发明将C含量控制在0.21%~0.24%。
Si:能溶于铁素体,可提高铁素体强度。Si不形成碳化物,能够有效的抑制碳化物析出。但Si过量添加可使钢板表面产生Si的氧化物,影响钢板的表面质量。因此本发明将Si含量控制在1.2%~1.6%。
Mn:固溶于铁素体和奥氏体中,能扩大奥氏体相区。能降低钢中马氏体转变温度和钢中相变速度,进而提高钢的淬透性,并增加残余奥氏体含量。锰含量过低,会导致残留奥氏体稳定性较差,并导致钢板强度较低;锰含量过高,会导致Mn偏析,使钢的成形性较差。因此本发明将Mn含量控制在2.3%~2.7%。
P:溶于铁素体,能提高钢的强度与硬度。但P在钢中会产生偏析,对焊接也有不良影响;总的来说P是有害元素,应该严加控制。因此本发明将P含量上限控制在0.01%。
S:在钢中为有害元素,其与Mn形成MnS夹杂,亦是裂纹萌生的起点,进而降低钢板的翻边性能,因此本发明将S含量上限控制在0.08%。
Al:能与钢中O形成高熔点的Al2O3,减低钢中氧化物夹杂;也可与钢中N结合形成AlN,阻碍奥氏体晶界迁移,阻止奥氏体晶粒粗化。但过高的Al会增加钢水粘度,堵塞连铸水口,因此本发明将Al含量控制在0.1%~0.12%。
Cr:能有效提高钢的淬透性,使钢获得足量马氏体,从而保证钢的强度;同时Cr元素为铁素体区扩大元素,过量Cr元素会缩小两相区,因此本发明将Cr含量控制在0.3%~0.6%。
Mo:能有效提高钢的淬透性,并能有效推迟珠光体转变,获得更多的贝氏体与马氏体组织,保证钢的高强度。但Mo成本较高,因此本发明将Mo含量控制在0.22%~0.50%,同时控制Cr+Mo:0.60%~0.95%。
Ti:可以与钢中C、N元素形成TiC、TiN析出,细化晶粒,能显著提升钢的屈服强度。但过多的钛化物析出会降低钢的成形性能,因此本发明将Ti含量控制在0.03%~0.06%。
Nb:可以与钢中C元素形成NbC析出,有效阻止铁素体晶粒长大,从而细化晶粒;在铁素体中弥散分布的铌化物能提高钢的屈服强度,从而使钢板有较高的扩孔性能。但Nb元素过量添加会增加钢的生产成本,因此本发明将Nb含量控制在0.03%~0.06%,同时控制Ti+Nb:0.07%~0.11%。
B:能强烈增加钢的淬透性,降低相变发生时的冷却速度,同时能减少P偏聚,因此本发明将B元素含量控制在0.0003%~0.0005%。
本发明所述一种塑性增强抗拉强度1370MPa以上的冷轧复相钢制备方法:包括连铸、热轧、卷曲、酸洗、冷轧,连续退火、平整等一系列工序。具体控制如下过程:
1)连铸;具有设定化学成分的钢水通过转炉冶炼后,再经连铸得到板坯;
2)热轧;
① 加热温度控制在1230℃~1250℃,保温1~2h;加热期间保证Ti(C,N)析出,可以钉扎原始奥氏体晶界,阻止奥氏体晶界迁移,起到细化奥氏体晶粒的作用;适宜的保温时间可以使合金元素完全固溶,并防止TiN析出粗化而导致晶界强度降低。
②开轧温度为1050℃~1130℃,终轧温度为890℃~930℃;开轧温度处于奥氏体区,保证奥氏体再结晶;轧后钢板经层流冷却至600℃~650℃,热轧板的厚度为2.5~3.2mm。
3)卷曲;卷曲温度为550℃~650℃,保温2小时以上,随后空冷至室温;卷曲温度是根据成分相变温度来制定的,卷曲后得到钢板组织为铁素体、贝氏体、马氏体组织。卷曲温度过高会造成钢板表面质量差及塌卷等缺陷;卷曲温度过低会导致热轧板强度过高,给后续冷轧带来困难。
4)酸洗;用以除去热轧钢板表面生成的氧化铁皮。
5)冷轧;冷轧压下率为50%~65%;保证50%以上的压下率,目的是使钢板有足够的形变储能,有利于退火时再结晶;同时控制压下率在65%以下,因为如果变形量过大,在轧制过程中容易出现边裂甚至断带。
6)连续退火;包括加热、保温、缓冷、第一阶段快冷、过时效保温、第二阶段冷却等过程。
钢板以5~10℃/s速度加热到820℃~870℃,保温150s~220s,缓冷到770℃~800℃,缓冷冷速为1.5~4℃/s,第一阶段冷却至350℃~380℃,快冷冷速大于25℃/s,过时效保温350s~600s后,第二阶段以20~25℃/s冷却到室温。
连续退火各工艺参数选择理由如下:
① 钢板以5℃/s~10℃/s的加热速率加热;若加热速率过小,钢板在加热炉内时间过长,不仅会使奥氏体晶粒长大影响钢强度,而且会降低生产效率;若加热速率过大,造成温度过冲,会增加设备控制难度。
② 加热到820℃~870℃;此温度处于两相区,加热温度过低会使贝氏体与马氏体总含量不足,导致产品抗拉强度不足;加热温度过高,在二次冷却过程中得到的马氏体多,会降低产品成形性能。
③ 保温150s~220s;保温时间过短,合金元素不能均匀分布;保温时间过长,奥氏体晶粒会逐渐长大;保温时间过短和过长都会影响产品最终性能。
④ 缓冷到770℃~800℃,是为获得一定量的取向附生铁素体,其较两相区铁素体有更高的合金含量,作为软相可协调组织变形,提高扩孔性能。
⑤ 以不小于25℃/s的冷速完成第一阶段冷却;此冷速避开了珠光体转变,使过冷奥氏体到贝氏体相变区进行贝氏体相变。
⑥ 冷却至350℃~380℃过时效;此温度为贝氏体相变温度,如果过时效温度过低,会导致贝氏体含量低,在接下来的冷却过程中马氏体含量较多,残余奥氏体中碳含量较低会降低其稳定性,在随后的平整过程中会发生马氏体相变,降低产品延伸率,扩孔性能也会降低。如果过时效温度过高,生成的贝氏体较多,在随后冷却过程中生成的马氏体较少,产品抗拉性能无法达到1370MPa。
⑦ 保温350s~600s;通过控制过时效时间保证获得一定量贝氏体,贝氏体中的碳原子向马氏体中扩散,增加了过冷奥氏体稳定性,在随后冷却过程中获得一定量残余奥氏体,保证钢的成形性能。
⑧ 第二段冷却以20℃/s~25℃/s冷却到室温;目的是获得一定量的马氏体与残余奥氏体,以及一定量的马氏体,保证钢板强度;一定量的残余奥氏在变形过程中发生相变,能够提升钢板塑性。
7)平整;平整时的延伸率为0.2%~0.4%,目的是提高钢板的屈服强度。通过平整可使钢板表面产生适宜的粗糙度(平整延伸率过小或者过大都会改变钢板表面粗糙度)。另外,平整延伸率过大会使钢中残余奥氏体发生马氏体转变,降低钢材塑性。
为使本发明的目的、技术方案和技术效果更加清楚,现对本发明实施例中的技术方案进行清楚、完整地描述。但以下所描述的实施例仅是本发明一部分实施例,而不是全部的实施例。结合本发明中的实施例,本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其它实施例,都属于本发明保护的范围。
实施例1:
表1中列出了各实施例钢的化学成分,表2中列出了各实施例钢的连铸和热轧工艺参数,表3中列出了各实施例钢板的冷轧和连续退火工艺参数,表4中列出了各实施例成品钢板的力学性能。
图1为实施例1所制备成品钢板的金相组织图。
表1钢的化学成分,wt%
实施例 C Si Mn P S Al Cr Mo Ti Nb B
1 0.213 1.34 2.63 0.008 0.06 0.118 0.53 0.33 0.044 0.053 0.0004
2 0.225 1.29 2.46 0.005 0.05 0.111 0.47 0.44 0.053 0.039 0.0003
3 0.231 1.32 2.31 0.005 0.05 0.102 0.33 0.29 0.053 0.050 0.0005
4 0.219 1.27 2.59 0.007 0.04 0.115 0.56 0.37 0.036 0.032 0.0004
5 0.236 1.40 2.33 0.006 0.05 0.107 0.33 0.41 0.043 0.037 0.0004
6 0.227 1.51 2.42 0.007 0.05 0.109 0.60 0.22 0.035 0.044 0.0003
表2 钢的连铸和热轧工艺参数
实施例 加热温度/℃ 开轧温度/℃ 终轧温度/℃ 卷曲温度/℃ 热轧板厚度/mm
1 1233 1067 897 609 2.92
2 1245 1087 904 637 3.08
3 1247 1118 914 642 3.14
4 1230 1079 900 614 3.02
5 1250 1122 921 621 2.89
6 1242 1098 902 618 2.97
表3 钢板冷轧、连续退火及平整工艺参数
实施例 冷轧压下率/% 加热温度/℃ 保温时间/s 缓冷温度/℃ 缓冷冷速/℃/s 第一段冷速/℃/s 过时效温度/℃ 保温时间/s 第二段冷速/℃/s 平整延伸率%
1 56 862 164 777 3.1 26 359 433 21.4 0.23
2 62 869 178 782 2.6 27 366 358 20.7 0.31
3 51 842 215 788 2.3 32 352 374 24.2 0.27
4 56 857 191 776 3.2 29 377 392 21.9 0.29
5 62 881 187 793 1.9 34 361 469 23.8 0.33
6 60 860 182 783 2.7 39 369 504 22.6 0.38
表4 成品钢板的力学性能
实施例 屈服强度/MPa 抗拉强度/MPa 延伸率(A50)/% 扩孔率λ/%
1 1036 1389 8.5 38.5
2 1126 1385 8.7 43.4
3 1228 1403 8.1 36.4
4 1173 1382 8.5 45.2
5 1201 1395 8.4 35.3
6 1156 1377 9.3 42.7
以上所述,仅为本发明较佳的具体实施方式,但本发明的保护范围并不局限于此,任何熟悉本技术领域的技术人员在本发明揭露的技术范围内,根据本发明的技术方案及其发明构思加以等同替换或改变,都应涵盖在本发明的保护范围之内。

Claims (5)

1.一种抗拉强度1370MPa以上的冷轧塑性增强复相钢,其特征在于,钢中化学成分按质量百分比计为C:0.21%~0.24%,Si:1.2%~1.6%,Mn:2.3%~2.7%,P≤0.01%,S≤0.08%,Al:0.1%~0.12%,Cr:0.3%~0.6%,Mo:0.22%~0.50%,Ti:0.03%~0.06%,Nb:0.03%~0.06%,B:0.0003%~0.0005%,且Cr+Mo:0.60%~0.95%,Ti+Nb:0.07%~0.11%,其余为Fe和不可避免的杂质元素。
2.根据权利要求1所述的一种抗拉强度1370MPa以上的冷轧塑性增强复相钢,其特征在于,成品钢板的金相组织包括临界区铁素体、外延铁素体、贝氏体铁素体、马氏体及残余奥氏体;且按体积百分比计,临界区铁素体:3%~6%,外延铁素体:4%~9%,贝氏体铁素体:50%~65%,马氏体:22%~40%,其余为残余奥氏体;其中:贝氏体铁素体板条宽度小于5μm,马氏体板条宽度小于5μm;基体中还弥散分布有包括碳化物、氮化物及碳氮化物在内的细小析出物,细小析出物的直径为40~60nm。
3.根据权利要求1所述的一种抗拉强度1370MPa以上的冷轧塑性增强复相钢,其特征在于,成品钢板的屈服强度为1020~1250MPa,抗拉强度≥1370MPa,延伸率≥8%,扩孔率≥35%。
4.如权利要求1-3任意一种所述抗拉强度1370MPa以上的冷轧塑性增强复相钢的制备方法,其特征在于,包括连铸、热轧、卷曲、酸洗、冷轧、连续退火及平整工序;其中控制如下工序:
1)热轧;板坯加热温度为1230℃~1250℃,保温1~2h;开轧温度为1050℃~1130℃,终轧温度在890℃~930℃;轧后钢板经层流冷却至600℃~650℃;卷曲温度为550℃~650℃,保温2h以上,随后空冷至室温;
2)冷轧;冷轧压下率为50%~65%;
3)连续退火;包括加热、保温、缓冷、第一阶段快冷、过时效保温及第二阶段冷却过程;带钢以5~10℃/s的速度加热到820℃~870℃,保温150s~220s,缓冷到770℃~800℃,缓冷冷速为1.5~4℃/s,第一阶段快冷冷却至350℃~380℃,快冷冷速>25℃/s,过时效保温350s~600s,最后第二阶段冷却以20~25℃/s冷却到室温;
4)平整;平整时的延伸率为0.2%~0.4%。
5.根据权利要求4所述一种抗拉强度1370MPa以上的冷轧塑性增强复相钢的制备方法,其特征在于,热轧钢板的厚度为2.5~3.2mm,成品钢板的厚度为0.8~2.0mm。
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CN113528946A (zh) * 2021-06-18 2021-10-22 首钢集团有限公司 一种1200MPa级增强成形复相钢及其制备方法
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CN102409235A (zh) * 2010-09-21 2012-04-11 鞍钢股份有限公司 高强度冷轧相变诱导塑性钢板及其制备方法
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