weldox960高强钢焊接性研究.doc

WELDOX960高强钢焊接性研究

 
摘  要

WELDOX960作为新一代低合金高强钢，具有细晶粒、超洁净度、高均匀性、高强度、高韧性和良好综合性能的新材料，主要应用于矿山机械、桥梁、铁路、汽车起重机等重载领域。本文结合军用车载桥梁的实际生产条件根据“低强匹配”原则选取瑞典生产的ED-FK 1000高强焊丝设计了WELDOX960高强钢的Ar＋CO2混合气体保护焊工艺，在预热75℃、焊接线能量1.0～1.2KJ/mm、层间温度80～85℃的条件下进行多层多道焊接。分别对WELDOX960高强钢焊接接头进行拉伸、弯曲、冲击等力学性能试验和斜Y型坡口试验、搭接接头试验及热影响区最高硬度等抗裂性试验研究，并利用光学显微镜和扫描电镜等分析手段对WELDOX960高强钢的焊缝、熔合区和热影响区的微观组织及断口进行分析，研究了预热温度、焊接热输入和后热温度等工艺因素对接头强度、弯曲性能和热影响区冲击韧性的影响，分析了微观组织对接头强韧性的影响以及该钢在实际生产条件下的焊接适应性。
测试结果表明在本试验条件下该钢冷裂和热裂敏感性小，接头屈服强度为928.8Mpa，失强率14.2%，达到设计要求；焊接热输入及层间温度对接头性能有重要影响，焊接热输入太小，导致接头冷却速度过快，温度梯度大，淬硬性大，从而使冷裂倾向增大；但热输入太大时又容易使接头内应力叠加增大，半熔化区奥氏体晶粒粗化，降低接头的强度及抗裂性能；微观分析表明，焊缝及热影响区分布的贝氏体和低碳马氏体是接头高强度和高韧性的基本条件，因此要合理控制焊接热输入在1.0～1.2 KJ/mm范围内，保证焊缝组织为粒状贝氏体和少量的低碳马氏体，从而保证接头的强韧性。
关键词  高强钢，焊接接头，力学性能，焊接性，混合气体保护焊
 

ABSTRACT

As a high strength low and alloyed structural steel, WELDOX960 is characterized by fine grain, super-metallurgical purification and homogenization, high strength and toughness, and it is widely applied in the field of mine-machine, bridge, railway and mobile crane etc. High-strength MAG-wire ED-FK 1000 is selected as consumed material according to “lower strength match”to be used in mixed gases (Ar+CO2) shielded metal arc welding(GMAW). During multiplayer welding, WELDOX960 is welded with welding parameters as follow: preheat temperature is 75℃，heat input is 1.0～1.2KJ/mm，Interpass temperature is 80～85℃.
Mechanical tests (tensile test, bending test and impact test) and crack tests (Y-groove and CTS cracking test, peak hardness of HAZ test) were carried out to study on its weldability; and microstructures of weld metal, fusion zone, HAZ and fractography were investigated by means of light microscopy and SEM; the effect of processing factors and microstructures of welding joint on strength and toughness of welding joint was analyzed.
Experimental results indicated that WELDOX960 has a good capacity of resisting cool cracking and hot cracking with suitable welding parameters. CET is a key factor to the performance of joint. With a small value of CET, the joint will be apt to get cracking due to fast cooling and big temperature grade while a big value of CET will damage the performance of joint sharply due to coarse grain and welding interstress. Microanalysis indicated that granular bainite and low-carbon martensite were found in weld and HAZ, which contributed to high strength and toughness of joint. So CET must be limited in the range of 1.0～1.2 KJ/mm to make sure that granular bainite and low-carbon martensite be acquired in weld.

KEY WORDS　high strength steel,  welded joint, mechanical property,  weldability, GMW

目     录
第一章 概述 1
1.1 新一代低合金高强钢的发展概况 1
1.1.1 我国低合金高强钢的发展现状及面临的挑战 3
1.1.2 国外新一代低合金高强钢的发展及使用情况 4
1.2 新一代低合金高强钢的主要特点 5
1.2.1 新一代低合金高强钢的冶金特点 5
1.2.2 新一代低合金高强钢的强化途径 6
1.3 新一代低合金高强钢对焊接材料的要求 7
1.3.1 新一代低合金高强钢的焊接性 7
1.3.2 新一代低合金高强钢对焊接材料的要求 8
1.4 本课题的研究背景及意义 9
1.5 本课题预期达到的目的 10
第二章 WELDOX960高强钢的生产工艺及性能 11
2.1 WELDOX960高强钢的生产工艺 11
2.1.1 WELDOX960高强钢的轧制工艺 12
2.1.2 WELDOX960高强钢的淬火和退火工艺 12
2.2 WELDOX960高强钢的机械性能 15
2.2.1 WELDOX960高强钢的冶金特点 15
2.2.2 WELDOX960高强钢的机械性能 17
2.3 WELDOX960高强钢的强化机理 17
2.3.1 晶界强化 17
2.3.2 应变强化 18
2.3.3 固溶强化 19
2.3.4 沉淀强化 19
2.3.5 马氏体相变强化 20
2.4 韧化机理 20
2.4.1 金属材料的净化 21
2.4.2 晶粒的细化 21
2.4.3 显微组织的优化 21
2.5 本章小节 22
第三章 WELDOX960高强钢焊接性研究 23
3.1 WELDOX960高强钢焊接性理论分析 23
3.1.1 碳当量法 24
3.1.2 预热温度Tp的计算 25
3.1.3 热影响区最高硬度HVmax与t8/5的关系 26
3.1.4 焊接工艺参数曲线 27
3.1.5 焊接材料的选择 30
3.1.6 试验设备及仪器 31
3.2 焊接性试验的目的及内容 31
3.3 WELDOX960高强钢抗裂性试验结果及分析 32
3.3.1 斜Y型坡口焊接裂纹试验 32
3.3.2 热影响区最高硬度试验 35
3.3.3 搭接接头焊接裂纹试验 38
3.4 WELDOX960高强钢力学性能试验及结果分析 41
3.4.1 焊接接头抗拉强度试验 41
3.4.2 焊接接头微观组织分析 45
3.4.3 焊接接头弯曲试验 46
3.4.4 焊接接头冲击试验 50
3.5 本章小结 55
第四章 结论 57
参 考 文 献 58
致      谢 61