烘烤硬化钢的时效性

1、烘烤硬化钢(低碳型H220BD )的时效性The Aging Character of Bake Hardening Steel (H220BD of ULC)摘要brief标准规定，烘烤硬化钢的力学性能值适用时间为3个月。那么在3个月内和3个月以外，力学性能值的 变化规律是什么？在目前所能见到的文献上查不到答案。通过实测，烘烤硬化钢在3个月内已经发生时 效，如果不适当提高初始性能值的话，无法保证全部力学性能都在3个月内适用。弓I言 foreword烘烤硬化钢是对时效比较敏感的钢种，在成型之前，人们不希望其有时效反应在成型 后，人们希望通过烤漆过程提高材料的屈服强度，从而获得加工性能和使用性能

2、完美结合。 但是自然规律是不以人的愿望而转移的，随着时间的推移，时效总是要发生的，问题的关 键是发生这个变化程度和规律是什么。为了规范供需双方验收和使用，相关标准规定烘烤 硬化钢力学性能适用期为3个月，那么在3个月内是否力学性能变化不大？如果不能及时 使用，3个月以后会有何种影响？影响相关性能变化的主要因素是什么？为了回答这个问 题，本文设计了5组对应实验，在自然条件下时效不同时段，试图揭示其变化规律。实验材料与方法 experiment that materials and methods分别作了 5组对比试验：A组，储存3个月。B组，储存6个月。C组，储存9个月。D组，储存12 个月。E组

3、，储存17.5个月。各组试样代号如下表所示：test groupaging timespecimen No.A3 monthesA1A2A3A4A5B6 monthesB1B2B3B4B5B6B7B8B9C9 monthesC1C2C3C4C5C6C7C8C9D12 monthesD1D2D3D4D5D6D7D8D9D10D11D12D13D14E17.5 monthesE1E2E3E4各组材料化学成分构成如下表chemistry componentstest groupaging timeCSiMnPSAlCrCuNiNbNTiVBgroup A3 monthes0.0790 00 330

4、010 00.030 020 00 00 00 00 0000.0017group B6 monthes0.0660.00.290.010.00.030.010.00.00.00.00.00.00.0009group C9 monthes0.0640.00.290.010.00.030.020.00.00.00.00.00.00.0022group D12 monthes0.0590.00.280.010.010.030.010.00.00.00.00.00.00.0025group E17.5 monthes0.0620.00.290.010.010.030.00.00.00.00.00.0

5、0.00.0时效前后力学性能实测结果 measurement results of the mechanical capability 抗拉强度Rm测试结果tensile strength (Rm) Tensile fresh Tensile aging for 3 monthA1A2A3A4A5mspecimen codecompare Rm of aging for 6 monthes with fresh oneTensile fresh Tensile aging for 6 month Tensile fresh Tensile aging for 9 monthmcompare R

6、m of aging for 12 monthes with fresh one Tensile fresh Tensile aging for 12 monthmE1E2E3E4mTensile fresh Tensile aging for 17.5 monthspecimen code屈服强度Rp02测试结果yield strength (Rp02)compare Rp02 of aging for 3 monthes with fresh oneRp02 fresh Rp02 aging for 3 monthA1A2A3A4A5specimen codeRp02 freshRp02

7、aging for 6 monthB2 B3B4B5 B6B7 B8 B9specimen codecompare Rp02 of aging for 9 monthes with fresh oneRp02 fresh Rp02 aging for 9 monthRp02 fresh Rp02 aging for 12 month265220D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13 D14specimen codecompare Rp02 of aging for 17.5 monthes with fresh oneRp02 freshRp02

8、aging for 17.5 month延伸率A80测试结果elongation (A80)A80 value fresh A80 value aging for 3 month38.0037.00% noifeanoreQaA36.0035.0034.0033.0032.0031.00compare A80 of aging for 6 monthes with fresh one-* A80 value fresh A80 value aging for 6 month% notaanole O8Anotaonole QaA* A80 value fresh A80 value aging

9、 for 9 monthC1 C2 C3 C4 C5 C6 C7 C8 C9140.0039.0038.00% 37.0036.0035.0034.0033.0032.0031.0030.0029.00specimen codecompare A80 of aging for 12 monthes with fresh oneA80 value fresh -A80 value aging for 12 month% notaonole QaA39.0038.0037.0036.0035.0034.0033.0032.0031.0030.0029.00D1 D2 D3 D4 D5 D6 D7

10、D8 D9 D10 D11 D12 D13 D14A80 value fresh A80 value aging for 17.5 month-O.O.O.O.O.O.O 5 4 3 2 1 3 3 3 3 3 3 2 % noifeanoKensAE1E2 specimen coden 值测试结果 strain hardening indexcompare n value of aging 3 monthes with the fresh onen value fresh specimen n value aging for 3 month0.2000.1900.1800.1700.1600

11、.1500.1400.130specimen code0.210seu.pwvnt n value fresh specimen t n value aging for 6 monthseu.av n0.2100.2000.1900.1800.1700.1600.1500.1400.130specimen codecompare n value of aging for 9 monthes with fresh onei n value fresh specimen n value aging for 9 montheu-RV n0.2100.2000.1900.1800.1700.1600.

12、1500.1400.130eu-RV n0.2100.2000.1900.1800.1700.1600.1500.1400.130D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13 D14specimen codeeu!av n0.2100.2000.1900.1800.1700.1600.1500.1400.130E1E2specimen coden value fresh specimen n value aging for 17.5 month烘烤硬化值 dBH2 测试结果 bake hardening value (dBH2)初始值较低的，库存3个月后

13、烘烤硬化值增加了，而初始值较高者(A1 and人2)库存3个月后烘烤硬化 值却下降了。compare dBH2 of aging for 3 monthes with fresh onedBH2 fresh dBH2 aging for 3 month39 38 1111A1A2A3A4A5specimen codedBH2 freshdBH2 aging for 6 monthcompare dBH2 of aging for 9 months with fresh one*dBH2 fresh dBH2 aging for 9 monthdBH2 fresh dBH2 aging for

14、12 month-554444444444lanM/L9HBaD1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13 D14specimen codecompare dBH2 of aging for 17.5 monthes with fresh onespecimen codei dBH2 fresh dBH2 aging for 17.5 month加工硬化值 dBH0 测试结果 work hardening values (dBH0)J*dBH0fres JdBH0 aging for 3 monthcompare work hardening of ag

15、ing with fresh one*-dBH0 fresh dBH0 aging for 6 monthdBH0 freshonedBH0 aging for 9 monthspecimen codecompare work hardening of aging with fresh onedBH0 fresh y dBH0 aging for 12 monthspecimen codedBH0 fresh dBH0 aging for 17.5 month35.030.0M250 g 20.0n 15.0W 10.05.00.0屈服平台延伸 R 测试结果 classification yi

16、eld point extensionclassification yield point extensiontest groupfreshaging for 3 monthtest groupfreshaging for 6 monthtest groupfreshaging for 9 monthtest groupfreshaging for 12 monthtest groupfreshaging for17.5monthARRRRRCRRDRRFRRA121_J10C104D104E144A222B201C201D212E204A39?4?B3_11C304D304E3_14A423

17、B411C412D412E404A500B514C52_2D50_3B604C612D621B7_0_0C7_2_3_D7_11B800C822D822B904C900D914D1001D1_2_1D1212m_0_4D1422ave. A1.51.5ave. B0.441.7ave. C0.892.20.932.41.254.0讨论 discussion烘烤硬化的微观机理是薄钢板经过成形预变形后，基体内位错密度增加，使间隙固溶原子C、N向位错扩散 的距离缩短，当高温烘烤时效处理时它们的热激活能增加，促使其向位错的扩散速度加快，使得C、N原子 钉扎位错,从而使得钢板再次受载变形时屈服强度得到提

18、高。因此，烘烤硬化性实质上同常温时效性一样 都属于应变时效机理，但BH值反映的是由钢中的间隙固溶原子C、N所产生的高温应变时效现象。烘烤硬 化钢板的BH值通常约为40MPan值的变化比较compare n valuesn值是对时效比较敏感的，贮存3个月后已经明显发生时效，而且基本稳定下来。初始值的高低决定了时 效后n值的高低。从以下几个图表中可以看出来，其脉动规律是一致的。It is a hypersensitive for n value of aging, there are distinct change when store it for 3 months and then since

19、 that decrease n value of every test group not distinct change. Higher or lower n value of fresh one that choose for final n value whether higher or lower.n value compare aging with freshn value fresh n value after agingseHrav0.2100.2000.1900.1800.1700.1600.1300.120nA1a3 净声攻中申c1c3 c5c7c9 c2 D4 c6 c8

20、D10D12D14E2E4specimens code烘烤硬化值dBH2的变化比较compare dBH2烘烤硬化值在储存一年内与原始值比较变化不大，自然时效6个月时达到最大，然后逐渐衰减，一年后 甚至出现负增长。Bake hardening value of storage different time in 1 year, there were not bigger increase and change, but more than 1 year, there were more change with minus value.laM(an.nearan eKaD765432109876

21、543444 4444 43333 333初始加工硬化值dBH0和时效后dBH0比较compare dBH0加工硬化值随着时效时间的增加而增加，但是超过一年以后加工硬化值反而出现负增加。Work hardening value was more and more higher in 1 year, but more than 1 year, there were change with minus pare work hardening of aging with fresh one0group Agroup Bgroup Cgroup Dgroup Efresh dBH0aging dBH0

22、test group code屈服强度的变化比较compare yield strength时效初始（3个月时）屈服强度增加的较少，在6个月到一年内增加值较稳定。超过一年，或许是进入 另外一个温度变化周期，屈服强度变化陡增。compare yield strength of aging with frsh oneaging Rp02fresh Rp02245.00YaM/lnTSHrtsderygroup Agroup Bgroup Cgroup Dgroup Etest group code抗拉强度变化比较compare tensile strength自然时效3个月时抗拉强度已经明显发生，

23、此后随着时间增加，抗拉强度变化值不再明显增加。compare average tensile strength of aging with fresh one fresh Rm . aging Rmtest group code时效前后延伸率变化比较compare elongation自然时效3个月后延伸率已经明显发生降低，此后随着时间增加，延伸率降低不再明显增加。为了满足 标准规定的A80崩2%，延伸率的初始值不应小于35%。compare elongation A80 of aging with fresh one*freshA80-aging A803837group Agroup B group C group Dgroup Etest group code屈服点延伸长度变化比较compare yield point extension自然失效不同时间后，屈服点延伸变化特征如下图：在时效3个月内，屈服点延伸没有明显变化；超过3 个月后时效特征逐渐显现出来，在一年内增加相对值变化不大。超过一年后突然放大。似乎跟季节有规 律的温度变化有关。但是，初始值偏高的话，时效后的值也按比例