WELDOX960高強鋼焊接性研究

 
摘  要

WELDOX960作為新一代低合金高強鋼，具有細晶粒、超潔凈度、高均勻性、高強度、高韌性和良好綜合性能的新材料，主要應(yīng)用于礦山機械、橋梁、鐵路、汽車起重機等重載領(lǐng)域。本文結(jié)合軍用車載橋梁的實際生產(chǎn)條件根據(jù)“低強匹配”原則選取瑞典生產(chǎn)的ED-FK 1000高強焊絲設(shè)計了WELDOX960高強鋼的Ar＋CO2混合氣體保護焊工藝，在預(yù)熱75℃、焊接線能量1.0～1.2KJ/mm、層間溫度80～85℃的條件下進行多層多道焊接。分別對WELDOX960高強鋼焊接接頭進行拉伸、彎曲、沖擊等力學性能試驗和斜Y型坡口試驗、搭接接頭試驗及熱影響區(qū)最高硬度等抗裂性試驗研究，并利用光學顯微鏡和掃描電鏡等分析手段對WELDOX960高強鋼的焊縫、熔合區(qū)和熱影響區(qū)的微觀組織及斷口進行分析，研究了預(yù)熱溫度、焊接熱輸入和后熱溫度等工藝因素對接頭強度、彎曲性能和熱影響區(qū)沖擊韌性的影響，分析了微觀組織對接頭強韌性的影響以及該鋼在實際生產(chǎn)條件下的焊接適應(yīng)性。
測試結(jié)果表明在本試驗條件下該鋼冷裂和熱裂敏感性小，接頭屈服強度為928.8Mpa，失強率14.2%，達到設(shè)計要求；焊接熱輸入及層間溫度對接頭性能有重要影響，焊接熱輸入太小，導致接頭冷卻速度過快，溫度梯度大，淬硬性大，從而使冷裂傾向增大；但熱輸入太大時又容易使接頭內(nèi)應(yīng)力疊加增大，半熔化區(qū)奧氏體晶粒粗化，降低接頭的強度及抗裂性能；微觀分析表明，焊縫及熱影響區(qū)分布的貝氏體和低碳馬氏體是接頭高強度和高韌性的基本條件，因此要合理控制焊接熱輸入在1.0～1.2 KJ/mm范圍內(nèi)，保證焊縫組織為粒狀貝氏體和少量的低碳馬氏體，從而保證接頭的強韌性。
關(guān)鍵詞  高強鋼，焊接接頭，力學性能，焊接性，混合氣體保護焊
 

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 “l(fā)ower 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     錄
第一章 概述 1
1.1 新一代低合金高強鋼的發(fā)展概況 1
1.1.1 我國低合金高強鋼的發(fā)展現(xiàn)狀及面臨的挑戰(zhàn) 3
1.1.2 國外新一代低合金高強鋼的發(fā)展及使用情況 4
1.2 新一代低合金高強鋼的主要特點 5
1.2.1 新一代低合金高強鋼的冶金特點 5
1.2.2 新一代低合金高強鋼的強化途徑 6
1.3 新一代低合金高強鋼對焊接材料的要求 7
1.3.1 新一代低合金高強鋼的焊接性 7
1.3.2 新一代低合金高強鋼對焊接材料的要求 8
1.4 本課題的研究背景及意義 9
1.5 本課題預(yù)期達到的目的 10
第二章 WELDOX960高強鋼的生產(chǎn)工藝及性能 11
2.1 WELDOX960高強鋼的生產(chǎn)工藝 11
2.1.1 WELDOX960高強鋼的軋制工藝 12
2.1.2 WELDOX960高強鋼的淬火和退火工藝 12
2.2 WELDOX960高強鋼的機械性能 15
2.2.1 WELDOX960高強鋼的冶金特點 15
2.2.2 WELDOX960高強鋼的機械性能 17
2.3 WELDOX960高強鋼的強化機理 17
2.3.1 晶界強化 17
2.3.2 應(yīng)變強化 18
2.3.3 固溶強化 19
2.3.4 沉淀強化 19
2.3.5 馬氏體相變強化 20
2.4 韌化機理 20
2.4.1 金屬材料的凈化 21
2.4.2 晶粒的細化 21
2.4.3 顯微組織的優(yōu)化 21
2.5 本章小節(jié) 22
第三章 WELDOX960高強鋼焊接性研究 23
3.1 WELDOX960高強鋼焊接性理論分析 23
3.1.1 碳當量法 24
3.1.2 預(yù)熱溫度Tp的計算 25
3.1.3 熱影響區(qū)最高硬度HVmax與t8/5的關(guān)系 26
3.1.4 焊接工藝參數(shù)曲線 27
3.1.5 焊接材料的選擇 30
3.1.6 試驗設(shè)備及儀器 31
3.2 焊接性試驗的目的及內(nèi)容 31
3.3 WELDOX960高強鋼抗裂性試驗結(jié)果及分析 32
3.3.1 斜Y型坡口焊接裂紋試驗 32
3.3.2 熱影響區(qū)最高硬度試驗 35
3.3.3 搭接接頭焊接裂紋試驗 38
3.4 WELDOX960高強鋼力學性能試驗及結(jié)果分析 41
3.4.1 焊接接頭抗拉強度試驗 41
3.4.2 焊接接頭微觀組織分析 45
3.4.3 焊接接頭彎曲試驗 46
3.4.4 焊接接頭沖擊試驗 50
3.5 本章小結(jié) 55
第四章 結(jié)論 57
參 考 文 獻 58
致      謝 61